Field Characterization of Partial Resistance to Gray Leaf Spot in Elite Maize Germplasm

Abstract

Forty-eight inbred lines of maize with varying levels of resistance to gray leaf spot (GLS) were artificially inoculated with Cercospora zeina and evaluated to characterize partial disease resistance in maize under field conditions from 2012 to 2014 across 12 environments in western Kenya. Eight measures of disease epidemic—that is, final percent diseased leaf area (FPDLA), standardized area under the disease progress curve (SAUDPC), weighted mean absolute rate of disease increase (ρ), disease severity scale (CDSG), percent diseased leaf area at the inflection point (PDLAIP), SAUDPC at the inflection point (SAUDPCIP), time from inoculation to transition of disease progress from the increasing to the decreasing phase of epidemic increase (TIP), and latent period (LP)—were examined. Inbred lines significantly (P < 0.05) affected all measures of disease epidemic except ρ. However, the proportion of the variation attributed to the analysis of variance model was most strongly associated with SAUDPC (R2 = 89.4%). Inbred lines were also most consistently ranked for disease resistance based on SAUDPC. Although SAUDPC was deemed the most useful variable for quantifying partial resistance in the test genotypes, the proportion of the variation in SAUDPC in each plot was most strongly (R2 = 93.9%) explained by disease ratings taken between the VT and R4 stages of plant development. Individual disease ratings at the R4 stage of plant development were nearly as effective as SAUDPC in discerning the differential reaction of test genotypes. Thus, GLS rankings of inbred lines based on disease ratings at these plant developmental stages should be useful in prebreeding nurseries and preliminary evaluation trials involving large germplasm populations.

Genetic association of agronomic traits with partial resistance to gray leaf spot in elite maize germplasm

“…Of the six disease variables used to quantify resistance, SAUDPC explained the greatest proportion of the variation ( R 2 = 89.4%) in the ANOVA model. Among other factors (Nyanapah et al., 2020), SAUDPC was thus selected as the primary disease variable for subsequent evaluation of the relationship between GLS resistance and agronomic traits.…”

“…To limit specific host × pathogen interaction that would confound host genotype × environment interaction, a wildtype mixed population of C. zeina was used to inoculate plants between V2 and V3 growth stage as described by Nyanapah et al. (2020).…”

“…Five measures of disease severity, that is, percent diseased leaf area (PDLA), CIMMYT (1985) disease severity grade (CDSG), final PDLA (FPDLA), standardized area under disease progress curve (SAUDPC), and percent diseased leaf area at the inflection point (PDLA IP ) and two disease resistance components, that is, late period (LP) and the weighted mean absolute rate of disease increase (ρ), were quantified and reported as described by Nyanapah et al. (2020).…”

“…The most useful disease assessment or resistance component variable to quantify disease resistance for inclusion in the genetic analyses was determined as described by Nyanapah et al. (2020). The ANOVA of appropriately corrected data of each trait nested within trial environments were all based on the following linear model: $${Y}_{ijkx} = {{{\mu}}}_x + {G}_{ix} + {R}_{jx} + {e}_{ijkx}$$, where x is the trait of interest, and all other variables are as described above.…”

Multi‐parental QTL mapping of resistance to white spot of maize (Zea mays) in southern Brazil and relationship to QTLs of other foliar diseases

“…Daniels (Nyanapah et al, 2020) with the first being predominant in Brazil (Kuki et al, 2018). The pathogens causing GLS are necrotrophic fungi that produce greyish rectangular lesions on maize leaves.…”