[Biomass, sporulation and aphid-infecting virulence of Pandora neoaphidis mycelia produced in repeated liquid culture].

Repeated culture of entomophthoraceous isolates is a suspectable factor leading to their virulence decline of biological variation. In the present study, an isolate of Pandora neoaphidis, F98028, was repeatedly cultured six times at the regime of 20 degrees C and 80 r/min in Sabouraud dextrose broth(SDB) at three inoculation ratio of 1/20, 2/20, and 4/20 (seed culture over fresh SDB). Mycelial biomass(MB), sporulation capacity(SC), and virulence to the green peach aphid, Myzus persicae, were assessed for each of the subcultures. The repeated liquid cultures, initiating from seed culture with MB 8.84 mg/mL ad SC 7.22 x 10(5) conidia/mg, yielded MB and SC in a range of 6.4-10.0 mg/mL and 7.3 x 10(5)-10.8 x 10(5) conidia/mg at the ratio of 1/20(72 h culture), 5.7-8.5 mg/mL and 10.0 x 10(5)-12.1 x 10(5) condia/mg at 2/20(60 h culture), and 5.5-10.9 mg/mL and 6.4 x 10(5)-10.9 x 10(5) conidia/mg at 4/20(48 h culture), respectively. There was no significant difference in both MB and SC among the cultures(F = 0.299, P = 0.903) or the three inoculation ratios (F = 0.561, P = 0.587). Inocula from each of the cultures at the inoculation ratio of 1/20 were repeatedly bioassayed on the second and third instar colonies of M. periscae. Based on time-dose-mortality analysis, the estimates of LD50 s for all batches of the inocula were 22.8-162, 4.7-49.4, 2.8-16.7, 2.3-9.5, and 1.8-5.2 conidia/mm2 3-7 d after inoculation, respectively. All the estimates for the repeated cultures fell within a range previously reported. Thus, the method used for repeated liquid culture in this study did not cause a visible decline in the virulence of P. neoaphidis F98028.