Evaluation and screening of fire blight resistance in Malus plants

Fire blight, a devastating bacterial disease, primarily infects fruit trees of Rosaceous, leading to their decline and eventual death. This study aims to evaluate and screen the fire blight resistance in 19 Malus plants; additionally, the effectiveness and applicability of three inoculation methods were compared. The toothpick acupuncture method in young leaves, shoots in vitro, and young plants in vivo were used in this study. The results were significantly different from the three inoculation methods for some Malus plants. Under the inoculation conditions of young leaves in vitro, only Shidong Caiping No. 1 was tolerant to fire blight, exhibiting the highest resistance level, while others showed susceptibility at graded severity levels. Under the inoculation condition of young shoots in vitro, nine highly resistant resources were screened, such as OT3, SH3, SH6, etc. Under the inoculation condition of young plants in vivo, six highly resistant resources were obtained, included E Shanjingzi No. 2, Xiaogucheng Lenggunzi No. 1, Yingyehaitang, and so on. For practical applications, the evaluation of young shoots in vitro, and young plants in vivo should be integrated to achieve a comprehensive and accurate result. A total of three resistance resources were obtained, namely E Shanjingzi No. 2, Xiaogucheng Lenggunzi No. 1, and Yingyehaitang, which can be used for the breeding of parents of fire blight resistant varieties.