Effect of genotype and leader type on benzyladenine induced sylleptic branching in apple nursery trees

The planting of branched nursery trees is an essential component of most high-density orchard planting systems to induce precocity. However, in apples, most cultivars do not produce the desired numbers of sylleptic shoots naturally due to the presence of apical dominance. Benzyladenine (BA) applications alter the apical dominance and consequently encourage sylleptic shoot formation in nursery trees. However, the response to an exogenous BA application can vary with the genotype. Currently, most nurseries produce branched apple nursery trees using the renewal leader method. However, apart from the renewal leader method, branched nursery trees can also be produced using the central leader method. A comparative study of these two methods had not been conducted previously, and this investigation aimed to determine the effects of both the central and renewal leader methods, as well as the genotype, on sylleptic branching in apple nursery trees in response to repeated BA sprays. The genotype showed significant variation in the sylleptic shoot numbers (5.25-9.41), their average length (26.86-33.34 cm), and crotch angle (48.95˚-54.27˚) in response to the BA application. Among the genotypes, 'Shireen' produced the highest number of sylleptic shoots, whereas the opposite results were obtained in 'Top Red'. Furthermore, irrespective of the genotype, the central leader method was found to be more effective than the renewal leader for the development of high-quality branched nursery trees. The central leader method not only significantly increased the number of sylleptic shoots on the tree but also positively affected their length, final tree height, and diameter.