RESUMO
Aims@#Bacterial heart rot (BHR) disease caused by Erwinia chrysanthemi or the new nomenclature Dickeya zeae was identified as the lethal disease of pineapple and caused massive losses for the farmers due to non-satisfactory solutions. Thus, this study aims to understand the disease dissemination pattern and screen for tolerance pineapple variety prior to establishment of disease management strategies. @*Methodology and results@#Dissemination of BHR disease was observed visually in 2 study plots consisting 200 plants in each plot. Single plant inoculation of the pathogen was done in each plot namely Plot A at the edge and Plot B at the middle. Disease incidence was recorded at weekly interval for 12 weeks. The pattern of disease spreading in both plots was then mapped based on the results. Separately, 8 commercial pineapple varieties (Maspine, N36, MD2, Morris, Sarawak, Kristal, Gandul and Josapine) were screened for their resistance towards BHR. The varieties screening study was carried out using complete randomized block design. Overall, disease incidence (DI) was observed lower in plot A compared to Plot B. Percentage of DI in Plot A increased continuously from week 1 to 12, but in plot B the DI was stagnant starting from week 3 onwards. This study revealed that there is highly significant difference in percentage of infection between varieties tested. Josapine and MD2 were the most infected varieties based on lesion on plant. Both were found susceptible to BHR. Besides that, Chrystal Honey, Maspine and Sarawak varieties were less infected and classified as moderately resistance compared to other varieties. @*Conclusion, significance and impact of study@#Inoculum source was recognized as determinant factor for dissemination of BHR. Aggregation pattern was observed, and disease spreading was severe when disease started from the edge of the plot compared to in the middle. These findings will help farmers to choose the varieties of interest and plan for disease control measure based on first observed disease symptom in their field. This study is also important to researchers and plant breeders for varietal improvement in the future.
RESUMO
Aims@#The objective of this study is to identify the causal agent of a new fruit rot disease on jackfruit which was observed in the jackfruit-growing area in Taman Kekal Pengeluaran Makanan (TKPM), Pahang State of Malaysia in late 2016. The disease has been continuously spreading and caused huge economic loss to jackfruit farmers in Malaysia. @*Methodology and results@#Bacterial strains isolated from the disease plant were preliminary identified using basic morphological and physiological test and confirmed by polymerase chain reaction (PCR) and sequencing of the 16S rRNA gene. The isolates from infected tissue were Gram-negative and motile rods bacteria producing circular, mucoid colonies on LB medium that are 2 mm wide after 48 h at 28 °C. It appeared creamy to white in colour on NA medium with more watery consistency. The 16S rRNA was amplified for the isolated strains and sequences were compared with the NCBI database using BLAST. The results showed 97 to 99% identity similarity to Dickeya fangzhongdai, strain JS5 (accession no. KT992690). Phylogenetic analysis indicated that the isolates from this study were clustered together in the clade of D. fangzhongdai. Sequence data from isolated strains were deposited in GenBank (accession no. MH197139, MH842152 and MH842153). Characteristic symptoms of fruit rot disease appeared after 2 days of post inoculation though Koch’s postulate. @*Conclusion, significance and impact of study@#To the best of our knowledge, this is the first report of a new bacterial fruit rot disease of jackfruit caused by species of Dickeya in Malaysia. The bacterium is now considered as one of several bacterial causing diseases which impacted major loses of jackfruit industry in Malaysia.