Development of near-isogenic lines with different alleles of Piz locus and analysis of their breeding effect under Yangdao 6 background

Rice blast is one of the most destructive diseases of rice. The most effective way of managing this disease is to develop resistant cultivars by introducing resistance genes into elite rice recipients. In this study, the near-isogenic lines (NILs) of six resistance alleles of the Piz locus (Pizt, Pi2, Pigm, Pi40, Pi9 and Piz) were constructed with Yangdao 6 as genetic background. Seedling inoculation tests showed that most of the NILs, namely NIL-Pi2, NIL-Pigm, NIL-Pi9, NIL-Pizt and NIL-Pi40, exhibited good resistance to blast with resistance frequencies (RFs) of over 82.50 %, execpt NIL-Piz which showed lower resistance with a RF of only 36.13 %. Furthermore, the improved-resistance NILs exhibited high similarity of their resistance spectra, with overlapping degrees of resistance spectrum (OD) of more than 75.83 %. However, the RF of panicle blast for all NILs decreased significantly compared with seedling blast in an artificial inoculation test. Although NIL-Pigm showed a higher panicle blast RF of 80 %, other NILs with outstanding performance in seedling blast resistance, namely NIL-Pizt, NIL-Pi2, NIL-Pi9 and NIL-Pi40, exhibited middle or low RFs of panicle blast with values from 56.67 to 33.30 %. Natural induction in a disease nursery showed a consistent trend in artificial inoculation results at seedling and heading stages. While NIL-Pigm was found to exhibit good resistance to leaf blast and panicle blast, NIL-Pi9 and NIL-Pizt were further demonstrated to show excellent resistance in Suichuan, Jiangxi province and Enshi, Hubei province, respectively, because of the race–region specificity. Agronomic traits of NILs were also investigated in order to evaluate the linkage drag effect of different alleles of the Piz locus. The resistance effects of the different alleles of the Piz locus under identical genetic background against seedling blast and panicle blast was first reported in this study, and the above results are expected to provide a theoretical support for the rational utilization of broad-spectrum resistance genes in breeding practice.