Effect of light and temperature on seed germination of selected African leafy vegetables

Published Date

July 2015, Vol.99:29–35, doi:10.1016/j.sajb.2015.03.185

Title 

Effect of light and temperature on seed germination of selected African leafy vegetables

• Author 

• M.M. Motsa ^a,,
• M.M. Slabbert ^b,
• W. van Averbeke ^a,
• L. Morey ^a,c,

• aCentre for Organic and Smallholder Agriculture, Department of Crop Sciences, Tshwane University of Technology, Private bag X680, Pretoria 0001, South Africa
• bDepartment of Horticulture, Tshwane University of Technology, Private bag X680, Pretoria 0001, South Africa
• cAgricultural Research Council, Central Office (ARC-CO), PO Box 8783, Pretoria 0001, South Africa

Received 29 April 2014. Revised 4 March 2015. Accepted 11 March 2015. Available online 2 April 2015. Edited by MI Daws

Highlights

• •
  Investigation of the effect of temperature and light on seed germination and emergence of eight African leafy vegetables.
• •
  Maximum germination was found to be at 29–36 °C.
• •
  Maximum emergence was found to be at 25–31 °C.
• •
  Three African leafy vegetables are photosensitive, whilst five are indifferent to light sensitivity.
• •
  Seed germination and emergence were temperature dependent; light positively influenced onset and final germination of three vegetable species.

Abstract

Using laboratory incubation, the response of seed germination and emergence to variability in temperature and light was examined for spider flower (Cleome gynandraL.), amaranth (Amaranthus cruentus L.), non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis), nightshade (Solanum retroflexum Dun.), pumpkin (Cucurbita maxima Duchesne), tsamma melon (Citrullus lanatus Thunb.), Jew's mallow (Corchorus olitorius L.) and cowpea (Vigna unguiculata (L.) Walp.). Effect of temperature on seed germination and emergence was monitored under continuous darkness and at constant temperatures that ranged from 4 °C to 44 °C with 4 °C increments. The effect of light on seed germination was measured at 25 °C. Temperature affected germination rate and final germination percentage of all species tested in ways that were characteristic for each of the species tested. Generally, optimum germination occurred at temperatures ranging between 29 °C and 32 °C but at higher temperatures for V. unguiculata (36 °C) and C. olitorius (35 °C). The minimum temperature for germination ranged between 8 °C and 15 °C, and the maximum between 36 °C and 44 °C. Optimum temperatures for seedling emergence ranged from 25 °C to 31 °C, the maximum between 32 °C and 40 °C and minimum between 2 °C and 13 °C. Light positively (p < 0.01) affected onset of germination in A. cruentus, B. rapa subsp. chinensis and C. olitorius, and final germination percentage of B. rapa subsp. chinensis, C. lanatus and S. retroflexum. The results suggested that under South African conditions, seeds of the eight species will typically germinate optimally as temperatures rise during spring before the occurrence of very hot temperatures in summer. Due to their positive response to light, germination of B. rapa subsp. chinensis, C. lanatus and S. retroflexum seeds is expected to be optimal when sown at or close to the soil surface.

Keywords

• Cardinal temperatures
• Light
• Germination
• Emergence
• African leafy vegetables

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