MSc

Black pepper, the most valued and popular spice of India is often severely
infected by the fungal pathogen, Phytophthora capsid causing 'foot rot' disease.
Almost all the cultivated species and varieties of Piper are found susceptible
to the disease while P. colubrinum is the only species expressing resistance to
infection. Little is known about the host-pathogen interaction and is the main
limiting factor in formulating strategies for disease management in this valuable
crop. In the present study, an attempt was made to unravel the defense mechanism
in Piper spp. through studying the pathogenesis related proteins in relation to
Phytophthora foot rot disease.
Two species of Piper viz, P. nigrum and P. colubrinum were infected with
the fungal pathogen and the reaction of the host was studied in relation to
development of disease symptom, expression of PR proteins and activity of PR
related enzymes. Both the varieties of P.nigrum studied, namely Panniyur-l and
Kalluvally expressed foliar symptoms within three days after inoculation with the
fungus while P. colubrinum remained healthy throughout the experiment. The
variety Panniyur-l was found to be more susceptible to the infection.
Significant difference was observed in the expression of PR proteins and
activity of PR enzymes assayed. Upon infection with the fungus, the protein
extracted at pH 2.8 was found reduced in P. nigrum varieties (Panniyur-l and
Kalluvally) while no significant difference was observed for P. colubrinum. In
PAGE analysis, five basic proteins were found expressed in the healthy plants and





the banding pattern was unique for P. nigrum varieties and for P. colubrinum. An
additional protein of Rm value 0.56 was found expressed in the infected plants
of P. nigrum on the sixth day after infection with P. capsid. This additonal
protein was also found expressed in the healthy plants of resistant species,
P. colubrinum indicating its role in the defence mechanism.
SDS-PAGE analysis of the PR proteins extracted at pH 2.8 also showed
distinct banding pattern in P. nigrum varieties and P. colubrinum. Two
additional bands (16.5 kD and 8.0 kD) were found expressed in P. nigrum
varieties upon infection with the fungal pathogen. The relatively tolerant variety,
Kalluvally recorded early expression of these specific PR proteins. It was also
interesting to note the expression of these proteins in the resistant specres
P.colubrinum indicating their significance in the defence mechanism.
The activity of the PR enzyme, 8-1 ,3-glucanase was found to be relatively
high in P. colubrinum. Among the P.nigrum varieties, Kalluvally recorded better
activity related to its better tolerance. The PAL activity increased substantially in
P. nigrum varieties, immediately after infection with the fungal pathogen and the
rate of increase later declined. The resistant species P. colubrinum recorded low
PAL activity. Chitinase activity was almost nil in healthy and infected plants of
P. nigrum and P. colubrinum. Thus among the pathogenesis related enzymes
studied, 8-1,3-glucanase and phenylalanine ammonia lyase were found to have a
positive role in the defence mechanism of black pepper in relation to Phytophthora
foot rot disease.