Parental Inbred Lines of the Nested Association Mapping (NAM) Population of Corn Show Sources of Resistance to Tar Spot in Northern Indiana

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 analysis and mapping of tar spot resistance in corn.

Uncovering the environmental conditions required for Phyllachora maydis infection and tar spot development on corn in the United States for use as predictive models for future epidemics

“…As P. maydis continues to establish itself across several states in the U.S., an integrated management approach to mitigate the yield losses is needed. Partial genetic resistance for tar spot has been identified in corn germplasm 13 , 14 , but many current commercial corn hybrids are considered highly susceptible. Fungicides are currently the most effective method for reducing tar spot development and yield losses, especially when two or three fungicide classes are used 15 .…”

Tar spot disease of sorghum plants caused by Phyllachora sp. in Bogor, Gunung Kidul and West Lombok, Indonesia

“…From these numbers, we can conclude that the Latu Keta sorghum variety has much greater resistance to tar spot disease than the Samurai variety, which is susceptible to tar spot disease. The percentage number 32.4% in the Letu Keta variety according to Singh et al (2022) from the Maximum Disease Severities (MDS) for tar spot is susceptible (30.0-48.3% MDS), which means medium severity of tar spot. According to the MDS number, the percentage number of 87.9% in Samurai variety is the most susceptible (more than 48.3% MDS) or high severity of tar spot.…”

Pseudomonas syringaepv.tomatoDC3000 induces defense responses in diverse maize inbred lines

“…The maize Nested Association Mapping (NAM) recombinant inbred lines (RILs) representing global maize diversity were derived from twenty-six inbred founder lines and are a valuable genetic resource for discovering allelic diversity against plant pathogens of maize (Gage et al, 2020; Singh et al, 2023). For example, Kump and colleagues (2011) used the NAM population to identify thirty-two quantitative trait loci associated with resistance to Cochliobolus heterostrophus , the causative pathogen of Southern Leaf Blight disease, in maize.…”