ABSTRACT
Title: Identification of bacterial agent causing gummosis stem canker on jackfruit (Artocarpus heterophyllus Lam.)
Gummosis stem canker is a new emerging disease on jackfruit cv. Sieu Som in Vietnam causing stem canker, gummosis, and vascular brownish discoloration. The disease may quickly kills the above parts of infected branches or trunks. This study was conducted to determine the causal agent of the disease through the Koch postulates combined with molecular and biochemical methods. The isolated bacterium from infected jackfruit is able to cause hypersensitive reaction on chili leaf by leaf infiltration. When the bacterial solution was injected into jackfruit stems, the bacteria were seen flowing to the upper xylem and turning the infected xylem to brown (stem canker) three weeks after the injection. Bacterial reisolation from the stem canker obtained bacterial strain similar to the initial artificial inoculation. Based on testing bacterial characteristics including solubilization on 3% KOH, using Glucose in both aerobic and anaerobic conditions, and white colony on YDC medium, the bacterial isolate was classified belong to Pectobacterium genus. By sequencing the 16S rRNA gene of the bacterial isolate after PCR amplification with 27F/1492R primers and then comparing with the published sequences on NCBI by BLAST, the bacterial isolate showed high similarity with two species P. carotovorum and P. aroidearum. Based on its characteristic without growth in Tween 80, the bacterial isolate was clarified as P. carotovorum. Therefore, the causal agent of gummosis stem canker and die-back on jackfruit cv. Sieu Som was proved as P. carotovorum.
Keyword: gummosis stem canker, causal agent, jackfruit cv. Sieu Som