Most of the existing three-line hybrid rice combinations show relatively poor disease resistances,and their resistances are closely related to their parents including the restorer and male sterile lines.Therefore,introduction of disease resistant genes into both parents is the key to improve the resistances of hybrid rice.Recently,the resistance breeding of hybrid rice is mainly based on conventional breeding methods.However,the conventional breeding methods have their inherent limits such as the environmental flexibility in identification of resistances,linkage drag and hardness to pyramid dominant resistant genes and recessive resistant genes in transfer of resistant genes.The molecular maker-assisted selection(MAS) has made good progress in both introduction of single resistance genes and pyramiding of different resistance genes in the breeding of three-line hybrid rice parents.In this paper,the authors discussed the issues of resistances of rice blast and bacterial leaf blight in three-line hybrid rice breeding and proposed corresponding research strategy for improving the disease resistances of hybrid rice.
The research on the resistance improvement by space mutation is drawing more and more attention.Some new varieties and resources resistant to blast have been selected since rice breeding by space mutation was conducted in China.The characteristics and research progress in mechanism of resistance variation of rice lines to blast by space mutation were reviewed.Additionally,the prospect of research on resistance to blast by rice space mutation breeding was discussed.
35 monogenic differentials and 12 Kiyosawa′s differentials were used to differentiatethe pathogenicity of indica rice blast isolates in South China.147 rice blast isolates were divid-ed into 28 different pathotypes.74.8% of isolates tested belongs to pathotypes I-04,I-02 andI-01 which were predominant,and these isolates showed more broad virulence spectrum thanothers.The results showed that monogenic differential F80-1(Pi-k),IRBL7(Pi-kp),IRBL16(Pi-sh(1)),IRBL21(Pi-7(t)),IRBL3(Pi-i),IRBL9(Pi-z),IRBL19(Pi-3),IRBL10(Pi-z5),IRBL11 (Pi-zt),IRBL18(Pi-1),IRBL10(Pi-2),F128-1(Pi-ta~2 ),F145-2(Pi-b),and IR-BL22(Pi-9(t))from 47 tested differentials could be used for differentiating pathogenicity of in-dica rice blast isolates.F80-1(Pi-k),IRBL7(Pi-kp),IRBL16(Pi-sh(1)),IRBL21(Pi-7(t)),IRBL3(Pi-i),IRBL9(Pi-z),IRBL19(Pi-3)and IRBL10(Pi-z5)had the most differ-ential ability.The interactions of isolates of predominant pathotypes I-04,I-02 and I-01 withthese monogenic differentials showed RRSRSSSMR,SSSSSSSS and SSRSSSSR,respectively.
Pathogenicity of 146 Magnaporthe grisea single spore isolates from indica rice in Guangdong was analyzed against 30 rice blast monogenic lines. Seventeen lines were selected to be the candidates for further construction of differentials. Factor analysis with principal component method of the variance matrix based on the interaction between 17 monogenic lines and 146 blast isolates had been conducted. Nine monogenic lines explaining 80.437% of the total variance were abstracted. According to their contribution to the percentage of variance, they were listed as follows: IRBLkp-K60(Pi-k~p), IRBLi-F5(Pi-i), F128-1(Pi-ta~2), IRBL9-W(Pi-9(t)), IRBLsh-S(Pi-sh(1)), IRBLz-Fu(Pi-z), IRBLkh-K3(Pi-k~h), IRBL1-CL(Pi-1) and IRBLz5-CA(Pi-z~5).Those lines were recommended to be blast monogenic dif-(ferentials) with which 83 races were identified among the 146 Guangdong isolates and 26 races among 54 (isolates) from indica rice cultivars in other six provinces. The results showed that 9 selected monogenic lines had good abilities for differentiating the pathogenicity of indica rice blast in South China. Based on the monogenic differentials, cluster and variance analysis method might be applied for the representative isolates selection in the blast resistance evaluation.
By crossing two durably resistant cultivars (Sanhuangzhan 2, Sanluzhan 7), and two resistant cultivars (Waixuan 35, Aisanluzhan), with two popular sterile lines susceptible to rice blast (Guang A, Bo A), their hybrid rice combinations were studied with respect to qualitative resistance, quantitative resistance and field resistance in different blast-conducive areas. Results indicated that the combinations with durably resistant donor showed the same durably resistant characteristics as correspondingly durably resistant cultivars. Quantitative resistance and field resistance in different blast-conducive areas could be as indicators of durability of resistance. Quantitative resistance was closely related to field resistance in different blast-conducive areas, and might be an important indicator of durable resistance to blast.
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