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Alternaria leaf spot is an emerging disease of Jerusalem artichoke (Helianthus tuberosus L.) in tropical regions. The lack of known resistant germplasm sources is an important constraint to development of Jerusalem artichoke varieties with resistance to Alternaria leaf spot. The objectives of this study were to identify variability of Jerusalem artichoke genotypes for resistance to Alternaria leaf spot under field conditions and to investigate the relationships among resistance characters, yield, and yield components for selection of resistant varieties. Ninety six accessions of Jerusalem artichoke were evaluated in replicated trials under field conditions in early rainy and late rainy seasons in Khon Kaen, Thailand during 2014. Parameters evaluated included disease incidence, disease score, disease severity index, area under disease progress curve of disease incidence, area under disease progress curve of disease severity index, number of tubers/plants, tuber size, and fresh tuber yield. The genotypes HEL 335, HEL 256, HEL 317, HEL 308, and JA 86 were identified as sources of leaf spot resistance in both seasons. These genotypes can be used as sources of leaf spot resistance for Jerusalem artichoke breeding programs. HEL 293 and HEL 246 showed susceptibility to leaf spot disease in both seasons and should be used as standard susceptible checks.

Cloning and disruption of Rga1, the gene encoding the G protein a subunit in the rice sheath blight fungus Rhizoctonia solani, was investigated. The deduced primary structure of the Rga1-encoded protein showed high identity to those of Ga subunits from other filamentous fungi. Disruption of Rga1 led to decreased vegetative growth and pathogenicity. The Rga1 disruptant showed altered colony morphology. In addition, the sclerotia formation ability of the disruptant was completely lost. These results suggest that the Ga subunit encoded by Rga1 is involved in a signal transduction pathway in R. solani that controls growth, development and pathogenicity.

Suwannual T., Chankaew S., Monkham T., Saksirirat W., Sanitchon J. (2017): Pyramiding of four blast resistance QTLs into Thai rice cultivar RD6 through marker-assisted selection. Czech J. Genet. Plant Breed., 53: 1-8.Thai rice cultivar RD6 is well known for its cooking and eating qualities. However it is susceptible to blast disease, a major rice disease caused by the fungus Magnaporthe oryzae. This study focused on the pyramiding of four QTLs for blast resistance located on chromosomes 1, 2, 11 and 12, from two RD6 introgression lines. Marker-assisted selection was performed and facilitated the selection with 8 microsatellite flanking markers to enable the selection in BC 2 F 2:3 lines. All possible combinations of the four QTL alleles were assessed for blast resistance by artificial inoculation using 8 diverse isolates in a greenhouse and under field conditions using the upland short row method. The results showed that the RD6 introgression lines carrying a high number of QTLs for blast resitance achieved from pyramiding have high levels of blast resistance and broad spectrum of resistance to the blast pathogens prevalent in the region. Only one of the M. oryzae isolates, THL185, was virulent to all the breeding lines, suggesting that the identification of new blast resistance genes or QTLs and pyramiding them into RD6 for durable blast resistance and no yield penalty should be the focus of further research.