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Many elite rice varieties have been developed in the last decades by Thai rice breeders. No information about the genetic gene pool of these elite rice varieties is available. This study evaluated the genetic relationship of 15 elite Thai rice cultivars using Indel markers. Of the 133 markers screened, 44 were polymorphic. The PIC scores ranged from 0.06 to-0.50. By the UPGMA clustering method, they were separated into three major groups. Several markers identified specific DNA bands to certain rice cultivars, e.g., RD0305 and Rd0806 detected DNA bands specific for four photoperiod-sensitive rice cultivars. The gene pool of 15 elite Thai rice cultivars was moderately wide, and some closely related rice varieties were observed. The clustering result was consistent with the breeding pedigree. The data of this study can be used for the sustainable development of elite rice varieties in the future.

Rice blast disease, caused by the filamentous fungus Pyricularia oryzae, is one of the most destructive diseases in rice worldwide. Breeding of resistant rice cultivars remains a cost‐effective and environment‐friendly means for controlling blast disease, but the resistance tends to break down over time because of the pathogen's rapid adaptation. In this study, AVRPiz‐t gene sequences of 46 rice blast isolates were evaluated using a Southern blot analysis. The AVRPiz‐t gene was present in 24 of 46 (52.2%) rice blast isolates. The pathogenicity assay showed that all blast isolates were avirulent against Japanese rice cv. Toride 1, which carries several rice blast resistance genes including Piz‐t, Pii, Pi37, and Pi‐ta. Screening for the Piz‐t gene in Thai rice germplasm revealed that less than 20% of rice varieties harbour the Piz‐t gene. Therefore, the Toride 1 rice variety could serve as an effective donor of rice blast resistance to be used in rice breeding programmes in Thailand. This study provides evidence for co‐evolution between the rice blast resistance gene Piz‐t and the rice blast fungal avirulence gene AVRPiz‐t. Understanding this relationship will facilitate the sustainable development of breeding for rice blast resistance in the future.

Rice blast disease, caused by Magnaporthe oryzae, is one of the most damaging diseases of rice worldwide. Cultivation of rice varieties carrying resistance genes is the most economic and successful strategy to control the disease. In this study, 451 rice varieties from around the world including 363 Thai landrace rice varieties, 21 Thai improved rice varieties, 43 Japanese rice varieties and 24 worldwide rice varieties were screened by PCR technique using gene-specific markers for 10 rice blast resistance genes: Pi9, Piz-t, Pi50, Pigm(t), Pid2, Pid3, Pia, Pik, Pi54 and Pita. The results showed that 382 (99.48%) Thai rice varieties have at least one resistance gene and two rice varieties, ‘Hom’ and ‘Bak muay’, contained eight out of ten screened rice blast resistance genes. 320 rice varieties (83.33%) contained three or more rice blast resistance genes. The frequency of the rice blast resistance gene ranges from 87.76–9.64 per cent, of which the Pid3 gene has the highest frequency and the Pi54 gene has the lowest frequency. Two major resistance genes, found in Japanese rice varieties, are the Pik gene (76.74%) and the Pi9 gene (72.09%). While two major resistance genes, found in the international rice varieties are the Pi9 gene (66.67%) and the Pi54 gene (62.50%). The disease resistance gene profile of each rice variety obtained from this study will benefit the rice blast resistant breeding programme in the future.