MSc

The study entitled “Biocontrol potential of plant associated bacteria from Piper spp. against Phytophthora capsici infecting black pepper” was conducted at the Department of Agricultural Microbiology, College of Agriculture, Vellayani and Coconut Research Station, Balaramapuram during 2015-2017 with the objective to study the antagonistic effect of plant associated bacteria from Piper colubrinum and Piper nigrum, and their potential for the biological control of Phytophthora capsici induced foliar infection in black pepper in the nursery.
Plant associated bacteria were isolated from phylloplane, stem surface and within the leaves, stem and roots of P. colubrinum and P. nigrum on different bacteriological media. A total of 70 isolates were obtained, out of which 39 were from P. colubrinum and 31 from P. nigrum. The isolates were grouped based on cultural and morphological characters.
In the initial in vitro screening using dual culture plate assay, it was found that out of the 70 isolates obtained, 16 isolates showed inhibitory effect against P. capsici. The results revealed that the isolates PCSE8 and PCSE10 had the maximum zone of inhibition. The dual culture plate assay was followed by a detached leaf assay using the 16 isolates showing inhibition. It was found that minimum lesion size was observed in leaves sprayed with isolate PCSE10 which caused 79.02% disease suppression over the control, which was on par with leaves sprayed with PCSE5.
Biochemical characterization of the selected isolates were carried out using biochemical kits and a tentative genus level identification was done. Molecular level characterization was done and the plant associated bacteria from Piper spp. having biocontrol potential against P. capsici were identified as Burkholderia cenocepacia, Acinetobacter sp, Staphylococcus epidermidis, Streptomyces deccanensis, Bacillus sp, Rhizobium sp, Pantoea dispersa, Bacillus velezensis, Enterobacter sp, Acinetobacter baumannii and Bacillus subtilis.
A greenhouse experiment was carried out at Coconut Research Station, Balaramapuram, to study the effect of selected isolates on plant growth promotion and suppression of P. capsici induced foliar infection in the black pepper var. Karimunda. Suppression of foliar infection was studied by challenge inoculation with the pathogen on the foliage. Following artificial inoculation with the pathogen, the lowest lesion size was observed in plants treated with Rhizobium sp PCRE10 (1.18 cm) which caused 75.05% disease suppression over the pathogen control with the lowest disease index of 0.2. The isolate B. velezensis PCSE10 resulted in 53.69% disease suppression over pathogen control with a disease index of 0.32.
The plant growth promotion aspects of the plant associated bacteria were studied by analysing the biometric characters of rooted cuttings of black pepper var. Karimunda at 70 DAP. Maximum leaf number was observed in plants treated with B. velezensis PCSE10 (2.25). The treatments had significant effect on the rooting of the cuttings. The highest root number was observed in plants treated with isolate Rhizobium sp PCRE10 (12.33) followed by S. deccanensis PCRE1 (10.92). A similar trend was observed in root fresh weight and root dry weight. The shoot dry weight was highest in plants treated with B. velezensis PCSE10 followed by plants treated with B. velezensis PCSE8.
The study revealed that wild relative of black pepper, P. colubrinum is a good source for isolation of antagonistic bacteria against P. capsici. Bacterization with endophytes improved the plant growth characteristics and helped in better establishment of plants. Treatment with plant associated bacteria from P. colubrinum and P. nigrum suppressed the development of foliar infection of P. capsici. The endophytes of P. colubrinum, Rhizobium sp PCRE10 and B. velezensis PCSE10 were selected as best candidates when both disease suppression and plant growth promotion were considered..