Study on Gummosis and Sudden Decline Disease of Mango Plants in Rajshahi Region of Bangladesh

Abstract

Mango is one of the most important fruit in Bangladesh suffering from many diseases. Among the diseases gummosis and sudden decline disease of mango plant is a new disease in Bangladesh. Day by day it is becoming a serious threat to the mango growers of the country. In order to study about the disease a set of four experiments were conducted. A field survey was conducted at five upazilas of Chapainawabganj district and three upazilas of Rajshahi district of Bangladesh during January 2016 to October 2017 to study the incidence and severity of the disease. It was observed that the disease was found in all the surveyed area under investigation. Among the eight upazilas the highest incidence (3.47%) and severity index (10.70%) were recorded in Shibganj upazila of Chapainawabganj district where as the lowest incidence (1.77 %) and severity index (6.00 %) were recorded in putia upazila of Rajshahi district. In case of varietal reaction the highest incidence (3.55 %) and severity index (14.87 %) were recorded in Fazli variety whereas the lowest incidence (0.26 %) and severity index (2.16 %) were recorded in BARI Aam-4. From the experiment it was observed that among the varieties surveyed fazli was very much susceptible to gummosis and sudden decline disease. These studies indicate that older plants might be more susceptible to the disease compared to younger plants. From the results it was observed that the maximum disease incidence was noted in the month of April and the minimum in July. During the survey samples of diseased plant parts were collected and the causal agent was isolated on potato dextrose agar media and identified. The isolated fungus was identified as Lasiodiplodia theobromae that was confirmed by pathogenicity test using mango seedlings as test crops following stem inoculation method. Lasiodiplodia theobromae, isolated from the diseased plant parts which was able to cause the same xvi symptom on inoculated mango seedlings. In this study molecular identification and characterization of isolated fungus was conducted using genome sequencing of its region from northern parts of Bangladesh. The BLASTn search revealed that the fungus derived from gummosis and sudden decline disease of mango is Lasiodiplodia theobromae. In vitro fungi toxicity of eight fungicides from different groups were tested for their efficacy against L. theobromae, by following poisoned food technique, proved that Carbendazim was the most effective fungicide followed by Copper hydroxide, Propiconazole and mixture of Pyraclostrobin with Metiram. Six treatments were applied at field condition to manage the disease and it was observed that among the treatments the lowest severity (2.96%) as well as the highest disease reduction (95.56%) after the application of Bordeaux paste along with spraying Carbendazim @ 2gm/L.