Transmission tests were conducted with field-collected Bunchy Top Symptoms (BTS) phytoplasma-infected specimens of Empoasca papayae. BTS developed in all eight inoculated papayas 3 months later. The BTS phytoplasma was identified in six of eight inoculated papayas, whose partial 16S rRNA sequence (GenBank Accession no. FJ6492000) was 99.9% identical with those from the collected papayas (GenBank Accession no FJ649198) and E. papayae (GenBank Accession no. FJ649199), all of which are members of group 16SrII, ÔCandidatus Phytoplasma aurantifoliaÕ. Results confirmed the ability of E. papayae to transmit the BTS phytoplasma.

Nearby fruit and vegetable fields in Islamabad, Pakistan were surveyed for phytoplasma infection. ÔCandid-atus Phytoplasma asterisÕ (Group 16SrI) was found infecting mango, citrus, loquat, geranium, periwinkle, radish, blackberry and potato. Results suggest that a polyphagous vector may be involved in phytoplasma transmission to these plant species, which are first host records of 16SrI phytoplasma infection in Pakistan.

No abstract

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.

In August of 2009, powdery mildew was observed on peppermint (Mentha piperita L.) in several commercial fields in the Fall River Valley of eastern Shasta County, California. Plant growth was apparently reduced by the disease, but its impact on yield was unknown. White fungal growth was restricted to the adaxial surfaces, where colonies were thin and effused. Heavily infected leaves developed a reddish tint as growth prematurely ceased. Doliform conidia ([26.6-] 29.2 [-31.7] × [13.2-] 15.6 [-16.8] μm) were produced in chains of approximately six conidia. Foot cells were cylindrical ([41.3-] 55.2 [-75.0] × [11.2-] 12.0 [-12.8] μm). Immature chasmothecia were yellowish brown and approximately 100.0 μm in diameter with flexuous, mycelium-like appendages up to 200 μm long. All these features were consistent with those of Golovinomyces biocellatus. Asci were not observed. To confirm the identity of the fungus, nuclear rDNA internal transcribed spacer (ITS) regions were amplified by PCR with universal primers ITS4 and ITS5. The sequence (537 bp) was an exact match for several submissions of G. biocellatus in GenBank (e.g., Accession No. EU035602, a sequence of the fungus from mint in Australia [1]). Pathogenicity was confirmed by brushing spores from naturally infected leaves onto three rooted cuttings of M. piperita ‘Black Mitchum’. After the plants were covered with a plastic bag for 36 h to maintain high humidity, they were kept on a greenhouse bench at 23 to 28°C. Three noninoculated plants, which served as controls, were placed in another greenhouse in similar conditions. The experiment was repeated once. All inoculated plants developed signs of powdery mildew within 7 days of inoculation whereas noninoculated plants remained disease free. The fungus on inoculated leaves was morphologically indistinguishable from the one used to inoculate the plants. To our knowledge, this is the first report of G. biocellatus on peppermint in California. References: (1) J. R. Liberato and J. H. Cunnington. Australas, Plant Dis. Notes 2:38, 2007.