Reference "A 'defeated' rice resistance gene acts as a QTL against a virulent strain of Xanthomonas oryzae pv. oryzae"

Reference ID

2427

Title

A 'defeated' rice resistance gene acts as a QTL against a virulent strain of Xanthomonas oryzae pv. oryzae

Source

Molecular & General Genetics, 1999, vol. 261(1), pp. 58-63

Authors (10)

Li-Z-K	Luo-L-J
Mei-H-W	Paterson-A-H
Zhao-X-H	Zhong-D-B
Wang-Y-P	Yu-X-Q
Zhu-L	Tabien-R

Abstract

The genetic components responsible for qualitative and quantitative resistance
of rice plants to three strains (CR4, CXO8, and CR6) of Xanthomonas oryzae pv.
oryzae (Xoo) were investigated using a set of 315 recombinant inbred lines
(RILs) from the cross Lemont (japonica) x Teqing (indica) and a complete linkage
map with 182 well distributed RFLP markers. We mapped a major gene (Xa4) and ten
quantitative trait loci (QTLs) which were largely responsible for segregation of
the resistance phenotype in the RILs. The Teqing allele at the Xa4 locus, Xa4T,
acted as a dominant resistance gene against CR4 and CXO8. The breakdown of Xa4T-
associated resistance mediated by the mutant allele at the avrXa4 locus in the
virulent strain CR6 results from significant changes in both gene action (lose
of dominance) and the magnitude of gene effect (approximately 50% reduction).
Nevertheless, Xa4T still acted as a recessive QTL with a significant residual
effect against CR6. The mutant alleles at the avrXa4 locus in CXO8 and CR6 that
lead to a reduction in effect, or "breakdown", of Xa4T were apparently
accompanied by corresponding penalties for their fitness. The quantitative
component of resistance to Xoo in the RILs was largely due to a number of
resistance QTLs. Most resistance QTLs mapped to genomic locations where major
resistance genes and/or QTLs for resistance to Xoo, blast and sheath blight were
identified in the same cross. Most QTLs showed consistent levels of resistance
against all three Xoo strains. Our results suggest that a high level of durable
resistance to Xoo may be achieved by the cumulative effects of multiple QTLs,
including the residual effects of "defeated" major resistance genes.