Death and decay in the trees of Mango (Mangifera indica L.)

Death and decay of trees of Mango (Mangifera indica L.) var. Kesar due to fungal infection was studied histologically. Fungal infection in the trees was observed due to various reasons like mechanical injuries in the stem, pruning of the branches, through the inflorescences, attack of Ambrosia beetle and termites. In the initial stage, fungal spores get settled on the flowers due to presence of nectar, followed by their germination and entry of the hypha into peduncle, which gradually spreads into younger branches. The inflorescences were first attacked by Fusarium moniliformis followed by other fungi like Alternaria, Chetomium sp., Aspregillus ellipticus, Aspregillus niger, etc. Fungal mycelia gradually invade the xylem tissues from the top of the branches and spread basipetally ultimately causing death of the infected branches. During monsoon, the crevices on the surface of bark of the healthy plants supported the growth of fungi like Pleurotus, Auricularia, Xyleria, Daldinia sp., and Polyporous sp. The removal of bark from such infected trees revealed minute holes on the surface of the woody cylinder made by Ambrosia beetles. During wet season fungal mycelia makes an easy entry into the xylem through the wounded portion of the stem or pruned branches. Initial entry of the hyphae into xylem was seen through the ray cells. Then the hyphae enter into the lumen of axial elements lining the ray cells through pits and intracellular spaces. The vessel elements located in the xylem (transition zone) between healthy and infected portion were filled with tyloses while axial and ray parenchyma showed heavy accumulation of tannin contents. On the other hand, the infected xylem was also found devoid of reserve metabolites while in normal trees, axial and ray parenchyma showed heavy accumulation of starch grains.