Extending the harvest window

Advancing or delaying mango flowering has the potential to improve the efficiencies and profitability of the Australian mango industry. Spreading mango production will create a more regulated supply of fruit from the start until the end of the season. This control will assist in managing the overlap between production regions and expand the duration of cropping, ideal for growing export demand.

A deeper understanding of the mechanisms within a mango tree that control flowering and fruiting is being studied by two complementary projects. Through the knowledge of what stimulates the genes associated with flowering, more targeted practices to effectively manipulate mango crops will be developed. The information will be used to develop tools and methodologies to monitor and manipulate flowering to maximise profit.

The process of mango gene expression is thought to be a key factor in expanding the harvest window. Researchers will identify treatments, such as growth regulators, that inhibit or stimulate the activity of these genes and understand more about their role in flower initiation and subsequent effects on harvest timing. To enable screening of chemical uptake and precise monitoring of tree responses, an aeroponics system to monitor root and vegetative growth has been developed. This enables rapid screening of existing and new cultivars without the need to plant and wait for the new orchards to develop.

Project Leader Mark Hickey said that he estimates this technology could extend the harvest window by three to five weeks on individual properties.

“Improved practices will give mango growers more tools to know if and when their trees will flower and whether treatments to induce mango flowering were successful before flowers appear. Being able to shift the time that flowering occurs will expand export opportunities. It will also increases the return on investment for equipment that can be utilised for a longer period of time and will reduce reluctance by producers to invest in new technology which potentially is only utilised for a few weeks of the year,” he said.

The success of these technologies relies on their effectiveness under commercial orchard conditions and integration with existing on-farm practices. The potential benefits of crop manipulation for the Australian industry are considerable. A recently conducted benefit/cost analysis demonstrated that these projects would yield a return for the Northern Territory industry of up to $2 million per season from 2019/20 onwards. This additional value is due to an extended harvest window and reduction in losses due to over concentration of the harvest period.

“The key to managing flowering is to understand when buds start developing. In the early stages of development, old mature leaves detect and are responsive to temperature and inductive treatments. Early season flowering in the Darwin region can be triggered by evening temperatures below 20°C. These conditions are produced by high pressure systems travelling easterly across Australia from the Western Australian coast. Growers can promote bud growth in anticipation of these conditions by applying timed sprays of potassium nitrate,” Mr Hickey said.

“Promoting early flowering and cropping is practiced by some growers in Australia to access higher priced market windows. A number of methods are used including chemical treatments, selective pruning, restricting irrigation and organic amendments. The success of these programs has been limited by a misunderstanding of the role weather conditions has on the process and an incomplete suite of tools to redress the situation if orchards become out of synchrony with environmental conditions.

The first stage of the research has involved optimising chemicals used worldwide that can potentially control flush growth and initiate and regulate flowering. Ethephon was thought to mature vegetative flush but Australian research has shown that it can reset flushing patterns and remove insensitive immature leaves. This treatment increases the likelihood of trees being in a prime condition to receive the triggers to flower. Similarly potassium nitrate has been widely used to give flowering more uniformity in Australia and work in the NT has shown that it can induce flowering in Kensington Pride trees in the absence of inductive temperatures. A better understanding of the long term impacts and environmental effects of these chemicals on mango trees and pesticide residues need to be understood and will be a component of this research.

“We have been investigating flower manipulation techniques used by Cambodian mango farmers to induce out of season flowering and double crop their mango trees. While double cropping may not be feasible in Australia, the techniques used to manipulate flowering and long term impacts on tree health are of interest to our team,” Mr Hickey said.

The project Building a resilient mango industry in Cambodia and Australia through improved production and supply chain practices is funded by the Australian Centre for International Agricultural Research and managed by the New South Wales Department of Primary Industries. ACIAR fund international and domestic research to improve the productivity and profitability of agricultural systems in partner countries as well as providing benefits to Australian industries. The projects is supported by project Manipulating mango flowering to extend harvest window which is co-funded by the Northern Territory Department of Primary Industries and Fisheries and Horticulture Innovation Australia.

Read the ABC story: Mango tree manipulation trial starts to bear fruit near Darwin