Histological Study of Peanut Hull: Initial Barrier Against Fungal Invasion?

Research on the cataloging of microstructures and chemical compound localization in peanut hulls in relation to fungal tolerance remains limited. The hull (pericarp) is the first physical interface with the soil environment and may contribute to defense against fungal invasion. Here, hull microstructure and histochemical localization of alkaloid-like compounds, cellulose, lignin, starch, and total proteins were characterized across reproductive developmental stages R3-R6 in three commercially grown cultivars (Georgia-06G, Georgia-12Y, and Georgia-18RU). Stained sections were examined by light and fluorescence microscopy, and images were quantified in Fiji-ImageJ as stained area percentage. Among the compounds studied, the highest area percentages were observed at later stages (R5 and R6). Alkaloid-like compounds, cellulose, and starch were higher at the R5 stages of G-18 (9.61 ± 0.75), G-12Y (22.96 ± 5.84), and G-06 (6.31 ± 1.13) respectively, while lignin and total proteins were highest at the R6 stage of G-18 (respectively, 14.49 ± 1.43 and 13.90 ± 1.45). The lowest histochemical presence for most metabolites occurred in the early stages (R3-R4). This indicates that hull maturation is accompanied by increased physical (sclerenchyma and lignified cells) and biochemical (alkaloid-like compounds, proteins) features consistent with protective roles. As the analysis was based on representative sections and regions of interest (ROI)-level quantification, the results are intended to guide future studies on hull-mediated defense and breeding for Aspergillus tolerance.