Abstract
Viability and vigour are seed quality parameters that affect the seed chain. Seed vigour is a measure of accumulated damage in seed as viability declines from physiological maturity. This study aimed at determining the seed vigour of various sorghum genotypes stored ex situ for 10 years using the Heat Shock Stress Test (HSST), Cold Test (CT), Standard Germination Test (SGT) and field germination. The samples from the regeneration trial were kept in ex situ storage at 0-4°C and 40% relative humidity from 2003 to 2014. The experiments were arranged in a completely randomised design with four replication and differences in radicle length, shoot length for the 65 genotypes evaluated at 5% level of significance. An unpaired T- test was used to compare the accuracy of the quality methods in predicting field emergence. All the evaluated genotypes responded differentially to all the vigour test methods. There were significant differences (P<0.01) in the performance of genotypes with respect to radical and shoot length in response to the CT, HSST and the SGT. The results of CT and HSST predicted field emergence better than the standard germination test. None of the quality test methods and a strong and significant correlation with field emergence. Genotypes IS 30260 and IS 34637 were vigourous as they had the highest shoot length of 43.75 and 42.38 mm and IS 30063 had 45.52 mm in root length after 48 h of incubation. Overall, this study showed that field emergence of sorghum cannot be accurately predicted from a standard germination, HSST and CT. Key words: Sorghum bicolor, seed quality, cold test, heat shock stress test, germination test.
Highlights
Sorghum (Sorghum bicolor L.) in Africa is among the leading cereal grains and in Zimbabwe it ranks the third most important cereal crop after maize and wheat (FAO, 2002)
For example genotype IS 30260 had the highest shoot length of 43.75 mm in the Cold Test (CT), which was followed by the Standard Germination Test (SGT) and Heat Shock Stress Test (HSST) with lengths of genotypes IS 34637, 42.38 mm and IS 30086, 20.50 mm respectively
Control genotypes IS 29751 and IS 29747 which were stored in 2013 had the least germination capacity in the CT and HSST with 74% and 72% respectively
Summary
Sorghum (Sorghum bicolor L.) in Africa is among the leading cereal grains and in Zimbabwe it ranks the third most important cereal crop after maize and wheat (FAO, 2002). It is grown mainly in the semi-arid areas of the tropics as a staple food for poor people (ICRISAT, 2004) and in subtropics (FAO, 2005). High quality seed lots may improve crop yield in two ways: firstly, seedling. The standard germination test, which is considered the universal test for seed quality, evaluates the maximum potential of a particular seed lot under an ideal set of conditions (ISTA, 1985; AOSA, 1986). Conditions in which the seed is found during standard germination test are often in conflict with the conditions in the field, and seed vigour test is necessary (Morab, 2013)
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