Fusiform Rust Fr Genes by Bulked Inocula Interactions in Loblolly Pine

Challenging progeny of loblolly pine (Pinus taeda L.) from known mother trees with single genotype lines of the fusiform rust fungus (Cronartium quercuum sp. fusiforme, hereafter called Cqf) has shown that single-gene interactions can predict disease expression with high accuracy in controlled inoculations (Wilcox et al. 1996; Jordan 1997). A host tree carrying a R (resistance) allele at a specific Fr gene performs as a resistant (non-diseased) host when the challenging pathogen has an avirulence (Avr) allele at the corresponding pathogen gene; however, if the challenging pathogen carries a virulence (avr) allele at the corresponding gene the interaction results in disease even when the R allele is present. Hosts having only r (non-resistance alleles) typically develop disease when challenged with either an Avr or avr pathogen isolate. Considerable progress has been made in understanding the Fr gene resistance system by using controlled inoculations with single-genotype fungal isolates, but the response of Fr genes to mixtures of pathogen samples has not been investigated thoroughly. Understanding these interactions is crucial to tree improvement programs’ abilities to increase genetic gains through deployment of pine genotypes that are resistant to fusiform rust disease under field conditions, where many different pathogen genotypes may be present. In this study, we investigated the interactions of maternally inherited R and r pine genotypes in progeny challenged with different bulked Cqf inocula to evaluate their responses and to draw conclusions on deployment of R pine genotypes.

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Author(s): Fikret Isik, Henry Amerson, Ross Whetten, Saul Garcia, Steve McKeand

Publication: Tree Improvement and Genetics - Southern Forest Tree Improvement Conference - 2009