Pathogenicity of Macrophomina phaseolina to Mature Plant Tissues of Alfalfa and White Clover

Abstract

Macrophomina phaseolina has been observed on alfalfa and white clover in North America, but its pathogenicity to mature plants of these species has not been adequately documented and Koch's postulates have not been fulfilled. Isolates of M. phaseolina from alfalfa and white clover were evaluated for pathogenicity by inoculating tissues of mature plants with infested toothpick pieces. Excised leaf tissues also were inoculated with mycelium. In stolons of white clover and stems of alfalfa, M. phaseolina caused a brown-black, basipetally progressive necrosis of vascular tissue with subsequent collapse of the surrounding pith and epidermis to produce radially constricted, expanding lesions. In taproots and crowns of alfalfa, M. phaseolina caused dark discoloration of vascular tissues in bands or streaks above and below inoculation points with subsequent invasion and death of cortical tissues, lateral roots, and stems. Sclerotia formed in all tissues of both species. Excised leaf tissues were rapidly parasitized, but significant differences in rates of parasitism between genotypes suggested that differences in host resistance to M. phaseolina may be present in both species. Pycnidia formed on leaves of bean, lima bean, and cotton. All isolates of M. phaseolina were reisolated from margins of necrosis in all types of inoculated tissues and regrown in pure culture. These results fulfill Koch's postulates for M. phaseolina as a pathogen of mature white clover and alfalfa in North America, and they demonstrate its capacity to parasitize a variety of tissues of both species in the absence of other pathogens. Results indicate that M. phaseolina should be considered a potential cause for lack of persistence of white clover and alfalfa during summer months in the southeastern United States.

Growth of White Clover Ecotypes, Cultivars, and Germplasms in the Southeastern USA

“…1) Stolon length declined throughout the summer, reaching minimum values in October, until few differences in stolon length existed among the eight entries. This annual decline in white clover growth (Brink et al, 1998), which occurs in the fall in much of the Southeast because of high summer temperatures, declining precipitation, and a virus disease–insect pest complex (Pederson et al, 1991), was exhibited by all entries to the same relative degree regardless of previous growth. After October 1996, stolon growth rates of GA‐N, AL, and MS resulted in these ecotypes having greater stolon length in January, April, and July 1997 than all cultivars and germplasms except Grasslands Prestige.…”

Temporal analysis of charcoal root rot in forest nurseries under different pathogen inoculum densities and soil moisture content

“…In sorghum, for example, the increase of disease incidence was not related with the density of M. phaseolina inoculum in the soil, even under conditions favorable for disease development (Gonzalez et al, 2007). These discrepancies can be explain by several factors including the degree of susceptibility of the host (Mayek-Pérez et al, 2001) and the aggressiveness of the pathogen strain (Pratt et al, 1998).…”

Infection of Sweetpotato by Fusarium solani and Macrophomina phaseolina Prior to Harvest

“…Often, one fungus predominates; however, in recent isolations we detected E. solani and M. phaseoiina simultaneously infecting the same lesions (W. L. da Silva, personal communication). One month after transplanting, vines were mock inoculated with a sterile toothpick or inoculated with the specific fungus at the soil line, by a modification of the method of Pratt et al (27). These findings storage roots during growth and development of the plant, a greenhouse experiment was designed using vines from tissue culture plants (screened for the absence of M. pha.^eoUna and F. soiani).…”