MIXED-MODEL FOR ESTIMATING THE EFFECTS OF THE RHT1 DWARFING ALLELE, BACKGROUND GENES, CCC AND THEIR INTERACTION ON CULM AND LEAF ELONGATIONOF TRITICUM-AESTIVUM L, SPRING WHEAT

A model for the effects of a single gene (SG), background genes (BG), an environmental factor (EF) and the effects of their interactions on quantitative traits is developed. It is a mixed model where SG and EF have fixed effects while BG have a random effect. This model is applie d to the analysis of the effects of the dwarfing alleles at the Rht1 l ocus (SG), interfamily variation (representing BG) and the growth regu lant CCC (EF) on coleoptile, leaf and culm length of spring wheat. Cul m length of F, families was tested in a field experiment in the absenc e of lodging. Coleoptile and leaf lengths of F, seedlings were examine d in a growth room at 18 degrees C. Each family was descended from a s ingle F, plant, heterozygous at the Rht1 locus. Within each family the homozygous tall (rht1) and the homozygous semi-dwarf (Rht1) genotypes were identified. Thus, comparing nearly isogenic genotypes within ran dom families in advanced generations enabled the estimation of all the main effects and interactions between SG, BG and EE The restricted ma ximum likelihood (REML) method was used in the analysis of variance. I n all the three organs CCC caused significant shortening which was som ewhat greater in the rht1 than in the Rht1 genotype and the CCC x Rht1 interaction effect on culm length was significant. Considerable and s ignificant interfamily variation was found for all three characters. A significant CCC x family interaction effect on the length of the firs t leaf was obtained. This interaction effect was of a specific trend i ndicating a distinct increase in the response to CCC with greater leaf length. No CCC x Rht1 x family or Rht1 x family interaction effects w ere detected. The use of two graphical/analytical methods proved to be complementary for a complete evaluation of two-way interactions (CCC x families and CCC x Rht1 in the present study).