Evolution of pathogenicity-associated genes in Rhizoctonia solani AG1-IA by genome duplication and transposon-mediated gene function alterations.

BACKGROUND: Rhizoctonia solani is a polyphagous fungal pathogen that causes diseases in crops. The fungal strains are classified into anastomosis groups (AGs); however, genomic complexity, diversification into the AGs and the evolution of pathogenicity-associated genes remain poorly understood. RESULTS: We report a recent whole-genome duplication and sequential segmental duplications in AG1-IA strains of R. solani. Transposable element (TE) clusters have caused loss of synteny in the duplicated blocks and introduced differential structural alterations in the functional domains of several pathogenicity-associated paralogous gene pairs. We demonstrate that the TE-mediated structural variations in a glycosyl hydrolase domain and a GMC oxidoreductase domain in two paralogous pairs affect the pathogenicity of R. solani. Furthermore, to investigate the association of TEs with the natural selection and evolution of pathogenicity, we sequenced the genomes of forty-two rice field isolates of R. solani AG1-IA. The genomic regions with high population mutation rates and with the lowest nucleotide diversity are enriched with TEs. Genetic diversity analysis predicted the genes that are most likely under diversifying and purifying selections. We present evidence that a smaller variant of a glucosamine phosphate N-acetyltransferase (GNAT) protein, predicted to be under purifying selection, and an LPMP_AA9 domain-containing protein, predicted to be under diversifying selection, are important for the successful pathogenesis of R. solani in rice as well as tomato. CONCLUSIONS: Our study has unravelled whole-genome duplication, TE-mediated neofunctionalization of genes and evolution of pathogenicity traits in R. solani AG1-IA. The pathogenicity-associated genes identified during the study can serve as novel targets for disease control.

Degradation pattern and risk assessment of carbendazim and mancozeb in mango fruits.

A supervised field trial was conducted at four different agroclimatic locations in India to evaluate the dissipation pattern and risk assessment of carbendazim and mancozeb in mango fruits following foliar application of mixed formulation of carbendazim 12% and mancozeb 63% fungicide (SAAF-75WP) at recommended dose (90 + 472.5) and double the recommended dose (180 + 945 g a.i. ha(-1)). Average initial deposition of carbendazim was in the range of 1.12 to 2.7 and 1.95 to 4.09 mg kg(-1) and for mancozeb in the range of 2.25 to 2.71 and 4.17 to 5.96 mg kg(-1), given at respective doses. Residues of carbendazim and mancozeb were dissipated to the below detectable limit 7 days after spray at recommended dosage in all the locations. The fungicide degradation followed a first order kinetics with half-lives of 1-5 and 1-3 days, for carbendazim and mancozeb, respectively. The TMRC values, calculated from residue data generated from all four locations, were found to be below the MPI in mango fruit, and hence, the fungicide will not cause any adverse effect after consumption of mango fruits. This data could provide guidance for the proper and safe use of this fungicide mixture for managing disease incidence in mango in India.

Effect of culture media and environmental factors on mycelial growth and pycnidial production of Lasiodiplodia theobromae in physic nut (Jatropha curcas).

Physic nut (Jatropha curcas) is an important commercial bio-diesel plant species and is being advocated for development of waste and dry land. The collar and root rot caused by Lasiodiplodia theobromae is an important soil borne disease which causes considerable yield loss in this crop. In this study, the effects of culture media, temperature, photoperiod, carbon and nitrogen sources and pH on mycelial growth and pycnidial production were evaluated. Among the growth media tested, potato dextrose agar supported the highest growth followed by potato sucrose agar and corn meal agar. Among several carbon sources tested, carboxy methyl cellulose and sucrose were found superior for growth and pycnidial production. The nitrogen sources viz., ammonium oxalate and ammonium dihydrogen phosphate were recorded maximum mycelial growth and pycnidial production. The fungus grows at pH 5.0-9.0 and optimum growth was observed at pH 7.0.

Limnological features of Thirumullavaram temple pond of Kollam municipality, Kerala.

Thirumullavaram temple pond associated with Sree Mahavishnu temple is located very close to the Arabian sea in Kollam municipality of Kerala. Physicochemical characteristics of water and sediment, productivity, plankton count, coliform count and correlation coefficients of various parameters were analysed for a period of one year from June 1999 to May 2000. It showed that the water characteristics such as conductivity, turbidity, colour, pH, total alkalinity, chloride, total hardness, silicate, phosphate, nitrate, iron, sodium and potassium; primary productivity, plankton count, and sediment characteristics such as pH, organic matter, potassium and nitrate registered higher values during non-rainy season. Coliform count recorded higher value during monsoon season. From the correlation study, it was inferred that several characteristics of water, sediment and primary productivity were interrelated. Comparison of water characteristics with BIS for drinking and swimming water showed that the pond water was mainly contaminated with coliform bacteria. However, the physico-chemical characteristics indicated that it could be used as a potential water source for drinking, swimming and for secondary production after proper treatment.

An optimum pH for the demonstration of chitin in Periplanata americana using Lugol's iodine.

Modification of chitosan test of Campbell is suggested with a controlled procedure involving heating with saturated potassium hydroxide at 160 degrees C for a period of 45 min and subsequent washing of the deacetylated chitin in running water and application of Lugol's iodine solution (1:2:300, w/w/v) at a pH range of 1.4 to 4.0, thus replacing the use of dilute sulphuric acid. Consistent results were obtained not only with the cuticle of Periplanata americana but also with the cuticle of Emerita asiatica (crustacea).

Studies on metachromasia. III. Toluidine blue-substrate interaction and metachromasia.

With salts as substrates the metachromatic responses of the thiazine dye, Toluidine blue are studied. It is found that generally salts produce a gamma-metachromatic response. The substrate-dye interaction is studied in detail and the results are discussed in the light of various interpretations of previous workers. It is suggested that toluidine blue may have two sites that are responsible for the exhibition of green and red metachromatic responses. The influence of water on metachromasia has been studied and is reported to bring about an oscillation of spectral colours. Spectrophotometric studies were also carried out.

Influence of carbonates and other salts in tissues on the Schiff's reagent.

Application of the Schiff's reagent on fresh and undecalcified cuticle of crustaceans such as Emerita asiatica and Ocypoda platytarsis showed positive results with their calcified layer which led to suggest that salts of calcium account for the staining. In vitro studies with carbonate and other salts furnished confirmatory evidence. It is suggested that in tests involving the Schiff's reagent proper removal of resident salts must be carried out.