Background: Rice genotypes exhibit notable diversity in grain zinc content, with wild types accumulating higher levels than cultivated varieties, even in zinc-deficient soils. This study focuses on the wild rice genotype Karuppunel (Zn tolerant), along with cultivated varieties CO51 (Zn responsive) and ADT39 (Zn sensitive). The research explores the relationship between the composition of organic acids in root exudates, proton efflux and root length at various growth stages under both +Zn and -Zn conditions. 
 
Methods: The experiment was conducted by growing rice genotypes Karuppunel, CO51 and ADT39 under two different zinc applied conditions. Non target based metabolomics was done to study the alterations in organic acid composition in root exudates using LC-MS/MS. Proton efflux was studied by the methodology given by Bashan et al.,&nbsp;(1989) and root length was measured from the plant&rsquo;s base to the tip of the longest root. The data was analyzed by using Metaboanalyst 5.0 software and Origin Pro 2023b, version 10.0.5.157. 
 
Result: By non-target metabolomics we identified 14 organic acids were identified in rice root exudates across growth stages in response to zinc. Random Forest analysis&rsquo;s variable importance plot consistently highlights nicotinic acid in Karuppunel, regardless of zinc conditions. Karuppunel exhibits higher proton efflux of 4.23 and 5.12 &igrave;mole H+ g fresh weight-1 h-1 followed by CO51 i.e., 3.76 and 4.14 &igrave;mole H+ g fresh weight-1 h-1 under +Zn and -Zn respectively, while ADT39 shows lower proton efflux. Despite varying zinc conditions, root length increases across stages, with Karuppunel consistently having the highest length, particularly at grain-filling of 16.65 cm under +Zn and 15.75 cm under -Zn. Understanding these physiological changes may contribute valuable insights for breeders in designing zinc nutrient acquisition-focused breeding programs.

Changes in Organic Acid Composition, Proton Efflux and Root Length in Rice Genotypes Differing in Grain Zinc Accumulation Efficiency

Background: Rice is a vital staple food for a large part of the global population and zinc deficiency poses health risks, particularly in rice-dependent regions. Studying genotypic differences in rice seed zinc content is vital for breeding zinc enriched varieties to address malnutrition and enhance food security. In the plant microbe partnership exploring the role of seed bacterial endophytes in influencing the plant physiology holds promise for Zn accumulation contributing to the broader goals of enhancing food quality, nutrition and crop production in a world facing increasing agricultural demands and challenges. 
 
Methods: Rice genotypes were surveyed and their seed zinc content was analysed using non-destructive X-ray fluorescence spectrometry. Surface sterilization of rice seed samples was performed to isolate endophytic bacteria, involving a series of treatments with distilled water, ethanol and sodium hypochlorite to remove surface microflora. The sterilized seeds were then macerated and diluted to obtain a countable number of colonies, which were subsequently spread-plated on nutrient agar, tryptic soy agar and soil extract agar to enumerate the different nutritional types of seed endophytic microflora. 
 
Result: In this study, 34 different rice genotypes, comprising traditional landraces and modern cultivars, were collected and analysed for their inherent zinc content. One variety in each category of low, medium and high seed Zn content was selected. The occurrence of all nutritional types of bacterial and their population was highest in the genotype Karuppunel followed by CO51 and ADT 39. Nutrient agar was found to promote a higher count of culturable bacterial endophytes compared to Tryptic soy agar and Soil extract agar.

Changes in Organic Acid Composition, Proton Efflux and Root Length in Rice Genotypes Differing in Grain Zinc Accumulation Efficiency

Survey of Rice Genotypes of Southern India for Seed Zinc Concentration to Explore its Seed Endophytic Microbial Diversity