Epicuticular wax content for shoot fly resistance in sorghum

Abstract

Epicuticular wax is an important trait in plant defense against insect pests. Its structure and morphology is known to contribute for antixenosis (host non-preference) resistance mechanism in several crop species. In this study, we report the differences in morphology and structure of epicuticular wax content using 168 recombinant inbred lines (RILs) developed from 296B (susceptible) and IS18551 (resistant) sorghum parents, and correlate with shoot fly resistance. Scanning electron microscope was used to study the variations in leaf surface wax morphology. The resistant parent (IS18551) and the resistant RILs showed smooth amorphous wax layer (glossy leaf morphology) which was significantly distinct from a dense meshwork of crystalline epicuticular wax layer (non-glossy) observed in susceptible parent (296B) and the susceptible RILs. The group differences in wax load on the leaf surface between the susceptible and resistant RILs was significant, which corresponded well with the high wax load observed in susceptible parent, 296B (8 µgcm-2) and low wax load of IS18551 (4 µgcm-2) respectively. The RIL phenotypic data for wax load was used for marker-trait association using single marker analysis (SMA). SMA identified 10 SSR markers significantly linked with epicuticular wax content. Of these, four SSRs co-located with QTL for shoot fly resistance traits reported earlier by our group. Two SSRs, XnhsbmSFC61E (on SBI-05) and Xtxp83 (on SBI-06) showed significant association with leaf epicuticular wax variation among the RILs. Co-location of QTL for leaf surface glossiness and epicuticular wax content on SBI-05 linked with XnhsbmSFC61, a genic marker, validated the role of wax in leaf surface glossiness. The study identified putative genomic regions with significant involvement in epicuticular wax content for shoot fly resistance. The results confirmed the role of morphological, structural differences of epicuticular wax in shoot fly resistance, identified major genomic regions tagged with SSR markers for marker-assisted breeding for shoot fly resistance in sorghum.