VARIABILITY IN SEEDLING ELONGATION OF WHEAT, AND SOME FACTORS ASSOCIATED WITH IT

Coleoptile lengths of 22 cultivars of wheat (Triticum aestivum L.) were measured in darkness at 2 depths of sowing (2 and 6 cm) under minimal mechanical stress and at 4 cm depth under 0.76 kPa mechanical stress. The experiments were done to describe variability in elongation abilities and to develop a technique for genotypic screening for tolerance of high soil strength. Of the 8 cultivars with shortest coleoptiles, 6 had cv. Condor parentage. Lengths of coleoptiles of all cultivars were reduced by 18% on average, under 0.76 kPa mechanical stress. Lengths were correlated with time to median emergence (r = 0.72) and total emergence percentage by 20 days after sowing (r = 0.77). Some cultivars with shorter coleoptiles took an extra 2-3 days to reach median emergence and attained a poorer total emergence percentage than those with long coleoptiles. A doubling of seed weight resulted in an increase of only 9% in coleoptile lengths, with no effect on emergence. The results suggest that cultivars appropriate for emergence from particular soil types or under adverse conditions could be selected under minimum soil stress because their performance ranking was similar under mechanical stress.