Comparative analysis of two emerging rice seed bacterial pathogens.

Seed sterility and grain discoloration limit rice production in Colombia and several Central American countries. In samples of discolored rice seed grown in Colombian fields, the species Burkholderia glumae and B. gladioli were isolated, and field isolates were compared phenotypically. An artificial inoculation assay was used to determine that, although both bacterial species cause symptoms on rice grains, B. glumae is a more aggressive pathogen, causing yield reduction and higher levels of grain sterility. To identify putative virulence genes differing between B. glumae and B. gladioli, four previously sequenced genomes of Asian and U.S. strains of the two pathogens were compared with each other and with two draft genomes of Colombian B. glumae and B. gladioli isolates generated for this study. Whereas previously characterized Burkholderia virulence factors are highly conserved between the two species, B. glumae and B. gladioli strains are predicted to encode distinct groups of genes encoding type VI secretion systems, transcriptional regulators, and membrane-sensing proteins. This study shows that both B. glumae and B. gladioli can threaten grain quality, although only one species affects yield. Furthermore, genotypic differences between the two strains are identified that could contribute to disease phenotypic differences.

Mapping quantitative trait Loci responsible for resistance to sheath blight in rice.

Rice sheath blight (ShB), caused by the soilborne pathogen Rhizoctonia solani, annually causes severe losses in yield and quality in many rice production areas worldwide. Jasmine 85 is an indica cultivar that has proven to have a high level of resistance to this pathogen. The objective of this study was to determine the ability of controlled environment inoculation assays to detect ShB resistance quantitative trait loci (QTLs) in a cross derived from the susceptible cv. Lemont and the resistant cv. Jasmine 85. The disease reactions of 250 F(5) recombinant inbred lines (RILs) were measured on the seedlings inoculated using microchamber and mist-chamber assays under greenhouse conditions. In total, 10 ShB-QTLs were identified on chromosomes 1, 2, 3, 5, 6, and 9 using these two methods. The microchamber method identified four of five new ShB-QTLs, one on each of chromosomes 1, 3, 5, and 6. Both microchamber and mist-chamber methods identified two ShB-QTLs, qShB1 and qShB9-2. Four of the ShB-QTLs or ShB-QTL regions identified on chromosomes 2, 3, and 9 were previously reported in the literature. The major ShB-QTL qShB9-2, which cosegregated with simple sequence repeat (SSR) marker RM245 on chromosome 9, contributed to 24.3 and 27.2% of total phenotypic variation in ShB using microchamber and mistchamber assays, respectively. qShB9-2, a plant-stage-independent QTL, was also verified in nine haplotypes of 10 resistant Lemont/Jasmine 85 RILs using haplotype analysis. These results suggest that multiple ShB-QTLs are involved in ShB resistance and that microchamber and mist-chamber methods are effective for detecting plant-stage-independent QTLs. Furthermore, two SSR markers, RM215 and RM245, are robust markers and can be used in marker-assisted breeding programs to improve ShB resistance.

Trichinella spiralis infection in pigs in eastern Bolivia.

Trichinellosis in pigs in Bolivia was first documented in 1993 following a small abattoir survey in a rural community in the Bolivian Altiplano. The present study investigated the presence of antibodies to Trichinella spiralis in pigs in the 2 largest departments in terms of pig production in Bolivia. Three geographically separate abattoir surveys were conducted to cover the major production areas in the Departments of Santa Cruz and Chuquisaca. Sera were tested using an enzyme-linked immunosorbent assay. Of the 1,327 sera analysed from the 3 areas, 13.4% overall tested positive. Results from the 3 individual surveys varied from 10.2% seropositivity to 17.1 per cent. However, within each of the 3 sample areas, highly significant variation in seropositivity was encountered, with those areas with the most extensive production systems having the highest percentage of positive sera. Such variation is probably due to differences in nutrition with foraging and household waste being important components of pig diets in extensive production systems. The results of this study were similar to those obtained from the previous survey in the Altiplano and indicate that trichinellosis is present throughout Bolivia and is a potentially important public health problem.