Evaluation location: Iowa, United States
Three hundred and eighty-four maize accessions were tested for resistance to Stewart's wilt, caused by Pantoea (Erwinia) stewartii. Plots were planted on 20-May-2005 at the NCRPIS farm at Ames, IA. Accessions were grown in three replications with 15-18 plants per plot. Two inoculations were done using the pinprick method, with one week between inoculations. The early maturing entries were inoculated on 17-JUN (6 to 8-leaf) and on 24-JUN. The rest of the entries were inoculated on 24-JUN and 30-JUN. Inoculum was grown from a mixture of two P. stewartii isolates of Iowa origin. Ratings were done by maturity (>50% of plants in plot with brown, dry silks) and took place from 21-JUL to 06-SEP. Individual scores (10-12 plants) were averaged to obtain plot ratings. Scores for the three plots were averaged for each accession. 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= lesions spread to the main 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 symptomatic; 8= severe systemic infection and stunting with 50-90% of the plant infected; and 9= 90-100% infection, severe necrosis or dead. Six inbreds were used as checks, Mo21R (resist.), B37 Ht (mod. res.), A629 (mid-check), A632 Ht (mod. susc.), Mt42 (mod. susc.) and C42 (very susc.). Disease development was nearly optimal with good separation of resistance.