Evaluation location: Iowa, United States
One hundred and twenty-three accessions were tested for resistance to Stewart's wilt caused by Pantoea (Erwinia) stewartii. Plots were planted on 05-June-2007 at the NCRPIS farm at Ames, IA. Three single-row plots were planted per entry with 16 plants per row. Inoculations were done by the pinprick method on 28-JUN-2007 at the 6-leaf stage and again on 05-JUL-2007 at the 8-leaf stage. Inoculum was produced from a mixture of two P. stewartii isolates (Iowa origin). Disease ratings were done between 20-AUG-2007 and 09-SEP-2007, and were based on plant maturity (>50% dry silks). Individual plant scores (10-12 plants per plot) to obtain a rating for each plot and the three reps were averaged. Disease reactions were scored on a 1-9 scale where:1= no appreciable spread of symptoms from pinpricks (within 1 cm); 2= limited spread of lesions from pinpricks (within 3 cm); 3= limited spread from pinpricks with water-soaking, chlorosis, or necrosis; spread occurring mainly toward tips of leaves; 4= abundant spread from pinpricks toward both ends of inoculated leaves, but no evidence of systemic infection; 5= minimal systemic infection observed; 6= moderate systemic infection with 5-25% symptomatic leaf area on non-inoculated leaves; 7= abundant systemic infection with 25-50% of the leaf area symptomatic; 8= severe systemic infection with 50-90% of the plant infected; and 9= 90-100% infection, severe necrosis or dead. Six inbred checks were used, Mo21R (resist.) with an average rating of 1.0, B37 Ht (mod. res.) with an average rating of 3.0, A629 (mid-check) with an average rating of 3.7, A632 Ht (mod. susc.) with an average rating of 6.0, Mt42 (mod. susc.) with an average rating of 9.0 and C42 (very susc.) with an average rating of 9.0. All checks performed as expected except Mt42, which was more susceptible than normal. Disease developed very rapidly after the first inoculation, but the weather soon became hot and dry which seemed to slow further development.