Control of Pythium Seed Rot and Preemergence Damping-off of Chickpea in the U.S. Pacific Northwest and Spain. Antonio Trapero- Casas, Former Visiting Scientist, USDA-ARS, Western Regional Plant Introduction Station, Washington State University, Pullman 99164-6402. Walter J. Kaiser, and David M. Ingram. Research Plant Pathologist, and Former Postdoctoral Research Associate, USDA-ARS, Western Regional Plant Introduction Station, Washington State University, Pullman 99164-6402. Plant Dis. 74:563-569. Accepted for publication 19 November 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/PD-74-0563.

Species of Pythium isolated from rotted chickpea seeds and damped-off seedlings and chickpea soils in the U.S. Pacific Northwest and southern Spain that caused seed rot and preemergence damping-off of chickpea were Pythium ultimum var. sporangiiferum, P. ultimum var. ultimum, and P. irregulare. P. oligandrum and unidentified Pythium spp. that were not pathogenic to chickpea were also isolated. P. ultimum var. sporangiiferum and P. ultimum var. ultimum were the most pathogenic to chickpea in field and growth chamber tests. In fumigated, reinfested soil in the field, these varieties caused 90 and 75% reduction in emergence and yield, respectively. In growth chamber studies, P. irregulare reduced emergence and caused stunting, but disease severity was highly influenced by the type and density of inoculum, temperature, soil type, and plant age. This species had no significant effect on emergence, plant growth, and yield in the field. Steamed soil infested with oospores or a sand-cornmeal mixture colonized with mycelium was used to reinfest fumigated soil with the test Pythium spp. in field trials at Central Ferry, Washington. Fumigation of field soil with methyl bromide reduced the population density of P. ultimum to nearly undetectable levels. Treating chickpea seed with the fluorescent pseudomonad Pseudomonas fluorescens strain Q29z-80 resulted in yield that was equivalent to that obtained with any of the fungicide seed treatments. Two other biological seed treatments, Penicillium oxalicum and Pythium oligandrum, were also effective against Pythium seed rot and preemergence damping-off in the field. Seed treatment chemicals metalaxyl, captan, benalaxyl and metalaxyl plus thiabendazole were effective in controlling Pythium seed rot of chickpea in both field and growth chamber tests. The four fungicide seed treatments were at least as effective as fumigating the soil with methyl bromide or treating seeds with various biological control agents.