UC Riverside

Bread wheat (Triticum aestivum L.) is the second most cultivated cereal crop after rice. Many present day bread wheats carry a centric rye-wheat translocation 1RS.1BL in place of chromosome 1B. The increased grain yield of translocation lines is positively associated with root biomass. To map loci controlling root characteristics, homoeologous recombinants of 1RS with 1BS were used to generate an integrated genetic map comprised of 20 phenotypic and molecular markers, with an average spacing of 2.5 cM. To identify the chromosomal region associated with rooting ability, root phenotypic data were subjected to Quade analysis to compare genotypes. The distal 15% of the rye 1RS arm may carry QTL for greater rooting ability in bread wheat.

To identify QTL for individual root traits, a phenotyping experiment was conducted involving recombinants from each marker interval of the 1RS-1BS genetic map. An empirical Bayes method was applied to estimate additive and epistatic effects for all possible marker pairs simultaneously in a single model. This method has an advantage for QTL analysis in minimizing the error variance and detecting interaction effects between loci with no main effect. Four common regions were identified to involve a total of 15 QTL effects, six additive and nine epistatic, for different root traits in 1RS wheat. Three of four regions were localized in the distal 15% of the 1RS arm.

The effect of different dosages (0 to 4) of the 1RS translocation on root morphology and anatomy in bread wheat was determined. The F1 hybrid with single dose of 1RS and 1AS arms showed heterosis for root and shoot biomass. Root biomass was positively associated with increase in dosage of 1RS. This study also provided evidence of the presence of gene(s) influencing root anatomical traits. The central metaxylem vessel diameter was negatively associated with increasing 1RS dosage. Wheat genotypes with higher number of 1RS translocation arms may have inherent morphological and anatomical advantage over normal bread wheat to survive under stress conditions.