Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/27/2010
Publication Date: 11/1/2010
Publication URL: http://hdl.handle.net/10113/45958
Citation: Ma, A., Hill, C., Hartman, G.L. 2010. Production of Macrophomina phaseolina conidia by multiple soybean isolates in culture. Plant Disease. 94:1088-1092. Interpretive Summary: A soilborne fungus called Macrophomina phaseolina is the cause of charcoal rot, a major disease of soybean that is difficult to control. Resistance is only partial as even the most resistant soybean types get the disease. High-throughput methods to efficiently screen large numbers of plants is important when searching for new sources of resistance or evaluating experimental lines. The objective of this study was to develop a reliable method for producing sufficient quantity of conidia (fungal spores) to inoculate soybean plants. Three different media were used to grow the fungus to compare which of the media provided the most fruiting bodies (sporulation) of the fungus. Four fungal isolates were tested on each medium. Conidia (spores developed in the fungal fruiting structures) were produced in greatest numbers on detached soybean leaflets on agar with germination rates between 84 and 89%. Inoculation of soybean radicles with conidia resulted in lesion lengths that were significantly different between the soybean genotype DT97-4290, with partial resistance (6.7 mm) and the susceptible genotype LS98-0358 (12.6 mm). Results of this study indicated that detached soybean leaflets on agar to produce conidia could facilitate charcoal rot resistance screening evaluation and help contribute to the development of new, charcoal rot-resistant soybean cultivars. This information will be used by soybean pathologist and breeders that work on charcoal rot and soybean resistance to charcoal rot.
Technical Abstract: Macrophomina phaseolina (Tassi) Goid is the cause of charcoal rot of soybean, Glycine max (L.) (Merr.). Soybean resistance to M. phaseolina in commercial cultivars is not common, but is especially needed in locations where the disease is chronic and severe. The objective of this study was to develop a reliable method to produce sufficient M. phaseolina conidia to inoculate soybean plants in a high-throughput resistance-screening program. Three media to induce pycnidia production were compared: detached soybean leaflets, peanut butter extract agar and soy nut butter extract agar. Four M. phaseolina isolates were tested. Pycnidial production ranged from 20 to 43 pycnidia per cm2, and conidia germination ranged from 84 to 89%. The highest overall production of conidia was on soybean leaflets (5,900 conidia/cm2). Inoculation of soybean radicles with conidia resulted in lesion lengths that were significantly (P < 0.001) different between the soybean genotype DT97-4290, with partial resistance (6.7 mm), and the susceptible genotype LS98-0358 (12.6 mm). Results of this study indicated that detached soybean leaflets on agar could reliably produce M. phaseolina conidia inoculum to facilitate charcoal rot resistance screening evaluation.