Seed transmission of peanut mottle virus in peanuts.

ADAMS, D. B., and C. W. KUHN. 1977. Seed transmission of peanut mottle virus in peanuts. Phytopathology67:1126-1129. Seed transmission of peanut mottle virus (PMV) in frequency (0.23%) in small-seeded ones. When seed were peanuts is a consequence of embryo infection. Virus was harvested from individual plants, seven of 30 peanut plants isolated from embryos but not from seed coats or cotyledons. produced 777 seed free of PMV-M3 whereas the seed Four isolates of PMV differed in frequency of seed transmission varied from 0.5 8.3% of the remaining plants. transmission in Starr peanut: MI = 0.3%, M2 = 0.0%, M3 = Seed transmission of PMV was unrelated to the level of virus 8.5%, and N = 0.0%. Isolate M3 was transmitted at similar in leaves and flowers. When peanut plants were maintained at frequencies (average = 7.1%) in seed of four peanut cultivars. 21 or 35 C during flowering and pegging, seed transmission Isolate M2, however, was not seed-transmitted in largewas reduced threefold when compared to greenhouse-grown seeded peanuts although it was transmitted at a low peanuts. Additional key words: epidemiology, primary source of inoculum. Seed transmission of peanut mottle virus (PMV) Pisum sativum 'Little Marvel' and isolate M3 in peanut occurs in peanuts (Arachis hypogaea L.) at relatively low cultivar Starr. frequencies (1, 3, 10, 13, 14). The importance of seed For most of the seed transmission studies, 10to 15transmission has been established by epidemiological day-old peanut seedlings, grown in the greenhouse or studies during the last five years; in Georgia, PMVfield, were mechanically inoculated with PMV (13). In the infected peanut seed provide the primary source of study to determine seed transmission in individual plants, inoculum for diseases of two major crops, peanuts and the test plants became naturally infected from a centrallysoybeans, Glycine max (L.) Merr. (7, 8, 11, 14). No located row manually inoculated with virus. Mature pods natural reservoir for PMV has been found, and the virus on infected plants were handpicked 120-140 days after is not seed-transmitted in four hosts which have been planting. found infected in nature: Vigna unguiculata (L.) Walp. Frequency of seed transmission was determined by subs. unguiculata(1, 6), soybeans (6,7), Pisum sativum L. planting seed from PMV-infected plants in 10-cm (1), and Cassia obtusifolia L. (1). Behncken and diameter pots containing methyl bromide-treated soil McCarthy (4) found PMV in navy beans (Phaseolus (four seed/pot). Plants were maintained in a aphid-free vulgaris L.) in Australia and reported a low frequency of greenhouse and observed for PMV symptoms for at least seed transmission. However, no strains of PMV have 30 days. Seed from the PMV-infected small-seeded been found which systemically infect beans in the United peanut cultivars (Spanish type) were planted immediately States. The objectives of this study were to determine the after harvest or stored at 5 C. To obtain high percentage location of the virus in infected peanut seed and to germination, seed of the large-seeded peanut cultivars determine factors which affect seed transmission. (runner or Virginia type) were stored at 25-30 C for at least 60 days before planting (2) or the seed dormancy was MATERIALS AND METHODS broken by placing the seed in a sealed plastic container with slices of apples. Three isolates of PMV, described previously (13), were The presence of PMV in peanut plants with PMV used in this study: two (M l and M2) caused mild mottle symptoms was verified by grinding one leaflet in 1-2 ml of symptoms on peanut and the third (N) caused necrosis 0.01 M phosphate buffer, pH 7.5, containing 0.2% and stunting. A fourth isolate, designated M3, was sodium bisulfite, 0.2% sodium diethyldithiocarbamate, obtained from a field-infected peanut plant in 1974. The and I% Celite in a mortar and inoculating the PMV local new isolate caused mild mottle symptoms on several lesion host, Topcrop bean. Furthermore, all abnormalpeanut cultivars and could not be distinguished from appearing plants and about 2,000 symptomless ones, isolates Ml and M2 by symptoms on peanuts, host range, grown from seed of PMV-infected plants, were tested or serology. Isolates MI, M2, and N were maintained in similarly for PMV; none had the virus. The relative infectivity of PMV in various plant parts Copyright © 1977 The American Phytopathological Society, 3340 was determined by conducting half-leaf assays on Pilot Knob Road, St. Paul, MN 55121. All rights reserved. Topcrop bean (eight replications/treatment distributed