A STUDY ON THE DISEASE RESISTANCE IN HEVEA BRASILIENSIS TO COLLETOTRICHUM GLOEOSPORIOIDES

Abstract

Attached

The factors responsible for disease resistance of Hevea clones to ~. gloeosporioides were st~died. First, field observations showed that the s~sceptibility of Hevea to the disease varied in different clones and an interaction was seen between clones and locations. When the infection was low incidence and severity of the disease were linearly related; a c~rvilinear relationship was evident when the level of infection was high. Isolates of £. gloeosporioides varied in their growth characteristics, morphology and spore prod~ction. They showed differential s~sceptibility to vario~s clones. Leachate of resistant clones suppressed the growth of the pathogen and favo~ed appressorium formation. 1£ vitro st~dies indicated that growth promoting s~bstances were not cond~cive for formation of appressoria. There was no difference either q~antitatively or q~alitatively in s~gars and amino acids in the leachate of different clones. Waxes and s~bstances associated with it are inhibitory on the pathogen at high concentrations. These substances separated by TLC showed two inhibitory zones. Phenolic and acidic s~bstances are associated with the cr~de wax extract. Leaves of resistant clones s~pported less germt~be growth than s~sceptible leaves, b~t favoured appressori~m formation. On penetration of resistant tiss~es a rapid disorganization of the cell content was observed, arresting hyphal growth. In s~sceptible clones hyphae invaded deeper in to the tissues and colonized the mesophyll cells both inter and intracell~lerly; VIII aoervuli were formed 12 h after inoculation. The migration of nuolei towards the site of penetration was observed in resistant olones. There was no relationship between either total or orthodihydroxy phenol level and field resistance of Hevea olones. But the infection was accompanied by a change in the orthodihydroxy phenol level, particularly in resistant clones. In Hevea,peroxidase activity was higher than polyphenoloxidase and inorease in peroxidase level with the infection was more pronounced in resistant clones. Infection also resulted in the increase of soluble protein content.