The parental inbred lines of the Nested Association Mapping (NAM) population of corn show sources of resistance to tar spot in northern Indiana

Authors: Singh, Raksha; SHIM, SU - Purdue University; TELENKO, DARCY - Purdue University; Goodwin, Stephen - Steve

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2022
Publication Date: 2/14/2023
Citation: Singh, R., Shim, S., Telenko, D., Goodwin, S.B. 2023. Parental inbred lines of the Nested Association Mapping (NAM) population of corn show sources of resistance to tar spot in northern Indiana. Plant Disease. 107(2):262-266. https://doi.org/10.1094/PDIS-02-22-0314-SC.
DOI: https://doi.org/10.1094/PDIS-02-22-0314-SC

Interpretive Summary: Tar Spot is a disease of corn, caused by the fungus Phyllachora maydis, that was first identified in the United States in 2015. This pathogen is a major threat to corn production in the United States and other countries. To reduce yield loss, it is important to identify maize that is most resistant to P. maydis. In this study, 26 corn lines were evaluated over a three-year period. Though all 26 corn lines tested were susceptible to some extent, some showed significantly less disease than others. Nine corn lines were tolerant, six were moderately tolerant, two were moderately susceptible, and the remaining eight were susceptible. This study provides a source of new genes for tar spot resistance in corn.

Technical Abstract: Tar spot is a major foliar disease of corn caused by the obligate fungal pathogen Phyllachora maydis, first identified in Indiana in 2015. Under conducive weather conditions P. maydis causes significant yield losses in the U.S. and other countries constituting a major threat to corn production. Relatively little is known about resistance to tar spot other than a major quantitative gene that was identified in tropical maize lines. To test for additional sources of resistance against populations of P. maydis in North America, twenty-six parental inbred lines of the Nested Associated Mapping (NAM) population were evaluated for tar spot resistance in Indiana in replicated field trials under natural infection for 3 years. Tar spot disease severity was scored visually using a 0 to 100 % scale. Maximum disease severities (MDS) for tar spot scoring at reproductive growth stage ranged from 0 to 48.3 % with 0% being most resistant and 48.3% being most susceptible. Nine inbred lines were resistant to P. maydis with MDS ranging from 0 to 5.0%, six were moderately resistant (5.2 to 10.6% MDS), two were moderately susceptible (11.7 to 26.0% MDS) and the remaining eight inbred lines were rated as susceptible (30.0 to 48.3% MDS). There was some variability between years, due to higher disease pressure after 2019. Inbred B73, the common parent of the NAM populations, was rated as susceptible with MDS of 30.0%. The nine highly resistant lines provide a potential source of new genes for genetic dissection and mapping of tar spot resistance in corn.