Quantitative analysis of two important epidemiological features of the common bean: Phaeoisariopsis griseola pathosystem

Abstract

This work quantifies two important epidemiological features of the bean (Phaseolus vulgaris)/Phaeoisariopsis griseola pathosystem. The first is the effect of the number of nights of leaf wetness on infection efficiency. Infection efficiency was below 10% when inoculated leaflets were exposed to less than two nights of leaf wetness. Optimum infection efficiencies were obtained after three to four nights of leaf wetness, at about 50%. Further nights of leaf wetness did not increase the infection efficiency. The second feature quantified is the relative rate of leaflet defoliation for varying levels of angular leaf spot severity. It increased with disease severity according to a logarithm-like curve, and a relative rate of 0.23 day-1 was estimated for a severity of 18%. The implications of these results on the disease epidemiology are discussed.

Epidemiological Characteristics of Angular Leaf Spot of Bean: A Systems Analysis

“…For instance, a relative rate of defoliation of 0.23 day )1 was Table 1 for meaning of abbreviations and dimensions and legend of Figure 2 for meaning of symbols. estimated for a severity of 18% (Willocquet et al, 2004). Similar positive correlations were found in many leaf spot diseases of annual legumes, such as Cercosporidium personatum (Phaeoisariopsis personata) on groundnut (e.g., Watson et al, 1986).…”

“…These results concur with earlier reports concerning lesion establishment, where relative humidity in the air or leaf wetness duration (Cardona-Alvarez and Walker, 1956;Llanos, 1957;Campos-Avila and Fucikovsky Zak, 1980;Sindhan and Bose, 1980a) were varied. Recent results from Willocquet et al (2004) also show that a single long continuous period of wetness is not necessary for infection to occur, because the authors exposed the inoculated plants to high humidity only during nights (16 h at 70-100% RH during nights and 8 h at 50-80% RH during days). Radiation does not appear to have a measurable effect on infection processes (Cardona-Alvarez and Walker, 1956).…”

“…However, disease development does occur at cool temperatures (16°C), as reported by Inglis and Hagedorn (1986). Infection efficiency (the ratio of established lesions to deposited spores) (Zadoks and Schein, 1979) was specifically studied by Willocquet et al (2004), and was below 0.1 when inoculated plants were exposed to less than two consecutive nights of leaf wetness (i.e. two 16 h periods of continuous wetting at 70-100% RH with 8 h dry intervals at 50-80% RH).…”

Quantifying and Modelling the Mobilisation of Inoculum from Diseased Leaves and Infected Defoliated Tissues in Epidemics of Angular Leaf Spot of Bean

“…The rate of defoliation of infectious sites on canopy leaves (RDEFi) is a function of a relative rate of defoliation (RRDEFi), which itself depends on disease severity (SEV). A negative exponential model was fitted to data (R 2 =0.96) using data from Willocquet et al (2004) to relate these two later parameters as:…”

Comparative epidemiology of grapevine and soybean rusts

“…pachyrhizi on their hosts is senescence acceleration, which is associated with early leaf fall and negatively related to grapevine and soybean yields. In order to simulate yield losses caused by Phakopsora rusts, it is necessary to estimate a parameter representing the rate of leaf fall that is related to disease severity and incorporate this parameter into the simulation model (Willocquet et al, 2004;Allorent et al, 2005).…”