Development and Evaluation of Near-Isogenic Lines with Different Blast Resistance Alleles at the Piz Locus in japonica Rice from the Lower Region of the Yangtze River, China

Rice blast, caused by Magnaporthe oryzae, threatens rice production in most of the rice-growing areas in China, especially in regions that have grown Oryza sativa subsp. japonica in recent years. The use of resistance genes is the most effective and economical approach for blast control. In our study, a set of six near-isogenic lines (NIL) were developed by introgression of six resistance alleles of the Piz locus (Pi2, Pigm, Pi40, Pi9, Piz, and Pizt) into a blast-susceptible, high-yielding, high-quality japonica '07GY31' via marker-assisted backcross breeding. Artificial inoculation using 144 M. oryzae isolates collected from the lower region of the Yangtze River, China, revealed that most of the NIL, including NIL-Pi2, NIL-Pigm, NIL-Pi40, NIL-Pi9, and N1L-Pizt, exhibited broad-spectrum resistance against rice blast at the seedling stage, with resistance frequencies (RF) of 93.06 to 98.61%. NIL-Piz was an exception, with an RF of 21.53%, which was slightly higher than the recurrent parent 07GY31. NIL-Pi40 and NIL-Pigm had broad-spectrum resistance (RF of 93.33 and 71.67%, respectively) at the heading stage following inoculation of 60 isolates of M. oryzae. Field trials with artificial inoculation at the seedling and heading stage showed that NIL-Pigm and NIL-Pi40 were highly resistant in four locations under high disease pressure. NIL-Pizt showed effective resistance in three locations from Zhejiang and Jiangsu Provinces. This study shows that O. sativa subsp. japonica alleles of the Piz locus confer resistance to M. oryzae, and provides an effective method to enhance seedling and panicle blast resistance in rice plants in the lower region of the Yangtze River, China.