Coleoptile length variation of near-isogenic Rht lines of modern CIMMYT bread and durum wheats

A set of 10 bread wheat (Triticum aestivum L.) and six durum wheat (T. turg idum L.) genotypes near-isogenic for either the Rht1 or Rht2 dwarfing genes were analyzed for plant height, kernel weight, coleoptile length and grain yield. Coleoptile length was measured at three different temperatures and plant height, kernel weight and grain yield determined in six different env ironments. Durum wheat, regardless of stature, produced longer coleoptiles than bread wheat at higher temperature. Within the non-Rht isolines, plant height and coleoptile length were independent characters. The tall durum wh eats tended to be taller than their bread wheat counterparts, indicating an absence of minor genes for reduced height. However, a number of bread whea t cultivars showed relatively small height increases following removal of t he Rht gene and substantially greater increases in coleoptile length. Coleo ptile length was more highly correlated (r(2) = 0.53, P < 0.01) with seed w eight among the non-Rht isolines compared to cultivars containing either Rh t1 or Rht2. Grain yield and plant height were positively correlated among t he semi-dwarf Rht isolines in 5 of 6 environments. No equivalent relationsh ip existed among the non-Rht materials. Grain yield (standard sowing depth 3 cm) and coleoptile length were generally not significantly correlated wit hin each isogenic grouping. Plant breeders should be able to select short statured, non-Rht1 or non-Rht 2 hexaploid bread wheat with better emergence characteristics. The non-Rht genotypes developed from the bread wheat cultivars Seri 82 and Culiacan 89 were identified as meeting these criteria. Wheats such as these could offer significant advantages to farmers in environments where deep sowing into s tored soil moisture is practiced. (C) 2001 Elsevier Science B.V. All rights reserved.