33. QTL analysis for Field resistance to rice blast using RFLP markers

S. fukuoka and K. okuno

Laboratory of Plant Genetic Diversity, National Institute of Agrobiological Resources, Kannondai 2-1-2, Tsukuba, lbaraki, 305 Japan

Resistance to rice blast is of two types; true resistance and field resistance. Field resistance is defined as the resistance which allows effective control of a parasite under natural field conditions and is durable when exposed to new races of blast. After observing the rapid breakdown of true resistance genes to blast such as Pik, rice breeders have tried to develop breeding lines with field resistance to blast. Japanese upland rice varieties are potential gene donors for field resistance. Linkage analysis with conventional genetic markers has indicated several different loci conferring field resistance to blast (Goto 1970; Shinoda et al. 1971; Higashi and Saito 1985).

We studied the chromosomal location of genes controlling field resistance to blast in Japanese upland rice using restriction fragment length polymorphism (RFLP) markers. More than 40% of RFLP markers located on the rice linkage map showed polymorphism between lowland and upland rice varieties.

One hundred and forty-six F4 progeny lines from the cross between Nipponbare (moderately susceptible, lowland) and Owarihatamochi (resistant, upland) were used for QTL analysis. F4 lines were tested for resistance to leaf blast in the field and scored for the resistance based on the percentage of diseased leaf area. DNA was extracted from bulked F4 seedlings. A total of 62 RFLP markers were used to determine the genotype of individual F4 lines. QTL analysis was performed using MAPMAKER/QTL (Lander and Botstein 1989).

Five QTLs at a LOD threshold of 2.0 were detected on chromosomes 2, 4, 9 and 12 (Table 1). Four QTLs located on chromosomes 2, 4 and 12 were derived from Owarihatamochi and one QTL on chromosome 9 was derived from Nipponbare. Out of 5 QTLs, two were located on chromosome 4. QTL which was linked to an RFLP marker, G271, at the middle of chromosome 4 held 47.8% of the phenotypic variance for resistance to blast. Another QTL on chromosome 4 held 31.0% of the variance for resistance.

Research Notes

Table 1. Markers linked to QTLs conferring field resistance to rice

blast

Markers

Linked

Chrom-osomes

Origin of

Resistance1)

LOD2)

% variation

explained 2)

G271

4

0

20.5

47.8

Y8026L

4

0

11.7

31.0

G2140

12

0

4.5

13.3

C777

2

0

2.0

6.3

G103

9

N

2.0

6.2

1) 0 and N indicate Owarihatamochi and Nipponbare, respectively.

2) LOD and % variation explained were calculated at the putative QTLs by MAPMAKER/QTL (Lander and Botstein 1989).

It was concluded that these 2 loci on chromosome 4 played a major role in the expression of field resistance in Japanese upland rice.

References

Goto, I., 1970. Genetic studies on the resistance of rice plant to the blast fungus. 1. Inheritance of resistance in

cross Sensho x H-79 and Imochi-shirazu x H-79. Ann. Phytopathol. Soc. Jpn. 36: 304-312.

Higashi, T. and S. Saito, 1985. Linkage group of field resistance genes of upland rice variety "Sensho" to leaf

blast caused by Pyricularia oryzae Cav. Japan. J. Breed. 35: 438-448.

Lander, E.S. and D. Botstein, 1989. Mapping Mendelian factors underlying quantitative traits using RFLP

linkage maps. Genetics 121: 185-199.

Shinoda. H., K. Toriyama, T. Yunoki, A. Ezuka and T. Sakurai, 1971. Studies on varietal resistance of rice to

blast. 6. Linkage relationship of blast resistance genes. Bull. Chugoku Nat. Agric. Exp. Sta. A20: 1-25.