Evaluation of cultural practices (surface burning,deep ploughing,organic amendments) for management of rice root-knot nematode in rice - onion cropping system and their effect on onion (Allium cepa L.) yield

Rice hull burning (RHB) is a traditional cultural practice of many onion growers in San Jose City, Nueva Ecija, Philippines, mainly for weed control and increased yield. The resulting carbonized rice hull (ash) is incorporated into the soil during land preparation before transplanting of onion. Studies to evaluate the effect of RHB on the population of the rice root-knotnematode, Meloidogyne graminicola, and onion yield were conducted in a farmer's field naturally infested with the pathogen. Burning of 15-cm-deep rice hulls significantly reduced the nematode populations in the soil and increased onion yield. Increasing the thickness of rice hulls burned to 30 cm deep resulted in a yield increase of 44.2% over no RHB and 11.9% over 15-cm-deep rice hulls, while the yield increase with 15-cm-thick hulls was 28.8% over no RHB. Plots that received rice hulls 30 cm deep also produced 37.7% more large bulbs for export than those plots that received 15-cm-deep hulls, and 151.7% more than those plots with no RHB. Deep ploughing did not significantly affect nematode populations compared with standard ploughing. Organic amendment did not contribute to an increase in onion yield and has no effect on the population of rice root-knot nematode.     

Phylogenetic relationships of Ralstonia solanacearum species complex strains from Asia and other continents based on 16S rDNA, endoglucanase, and hrpB gene sequences

The 16S rDNA, endoglucanase, and hrpB genes were partially sequenced for Asian strains of Ralstonia solanacearum spp. complex, including 31 strains of R. solanacearum and two strains each of the blood disease bacterium (BDB) and Pseudomonas syzygii. Additional sequences homologous to these DNA regions, deposited at DDBJ/EMBL/GenBank databases were included in the analysis. Various levels of polymorphisms were observed in each of these DNA regions. The highest polymorphism (approximately 25%) was found in the endoglucanase gene sequence. The hrpB sequence had about 22% poly-morphism. The phylogenetic analysis consistently divided the strains into four clusters, as distinctly shown on the phylogenetic trees of 16S rDNA, hrpB gene, and endo-glucanase gene sequences. Cluster 1 contained all strains from Asia, which belong to biovars 3, 4, 5, and N2. Cluster 2 comprised the Asian strains of R. solanacearum (as biovars N2 and 1) isolated from potato and clove, as well as BDB and P. syzygii. Cluster 3 contained race 3 biovar 2 strains from potato, race 2 biovar 1 strains from banana, and race 1 biovar 1 strains isolated from America, Asia, and other parts of the world. Cluster 4 was exclusively composed of African strains. The results of the study showed the distribution and diversity of the Asian strains, which are present in three of the four clusters. The similarity of Asian strains to those in the other regions was also observed.The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AY464950 to AY465050     

Diversity of Ralstonia solanacearum Infecting Eggplant in the Philippines

ABSTRACT The diversity of Ralstonia solanacearum strains isolated from eggplant (Solanum melongena) grown in five provinces of the Philippine island group of Luzon was assessed using a recently described hierarchical system. All strains keyed to race 1, biovar 3 or 4. Phylotype-specific multiplex polymerase chain reaction (PCR) indicated that, like most other strains of Asian origin, all the strains in our Philippine collection belong to phylotype I. Taxometric and phylogenetic analyses of partial endoglucanase gene sequences of strains from this collection and those previously deposited into GenBank revealed at least four subgroups among the otherwise monophyletic phylotype I strains. Nucleotide polymorphisms within each subgroup were infrequent and, among the subgroups identified in this study, variation was always <1.3%, indicating that the large majority of strains could be assigned to a single sequevar. Genomic DNA fingerprinting using enterobacterial repetitive intergenic consensus (ERIC)-PCR revealed additional fine-scale genetic variation that was consistent with the endogluconase sequence data. Whole-pattern and band-based analyses of the genomic fingerprint data revealed four and eight distinct genotypes, respectively, within our collection. Eggplant from infested fields in different provinces tended to harbor mixed populations of ERIC genotypes, with the predominant genotype varying by location.