Biological control of weeds: tracking the resistance mechanisms

Quantitative resistance of Senecic vulgaris L. to the rust fungus Puccinia lagenophorae Cooke was investigated in terms of underlying mechanisms and relevance for biological weed control following the system management approach. The infection process of P. lagenophorae on S. vulgaris was studied by light, fluorescence and scanning electron microscopy. The infection process was quantified using component analysis. The most sensitive phase of the infection process was the development of a penetration peg from an appressorium. Resistance was determined at this stage of the infection process. Results of a further series of experiments using three plant lines of S. vulgaris and three P. tagenophorae lines indicated that resistance was race non-specific. An aggressive strain of P. lagenophorae might control S. vulgaris. The use of an aggressive strain does, however, not eliminate differences in resistance between plant lines. On a long time scale, resistance to P. lagenophorae might theoretically increase in S. vulgaris populations due to biological weed control. However, differences in susceptibilitty among plant lines were relatively small. Other factors influencing the fitness of S. vulgaris plants may alleviate or override the plantline-specific effects imposed by the rust pathogen and thus, enhance the sustainability of the envisaged biological control strategy.