Antibacterial substance produced by Streptomyces sp. No. 87

An antimicrobial substance produced by Streptomyces sp. No. 87 was partially purified and studied for its antibacterial characteristics using the swab paper disc technique. The cell-free culture filtrateshowed antibacterial activity against several species of pathogens including Gram-positive bacteria, i.e. Bacillus cereus ATCC 11778, B. subtilis TISTR 008, B. megaterium, Staphylococcus aureus, S. aureusATCC 25923, and S. epidermidis and Gram-negative bacteria, i.e Klebsiella pneumoniae ATCC 27736, K. pneumoniae, Salmonella typhi ATCC 5784, Vibrio cholerae and Xanthomonas sp. 60% ammoniumsulfate precipitation of the culture supernatant shows markedly antibacterial activity against B. cereus ATCC 11778. Then supernatant was purified by gel filtration chromatography with sephadex G-25 resin.Five peaks namely P1, P2, P3, P4 and P5 were obtained. Results indicate that P3 is the only peak possessing the antibacterial activity, therefore, the final purification of P3 was conducted using FPLCwith a superdex 30 column. Only one peak, namely P3-1 retained the antibacterial activity. P3-1 showed that its activity was insensitive to proteolytic enzymes such as trypsin, pepsin and proteinase K. Inaddition, the activity of P3-1 could be observed temperatures of 50 -121oC and no protein or polypeptide band was seen when P3-1 was analyzed by SDS-PAGE. These results suggest that P3-1 might not beproteinacious in nature

Pyramiding of blast and bacterial leaf blight resistance genes into rice cultivar RD6 using marker assisted selection

Blast caused by the fungus Magnaporthe oryzae (Hebert) Barr. and bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) are two major diseases of rice (Oryza sativa). The use of varietal resistance is the most appropriate strategy for controlling the diseases, and molecular assisted selection can potentially accelerate breeding programs. The objective of this study was to pyramid genes conferring resistance to blast and bacterial leaf blight diseases to rice cultivar RD6, using molecular assisted selection. Near-isogenic lines (NIL) derived from two blast resistant crosses (RD6 × P0489 and RD6 × Jao Hom Nin) were pyramided with IR62266 (xa5), to transfer bacterial leaf blight resistance to RD6 introgression lines. Five flanking sets of simple sequence repeat (SSR) markers (RM319/RM212, RM48/RM207, RM224/RM144, RM313/RM277 and RM122/RM159: four for blast and one for BLB resistance) were used for screening of introgression lines carrying five quantitative trait loci (QTLs) from the BC1F2 generation through to BC2F2:3 generation, and 12 pyramiding lines were identified. Gene validation for blast and bacterial leaf blight diseases was accomplished using artificial inoculation under greenhouse conditions. BC2F2:3 2-8-2-24 and BC2F2:3 2-8-2-25 showed greater levels of blast broad spectrum resistance (BSR) whereas BC2F2:3 2-8-2-36 expressed the highest of bacterial leaf blight resistance with a high blast BSR.Keywords: Gene pyramiding, introgression lines, molecular marker, Near-isogenic lines, SSR.African Journal of Biotechnology Vol. 12(28), pp. 4432-443

Stability of Four New Sources of Bacterial Leaf Blight Resistance in Thailand Obtained From Indigenous Rice Varieties

Bacterial leaf blight (BLB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious diseases in rice production. Breeding varieties specifically for their resistance to BLB disease is therefore an efficient and cost-effective strategy. However, the resistance gene for BLB can be race and non-race specific, meaning it is often overcome by the pathogen. The identification of new sources of resistance genes for Xoo is crucial in rice breeding programmes. In this study, six rice varieties were assessed using six Xoo isolates in multiple screening conditions. The GGE biplot analysis considers both genotype (G) and genotype environment (GE) interaction effects and demonstrates GE interaction. The first two principal components (PCs) accounted for 95.46% of the total GE variation in the data. Based on lesion length and stability performance, Phaladum was the most ideal genotype against all Xoo isolates in the four screening conditions. The results relayed that Phaladum indigenous rice varieties could be considered as new sources of bacterial leaf blight resistance in Thailand. In the future, the BLB resistance gene in this variety will be identified in regard to mode of inheritance and used as parental line in rice breeding programmes for resistance to BLB