DEVELOPMENT OF A MICROBIAL COMMUNITY OF BACTERIAL AND YEAST ANTAGONISTS TO CONTROL WOUND-INVADING POSTHARVEST PATHOGENS OF FRUITS

Two antagonists, the bacterium Pseudomonas syringae and the pink yeast Sporobolomyces roseus, against blue mold (caused by Penicillium expan sum) on apple controlled this disease more effectively when combined a t approximately equal biomass (50:50 of the same turbidity) than in in dividual applications. Addition of L-asparagine enhanced the biocontro l effectiveness of P. syringae but decreased that of S. roseus and had no significant effect when the antagonists were combined, Populations of both antagonists increased in apple wounds and were further stimul ated by the addition of L-asparagine, The carrying capacity of wounds for P. syringae was not affected by S. roseus. Populations of P. syrin gae in wounds inoculated individually or in a 50:50 mixture with S. ro seus reached the same level after 3 days at 22 degrees C. However, pop ulations of S. roseus recovered after applications of the mixture were consistently lower than those recovered after individual applications . Similar effects were observed in in vitro tests in which populations of S. roseus grown in mixtures with P. syringae were consistently low er than those grown alone, while the populations of P. syringae were n ot affected by the presence of S. roseus. A total of 36 carbon and 35 nitrogen compounds were tested for utilization by both antagonists. Fo urteen nitrogenous compounds were utilized by both P. syringae and S. roseus, and an additional nine compounds were utilized by P. syringae. S. roseus and P. syringae utilized 17 and 13 carbon sources, respecti vely; 9 sources were common to both antagonists, Populations of these antagonists in apple wounds appear to form a relatively stable communi ty dominated by P. syringae. This domination is probably due to the gr eater ability of this organism to utilize nitrogen sources, which is t he limiting growth factor in carbon-rich apple wounds.