MSc

The study entitled “Plant growth-promotion and root knot nematode management in tomato by Piriformospora indica and rhizobacteria” was conducted at the Department of Agricultural Microbiology College of Agriculture,Vellayani during the period 2014-2016 with the objective to assess the potential of the root endophytic fungus Piriformosporaindicaand plant growth-promoting rhizobacteria in improving plant growth and suppressing root knot nematode infestation in tomato.

The experiment was conducted as in vitro and in vivo studies involving interaction assay between the biological agents and the nematode pest, andin vivo pot culture studies. Egg hatching and J2 mortality asinfluenced by treatment withrhizobacteriaand their cellfree extracts (CFE) were analyzed.Cell free extracts of rhizobacteria significantly reduced egg hatching and increased the mortality ofMeloidogyne incognitajuveniles. After 72 hours, the minimum egg hatching was with CFE of Pseudomonas fluorescensAMB8 (22.33 %) followed by B. amyloliquefaciens (22.66 %) and the maximum was with B. subtilis(27%).Juvenile mortality was highly influenced by the cell free extracts of all the isolates. Higher rate of mortality was observed with undiluted CFE than the diluted ones. Mortality percentage ranged from 68.21% to 99.71% with highest accounted for CFE of B. amyloliquefaciens. Treatment with undiluted CFE of P. indicaresulted in mortality of the J2 by 98% and egg hatching was reduced to 23.33%.

Allthe rhizobacterial strains(1x107bacterial cell/ml)negatively influenced the egg hatching(from 30 to 50%) as compared to the control(99 % hatching). Upon 72 hours of incubation, there was only 30 % egg hatching in the case of egg masses treated with Pseudomonas fluorescensAMB8 and in the case of Bacillus amyloliquefaciensit was 30.66 per cent. However, reducing the cell concentration in the test suspension of all the rhizobacterial strains had positive effect on egg hatching. Treatments with cell suspension of all rhizobacterial strainsshowed significantly low mortality of J2 juveniles, with highest mortality forB. amyloliquefaciens (8.56 %) indicating less influence by the rhizobacteria as such.
Piriformosporaindicashowed no egg parasitism.Compatibility between Piriformosporaindicaandrhizobacteriawas assessed by dual culture plate assayunder in vitrocondition and it was found that B. pumilus and Pseudomonas fluorescensAMB8 were compatible with the fungus though the test medium differed. The compatible bacteria as single inoculation and combination with P. indicawere used for in vivo analysis.
Pot culture experiments using sterile planting medium with single inoculation of the selectedrhizobacteria, Piriformosporaindica, and theircombinationsin the presence or absence of nematode were carried out. All treatments with P. indicashowed root colonization by the fungus.In the presence of nematode, percentage root colonization was found to be increased and the highest was for combination of P. indica and P. fluorescens AMB8. Higher biometric characteristics were observed with nematode untreated plants for all parameters.In the nematode inoculated treatments, application of combination of P. indicaandP. fluorescensAMB8had positive effect on leaf number, fruit number, shoot weight and root weight when compared to the control.Treatment withP.indica resulted in formation of less galls/plant (33.30), egg mass/root system (3.41), eggs/egg mass (306.405), number of nematodes/g of root (54.415) and final nematode population/100cc soil (58) as compared to the control plants, where the values were 142.24, 24.91, 663.54, 220.57, 294.16 respectively.
The study established the biocontrol potential of P.indicaagainst root knot nematode in tomato. Application of P. indica in the protray seedling production ensures better performance in terms of plant growth and suppression of root knot nematode infection in the main field.