Relationships of aphid and mite infestations to control ofBotrytis cinerea byClonostachys rosea in rose(Rosa hybrida) leaves

Abstract

Infestations of aphids(Macrosiphum rosae L.) and of twospotted spider mites(Tetranychus urticae Koch) were examined in relation to growth and sporulation ofClonostachys rosea andBotrytis cinerea, and to suppression of the pathogen by the agent, in green rose leaves. Leaves were infested artificially with 10 aphids/leaflet for 3 h, or naturally with 15-30 aphids/leaflet for 7-12 days or with undetermined numbers of mites for 10-12 days. Leaves that had or had not been infested were inoculated withC. rosea, withB. cinerea, or withC. rosea plusB. cinerea. Germination incidence and germ tube growth ofC. rosea andB. cinerea on the phylloplane in most instances were much greater in leaves previously infested with aphids or mites compared with noninfested leaves. After combined inoculation,C. rosea suppressed germination ofB. cinerea from 47% to 19% in noninfested leaves, but in leaves that had been infested the agent was ineffective and germination incidence of the pathogen increased to 75-93%. Previous infestation with naturally introduced aphids or mites, but not brief infestations of artificially introduced aphids, markedly increased sporulation ofC. rosea after the leaves died during an initial 7-15 days of incubation on a paraquat agar medium, regardless of whether or notB. cinerea was present. Sporulation ofB. cinerea was similarly increased when inoculated alone. After 15-20 days, however, conidiophores of the agent or pathogen covered most of the leaf surface in these treatments. In leaves inoculated withC. rosea plusB. cinerea, the agent suppressed sporulation of the pathogen almost completely in both previously infested and noninfested leaves. Thus, aphid and mite infestations did not compromise the ability ofC. rosea to suppress inoculum production byB. cinerea in the leaves. Increased nutrient availability on the phylloplane through exudation or as honeydew or frass is proposed as a basis to explain effects of the pest infestations onC. rosea andB. cinerea.