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Comparative Evaluation of Four Techniques for Screening Winter Peas for Resistance to Phoma medicaginis var. pinodella

Four techniques were evaluated for screening eight winter field pea lines [Pisum sativum subsp. arvense (L.) Poir] for resistance to foot rot and foliar infections caused by Phoma medicaginis var. pinodella (L. K. Jones) Boerema. The best differential follar symptoms in the greenhouse were obtained when 11-day-old seedlings were sprayed with a fine mist containing 1 x 10⁶ pycnidiospores/ ml of water, incubated for 10 days in a mist chamber and evaluated to determine the area of leaves and stems covered by lesions. The best differential foot rot symptoms in the greenhouse occurred when each seed was inoculated with 1 ml of a suspension containing 1 x 10⁶ spores as they were planted in fiats of sand, incubated for 14 days and evaluated on the basis of root lesion length. Differential foliar symptoms in the laboratory, occurred when excised leaflets were sprayed with a 2 x 10⁶ spores/ml suspension, incubated on moist filter paper in petri plates for four days, and evaluated on the percentage of leaf area covered by lesions. Differential foot rot symptoms were measured in the laboratory by imbibing pea seeds in a suspension of 2 x 10⁶ spores/ml in petri plates under continuous fluorescent light for three days and evaluated for the degree of inhibition of germination.

Seven of the winter pea lines evaluated in the greenhouse and laboratory were also evaluated for the severity of foliar symptoms in the field during the spring of 1980. Results from the greenhouse and laboratory evaluations for resistance to foot rot symptoms were correlated with the resistance to foliar symptoms measured in the field (r = 0.95**, df = 5 and r = 0.78*, df = 5; respectively). Greenhouse and laboratory evaluations of resistance to foliar infection were not significantly correlated with foliar symptoms measured in the field (r = 0.69, df = 5 and r 0.60, df = 5; respectively). Both the laboratory and greenhouse foot rot screening techniques can be used to identify winter field pea lines with resistance to P. medicaginis under field conditions.

Key Words: Phoma medicaginis var. pinodella • Ascochyta pinodella • Pisum sativum subsp. arvense • Foot rot • Ascochyta blight • Disease screening

² Former graduate research assistant and associate professor of plant breeding and genetics, respectively.

Received for publication January 26, 1981.