Evaluation location: Iowa, United States
Two hundred and eight maize accessions were tested for resistance to Stewart's wilt caused by Pantoea (Erwinia) stewartii. Plots were planted on 08-June-2013 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 10-JUL at the 6 to 8-leaf stage and on 16-JUL at the 8 to 10-leaf stage. Inoculum was produced from a mixture of three isolates, ES9239, ES9245, and ES9264 (Iowa origin). Disease ratings were done from 26-AUG to 31-AUG. 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. Seven inbreds were used as checks, WIL500 (highly resist.) with an average rating of 1.0, Mo21R (resist.) with an average rating of 1.6, B37 Ht (mod. res.), with an average rating of 2.7, A629 (mid-check) with an average rating of 4.0, A632 Ht (mod. susc.) with an average rating of 6.5, Mt42 (very susc.) with an average rating of 8.0 and C42 (highly susc.) with an average rating of 8.4.