Pathogenicity and host specificity of Brazilian and African isolates of the acaropathogenic fungus Neozygites tanajoae to mite species associated with cassava

Abstract

Abstract Neozygites tanajoae is a host‐specific acaropathogen introduced in the late 1990s from Brazil into cassava fields in West Africa for biocontrol of the cassava green mite (Mononychellus tanajoa). Local African isolates of N. tanajoae are morphologically similar to introduced Brazilian strains but the two origins can be distinguished by diagnostic PCR. In this study it was explored whether differential traits in acaropathogenic performance and host specificity exist between Brazilian and African isolates. Pathogenicity and host specificity of two Brazilian and two African isolates of N. tanajoae were compared in leaf discs laboratory bioassays or on whole cassava plants in the greenhouse by exposing adult female mites to inoculum delivered from N. tanajoae infested mite mummies. The results show that all four N. tanajoae isolates caused significant mortality of M. tanajoa, both on leaf discs and on whole plants. However, on leaf discs the Brazilian isolate collected directly from Alto Alegre in Brazil (Brazil–Brazil isolate) caused a significantly higher mortality (80%) than the Brazilian isolate collected about 9 years post‐release from a field in Adjohoun (Brazil–Benin isolate) (61.3%). The two African isolates collected in Benin and Tanzania caused a mortality similar to the African–Brazilian isolate (62.3% and 61.3% respectively). On whole cassava plants, the four fungal isolates did not show any significant differences in incidence of M. tanajoa infection. The host specificity study was conducted on leaf discs against a collection of mite species typically associated with cassava plants in Africa, Typhlodromalus aripo, Euseius fustis, Tetranychus urticae and Oligonychus gossypii. It demonstrated that the African and Brazilian isolates of N. tanajoae had similar host specificity for M. tanajoa.