Spot blotch disease of wheat as influenced by foliar trichome and stomata density

Spot blotch, caused by Bipolaris sorokiniana, is a potent biotic constraint to wheat crop leading to substantial yield abatement in warm humid South Asia (e.g. India, Nepal and Bangladesh) and other major wheat-growing countries such as Canada, the United States, Brazil and Australia. A set of 98 bread wheat genotypes were evaluated over two growing seasons to investigate the relationship among foliar trichome, stomata density, and susceptibility to the spot blotch pathogen. The higher density of trichomes (90-140 mm(-2)) on the adaxial surface of flag leaves entrapped 32-74 mm(-2) pathogen spores. It restricted the dew droplets size (0.15-0.3 mm(2)) on the flag leaves and thus prevented direct contact between the spores and the leaf epidermis. Trichome density was negatively associated with the disease development and spore germination but positively associated with grain size and the number of spores entrapped on trichomes per mm(2). Conversely, stomata density was positively associated with the development of the disease. Cluster and principal component analyses divided trichome density, the number of spores trapped on trichome per mm(2), and thousand grain weight into one group and stomata density, the area under disease progress curve, percent spore germination, and dew scale into another group. The results from this study provided a novel insight to breeders where the selection of bread wheat genotypes with high trichome (90-140 mm(-2)) and low stomata density (72-90 mm(-2)) on foliage could enhance spot blotch resistance in wheat.