Studies on Colony Morphology and Sporulation of Ganoderma Isolates, Causing Basal Stem Rot Disease of Oil Palm

Basal stem rot is an important disease of oil palm caused by different species of Ganoderma. A survey has been made in the oil palm gardens of different states and collected suspected BSR affected tissues (root bits/stem tissues/basidiomata). During the study, 11,184 palms were surveyed, (7574 from Andhra Pradesh, 144 from West Bengal and 3466 from Kerala) and 46 palms were suspected to be affected by BSR. All the suspected samples were cultured and 41 isolates could be purified, which were subjected to PCR analysis by using two pairs of Ganoderma specific primers namely Gan 1 & Gan 2 and ITS3 & Gan ET. Total 21 isolates (15 from Andhra Pradesh, 3 from West Bengal and 3 from Kerala) were found to be Ganoderma positive through PCR analysis. The positive isolates were further grown on Potato Dextrose Agar medium for studying the cultural variability. Growth rate, colony morphology and colony colour were recorded at one-week interval up to third week. Wide variability was observed in the colony morphological characters of the different isolates even among the isolates collected from a specific location. Eight positive isolates from Rajahmundry formed three groups where as three isolates from Palode formed two groups. All the 21 isolates formed five groups based on the colony morphology. Major group containing 14 isolates showed white cottony growth with no colour change at the bottom (under side). All three isolates from Mohitngar (West Bengal) showed same colony morphology. Two of the isolates showed unique colony morphology, one with white thin colony and concentric marks, which later turned to grey and another isolate with white cottony growth initially and later turned to light yellowish having radial corrugations visible on both sides. Out of twenty-one cultures seven of them were only found spore forming. Ellipsoid shape spores were observed in case of six isolates, where as one isolate from Rajahmundry exhibited ovoid shape spore.