GENETIC CORRELATIONS BETWEEN CULM LENGTH, GRAIN-YIELD AND SEEDLING ELONGATION WITHIN TALL (RHT1) AND SEMIDWARF (RHT1) SPRING WHEAT (TRITICUM-AESTIVUM L.)

The purpose of this study was to obtain information on the genetic cor relations between culm length, grain yield and seedling elongation wit hin tall (rht1) and semi-dwarf (Rht1) nearly isogenic spring wheat gen otypes. Thirty random F-7 families and 25 of their offspring in F-8 we re tested in held experiments in the absence of lodging. Coleoptile an d leaf lengths of F-9 seedlings were examined in a growth room at 18 d egrees C. Each family was descended from a single F-5 plant, heterozyg ous at the Rht1 locus. Within each family, the homozygous tall (rht1) and homozygous semi-dwarf (Rht1) were identified; the differences betw een the families represent the effect of background variation. A signi ficantly high positive genetic correlation between culm length and gra in yield was found in the Rht1 genotype. Based on our results, we sugg est that spring wheat breeders first select for long culms within the semi-dwarf population. This should be followed by selection for resist ance to lodging and high grain yield, with a special emphasis on genot ypes excelling in high grain number per area, due to the highly signif icant positive genetic correlation, found between this character and g rain yield. The markedly significant positive correlation found betwee n seedling elongation and culm length suggests the advantage of select ing for long culm genotypes within the semi-dwarf population by using the seedling-elongation test. This selection is accompanied by indirec t selection for long coleoptiles, which are advantageous in the event of seedling-emergence difficulties. (C) 1998 Elsevier Science B.V.