Abstract

Major gene resistance and the application of fungicides have together formed the main arsenal against pathogens through the latter half of the 20th century. However both major gene resistance and fungicides often have an effective lifespan from deployment of around a decade or less before new pathogens strains render them ineffective [1]. Both partial resistance and cultivar mixtures have been suggested as durable methods of resistance, and have several other advantages over monocultures of a single cultivar with a single resistance gene [2]. Several authors have investigated the mixture effect achieved by mixtures of cultivars with major gene (absolute) resistance. However, little is known about whether growing more than one partially resistant cultivar in a mixture could provide the same benefit found in mixtures of cultivars with major-gene resistance. Using a variety of modelling approaches we have examined this question, by combining host types with different resistance parameters and determining the severity and velocity of a new pathogen in such a mixture. Beneficial mixture effects were found to arise under certain mixtures, but it is equally likely that mixtures of this sort could increase the pathogen severity over what might be expected.

Real quantitative resistance parameters from published data were then used to parameterise the above models for leaf stripe rust on barley under realistic host landscapes, and the results produced so far suggest that, while the benefits predicted can occur in real situations, quantitatively the benefits accrued are relatively small.

References:

1. Parlevliet, J.E., Durability of resistance against fungal, bacterial and viral pathogens; present situation. Euphytica, 2002. 124(2): p. 147-156.

2. Mundt, C.C., Use of multiline cultivars and cultivar mixtures for disease management. Annual Review of Phytopathology, 2002. 40: p. 381-410.