Enhanced defense responses of tomato plants against late blight pathogen Phytophthora infestans by pre-inoculation with rhizobacteria

The efficacy of resistance in tomato plants, induced by rhizobacteria isolated from Jeju Island in Korea, against late blight disease caused by Phytophthora infestans was tested. Among the bacterial isolates tested, pre-inoculation with four isolates induced an effective defense against late blight. The four isolates, TRH423-3, TRH427-2, KRJ502-1 and KRY505-3, were identified as Burkholderia gladioli, Miamiensis avidus, Acinetobacter quenomosp and Bacillus cereus, respectively, by sequencing the ribosomal intergenic spacer region. They also promoted the growth of tomato seedlings. To illustrate resistance mechanisms, the infection process by P. infestans was examined using a fluorescence microscope. There were no noticeable differences in the rate of germination and appressorium formation between the untreated and pre-inoculated plants. However, callose was more frequently formed at the penetration sites on the leaves of pre-inoculated plants than the untreated plants, suggesting that these rhizobacterial isolates induce defense responses against P. infestans.

Research highlights
► In this manuscript, mechanism of systemic resistance was studied using fluorescence microscope. The microscopical observations revealed that there were no noticeable differences in the rate of germination and appressorium formation between the untreated and pre-inoculated plants. However, callose was more frequently formed at the penetration sites on the leaves of pre-inoculated plants compared with untreated plants. These results suggested that the callose formations at the penetration site may play an important role in expressing resistance against late blight in the tomato pre-inoculated with the selected bacterial isolates.