ABSTRACT
Anthracnose of grapes is an economically devastating disease caused by Elsinoe ampelina (2). Warm, humid weather favors disease development, and therefore in the United States, it is generally restricted to grape-growing areas east of the Rocky Mountains. Vitis vinifera is highly susceptible to the disease, which is one of the principal factors preventing the development of an industry with this high-quality grape in the southeastern United States. Growers in this area produce local species-such as muscadine grapes (V. rotundifolia Michx.) and hybrids. Muscadine grapes are known for their resistance or "immunity" to many diseases found in bunch (Euvitis spp. Planch.) grape species (1). As yet, there has been no formal report of anthracnose or its causal agent on muscadine grapes. E. ampelina was detected on muscadine leaves for the first time in the experimental vineyard at the Center for Viticulture and Small Fruit Research during the summer of 2006. Approximately 40% of the 52 muscadine cultivars in the collection showed circular or irregular black spots typical of anthracnose mainly on young leaves and tendrils. However, no symptoms were observed on fruits, shoot tips, or any other plant part. To confirm the causal agent, infected leaves were surface sterilized with 75% ethanol, dipped in 2% sodium hypochlorite for 15 s, rinsed in distilled water, dissected into small 0.5-cm leaf discs, and plated on potato dextrose agar (PDA) and incubated at 28°C. Single-spore isolates were grown on PDA. Colonies were slow growing and appeared as dark red mounds with some mycelia. Conidia were cylindrical and hyaline with pointed ends consistent with previous reports for E. ampelina (2). The identity was also confirmed by using the following PCR primers to the 18S RNA: left primer; TCCGTAGGTGAACCTGCGGA and right primer; TCCTACCTGAT CCGAGGTCA designed on the basis of the alignment of E. ampelina sequences deposited in NCBI database. To fulfill Koch's postulates, symptoms were reproduced by artificial inoculation onto young muscadines (cv. Carlos) and bunch (cv. Cabernet Sauvignon) grapevines. A conidial suspension was prepared from single-conidial cultures, and three experimental vines of each species were sprayed with 0.5 ml of suspension (2 × 105 conidia per ml), whereas three control plants were sprayed with distilled water. The plants were incubated in a moist chamber at 28°C with 16 h of light. The first typical symptoms appeared on V. vinifera 4 days postinoculation and on the muscadines 6 days postinoculation. To our knowledge, this is the first report confirming anthracnose disease on muscadine grapes. References: (1) J. Lu et al. Acta Hortic. 528:479, 2000. (2) R. C. Pearson and A. C. Gohen. Anthracnose. Pages 18-19 in: Compendium of Grape Diseases. The American Phytopathological Society. St. Paul, MN, 1994.
ABSTRACT
The cloning and characterization of genes expressed in plant disease resistance could be an initial step toward understanding the molecular mechanisms of disease resistance. A metallothionein-like gene that is inducible by tobacco mosaic virus and by wounding was cloned in the process of subtractive cloning of disease resistance-response genes in Nicotiana glutinosa. One 530-bp cDNA clone (KC9-10) containing an open reading frame of 81 amino acids was characterized. Genomic Southern blot hybridization with the cDNA probe revealed that tobacco metallothionein-like genes are present in few or in one copy per diploid genome. Northern blot hybridization detected strong induction of a 0.5-kb mRNA by wounding and tobacco mosaic virus infection, but only mild induction was detected when copper was tested as an inducer. Methyl jasmonate, salicylic acid, and ethylene were also tested as possible inducers of this gene, but they had no effect on its expression. The possible role of this gene in wounded and pathogen-stressed plants is discussed.