Evaluation location: Iowa, United States
One hundred and sixty maize accessions were tested in 2014 for resistance to Stewart's wilt caused by Pantoea (Erwinia) stewartii. Plots were planted on 11-June-2014 at Ames, IA. Three replications of single-row plots were planted per entry and thinned to 16 plants per row. Inoculations were done by the pinprick method on 15-JUL at the 6 to 8-leaf stage and on 23-JUL at the 8 to 10-leaf stage. Inoculum was produced from a mixture of three isolates, ES9211, ES9239, and ES9245 (Iowa origin). Disease ratings were done from 05-SEP to 09-SEP-2014. Ten to 12 plants were rated per plot and an average rating was calculated for each plot. Disease reactions were scored on a 1-9 scale where: 1= no appreciable spread of symptoms from pinpricks (less than 1 cm); 2= limited spread of lesions from pinpricks (1 to 3 cm); 3= lesions spreading from the point of inoculation mainly toward tips of leaves with water-soaking, chlorosis, and necrosis; 4= abundant spread of lesions in both directions on inoculated leaves, with water-soaking, chlorosis, and necrosis, but no evidence of systemic infection; 5= lesions spread to the leaf base and reach the stalk; minimal systemic infection observed; 6= moderate systemic infection with 5-25% symptomatic leaf area on non-inoculated leaves; 7= abundant systemic infection and stunting with 25-50% of the leaf area affected; 8= severe systemic infection and stunting with 50-90% of the plant infected; 9= 90-100% infection, severe necrosis or dead. Accessions with 1, 2 (highly resistant) and 3 (resistant) ratings have definite resistance. Accessions with 4,5,6 ratings are moderately susceptible and accessions with 7,8,9 ratings are highly susceptible. Six inbreds were used as checks, WIL500 (highly resist.) with an average rating of 1.0, Mo21R (resist.) with an average rating of 1.7, B37 (mod. res.), with an average rating of 3.5, A629 (mid-check) with an average rating of 3.8, A632 Ht (mod. susc.) with an average rating of 5.6, and Mt42 (very susc.) with an average rating of 8.9.