The fungus Macrophomina phaseolina is a causative agent of diseases in more than 500 plant species. The fungus is primarily soil-inhabiting but is also seed-borne in many crops including soybean. It survives in the soil mainly as microsclerotia that germinate repeatedly during the crop-growing season. Low C : N ratio in the soil and high bulk density as well as high soil moisture content adversely affect the survival of sclerotia. The disease can be managed to some extent by cultural practices, organic amendments, seed treatment and genetic host resistance. The scattered literature on these aspects is reviewed in this paper.

Biology, Epidemiology and Management of the Pathogenic Fungus Macrophomina phaseolina (Tassi) Goid with Special Reference to Charcoal Rot of Soybean (Glycine max (L.) Merrill)

Detection and Significance of Symptomless Latent Infections of Monilinia Fructicola in Plums

Measurements of competitive saprophytic colonization were used to evaluate the activity of Tricho? derma harzianum in non-sterile soil under conditions of varying soil moisture and temperature. Esti? mates of activity based on levels of colonization, determined after homogenization of substrate pieces, were more discriminating than those based on the number of colonized pieces. T. harzianum was found to be most active at soil matric potentials from -0.5 to -1.0 bar, with activity declining at matric potentials of 0.0, -7.5, and -15.0 bars. The saprophytic activity of T. harzianum was greatest at temperatures from 15 to 21 C. The optimum temperature for competitive colonization was several

Effects of Soil Moisture and Temperature on the Saprophytic Ability of Trichoderma Harzianum

Charcoal rot [Macrophomina phaseolina (Tassi) Goid] of soybean [Glycine max (L.) Merr.] is an important but commonly misidentified disease, and very few summary articles exist on this pathosystem. Research conducted over the past 10 yr has improved our understanding of the environment conducive to disease development, host resistance, and improved disease diagnosis and management. This article summarizes the currently available research with an emphasis on disease management.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1341&context=agron_pubs

Advancing Our Understanding of Charcoal Rot in Soybeans

Paraquat: a tool for the quick development of latent fungal infections and endophytic fungi.

Detached winter wheat leaves without any symptom of fungal infection were thoroughly washed, surface desinfected, treated with paraquat (0.03–0.32% a.i.) and incubated on nutrient agar or in moist chambers under sterile conditions. Microscopic examinations showed that hypae and yeast cells emerged from several stomata within 48–72 h after treatment. Fungal colonies developed on agar within the same period of time. More than 27 filamentous fungal genera and yeasts were identified during a wheat cropin healthy, green leaves. Non-treated leaves showed very few early emergences of fungi from stomata, but senescent leaves eventually yielded several fungal taxa observed after paraquat treatment. Similar observations were made on non-detached wheat leaves, and on detached sugarbeet leaves. Paraquat also induced development of Fusarium spp. from detached healthy winter wheat ears before or after heading. In grape berries, paraquat induced the development of latent infections of Botrytis cinerea, a few days after treatment.

The usefulness of paraquat for the detection of endophytes and for the diagnosis of early and latent fungal infections in plants, and the possible involvement of endophytes in tissue senescence are discussed.

Le Paraquat, un Outil pour la Révélation Rapide d'Infections Fongiques Latentes et de Champignons Endophytes

Alternaria sp., Colletotrichumdematium var. truncatum, Macrophomina phaseolina and Phomopsis sp., isolated from soybean ( Glycine max ) seeds, differed in tolerance to paraquat as measured by mycelial production, linear mycelial growth, spore germination and glucose consumption. Alternaria sp. was most sensitive to paraquat; Phomopsis sp. least sensitive with M. phaseolina being intermediate. The growth of C. dematium var. truncatum was variable. Colonization by M. phaseolina and Phomopsis sp. of soybean stem pieces treated with different concentrations of paraquat and then surface sterilized, was inhibited and stimulated, respectively. Paraquattreated soybean pods released electrolytes and amino acids. These results are discussed in relation to the occurrence of C. dematium var. truncatum and Phomopsis sp. on soybeans sprayed with paraquat in the field and the use of paraquat in the laboratory for the detection of latent colonization by these and other fungi.

Effect of paraquat on soybean pathogens and tissues

The effect of paraquat, glyphosate and sodium chlorate : sodium borate (50:50), applied at commercial rates was tested on the competitive saprophytic colonization by Macrophomina phaseolina of greenhouse and field grown soybean stems at three different growth stages in two soils. A significant difference in colonization was recorded between herbicide treatments and controls in soil with a high organic content but no significant difference in colonization was found between herbicides. The highest levels of stem colonization occurred 10 days after incubation in soil. Colonization in treated and untreated stems progressively declined at similar rates for all growth stages and in both soil types. In both soils, field stems had greater levels of colonization when sampling time and herbicide factors were excluded. The nonpersistence of M. phaseolina in stems in soil suggests that the saprophytic activity of the fungus does not effectively increase its inoculum density in soil.

R.F. Cerkauskas

Papers

Effect of paraquat on soybean pathogens and tissues

Effect of herbicides on competitive saprophytic colonization by Macrophomina phaseolina of soybean stems