Survey and Molecular Characterization of Major Bacterial Pathogens of Potato (Solanum Tuberosum L.) for Export Promotion

Abstract

India contributes approximately 7.5 percent of the world’s total potato production. The export performance of Indian potato is quite dismal as we have rarely been able to export near about 0.7% of our domestic production. The situation is further worsening as Indian potato exports have fallen during current half decade due to brown rot disease and potato tuber moth. The ISPMs provide guidance to member countries in implementing national programmes and fulfilling requirement of the IPPC and NSPM provide guidelines for declaration of disease free areas in India.The production of potato is adversely affected by many diseases caused by fungi, bacteria, nematode, phytoplasma, viruses and viroids etc.Among thembacterial diseases, Brown rot (Bacterial wilt)back leg/Soft rot and common scab are considered as the most important diseases.In the present investigation, survey was conducted during September to April 2019-2020 and 2020-2021 in 35 village of Daurala block and its surroundings to find out the presence of brown rot, soft rot and common scab in potato. The samples were collected from pre cropping (soil), cropping (stem) and post-harvest (tuber). A total of 338 samples were collected from different farmer’s field and cold storage for isolation and confirmation of three major bacterial pathogens of potato i.e. R. solanacearum, Pectobacterium carotovorum subsp. cartovorum and Streptomyces scabiei. Out of 283 samples, 263 were processed for isolation of R. solanacearum; Isolation of pathogens was done on specific media. Based on cultural, morphological, biochemical and molecular confirmation R. solanacearum and Pectobacterium carotovorum subsp. carotovorum was not detected in collected samples.18 Streptomyces spp. were isolated from 50 infected tubers.Based on cultural, morphological and biochemical test, only 10 isolates produced the similar cultural characteristics of Streptomyces spp. 5 isolates were conformed as S. scabiei on the basis of pathogenicity and molecular characterization of 16S rDNA sequence. It was found that common scab disease was more prevalent in some villages of Daurala block. Molecular characterization of Streptomyces scabiei isolates was done based on pathogenicity related txtA and nec1genes. Thaxtomin gene (txtA) is responsible for the synthesis of thaxtominA toxin and nec1 gene is production of necrosis factor 1 which is important virulence factor of pathogenic Streptomyces spp. It was found that all the 5 isolates have txtA and nec1 gene.All the Streptomyces scabiei isolates were characterized on different media. Creamy white to white brown colony colour was observed on SCA and Yeast extract–malt extract agar. Different drugs were tested against all the Streptomyces scabiei isolates and found that Amikacin, Gentamicin, Piperacillin, Tobramycin, Norfloxacin, Ciprofloxacin, Cefoperazone, Levofloxacin, Ticarcillin, Ofloxacin Mezlocillin Gatifloxacin, Piperacillin/Tazobactam, Netillin effective to all the isolates.Different bio-agents were evaluated against the Streptomyces scabiei and found that highest zone of inhibition by the T. harzianum followed by Bacillus pumilus and Bacillus subtilis. The findings can be used for the recommendation of larger sampling with more coverage area to obtain significant results to declare it disease free zone to improve potato export.