Morphology and Anatomy of Sylleptic Shoots of Plum Trees (Prunus domestica L.) as Influenced by Different Dates of Shoot Heading During Summer Pruning

This study was conducted during two years under the environmental conditions of ^a~ak
(western Serbia) to evaluate the effects of different dates of shoot heading during summer pruning on
the intensity of sylleptic shoot formation and the main morphological and anatomical traits of sylleptic shoots in plum cultivar ‘^acanska Rodna’ grafted on Myrobalan rootstock during five and six
years after planting. The experiment was established with a spacing of 4 m × 2 m (1,250 trees ha-1).
Shoots were headed back to four buds from the base at five different dates to stimulate sylleptic shoot
development. The first heading-back date (T1) was 30 days upon the beginning of shoot growth and
the remaining ones (T2, T3, T4, and T5) continued at 15-day intervals. At the end of winter dormancy (February), measurements of morphological traits of sylleptic shoots, including length and diameter of sylleptic shoots (cm), node number, node length (cm), and number of vegetative and flowering buds, as well as of anatomical traits, i.e., xylem area width (μm), number of tracheae per mm2 and
trachea diameter (μm) were made. Results showed that T4 and T5 were late shoot heading dates
(around July 5 and July 20, respectively), given the very poor development of sylleptic shoots until
the end of the growing season. Among the remaining three shoot heading dates, T3 (around June 20)
was the most favorable as it produced sylleptic shoots of moderate length, i.e., vigour, having a very
good ratio of flower buds to vegetative buds, and normal anatomical traits. These results provide new
insight into dates and methods of summer pruning of plums grown in a high density planting system
aimed at regulating tree vigor and improving cropping potential.