Effects of osmotic potential and temperature on growth of two pathogens of figs and a biocontrol agent

Growth of Aspergillus niger and growth and sporulation of Fusarium moniliforme, causing smut and endosepsis, respectively, in figs, were evaluated 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 conditions. Experiments also were conducted in the field to study the optimal time for spraying P. lilacinus as a biocontrol agent. The growth of all three fungi was affected more by temperature than by osmotic potential. The optimum temperature for linear growth of both A. niger and P. lilacinus was 30 C. At optimal temperatures, decreasing osmotic potentials had the least effect on the growth of A. niger and the most effect on P. lilacinus. The growth of F. moniliforme was reduced significantly 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. moniliforme > P. lilacinus. Regardless of osmotic potential, low temperatures (15 and 20 C) limited the growth of A. niger and explained, in part, why it does not frequently occur in caprifigs. Regardless of temperature, decreasing osmotic potentials limited the growth of P. lilacinus, and thus, among the three fungi tested, it had the least ability to utilize available water, yet for P. lilacinus to be effective as a biocontrol agent, adequate moisture is required. Spraying a spore suspension of P. lilacinus on caprifigs in mid-March suppressed incidence of endosepsis in fruits by 50% in comparison with unsprayed trees; the same spray treatments did not reduce disease on Calimyrna fig trees because of low-moisture conditions. During the caprifig growing season, temperatures did not exceed 30 C, and there were frequent rains to provide adequate moisture for P. lilacinus.