Reproductive phenology calendar and its correlation with air temperature in five Mediterranean almond [Prunus dulcis (Mill.) D.A. Webb] cultivars grown in Morocco

Abstract

Agro-climatic requirements are of crucial importance for establishment and management of nut tree orchards. In this work, we investigated timing and duration of key reproductive phenology events and their chilling units (CU) and heat requirements namely growing degree-days (GDD) and degree-hours (GDH) in five Mediterranean almond cultivars of early (‘Marcona’), intermediate (‘Fournat de Brézenaud’), and late flowering time (‘Ferraduel’, ‘Ferragnès’, and ‘Tuono’). Field phenological observations were performed during three growing seasons (2016–2018) across five contrasting sites in northern and eastern Morocco. Phenological records consisted of timing of initial inflorescence (Inf), inflorescence duration (Inf D), initial flowering (Ini F), full flowering (Ful F), final flowering (Fin F), flowering duration (FD), ripening (Rip), fruit development period (FDP). Our outcomes reveal that ‘Marcona’ and ‘Fournat de Brézenaud’ presented low CUs. ‘Tuono’, ‘Ferraduel’, and ‘Ferragnès’ required higher GDD and GDH to reach flowering time. Additionally, ‘Marcona’ had the highest FDP and GDD and GDH for ripening. Sites of northern Morocco exhibited a delayed timing of inflorescence and flowering and longer Inf D, FD, and FDP and high GDD and GDH for different phenological events. 2016 had low CU resulting in delayed timing of inflorescence and flowering but shortened Inf D and FD. Important correlations were outlined among phenological events and agro-climatic requirements. Principal component analysis explains data variation through first principal component (PC, genotypic), the second and the third PC discriminated sites and growing seasons, respectively (environmental components). In conclusions, owing to their early flowering and fruit set, ‘Fournat de Brézenaud’ and ‘Marcona’ should be grown in areas with low frost risks. ‘Marcona’ is not recommended for warmer environments because of its longer FDP. Chill decline induced by global warming may threaten production of high chilling requirement cultivars (‘Ferraduel’, ‘Ferragnès’, and ‘Tuono’).