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Title: PINK ROOT OF MUSKMELON AND WATERMELON CAUSED BY PHOMA TERRESTRIS

Author
item Bruton, Benny
item BILES, C - EAST CENTRAL UNIVERSITY
item DUTHIE, J - OKLAHOMA STATE UNIVERSITY

Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Numerous fungi have been suspected or shown to contributed to vine declines of cucurbits. Intensive cultivation of these crops with inadequate rotation has resulted in an increase in both the number and severity of diseases involved in the vine decline complex and consequently has accounted for significant economic losses. We found that the fungus, Phoma aterrestris, caused pink root of cucurbits although little damage is inflected by the fungus on its own. However, the combined effects of the pink root pathogen along with other root rot pathogens may contribute significantly to the vine decline of cucurbits. It was determined for the first time that fungal fruiting bodies called microsclerotia produced by the pink root pathogen are capable of germinating and therefore may be involved in the development of the disease. These microsclerotia are resistant bodies that can withstand harsh environmental conditions for extended periods of time which makes rotation of less than 4 or 5 years inadequate.

Technical Abstract: Phoma terrestris was established as the cause of pink root of cucurbits. Disease reaction in cantaloupe using nine isolates obtained from cucurbit roots ranged from essentially non-pathogenic to moderately virulent. The isolates caused little or no reduction in root or foliar dry wt after sixty da in the greenhouse. Based on disease reaction, pink root development, and microsclerotial production, the cucurbit isolates were similar in all respects to onion isolates (ATCC 16993 and ATCC 64403). Therefore, P. terrestris qppears to cause little damage to cucurbits in the southwestern United States, but the fungus clearly causes pink root or browning of the roots and thus contributes to the vine decline disease complex in cucurbits. In a limited host range study, disease reaction was similar in cantaloupe, watermelon, onion, and tomato using both cucurbit and onion isolates. P. terrestris isolated from cucurbit root tissue produced pycnidia with pycnidiospores and microsclerotia on PDA, V8A, and SNA. Microsclerotia were produced in cantaloupe roots under greenhouse conditions by three cucurbit isolates and one ATCC isolate. Germination of microsclerotia was demonstrated for the first time suggesting a possible role in the epidemiology of pink root. P. terrestris produced microsclerotia that are similar to those produced by Pyrenochaeta lycopersici, Rhizopycnis vagum, Verticillium dalhiae and Macrophomina phaseolina.