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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of Cantaloupe Fruit Decays Caused by Didymella Bryoniae and Phomopsis Cucurbitae at Different Fruit Developmental Stages

Authors
item Zhang, Jiuxu
item Bruton, Benny
item Miller, M. - TEXAS A&M UNIVERSITY
item Isakeit, T. - TEXAS A&M UNIVERSITY

Submitted to: South Texas Melon Committee Annual Research Report
Publication Type: Experiment Station
Publication Acceptance Date: November 20, 1998
Publication Date: N/A

Interpretive Summary: Didymella bryoniae and Phomopsis cucurbitae can cause both vine-decline and fruit rot of cantaloupe. D. bryoniae causes both pre- and post-harvest decay (black rot) of cantaloupe fruit, but P. cucurbitae only causes post- harvest decay. There is limited published information on etiology, disease development, and disease control of cantaloupe fruit. The mechanisms of cantaloupe fruit infection and decay with respect to fruit development stages are largely unknown. A study was conducted to compare fruit decays caused by the above two important fungal pathogens at different cantaloupe fruit developmental stages. Inoculation of fruit at different developmental stages with D. bryoniae and P. cucurbitae showed two distinct patterns of fruit susceptibility with respect to fruit developmental stage. Immature fruit (10 days or less post-pollination) were more susceptible to black rot as compared with more mature fruit. In contrast, immature fruit were the more resistant to P. cucurbitae decay as compared to mature cantaloupe fruit. P. cucurbitae is much more aggressive than D. bryoniae as a post-harvest decay of cantaloupe. This indicates that shipping Phomopsis infected fruit may be much riskier than that of Didymella infected fruit. Understanding the mechanisms for the two distinct fruit rot patterns caused by D. bryoniae and P. cucurbitae will provide valuable information for eventual control of these fruit rots.

Technical Abstract: Didymella bryoniae causes both pre- and post-harvest decay (black rot) of cantaloupe fruit. In contrast, Phomopsis cucurbitae only causes post- harvest decay. In the Lower Rio Grande Valley of Texas, black fruit rot caused by D. bryoniae can be in epidemic when environmental conditions and fruit developmental stages are favorable for infection. A comparison of D. .bryoniae and P. cucurbitae in relation to fruit susceptibility and fruit developmental stages was made. Inoculation of fruit at different developmental stages with D. bryoniae and P. cucurbitae showed two distinct patterns of fruit susceptibility with respect to fruit developmental stage. Immature fruit (10 days or less post-pollination) were more susceptible to black rot as compared with more mature fruit. Fruit (20 days post- pollination or more) showed similar susceptibility to black rot. In contrast, immature fruit were the more resistant to P. cucurbitae decay as compared to mature cantaloupe fruit. Mature fruit (40 days or more post- pollination) were very susceptible to Phomopsis decay. P. cucurbitae is much more aggressive than D. bryoniae as a post-harvest decay of cantaloupe. Therefore, shipping Phomopsis infected fruit has much more risk than that of black rot infected fruit as long as the lesions do not penetrate the orange flesh. The primary avenue for infection of both D. bryoniae and P. cucurbitae is through the epidermis during net development. Symptoms caused by P. cucurbitae are soft, water-soaked, symmetrical, and easily distinguished from healthy tissue under both artificial inoculation and natural infection. Symptoms of black rot of cantaloupe fruit are relative dry, somewhat irregular, and tend to be quite shallow below the epidermis.

Last Modified: 4/21/2014
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