Application of Endophytic Bacillus subtilis and Salicylic Acid to Improve Wheat Growth and Tolerance under Combined Drought and Fusarium Root Rot Stresses

In nature, plants are constantly exposed to a varied abiotic and biotic stresses or their combinations, limiting the productivity of major crops, including wheat. Combinations of drought and soil-borne Fusarium-instigated diseases are the most common combinations of stresses, significantly reducing wheat yield around the world. Here, were analyzed the potential of application of endophytic bacteria Bacillus subtilis (strain 10–4) together with the natural signal molecule salicylic acid (SA) to improve growth and tolerance of Triticum aestivum L. (wheat) plants under combined drought and Fusarium culmorum-instigated root rot (FRR) stresses. It was revealed that pre-sowing treatment with B. subtilis 10–4, SA, and B. subtilis 10–4 + SA, both under normal and combined drought conditions, notably reduced (by 50–80% or more) the incidence of FRR development in wheat plants, with the most notable effect for B. subtilis 10–4 + SA (wherein disease symptoms were almost absent). Moreover, B. subtilis 10–4, SA, and especially B. subtilis 10–4 + SA increased plant growth (root and shoot length, fresh and dry biomass) under normal (up to 20–50%), drought (up to 15–40%), FRR (up to 15–30%), and combined drought + FRR stresses (up to 20%), with the maximum effect for B. subtilis 10–4 + SA. Additionally, B. subtilis 10–4, SA, and B. subtilis 10–4 + SA decreased stress (drought, FRR, and combined drought + FRR)-instigated lipid peroxidation and osmotic damages of plant cells. The findings indicate that endophytic bacteria B. subtilis 10–4 alone and in a mixture with SA may be used as an effective eco-friendly agent to improve wheat growth and tolerance under the influence of drought, FRR, and combinations of these stresses

Improving the Biocontrol Potential of Endophytic Bacteria <i>Bacillus subtilis</i> with Salicylic Acid against <i>Phytophthora infestans</i>-Caused Postharvest Potato Tuber Late Blight and Impact on Stored Tubers Quality

Potato (Solanum tuberosum L.) tubers are a highly important food crop in many countries due to their nutritional value and health-promoting properties. Postharvest disease caused by Phytophthora infestans leads to the significant decay of stored potatoes. The main objective of this study was to evaluate the effects of the endophytic bacteria, Bacillus subtilis (strain 10–4), or its combination with salicylic acid (SA), on some resistance and quality traits of stored Ph. infestans-infected potato tubers. The experiments were conducted using hydroponically grown potato mini-tubers, infected prior to storage with Ph. infestans, and then coated with B. subtilis, alone and in combination with SA, which were then stored for six months. The results revealed that infection with Ph. infestans significantly increased tuber late blight incidence (up to 90–100%) and oxidative and osmotic damage (i.e., malondialdehyde and proline) in tubers. These phenomena were accompanied by a decrease in starch, reducing sugars (RS), and total dry matter (TDM) contents and an increase in amylase (AMY) activity. Moreover, total glycoalkaloids (GA) (α-solanine, α-chaconine) notably increased in infected tubers, exceeding (by 1.6 times) permissible safe levels (200 mg/kg FW). Treatments with B. subtilis or its combination with SA decreased Ph. infestans-activated tuber late blight incidence (by 30–40%) and reduced oxidative and osmotic damages (i.e., malondialdehyde and proline) and AMY activity in stored, infected tubers. Additionally, these treatments decreased pathogen-activated GA accumulation and increased ascorbic acid in stored tubers. Thus, the results indicated that endophytic bacteria B. subtilis, individually, and especially in combination with SA, have the potential to increase potato postharvest resistance to late blight and improve tuber quality in long-term storage

Effects of Endophytic Bacillus Subtilis and Salicylic Acid on Postharvest Diseases (Phytophthora infestans, Fusarium oxysporum) Development in Stored Potato Tubers

Postharvest diseases of potato lead to significant food and economic losses worldwide. The exogenous application of eco-friendly methods plays an important role in the control of postharvest decay. In this work the effects of endophytic bacteria B. subtilis (10-4, 26D) were studied in the context of two application parameters: concentration, with a range between 103&ndash;108 CFU/mL tested, and synergistic effects of the signal molecule salicylic acid (SA) (0.05 mM) on potato tubers&rsquo; resistance to Phytophthora infestans and Fusarium oxysporum during storage. The experiments were carried out on hydroponically grown potato (Solanum tuberosum L.) mini-tubers. This study demonstrates the suppressive effect of B. subtilis (10-4, 26D) on diseases of potato during storage and reveals that this effect happens in a dose-dependent manner, both individually and in combination with SA. The most effective concentrations of B. subtilis for suppression of both Ph. infestans and F. oxysporum are 108 CFU/mL (10-4 and 26D), 107 CFU/mL (10-4 + SA) and 106 CFU/mL (26D + SA). The ability of B. subtilis (10-4, 26D) to effectively penetrate and colonize the internal tubers&rsquo; tissues when applied immediately prior to storage, and the ability of SA to accelerate these processes, have been proven. B. subtilis (10-4, 26D), individually and in compositions with SA, increased ascorbic acid content and decreased pathogen-induced proline accumulation and lipid peroxidation in tubers. This indicates a protective effect conferred to cells against reactive oxygen and an extension of aging processes, manifested by a prolonged shelf life and extended preservation of fresh appearance

Role of Endogenous Salicylic Acid as a Hormonal Intermediate in the Bacterial Endophyte <i>Bacillus subtilis</i>-Induced Protection of Wheat Genotypes Contrasting in Drought Susceptibility under Dehydration

Endophytic Bacillus subtilis is a non-pathogenic beneficial bacterium which promotes plant growth and tolerance to abiotic stresses, including drought. However, the underlying physiological mechanisms are not well understood. In this study, the potential role that endogenous salicylic acid (SA) plays in regulating endophytic B. subtilis-mediated drought tolerance in wheat (Triticum aestivum L.) was examined. The study was conducted on genotypes with contrasting levels of intrinsic drought tolerance (drought-tolerant (DT) cv. Ekada70; drought-susceptible (DS) cv. Salavat Yulaev). It was revealed that B. subtilis 10-4 promoted endogenous SA accumulation and increased the relative level of transcripts of the PR-1 gene, a marker of the SA-dependent defense pathway, but two wheat cultivars responded differently, with the highest levels exhibited in DT wheat seedlings. These had a positive correlation with the ability of strain 10-4 to effectively protect DT wheat seedlings against drought injury by decreasing osmotic and oxidative damages (i.e., proline, water holding capacity (WHC), and malondialdehyde (MDA)). However, the use of the SA biosynthesis inhibitor 1-aminobenzotriazole prevented endogenous SA accumulation under normal conditions and the maintenance of its increased level under stress as well as abolished the effects of B. subtilis treatment. Particularly, the suppression of strain 10-4-induced effects on proline and WHC, which are both contributing factors to dehydration tolerance, was found. Moreover, the prevention of strain 10-4-induced wheat tolerance to the adverse impacts of drought, as judged by the degree of membrane lipid peroxidation (MDA) and plant growth (length, biomass), was revealed. Thus, these data provide an argument in favor of a key role of endogenous SA as a hormone intermediate in triggering the defense responses by B. subtilis 10-4, which also afford the foundation for the development of the bacterial-induced tolerance of these two different wheat genotypes under dehydration