Simulation of tree growth for three almond cultivars with contrasting architecture with the L-ALMOND model

Abstract

The L-PEACH and L-ALMOND models use L-systems to simulate the architectural development and carbohydrate dynamics (assimilation, transport, distribution, storage and remobilization) of growing peach and almond trees, respectively. The models were able to successfully simulate tree growth and development and produce realistic estimates of tree size, structure and productivity over several years after planting, but always only for a specific cultivar. We here show how L-ALMOND can be adapted to simulate the architectural growth of three cultivars (‘Nonpareil’, ‘Aldrich’, and ‘Winters’) differing in tree architecture after three steps for each cultivar: i) inclusion of specific shoot architectures for six types of shoots (watersprouts, long, medium-long, medium, medium-short, and small shoots). Branching patterns and flowering occurrence for each type of shoot were previously assessed by developing hidden semi-Markov statistical models based on field research. Spur morphology was the same. Very different patterns emerged of sylleptic shoot production from lateral meristems on watersprouts, long, and medium-long shoots. ‘Aldrich’ and ‘Winters’ produced many more sylleptic shoots than ‘Nonpareil’. No sylleptic shoot growth appeared from medium, medium-short, and small shoots in any cultivar; ii) definition of the type of shoot derived from a sylleptic shoot. In ‘Aldrich’ and ‘Winters’ most sylleptic shoots were spurs and short shoots, respectively, while in ‘Nonpareil’ their length varied widely (spurs, small, medium-short, and medium shoots); and iii) adjustment of a parameter to modify shoot bending to simulate differences in growth habit observed in the field. ‘Aldrich’ was more erect than ‘Winters’ and ‘Nonpareil’. After modifications, L-ALMOND 3-dimensional tree simulations were similar to actual pictures of field trees, demonstrating how different shoot architectures result in different tree architectures over time, and especially the role that sylleptic shoot production plays in determining final tree architecture in almond.