Growth and flowering responses to abiotic parameters of amaryllis belladonna L. for horticultural applications

Abstract

Amaryllis belladonna L. is an endemic bulbous species from the opulently diversified Cape Floral Region of the Western Cape, South Africa. Previously a monotypic genus of the Amaryllidaceae family, it has naturalised in many Mediterranean regions worldwide. The hysteranthous autumn flowering geophyte displays white to pink trumpet-shaped florets in a seasonal single-harvest inflorescence following a summer dormancy. However, the species faces development constraints of protracted bulb juvenility, offset generation for competent flowering size, and inconsistent and transient flowering behaviours upon reproductive bulb maturity. Likewise, there is a lack of scientific research and quantitative empirical data on cultivation methods, from planting to flowering, which has irrefutable economic potential. This study investigated the cultivation methodology and environmental conditions of A. belladonna at different bulb development phases, focusing on the effects of abiotic parameters on growth, development, and seasonal flowering. A literature review, four descriptive reviews, a field study, and three greenhouse experiments were included, forming a coherent body of work on related research questions and hypotheses testing for A. belladonna. The study objectives were: Chapter 3 determined the factors stimulating flower initiation in A. belladonna. Findings revealed several factors associated with bulb size, age, dormancy, bulb planting establishment, cultivation methods, and environmental variables, such as temperature, hydration, day length, and seasonal fire, to promote flower initiation in the species. Chapter 4 determined the horticultural and floricultural market potential of A. belladonna. Findings established that the species has attracted international interest because of its adaptability, attractiveness, drought resilience, and fire-stimulated flowering attributes. Likewise, it alluded to the applications and design uses of the species within the broader fringes of the floriculture and horticulture arena. Among these are the ornamental functional design and use of A. belladonna in garden landscapes, naturalistic and roadside plantings, packaged retail flower bulbs, potted plants, and cut flowers. Chapter 5 evaluated the hydroponic cultivation capacity of ornamental bulbous species. Findings established limited accounts of scientific studies and cultivation of species variety, vegetation induction, and bulb regeneration to expand bulb size and yield and offset production compared to flowering-forcing under these conditions. Chapter 6 determined the impact of fire-stimulated flowering on South African geophytic biodiversity. Findings of initiated flowering and regenerative growth of selected geophytic taxa that inhabit different regions and vegetation habitats of South Africa following wildfires have been documented; however, these are primarily denoted in the species’ natural habitats, with little account for those under cultivation. Moreover, there is limited knowledge and studies on how fire-associated factors initiate geophytic flowering mechanisms and their distinctive roles in preserving species richness and biodiversity, ecotourism, and the survival and well-being of natural above- and below-ground ecosystems. Chapter 7 assessed the inhabited bulb planting life strategy and flowering prolificacy of A. belladonna by examining the population attributes, habitat features, and cultivation practices under ex situ garden conditions. The two-year study used purposive sampling to recruit six ex situ bulb populations from the Pinelands residential area. Results found bulbs to have enduring longevity and were recruited primarily through vegetative offsets. Flowering heterogeneity ranged from 4.9% to 58.3% within and between seasons; however, commonalities alluded to a broad influence of temperature. The study concluded that in addition to favourable habitat features and climatic growing conditions, population attributes (bulb size, structure, position, density, and establishment) and cultivation practices (premature defoliation, soil amendments, planting interference, and re establishment) were significant synergistic constituents of flowering proficiency. Chapter 8 determined the effects of Kelpak® seaweed extract on the morphological and physiological growth and yield of A. belladonna bulbs grown in a greenhouse. The 24-week study comprised Kelpak® concentration dilutions of 0%, 0.2%, 0.4%, and 1% (v/v), administered to 5 consecutive juvenile bulb age groups as a monthly soil drench. Results showed that Kelpak® treatment improved phyto-stimulatory responses in bulb aerial and below-ground storage organs. Moreover, bulb age varied, with older bulbs establishing higher yields than their younger counterparts; however, bulb circumference, weight coefficients, and chlorophyll content showed that 1- and 2-year-old bulbs were most receptive to treatment. This study concluded that 1% Kelpak® is applied at an early developmental stage within the first two years to maximise the efficacy and proliferation rate of A. belladonna. Chapter 9 determined the effects of root zone water temperature and soilless media on bulb yield and offset A. belladonna bulb production in a deep water culture hydroponic system. The 18-month study included dormant juvenile bulbs that were planted in plastic cavity trays filled with soilless media (silica sand or Leca clay) and suspended in heated water reservoirs at different temperatures (16 °C, 22 °C, 28 °C, and 34 °C). Results found that the autonomous analysis of water temperature, as opposed to soilless media and combinations, was significant. Warm root zone temperatures from 16 °C to 28 °C promoted the growth and development of larger juvenile mother bulbs and offset generation without premature detachment; however, bulbs were depleted at an excessively high temperature of 34 °C. This study concluded that a water temperature of 22°C is needed for long-term sustainable production of optimal reclaimable bulbs and offsets to abridge the timeous cultivation of continuous vegetative bulb stock of A. belladonna. Chapter 10 determined the effects of a warm storage period on A. belladonna bulbs’ flowering yield, flowering time, quality characteristics, and foliage growth. The 10-month study involved dormant flower-sized bulbs placed in storage regimes of 0-, 4-, 6-, 8-, 10-, or 12-weeks at a continuous warm temperature of 23 ± 1 °C before greenhouse planting. Results showed that flowering production (64.3% flowering after 12-week storage), flowering time (anthesis 9 days after 10- and 12-week storage), and quality attributes (inflorescence floret numbers, fullness ratio, pot longevity and scape diameter) of A. belladonna were significantly influenced by warm bulb storage, but not foliage growth. Extended bulb storage did not advance flowering time despite greater harvest and shorter cultivation periods after planting. Bulbs should be stored at elevated temperatures for 8–10 weeks for optimal floret quality and longevity. However, this study concluded that 12 weeks of warm storage would be needed for economically sustainable greenhouse and specialty cut flower production of A. belladonna. The current study’s comprehensive findings and recommendations contribute valuable and novel material towards developing and advancing cultivation practices, perpetuating prospects for enhanced economic value, quality, and reproducible commercial production for the competitive differentiation of A. belladonna in the floricultural and horticultural markets.