Browsing by Browse by SEO 2008 "820214 Tropical Fruit"

Custard apple has cryptic axillary buds, hidden from view by the base of the petiole. This has led to confusion about custard apple’s flowering habit. Flowering only occurs during early branch development, and can be forced at any time of the growing season simply by removing leaves. Here, we show that flowering is terminal, not extra-axillary, and that the apparent continuation of the main stem beyond the flower is, instead, a sympodial branch. Secondary (including sympodial) branching only occurs during early branch development. Thereafter, axillary bud release is inhibited by the subtending leaf. Here, we show that summer tip-pruning of all branches arrests canopy development until the following spring owing to this inhibition. Although summer tip-pruning prevented new vegetative growth in the canopy, fruit size decreased relative to the control trees by ca. 23%. The reason for this decrease was probably related to increased carbon limitation to growth given that dawn water soluble and total nonstructural carbohydrate concentrations were lower in the tip-pruned trees. Thus, it appears that the reduced competition between fruit development and new vegetative growth in the tip-pruned trees was more than matched by lower photosynthetic capacity in the arrested canopy. Trees grown inside a shade-house were more vigorous than those grown outside. The difference in vigour had little effect on fruit size.

We examined the effect of ethylene concentration and duration on 1-MCP efficacy with regards to shelf life and fruit quality in bananas (cv. Williams) from the middle section of bunches harvested during winter 2004 and summer 2005. Before storage, fruit was treated with ethylene (2, 20, 50 or 100 µL•L⁻¹) for two consecutive days or 100 µL•L⁻¹ for the first and 2 µL•L⁻¹ for the second day, prior to 1-MCP (300 nL•L⁻¹) exposure for 24 hrs at 22°C. To examine the effect of duration, bananas were treated with 100 µL•L⁻¹ ethylene for 30, 40 or 50 hrs prior to 1-MCP treatment (300 nL•L⁻¹) at 22°C. 1-MCP was most effective at increasing shelf life and firmness when fruit were treated with 100 µL•L⁻¹ ethylene for the first day and 2 µL•L⁻¹ for the second day. Interestingly, fruit harvested in winter initially treated with ethylene at the lowest concentration (2 µL•L⁻¹) or exposed to the shorter duration of ethylene (30 hrs) did not ripen and remained green when treated with 1- MCP. However, winter-harvested bananas that were exposed to ethylene for 50 hrs had a longer shelf life compared to bananas treated with ethylene for 40 hrs. 1-MCP was only more effective in summer-harvested fruit when they were exposed to ethylene for 40 hrs with an increase in firmness. The discolouration index (DI) of 1- MCP treated fruit increased significantly when fruit were exposed to the ethylene for shorter durations than 50 hrs in winter, but no differences were observed in DI of 1-MCP treated bananas that were ripened with ethylene at different concentrations. These observations suggest that the efficacy of l-MCP to improve shelf life and quality of bananas is reliant on not only the harvest season of fruit but also the concentration and duration of ethylene application prior to 1-MCP usage.

Climate change will significantly impact the future viability and security of food production systems, with increased frequency and intensity of droughts, floods, storms and other extreme climatic events predicted in many regions. In order for food production systems to remain viable and resilient under a changing climate, novel approaches, which integrate risk management (i.e. adaptation) and risk transfer strategies, such as insurance, are required. We argue that the coordinated integration of risk management and risk transfer approaches will support greater resilience of food production systems under climate change. Conversely, if risk management and risk transfer strategies are not carefully integrated, there is potential to undermine adaptive capacity (e.g. insurance subsidies may dissuade farmers from investing in climate adaptation) and ultimately reduce the capacity of food production systems to cope with and recover from the adverse impacts of climate change. Here we propose a resilience-based conceptual framework for integrating risk management and risk transfer strategies along with four key principles, which we believe could underlie their successful integration and thus enhance food production system resilience under climate change. These are as follows: (1) pro-active investments in farmer climate adaptation rather than re-active disaster relief, (2) structuring of government subsidies around insurance and climate disaster relief to incentivise farmer climate adaptation, (3) rewarding farmer efforts towards climate adaptation with cheaper insurance premiums for those farmers that invest resources into climate adaptation and (4) recognising investments in the integration of farm climate adaptation and risk transfer schemes within the broader context of future climate disaster risk management and global food security. Such an integrated investment approach could substantially reduce future economic losses for farmers while also enhancing food security under climate change.

Bananas are the world's most popular fruit and an important staple food source. Recent outbreaks of Panama TR4 disease are threatening the global banana industry, which is worth an estimated $8 billion. Current methods to map land uses are time- and resource-intensive and result in delays in the timely release of data. We have used existing land use mapping to train a U-Net neural network to detect banana plantations in the Wet Tropics of Queensland, Australia, using high-resolution aerial photography. Accuracy assessments, based on a stratified random sample of points, revealed the classification achieves a user’s accuracy of 98% and a producer's accuracy of 96%. This is more accurate compared to existing (manual) methods, which achieved a user’s and producer's accuracy of 86% and 92% respectively. Using a neural network is substantially more efficient than manual methods and can inform a more rapid respond to existing and new biosecurity threats. The method is robust and repeatable and has potential for mapping other commodities and land uses which is the focus of future work.

The effects of different levels of carbon limitation on the flower development of custard apple were studied in two defoliation experiments. The duration of flower development was unaffected by moderate carbon limitation, but increased with severe limitation. Both moderate and severe limitation caused a decrease in flower dry weight. Some of the data collected were combined with data from an earlier study to develop a model of the dependency of the duration of flower development on temperature. The model was applied to long-term weather records from Alstonville, northern New South Wales, to illustrate the effects of late 20th century warming on the duration of flower development.

Many pollinator species visit multiple crops in multiple regions, yet we know little about their pollination service provisioning at local and regional scales. We investigated the floral visitors (n = 13,200), their effectiveness (n = 1718 single visits) and response to landscape composition across three crops avocado, mango and macadamia within a single growing region (1 year), a single crop (3 years) and across different growing regions in multiple years. In total, eight wild visitor groups were shared across all three crops. The network was dominated by three pollinators, two bees (Apis mellifera and Tetragonula spp.) and a fly, Stomorhina discolor. The visitation network for the three crops was relatively generalised but with the addition of pollen deposition data, specialisation increased. Sixteen managed and wild taxa were consistently present across three years in avocado, yet their contribution to annual network structure varied. Node specialisation (d’) analyses indicated many individual orchard sites across each of the networks were significantly more specialised compared to that predicted by null models, suggesting the presence of site-specific factors driving these patterns. Identifying the taxa shared across multiple crops, regions and years will facilitate the development of specific pollinator management strategies to optimize crop pollination services in horticultural systems.

Tree condition, pruning and orchard management practices within intensive horticultural tree crop systems can be determined via measurements of tree structure. Multi-spectral imagery acquired from an unmanned aerial system (UAS) has been demonstrated as an accurate and efficient platform for measuring various tree structural attributes, but research in complex horticultural environments has been limited. This research established a methodology for accurately estimating tree crown height, extent, plant projective cover (PPC) and condition of avocado tree crops, from a UAS platform. Individual tree crowns were delineated using object-based image analysis. In comparison to field measured canopy heights, an image-derived canopy height model provided a coefficient of determination (R²) of 0.65 and relative root mean squared error of 6%. Tree crown length perpendicular to the hedgerow was accurately mapped. PPC was measured using spectral and textural image information and produced an R² value of 0.62 against field data. A random forest classifier was applied to assign tree condition into four categories in accordance with industry standards, producing out-of-bag accuracies >96%. Our results demonstrate the potential of UAS-based mapping for the provision of information to support the horticulture industry and facilitate orchard-based assessment and management.

We take three approaches to more clearly define the role of carbohydrate (CHO) reserves in the development of evergreen trees. First, we examine the lychee and macadamia literature to develop a whole tree carbon budget to show that current photosynthatemakes a greater contribution to the carbon for new growth than CHO reserves. Second, we show that the presence of leaves is sufficient for the production of a functional new shoots on small, girdled branches with few CHO reserves. Third, we use a shade experiment to show that short-term suppression of whole-tree photosynthesis can severely affect new shoot development. Subsequent decapitation of all branches on both the shaded and control trees resulted in faster bud release in the shaded trees, notwithstanding lower CHO reserves. Overall we argue that the main role of CHO reserves is to buffer the pool of current photosynthate. Although such buffering can be quite strong during periods of high carbon demand, even then CHO reserves are a secondary source of carbon.

An object-based classification and a pixel-based classification were compared for classifying land use using SPOT5 satellite imagery. Object-based classification can potentially offer more rapid and realistic capture of land use features than the more traditional method of pixel-based classification. To test the capability of the object-based classification, we chose pineapple crops because they are an intensive crop, they have characteristic spatial features and they are common in south-east Queensland, Australia. A region-merging multi-resolution segmentation and a hierarchical classification was used for the object-based classification using Definiens Professional version 5 and a supervised maximum likelihood classifier (MLC) was employed for the pixel-based classification. The panchromatic band of the SPOT5 image was enhanced by using a Fast Fourier Transform to optimise segmentation of pineapple crops. The Kappa statistic for the object-based classification was 0.84 compared to 0.74 for the pixel-based classification, however less than a day of editing improved the Kappa statistic of the object-based classification to 0.95. We believe this shows that object-based classification offers an improved method for classifying horticultural crops, because of its ability to segment satellite imagery into real-world objects using hierarchical scales, feature shape and context, as well as allowing the user to include expert knowledge and manually edit results.

To examine the effect of early-climacteric (postripening) 1-methylcyclopropene (1-MCP) exposure on the shelf-life and quality of green Cavendish bananas ('Musa acuminata' cv. Williams) from the middle section of the bunch, bananas were harvested bimonthly and treated with 100 μL L−¹ ethylene for 2 consecutive days prior to exposure to 0, 100, 300, 1000, 3000 or 10 000 nL L−¹ 1-MCP for 24 h prior to storage at 22°C. 1-MCP treatment at a concentration of 300 nL L−¹ or above increased banana shelf-life significantly compared with the control, regardless of the month in which fruit were harvested except March where a higher concentration was needed (3000 nL L−¹). Fruit harvested in May were the most responsive with a greater than twofold increase in shelf-life. To examine the effect of fruit position in the bunch on 1-MCP efficacy, green fruit from the top or bottom of bunches were treated with 100 μL L−1 ethylene for 2 consecutive days prior to early-climacteric 1-MCP (300 nL L−1) exposure for 24 h at 22°C. In spring and autumn but not in summer, application of 1-MCP to early-climacteric fruit was more effective in fruit from the top than in those treated from the bottom of the bunch, increasing shelf-life. Firmness of 1-MCP-treated fruit was up to 19% greater than that of the control across the year, except in fruit from the bottom of the bunch. Given that 1-MCP is less effective in extending the shelf-life of summer-harvested fruit (particularly those from the bottom of the bunch), we conclude that preharvest conditions and fruit position in the bunch affect their responsiveness to ethylene and their behaviour during the ripening process.