Abstract:
Mango fruit at the ripe stage is susceptible to infection by Colletotrichum gloeosporioides
causing Anthracnose disease. The pathogen remains quiescent in unripe fruit due to an elaborate
arsenal of pre-formed defences. However, induced defences of mango fruit have been reported to
contribute to the restriction of the pathogen during initial stages of infection in unripe fruit.
Rapid localized generation of superoxides and hydrogen peroxide as an early defence response
and increases in phenylalanine ammonialyase and chitinases have been reported. This paper
reports the changes in phenol composition in fruit peel following infection by C.
gloeosporioides. Conidia were seen to germinate and form appressoria within 24 hours of
inoculation. Browning of cell walls was seen in cells in immediate contact with the penetration
peg. Histochemical studies proved the accumulation of phenols and tannins at sites of attempted
penetration by the pathogen. Quantification of phenols in the fruit peel tissues showed the total
soluble phenol content in the mango fruit peel to be higher in peel of inoculated fruit compared
to the peel of control fruit, however, the increase was not significant. The cell wall bound
phenols in inoculated fruit peel tissue was significantly higher, when compared with the control.
It can be concluded that, in addition to the elaborate preformed defences present in mango fruit
peel, induced defences are present in the mango fruit peel. The induction of phenols at sites of
attempted penetration possibly contribute towards restricting and delaying the pathogen from
entering the mature, yet unripe fruit and causing disease. |
