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Etiology and Control of Seed Decay and Preemergence Damping-Off of Chickpea by Pythium ultimum. Walter J. Kaiser, Research Plant Pathologist, Regional Plant Introduction Station, USDA, ARS, Washington State University, Pullman 99164. Richard M. Hannan, Laboratory Technician, Regional Plant Introduction Station, USDA, ARS, Washington State University, Pullman 99164. Plant Dis. 67:77-81. Accepted for publication 26 May 1982. 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, 1983. DOI: 10.1094/PD-67-77.

Emergence of several cream-colored chickpea (Cicer arietinum) Plant Inventory (PI) accessions in field trials at various locations in the Palouse region of eastern Washington was erratic and/or reduced because of a seed rot and preemergence damping-off disease caused by Pythium ultimum. Fusarium solani and P. ultimum were isolated most frequently from decayed seeds, while fungi isolated occasionally were Mucor sp. and other Pythium spp. Seedling emergence of cream-colored PI 458870 was reduced from 86% in the uninfested control to 58, 24, and 2% in soil artificially infested with 5, 50, and 500 propagules per gram of soil (ppg) of P. ultimum, respectively. In the same test, brown- and black-seeded PI accessions 273879 and 458869, respectively, were highly resistant to seed rot and preemergence damping-off compared with PI 458870. Untreated seeds of PI 458870 failed to emerge in natural field soil at 10, 15, 20, or 25 C, whereas emergence of metalaxyl-treated seeds was >80% at these temperatures. Seedling age greatly influenced susceptibility to seed decay and damping-off. When pregerminated in moist vermiculite, transplanted seedlings developed resistance to P. ultimum in naturally infested soil after 4896 hr. In soils collected in the top 16 cm of 12 cropped and fallowed fields in eastern Washington and northern Idaho, populations of P. ultimum ranged from 56 to 1400 ppg and emergence of untreated seeds was reduced by >90%. Soil fumigation with methyl bromide and treatment of seeds with different fungicides significantly increased emergence and yields of PI 458870 in field trials at Central Ferry. WA. Metalaxyl (Ridomil) and captan were the most effective seed-treatment fungicides for preventing seed rot and preemergence damping-off and in increasing yields. In soil artificially infested with P. ultimum, seeds treated with metalaxyl, captan, ethazol, ethazol + thiophanate, thiram, or fenaminosulf significantly increased emergence over the untreated control. Fenaminosulf (Dexon) delayed germination and stunted seedlings. Metalaxyl-treated seeds stored at 4 C for up to 464 days before planting were protected when planted in field soil heavily infested with P. ultimum.

Keyword(s): fungicide seed treatment, soilborne.