Ultrastructural and morpho-anatomical features of rice plants confer first-level of defense against yellow stem borer (Scirpophaga incertulas Walker) infestation

Yellow stem borer (YSB) is a serious pest of rice throughout the year in Asia and causes 40-50% yield loss. Screening genotypes and breeding resistant varieties are effective strategies for its management. The present study demonstrates the importance of ultrastructural and morpho-anatomical features of rice stem that confer resistance to YSB. A total of 188 rice genotypes were evaluated for dead heart and white ear damage of YSB. The crop booting stage of 113 genotypes coincided with peak YSB invasion. Forty-five days after transplanting (DAT), dead heart damage was recorded and 17 genotypes were found to be resistant. However, only one genotype, RG109, exhibited resistance based on white ear damage at crop maturity. Six genotypes selected based on dead heart damage were characterized for stem features using scanning electron microscopy, and their defense response against YSB was explored. Among the six genotypes, RG109 had a greater number of vascular bundles, density and width of silicified microstructures (SMS), and the density of trichomes. The elemental silica content inside and outside of the stem was mapped with SEM-supported energy-dispersive X-ray spectroscopy and found that RG109 had a higher silica content (17.85%) than the susceptible control, TN1 (1.12%), in the outer stem. Similarly, the adaxial side of the leaf blade and aerenchymatous region of the stem were studied extensively between the resistant (RG109) and susceptible (TN1) genotypes, further reiterating the differences in resistance level. Hence, surface morphological structures such as trichomes and SMS, their spatial distribution pattern and the elemental silica content hindered larval feeding behavior, which facilitates host plant-mediated YSB management in rice cultivation.