Northern leaf blight assay

A 2 × 2 factorial experimental design included three replications, B73 and Mo17 genotypes, and two treatments (with or without PPZ) within each replication. B73 and Mo17 were planted (n>7) in 10 cm pots (1 plant per pot) in the greenhouse. At the V6-stage, the plants were treated with either 400 µM PPZ or mock solution through soil fertilizer drenching every 3 to 4 days. Four days after the initial PPZ treatment, the plants were inoculated with a 500-µl liquid spore suspension of Setosphaeria turcica isolate NY001 (race1), containing 4000 spores/ml, into the whorl during the late afternoon. An overhead mister provided water for 10 s every 10 min for approximately 15 h. Disease phenotype was measured as the incubation period (IP), the number of days following inoculation when a necrotic lesion was first observed. Forty-eight days following inoculation, the disease measurements were concluded; a survival analysis was performed in JMP® Pro Version 13.1.0 (SAS Institute, Inc, Cary, NC, 1989–2019) to test for differences within each genotype for the effect of PPZ on IP using a log-rank test statistic and visualized in a Kaplan-Meier plot.