New phenological growth stages of garlic (Allium sativum)

Abstract

The advantages of using Biologische Bundesanstalt, Bundessortenamt and Chemische Industrie (BBCH) phenological scales are well-known in the field of agronomy. Currently, specific scales exist for the majority of crops. Although garlic has international importance due to its worldwide cultivation, a specific phenological scale has not been developed; in general, garlic is integrated into the BBCH description for onion. While garlic and onion belong to the same genus, this generalisation should be avoided due to their many differences. The means of propagation of garlic is vegetative, from cloves of the previous cycle, and the concurrence of the bulbing phase and the emergence of the inflorescence (bolting types) cause garlic to perpetually remain in a ‘second year stage’ of its biological cycle. In contrast, onions and other bulbous Liliaceae that produce seeds undergo biannual development. In addition to this complexity, its physiological complex is strongly influenced by environmental factors, such as temperature and photoperiod; distinct conditions are required for overlapping or simultaneously occurring phases (bulbing/flowering). Nevertheless, ambiguity and lack of consensus exist concerning the start of different phenological phases due to the complex morphology of the bulb (composed of a bulb of bulbs/cloves). During bulbing, for example, two distinct, consecutive processes are involved: the differentiation of lateral buds and inflorescence (bolting types) and the thickening of the storage leaf of each bud (cloves). In the present study, an extended BBCH scale was developed for garlic (Allium sativum). Seven principal growth stages divided into secondary growth stages are described in detail and are represented by a two- or three-digit code. Descriptions begin with garlic cloves in a stage of dormancy, destined for planting and end with complete bulb maturity. The most complex growth stages of garlic were described from a morphological and physiological perspective, that is complete bolting types (hard-neck cultivars). Illustrations of different stages are included to clarify the application of the code system. The proposed BBCH garlic scale aims to fill gaps in the knowledge of this important crop and will serve as a useful tool for researchers, technicians and farmers. Thus, experimental findings may be standardised and complementary, which may lead to improvements in management practices and their comparisons.