18. Genetic analysis of the blast resistance at vegetative and reproductive stages in rice

J.Y. ZHUANG1, R.Y. CHAI2, W.B. MA3 , J. LU1, M.Z. JIN2 and K.L. ZENG1

1) Biotechnology Department, China National Rice Research Institute, Hangzhou. 310006 China
2) Institute of Plant Protection, Zhejiang Academy of Agricultural Sciences, Hangzhou, 310021 China
3) Biology Department. Xiamen University, Xiamen, 361005 China

Using a commercial rice variety Zhong 156 as the female parent and a semidwarf variety Gumei 2 with durable resistance to rice blast as the male parent, an indica-indica cross was made and used to develop F7 recombinant inbred lines (RILs). Most of the RILs bred-true at DNA marker loci and normal segregation among these RILs was observed.

Blast resistance of the two parents was evaluated in 1995. Among 20 races of blast fungus tested, ZC15 was able to infect Zhong 156 only at the reproductive stage and unable to infect Gumei 2 at both vegetative and reproductive stages. The resistance of 148 RILs to ZC15, was tested in 1996 and 1997. To evaluate the resistance of the RILs at the vegetative stage (leaf resistance), 12 seedlings of each line were used with three replications each year. To evaluate the resistance of the RILs at the reproductive stage (neck resistance), five and ten panicle necks were inoculated in vitro in 1996 and 1997, respectively. In two years, agreements on the leaf resistance and the neck resistance were observed for 146 and 127 lines, respectively (Table 1), on which further analysis was carried out. The segregation of 127 resistant and 19 susceptible lines at the seedling stage agreed with the ratio of 7:1 (P=0.800), suggesting a possibility that more than a single gene is responsible for this character. The segregation of 89 resistant lines and 38 susceptible lines at the reproductive stage agreed with the ratio of 3:1 (P=0.200), suggesting that the neck blast resistance was controlled by dominant homozygous alleles derived from one of the two genes. In addition, all the 19 lines susceptible at the seedling stage were also susceptible at the reproductive stage, and 18 of the lines resistant at the seedling stage were susceptible at the reproductive stage, indicating that some genes responsible for leaf blast resistance was not effective at the reproductive stage.

DNAs were extracted from the parents and bulked samples of 20 individuals for each line, and RAPD analysis was made. Sixty-nine out of 280 random decamers produced major polymorphic bands between the parents and were applied to the RILs. Two RAPD markers OPD10800 and OPH11400 having genetic distance of 2.1 cM, co-segregated with the leaf blast resistance in the group 1 lines. However, the same pattern of co-segregation was not observed among the 18 lines of the group 2. As expected, the resistant allele was derived from Zhong 156 (Table 2).

Three RAPD markers, OPK171400, OPA7550 and OPB10450-750 indicated a linkage relation with the resistance phenotypes among the 38 lines showing the neck blast susceptibility. It was estimated that the resistance gene was located between K171400 and A7550, having genetic distances of 2.4 cM to K171400 and 7.5 cM to A7550. As expected, the resistant allele was derived from Gumei 2 (Table 2).

Results obtained so tar have provided strong evidences that the genetic control of the blast resistance in rice may vary at different developmental stages. Work on tagging another resistance gene and RFLP mapping of the resistance genes is underway.

Table 1. Resistance of the RILs to blast race ZC15 in two years

Group

Resistance a

No. of Lines

Leaf

Neck

Group 1

SS

SS

19

Group 2

RR

SS

18

Group 3

RR

RR

89

Group 4

-

SS

1

Group 5

RR

-

20

Group 6

-

-

1


a. RR = resistant in both years.
SS = susceptible in both years.
- = missing data, different results
were obtained in two years.


Table 2. Segregation of RAPD markers linked to the resistance genes

Group

Resistance

Maker typea

Marker

Leaf

neck

D10

H11

K17

A7

B10

Group 1

SS

SS

A

0

0

17

16

17

 

 

 

B

19

19

1

2

1

Group 2

RR

SS

A

13

14

16

15

14

 

 

 

B

5

4

0

1

2

a. A = Zhong 156; B = Gumei 2.