Evaluation of Rhizobacterial Isolates against Pythium and Phytophthora spp. Associated with Chilli and Tomato Crops

Abstract

Tomato (Solanum lycopersicum Mill.) and chilli (Capsicum annuum L.) crops are of significant importance regarding their nutritional and economic concerns. The yield of the produce is relatively low as compared to the other countries of the world due to pre and post-harvest losses caused by various biotic and abiotic limiting factors. Pythium and Phytophthora spp. are notorious fungal-like pathogenic oomycetes associated with damping off, seed rot and late blight diseases in chilli and tomato crops. Synthetic agrochemicals are extensively used to control these pathogens and can be toxic and can pollute the environment. Moreover, this method of disease control is not much effective due to the soil-borne nature and rapid multiplication ability of these pathogens. The present study was conducted to explore the antagonistic potential of naturally occurring rhizobacteria against these pathogens. For this purpose, an extensive survey was conducted during 2015 - 2016 cropping year in major tomato and chilli growing areas in various districts of Punjab province viz., Attock, Chakwal, Faisalabad, Gujranwala, Gujrat, Jhelum, Okara, Rawalpindi, and Sialkot. The survey revealed maximum disease incidence 45.5 % and 41.6 % from chilli fields in Okara and Sialkot districts respectively while from tomato fields, 40.1 % and 39.15 % disease incidence was recorded from Sialkot and Okara districts respectively. From Phytophthora spp. infected tomato fields, maximum disease incidence was recorded at 66.3 % and 55.6 % from Okara and Sialkot districts respectively. Rhizobacteria are rhizospheric beneficial agents which colonize plant roots, aid in disease suppression and plant growth enhancement. A total of 130 rhizobacterial isolates were recovered from soil. Out of the total, 10 isolates were found highly effective antagonists against Pythium and xxix Phytophthora spp. Based on their morphological, biochemical and molecular analysis these rhizobacterial isolates were identified as Pseudomonas koreensis, P. asaccharolticum, Serratia marcscens, S. marcscens, P. putida, P. putida, P. libanensis, P. aeruginosa, Bacillus subtilis, B. megaterium, B. cereus, B. cereus and Burkholderia spp. All these rhizobacteria were compatible with each other and showed significant antibiotic resistance against Ampicillin and Penicillin G while B. subtilis showed resistance against all the tested antibiotics except Streptomycin and Rifampicin at highest concentration of 500 ppm. Rhizobacteria with high antagonistic potential viz., B. subtilis, B. cereus, P. putida and P. fluorescens were mass cultured on four (4) carrier materials viz, Sugarcane straw, wheat straw, wheat porridge and peat soil. All these rhizobacteria showed maximum viability on sugarcane baggas followed by wheat straw at 4 °C up to eighty (80) days. Seed treatment with rhizobacteria + sugarcane baggas (B. subtilis + SB) resulted into maximum seed germination (98 %), minimum seedling mortality (3.25 %) and improvement in plant growth characters viz, shoot and root length, fresh shoot weight, root weight and vigor index. Out of the ten (10) potential antagonists, nine (9) are first time reported against oomycetes from Pakistan that could be further tested for their antagonistic ability against other phytopathogens.