Genetic Evaluation and Multiple Trait Selection for Resistance to Pseudomonas syringae pv. actinidiae and Fruit Characters in Diploid Actinidia chinensis (Kiwifruit) Populations

Bacterial canker of kiwifruit, caused by a virulent strain of Pseudomonas syringae pv. actinidiae (Psa), has seriously damaged the kiwifruit industry worldwide. A quantitative genetic approach was used to understand genetic variation in fruit characters and in resistance to the pathogen in two disconnected factorial mating populations of diploid Actinidia chinensis Planch. Heritabilities and genetic correlations were estimated, using a mixed model method based on restricted maximum likelihood method with pedigree information. Significant variation in all characters was found, and this appeared to be under polygenic control. Results indicated the extent and nature of genetic variation in Psa resistance available in our breeding gene pool. Estimates of narrow-sense heritability were high for dry matter (DM) (0.72) and soluble solids contents (SSC) (0.90), but lower for Psa resistance (0.42), yield (0.50), and fruit weight (0.59). The moderate heritability for Psa resistance indicated some genetic control of the observed variation, and that selection for Psa resistance could be possible. Psa resistance had a negative genetic correlation with yield (-0.62), but a positive correlation with DM (0.46) and SSC (0.59). There was no genetic correlation with fruit weight in these populations. The results implied that a yield penalty of Psa resistance might exist in kiwifruit. Estimated breeding values for multiple traits were calculated for all female seedlings, using multivariate pedigree-BLUP (best linear unbiased prediction). Parents useful for improving Psa resistance, yield and DM simultaneously were identified.