Bacterial Wilt of Cucurbits: Resurrecting a Classic Pathosystem.

Bacterial wilt threatens cucurbit crop production in the Midwestern and Northeastern United States. The pathogen, Erwinia tracheiphila, is a xylem-limited bacterium that affects most commercially important cucurbit species, including muskmelon, cucumber, and squash. Bacterial wilt is transmitted and overwintered by striped and spotted cucumber beetles. Since there are few commercially available resistant cultivars, disease management usually relies on use of insecticides to suppress vector populations. Although bacterial wilt was initially described more than 100 years ago, our knowledge of disease ecology and epidemiology advanced slowly for most of the 20th century. However, a recent wave of research has begun to fill in missing pieces of the bacterial wilt puzzle. This article-the first review of research toward understanding the cucurbit bacterial wilt pathosystem-recounts early findings and updates our understanding of the disease cycle, including pathogen and vector biology. We also highlight research areas that could lead to more efficient and ecologically based management of bacterial wilt.

Watermelon juice: a promising feedstock supplement, diluent, and nitrogen supplement for ethanol biofuel production.

BACKGROUND: Two economic factors make watermelon worthy of consideration as a feedstock for ethanol biofuel production. First, about 20% of each annual watermelon crop is left in the field because of surface blemishes or because they are misshapen; currently these are lost to growers as a source of revenue. Second, the neutraceutical value of lycopene and L-citrulline obtained from watermelon is at a threshold whereby watermelon could serve as starting material to extract and manufacture these products. Processing of watermelons to produce lycopene and L-citrulline, yields a waste stream of watermelon juice at the rate of over 500 L/t of watermelons. Since watermelon juice contains 7 to 10% (w/v) directly fermentable sugars and 15 to 35 micromol/ml of free amino acids, its potential as feedstock, diluent, and nitrogen supplement was investigated in fermentations to produce bioethanol. RESULTS: Complete watermelon juice and that which did not contain the chromoplasts (lycopene), but did contain free amino acids, were readily fermentable as the sole feedstock or as diluent, feedstock supplement, and nitrogen supplement to granulated sugar or molasses. A minimum level of ~400 mg N/L (~15 micromol/ml amino nitrogen) in watermelon juice was required to achieve maximal fermentation rates when it was employed as the sole nitrogen source for the fermentation. Fermentation at pH 5 produced the highest rate of fermentation for the yeast system that was employed. Utilizing watermelon juice as diluent, supplemental feedstock, and nitrogen source for fermentation of processed sugar or molasses allowed complete fermentation of up to 25% (w/v) sugar concentration at pH 3 (0.41 to 0.46 g ethanol per g sugar) or up to 35% (w/v) sugar concentration at pH 5 with a conversion to 0.36 to 0.41 g ethanol per g sugar. CONCLUSION: Although watermelon juice would have to be concentrated 2.5- to 3-fold to serve as the sole feedstock for ethanol biofuel production, the results of this investigation indicate that watermelon juice, either as whole juice fermented on-site or as a waste stream from neutraceutical production, could easily integrate with other more concentrated feedstocks where it could serve as diluent, supplemental feedstock, and nitrogen supplement.

Isolation and identification of hexaketides from a pigmented Monosporascus cannonballus isolate.

Monosporascus cannonballus causes severe production losses to muskmelon and watermelon in the United States and other countries. Wild types of the fungus produce no pigments when grown on potato dextrose agar (PDA). After long-term storage on soil/oat hull mix, however, some isolates of the fungus produce yellow to brown pigments and no perithecia when grown on PDA. Five colored metabolites from pigmented cultures of M. cannonballus isolate TX923038 have now been identified. Two of these, monosporascone and dehydroxyarthrinone, have been isolated from other fungi, and three, demethylcerdarin, monosporascol A and azamonosporascone, have not previously been reported. The (1)H NMR and (13)C NMR of all five compounds are reported.

Identification of 1,8-dihydroxynaphthalene melanin in Monosporascus cannonballus and the analysis of hexaketide and pentaketide compounds produced by wild-type and pigmented isolates of the fungus.

Monosporascus cannonballus causes root rot and vine decline in muskmelons and watermelons. Wild types of this fungus often undergo degenerative changes that have been associated with yellow to brown pigmentation, hypovirulence, dsRNA infection, and decreased production of perithecia. In this study, degenerate isolates that produced yellow to brown pigments and no perithecia were obtained from wild-type cultures that had been stored for extended periods of time. Cultures of the degenerate isolates were found to accumulate five related hexaketides when grown on potato-dextrose agar (PDA). In contrast, these hexaketides were present only in minute amounts in wild-type cultures unless grown on NaCl-amended PDA. 1,8-Dihydroxynaphthalene melanin was established to be present in wild-type M. cannonballus and absent in the degenerate isolates. Various melanin-related metabolites, however, were produced by the variants. Tricyclazole in PDA cultures blocked melanin biosynthesis by the wild types but had little effect on hexaketide production by the degenerate isolates.