Brown planthopper (BPH) is a phloem sap-sucking insect pest of rice, which causes severe yield loss annually. Gayabyeo, a Tongil type rice variety, is known to have broad spectrum resistance to BPH. Before, it was estimated that Gayabyeo has at least two BPH resistance genes. We started a research for mapping resistance genes of Gayabyeo. We did a cross between Taebaekbyeo, a BPH susceptible Tongil type rice variety, and Gayabyeo, We grew F1 plants in winter season of 2014-2015, and planted F2 population in this year. About 100 DNA markers (SSR and InDel markers) showing polymorphism between Gayabyeo and Tabaekbyeo were selected. In addition, we are going to do resequencing Gayabyeo and Taebaekbyeo using Illumina Hiseq2000 to find much more DNA polymorphisms between the two varieties and develop new markers for mapping. The BPH response data will be acquired using F3 plants from the cross between Gayabyeo and Taebaekbyeo next year. In a while, crosses between Gayabyeo and high quality japonica rice varieties are being carried out to introduce BPH resistance genes of Gayabyeo into japonica high quality rice varieties. We expect to develop new DNA markers for BPH resistance genes of Gayabyeo through mapping and produce several japonica high quality rice lines harboring those genes at the end of this project.

Plants have evolved a set of protecting mechanisms against pathogens, which include secondary metabolites and induced defense responses to pathogen attack. The biological role of purine alkaloids including caffeine is largely unknown. It has been proposed that caffeine confers a resistance against pathogenic bacteria and herbivores. We, in this study, tested direct effects on the growth of rice pathogenic microbes, Xanthomonas oryzae pv. oryzae (Xoo) causing a bacterial leaf blight and Magnaporthe grisea (M. grisea) causing a rice blast. Cell growth of Xoo and M. grisea were significantly retarded in presence of high concentration (2mM) of caffeine. Exogenous caffeine (5mM) induced resistance of wild type rice (cv. Dongjin, susceptible to Xoo and M. grisea) against those pathogens. These results indicated that caffeine enhanced the basal resistance to infection with Xoo. In addition, expression of pathogenesis-related (PR) genes was tested in the caffeine treated rice to elucidate the acquired resistance by caffeine, resulted in induction of PR genes including OsPR1a and OsPrb1. We have generated a transgenic rice producing caffeine by introduction of three N- methyltransferase genes (CaXMT1, CaMXMT1, CaDXMT1) identified from coffee plant. The transgenic rice successfully expressed the three genes, synthesized caffeine up to 5ug/g and showed enhanced resistance to Xoo. We also observed that transcripts of PR genes such as the OsPR1a and OsPrb1 encoding PR-1 type pathogenesis-related protein increased in the caffeine-producing rice. These result showed that caffeine is likely to act a powerful factor to increase level of rice defense as a natural and non-harmful metabolite.

Fungal blast caused Magnaporthe oryzae, bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo), bacterial streak caused by Xanthomonas oryzae pv. oryzicola (Xoc) are devastating diseases of rice worldwide. Application of host resistance to these pathogens is the most economical and environment-friendly approach to solve this problem. Some major disease resistance (MR) genes controlling qualitative resistance and quantitative trait loci (QTLs) controlling quantitative resistance are valuable sources for broad-spectrum and durable disease resistance. We have characterized a number of rice MR genes and resistance QTL genes that confer a broad-spectrum or durable resistance to M. oryzae, Xoo, and Xoc. How to efficiently use these genes for rice improvement will be discussed.

Disease is one of the devastating obstacles in the stable crop production. Numerous agronomical and chemical controls have been developed to overcome this problem, but the former is not sufficient for the maintaining the disease under the economic threshold level and the latter is not free from the environmental regulation. One of the most ideal solutions is resistance breeding. Resistance breeding has been majorly dependent on the resistance (R) genes conferring race-specific vertical resistance effective for limited populations within the pathogen species harboring avirulence (Avr) genes encoding effectors exactly matching with R gene products. In spite of its outstanding efficiency, improper management of above cultivars frequently resulted in the resistance break down due to the appearance and domination of the new races in the field. During the last two decades, mechanisms of disease resistance have been characterized and analyzed in the respect of genetics, biochemistry, molecular biology, cell biology, and evolution. Especially, a growing body of investigations has been focused on the resistance effective for multiple races or even more species of pathogen’s infections and also durable and long-lasting. In this manuscript, we will introduce the investigations searching for durable and broad-spectrum resistance and the considerations for their applications in the crop production will be presented.