RESUMO
During the rainy season in Vietnam, leaf blight disease caused by Rhizoctonia solani often occurs on 3- to 5-year-old durian (Durio zibethinus). Symptoms appear as large, pale brown, blighted lesions with an irregular border. In excessive moisture conditions, yellowish white hyphae appear on the lesions, and the affected leaves turn dark brown and wilt. There are no reports describing the anastomosis groups (AG) and subgroups of Rhizoctonia solani occurring in durian. In June of 2004, two isolates of R. solani were obtained from leaf blight lesions on durian growing in Binh Duong and Dong Nai provinces. The durian isolates were identified as AG 1 based on hyphal anastomosis. In pathogenicity tests, the durian isolates infected cucumber, mung bean, and leaf mustard seedlings grown on water agar in petri dishes. The rDNA-ITS sequence of the durian isolates was determined (GenBank Accession Nos. EF197797 and EF197798) and aligned with those of AG 1-IA, AG 1-IB, AG 1-IC, and AG 1-ID available in the GenBank database. The sequence similarity of the total rDNA-ITS region (including 5.8S) within the durian isolates was 99.9%. The sequence similarity of the durian isolates and AG 1-ID isolates was 99.1 to 100%, but similarity with other AG 1 subgroups was 89.1 to 94.0%. The results suggest that the two Vietnam durian isolates of R. solani are members of AG 1-ID. AG 1-ID has only been reported causing necrotic leaf spots on coffees in the Philippines (1). To our knowledge, this is the first report of R. solani AG 1-ID on durian and the first report of the presence of R. solani AG 1-ID in Vietnam. Reference: (1) A. Priyatmojo et al. Phytopathology 91:1054, 2001.
RESUMO
In Asian developing countries, large amounts of municipal wastes are dumped daily in open dumping sites without proper management. This practice may cause several adverse environmental consequences and increased health risk to local communities. To elucidate contamination by persistent organic pollutants (POPs)--including dichloro-diphenyl-trichloroethane and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), chlordanes, hexachlorobenzene (HCB), and polychlorinated biphenyls (PCBs)--in such dumping sites, soil samples were collected from open dumping sites and respective control sites in Cambodia, India, and Vietnam from 1999 through 2001. Our results demonstrated that DDTs, PCBs, and HCHs were dominant contaminants in the dumping sites. However, the contamination pattern was not consistent, showing higher HCHs in India than in Cambodia and Vietnam. Interestingly, in all of the countries, extremely higher levels of POPs were observed in the dumping sites compared with those in the respective control sites, suggesting significant amplification of POP contamination in the dumping sites of Asian developing countries. Mean concentrations of DDTs and PCBs were 350 and 140 ng/g dry weight, respectively, in the dumping sites of Cambodia and 26 and 210 ng/g, respectively, in India. These residue levels were hundreds to thousands times higher than those in general soils, implying possible risk to human health of the local communities, especially to the rag pickers, including children who work in these sites to collect recyclable materials. Composition of DDT compounds suggested their recent use in populated areas, which in turn might have caused increased levels of DDTs in the open dumping sites. In addition, composition of HCH isomers revealed their different use pattern in different countries.
