Progress 10/01/04 to 09/30/05
Outputs
Batches of approximately 2,000 bacterial fruit blotch(BFB)-infected melon and watermelon seeds were subjected to various wet seed treatments. Percent seed transmission in the batches was determined by greenhouse grow out assay for BFB. The most effective wet seed treatments were hydrochloric acid, peroxyacetic acid, and overnight fermentation. The addition of Lactobacillus brevis and L. plantarum to the fermentation mix may be beneficial. Seed treatments are being evaluated on other BFB-infested cucurbit seeds, including cantaloupe, summer squash, winter squash, pumpkin, and cucumber seeds. As on watermelon, peroxyacetic acid, acetic acid, and fermentation were effective seed treatments; however, none of the treatments were very effective on BFB seed transmission in pumpkin. Heat treatments of dry seeds at 45C, 50C, 55C, or 60C for 1 to 4 hours did not reduce BFB seed transmission in watermelon. The most likely means of persistence of Acidovorax avenae subsp. citrulli
(cause of BFB) in an area is on plant hosts. A. avenae subsp. citrulli could be recovered from tomato, pepper, eggplant, citron, creeping cucumber, corn, and field peas for at least 1 to 2 months after it was misted onto the foliage. The bacterium could not be recovered from bean, alyce clover, balsam apple, or rye one month after inoculation. To evaluate field control of BFB, Charleston Gray watermelon seedlings, grown in Fafard 2S potting mix in 1 inch x 1 inch x 2 inch cells in the greenhouse, were transplanted into the field plots. At least 1 symptomatic plant that had been inoculated with Acidovorax avenae subsp. citrulli was transplanted into each plot. In the nontreated plots, 59% of the fruit developed BFB symptoms. In the currently recommended copper spray and copper spray plus Actigard treatments, there were only 14% and 10% symptomatic fruit, respectively. Twice weekly applications of peroxyacetic acid at 80 ppm did not reduce the incidence of fruit symptoms when compared
to the nontreated.
Impacts
The most effective control of BFB of watermelon, and other cucurbits, currently available is the exclusion of the bacterium. Seed infection of cucurbits is the primary means of introducing the bacterium into a production area. Seed transmission can occur with any cucurbit, but watermelon, honeydew melons, and cantaloupe are especially susceptible. The seed treatments developed in this project should prevent the introduction of the bacterium on seed. If the bacterium were introduced into areas of the Caribbean, such as Puerto Rico and the Virgin Islands, it would pose a serious threat to their cucurbit industry. Most of the major outbreaks of BFB have involved infected transplants. The warm, humid environment of a transplant house is favorable for bacteria from infected seeds to produce disease and spread on the developing seedling. The development of effective seed treatments and controls for transplant house spread of BFB could eliminate this threat to the cucurbit
industry in the Caribbean and prevent the approximately $1 million loss that the industry has each year in Florida and the Southeast.
Publications
- Hopkins, D.L. 2005. Control of greenhouse spread of bacterial fruit blotch of cucurbits with peroxyacetic acid and ionized copper in the irrigation water. Phytopathology 95:S44.
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Progress 09/15/03 to 09/14/05
Outputs
The primary goal of the project was to develop an integrated system to prevent the introduction of Acidovorax avenae subsp. citrulli, cause of bacterial fruit blotch (BFB) into new areas and to control this invasive bacterium where it already occurs. Contaminated seedlots has been the primary way in which BFB has been introduced into cucurbit fields or transplant houses. Peroxyacetic acid, hydrochloric acid, and acetic acid were found to be effective in eliminating seed transmission of BFB in watermelon; however, HCl can adversely affect seed quality. When introduced into a transplant house, BFB can be spread rapidly by overhead irrigation. Weekly sprays of cupric hydroxide at 840 ppm plus acibenzolar-S-methyl at 50 micrograms per ml applied at emergence and 6 days later effectively reduced spread of BFB symptoms. The best control of BFB spread in the transplant house was provided by peroxyacetic acid at 80 micrograms per ml or ionized copper at 1.0 microgram per ml in
the irrigation water plus two applications of acibenzolar-S-methyl. When introduced into the field, BFB spreads rapidly, especially during summer storms. In field studies on control of BFB, weekly applications of cupric hydroxide were effective. Although it was effective in the transplant house irrigation water, peroxyacetic acid twice weekly at 80 ppm was not effective in reducing spread in the field. The most likely means of persistence of A. avenae subsp. citrulli in an area is either in the soil or on alternate hosts. The bacterium survived for less than 2 weeks in the soil in Florida in the summer. A. avenae subsp. citrulli could be recovered from tomato, pepper, eggplant, corn, field peas, beans, balsam apple, citron, and creeping cucumber 4-6 weeks after it was misted onto the foliage in the field.
Impacts
The most effective control of BFB of watermelon, and other cucurbits, currently available is the exclusion of the bacterium. Seed infection of cucurbits is the primary means of introducing the bacterium into a production area. Seed transmission can occur with any cucurbit, but watermelon, honeydew melons, and cantaloupe are especially susceptible. The seed treatments developed in this project should prevent the introduction of the bacterium on seed. If the bacterium were introduced into areas of the Caribbean, such as Puerto Rico and the Virgin Islands, it would pose a serious threat to their cucurbit industry. Most of the major outbreaks of BFB have involved infected transplants. The warm, humid environment of a transplant house is favorable for bacteria from infected seeds to produce disease and spread on the developing seedling. The development of effective seed treatments and controls for transplant house spread of BFB could eliminate this threat to the cucurbit
industry in the Caribbean and prevent the approximately $1 million loss that the industry has each year in Florida and the Southeast.
Publications
- Hopkins, D.L. and Thompson, C.M. 2006. Treatments to prevent seed transmission of bacterial fruit blotch of watermelon. Proc. Cucurbitaceae 2006, pp 436-443.
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Progress 10/01/03 to 09/30/04
Outputs
Bacterial fruit blotch(BFB)-infected `Charleston Gray' watermelons and `Honeybrew' melons were grown on the research farm at Apopka. Seeds were collected by hand from fruit with symptoms and were bulked, washed, and divided into batches of approximately 2,000 seeds for treatment. Percent seed transmission of BFB was determined in a greenhouse grow out assay of treated seeds. Hydrochloric acid, peroxyacetic acid, and acetic acid were good wet seed treatments for the control of seed transmission of A. avenae subsp. citrulli. Sodium and calcium hypochlorite controlled seed transmission in melons and in all but a very low percentage of the watermelon seeds. Fermentation of watermelon seeds in the pulp from the fruit for 24 to 48 hrs was found to be an effective way of eliminating seed transmission of bacterial fruit blotch. The problem with this long fermentation treatment (and with HCl treatments) was its effect on seed quality, especially with triploid seed. Therefore,
we evaluated shorter fermentation times with bacteria and yeast additives added to the pulp. Three hours fermentation was not sufficient to eliminate seed transmission in watermelon regardless of the additive. With 16 or 24 hrs fermentation, some bacterial additives resulted in no seed transmission. Natural fermentation in the watermelon pulp for 16 - 24 hrs eliminated most seed transmission but not all of it. There was an apparent benefit from adding bacteria (Lactobacillus spp.) to the fermentation mixture. There did not appear to be any benefit from adding yeast to the pulp prior to fermentation. Hot water treatments were not effective in controlling seed transmission. When introduced into a transplant house, BFB can be spread rapidly by overhead irrigation. Cupric hydroxide at 840 ppm copper applied weekly as well as peroxyacetic acid at 80 ppm and ionized copper at 1.0 - 1.5 ppm applied daily in the irrigation water controlled the spread of BFB in the transplant house. When
transplants were maintained in the transplant house for more than 7-10 days, the best control of BFB spread was provided by ionized copper or peroxyacetic acid plus two weekly applications of acibenzolar-S-methyl.
Impacts
The most effective control of BFB of watermelon, and other cucurbits, currently available is the exclusion of the bacterium. Seed infection of cucurbits is the primary means of introducing the bacterium into a production area. Seed transmission can occur with any cucurbit, but watermelon, honeydew melons, and cantaloupe are especially susceptible. If the bacterium were introduced into areas of the Caribbean, such as Puerto Rico and the Virgin Islands, it would pose a serious threat to their cucurbit industry. Most of the major outbreaks of BFB have involved infected transplants. The warm, humid environment of a transplant house is favorable for bacteria from infected seeds to produce disease and spread on the developing seedling. The development of effective seed treatments and controls for transplant house spread of BFB could eliminate this threat to the cucurbit industry in the Caribbean and prevent the approximately $1 million loss that the industry has each year
in Florida and the Southeast.
Publications
- Hopkins, D.L., Thompson, C.M., Hilgren, J., and Lovic, B. 2003. Wet seed treatment with peroxyacetic acid for the control of bacterial fruit blotch and other seedborne diseases of watermelon. Plant Dis. 87:1495-1499.
- Hopkins, D.L. 2003. Field control of bacterial fruit blotch of watermelon with a plant defense activator. Phytopathology 93:S37.
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