Histological Investigation of Fungal Endophytes in Healthy Tissues of Azadirachta indica A. Juss.

Abstract

The presence of endophytic fungal mycelia within healthy tissue is most commonly detected by long incubation of small pieces of surface-sterilized healthy tissue on agar plates and the emergence of their mycelia or spores. Thus, to understand their biology and distribution within the host, it is mandatory to use histological tools to locate the endophytic mycelia as well as spores in vivo within healthy tissue. Thin microtome sections were stained with KOH-aniline blue procedures. The prominent fungal structures visualized were the fungal mycelia and occasionally spores. Mostly, the intercellular compact mycelia were observed with a few haustoria and clamp-like structures, while at several locations, the position was ambiguous. A few spore-like structures were also visible which were suspected to be the spores of Humicola or Nigrospora, since these genera have been reported as frequent endophytes from the same host (Azadirachta indica A. Juss.) by isolation methods. Some smaller hyphae were found under the cuticle and within the epidermal cells; however the larger hyphae were observed within all tissues including mesophylls, palisade and spongy parenchyma and vascular tissue. The study emphasized the localization, distribution and signifi cant presence of fungal endophytes of Azadirachta indica within healthy tissues, which may eliminate the suspicion with which some scientists view the presence of endophytes. The study provided further insight in the biology of the host-endophyte relationship as well as encouraging future investigations pertaining to host-endophyte interactions.