Genetic variation in stem strength in field pea (Pisum sativum L.) and its association with compressed stem thickness

We assessed genetic variation in stem strength in field pea ( Pisum sativum L.) using physical and biological measures in order to develop selection criteria for breeding programs. A diverse group of 6 pea genotypes was subjected to 2 levels of disease (ascochyta leaf and stem blight), high and low. Stem samples were tested for physical stem strength ( load at breaking point and flexion) using a universal testing machine. Stem diameter and compressed stem thickness were measured as biological indicators of stem strength. The genotypes varied significantly in physical and biological measures of stem strength, and in resistance to ascochyta blight. Load at breaking point was strongly associated with compressed stem thickness but only weakly associated with stem diameter. Significant variation in compressed stem thickness was present among pea genotypes, supporting this as an inexpensive, reliable, and quantitative measure for use in the field. There was no variation in stem lignin content among genotypes. Ascochyta blight resistance and stem strength, as assessed by load, flexion, or compressed stem thickness, were independent traits ( the main effects of disease level and genotype x disease level interactions for load, flexion, and compressed stem thickness were non-significant). Therefore, concurrent genetic gains in both ascochyta resistance and stem strength should be possible in the same pea breeding population.