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Germination and effect of reduced humidity on expression of pathogenicity in Verticillium lecanii against the glasshouse whitefly Trialeurodes vaporariorum
Author(s) -
DRUMMOND J.,
HEALE J. B.,
GILLESPIE A. T.
Publication year - 1987
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1987.tb01446.x
Subject(s) - trialeurodes , biology , spore , germination , humidity , whitefly , inoculation , horticulture , botany , veterinary medicine , homoptera , pest analysis , thermodynamics , medicine , physics
SUMMARY Fifteen isolates of the entomopathogenic fungus Verticillium lecanii , from various hosts and locations, were bioassayed in the laboratory at 19 ± 1°C and > 95% r.h. against fourth instar scales of Trialeurodes vaporariorum. Highly pathogenic isolates generally originated from whitefly; however, there was no correlation between conidiospore size or germination rate on agar, and pathogenicity. LT 50 values ranged from 5.7 to > 9 days and LC 50 (7 days) from 1.3 × 10 5 to 4.2 × 10 7 spores/ml. The effect of periods in low humidity (70% r.h.) following 16 or 96 h at > 95% r.h. after immersion of whitefly scales on tomato leaf discs in a suspension of 1 × 10 6 spores/ml, was compared for five isolates. Progressively longer periods at 70% r.h. following 16 h at > 95% r.h., reduced significantly ( P < 0.001) the pathogenicity of all isolates. In these conditions isolate A was least affected by low‐humidity transfer. The high pathogenicity of isolate A was associated with its more rapid development on the host cuticle during the first 16 h in high humidity. When inoculated whitefly scales were transferred to 70% r.h. after a preliminary 96 h incubation in high humidity, all five isolates achieved a higher level of pathogenicity compared with their transfer to low humidity after 16 h high humidity. Thus the screening of V. lecanii isolates in limiting humidity conditions provided a more critical assessment of their pathogenicity and of their potential success in whitefly control relevant to the glasshouse environment.