Influence of temperature on Pythium splendens -: induced root disease on carambola, Averrhoa carambola

A series of glasshouse and incubator studies were conducted to investigate the role played by Pythium splendens in a decline disorder of carambola, Averrhoa carambola. Plants, 4-6 months old, were grown in native calcareous soil either infested or not infested with the pathogen. Isolates recovered from atemoya, carambola and passion fruit grew optimally at 30degreesC, and significantly (P<0.05) increased root necrosis and reduced root, shoot and total biomass of carambola. Temperature had a profound impact on the latter relationships. Two or more times more necrosis developed at 10 and 15°C than at 25 and 30°C. Total biomass accumulations were over four times greater at 30°C than at 10°C, and were always lower in soil infested with P. splendens. When biomass totals from infested and noninfested soil were compared, relative values were lowest at 15 and 20°C and were almost two times greater at 30°C than at 20°C. Root infection by P. splendens was greatest at 15 and 20°C, far below the species' optimum for growth, and at 30°C was over nine times lower than at 15 and 20°C. This is the first detailed report of P. splendens as a pathogen of carambola.