EFFECTS OF OSMOTIC POTENTIAL AND TEMPERATURE ON GROWTH OF 2 PATHOGENSOF FIGS AND A BIOCONTROL AGENT

Growth of Aspergillus niger and growth and sporulation of Fusarium mon iliforme, causing smut and endosepsis, respectively, in figs, were eva luated at 10 osmotic potentials ranging from -0.46 to -4.46 MPa at 15, 20, 25, 30, and 35 C. Paecilomyces lilacinus, a fungus that naturally occurs in the cavities of figs, was evaluated under similar condition s. Experiments also were conducted in the field to study the optimal t ime for spraying P. lilacinus as a biocontrol agent. The growth of all three fungi was affected more by temperature than by osmotic potentia l. The optimum temperature for linear growth of both A, niger and P. l ilacinus was 30 C. At optimal temperatures, decreasing osmotic potenti als had the least effect on the growth of A. niger and the most effect on P. lilacinus. The growth of F. moniliforme was reduced significant ly at 35 C by high osmotic potentials (>-3.12 MPa) and at 15 C by low osmotic potentials (<-1.79 MPa). Based on their ability to grow in hot , dry environments, the three fungi can be ranked A, niger > F. monili forme > P. lilacinus. Regardless of osmotic potential, low temperature s (15 and 20 C) limited the growth of A. niger and explained, in part, why it does not frequently occur in caprifigs. Regardless of temperat ure, decreasing osmotic potentials limited the growth of P. lilacinus, and thus, among the three fungi tested, it had the least ability to u tilize available water, yet for P. lilacinus to be effective as a bioc ontrol agent, adequate moisture is required. Spraying a spore suspensi on of P. lilacinus on caprifigs in mid-March suppressed incidence of e ndosepsis in fruits by 50% in comparison with unsprayed trees; the sam e spray treatments did not reduce disease on Calimyrna fig trees becau se of low-moisture conditions. During the caprifig growing season, tem peratures did not exceed 30 C, and there were frequent rains to provid e adequate moisture for P. lilacinus.