ประสิทธิภาพของแบคทีเรีย Bacillus spp. ในการควบคุมเชื้อ Burkholderia gladioli สาเหตุโรคใบขีดและลำต้นเน่าของข้าวโพดหวาน

Abstract

The objectives of this study were to study and identify the causal agent of sweet corn disease found in the field, the efficacy of Bacillus spp. in controlling the causal agent under in vitro and in vivo conditions and detected antibiotic synthesis-related genes from Bacillus spp. to inhibitory mechanisms of plant pathogens. The bacterial disease symptoms of sweet corn disease were observed at the Agricultural Resource System Research Station (ARS) of Chiang Mai University, Chiang Mai and the farmer’s field at Phan, Chiang Rai. A total of forty-four bacterial isolates were isolated from sweet corn disease. Twenty-seven bacterial isolates were isolated from the vegetative stage of sweet corn and seventeen bacterial isolates were isolated from the reproduction stage of sweet corn. All bacterial isolates from sweet corn were tested on potato, carrot and Chinese radish slices, the results showed that four isolates including MHSL01, MHSL05, MHSL06 and MHSL07 were positive for enzymes related to maceration and soft rot on potato, carrot and Chinese radish. Four positive isolates for hypersensitive reaction showed necrotic tissue appeared in tobacco leaves 48 hours after infiltration. The pathogenicity assays were performed on three types of corn namely sweet corn, waxy corn and maize. The result showed that isolate MHSL06 was the most severe pathogen, after inoculation with injection and drop of the bacterial suspension. The causal bacterium was identified as Burkholderia gladioli based on the comparison of physiological, biochemical, and 16S rRNA gene sequence. Moreover, B. gladioli isolate MHSL06 produced toxoflavin and caused similar diseases in other plants including rice, onion, gladiolus and soybean. A total of 16 isolates of Bacillus spp. were prescreened with the dual culture method, and the result showed Bacillus sp. isolate BB35 had the best biocontrol efficiency against Burkholderia gladioli causal agent of leaf stripe and stem rot disease of sweet corn. Based on 16S rRNA, gyrA and rpoB gene sequence, the Bacillus sp. isolate BB35 was identified as Bacillus velezensis. Moreover, the Bacillus velezensis isolate BB35 performed as a hydrolytic enzyme (amylase and protease) and plant growth-promoting rhizobacteria (PGPR) by inorganic phosphate solubilization, potassium desolvation and producing siderophore. Antibiotic synthesis related genes were also investigated for the isolate BB35, the results indicated that surfactin, fengycin, bacillomycin D and itulin A biosynthesis genes were investigated. On 14-day-old sweet corn, the B. velezensis isolate BB35's in vivo effectiveness was evaluated. Spraying B. velezensis isolate BB35 one day prior to inoculating B. gladioli, the cause of leaf stripe and stem rot disease in sweet corn, had the highest efficacy of all the treatments at 17.91%. B. velezensis isolate BB35 spraying and B. gladioli inoculation came next, with a controlled efficacy of 14.93%. A controlled efficacy of 13.43% was obtained from the inoculation of B. gladioli into sweet corn seed that was 14 days old and soaked in suspensions of B. velezensis isolate BB35 before growing. Additionally, the least effective control was achieved with 7.46% when B. gladioli was inoculated 1 day later with B. velezensis isolate BB35.