VIRULENCE OF FUSARIUM SPECIES CAUSING FIG ENDOSEPSIS IN CULTIVATED AND WILD CAPRIFIGS

Fusarium spp. associated with endosepsis of figs were characterized fo r growth rate, sporulation, temperature optima, and virulence. F. moni liforme and F. solani were the dominant causal agents of fig endosepsi s. A total of 62 Fusarium isolates were collected from cultivated and wild caprifigs with endosepsis symptoms from most fig-production areas of California. One isolate was F. dimerum, seven were F. solani, and 54 were F. moniliforme. In vitro growth rates of isolates within speci es differed significantly. Sporulation was determined after colony dia meters were recorded by flooding the colonies with 10 ml of sterile de ionized water and determining the number of spores using a hemacytomet er. Sporulation correlated significantly (r = 0.43; P = 0.0001; and n = 236) with growth rate. The majority of F. moniliforme and F. solani isolates had a temperature optimum of 25 C; the F. dimerum isolate had an optimum temperature of 30 C for linear growth. The solitary F. dim erum isolate was moderately virulent; F. solani isolates were either v irulent or highly virulent; and among F. moniliforme isolates, approxi mately 11% were avirulent, 67% were weakly to moderately virulent, and 22% were virulent to highly virulent. The teleomorph of most F. monil iforme isolates was Gibberella fujikuroi mating population A, and only a few were population F. F. moniliforme isolates from wild caprifigs were significantly more virulent than those from cultivated caprifigs, but no such differentiation was found with F. solani. Infusion of F. moniliforme from wild caprifigs into cultivated figs may cause signifi cant, long-term problems for the fig industry in California.