Impact of Culturable Endophytic Bacteria on Soil Aggregate Formation and Peanut (Arachis hypogaea L.) Growth and Yield Under Drought Conditions.

The profile of endophytic bacteria in groundnut and their potential contribution to the reduction of drought stress are incompletely understood. Therefore, the current study is concentrated on examining the groundnut-culturable endophytic bacterial diversity, which has practical implications for reducing drought stress. Polyethylene glycol (PEG 6000) was used to identify the osmotic stress-tolerant bacterial isolates, and 51 strains were selected based on their tolerance. Fourteen potential bacterial strains with drought alleviation capacity and plant growth-promoting properties were selected and their identity was confirmed using 16S rRNA analysis. These isolates were positive for 1-aminocyclopropane-1-carboxylate deaminase, ammonia, minerals solubilization, and indole acetic acid. When applied to the groundnut seeds under water deficit conditions, the bacterial consortium (A. deltaense AMT1/Rhizobium sp. (N-Fixer) Caballeronia zhejiangensis BPT9 (PSB), Burkholderia dolosa BPT8 (KRB), and Bacillus safensis BPT6 (Drought-Mitigating Isolate)) increased the peanut germination by 91%. Soil application improved the aggregate formation. Further testing was carried out in the pot culture, where bacterial consortium improved the shoot length, root length, relative water content, chlorophyll content, nodule number, oil content, and kernel yield at 75% Water Holding capacity (WHC). Moreover, the treatment with bacterial consortia further stimulated the drought-protective mechanisms and resulted in higher efficiency of nitrogen, phosphorous, potassium uptake, electrolytes leakage, and soil enzymes such as dehydrogenase and alkaline phosphatase at 75% WHC. Microbial consortia inoculation controlled groundnut water absorption, photosynthetic performance, and stress metabolites, reducing drought-induced damage; hence, it is believed that endophytes have potential application in the improvement of yields of crops.

Microbial and genetic ecology of tropical Vertisols under intensive chemical farming.

There are continued concerns on unscientific usage of chemical fertilizers and pesticides, particularly in many developing countries leading to adverse consequences for soil biological quality and agricultural sustainability. In farmers' fields in tropical Vertisols of peninsular India, "high" fertilizer and pesticide usage at about 2.3 times the recommended rates in black gram (Vigna mungo) did not have a deleterious effect on the abundance of culturable microorganisms, associative nitrogen fixers, nitrifiers, and 16S rRNA gene diversity compared to normal rates. However, "very high" application at about five times the fertilizers and 1.5 times pesticides in chilies (Capsicum annuum) adversely affected the populations of fungi, actinomycetes, and ammonifiers, along with a drastic change in the eubacterial community profile and diversity over normal rates. Actinobacteria were dominant in black gram normal (BG1) (47%), black gram high (BG2) (36%), and chili normal (CH1) (30%) and were least in chili very high (CH2) (14%). Geodermatophilus formed 20% of Actinobacteria in BG1 but disappeared in BG2, CH1, and CH2. Asticcacaulis dominated at "very high" input site (CH2). Diversity of nitrogen fixers was completely altered; Dechloromonas and Anaeromyxobacter were absent in BG1 but proliferated well in BG2. There was reduction in rhizobial nifH sequences in BG2 by 46%. Phylogenetic differences characterized by UniFrac and principal coordinate analysis showed that BG2 and CH2 clustered together depicting a common pattern of genetic shift, while BG1 and CH1 fell at different axis. Overall, there were adverse consequences of "very high" fertilizer and pesticide usage on soil microbial diversity and function in tropical Vertisols.