Methodology to Improve the Efficiency of Evaluation of the Severity of Angular Leaf Spot in Common Bean

Disease severity assessment by means of a scoring scale, especially for angular leaf spot (Pseudocercospora griseola) in common bean, is hindered in experiments for assessment of progenies and/or breeding lines due to lack of uniformity of occurrence of the pathogens and segregation within progenies. The purpose of this study was to estimate the efficiency of the use of one plant per plot in assessing the severity of angular leaf spot in experiments for assessment of progenies and/or breeding lines in the common bean crop. To that end, two experimental strategies were used – one of them using one plant per plot and another using a standard size plot (SPP) (2–4‐m length rows). The experiments were conducted in the period from November 2011 to May 2012 in the municipalities of Lavras and Lambari, state of Minas Gerais, Brazil. Forty‐one lines from the breeding programme of the Universidade Federal de Lavras (UFLA) and from other research institutions were assessed, which differed in regard to their degree of susceptibility to P. griseola. The lines were assessed in regard to the severity of said disease using a five‐degree diagrammatic scale. In all the one plant per plot experiments, severity scores of angular leaf spot from the beginning of its occurrence, and later in intervals ranging from 7 to 12 days, were obtained. In the experiment with the SPP, assessment was made a few days prior to grain harvest. Estimates of the correlations between severity scores and grain yield (GY) were mostly of small magnitude. There was good coincidence between the lines classified as more resistant or more susceptible to the pathogen under the two conditions.