Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 1996
Publication Date: N/A
Interpretive Summary: Aphanomyces root rot is the most destructive disease of peas world wide. The disease was first described in the Midwest in the 1920's and in the Pacific Northwest in the 1980's. Until recently, this disease has not yielded to any control measures, short of not growing peas in an infested field for at least 10 years. Until recently, no resistant pea germplasm or varieties with acceptability in the marketplace were available from private companies or public researchers. Pea germplasm has now been developed by ARS and by University researchers with measurable resistance to this disease. These germplasm lines also possess sufficient desirable horticultural traits so that private breeders are now using them to develop more resistant varieties. In order for commercial breeders to efficiently utilize these lines, information on how this resistance is expressed is needed to identify those progeny which possess the desirable resistant traits. This paper describes and measures this resistance in 3 ways: a) the rate of disease spread within the inoculated root system; b) the rate of pathogen buildup within inoculated roots; and c) the differences in attraction of the pathogen to the root system. By quantifying this resistance, the genetic mechanisms responsible can be identified and manipulated by private breeders. Because this disease is chronic where most peas are grown commercially in the United States, the development of commercial varieties with resistance to Aphanomyces root rot will be a great aid in stabilizing yields and quality in future processing, dry and seed pea production.
Technical Abstract: Previous attempts to quantify resistance in pea to Aphanomyces euteiches have involved oospore counts in infected root tips and disease severity ratings to separate resistant from susceptible lines. In a controlled environment with known zoospore inoculum levels, differences in oospore production in infected roots, rate of lesion development in taproots, and zoospore germination in seedling exudates were evident in resistant and susceptible pea lines. Indirect ELISA measurements of infected root tissue within a visible lesion revealed a positive, linear regression of lesion length on ELISA readings at 405 nm (R**2 = 0.91). Zoospore germination was reduced in seedling exudates from resistant but not from susceptible pea lines. Resistance in pea roots to A. euteiches is associated with reduced oospore production, pathogen multiplication, zoospore germination, and slower lesion development.