Mining Saline Soils to Manifest Plant Stress-Alleviating Halophilic Bacteria.

The connection between soil and microbes plays a critical role in soil health and quality and can be elastic with the application of soil amendments and/or crop rotations. Inappropriate management of soil and application of impermissible levels of fertilizers ruptures the overriding connection between the soil and microbes. This is currently evidenced in the degraded soils (i.e., saline soils of India) which are caused by modern agricultural practices. Reclamation of saline soils with a saturated package of practices and conventional breeding methods requires biological intervention. Shortfall of nutrients is one of the chief constraints for plant growth in salt-affected soils. In the present investigation, we have observed an arsenal of fifty halophilic bacteria carrying an absolute requirement of 3% NaCl for solubilizing the insoluble minerals (ZnCO3, ZnO, Mica and tri-calcium phosphate) under in vitro conditions; however, increasing the amount of NaCl over and above resulted in loss of solubilization capacity. Of the isolates solubilizing zinc carbonate and zinc oxide at 3% NaCl concentration, there were 29 isolates; at 10% concentration, 10 isolates were positive for the presence of zinc carbonate. At 3% NaCl concentration, HB-5 showed 23.16 mm zinc carbonate solubilization, HB-20 showed 13.3 mm Zinc oxide solubilization, and HB-7 showed 13.4 mm tri-calcium phosphate solubilization. Mica solubilization was peaked at 6% NaCl and maximum solubilization was observed in HB-27 (18.03 mm). When compared to the zinc carbonate solubilization, zinc oxide solubilization was slow to reach desired levels. Solubilization lasted for up to 9 days and ceased thereafter in all the tests. Eight elite isolates were identified as Bacillus albus, Bacillus safensis, Pseudomonas stutzeri (2), Lysinibacillus sphaericus, Staphylococcus xylosus, and Bacillus cereus (2) based on 16S rRNA analysis.

Off-season survival and life history of beet armyworm, Spodoptera exigua (Hubner) on various host plants.

The beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae), has become a significant pest of chickpea in recent years. The polyphagous nature allows it to survive on various hosts during the off-season, creating a great menace to the crop in the following season. To assess the incidence and document the alternate hosts of S. exigua, a rapid roving survey was conducted in 11 chickpea-growing areas of Prakasam district, Andhra Pradesh, India. Additionally, the life history traits of S. exigua were studied on major alternate host plants under laboratory conditions (27 ± 1 °C and 70 ± 2% RH) to understand the survival, life expectancy and potential contribution to future populations. The results show that, among the different crops surveyed, the maximum larval incidence was noticed in maize (1.93 larvae/plant), cowpea (1.73 larvae/plant), and sunflower (1.68 larvae/plant) during the off-season. Life history studies of S. exigua showed that highest larval survival percentage was observed on chickpea (83.6%), while the lowest was on maize (44.5%). The mean developmental time for larvae was longest on maize (27.1 days) and shortest on chickpea (14.9 days). Larvae did not develop beyond the third instar when fed with chilli. The growth index statistics showed chickpea (9.2) was the most suitable host plant, whereas maize (0.9) was the least suitable host. The age-stage-specific survival rate (Sxj) varied across developmental stages, and the survival curves overlapped, indicating different growth rates among individuals. The life expectancy (exj) at age zero was highest on groundnut (37.06 days). The intrinsic rate of increase (r) of S. exigua was lowest on maize (0.10 ± 0.0013) and highest on chickpea (0.22 ± 0.0010). Similarly, the net reproductive rate (R0) was highest on chickpea (846.39 ± 18.22) and lowest on maize (59.50 ± 2.06). The population doubled every 3.08 ± 0.011 days on chickpea compared to 7.22 ± 0.80 days on maize. The study conclusively indicates that chickpea and sunflower, primarily cultivated during the rabi season in India, are the most preferred hosts for S. exigua. In contrast, maize and cotton, mainly grown during the kharif season, are less preferred and merely support the pest's survival. Consequently, S. exigua switches hosts between different crops growing seasons, so effective management of S. exigua during the kharif season can help prevent pest outbreaks during the rabi season.

ROS generated from biotic stress: Effects on plants and alleviation by endophytic microbes.

Aerobic living is thought to generate reactive oxygen species (ROS), which are an inevitable chemical component. They are produced exclusively in cellular compartments in aerobic metabolism involving significant energy transfer and are regarded as by-products. ROS have a significant role in plant response to pathogenic stress, but the pattern varies between necrotrophs and biotrophs. A fine-tuned systemic induction system is involved in ROS-mediated disease development in plants. In regulated concentrations, ROS act as a signaling molecule and activate different pathways to suppress the pathogens. However, an excess of these ROS is deleterious to the plant system. Along with altering cell structure, ROS cause a variety of physiological reactions in plants that lower plant yield. ROS also degrade proteins, enzymes, nucleic acids, and other substances. Plants have their own mechanisms to overcome excess ROS and maintain homeostasis. Microbes, especially endophytes, have been reported to maintain ROS homeostasis in both biotic and abiotic stresses by multiple mechanisms. Endophytes themselves produce antioxidant compounds and also induce host plant machinery to supplement ROS scavenging. The structured reviews on how endophytes play a role in ROS homeostasis under biotic stress were very meager, so an attempt was made to compile the recent developments in ROS homeostasis using endophytes. This review deals with ROS production, mechanisms involved in ROS signaling, host plant mechanisms in alleviating oxidative stress, and the roles of endophytes in maintaining ROS homeostasis under biotic stress.