Thermotolerant and Halotolerant Endophytic Bacteria from Karbala, Iraq: Promising Biocontrol Agents against Xanthomonas gardneri

Abstract

Tomato is Significant for Iraq's food security and agricultural economy. Primarily serving regional and national markets, the Al-Sharia agricultural area in Karbala Governorate serves as a major production hub. Most especially bacterial spot brought on by Xanthomonas gardneri, phytosanitary problems always threaten the viability of this sector. This pathogen causes extreme defoliation and fruit damage, which results in major financial losses. Certain unique environmental conditions make disease control in Iraq more challenging. The region is defined by calcareous soils and summer temperatures typically exceeding 40°C. These conditions not only help the pathogen to spread through irrigation but also make some of the commercially available biocontrol products from temperate regions less effective. These products usually have trouble surviving in such challenging environments. The reliance on copper-based bactericides has raised concerns about environmental pollution and the development of resistant pathogen strains. Consequently, biological control using endophytic bacteria looks to be a wise choice. This study aimed to find local endophytic bacteria fit for these circumstances and determine their capacity to ward off other bacteria. Sixty bacterial isolates were obtained; seventeen different endophytes selected for characterization were discovered. Koch's postulates supported confirmation of the local X. gardneri isolate's pathogenicity. On the basis of phenotypic and biochemical characteristics, the promising isolates were distributed among the Bacillus and Pseudomonas genera. Significantly, isolates KSH-04 and KSH-07 (Pseudomonas sp.) were quite resilient; they grew at 5% NaCl concentrations and 42°C. In vitro studies revealed significant antagonism against X. gardneri linked to siderophore production. Greenhouse studies showed that, in comparison to the control, pre-treating with these stress-tolerant isolates reduced disease severity by more than 50%. According to this study, selecting ecologically friendly strains is vital as it offers a sustainable means of tomato production in dry and salty agroecosystem .