Résumé
Shoot structure, resulting from lateral branching and flowering patterns, determines final tree form, fruit bearing habit, and cropping potential. The genetic make-up of different cultivars controls vegetative and reproductive growth, but few structural studies have been done to systematically describe almond shoot structure. A specific class of Markovian models, referred to as hidden semi-Markov chains (HSMC), has been proposed to identify and characterize branching and flowering patterns in fruit trees. This type of model is particularly appropriate when the shoot structure is organized as a succession of homogeneous branching zones and captures the variable character of the observed patterns. This study reports the first almond HSMC analysis of shoot structure based on data collected from epicormic shoots and five length categories of proleptic shoots in three almond cultivars with distinctly different tree architecture. 'Nonpareil' is the most important cultivar grown in California and has a relatively spreading tree habit. 'Aldrich' is a newer cultivar with an upright growth habit, and 'Winters' has a spreading habit with a high tendency for sylleptic branching on proleptic shoots. Shoots of these three cultivars were analyzed to determine different zones that could be classified according to lateral bud fates and the number of flower buds at each node. This modeling technique showed that almond shoot structures are highly organized and predictable. Substantial differences were found in the structure of the proleptic shoots of similar length, among the cultivars, but fewer differences were found among epicormic shoots. For long shoots, 'Aldrich' had the highest probability of flower buds and 'Winters' had the greatest lateral branching distributed along shoots. 'Nonpareil' had similar branching probabilities as 'Aldrich' and its probability of flower buds was similar to 'Winters'. It is anticipated that these HSMC will be useful for identifying desirable shoot structures for cultivar improvement and will help to explain the differences in tree architecture and cropping potential among cultivars.