Infection process and resistance in the weed pathosystem Senecio vulgaris - Puccinia lagenophorae and implications for biological control

Abstract

The infection process and the level and type of resistance in the pathosystem of a native weed and a naturalized rust fungus, Senecio vulgaris L. - Puccinia lagenophorae Cooke, were examined. Four inbred plant lines from Switzerland (2), The Netherlands, and the United Kingdom, each at two stages of devolpment, were exposed to corresponding rust lines under controlled conditions. Fluorescence and light microscopy were used to assess the infection process and to quantify genotype effects. Component analysis was used to partition disease development and define the infection process. Germinating aeciospores of P. lagenophorae showed all the characteristics of the monokaryotic parasitic stage of rust infection with direct penetration and monokaryotic haustoria formation. Haustoria formed between 3 and 6 days after inoculation at low frequency. The highest level of resistance, for which differences between plant lines were detected, occurred at penetration peg formation. All the studied host-pathogen interactions were compatible. The Dutch plant line was most susceptible to all rust lines, and the Dutch rust line was the most aggressive. Susceptibility of leaves increased with the leaf developmental stage. There was a continuous range of variation in susceptibility without differential genetic interactions, thus indicating race-nonspecific quantitative resistance. The use of the more aggressive Dutch rust line may increase the level of disease, thus stimulating epidemics for biological control. Over the long term, less susceptible genotypes of the weed may be selected, although differences in susceptibility among plant lines were relatively small.Key words: rust fungus, infection structures, direct penetration, component analysis, race-nonspecific quantitative resistance.