Endophytic Bacillus spp. as a Prospective Biological Tool for Control of Viral Diseases and Non-vector Leptinotarsa decemlineata Say. in Solanum tuberosum L

Abstract

Viral diseases and their damage causing significant loss to economically important crops have increased by several folds during the last decade. All the conventional approaches are not able to eradicate the viral infection. Therefore, there is a need to look for efficient and eco-friendly viral disease-preventive measures. The genomic material of the majority of deleterious viruses of higher plants is RNA. One of the possible measures to control viruses is the use of ribonucleases (RNases), which can cleave RNA in the viral genome. Based on this, we investigated the RNase activity of endophytic Bacillus spp., which can enrich in 10³-10⁵ colony-forming units per gram of wet mass of aboveground part of potato plants. A high level of RNase activity was observed in the culture medium of Bacillus thuringiensis B-6066, Bacillus sp. STL-7, Bacillus sp. TS2, and Bacillus subtilis 26D. B. thuringiensis B-5351 had low RNase activity but high ability to colonize internal plant tissues, Bacillus sp. STL-7 with high RNase activity have relatively low number of cells in internal tissues of plants. B. thuringiensis B-6066, B. subtilis 26D, and Bacillus sp. TS stimulate RNase activity in potato plants for a long time after application. Strains with high ability to colonize internal plant tissues combined with high RNase activity reduced severity of viral diseases symptoms on plants and reduced the incidence of potato viruses M, S, and Y. It is worth noting that Bacillus spp. under investigation reduced the number of Leptinotarsa decemlineata Say. egg clusters and larvae on treated plants and showed antifeedant activity. This results in increase of potato productivity mainly in the fraction of major tubers. B. subtilis 26D and Bacillus sp. TS2 combining endophytic lifestyle, RNase, and antifeedant activity may become the basis for the development of biocontrol agents for plant protection.

Keywords: Bacillus; RNases; Solanum tuberosum; endophyte; viruses.

FIGURE 1

Effect of bacterial agents and Bitoksibacilline (BTB) treatments of potato plants on the total number of eggs (I) and larvae (II) of Colorado potato beetle (CPB) per plant during the whole seasons of 2019 and 2020 (data pooled over the experimental period) (1 + 2, early instar larvae; 3 + 4, last instar larvae). Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.

FIGURE 2

Effect of bacterial agents and Bitoksibacilline (BTB) treatments of potato plants on the prevalence of potato virus Y (PVY), potato virus M (PVM), and potato virus S (PVS) on potato plots on the 17th day after treatment: percentage of samples that tested positively for each virus (I) and samples that tested positive for two viruses simultaneously (II). Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.

FIGURE 3

Effect of bacterial agents and Bitoksibacilline (BTB) treatments of potato plants on the prevalence of potato virus Y (PVY), potato virus M (PVM), and potato virus S (PVS) in potato plots on the 31st day (2019) and 29th day (2020) after treatment: percentage of samples that tested positively for each virus (I) and samples that tested positive for two viruses simultaneously (II). Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.

FIGURE 4

RNase activity in potato plants treated with bacterial strains and Bitoksibacilline (BTB) on the 17th day (I) and the 31st day after treatment (II). Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.

FIGURE 5

Defoliation of potato plants caused by Leptinotarsa decemlineata (I) and percentage of viral diseases damaged leaves (II) of potato plants treated with bacterial agents and Bitoksibacilline (BTB). Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.

FIGURE 6

Effect of bacterial agents and Bitoksibacilline (BTB) treatments of potato plants on the total potato yield. Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.

FIGURE 7

Effect of bacterial agents and Bitoksibacilline (BTB) treatments of potato plants at different fractions. (I) Number of tubers in fraction; (II) weight of tubers in fractions. Data represented as mean values ± standard error; values followed by the same alphabet within a column are not significantly different from each other according to Tukey’s honestly significant difference (HSD) multiple-range test at P < 0.05.