Evaluation efficiency of severity of angular leaf spot in common bean based on diseased and healthy leaf area

Rafael Augusto Da Costa Parrella,João Bosco Dos Santos,Nádia Nardely Lacerda Durães Parrella,Diego Velásquez Faleiro E Silva

doi:10.1590/s1984-70332013000300005

Abstract

This study compared severity of angular leaf spot in common bean lines, based on the healthy and diseased leaf area, and the graded scale. We used 12 common bean lines in the dry and rainy seasons. Two contiguous experiments were conducted in each season, with and without chemical control of the pathogen. We evaluated the percentage of the healthy and diseased leaf area; severity based on a graded scale and the area under the disease progress curve; and yield. The diseased or healthy leaf area is efficient to evaluate the severity of angular leaf spot with a sample of 20 to 30 leaflets per plot. For all traits, the results of central and border areas did not differ, indicating that the evaluation of border rows is unnecessary and, finally, the severity assessment of the upper plant half can discriminate the lines more efficiently.

Highlights

Common bean (Phaseolus vulgaris L.) is one of the most important constituents of the diet of Brazilian people, mainly because of its tradition and nutritional qualities (Borém and Carneiro 2006, Silva et al 2012)
The score evaluation is little correlated with grain yield (Bergamin Filho et al 1995, Jesus Júnior et al 2003, Couto et al 2005), which complicates the decision-making in breeding programs for resistant and high-yielding cultivars
The lack of correlation between score evaluation and grain yield is due to the lifetime and absorption of the healthy leaf area of the host rather than of the diseased area, on which the graded scales are based (Bergamin Filho et al 1995)

Summary

Introduction

Common bean (Phaseolus vulgaris L.) is one of the most important constituents of the diet of Brazilian people, mainly because of its tradition and nutritional qualities (Borém and Carneiro 2006, Silva et al 2012). In breeding programs for selection of resistant genotypes, the main form of assessment of the severity of angular leaf spot is by means of a graded scale, with scores ranging from 1 to 9, based on visual ratings (Godoy et al 1997). This kind of evaluation is subjective and depends on the experience of the evaluator. The lack of correlation between score evaluation and grain yield is due to the lifetime and absorption of the healthy leaf area of the host rather than of the diseased area, on which the graded scales are based (Bergamin Filho et al 1995)

Objectives

Methods

Results