Submitted to: South Texas Melon Committee Annual Research Report
Publication Type: Experiment Station
Publication Acceptance Date: 11/15/1998
Publication Date: N/A
Interpretive Summary: Cucurbit diseases caused by Fusarium spp. are responsible for the greatest losses in yield due to fruit rot and can cause severe postharvest losses as well. Little is known about the fruit rots caused by Fusarium spp. Fusarium fruit rot is the leading cause of cantaloupe fruit losses in the Lower Rio Grande Valley of Texas. Mode of infection and species of Fusarium involved in fruit rot has never been determined. This study was undertaken to determine the frequency of different species of Fusarium how the fungus penetrates the fruit. We established that Fusarium semitectum and Fusarium solani were the predominant species causing fruit rot in the Lower Rio Grande Valley. Fusarium equiseti was isolated infrequently. Fruit infection by both Fusarium semitectum and Fusarium solani occurred between 12 and 16 hours and appeared to be restricted primarily to the developing net between 12 and 25 days post-pollination. This study provides evidence that the net of cantaloupe appears to be the primary avenue for infection by Fusarium species. Although fungicides have not been effective in the past, it may be due to timing rather than adequate coverage of the fruit. Fungicide applications should be timed to coinside with net development. Work is in progress to study Fusarium fruit rot with an emphasis on the infection process and the enzymes required for pathogenesis with the ultimate goal of developing control measures for the disease.
Technical Abstract: Fusarium fruit rot is generally the leading cause of fruit losses in the Rio Grande Valley of Texas. Fusarium semitectum and F. solani were the most prominent species isolated from four commercial fields during 1998. F. equiseti was isolated infrequently. Fruit infection by both F. semitectum and F. solani appeared to be restricted primarily to the developing net between about 12 and 25 days post-pollination. Symptoms of Fusarium fruit rot can vary greatly depending on size of lesion, preharvest, and postharvest. Preharvest lesions caused by F. semitectum, F. solani, and F. equiseti often exhibit an epidermal split in the lesion with a green halo surrounding the lesion. Internal fruit lesions are generally shallow and a reddish-brown color. In mature fruit, especially postharvest, the lesion exhibits a corky brown discoloration below the epidermis with a white halo surrounding the corky brown lesion. In early season, Fusarium fruit rot can be confused with black rot lesions caused b Didymella bryoniae. However, as fruit mature, internal symptoms of Fusarium fruit rot are characterized by the corky brown center with a white halo surrounding it. In contrast, internal symptoms of black rot are characterized by the black discoloration in the center of the lesion.