Bacterial Blight Resistance in Rice - Translational Genomics for Crop Breeding: Biotic Stress - page 11

Chapter 2

Bacterial Blight Resistance in Rice

YanjunKouandShipingWang

Abstract

Rice is one of the most important cultivated food crops. Bacterial blight (BB) caused by Xanthomonas
oryzae pv. oryzae ( Xoo ) is one of the major constraints for sustainable production of rice. Researchers
have made tremendous progress in trying to elucidate the interaction between rice and Xoo .The
genomes of three Xoo strains have been sequenced. Some factors affecting pathogenicity of Xoo , such
as type III secretion system, effectors translocated by type II and III secretion systems, have been
identified. In rice, a number of genes contributing to qualitative and quantitative resistance against Xoo
have been characterized. At least 37 major disease ( MR ) genes have been identified and named, and
7( Xa1 , Xa3/Xa26 , xa5 , xa13 , Xa21 , xa25 , and Xa27 ) of them have been isolated. Importantly, some
key components functioning in Xa3/Xa26 - and Xa21 -mediated defense signaling pathways have been
characterized, which is helpful to understand molecular mechanisms of qualitative resistance to BB.
At least 74 resistance QTLs against Xoo have been identified in different rice cultivars interacting with
different Xoo strains. One major resistance QTL ( WRKY45 ) and eight minor resistance QTLs ( NRR ,
WRKY13 , OsDR8 , MPK6 , GH3-1 , GH3-2 , GH3-8 , and C3H12 ) have also been identified. The wealth
of information about molecular components that function in rice defense response is now accessible
for rice improvement in breeding programs.
Rice ( Oryza sativa L.) is perhaps the most widely cultivated food crop worldwide; it is consumed
by approximately 50% of the world's population, and its consumption has been dramatically increased
in many parts of the world (White 1994). Various factors affect rice productivity, including diseases.
Bacterial blight (BB) is the most devastating bacterial disease of rice. It occurs in epidemic areas of
the world and can result in yield loss of up to 50% (Ou 1985). Traditional management methods,
including cultivation strategies, chemical control, and biological control, are useful tools to combat
BB. However, these methods can be labor intensive, expensive, and may cause environment pollution.
The most economical and environmentally friendly way to control BB is to use resistant varieties
carrying major disease resistance ( MR ) genes and/or resistance quantitative trait loci (QTLs) in
combination with agricultural management practices. Resistance genes and QTLs have been identified
and provide valuable resources for developing broad-spectrum and/or durable resistance against BB
in rice breeding programs.