Microbiological control in phytosanitary optimization technologies for agroecosystems: research and practice (review)

Phytosanitary optimization of agroecosystems targeted to control harmful arthropods and plant pathogens should use a complex of multifunctional biologics based on microbial antagonists of pathogens, producers of bioactive substances and entomopathogens (V.D. Nadykta et al., 2010; Rohini et al.; 2016, M. Ghorbanpour et al., 2017). The most promising microbial strains for plant protection are those possessing not only a direct target effect but also the ability to increase plant disease resistance due to phytoregulatory activity (I.I. Novikova, 2016). The holistic concept of microbiological protection involves the development and use of biological products based on living cultures of entomopathogenic microorganisms and antagonistic microbes with preventive and prolonged action, as well as formulations based on metabolite complexes to quickly reduce the density of phytopathogen populations (I.I. Novikova et al., 2016). Creating multifunctional biological products for plant protection is based on technological strains with high biological activity that are safe for humans and warm-blooded animals. It has been shown that the role of entomopathogenic viruses, microsporidia, bacteria and fungi in the dynamics of the number of phytophagous insects is determined by the type of pathogenesis (obligate or facultative). In case of intracellular obligate parasitism of baculoviruses and microsporidia, mass epizootics were observed in unpaired silkworms ( Lymantria dispar Linnaeus), leafworms (family Tortricidae Latreille), cabbage whitewash ( Pieris brassicae Linnaeus), meadow and corn moths ( Loxostege sticticalis Linnaeus, Ostrinia nubilalis Hübner), ginger pine ( Neodiprion sertifer Geoffroy) and black bread ( Cephus pygmeus Linnaeus) sawflies, Siberian silkworm ( Dendrolimus sibiricus Tschetverikov), cotton ( Helicoverpa armigera Hübner) and gray grain scoops ( Apamea anceps Denis & Schiffermüller) (I.V. Issy, 1986; A. Vey et al., 1989; A.N. Frolov et al., 2008; V.A. Pavlyushin et al., 2013). The regulatory role of Entomophthora infection is most pronounced in various species of aphids and some species of locusts (G.R. Lednev et al., 2013). For facultative parasitism which is characteristic of entomopathogenic fungi of genera Beauveria , Metarhizium , Lecanicillium , etc. (E. Quessada-Moraga et al., 2004), as well as bacteria of Bacillus thuringiensis group (N.V. Kandybin, 1989) and genus Xenorhabdus members, the most important factor of virulence is toxigenicity against host insects (M. Faria et al., 2007). Hydrolytic enzymes (chitinases, lipases, proteases), toxins, and antiphagocytic defense are factors of virulence of entomopathogenic fungi. Microbiological protection of plants from diseases is based on the use of highly competitive strains that synthesize complexes of hydrolases and biologically active compounds and efficiently colonize suitable ecological niches (I.V. Maksimov et al., 2015; I.I. Novikova, 2016; I.I. Novikova et al., 2016). A number of active compounds produced by rhizosphere microorganisms possess elicitor activity and trigger induced resistance (J.W. Kloepper et al., 2009; N. Ohkama-Ohtsu et al., 2010). The effectiveness of biologicals developed at the All-Russian Research Institute of Plant Protection against the main harmful diseases of crops reaches 60-90%, which provides a 20-25 % increase in productivity and improves the quality of crop production (I.I. Novikova, 2017). The plant microbiological protection concept relies on the search for promising producers of novel biologicals among wider range of microbial species and strains, on the design of new formulations optimal in specific environmental conditions, and on biological plant protection and integrated plant protection management which combines biological products for various purposes depending on the specific complex of plant pathogens and the local phytosanitary situation in general (N.A. Belyakova et al., 2013).