Diplodia Ear Rot Resistance Qtl Identified In Maize (Zea Mays L.) Using Multi-Parent Double-Haploid Population Mapping

Diplodia ear rot (DER) caused by Stenocarpella maydis is one of the most important diseases of corn (Zea mays L.) that significantly affects its yield performance. A report from Wise et al. (2017) suggests yield loss in maize fields varying from 1-2% to as high as 80%. Symptoms of the disease are characterized generally by white mold in the ears, and small, black pycnidia produced by the fungus. Resistance to S. maydis is quantitatively inherited and highly influenced by environment. Studies were conducted in 2018 and 2019 wet seasons in Bukidnon, Philippines to locate QTL and marker positions involved in resistance to DER utilizing multi-parent double-haploid populations (MPDHP). A total of 720 in 2018 and 760 lines in 2019 were planted in augmented RCB design, resistant and susceptible checks were included in the study. Each line was artificially inoculated 15 days after silking. Genotyping was done using 15K Axiom (R) marker chip developed by Syngenta. QTL associated with DER were detected using composite interval mapping (CIM) with mppR package in R focusing on ancestral and multi-QTL effects (MQEs) model. Heritability estimate observed in 2018 (0.468) was relatively similar in 2019 (0.549). Using 2018 Diplodia Ear Rot Percentage (DLERP) data, QTL in chromosome (chr) 5 (394.1-396.5cM) was detected. MQEs model revealed two QTL located at chr 3 (8.3cM, biall) and chr 5 (395.6cM, par). QTL genetic effects for ancestral and MQEs models were estimated at 7.18% and 10.95%, respectively. In 2019, three QTL were identified on chr. 1 (446.5-551.2cM), chr. 5 (349.7-364.6cM), and chr 10 (174.2-213.0cM). MQEs revealed five QTL located at, chr. 1a (481.0cM, biall), chr. 1b (551.2cM, biall), chr. 2 (83.6cM, biall), chr. 5 (356.8cM, biall), and chr 10 (235.0cM, par) linked to DER. QTL genetic effects for the two models were estimated at 9.39% and 15.84%, respectively. Putative QTL was identified on chromosome 5 (qder5) across models and across years. Further implementation of multi-parent population (MPP) approach in different genetic backgrounds is recommended to validate consensus QTL identified in chromosome 5 conferring resistance to DER.