Effect of Temperature and Hose Genotype on Components of Resistance to Groundnut Rust

The effects of temperature on incubation period, infection frequency, lesion diameter, leaf area damage, pustule rupture, and sporulation were quantified for six groundnut genotypes, representing rust-resistant and susceptible reactions using detached leaves. Rust developed on all groundnut genotypes at 10, 15, 20, 25 and 30°C but not at 35 and 40°C. Incubation period decreased with increase in temperature but in susceptible genotypes it again increased at 30°C. Infection frequencies were highest for susceptible genotypes at 20°C and for resistant genotypes at 30°C. Lesion diameters were smallest at 15°C but increased with the increase in temperature. Optimal temperature for lesion diameters was at 30°C for most genotypes. In susceptible genotypes, the optimal temperature for the leaf area damage occurred at 25°C. The optimal temperature for resistant genotypes was at 25 or 30°C. Nearly 100% pustules ruptured on susceptible genotypes at most temperature. In resistant genotypes, the percentage of pustules ruptured was highest at 15°C but decreased at 20, 25, and 30°C with the exception of NC Ac 17090 at 30°C. Sporulation was highest on susceptible genotypes at 20 and 25°C. Resistant genotypes had high sporulation at 15 or 20°C but decreased at higher temperatures with the exception of NC Ac 17090. Resistant genotypes had longer incubation period, lower infection frequencies, smaller lesions, reduced number of ruptured pustules, lower sporulation, and leaf area damage than the susceptible genotypes. The differences between susceptible and resistant genotypes in some of the components were large only at certain temperatures.

Keywords
Arachis hypogaea, components of resistance, disease resistance, groundnut