Title
Genetic selection for improved nutritional quality of rice straw-a plant breeder's viewpoint
Author
Gurdev S. Khush1, Bienvenido O. Juliano2 and Domingo B. Roxas3
We discuss here collaborative research at IRRI examining the feasibility of improving the feed value of rice straw for ruminants.
Varietal differences have been suggested by many researchers, but others have reported little or no variation. Rice straw contains less lignin but more silica and oxalic acid than other cereal straws (Van Soest, 1981; Juliano, 1985).
Various morphological, chemical and environmental factors affect the nutritional value of cereal straws (Doyle et al, 1987; Neilson and Stone, 1987; Nicholson, 1984; Pearce, 1986; Preston and Leng, 1987; Van Soest, 1982). These include cell-wall content; content of lignin and silica; ratio of leaf blade, leaf sheath and stem; length of harvest straw; soil fertility and added fertilizer level; soil moisture and degree of senescence of straw at harvest; growth duration; resistance to pests; and plant height.
Cell contents (neutral-detergent solubles) are more readily digestible than cell walls, measured as neutral-detergent fibre (NDF) (Van Soest, 1982). Lignin and silica are reported to reduce the digestibility of rice straw (Van Soest, 1981). However, manipulation of the silica content of three rice varieties by hydroponics did not substantially change the invitro organic-matter digestibility of the total straw at harvest (Balasta et al, in press) (Table 1). Thus, lignin is probably the most important factor that limits digestibility of rice straw in ruminants (Neilson and Stone, 1987).
Harvest straw is made up of leaf blades, leaf sheaths, the stem and the panicle rachis. The proportions of these components are affected by straw length. In the Philippines, straw is cut 40-SO em below the base of the panicle to facilitate holding during threshing. The stem contains less ash and protein but more cellulose than the leaves (Doyle et al, 1986). In Malaysian rices, mean IVOMD of the plant parts were blades 44%; sheaths 45%; and stem internodes 42%. IVOMD varied more in blades than internodes (Doyle et al, 1986). Roxas et al (in press) found that IVOMD of stem internodes tends to be higher than that of leaf blades and leaf sheaths, although the NDF content of the internodes was not necessarily lower (Table 2). Internodes have a higher cellulose content than leaves.
Table 1. Crude silica content and in vitro organic matter digestibility of harvest straw of IR rices grown hydroponically with different levels of silica.
Current breeding efforts which aim at incorporating resistance to insects, diseases and lodging also lead to improvements in harvest straw quality by reducing straw damage. Duration of growth and nitrogen fertilizer levels also affect protein content of the straw. Early-maturing modern rices have higher grain and, possibly, higher straw protein contents than medium-maturing varieties (IRRI, 1985), and tend to have thinner straw and be more susceptible to lodging than medium-maturing rices (IRRI, 1984). Nutrient supply affects the ash content of straw. Soil N level affects protein content.
The brittle stem mutants of rice variety Balilla 28 have been reported to have higher lignin and hemicellulose and lower alpha-cellulose contents in the stem than the parent (Sharma et al, 1986). However, the IVOMD of their harvest straw (32-49%) overlapped with that of the Balilla 28 parent (36%) (Juliano et al, in press).
Semi-dwarf rices were shown to have similar if not greater harvest straw IVOMD than tall varieties such as H4 (Roxas et al, 1985) (Table 3). Selected strong- and weak-stemmed traditional and semi-dwarf varieties showed similar harvest straw IVOMD despite differences in straw length and blade:sheath:stem ratio (Juliano et al, in press) (Table 4). In addition, the quantity of harvest straw from traditional and modern varieties harvested traditionally and threshed for the same grain yield is similar. Only the quantity of stubble is higher in traditional varieties.
Table 3. IVOMD of IR36, IR42 and IR58 harvest straw.
Table 4. Properties of harvest straw of strong and weak stemmed IR and traditional rice varieties, 1986 dry season.
Using the pepsin-cellulase method, IVDMS of harvest straw of 22 IR rice varieties was found to range from 23.3 to 30.7% in the 1985 wet season crop and from 20.8 to 27.5% in the 1986 dry season (Bainton et al, 1987b; TDRI, unpublished data). Harvest straw IVDMS of the two crops were not significantly correlated (R=0.32). IVDMS was not significantly correlated with plant height or proportion of blade, stem and sheath in the harvest straw, but was higher in stems than blades and sheaths. Similar ranges of variation have been reported among IR36 straw samples at IRRI and among nine varieties in two crops of the International Rice Yield Nursery (Bainton et al, 1987a).
To estimate the relative contribution of variety and environment to variation in IVOMD of harvest straw, a cooperative experiment is underway for the 1987 wet season and 1988 dry season at IRRI using five tall and five semi-dwarf rices at 0 and 90 kg N ha-1 (applied basal). The harvest straw will be analysed jointly by TDRI, UPLB and IRRI scientists.
Table 5. Properties of 29 IR varieties and IR28150-84-3 plants at harvest 1985 wet season (WS) and 1986 dry season (DS) and their correlation1 with in vitro organic matter digestibility.
IR 36 and IR58 were multiplied at the IRRI Experimental Farm in the 1986 dry season to produce enough harvest straw and stubble for feeding trials with growing cattle. IVOMD was similar in IR36 harvest straw and stubble and IR58 harvest straw (Table 6). Voluntary intake and digestibility of the three samples were also similar (Table 6). Initially, intake of IR58 harvest straw was less than that of IR36 straw but after a week of feeding intakes were similar. We need to determine the minimum difference in IVOMD that would be reflected in a significant difference in in vivo digestibility in ruminants.
Table 6. Chemical and nutritional properties of IR36 and IR58 harvest straw and IR36 stubble fed to cattle, 1986 dry season.
Acknowledgements
The results reported here are from a collaborative project between IRRI, the Institute of Animal Science, University of the Philippines at Los Banos and the Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia 3083. The research was carried out under Australian Centre for International Agricultural Research Project 8373 with the School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria, Australia 3052. Screening for varietal difference in in vitro digestibility of harvest straw is a cooperative study (project A1482) with the Animal Feeds Section, Tropical Development and Research Institute, London WC1X 8LU, England.
Bainton S J. Plumb V E, Capper B S and Juliano B O. 1987a. Botanical composition, chemical analysis and cellulase solubility of rice straw from different varieties. In: Winter Meeting of the British Society of Animal Production. March 1987.
Bainton S J. Plumb V E, Drake M D, Juliano B O and Capper B S. 1987b. Effect of physiological and morphological characteristics on in vitro cellulase solubility of different varieties of rice straw. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1986. Proceedings of the Sixth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Los Banos, Laguna, Philippines, 1-5 April 1986. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Balasta M L F C, Perez C M, Juliano B O. Roxas D B and Villareal C P. (in press). The effect of silica level on some properties of rice plant and grain. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1985a. Variation in the nutritive value of rice straw in northern Thailand. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Fourth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Khon Kaen, Thailand, 10-14 April 1984. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1985b. Variation in the nutritive value of rice straw in northern Thailand: II. Voluntary feed intake and digestibility by sheep. In: M Wanapat and C Devendra (eds), Relevance of crop residues as animal feeds in developing countries. Proceedings of an International Workshop, Khon Kaen, Thailand, 29 November-2 December 1984. Khon Kaen University, Thailand.
Doyle P T. Devendra C and Pearce: G R. 1986. Rice straw as a feed for ruminants. International Development Programme of Australian Universities and Colleges, Canberra, Australia.
Doyle P T. Pearce: G R and Djajanegra A. 1987. Intake and digestion of cereal straws. In: Proceedings of the Fourth Animal Science Congress, Asian-Australasian Association of Animal Production Societies, Hamilton, New Zealand, 1-6 February 1987.
Goering H K and Van Soest P J. 1970. Forage fiber analysis. Agriculture Handbook No. 379. Agricultural Research Service, United States Department of Agriculture, Washington DC, USA.
Goto I and Minson D J. 1977. Prediction of the dry matter digestibility of tropical grasses using a pepsin-cellulase big-assay. Animal Feed Science and Technology 2:247-253.
Hart F J and Wanapat M. 1985. The effect of conservation of rice straw and stubble on its nutritive value. In: The utilization of fibrous agricultural residues as ruminant feeds project. Annual Report 1984-85. Department of Animal Science, Khon Kaen University, Thailand.
Hart F J and Wanapat M. 1986. Comparison of the nutritive value of straw and stubble from rice grown in the north-east of Thailand. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia.
IRRI (International Rice Research Institute). 1984. Annual Report for 1983. IRRI, Los Banos, Laguna, the Philippines.
IRRI. 1985. Annual Report for 1984. IRRI, Los Banos, Laguna, the Philippines.
Juliano B 0. 1985. Rice hull and rice straw. In: B O Juliano (ed.), Rice chemistry and technology. 2nd ed. American Association of Cereal Chemists, St Paul, MN, USA.
Juliano B 0, Roxas D B. Perez C M and Khush G S. (in press). Varietal differences in composition and in vitro digestibility of harvest rice straw. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Khush G S and Kumar I. 1987. Genetic selection for improved nutritional quality of fibrous crop residues of cereal crops - a plant breeder's viewpoint. In: Ruminant feeding systems utilizing fibrous agricultural residues - 1986. Proceedings of the Sixth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Los Banos, Laguna, the Philippines, 1-5 April 1986. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Minson D J and McLeod M N. 1972. The in vitro technique: Its modification for estimating digestibility of large numbers of tropical pasture samples. CSIRO Division of Tropical Crops and Pastures Technical Paper 8. Commonwealth Scientific and Industrial Research Organisation, Australia.
Neilson M J and Stone B A. 1987. Chemical composition of fibrous feeds for ruminants in relation to digestibility. In: Proceedings of the Fourth Animal Science Congress, Asian-Australasian Association of Animal Production Societies, Hamilton, New Zealand, 1-6 February 1987.
Nicholson J W G. 1984. Digestibility, nutritive value, and feed intake. In: F Sundstøl and E Owen (eds), Straw and other fibrous byproducts as feed. Elsevier, Amsterdam, the Netherlands.
Pearce G R. 1986. Possibilities for improving the nutritive value of rice straw without pretreatment. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Preston T R and Leng R A. 1987. Matching livestock systems to available feed resources in developing countries. University of Armidale Press, Armidale, NSW, Australia.
Rexen F and Munck L. 1984. Cereal crops for industrial use in Europe. Commission of the European Communities, Luxembourg and Carlsberg Research Centre, Copenhagen, Denmark.
Roxas D B. Castillo L S. Obsioma A R. Lapitan R M, Momongan V G and Juliano B O. 1984. Chemical composition and in vitro digestibility of straw from different varieties of rice. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Third Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Peradeniya, Sri Lanka, 17-22 April 1983. University of Melbourne, Australia.
Roxas D B. Obsioma A R. Lapitan R M, Castillo L S. Momongan V G and Juliano B O. 1985. The effect of variety of rice, level of nitrogen fertilization and season on the chemical composition and in vitro digestibility of straw. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Fourth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Khon Kaen Thailand, 10-14 April 1984. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Roxas D B. Aller M G and Juliano B O. (in press). Changes in chemical composition and in vitro digestibility of straw components from four rice varieties. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Sharma U. Brillouet J-M, Scalbert A and Monties B. 1986. Studies on a brittle stem mutant of rice, Oryza sativa L.; characterization of lignin fractions, associated phenolic acids and polysaccharides from rice stem. Agronomie 6:265-271.
Van Soest P J. 1981. Limiting factors in plant residues of low biodegradability. Agriculture and Environment 6:135-143.
Van Soest P J. 1982. Nutritional ecology of the ruminant. O & B Books, Corvallis, Oregon, USA.
Winugroho M. 1986. Intake and digestibility of the upper and lower fractions of rice straw by sheep and goats. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Khush: Generally low yields.
Mueller - Harvey: Are phenolic compounds of any significance in rice breeding?
Khush: Yes, in relation to insect resistance.
Ørskov: Are there no relationships between grain yield and straw quality?
Khush: No clear relationship has been found. Although plant breeders must concentrate on improving rain yields in rice, it is possible that straw quality can be given some attention.
Little: Do higher-yielding rice varieties have higher crude protein contents in their straw?
Capper: Traditional varieties may have about 4% crude protein, rising to 6 or 7% in improved varieties. From the research on rice to date it appears that selection for grain yield has not reduced straw quality. However, one problem in investigating rice straw quality is the variability both within and between plots and there seems to be no satisfactory explanation for this.
Little: It appears that there is only little genetically determined variation in the nitrogen content of straws. Will it be possible to select for this?
Khush: The direction breeding programmes take will depend upon priorities and the relative importance of grain and straw.
Thomson: At ICARDA the facilities devoted to examination of straw quality are modest and take up only a small proportion of the budget. I consider that it is not beyond the resources of the CG centres to address the question of straw quality.
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Genetic selection for improved nutritional quality of rice straw-a plant breeder's viewpoint
Author
Gurdev S. Khush1, Bienvenido O. Juliano2 and Domingo B. Roxas3
1. Principal Plant Breeder, Plant Breeding DepartmentInternational Rice Research Institute (IRRI), P.O. Box 933, Manila, the Philippines.
2. Chemist, Cereal Chemistry Department
3. Postdoctoral Fellow, Asian Rice Farming Systems Network
Introduction
In South and Southeast Asia, the primary agricultural activity is crop production. Plant breeders are engaged in increasing crop productivity per unit area per unit time and in improving grain quality. Straw quantity and quality have been secondary considerations, except as they directly affect crop yield, such as in resistance to insects, diseases and lodging (Khush and Kumar, 1987). Plant breeders are becoming increasingly aware of the need for whole-plant utilisation, and hence of the need to improve the utility of crop residues (Rexen and Munck, 1984). Ruminant livestock in the rice-producing areas of Asia are dependent on rice straw for part of their nutrient requirements during the cropping seasons and in dry or drought periods (Doyle et al, 1986). But the biodegradability and voluntary intake of rice straw by ruminants are low. The feeding value of rice straw can be improved by treating it with alkali or urea, but genetic improvement of straw quality would be a cheaper and more logical approach. However, feed value should be improved without reducing grain yield and quality. Harvest straw (upper 40-50 cm below the panicle neck) is the most economical fraction of the rice crop residue, since it is already collected and partly dried in threshing areas. Stubble is either burned or ploughed under.We discuss here collaborative research at IRRI examining the feasibility of improving the feed value of rice straw for ruminants.
Methods
Dry-matter, crude-protein and organic-matter contents of the straw of various rice genotypes were determined using AOAC (1970) procedures. Neutral-detergent fibre (NDF), cellulose, lignin and silica contents were determined according to Goering and Van Soest (1970). In vitro organic-matter digestibility (IVOMD) was measured as described by Minson and McLeod (1972). The rumen fluid was taken from a fistulated buffalo fed a rice-straw-based diet supplemented with a concentrate mix containing 15% crude protein at 1.0% liveweight. Cellulase solubility (in vitro dry matter solubles, IVDMS) was estimated at the Tropical Development and Research Institute (TDRI), London, by the method of Goto and Minson (1977).Variation in composition and in vitro digestibility
Variations in chemical composition and in vitro digestibility of rice straw have been summarised by Juliano (1985) and Doyle et al (1986).Varietal differences have been suggested by many researchers, but others have reported little or no variation. Rice straw contains less lignin but more silica and oxalic acid than other cereal straws (Van Soest, 1981; Juliano, 1985).
Various morphological, chemical and environmental factors affect the nutritional value of cereal straws (Doyle et al, 1987; Neilson and Stone, 1987; Nicholson, 1984; Pearce, 1986; Preston and Leng, 1987; Van Soest, 1982). These include cell-wall content; content of lignin and silica; ratio of leaf blade, leaf sheath and stem; length of harvest straw; soil fertility and added fertilizer level; soil moisture and degree of senescence of straw at harvest; growth duration; resistance to pests; and plant height.
Cell contents (neutral-detergent solubles) are more readily digestible than cell walls, measured as neutral-detergent fibre (NDF) (Van Soest, 1982). Lignin and silica are reported to reduce the digestibility of rice straw (Van Soest, 1981). However, manipulation of the silica content of three rice varieties by hydroponics did not substantially change the invitro organic-matter digestibility of the total straw at harvest (Balasta et al, in press) (Table 1). Thus, lignin is probably the most important factor that limits digestibility of rice straw in ruminants (Neilson and Stone, 1987).
Harvest straw is made up of leaf blades, leaf sheaths, the stem and the panicle rachis. The proportions of these components are affected by straw length. In the Philippines, straw is cut 40-SO em below the base of the panicle to facilitate holding during threshing. The stem contains less ash and protein but more cellulose than the leaves (Doyle et al, 1986). In Malaysian rices, mean IVOMD of the plant parts were blades 44%; sheaths 45%; and stem internodes 42%. IVOMD varied more in blades than internodes (Doyle et al, 1986). Roxas et al (in press) found that IVOMD of stem internodes tends to be higher than that of leaf blades and leaf sheaths, although the NDF content of the internodes was not necessarily lower (Table 2). Internodes have a higher cellulose content than leaves.
Table 1. Crude silica content and in vitro organic matter digestibility of harvest straw of IR rices grown hydroponically with different levels of silica.
Variety
|
Season
|
Property
|
SiO2 concentration (ppm)
|
LSD
| ||||
0
|
100
|
200
|
300
|
400
|
(5%)
| |||
| IR36 | 1985 WS | Crude silica (%) | 0.7 | 7.4 | 8.8 | 1.3 | ||
| IVOMD (%) | 52.0 | 47.8 | 50.7 | ns | ||||
| IR42 | 1985 WS | Crude silica (%) | 0.7 | 4.0 | 8.4 | 1.3 | ||
| IVOMD (%) | 57.4 | 50.0 | 50.1 | 4.6 | ||||
| IR58 | 1986 DS | Crude silica (%) | 0.4 | 4.5 | 9.4 | 12.1 | 15.4 | 1.9 |
| IVOMD (%) | 40.5 | 48.1 | 43.9 | 44.1 | 41.7 | ns | ||
| IR36 | 1986 DS | Crude silica (%) | 0.4 | 4.7 | 9.4 | 11.2 | 12.2 | 1.9 |
| IVOMD (%) | 46.8 | 44.7 | 43.9 | 35.4 | 46.2 | 9.6 | ||
WS = wet season: DS = dry season.Table 2. Composition of leaf blade 2 (LB), leaf sheath 2 (LS), and internode 2 (I) of IR36 and IR42 rice plant at harvest, 1984 wet season.
Source: Balasta et al (in press).
Property (%)
|
IR36
|
IR42
| ||||
LB
|
LS
|
I
|
LB
|
LS
|
I
| |
| IVOMD |
40
|
45
|
51
|
34
|
37
|
50
|
| NDF |
67
|
72
|
62
|
70
|
70
|
71
|
| Cellulose |
30
|
37
|
44
|
31
|
35
|
41
|
| Hemicellulose |
13
|
11
|
11
|
16
|
10
|
11
|
| Lignin |
6.2
|
3.3
|
3.7
|
5.5
|
4.5
|
7.7
|
Source: Roxas et al (in press).Stubble (basal residue after harvest) contains less crude protein and more cellulose than harvest straw (Hart and Wanapat, 1986; Winugroho, 1986). IVOMD was higher in stubble than harvest straw in rainfed lowland rice in northeast Thailand (Hart and Wanapat, 1986) and in Ciawi, Indoneasia (Winugroho, 1986), but lower in lowland rice at IRRI (Roxas et al, in press). In four lowland varieties at IRRI, IVOMD of harvest straw was higher than that of whole straw (45-50% vs 36-46%), suggesting that the IVOMD of stubble is lower than that of harvest straw (Roxas et al, in press). IVOMD of stubble increases when the stubble is left ungrazed (Hart and Wanapat, 1985), probably due to ratooning and continuing growth of unproductive tillers.
Current breeding efforts which aim at incorporating resistance to insects, diseases and lodging also lead to improvements in harvest straw quality by reducing straw damage. Duration of growth and nitrogen fertilizer levels also affect protein content of the straw. Early-maturing modern rices have higher grain and, possibly, higher straw protein contents than medium-maturing varieties (IRRI, 1985), and tend to have thinner straw and be more susceptible to lodging than medium-maturing rices (IRRI, 1984). Nutrient supply affects the ash content of straw. Soil N level affects protein content.
The brittle stem mutants of rice variety Balilla 28 have been reported to have higher lignin and hemicellulose and lower alpha-cellulose contents in the stem than the parent (Sharma et al, 1986). However, the IVOMD of their harvest straw (32-49%) overlapped with that of the Balilla 28 parent (36%) (Juliano et al, in press).
Semi-dwarf rices were shown to have similar if not greater harvest straw IVOMD than tall varieties such as H4 (Roxas et al, 1985) (Table 3). Selected strong- and weak-stemmed traditional and semi-dwarf varieties showed similar harvest straw IVOMD despite differences in straw length and blade:sheath:stem ratio (Juliano et al, in press) (Table 4). In addition, the quantity of harvest straw from traditional and modern varieties harvested traditionally and threshed for the same grain yield is similar. Only the quantity of stubble is higher in traditional varieties.
Table 3. IVOMD of IR36, IR42 and IR58 harvest straw.
Year
|
Season
|
Type of plot1
|
Harvest straw IVOMD (% of total)
|
Source
| |||
IR36
|
IR42
|
IR58
|
H4
| ||||
1982
|
DS
|
D
|
38
|
41
|
-
|
-
|
a
|
1982
|
WS
|
A/DP
|
53
|
47
|
-
|
45
|
b
|
1983
|
DS
|
A/DP
|
51
|
41
|
-
|
39
|
b
|
1984
|
WS
|
PB
|
50
|
50
|
45
|
47
|
c
|
1985
|
WS
|
D
|
45
|
41
|
42
|
-
|
d
|
1986
|
DS
|
D
|
33
|
36
|
34
|
-
|
d
|
1986
|
DS
|
M
|
52
|
-
|
49
|
-
|
e
|
1. D=demonstration plot; A/DP=agronomy/date of planting trial; PB=plant breeding plot;Recent studies by Roxas et al (1985) suggest that varieties differ in harvest straw IVOMD. In two seasons, IR36 had consistently higher IVOMD than its sister variety IR42 (Table 3). In other IRRI trials, relative IVOMD values for these two varieties were different from another early-maturing variety, IR58 (Roxas et al, 1984; in press; Juliano et al, in press). Differences in IVOMD were not related to differences in NDF, cellulose, lignin and silica contents of the straw.
M=multiplication plot.Sources: a. Roxas et al (1984); b. Roxas et al (1985); c. Roxas et al (in press); d.
Juliano et al (in press); e. IAS/UPLB-IRRI, unpublished data (see Table 6).
Table 4. Properties of harvest straw of strong and weak stemmed IR and traditional rice varieties, 1986 dry season.
Property
|
IR rices
|
Traditional rices
| ||
Non-lodging1
|
Lodging2
|
Strong stem3
|
Weak stem4
| |
| IVOMD (%) |
33
|
34
|
36
|
34
|
| NDF (%) |
69
|
70
|
67
|
68
|
| Crude ash (%) |
20
|
22
|
21
|
21
|
| Weight (% of total straw) |
76
|
78
|
47
|
39
|
| Blades: |
41
|
36
|
52
|
48
|
| Sheaths: |
43
|
37
|
30
|
29
|
| Stem ratio |
16
|
27
|
18
|
23
|
| Growth duration (d) |
132
|
116
|
123
|
127
|
1. IR8 and IR42.A survey of harvest straw of 29 IR varieties and IR28150-84-3 in two crop seasons (dry and wet) revealed differences in IVOMD among the semi-dwarf rices. However, sample ranking was not strictly maintained in the two seasons (Juliano et al, in press) (Table 5). IVOMD of IR36 harvest straw was higher than that of IR42 and IR58 harvest straw in the 1985 wet season but lower than that of IR42 straw in the 1986 dry season (Table 3). In both seasons IVOMD correlated negatively with crude ash; the correlation with straw N was positive in the first crop and negative in the second crop (Table 5). IVOMD and NDF showed a non-significant negative correlation. The correlation between seasons in IVOMD and content of NDF were not significant, suggesting large environmental influence on the chemical and nutritive properties of harvest straw.
2. IR36 and IR40.
3. Century Patna 231-SL0 17, Khao Dawk Mali 105, and Gam Pail.
4. Tetep, TKM 6, and Binato.Source: Juliano et al (in press).
Using the pepsin-cellulase method, IVDMS of harvest straw of 22 IR rice varieties was found to range from 23.3 to 30.7% in the 1985 wet season crop and from 20.8 to 27.5% in the 1986 dry season (Bainton et al, 1987b; TDRI, unpublished data). Harvest straw IVDMS of the two crops were not significantly correlated (R=0.32). IVDMS was not significantly correlated with plant height or proportion of blade, stem and sheath in the harvest straw, but was higher in stems than blades and sheaths. Similar ranges of variation have been reported among IR36 straw samples at IRRI and among nine varieties in two crops of the International Rice Yield Nursery (Bainton et al, 1987a).
To estimate the relative contribution of variety and environment to variation in IVOMD of harvest straw, a cooperative experiment is underway for the 1987 wet season and 1988 dry season at IRRI using five tall and five semi-dwarf rices at 0 and 90 kg N ha-1 (applied basal). The harvest straw will be analysed jointly by TDRI, UPLB and IRRI scientists.
Table 5. Properties of 29 IR varieties and IR28150-84-3 plants at harvest 1985 wet season (WS) and 1986 dry season (DS) and their correlation1 with in vitro organic matter digestibility.
Property
|
Range
|
Correlation coefficient with IVOMD
|
Correlation between seasons
| ||
1985 WS
|
1986 DS
|
1985 WS
|
1986 DS
| ||
| Growth duration (days) |
102-142
|
103-138
|
-0.01
|
-0.54**
|
0.97**
|
| Harvest index |
0.28-0.60
|
0.29-0.64
|
-0.28
|
-0.69**
|
0.54**
|
| N harvest index |
0.38-0.71
|
0.40-0.74
|
-0.36
|
-0.66**
|
0.32
|
| N content of straw (% w.b.) |
0.56-0.97
|
0.52-0.90
|
0.46**
|
-0.43*
|
0.47**
|
| N content of panicle (% w.b.) |
1.03-1.50
|
0.94-1.41
|
0.19
|
-0.51**
|
0.30
|
| Harvest straw (% of total) |
38-64
|
46-74
|
-0.25**
|
0.38*
|
0.73**
|
| IVDMD (%) |
34-47
|
33-44
|
0.88
|
0.76**
|
0.01
|
| IVOMD (%) |
34-49
|
27-42
|
-
|
-
|
0.22
|
| Crude ash (% d.b.) |
18-23
|
18-26
|
-0.38*
|
-0.65**
|
0.49**
|
| NDF (% d.b.) |
66-76
|
68-74
|
0.25
|
-0.11
|
0.13
|
Source: Juliano et al (in press).
Significant r = 0.361 at the 5% level and 0.463 at the 1% level (n=30).
Feeding studies
In addition to the environment-variety interaction on the chemical composition and IVOMD of rice straw, the correspondence of IVOMD to feed value (voluntary intake and in vivo digestibility) needs to be verified. Rice stubble with higher IVOMD than harvest straw (35 vs 25%) showed lower intake and digestibility when fed with concentrates to sheep and goats (Winugroho, 1986). However, among five Thai rainfed lowland rice varieties with similar IVOMD (45-51%), one variety showed higher organic-matter digestibilities in sheep than the others, although voluntary intakes were similar (Cheva-Isarakul and Cheva-Isarakul, 1985a; 1985b).IR 36 and IR58 were multiplied at the IRRI Experimental Farm in the 1986 dry season to produce enough harvest straw and stubble for feeding trials with growing cattle. IVOMD was similar in IR36 harvest straw and stubble and IR58 harvest straw (Table 6). Voluntary intake and digestibility of the three samples were also similar (Table 6). Initially, intake of IR58 harvest straw was less than that of IR36 straw but after a week of feeding intakes were similar. We need to determine the minimum difference in IVOMD that would be reflected in a significant difference in in vivo digestibility in ruminants.
Genetic selection for nutritional quality of straw
The results presented show that chemical composition and digestibility of straw varies among rice varieties. This variability presumably could be exploited to improve the nutritional value of the straw of future varieties. However, rice is grown primarily for grain and, at present, no attention is paid to the nutritional quality of the straw. With the present emphasis on increasing grain yield it is unlikely that any institution will undertake a selection programme to improve the nutritional value of straw but plant breeders may be persuaded to evaluate their advanced breeding lines for the nutritional value of the straw. Other traits being equal, plant breeders could then select lines with better nutritional quality of straw. However, availability of simple screening techniques for evaluating the straw quality of breeding materials is a prerequisite.Table 6. Chemical and nutritional properties of IR36 and IR58 harvest straw and IR36 stubble fed to cattle, 1986 dry season.
Property (% dry basis)
|
Harvest straw
|
IR36 stubble
| |
IT58
|
IR36
| ||
| Crude ash |
21.7
|
22.4
|
26.2
|
| Neutral-detergent fibre |
63.4
|
66.0
|
64.8
|
| Acid-detergent fibre |
54.9
|
55.6
|
58.8
|
| Hemicellulose |
8.5
|
10.4
|
6.1
|
| Cellulose |
35.9
|
35.7
|
35.0
|
| Lignin |
4.6
|
4.8
|
5.5
|
| Crude silica |
14.4
|
15.1
|
18.2
|
| IVDMD (% of total) |
46.2
|
48.6
|
44.3
|
| IVOMD (% of total) |
49.0
|
51.8
|
50.2
|
| Voluntary intake1 (% of body wt d-1) |
1.6
|
1.9
|
1.9
|
| In vivo dry-matter digestibility1 (%) |
39.0
|
43.0
|
45.0
|
1. Measured on growing cattle fed with rice straw/stubble and supplemented with concentrated mix at 1% of body weight. Differences among means were not significant. Source: IAS/UPLB-IRRI (unpublished data).
Summary
The wide variation in the ratio of leaf blade: leaf sheath:stem, chemical composition and IVOMD of harvest straw suggests that varietal differences in straw nutritional quality exist. However, environmental factors significantly affect IVOMD. Only after the environmental influence on IVOMD is understood and minimised can effective IVOMD screening be justified in a rice breeding programme. The screening method chosen should correlate with in vivo nutritional value of harvest straw. When selecting for straw quality, we must at the same time maintain or even improve grain yields and grain quality, the major goals of current rice breeding programmes.Acknowledgements
The results reported here are from a collaborative project between IRRI, the Institute of Animal Science, University of the Philippines at Los Banos and the Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia 3083. The research was carried out under Australian Centre for International Agricultural Research Project 8373 with the School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria, Australia 3052. Screening for varietal difference in in vitro digestibility of harvest straw is a cooperative study (project A1482) with the Animal Feeds Section, Tropical Development and Research Institute, London WC1X 8LU, England.
References
AOAC (Association of Official Analytical Chemists). 1970. Official methods of analysis. 11th ed. AOAC, Washington DC, USA.Bainton S J. Plumb V E, Capper B S and Juliano B O. 1987a. Botanical composition, chemical analysis and cellulase solubility of rice straw from different varieties. In: Winter Meeting of the British Society of Animal Production. March 1987.
Bainton S J. Plumb V E, Drake M D, Juliano B O and Capper B S. 1987b. Effect of physiological and morphological characteristics on in vitro cellulase solubility of different varieties of rice straw. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1986. Proceedings of the Sixth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Los Banos, Laguna, Philippines, 1-5 April 1986. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Balasta M L F C, Perez C M, Juliano B O. Roxas D B and Villareal C P. (in press). The effect of silica level on some properties of rice plant and grain. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1985a. Variation in the nutritive value of rice straw in northern Thailand. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Fourth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Khon Kaen, Thailand, 10-14 April 1984. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1985b. Variation in the nutritive value of rice straw in northern Thailand: II. Voluntary feed intake and digestibility by sheep. In: M Wanapat and C Devendra (eds), Relevance of crop residues as animal feeds in developing countries. Proceedings of an International Workshop, Khon Kaen, Thailand, 29 November-2 December 1984. Khon Kaen University, Thailand.
Doyle P T. Devendra C and Pearce: G R. 1986. Rice straw as a feed for ruminants. International Development Programme of Australian Universities and Colleges, Canberra, Australia.
Doyle P T. Pearce: G R and Djajanegra A. 1987. Intake and digestion of cereal straws. In: Proceedings of the Fourth Animal Science Congress, Asian-Australasian Association of Animal Production Societies, Hamilton, New Zealand, 1-6 February 1987.
Goering H K and Van Soest P J. 1970. Forage fiber analysis. Agriculture Handbook No. 379. Agricultural Research Service, United States Department of Agriculture, Washington DC, USA.
Goto I and Minson D J. 1977. Prediction of the dry matter digestibility of tropical grasses using a pepsin-cellulase big-assay. Animal Feed Science and Technology 2:247-253.
Hart F J and Wanapat M. 1985. The effect of conservation of rice straw and stubble on its nutritive value. In: The utilization of fibrous agricultural residues as ruminant feeds project. Annual Report 1984-85. Department of Animal Science, Khon Kaen University, Thailand.
Hart F J and Wanapat M. 1986. Comparison of the nutritive value of straw and stubble from rice grown in the north-east of Thailand. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia.
IRRI (International Rice Research Institute). 1984. Annual Report for 1983. IRRI, Los Banos, Laguna, the Philippines.
IRRI. 1985. Annual Report for 1984. IRRI, Los Banos, Laguna, the Philippines.
Juliano B 0. 1985. Rice hull and rice straw. In: B O Juliano (ed.), Rice chemistry and technology. 2nd ed. American Association of Cereal Chemists, St Paul, MN, USA.
Juliano B 0, Roxas D B. Perez C M and Khush G S. (in press). Varietal differences in composition and in vitro digestibility of harvest rice straw. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Khush G S and Kumar I. 1987. Genetic selection for improved nutritional quality of fibrous crop residues of cereal crops - a plant breeder's viewpoint. In: Ruminant feeding systems utilizing fibrous agricultural residues - 1986. Proceedings of the Sixth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Los Banos, Laguna, the Philippines, 1-5 April 1986. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Minson D J and McLeod M N. 1972. The in vitro technique: Its modification for estimating digestibility of large numbers of tropical pasture samples. CSIRO Division of Tropical Crops and Pastures Technical Paper 8. Commonwealth Scientific and Industrial Research Organisation, Australia.
Neilson M J and Stone B A. 1987. Chemical composition of fibrous feeds for ruminants in relation to digestibility. In: Proceedings of the Fourth Animal Science Congress, Asian-Australasian Association of Animal Production Societies, Hamilton, New Zealand, 1-6 February 1987.
Nicholson J W G. 1984. Digestibility, nutritive value, and feed intake. In: F Sundstøl and E Owen (eds), Straw and other fibrous byproducts as feed. Elsevier, Amsterdam, the Netherlands.
Pearce G R. 1986. Possibilities for improving the nutritive value of rice straw without pretreatment. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Preston T R and Leng R A. 1987. Matching livestock systems to available feed resources in developing countries. University of Armidale Press, Armidale, NSW, Australia.
Rexen F and Munck L. 1984. Cereal crops for industrial use in Europe. Commission of the European Communities, Luxembourg and Carlsberg Research Centre, Copenhagen, Denmark.
Roxas D B. Castillo L S. Obsioma A R. Lapitan R M, Momongan V G and Juliano B O. 1984. Chemical composition and in vitro digestibility of straw from different varieties of rice. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Third Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Peradeniya, Sri Lanka, 17-22 April 1983. University of Melbourne, Australia.
Roxas D B. Obsioma A R. Lapitan R M, Castillo L S. Momongan V G and Juliano B O. 1985. The effect of variety of rice, level of nitrogen fertilization and season on the chemical composition and in vitro digestibility of straw. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Fourth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Khon Kaen Thailand, 10-14 April 1984. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Roxas D B. Aller M G and Juliano B O. (in press). Changes in chemical composition and in vitro digestibility of straw components from four rice varieties. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Sharma U. Brillouet J-M, Scalbert A and Monties B. 1986. Studies on a brittle stem mutant of rice, Oryza sativa L.; characterization of lignin fractions, associated phenolic acids and polysaccharides from rice stem. Agronomie 6:265-271.
Van Soest P J. 1981. Limiting factors in plant residues of low biodegradability. Agriculture and Environment 6:135-143.
Van Soest P J. 1982. Nutritional ecology of the ruminant. O & B Books, Corvallis, Oregon, USA.
Winugroho M. 1986. Intake and digestibility of the upper and lower fractions of rice straw by sheep and goats. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia.
Discussion
Van Soest: What are the problems connected with low silica levels in the nutrient solutions on which rice plants were grown?Khush: Generally low yields.
Mueller - Harvey: Are phenolic compounds of any significance in rice breeding?
Khush: Yes, in relation to insect resistance.
Ørskov: Are there no relationships between grain yield and straw quality?
Khush: No clear relationship has been found. Although plant breeders must concentrate on improving rain yields in rice, it is possible that straw quality can be given some attention.
Little: Do higher-yielding rice varieties have higher crude protein contents in their straw?
Capper: Traditional varieties may have about 4% crude protein, rising to 6 or 7% in improved varieties. From the research on rice to date it appears that selection for grain yield has not reduced straw quality. However, one problem in investigating rice straw quality is the variability both within and between plots and there seems to be no satisfactory explanation for this.
Little: It appears that there is only little genetically determined variation in the nitrogen content of straws. Will it be possible to select for this?
Khush: The direction breeding programmes take will depend upon priorities and the relative importance of grain and straw.
Thomson: At ICARDA the facilities devoted to examination of straw quality are modest and take up only a small proportion of the budget. I consider that it is not beyond the resources of the CG centres to address the question of straw quality.
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