BLUP, a new paradigm in host-range determination

The centrifugal phylogenetic method has been the basis of selection of non-target plants to test for specificity of biological control agents for the last 35 years. In the last decade there has been increased attention paid to modernizing the approach and basing selection of test plants on molecular phylogeny rather than taxonomic classification. Recently mixed model equations (MME) and best linear unbiased predictors (BLUPs) were used to determine the probable host-range of two plant pathogens proposed for classical biological control of Russian thistle. BLUPs were derived with the MME by incorporating disease ratings, variances, and relationship matrices computed from genetic (DNA) distances among plant species related to Russian thistle. Although this work focused on evaluating disease severity on related plant species, the MME can be used with any biological weed control agent or target as long as the evaluation criterion is quantitative (or appropriately transformed) and variances and molecular genetic relationships among test species can be obtained. Moreover, since BLUPs can be generated for species with no observed data, the MME are ideally suited to both evaluation of test plant species and construction of test plant lists based on molecular phylogenetic relationships and reactions of the species to the biological control agent. Many biological control practitioners may be unfamiliar with this methodology. The objectives of this manuscript are to familiarize biological control researchers and regulators with some of the requirements and advantages of the MME and the use of the MME to construct test plant lists.