Abstract
Irregularity in fruit load from year to year, referred to as irregular bearing, is a phenomenon commonly observed in fruit trees. This pattern is linked to fluctuations in floral induction that result in irregular fruit production over consecutive years, whereby some years are characterized by high production (“ON years”) and others low production (“OFF years”). Irregular bearing affects quantity and stability of fruit production and increases demand for labor and/or chemical products to regulate fruit load. Despite the impact of irregular bearing on the agronomic and economic viability of fruit production, the genetic underpinnings of irregular bearing in apple are still not well characterized. A number of quantitative trait loci for this trait have been previously identified using biparental crosses and low-density genetic markers, however, the genetic architecture of this trait can be further resolved using genome-wide association (GWA) tools with higher-density genotypic data and a study population representing a broader scope of genetic diversity. Here, we aim to characterize the genetic architecture of irregular bearing using a French dessert apple core collection consisting of 239 cultivars and SNP genotypes from the Axiom Apple 480 K SNP array. Indices characterizing patterns of irregular bearing over a 6-year period, a Biennial Bearing Index and an autoregressive coefficient, are estimated for each tree. GWA testing is used to identify loci explaining variation in each of the indices among cultivars in the core collection. We will present the results of these GWA studies. Such findings help to identity candidate genes underlying irregular bearing and to identify relevant alleles for the selection of cultivars less prone to irregular bearing.