Occurrence of Nigrospora Lint Rot Caused by Nigrospora oryzae on Cotton in Alabama.

During 2000 and 2001, a lint rot of cotton bolls (Gossypium hirsutum L.) was reported in the coastal region of Alabama when precipitation was 55% lower than the 5-year average. Bolls at an early stage of opening contained gray mycelium within the locules. At maturity, the lint within the infected locules was discolored, and the fibers were compact resulting in the characteristic "gray lock" sign and symptom attributed to Nigrospora oryzae (Berk. & Broome) Petch. Roots, petioles, leaves, and bolls when present were sampled at the seedling, first bloom, full bloom, and maturity stages of cotton development. A total of 640 sections of tissue (approximately 5 mm) were surface sterilized for 20 s in 95% ethanol followed by 60 s in 0.525% NaOCl and aseptically plated on potato dextrose agar. Plates were incubated in the dark at 25°C for 3 to 10 days. N. oryzae was isolated at low frequencies from all plant tissues beginning at first bloom. Developing bolls at full bloom were colonized at a frequency of 48%. N. oryzae conidiophores were branched, flexuous, and pallid to brown with smooth walls 4 to 7 (5) μm thick. Conidiogenous cells were monoblastic, single, and 6 to 9 (7.5) μm in diameter. Conidia were single, smooth, broadly ellipsoidal, dark brown to black, single-celled, and 11 to 16 (14) μm in diameter (2). Principal component analysis was used to examine the relationship between disease incidence and weather parameters. Weather data was obtained from Auburn University Mesonet located in fields where the samples were collected. Principal components from weather data were ambient and soil maximum, minimum, and average temperature, maximum, minimum, and average relative humidity and precipitation. The first principal component, which is temperature, accounted for 61% of total joint variation among original observations. The second principal component, which was related to the moisture variables, accounted for 19% of the variation. The abundance of N. oryzae was correlated with the principal component factor moisture (r = -0.78**). The dry conditions experienced in this region were conducive to N. oryzae lint rot of cotton. This disease has been reported on cotton primarily in arid climates typical of the southwestern United States (1). To our knowledge, this is the first report of N. oryzae lint rot in the southeastern United States. References: (1) W. E. Batson. Boll rots. Pages 36-38 in: Compendium of Cotton Diseases. T. L. Kirkpatrick and C. S. Rothrock, eds. The American Phytopathological Society, St. Paul, MN. 2001. (2) M. B. Ellis. Dematiaceous Hyphomycetes, CAB, Kew, Surrey, England, 1971.