Histochemical Analysis for Lignin Differences Between Reniform Nematode-Resistant and Susceptible Cotton Genotypes

Reniform nematodes (Rotylenchulus reniformis) are a major constraint on cotton production, particularly in the southern United States. The reniform nematode is the second most important pest among more than 400 nematode species. These nematodes pose a threat to global food security. Increasing environmental and human health concerns and the cost of nematicides have intensified interest in resistant cotton germplasm. The plant cell wall, especially lignin, is a critical biopolymer involved in resistance to biotic stress. Because nematodes infect root tissues, cell wall components such as lignin may contribute to defense; however, lignin-mediated barriers in cotton roots are not well characterized. This study employed a standardized phloroglucinol-HCl histochemical staining protocol to visualize lignin deposition differences in reniform nematode-resistant (A2-514, A2-995) and susceptible cotton (Gossypium arboreum) genotypes at the true leaf stage under non-infected conditions. This stain binds specifically to hydroxy cinnamylaldehyde such as coniferyl aldehyde and sinapyl aldehyde of lignin in the presence of acid and generates a pinkish purple color to visualize lignin. Distinct lignin staining patterns were observed between resistant and susceptible genotypes, supporting a potential role for lignin-associated structural defenses.