CONICET | Buscador de Institutos y Recursos Humanos

The stem solidness trait in wheat has been the most effective control mechanism for management of the wheat stem sawfly (WSS) for the past six decades. Structural and temporal variations in pith expression may affect levels of resistance and influence efficiency of pest control; however little is known about temporal patterns of stem solidness expression in wheat. To address this issue, a study has been carried out using spring wheat genotypes that differed for the degree of stem solidness. Results showed that in one genotype, Conan, the solid pith undergoes rapid autolysis during the stem maturation period, resulting in significantly less solidness at maturity. In other solid-stemmed genotypes including the standard WSS-resistant cultivar Choteau, the amount of pith in the stem remains mostly unchanged throughout plant´s development. Conan plants also showed increased degree of early solidness, pith moisture, and stem density. Complementary bioassays using recombinant inbred lines (RILs) and near-isogenic lines (NILs) polymorphic for the solid stem locus, Qss.msub-3BL, confirmed that the Conan allele at this locus provides high levels of early stem solidness and a rapid rate of pith retraction during stem maturation. Genotypes carrying the Conan allele at Qss.msub-3BL showed increased WSS neonatal mortality in field trials. In cage trials, Conan plants were shown to be less preferred for oviposition by the WSS when compared to Choteau. Collectively, results provided evidence for allele-specific variation in temporal patterns of solidness expression and WSS resistance. Phenotypic selection should consider temporal variations in pith expression for best results. Molecular markers linked to Qss.msub-3BL allow differentiation of alleles at Qss.msub-3BL and may help breeders improve selection for early solidness expression.

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