Rice is believed to have originated from Indo-China, area between China and India, and then spread throughout the world. The Indochina region mainly includes countries like Thailand, Laos and Vietnam, which are the world’s major rice exporters. Rice varieties grown in this area are highly diverse due to their different environment, ecosystem and climatic conditions. The objective of this study was to evaluate the genetic relationship of Indochina rice varieties using intersimple sequence repeat (ISSR), sequence-related amplified polymorphism (SRAP) and insertion–deletion (InDel) markers. Forty-six rice varieties, including 16, 4,11 and 15 from Thailand, China, Laos and Vietnam, respectively were used in this study. Seventeen of the 20 ISSR primers showed 82.96% polymorphism. At the same time, 17 of the 30 primer pairs of SRAP marker showed clearDNA amplification, which resulted in 84.79% polymorphism. Ninety-seven of 133 InDel markers have about 99.47% polymorphism. Three markers showed average PIC score ranging from 0.20 to 0.26. When the analysis was conducted using UPGMA clustering method, it was found that the combined data from three markers gave a better result than each marker separately. The results from clustering analysis showed that all accessions can be grouped based on their location and can be categorized into two major groups. Useful results from this study could bring substantial benefits and ultimately help the rice breeders to develop elite rice varieties in future.

Rice blast disease, caused by Magnaporthe oryzae, is one of the most importance diseases of rice production worldwide. The keyrole of defense mechanism to combat this fungus in rice follows the gene-for-gene concept, which a plant resistant (R) gene product recognizes a fungal avirulent (AVR) effector and triggers the hypersensitive response. However, the AVR genes have been shown to be rapidly evolving resulting in high level of genetic diversity. The aims of this study were to examine the nucleotide sequence variation of AVR-Pita1 gene in Thai rice blast isolates and to identify the severity of blast disease using isogenic line of Pita gene. Seventy-six rice blast isolates collected from different parts of Thailand were used. Gene specific primers for AVR-Pita1 gene coding sequence were designed and used for identifying the genetic diversity of AVR-Pita1 gene by PCR amplification and sequencing. The obtained sequences were analysed for genetic variation and genetic relationship. Our results revealed the association between the sequence variations of AVR-Pita1 and selective forces from Pita gene. This phenomenon demonstrated the coevolution between rice blast resistant gene in rice and avirulent gene in blast fungus. The information about variation and evolutionary mechanisms of AVR gene obtained from this study can be used in rice blast resistant breeding programme.

Fourteen cucumber lines were tested for genetic homozygosity and performed pairwise comparison to identify a pair with thehighest DNA polymorphic level. Cucumber accessions CSL0067 and CSL0139 were selected to generate 315 F₂ populations. The geneticlinkage map based on 66 polymorphic SSR markers was constructed. It composed of eight linkage groups (LGs) spanning 474.4 cM.Downy mildew disease reaction was evaluated in cotyledons, first and second true leaf on 7, 10, and 14 day after inoculation. The resultsshowed that downy mildew resistance was controlled by multiple recessive genes. The susceptible to resistant ratio of F₂ progenies fit 9:7 susceptible/resistant segregation types corresponding to duplicate recessive epistasis. Fourteen QTLs were detected. The phenotypicvariance ranged from 5.0 to 12.5%, while LOD values ranged from 3.538 to 9.165. Two major QTLs and two QTL hotspots were identified.Moreover, the additive effects data explained that these QTL reduced downy mildew susceptibility.