VARIATION IN CARDINAL TEMPERATURES FOR GERMINATION AMONG WHEAT (TRITICUM-AESTIVUM) GENOTYPES

In most tropical regions where wheat is grown under irrigation, high t emperatures at sowing adversely affect crop establishment and subseque nt seedling survival. The objective of this study was to compare wheat (Triticum aestivum) genotypes for their ability to germinate and grow at high temperatures during the seedling stage. Twenty-five seeds eac h of 14 spring wheat cultivars were placed on moist filter paper at di fferent temperatures (5-degrees-C to 40-degrees-C) in a one-way thermo gradient plate to determine the cardinal temperatures for germination. Rate of germination at each temperature for each genotype was compute d as the inverse of time taken for 50% of the seeds to germinate. Rate of germination for each genotype at different temperatures was modell ed with temperature to determine the base (t(b)), and optimum (t(opt)) temperatures. Response of germination to temperature for each genotyp e was calculated as the slope of a linear regression of the rate of ge rmination on temperature below t(opt). Genotypes differed in their opt imum temperatures and Mexipak (= Kalyansona) had the lowest. Range in base temperature among the genotypes was between 0-degree-C and 2-degr ees-C differences but were not statistically significant though they m ight be biologically significant. Genotypes differed in their response to temperature with Gomam having the lowest rate, implying that it wa s slow to respond to increasing temperatures. Debeira and Cham 6 showe d a similar response. Three lines which had performed well in spring w heat evaluation trials for moderate rainfall areas under heat stress h ad the highest response rate. It is concluded that combining higher op timum temperatures with faster response rates would result in better-a dapted germplasm for regions where high temperatures persist at sowing .