Petunia as model for breeding mycorrhiza-responsive crop plants

Abstract

The arbuscular mycorrhiza is a mutualistic symbiosis between fungi of the phylum Glomeromycota and 80 % of all land plants. It is based on the exchange of mineral nutrients against carbohydrates. Mycorrhizal plants show in addition increased resistance or tolerance against pathogens and abiotic stress. Whether a symbiotic interaction results in increased performances of the plant is not only dependent on environmental factors, but also on the genotype of both partners. This leads to considerable differences between cultivars of crop plants in the response to colonization by a mycorrhizal fungus. If mycorrhiza should be applied in future production systems for increasing e.g. the tolerance against short-termed dry out or pathogen infestation, mycorrhiza responsiveness of plants has to be a trait to breed for.
Petunia hybrida is being used since ten years as model in mycorrhiza research. Gene maps and markers exist for a long time, but sequencing of the genomes of the two wild species Petunia axillaris und Petunia inflata open up new ways in breeding research. In a first step, the response of the two wild species to inoculation with a mycorrhizal fungus was compared. Differences were revealed concerning root colonization, in biomass changes and in mycorrhiza-induced resistance against a root-pathogenic fungus. In further experiments, the phenotypes of crossing populations are analyzed in order to map QTLs for the different responses. Using the genome sequences, genes can be identified which are involved in the responses of petunia to mycorrhization. Due to the availability of a population, where the genome is saturated with transposon insertions, it is possible to confirm the role of the genes in a relative short time. These genes and their orthologs can be used in future breeding programs for petunia and for other crop plants as functional markers for achieving new mycorrhiza-responsive cultivars.