Analysing Crop Loss in a Bean Rust Pathosystem: 1. disease progress, crop growth, and yield loss

Abstract

Progress of rust epidemics in one susceptible and one partially resistant haricot bean genotypes was manipulated by the application of a fungicide at five spray frequencies in a low external inputs production system. These resulted in differences in rust epidemics, crop growth and yield. Temporal progress of rust incidence, rust severity and crop growth indicated significant variations among treatments. Leaf area index increased with time and reached a maximum between 59 and 66 days after emergence, growth, stages at which rust severity also reached its plateau. For all parameters, progress curves showed more variation for the susceptible than for the resistant genotype. For the susceptible genotype, ‘Mexican 142’, differences between treatments were greatest during pod formation and under conditions of high disease pressure. Maximum yield loss was 85% for the susceptible, Mexican 142 and 30%
for the partially resistant genotype, ‘6-R-395’. The loss depended on location, season and resistance level of the genotype.