Arbuscular mycorrhizal fungal spore density and root colonization in cochineal-infested Opuntia ficus-indica plants in northern Ethiopia

Arbuscular mycorrhizal fungi (AMF) and herbivore insects are essential elements of ecosystems. They can influence each other on their common host plant. AMF support the plant growth by protecting against herbivore insect stresses. Opuntia ficus-indica (L.) miller is a multipurpose species which is under serious threat by cochineal insect (Dactylopius coccus (C.). The AMF and cochineal insect interaction on O. ficus-indica plants were not studied. This paper analyzed AMF spore density and root colonization of O. ficus-indica population in cochineal-infested and uninfested cultivated areas. Soil depth, season, and altitude were main environmental factors for the result observations. Soil and root samples were collected from the rhizosphere of O. ficus-indica plants. AMF spore density and root colonization were higher in uninfested plants than cochineal infested. AMF genus significantly varied along altitude and soil depth. Root colonization was higher during the rainy season than dry season, while spore density was lower in the rainy season. In the cochineal infested populations, spore density did not significantly varied with seasons. Spore density and root colonization were significantly higher on the upper soil depth than lower depth. Rhizosphere soil properties varied with altitude and soil depth. Soil available phosphorus (AVP) was significantly higher in the cochineal-infested populations. AVP showed significant negative correlation with mycorrhizal colonization. AMF-cochineal interaction in O. ficus-indica populations needs to be experimentally tested to understand the facilitative role of AMF to increase the performance of O. ficus-indica plants and to defend against the infestation of cochineal.