Evaluation location: Iowa, United States
Five hundred and twelve US inbred maize accessions were tested for resistance to Stewart's wilt caused by Pantoea (Erwinia) stewartii. Plots were planted on 23-May-2006 at the NCRPIS farm at Ames, IA. Two single-row plots were planted per entry, with 15-18 plants per row. Inoculations were done by the pinprick method on 22-JUN at the 6 to 8-leaf stage and again on 29-JUN-2006. Inoculum was produced from a mixture of two P. stewartii isolates (Iowa origin). Disease ratings (one time per plot) were done between 02-AUG-2006 and 02-SEP-2006, based on plant maturity (>50% dry silks). Individual plant scores (10-12 plants) were averaged to obtain a rating for each plot and the two plots 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 with water-soaking, chlorosis, or necrosis 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 1.1, B37Ht (mod. res.), with an average rating of 3.6, A629 (mid-check) with an average rating of 4.9, A632Ht (mod. susc.) with an average rating of 5.5, Mt42 (mod. susc.) with an average rating of 6.1 and C42 (highly susc.) with an average rating of 8.2. Disease pressure was higher in 2006 than in most years with the presence of considerable natural infection.