The Relationship Between Flower and Fruit Abscission and Alternate Bearing of ‘Hass’ Avocado

Despite profuse flowering, ‘Hass’ avocado (Persea americana Mill.) yields are low because of excessive flower and fruit abscission. Whether the dynamics of flower and fruit abscission are influenced by or contribute to alternate bearing, the production of a heavy on-crop followed by a light off-crop that is characteristic of many avocado cultivars, remains unresolved. The objective of this research was to determine whether abscission of reproductive structures from ‘Hass’ avocado trees during specific developmental stages, including flowering, fruit development, and fruit maturity, was influenced by crop status of the current or preceding year. Abscised reproductive structures were collected from commercially bearing trees during two complete crop years. Flower abscission began at about the same time but peaked 1 month later in the off-crop year compared with the on-crop year. Peak abscission rates were lower during the off-crop year than the on-crop year (compare 1836 ± 403 to 5378 ± 856 flowers per day and 50 ± 18 to 280 ± 23 immature fruit per day, respectively). The off-or on-crop status of the tree did not influence the percentage fruit set, average fruit diameter, or biomass of individual fruit that abscised at similar phenological stages. Furthermore, flower and fruit abscission were not influenced by the number of mature fruit from the previous year’s crop. In both years of the research, as immature fruit abscission declined, abscission of the preceding year’s crop increased, indicating that the processes were controlled independently. During the study, neither weather conditions nor tree nutrient status were associated with key abscission events. Taken together, these results provide evidence that the previous year’s yield does not influence flower or fruit abscission and the seasonal abscission of reproductive structures is an independent process that does not contribute to alternate bearing of ‘Hass’ avocado

Pre-clearing vegetation of the coastal lowlands of the Wet Tropics Bioregion, North Queensland

A pre-clearing vegetation map and digital coverage at approximately 1:50 000 scale for the coastal lowlands (up to about 200 m elevation) of the Wet Tropics Bioregion, North Queensland is presented. The study area covers about 508 000 ha from Cooktown, 420 km south almost to Townsville (latitude 15° 30’–18° 20’ longitude 144° 50’–146° 40’). Data sources included historical aerial photography, early surveyors’ plans, explorers’ journals, previous vegetation maps, and maps of soils and geology. The pre-clearing mapping was built around the remnant vegetation mapping of Stanton & Stanton (2005), and the vegetation classification of this latter work was adopted. Vegetation units were further classified into regional ecosystems compatible with the standard State-wide system used by Queensland government. The digital coverage is part of the current Queensland Herbarium regional ecosystem coverage (Queensland Herbarium and Wet Tropics Management Authority 2005). Coloured maps (1:100 000 scale) of the pre-clearing vegetation of the Herbert, Tully, Innisfail and Macalister/Daintree subregions are on an accompanying CD-ROM. An evaluation of vegetation loss through clearing on the coastal lowlands of the Wet Tropics revealed several nearextinct vegetation communities and regional ecosystems, and many others that are drastically reduced in area. Even ecosystems occurring on poorly drained lands have suffered a surprisingly high level of loss due to the effectiveness of drainage operations. Grassland ecosystems were found to be widespread on the Herbert and Tully floodplains, but are now close to extinction. The lowlands vegetation of the Wet Tropics that remains today continues to be fragmented and degraded despite the introduction of State-wide broad-scale tree-clearing laws in 1999, and the cessation of broadscale tree-clearing in December 2006

Developing a social practice-based typology of British drinking culture in 2009-2011: Implications for alcohol policy analysis

Background and aims: The concept of national drinking culture is well-established in research and policy debate but rarely features in contemporary alcohol policy analysis. We aim to apply the alternative concept of social practices to quantitatively operationalise drinking culture. We discuss how a practice perspective addresses limitations in existing analytical approaches to health-related behaviour before demonstrating its empirical application by constructing a statistical typology of British drinking practices and examining sociodemographic variation in practice. Design: Cross-sectional latent class analysis of drinking occasions derived from one-week drinking diaries collected for market research. Occasions are periods of drinking with no more than two hours between drinks. Setting: Great Britain, 2009-2011. Cases: 187,878 occasions nested within 60,215 nationally-representative adults (18+). Measurements: Beverage type and quantity per occasion. Location, company and gender composition of company. Motivation and reason for occasion. Day, start-time and duration of occasion. Age, sex and social grade. Findings: Eight drinking practices are derived. Three of the four most common practices are low risk, brief, relaxed, home-drinking (46.0% of occasions). The most high risk practices had diverse characteristics and were observed across all sociodemographic groups. Two often-high risk practices identified are rarely acknowledged in policy debate: lengthy weekend domestic gatherings of friends and/or family (14.4% of occasions) and lengthy, typically weekend occasions encompassing both on-trade and off-trade locations (10.4% of occasions). Conclusions: A practice-based perspective offers potential for a step-change in alcohol policy analysis by enabling evaluation of how much and why drinking cultures change in response to public health interventions

Growing healthy sweetpotato: best practices for producing planting material

Sweetpotato is a major food crop in Papua New Guinea, with about 2.9 million tonnes grown each year. But sweetpotato is prone to pests and diseases, particularly viruses, which can significantly reduce yields. Because there are no varieties known to be resistant to viruses, the next best solution is to produce planting material that is free from infection, and to make this readily available to growers. This manual is aimed at researchers and technicians, and describes how to test for sweetpotato viruses and to keep vines free from infection. The methods described should help locals in PNG and other Pacific nations produce disease-free planting material for sweetpotato and other root and tuber crops

The Impact of Outcrossing on Yields of ‘Hass’ Avocado

‘Hass’ avocado (Persea americana Mill.) is characterized by excessive flower and fruit abscission, resulting in extremely low fruit set. Low outcrossing rates might be a factor contributing to low yields. It is hypothesized that self-fertilized flowers and resulting fruit abscise at a much higher rate than fruit that are the product of outcrossing. However, significant relationships between outcrossing rates and yields have only been established in a few avocado studies. The objective of this research was to investigate the importance of outcrossing to yield in a commercial ‘Hass’ orchard containing ‘Bacon’, an effective pollinizer of ‘Hass’. Microsatellite markers were used to determine the rate of outcrossing of fruit persisting to harvest on ‘Hass’ trees. Experiments were conducted during sequential on-and off-crop years. During both years, outcrossing rates were not related to yield or alternate bearing. These results indicate that outcrossing was not the primary factor affecting flower and fruit persistence and ultimately yield in this orchard for the two sequential years of this research

PLANT GROWTH REGULATORS FOR AVOCADO PRODUCTION

ABSTRACT Plant growth regulators (PGRs) are the most powerful tools available for manipulating tree growth and yield in an established orchard. Understanding the phenology and physiology of the avocado (Persea americana Mill.) is critical for selecting the correct PGR and for properly timing the application annually to consistently elicit the desired response. Results from two recent multi-year PGR experiments have provided evidence of promising PGR strategies for increasing 'Hass' avocado yield and fruit size. Gibberellic acid (GA 3 ) (25 mg/L) applied at the cauliflower stage of inflorescence development or applied at the end of June-beginning of July significantly increased total yield and yield of large size fruit (packing carton sizes 60-40, 178-325 g/fruit) in kilograms per tree as 2-year average and 2-year cumulative yield (P ≤ 0.03). Benzyladenine (BA) (25 mg/L) applied at anthesis or GA 3 (25 mg/L) applied in mid-July followed by prohexadione calcium (ProCa) (125 mg/L) 30 days later significantly increased the yield of larger size fruit (packing carton sizes 40-28, 270-446 g/fruit) in kilograms per tree as 2-year average yield (P = 0.0069 and P = 0.0564, respectively) and 2-year cumulative yield (P = 0.0120 and P = 0.0624, respectively) without reducing total yield or yield of fruit of packing carton sizes 60, 48 and 40. These strategies will be tested in additional orchards