Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1996
Publication Date: N/A
Interpretive Summary: Vine decline and fruit rot cause serious losses in cantaloupe production and fruit quality. The charcoal rot fungus causes both a vine decline and fruit rot. Cantaloupe roots become infected soon after planting, but vine decline does not occur until about 10 days before harvest. During fruit maturation, distribution of nutrients within the plant changes as nutrients are assimilated in the fruit. Nutrient availability has been correlated to susceptibility of plants to the fungus. Photosynthates from leaves nearest the fruit are the most important in supplying carbohydrates to the fruit. The associated physiological changes in the plant may be related to with the development of vine decline. With the onset of vine decline, the crown leaves are the first to succumb, thus fruit quality and disease resistance are adversely affected. Nutrient distribution and availability within the plant are important for determining the host-pathogen relationship.
Technical Abstract: Carbon, nitrogen, vitamin, and pH requirements for mycelial growth were determined for the chromogenic cantaloupe fruit isolate Macrophomina phaseolina (TX-33) cultured in liquid and solid media. In liquid culture, the fungus best utilized, sucrose, maltose, fructose, mannose and starch as individual carbon sources when compared to glucose, the reference compound. In agar cultures, the fungus grew best on fructose, glucose, and sucrose. In regard to nitrogen sources, mycelial growth in liquid culture was greatest on glutamic acid, peptone, and asparagine when compared to the reference compound ammonium succinate. However, mycelial growth on ammonium succinate and peptone ranked highest on agar. Vitamin treatments suppressed mycelial growth in liquid culture but had little effect in agar. Mycelial growth of the cantaloupe isolate in liquid culture was suppressed above pH 4.6. Microsclerotial production was generally greater in nutrient studies that had the best mycelial growth. Conversely, as microsclerotial production decreased, microsclerotial size increased. The results of this study demonstrate the importance of substrate composition which may strongly influence the inoculum potential of M. phaseolina.