Phenological growth stages of soursop trees (Annona muricata L.) based on the extended BBCH-scale

The soursop is a species of tropical fruit well accepted by consumers due to its creamy white pulp and excellent flavor. Currently, Mexico is the largest producer and consumer; however, the agronomic practices in use were established without a systematic knowledge of A. muricata L. phenology. The objective of this work then, was to conduct such a study in two of the main producing regions of Mexico: Tepic and Compostela (both in the state of Nayarit). For this, a total of 20 ungrafted trees were selected and their growth stages described using the extended BBCH-scale (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie). Overall, eight main phenological stages were identified over the course of a year. These were: the development of buds (stage 0), leaves (stage 1),and shoots (stage 3), the emergence of flowers (stage 5), flowering (stage 6), fruit development and maturity (stages 7-8), and senescence of branches (stage 9). In addition, 37 secondary growth stages were also described and quantified. The highest number of vegetative shoots occurred from March-July, 2017 and the biggest increase in floral structures from July–September, 2017. Fruit setting to physiological maturity took an average of 114 days in both Tepic and Compostela, with the most intense defoliation occurring in October, 2017 in the former (Tepic) and in December, 2016 in the latter (Compostela). Hopefully, improved agronomic practices will be established using this information, as well as suitable protocols for future physiological studies.