New garden- and dry-pea breeding lines developed by Agricultural Research Service and cooperating scientists may offer growers added insurance against outbreaks of Aphanomyces root rot, a disease that can cause yield losses of 20 to 100 percent in the legume crop.
The moldlike culprit, Aphanomyces euteiches, infects roots and underground stems of susceptible pea plants and other legumes, rotting them and causing stunted growth, lesions, wilted leaves, and other symptoms.
Currently no fungicides are registered for use with peas to control Aphanomyces root rot. Growers must either avoid planting in fields with a history of the disease or try rotating in nonhost crops until pathogen numbers drop to acceptable levels.
But avoidance and crop rotation may not always be economically feasible. Breeding peas for Aphanomyces resistance has proven difficult because multiple genes are involved. Resistance genes are also associated with undesirable traits, which cultivated varieties can inherit when crossed with wild germplasm sources, notes Rebecca McGee, a plant geneticist in ARS’s Grain Legume Genetics Physiology Research Unit in Pullman, Washington.
McGee, ARS geneticist Clare Coyne, and colleagues have sought to develop pea germplasm lines that can tolerate the pathogen. Coyne is with ARS’s Plant Germplasm Introduction and Testing Research Unit, also in Pullman.
“We say the lines are ‘highly tolerant,’ or ‘partially resistant,’ because in severe disease conditions, even the best lines show some symptoms, though they may not have significant yield loss,” explains McGee, who collaborated with scientists from ARS, New Zealand, and Europe to develop the Aphanomyces-tolerant lines.
The pea lines are eighth-generation descendants of an inbred population of plants derived from an ARS cross, made in 1993, between the cultivar Dark Skin Perfection and germplasm line 90-2131. In addition to their high tolerance of Aphanomyces root rot, the lines were also selected for their acceptable agronomic characteristics.
The breeding lines themselves aren’t intended for commercial production, but rather as a source of Aphanomyces tolerance for incorporation into elite pea varieties. Such varieties could be welcome news for growers in Pacific Northwest and North Central states where Aphanomyces outbreaks threaten the valued role that peas and other legumes play in cereal-based crop rotation systems.
“Typically, cereals sown after legumes, especially peas and lentils, yield more than cereal-following-cereal plantings,” notes McGee. “But if Aphanomyces root rot is severe, pea crop losses can be 100 percent.”
In addition to releasing Aphanomyces-tolerant material, the scientists are working to make DNA markers that breeders can use in their programs, McGee says.—By Jan Suszkiw, Agricultural Research Service Information Staff.
"New, Disease-Resistant Pea Lines Developed" was published in the November/December 2013 issue of Agricultural Research magazine.