Seedling Diseases of Alfalfa in California. J. G. Hancock, Professor, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 67:1203-1208. Accepted for publication 29 April 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1203.

Emergence of alfalfa in several field trials in the Central Valley of California ranged between 30 and 65% of seeds planted. In the field and greenhouse, emergence of the cultivar Lahonton was consistently lower than that of Moapa 69. Percentages of emergence were between 75 and 85% of viable seeds, however, when either of these cultivars was planted in pasteurized field and artificial soils. In an untreated field soil, emergence was lower with both cultivars at a soil temperature regime with a daily cycle between 8 and 17 C than at a set of four constant soil temperature regimes (±2 C) with means of 16.5, 20.0, 25.5, and 26.5 C. Although differences between the two cultivars remained, the degrees of emergence for each cultivar were similar at the four temperatures; emergence was about 65 and 55% of viable seeds for Moapa 69 and Lahonton, respectively. Postemergence damping-off usually did not exceed 5% with either cultivar in the field or in greenhouse studies. Formation of multiple adventitious roots (“forked-root” disease) was frequently associated with fungal infection of seedling radicles. Plants with the forked-root disease were stunted but survived as multiple-taprooted mature plants in the field. Treatments of field soils with moderately narrow-spectrum fungicides (eg. ethazole) frequently increased emergence to percentages equivalent to those found in the pasteurized soils. Pythium ultimum, Rhizoctonia solani, and Fusarium roseum (= F. acuminatum and F. culmorum) were the most common fungi isolated from damped-off seedlings. In pathogenicity tests, all four of these soilborne fungi caused preemergence and postemergence damping-off, whereas only P. ultimum incited a significant amount of the forked-root symptoms.