Abstract
Conventional management of stem rot disease of potato, caused by Neocosmospora rubicola, through fungicide application is an environmentally unfavorable practice that calls for an alternative biocontrol approach. Plant growth-promoting bacteria (PGPB) are known to not only promote plant growth but also control diseases caused by various fungi. The study was designed to evaluate the potential of three strains of PGPB and synthetic fertilizer to manage stem rot of potatoes. In the first experiment, PGPB strains Azotobacter chroococcum, Azospirillum lipoferum, and Pseudomonas putida and their combinations were evaluated on PDA medium against N. rubicola using the dual culture technique. All three bacterial strains were found effective in reducing the radial growth of the fungus maximum up to 91%. In the second experiment, in the presence of half and full recommended doses of fertilizer nitrogen (N) and phosphorus (P), the potato growing medium was inoculated with N. rubicola alone, and with combinations of N. rubicola and PGPB strains (bacterial formulation; BF). N. rubicola increased stem and tuber rot, and decreased tuber weight by 11% compared to the control. On the other hand, sole inoculation with BF significantly increased tuber weight. In addition, a combined inoculation of N. rubicola and BF, or N. rubicola inoculation a week prior to BF inoculation did not affect tuber weight compared to control. However, inoculation of BF a week prior to N. rubicola, controlled rot symptoms and increased tuber weight by 32%. An increase in P application favored the PGPB strains in controlling rot in tubers. The interaction effect of fertilizer N with the inoculation combinations was non-significant; however, the main impact of N was to increase rot in tubers and decrease in potato stems. Hence a prerequisite application of PGPB formulation proved to be an effective tool against N. rubicola infestation in potatoes.
Highlights
Potato (Solanum tuberosum L.) is one of the most important staple crops, and its long-term cultivation faces a significant threat of plant diseases (Dahal et al, 2019)
The infected stem was sterilized with 10% sodium hypochlorite (NaClO) for 30 s, and pieces (2 mm2) of the stem were incubated on potato dextrose agar (PDA) followed by purification through single spore inoculation (Muhammad et al, 2018; Zheng et al, 2018)
Dual inoculation of “N. rubicola + A. chroococcum + P. putida” and “N. rubicola + A. chroococcum + A. lipoferum + P. putida” reduced radial growth of the fungus up to 91% in comparison to the control (Figure 1)
Summary
Potato (Solanum tuberosum L.) is one of the most important staple crops, and its long-term cultivation faces a significant threat of plant diseases (Dahal et al, 2019). These diseases are frequently managed by conventional agricultural practices, by using various types of fungicides, which have serious environmental concerns (Chandra et al, 2020; My et al, 2021). Sole and excessive use of chemical fertilizers to support intensive cropping systems negatively impacts the environment by causing soil infertility, groundwater contamination, climate change, and imbalance of soil and water ecosystems (Liu et al, 2015; Besser and Hamed, 2021). Nutrient management by integrating inorganic fertilizers, manure, and biofertilizers has beneficial effects over the sole application of chemical fertilizers (Tafesse and Leta, 2019). Some PGPB exhibits biocontrol properties and show antagonistic activity against various pathogenic fungi of crop plants (Mohammadi and Sohrabi, 2012; Pellegrini et al, 2020)
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