Studies on Survival of Trachysphaera Fructegina Tabor & Bunting Causing Mealy pod Disease of Cocoa Theobroma Cacao L.

ABSTRACT

Conidia of T. fructigena did not germinate at any relative humidity from zero to 10C% R.H. Germination in distilled water^was very poor, less than 2.0 per cent at the optimum temperature, 25 C. PDA encouraged 96.8 percentage germination at 25°C. The conidia germinated very poorly on PDA at 35°C and a temperature of 40 C killed the conidia in approximately 1 2 hours. T, Frutiger conidia would only survive in atmospheres of extremely high humidity. Best survival occurred at 10($ R.H. and 9 0.0 , 2 9 .7 and 0.6 percent of the conidia were viable after 1 0 , 20 and 40 days' storage, respectively. In comparison more than 50 percent of the spores perished in 20 minutes at 9Q& R.H. The conidia were well conserved in water and they survived longer than at 10Q$ R.H. Conidia at humidities from zero to 10Q/o R.H. eventually collapsed. Conidia exposed to atmospheres of humidities below 75^> R.H. shrank instantly. There was increasing delay of shrinkage with rise in relative humidity above 75^ R.H. Total shrinkage was observed after 1 hour, 1 § hours, 2 4 hours, 1 5 days and 30 days, respectively in conidia stored at 80, 85, 90, 95 and 10C$ R.H. The conidia were preserved longer at 20° than 28°C. Light up to 467.5 lux intensity had no effect on stored conidia. Removal of water from the spore by plasmolysis in 0.7M potassium nitrate, sodium chloride and sucrose solutions was not as damaging as loss of water during desiccation, and between 79*5 and 96.0 percent of the conidia endured an hour's plasmolysis. Damage only set in after prolonged immersion in the plasmolysing fluid beyond 1 2 - 2 4 hours. No germination occurred in either non-sterile or autoclaved extracts of soil and partially decomposed leaves from coooa farm. The fungistatic principle was seemingly non-volatile and non-fungicidal Highest survival of more than 50 percent was obtained in extracts of pH 8.0. Conidia, both live and dead, buried in soil on slides were attacked by other microorganisms. Conidia killed before introduction into the soil, however, suffered considerably greater attack and were lysed very quickly. T- fructigena showed limited competitive saprophytic ability. Reasonable percentage of baits was colonized only when large quantities of inoculum were used or when T. fructigena had earlier access to the bait than the other soil microorganisms. Sodium nitrate alone or a combination of sodium nitrate and dextrose encouraged greater saprophytic survival than ammonium tartrate, peptone or glucose applied separately.