First Report of Rhizoctonia solani on Mung Bean (Vigna radiata) Sprouts in California

In March 2007, mung bean (Vigna radiata) sprouts produced in an indoor sprouting facility in northern California developed brown lesions beginning 5 days after germination. Dark brown-to-reddish brown lesions with distinct margins developed on the stem, hypocotyl, and first true leaves of affected sprouts. Although all seed is routinely soaked in 20,000 mg Ca(OCl)2/liter of water for 15 min before germination, approximately 5 to 10% of the bean sprouts in several growing baskets (1.5 × 1.5 m) were affected and had to be discarded. Each basket contained approximately 1 t of sprouts. To isolate the causal organism, symptomatic stems were surface disinfested for 1 min in 0.5% NaOCl and incubated on acidified potato dextrose agar (PDA) at 25°C. Cultures were identified as Rhizoctonia solani on the basis of morphological features including right-angled branching of brown hyphae and the presence of sclerotia. PCR amplification of the internal transcribed spacer region was performed with primers RS1 and RS4 (2). Sequences were identical to R. solani AG4-HG-II in GenBank (Accession No. AF354074). To conduct pathogenicity tests, a 5-mm2-diameter disk from the margin of a culture of the fungus on PDA was placed in the center of 25 5-day-old germinated sprouts placed in a plastic box (15 × 10 × 5 cm) held at 25°C. Two isolates of R. solani cultured from different lots of sprouts were included in the assays. Controls received noncolonized agar. Treatments were replicated four times and each experiment was repeated three times. A moist paper towel was included in each box to maintain humidity. After 3 days, symptoms developed in the inoculated boxes but not in the noninoculated boxes. The fungus was reisolated from lesions, completing Koch's postulates. To our knowledge, this is the first report of R. solani on mung bean sprouts in a commercial sprouting facility. However, R. solani has been associated with root rot of mung bean plants in the field (1). References: (1) T. R. Anderson. Can. Plant Dis. Surv. 65:1, 1985. (2) C. Guillemaut et al. Can. J. Microbiol. 49:556, 2003.

Identification of geneticaly modified soybean seeds resistant to glyphosate

Advances in genetic engineering permit the modification of plants to be tolerant to certain herbicides that are usually not selective. For practical and commercial purposes, it is important to be able to detect the presence or absence of these traits in genotypes. The objective of this research was to develop a procedure for identifying genetically modified soybean (Glycine max L. Merr.) with resistance to the herbicide glyphosate. Two studies were conducted based on germination test. In the first study, soybean seeds were pre-imbibed in paper towel with the herbicide solutions, then transferred to moist paper towel for the germination test. In the second study, seeds were placed directly in herbicide solutions in plastic cups and tested for germination using the paper towel method. Eight soybean genotypes were compared: four Roundup Ready, that contained the gene resistant to the herbicide (G99-G725, Prichard RR, G99-G6682, and H7242 RR) and four non-transgenic parental cultivars (Boggs, Haskell, Benning, and Prichard). In the first study, the seeds were imbibed for 16 hours at 25°C in herbicide concentrations between 0.0 and 1.5% of the glyphosate active ingredient. In the second, seeds were subjected to concentrations between 0.0 and 0.48%, for one hour, at 30°C. The evaluation parameters were: germination, hypocotyl length, root length and total length of the seedlings. Both methods are efficient in identifying glyphosate-resistant soybean genotypes. It is possible to identify the genetically modified soybean genotypes after three days, by imbibing the seed in 0.12% herbicide solution, and after six days if the substrate is pre-imbibed in a 0.6% herbicide solution. The resistance trait was identified in all cultivars, independent of the initial physiological quality of the seed.