关键词: 杂交稻组合, 广8 A, 稻瘟病菌, 无毒基因, 抗稻瘟病单基因系

Abstract:

【Objective】 The objective of this study is to analyze the avirulent genotypes of Magnaporthe oryzae derived from the hybrid rice combinations of Guang 8 A, and to provide a reference for rational distribution of cultivars with different blast resistant genes in South China. 【Method】 A set of single-spore strain was subjected to pathotype analysis using blast monogenic differential lines. According to the functional markers of 8 Avr genes, which had been cloned and were associated with the rice blast pathogenicity, the haplotypes of Avr genes were analyzed. The DNA, which extracted from the 27 strains of rice blast fungi, was used as a template for PCR amplification. The PCR products of avirulent full gene or CDS region were analyzed by agarose gel electrophoresis and sequencing, and their sequences were compared to corresponding avirulent genes.【Result】 The tested strains showed high frequency (＞85%) of avirulence to the 5 monogenic differential lines, such as IRBLkh-K3 (Pikh), IRBLb-B (Pib), IRBLz5-CA (Pi2), NIL-e1 (Pi50) and IRBL9-W (Pi9), all strains were avirulent to IRBL9-W (Pi9) and NIL-e1 (Pi50). These strains showed relatively low frequency of avirulence (＜20%) to the 7 monogenic differential lines, such as IRBLks-F5 (Piks), IRBLa-A (Pia), IRBL19-A (Pi19) and so on, indicating that the strains from the combination of Guang 8 A showed different pathotypes to different rice blast-resistant lines. AvrPi9 and AvrPik fragments were almost present in all strains, and two haplotypes (AvrPik-D and AvrPik-E) of AvrPik were identified. But none of Avr1-CO39, AvrPii or AvrPia was amplified in any strain. The expected size products of AvrPiz-t, AvrPib and AvrPita could be detected in some strains, but they all appeared in lower frequency and different mutation types in the tested strain. Amplicon sequencing of 7 strains (GD13-621, GD14-349, GD15-291, et al.) revealed that the sequences of AvrPi9, AvrPita and AvrPiz-t were identical to those of the respective avirulent strains. This result indicated that these 3 Avr genes had a stable gene structure. Compared to AvrPib in an avirulent strain, AvrPib in the tested strains contained 2 nucleotide changes or 3 consecutive nucleotide insertions in the gene upstream region. The results indicated that AvrPib had a rich haplotype. The sequences of AvrPik in 6 strains were highly consistent, only contained one nucleotide changes in the coding region (136C/A), resulting in one amino acid substitutions (46H/N), which showed two haplotypes of AvrPik (AvrPik-D or AvrPik-E).【Conclusion】 In the strains from the major rice cultivars of Guang 8 A in South China, the distribution of AvrPi9 and AvrPik was relatively wide. In the susceptible areas of the above cultivars, the resistant cultivars carrying Pi9 and Pik could be used as rotation planting cultivars.

Key words: hybrid rice combinations, Guang 8 A, Magnaporthe oryzae, avirulent gene, rice blast-resistant lines