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Detection, Viability, and Possible Sources of Urediniospores of Puccinia recondita f. sp. tritici in Louisiana. K. V. Subba Rao, Graduate Research Assistant, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. J. P. Snow, and G. T. Berggren. Professor, and Associate Professor, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Plant Dis. 73:437-442. Accepted for publication 5 December 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0437.

Kramer-Collins 7-day spore samplers were operated continuously at two locations, Baton Rouge (BR) and Bossier City (BC) in Louisiana, and daily urediniospore counts were taken. The number and viability of spores trapped was maximum during the active epidemic period between February and May and was least during the summer. Viability of the urediniospores was significantly inversely correlated with ambient maximum temperature (r = 0.81 at BR and 0.59 at BC). The highest consecutive number of days that no urediniospores were trapped was 6 in 1986 and 7 in 1987 at BR, and 31 in 1986 and 14 in 1987 at BC. Cultivar McNair 1003, susceptible to the prevalent leaf rust population, was planted at BR from 1 May through 18 September in 1986 and 1987, at 14- to 20-day intervals. Leaf rust appeared in many plantings and survived temperatures up to 36 C for 82 days in 1986 and 74 days in 1987. McNair 1003 plants, in pots exposed at 14-to 15-day intervals during summer for 2 days in a field at BR and then incubated in an air-conditioned greenhouse, developed leaf rust with an incidence of 12.5100%. Rusts from Hordeum pusillum and Lolium multiflorum failed to infect wheat and vice versa. Surveys during mid-December 1986 and 1987, at Alexandria and Baton Rouge, showed uniform distribution of leaf rust over a large area, indicating the possibility of a major exodemic origin of inoculum for winter wheat in Louisiana for these years.

Keyword(s): epidemiology.