Evaluation location: Iowa, United States
Two hundred ninety-eight accessions were tested for resistance to Stewart's wilt, caused by Pantoea (Erwinia) stewartii. Plots were planted on 21-May-2009 at Ames, IA. Three single-row plots were planted per entry and thinned to 16 plants per row. Inoculations were done by the pinprick method on 01-JUL at the 6-leaf stage and on 08-JUL at the 8-leaf stage. Inoculum was produced from a mixture of three isolates, ES9211, ES9239 and ES9245 (Iowa origin). Disease ratings were done from 13-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= limited spread from pinpricks with water-soaking, chlorosis, or necrosis; lesions spreading mainly toward tips of leaves; 4= abundant spread of lesions in both directions on inoculated leaves, with water-soaking, chlorosis, or necrosis, but no evidence of systemic infection; 5= lesions spread to the leaf base, reaching 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. Plants with 1, 2 (highly resistant) and 3 (resistant) ratings have definite resistance. Plants with a 4,5,6 ratings are moderately susceptible and plants with a 7,8,9 ratings are highly susceptible. Six inbreds were used as checks, Mo21R (resist.) which had an average rating of 1.0, B37 Ht (mod. res.), with an average rating of 3.3, A629 (mid-check) with an average rating of 4.0, A632 Ht (mod. susc.) with an average rating of 5.1, Mt42 (very susc.) with an average rating of 7.0 and C42 (highly susc.) with an average rating of 8.1.