Influence of Temperature, Wetness Duration, and Leaf Type on the Quantification of Monocyclic Parameters of Bean Rust

Monocyclic parameters of bean rust (Uromyces phaseoli var. typical) were quantified in growth chambers, on rwo bean cultivars for three temperatures (17, 21, and 25 °C), two types of leaves (unifoliolate and trifoiiolate leaves), and nine leaf wetness periods (0, 4, 7, 10, 13, 16, 19, 22, and 25 hrs). The expression of disease was greatly influenced by past-inoculation temperatures. The incubation and latent periods were shortest at 21 °C for both cultivars and leaf types. For both cultivars, trifoiiolate leaves were more susceptible than unifoliolate leaves. A wetness period of at least four hours was required for disease to occur. The maximum disease efficiency for both cultivars occurred with 22 hrs of leaf wetness at 17 °C. The disease efficiencies for temperatures of 17–29 °C and leaf wetness periods of 0–25 hrs were adequately described by a response-surface model. Because of the great influence of temperature and leaf wetness on infection, bean rust is unlikely to occur at high temperatures (> 25°C) and short leaf wetness periods (< 7 hrs).