Arbuscular mycorrhizal fungi-induced resistance in Opuntia ficus-indica (L.) Miller plant against cochineal insects under various soil water levels

Herbivore insects affect the performance of plants. The cochineal insect (Dactylopius coccus (C.) is among the herbivores insects of cactus plants that severely destruct Opuntia ficus-indica plants. Host-plant fitness performance against herbivorous insects is controlled through symbiosis with arbuscular mycorrhizal fungi (AMF) and has been reported for different plant species. We studied the effects of AMF-inoculation in inducing resistance in the O. ficus-indica plant against cochineal insects under various soil water levels. In this study, spiny and spineless O. ficus-indica plants were grown with the presence and absence of AMF, and with four levels of soil water stress. The treated plants were grown in greenhouse conditions. After 24 months of growing, all treated cladodes were exposed to the cochineal insects through crawler inoculation. The findings indicated that AMF not only improved O. ficus-indica performance but also activated the defense response of O. ficus-indica against the cochineal insect. AMF colonization strongly affected the performance of the inoculated crawlers, mainly the number of established crawlers, survival rates, and number of crawlers that reached nymph I, first molting, nymph II, second molting, proto-pupa, and pupa, female and male adults. Female mass weight, egg, and crawler production were reduced in AMF O. ficus-indica plants. AMF colonization significantly affected the cochineal populations in the cladodes. Opuntia ficus-indica type and water treatment alone were not significant sources of variation for cochineal performances. Colonization of O. ficus-indica with AMF significantly increased morphological traits and nutrient concentrations of the cladodes. Improvements in morphological traits and nutritional concentration have been shown to play a key role in enhancing mycorrhizal O. ficus-indica plants resistance against cochineal.