Isolation of Drought-Tolerant Endophyte Bacteria From Local Tomato Plants

Assembly and Function of Seed Endophytes in Response to Environmental Stress

Seeds are colonized by diverse microorganisms that can improve the growth and stress resistance of host plants. Although understanding the mechanisms of plant endophyte-host plant interactions is increasing, much of this knowledge does not come from seed endophytes, particularly under environmental stress that the plant host grows to face, including biotic (e.g., pathogens, herbivores and insects) and abiotic factors (e.g., drought, heavy metals and salt). In this article, we first provided a framework for the assembly and function of seed endophytes and discussed the sources and assembly process of seed endophytes. Following that, we reviewed the impact of environmental factors on the assembly of seed endophytes. Lastly, we explored recent advances in the growth promotion and stress resistance enhancement of plants, functioning by seed endophytes under various biotic and abiotic stressors.

Isolation and Screening of Antagonistic Endophytes against Phytophthora infestans and Preliminary Exploration on Anti-oomycete Mechanism of Bacillus velezensis 6-5

Phytophthora infestans, the notorious pathogen of potato late blight, leads to a severe decline in potato yields and even harvest failure. We isolated 201 endophytic isolates from healthy root tissues of potatoes, among which 41 showed strong antagonistic activity against P. infestans. Further, the tolerance to stress and the potential application against potato late blight of these antagonistic isolates were tested. Most of them were extremely tolerant to stresses such as acid-alkali, temperature, UV, salt, and heavy metal stress. However, some antagonistic isolates with excellent stress tolerance might be pathogenic to potatoes. Combining the screening results, a total of 14 endophytes had excellent comprehensive performance in all the tests. In this paper, the endophyte 6-5 was selected among them for the preliminary exploration of the anti-oomycete mechanism. Analysis of the 16S rDNA sequence revealed that 6-5 had a high homology to the corresponding sequence of Bacillus velezensis (99.72%) from the NCBI database. Endophyte 6-5 significantly inhibited the mycelial growth of P. infestans, with an inhibition rate of over 90% in vitro assays, and deformed the hyphal phenotype of P. infestans. In addition, endophyte 6-5 could secrete protease and cellulase, and produce antagonistic substances with high thermal stability, which might be helpful to its antagonistic activity against P. infestans. Furthermore, it was demonstrated that 6-5 had the ability to improve the resistance of potato tubers to late blight. In short, our study described the process of isolating and screening endophytes with antagonistic activity against P. infestans from potato roots, and further explored the potential of biocontrol candidate strain 6-5 in potato late blight control.

Drought adaptive microbes as bioinoculants for the horticultural crops

Drought stress is among the most destructive stresses for agricultural productivity. It interferes with normal metabolic activities of the plants resulting, a negative impact on physiology and morphology of the plants. The management of drought stress requires various adaptive and alleviation strategies in which stress adaptive microbiomes are exquisite bioresources for plant growth and alleviation of drought stress. Diverse drought adaptive microbes belonging to genera Achromobacter, Arthrobacter, Aspergillus, Bacillus, Pseudomonas, Penicillium and Streptomyces have been reported worldwide. These bioresources exhibit a wide range of mechanisms such as helping plant in nutrient acquisition, producing growth regulators, lowering the levels of stress ethylene, increasing the concentration of osmolytes, and preventing oxidative damage under water deficit environmental conditions. Horticulture is one of the potential agricultural sectors to speed up the economy, poverty and generation of employment for livelihood. The applications of drought adaptive plant growth promoting (PGP) microbes as biofertilizers and biopesticides for horticulture is a potential strategy to improve the productivity and protection of horticultural crops from abiotic and biotic stresses for agricultural sustainability.