The effect of genotype, location and their interaction on early growth and branching in apricot trees

The purpose of this study was to identify relevant variables and appropriate stages in tree development to determine, as early as possible, genetic differences in growth and branching of apricot trees. Quantitative growth and branching traits of young trees were studied in four genotypes planted at three locations in the French growing area. Over the first three years of growth, the organisation of ten limbs was described for each genotype × location combination using 'AMAPmod' methodology. From the first year, the length, diameters, volume and sylleptic branching of limbs were influenced by genotype. In the second and third years, genetic variability was more clearly detected when cumulative variables, rather than annual variables, were considered on the cumulative components of limbs. At all three locations, the diameters, volume and number of long laterals were greatly affected, in particular, by genotype when the data were accumulated over the first 2 years. In addition, the abortion of short laterals developed on the first annual shoot was influenced by genotype. In contrast, from the second year, location clearly affected the length and number of “growth units” of limbs. As regards branching, location influenced the number of sylleptic shoots in the first year, then the number of long lateral shoots in the second year. Finally, the study showed that genetic differences in growth and branching need at least 3 years to be expressed on appropriate parts of the limbs and could be used to assess early breeding criteria for tree vigour and form.