Identification of Pisum sativum Germ Plasm with Resistance to Root Rot Caused by Multiple Strains of Aphanomyces euteiches.

Aphanomyces root rot is a serious disease of pea (Pisum sativum), and additional sources of resistance are needed for development of disease-resistant cultivars. Accessions (n = 123) from the P. sativum Plant Introduction (PI) collection with the highest relative levels of resistance to one strain of Aphanomyces euteiches were previously identified from among approximately 2,500 accessions evaluated. The chosen 123 accessions were evaluated in this study for resistance to root rot caused by multiple strains of this pathogen. Five strains representing different US geographical locations and pathogenicity characteristics were used to evaluate pea seedlings in a greenhouse. Disease severity (DS) and percent loss of fresh biomass (inoculated vs. non-inoculated plants) were determined 15 days after inoculation. Significant differences (P = 0.05) in levels of DS and biomass loss (BL) occurred among the accessions after inoculation individually with the five strains. The relative rank of accessions based on DS and BL varied with the strain of A. euteiches used for inoculations. The 20 accessions with the lowest DS after inoculation with each strain were identified. Based on lowest DS, two accessions were among the 20 identified with all five individual strains, and four other accessions were among the 20 identified with four of the five strains. The results suggest that the P. sativum PI collection contains useful accessions for breeding programs aimed at developing pea varieties with resistance to A. euteiches.