Artificial Panicle Blast Resistance Identification

The artificial identification of panicle blast resistance in the field was performed as described previously [2 (link)] using the mixed conidial suspensions (MCSs) containing five or six M. oryzae isolates. Isolates were mixed in equal proportions to form a conidial suspension of 30–40 conidia per field of view under a 10 × 10 microscope. All rice cultivars/lines were planted in Xinminzhou Lingang Industrial Park, Jingkou District, Zhenjiang City, Jiangsu Province, China. Each line contained 6 rows with 10 plants per row and a row spacing of 11.1 × 30 cm in a randomized complete block design. Artificial inoculation was carried out at the booting stage, and 5 tillers each line were injected with 1 mL conidial suspension of each MCS. Disease scores were rated at rice ripening stage according to the Technical Specification for Identification and Evaluation of Blast Resistance in Rice Variety Regional Test (NY/T 2646-2014) issued by the Ministry of Agriculture and Rural Affairs of the People’s Republic of China. According to their disease scores, each rice line was then classified into different resistant levels: highly resistant (0 ≤ disease grade < 1), resistant (1.0 ≤ disease grade < 3), moderately resistant (3.0 ≤ disease grade < 5.0), moderately susceptible (5.0 ≤ disease grade < 7.0), susceptible (7.0 ≤ disease grade < 9.0), and highly susceptible (disease grade = 9.0). On the basis of the disease scores of each panicle, the final disease grade of the variety was determined as follows: (1) If the disease grades of 5 inoculated panicles ranged less than 2, then the highest disease grade of the 5 inoculated panicles was used as the final disease grade of the variety. (2) If the 5 disease grades ranged more than 3 and the panicles with relatively high disease grades constituted the majority, then the highest disease grade of the 5 inoculated panicles was designated as the final disease grade of the variety. (3) If the 5 disease grades ranged more than 3 and the panicles with relatively low disease grades accounted for the majority, then the second disease grade of the 5 inoculated panicles from top to bottom was used as the final disease grade of the variety.