Evaluation of maize streak virus pathogenicity in differentially resistantZea mays genotypes

We devised a rapid technique for the objective and precise assessment of bo th the pathogenicity of maize streak virus (MSV) isolates and the MSV resis tance of maize genotypes. The technique involves the use of agroinoculation to infect maize seedlings and the objective symptom evaluation by quantifi cation of infection rates, stunting, and chlorotic leaf areas. In assessing the MSV resistance of 19 maize genotypes, we describe how the use of diffe rentially virulent virus isolates enables the analysis of MSV resistance ph enotypes, ranging from extremely susceptible to completely immune. We furth er demonstrate how quantification of chlorotic leaf areas by image analysis permits differentiation between degrees of MSV resistance that are indisti nguishable from one another using currently employed symptom assessment app roaches. Using chlorotic area measurements, we quantify the virulence of a diverse group of 10 MSV isolates and, through agroinoculation of differenti ally susceptible maize genotypes, we demonstrate the use of our technique i n evaluating the pathogenicity of these isolates.