![]() ![]() Indonesia, the Philippines, India, and China have released bacterial blight-resistant varieties for commercial production and are advancing breeding work to improve resistance further. Six Xa genes have been tagged with molecular markers and used to help identify new resistant lines, resulting in the release of resistant varieties in several countries. At present, 14 strains of the bacterial blight pathogen representing 10 races have been characterized in the Philippines alone. The availability of molecular markers for these genes, which help breeders improve the accuracy and speed of developing new varieties, has made improving resistance to bacterial blight more efficient.īreeders have identified over 30 bacterial blight resistance genes, named from Xa1 to Xa33. Many bacterial blight-resistant genes have been identified through IRRI’s breeding programs and are currently available for use in developing or improving popular commercial varieties. Breeders grow and carry out crop management of all screening field trials while pathologists inoculate and evaluate resistance of the breeding lines. Bacterial blightīreeders and pathologists work together to screen breeding materials that carry resistance to bacterial blight. In the Philippines, yield losses ranging from 50-85% were reported. Although blast is capable of causing very severe losses of up to 100%, little information exists on the extent and intensity of actual losses in farmers' fields. Its first known occurrence was as early as 1637 in China where the disease was known as rice fever disease.īlast is considered a major disease of rice because of its wide distribution and extent of destruction under favorable conditions. Blast is found in approximately 85 countries throughout the world. ![]() It attacks different parts of the plant: the collar, which can ultimately kill the entire leaf blade the stem, which turns blackish and breaks easily (node blast) the neck of the panicle, where the infected part is girdled by a grayish brown lesion, or when severe, causes the panicles to fall over or on the branches of the panicles which exhibit brown lesions when infected.īlast is highly destructive in lowland rice in temperate and subtropical Asia, and upland rice in tropical Asia, Latin America and Africa. Rice blast ( Pyricularia grisea) is a fungus that feeds on the rice plant, causing severe damage usually during the seedling stage. Makassane, a new IRRI-bred rice variety released in Mozambique in 2011, has improved resistance to blast - a major disease of the country. Pyramiding of two or more effective resistance genes/alleles into elite rice lines enhances the durability and spectrum of resistance. Of the various strategies tried, enhancing host-plant resistance is considered one of the important approaches to tackle this disease. Interplanting prevents the fungus from continuously building inoculum that had previously occurred in the monoculture fields of the glutinous varieties.Īlthough many resistant varieties have already been bred, the breakdown of blast resistance causes yield instability in several rice-growing areas in the world. Blast caused great yield loss on traditional glutinous rice varieties and farmers were spraying fungicides for up to seven times. IRRI scientists introduced the practice of interplanting glutinous rice varieties with blast-resistant hybrid varieties in Yunnan province, China. Recent studies showed that the use of rice line mix is an effective tool in blast management. Another method is by deploying resistant genes in mixed plant populations. However, its use has not been completely successful due to the presence of lineages (that may consist of different physiologic races) overcoming host resistance.įor the rice plant to effectively combat blast, scientists at IRRI are combining into the same rice type different race-specific genes and genes conferring quantitative resistance. ![]() Rice blastĭeveloping and using blast-resistant varieties is the most practical and economical approach to control blast. IRRI develops rice varieties that are resistant to major insect pests and diseases such as blast, bacterial blight, sheath blight, and tungro virus. ![]()
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