Abstract
Irregular flowering over years is commonly observed in fruit trees. The early prediction of tree behavior is highly desirable in breeding programmes. This study aims at performing such predictions, combining simplified phenotyping and statistics methods. Sequences of vegetative vs. floral annual shoots (AS) were observed along axes in trees belonging to five apple related full-sib families. Sequences were analyzed using Markovian and linear mixed models including year and site effects. Indices of flowering irregularity, periodicity and synchronicity were estimated, at tree and axis scales. They were used to predict tree behavior and detect QTL with a Bayesian pedigree-based analysis, using an integrated genetic map containing 6,849 SNPs. The combination of a Biennial Bearing Index (BBI) with an autoregressive coefficient (γg) efficiently predicted and classified the genotype behaviors, despite few misclassifications. Four QTLs common to BBIs and γg and one for synchronicity were highlighted and revealed the complex genetic architecture of the traits. Irregularity resulted from high AS synchronism, whereas regularity resulted from either asynchronous locally alternating or continual regular AS flowering. A relevant and time-saving method, based on a posteriori sampling of axes and statistical indices is proposed, which is efficient to evaluate the tree breeding values for flowering regularity and could be transferred to other species.
Highlights
Biennial bearing, defined as the irregular fruit or seed production over consecutive years, is a trait commonly observed in perennial crops (Monselise and Goldschmidt, 1982; Samach and Smith, 2013)
Predicting bearing habit as soon as possible from the beginning of the genotype’s production is of high interest. This strategy is reinforced by the existence of large differences among cultivars (Lauri et al, 1997, 2014) and the demonstration of genetic control of biennial bearing in an apple family derived from a cross between biennial and regular bearing parents (“Starkrimson R Red Delicious” × “Granny Smith”; single family (SG)) (Guitton et al, 2012)
We propose to extend the previous investigations by exploring new methods and indices based on the analysis of sequences of flowering shoots, and by performing a multi-family QTL detection to enlarge the genetic basis of biennial bearing variation in apple trees
Summary
Biennial bearing, defined as the irregular fruit or seed production over consecutive years, is a trait commonly observed in perennial crops (Monselise and Goldschmidt, 1982; Samach and Smith, 2013). Flowering Behavior Prediction strategy would be to select cultivars combining high fruit quality, long-term resistance to pests and diseases, tree architecture adapted to modern training systems and regular production. Predicting bearing habit as soon as possible from the beginning of the genotype’s production is of high interest. This strategy is reinforced by the existence of large differences among cultivars (Lauri et al, 1997, 2014) and the demonstration of genetic control of biennial bearing in an apple family derived from a cross between biennial and regular bearing parents (“Starkrimson R Red Delicious” × “Granny Smith”; SG) (Guitton et al, 2012)
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