Density, Orientation, and Distribution of Foliar Trichomes in Selected Philippine Traditional Rice Varieties with Resistance to Scirpophaga spp.

Abstract

Pest infestation restricts rice productivity and, among rice pests, the stem borers (Scirpophaga spp.) caused substantial damage of > 20% yield loss. Host resistance is considered the most effective, economical, and environmentally friendly way for rice pest management, and Philippine traditional rice varieties (TRVs) are potential sources of genes useful in breeding for pest resistance. Leaf trichomes are the first physical barrier against any invading plant pests and to characterize the quantitative variations of foliar trichomes of six selected TRVs identified to have resistance – namely, Dinorado, Hinumay, Inarciaga, RED 18, C-4 Dinorado, and Mukol – these TRVs were evaluated using digital light microscopy. RED 18 consistently had the highest trichome density (5.374–9.390/mm2) in each and across the 2018 wet season (WS), 2019 WS, and 2020 dry season (DS) – even significantly higher (P > 0.05) than the resistant check TKM6 (4.489–5.783/mm2). For trichome orientation, Mukol (59.151–71.617°), and Inarciaga (57.395–72.464°) consistently had higher and/or statistically comparable angle values to the resistant TKM6 (59.654–71.617°), across each and 2018 WS, 2019 WS, and 2020 DS (P > 0.05). Within- and between-genotype variability showed that adaxial foliar trichomes have varying density and were not uniformly distributed across the leaf surface: densest (4.560–5.456/mm2) and mostly distributed (49.086–50.532%) in the apical zone of the leaf surface, and least dense (2.623–2.834/mm2) and rarely distributed (16.439–18.806%) in the basal zone. Based on desirable trichome traits and statistical similarities to TKM6, hierarchical cluster analysis delineated RED 18, Inarciaga, and Mukol as excellent sources of trichome traits that will improve plant structural defense against stem borers.