Plant Growth Promotion and Biocontrol of Potato Fungal Diseases through Multi-stress tolerant Bacteria

Abstract

Biocontrol of phytopathogens by plant growth promoting bacteria (PGPB) appears to be a good alternative for currently used disease control approaches. Four studies were piloted to assess the potential of isolated PGPB for biocontrol of fungal diseases of Solanum tuberosum L. In the first study, 96 bacterial strains were isolated from the potato rhizosphere and different plant parts. Some isolated strains (21) were studied regarding the fungal mycelium inhibition and PGP-activities, of which, 4 strains (PM31, PM32, PM33, PM34) harboring the best antagonistic and PGP-activities were selected for further studies. In the dual culture experiment among all strains the strain PM31 showed maximum inhibition of Rhizoctonia solani, Fusarium solani, and Fusarium oxysporum. The 16S rRNA gene sequencing revealed the strains were closely related to Bacillus sp. (PM31), Bacillus subtilis (PM32), Bacillus cereus (PM33) and Bacillus aryabhattai (PM34). In the 2nd study, all strains were tested for multi-stress tolerance including salinity, heavy metals, heat, and drought stress. All 4 strains showed promising results regarding the multi-stress tolerance. In the 3rd study, all 4 selected antagonistic strains were characterized for antifungal metabolites through Liquid Chromatography and Mass Spectrometry (LCMS/MS). A total of 3 greenhouse experiments were conducted to assess plant growth promotion and biocontrol of fungal diseases (Stem canker/black scurf and Fusarium wilt) of potato. In the 1st experiment all 4 inoculated strains including PM31. PM32, PM33 and PM34 significantly enhanced the growth and yield of potato plants. In the second experiment the Bacillus sp. PM31, B. subtilis PM32 and B. aryabhattai PM34 were applied to potato plants with aim to control stem canker and black scurf caused by Rhizoctonia solani. Maximum increase in plant growth, yield, and disease suppression (stem canker and black scurf) were observed with strain PM32. In the 3 rd experiment two strains Bacillus sp. PM31 and B. subtilis PM32 were inoculated to potato plants under greenhouse conditions with aim to control Fusarium wilt disease triggered by Fusarium solani and Fusarium oxysporum. The application of strain PM31 showed maximum growth, yield of potato plants under fungal stress conditions. Biocontrol of Fusarium wilt of potato using Bacillus sp. is the first study reported from Pakistan till date. Both in-vitro and in-vivo experiments revealed native microflora of potato as the fungal disease control agent and potential growth promoter. Furthermore, the findings of current study have the potential to be employed in sustainable potato crop production