First Report and Epidemics of Buffelgrass Blight Caused by Pyricularia grisea in South Texas

Abstract

A blight on buffelgrass, Cenchrus ciliaris L., has been observed for several years in south Texas and Mexico. The disease did not reach epidemic proportions until 1996. The causal agent, identified as Pyricularia grisea (Cooke) Sacc., is a common pathogen of grasses and other cultivated crops. Several Pennisetum spp. have been reported as hosts of Pyricularia spp.; this is the first report of buffelgrass as a host of this pathogen (1,2). Pathogenicity of P. grisea on buffelgrass was confirmed by greenhouse inoculations of 2-month-old buffelgrass plants with conidia washed with distilled water from monoconidial isolations of the pathogen, grown on potato dextrose agar, from infected leaves collected in several locations in south Texas and Mexico. Plants were placed for 8 h every night inside a plastic enclosure with a humidifier, simulating the high relative humidity conditions prevalent during the epidemic. Typical lesions developed after 7 days. The pathogen was re-isolated from the lesions after 10 days, fulfilling Koch's postulates. Conidia harvested from the sporulating samples were hyaline, transversely septate, with one to three septa, most of them having two. Conidia were obpyriform, with hylum often protuberant, measuring 20.6 to 26.3 μm in length and 8.5 to 10.1 μm wide. These measurements are consistent with those given for Pyricularia spp. by Ellis (1). Conidiophores were hyaline, single, slender, and unbranched. Initial symptoms were dark, discolored spots on the leaf that developed into tan, round to elliptical, necrotic lesions with a dark red border and a yellow, chlorotic halo. With increasing severity, lesions can coalesce, killing the entire leaf blade. Under heat and moisture stress, leaves with few lesions and yellow discoloration will wilt completely. Except for the presence of distinct lesions, wilted plants appear to be suffering from severe drought stress or herbicide injury. Losses vary from a few lesions to wilted whole plants and entire pastures. The pathogen also reduces the quantity and quality of seed by infecting involucres of the head. In the absence of the disease, even under severe moisture or drought stress, buffelgrass is able to thrive. Common T-4464 buffelgrass, which is highly susceptible to P. grisea, was introduced into south Texas in the late 1940s and is currently grown on 8 to 10 million acres in south Texas and Mexico. Buffelgrass reproduces by obligate apomixis, in which seeds are formed without sexual fertilization. Consequently, the progeny are genetically identical to the maternal parent. The monoculture of this grass with its unique type of reproduction encompasses millions of acres with genetically identical plants. Interaction of inoculum with weather conditions (nights with 8 to 10 h of more than 75% relative humidity) in 1996, 1997, and the late summer of 1998 produced epidemics of buffelgrass blight throughout south Texas and northern Mexico. P. grisea was also isolated from lesions on grassburr Cenchrus incertus M. A. Curtis collected throughout the area. References: (1) M. B. Ellis 1971. Dematiaceous hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England. (2) D. F. Farr et al. 1989. Fungi of Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

Marker-assisted screening of breeding populations of an apomictic grass Cenchrus ciliaris L. segregating for the mode of reproduction

“…It is drought tolerant and well adapted to arid and semi-arid areas. A serious disease in buffelgrass is leaf blight caused by Magnaporte grisea, which reduces forage quality and yield (Rodriguez et al 1999). A natural source of resistance to this disease is known (Diaz-Franco and Mendez-Rodríguez 2005), but lack of sexual reproduction restricts genetic improvement of this species through hybridization.…”

Pyriculins A and B, two monosubstituted hex‐4‐ene‐2,3‐diols and other phytotoxic metabolites produced by Pyricularia grisea isolated from buffelgrass (Cenchrus ciliaris)

“…It is known from a broad spectrum of warm‐season grass hosts. It is the only foliar pathogen that has been recorded to reach epidemic levels that severely damage buffelgrass in the field . An epidemic blight disease caused by this organism in Texas during a series of unusual weather years prompted a search for a blight‐resistant buffelgrass strain .…”

Nutrient Content andin situDisappearance in Genotypes of Buffelgrass (Cenchrus ciliarisL.)

“…Data of DM yield, chemical constituents, ISDDM, ISDCP, ISDCW were statistically analyzed using a one-way analysis of variance. Comparisons were made between genotypes (Snedecor and Cochran, 1980).…”

“…Recently a blight of epidemic proportions on common buffelgrass has been reported in Mexico and South Texas and the fungi Pyricularia grisea (Cook) Sacc. has been identified a s the causal agent (Rodriguez et al, 1999).…”