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1) Agronomy Department, Zhejiang Agricultural University, Hangzhou, China
2) China National Rice Research Institute, Hangzhou, China
Extensive work on genetics of resistance to rice blast (Pyricularia oryzae Cav.) has been done. In many cases, a single dominant or two duplicate dominant genes governed rice blast resistance. There were recessive genes or interaction of genes in particular cases. Kiyosawa (1981) identified 13 resistance genes, some of which were linked.
By inoculating the F1, F2 and B1F1 plants ftom crosses of S X R cultivars (S: susceptible, R; resistant) or R X R cultivars with two Chinese fungus races, ZB15 and ZC15, resistance genes in nine Indica rice cultivars were analyzed. the results (Table 1) indicated that a total of 10 different dominant genes (genes 1-10) conferred
Table 1. Resistance genes in the nine cultivars to the two races
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Resistance genes
Race ___________________________________________________________
Hong- Hong- Suwao Ai-jiao- IR9782- Guo-ji-
Tetep IR36 yang- jiao- 300 bai-mi- 111-2-1-2 yoil- IR5105
ai 4 zhan zi zhan
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ZB15 1 1 1 1 1 1 2 3 4
ZC15 5 5 5 5 5,6 6,7 8 9 10
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Group I II III IV V
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Table 2. Linkage among resistance genes in backcrosses with EJQ,
a susceptible cultivar
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Cross R1R2 R1S2 S1R2 S1S2 X2
(1: 1: 1: 1)
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EJQ2/IR5105 9 14 9 9 1.83
EJQ2/Tetep 49 2 6 34 67.11**
EJQ2/AMZ 3 39 2 17 41 42.21**
EJQ2/HJZ 28 3 3 38 52.78**
EJQ2/IR9782-111-2-1-2 21 5 6 31 29.88**
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R1: Resistant to the race B 15
R2: Resistant to the race C 15
S1: Susceptible to the race B 15
S2: Susceptible to the race C 15
** P<O.O1 (df=3)
resistance to the two races in the cultivars studied, which could be
classified into 5 resistant groups based on their genotype. It was concluded
that if more races were used, more resistance genes would be identified.The relationship of genes for resistance to the two races was studied in five cultivars with a single dominant gene for resistance to each race: Tetep, Ai-mei- zao 3 (AMZ 3), Hong-jiao-zhan (HJZ), IR9782-111-2-1-2 and IR5105. Resistance response of plants from backcrosses of susceptible cultivar Er-jiu-qing (EJQ) to resistant cultvars to the two races was observed by injecting the same plants with the two races. The results (Table 2) indicated that the segregation of plants from EJQ2/Tetep, EJQ2/AMZ 3, EJQ2/HJZ, and EJQ2/IR9782-111-2-1-2 did not fit a 1 : 1 : 1 : 1 ratio for two pairs of independent resistant genes. Parental types were much more frequent than recombinant types indicating that the two pairs of genes in the four cultivars were linked. Segregation of the population EJQ2/ IR5105 fitted the expected ratio, indicating that the two genes in IR5105 segregated independently. Flores-Gaxiola et al. (1983) and Shen et al. (1986) also reported similar gene linkage, which might be a general characteristic of cultivars with broad spectrum resistance. Linkage among resistance genes could increase the level of resistance and efficiency of breeding for blast resistance. More detailed work is to be done.
References
Kiyosawa, S. Gene analysis for blast resistance. Oryza 18: 196-203.
Flores-Gaxiola, J. A. et al. 1983. Inheritance of blast (P. oryzae) resistance in rice. Intern. Rice Res. Newsl. 8(4): 5-6.
Shen, Z. T., W. G. Zhang, Z. H. He, S. Y. Sun, R. X. Tao, D. Shi, 1986. Genetic analysis for blast resistance in some Indica rice varieties (Oryza sativa L.). Chinese J. Rice Sci. l(l): 1-7-
