Papaya, Mango, Lychee, Longan, Rambutan and Durian

Part 2 of the fascinating possibilities of tropical fruit production using protected cropping in NZ – By Dr Mike Nichols

Papaya:

Several years ago, there was some interest in the production of a papaya like fruit (called babaco) in New Zealand.  It never really caught on, perhaps because it is inferior in taste (being less sweet) than the standard papaya.  Papaya is now grown in southern Europe in plastic greenhouses (at Almeria (37N) in southern Spain). (Hueso et al., 2019) This is similar in latitude to Kaitaia, but due to it’s Mediterranean climate is slightly cooler in winter and warmer in summer than Kaitaia. An international symposium on papaya is scheduled for 2023 in Almeria, where greenhouse production will obviously be discussed.

Greenhouse production of papaya in southern Spain for the European market means that the fruit can be harvested closer to maturity, and therefore much sweeter and attractive, compared with fruit which must be harvested slightly immature when grown in the tropics.  Freight costs are also reduced.

There is some talk of the Cook Islands growing Papaya for New Zealand, (Fotheringham, 2021) but (in my view) this has three major constraints, namely: the need to treat the fruit against fruit fly before it enters New Zealand: the airfreight costs: and the lack of modern horticultural knowledge in the Cook Islands.

Papaya can be grown from seed, which poses some problems in that plants can be either male or female or hermaphrodite, and it is only the hermaphrodite plants that are required.  This means that the seedlings must be grown on until they flower, in order to select only the hermaphrodite plants. A long term prospect may be the grafting of selected scions onto a seedling rootstock.  Intenzza (a hybrid from Mexico) is currently the most popular variety for greenhouse production and can reach yields of 200t/ha in a 2-year cropping cycle.  For greenhouse production precocious cultivars of moderate height are desirable.

Winter temperatures appear to be the important determinate of crop production and quality, and some heating during the winter may provide valuable economic advantages. 

Like most crops they are likely to perform better if grown hydroponically.

Mango:

Virtually all the fresh mangos sold in New Zealand are sourced from Australia's Queensland and Northern territory, where they are grown in large plantations.  Fruit fly is the major consideration for export to New Zealand.  Most mango trees are large and would be totally unsuited to any form of protected cultivation, but the development of dwarfing root stocks opens up the potential for high density plantings of easy to harvest fruit on trees only 3-4 m tall (see photo).   Although the control of flowering of mangos is not fully understood, it would appear that drought followed by rain are important.  ie like many of the tropical fruit crops (see Salakpetch, 2008) flowering is triggered by rain following floral imitation during a dry period.   The only real question is what the potential might be in growing the plants (trees) hydroponically.    There is no doubt that hydroponics offers considerable advantages in crop production over growing in the soil (see Gruda, 2021), e.g. better moisture control, efficient nutrient management etc.   The question is how does it measure up in dollars of profit?   

Lychee, Longan & Rambutan:

These all belong to the same plant family (Sapindaceae), and it appears from the literature that flower initiation requires a drought stress, followed by rains.  High tunnels (as rain shelters) will provide the opportunity to drought stress the trees—particularly if they are grown hydroponically in large pots rather than in the soil.  Control of flowering should also provide a significant control of plant vigour, and thus enable to trees to be grown  in a dwarf manner.      

Durian:

We are unlikely ever to see Durian fruit imported into New Zealand.    It has a disgusting smell yet has a very pleasant taste and texture.  For this reason, it is described as the king of the tropical fruits.  On one of my visits to Malaysia I was given a durian fruit by a former student but was refused entry into my hotel until I had eaten it.  It is certainly persona non grata on aeroplanes!!  I am sure that it would find a ready market if it could be successfully grown in New Zealand. 

Other tropical fruits?

There is a wide range of other tropical fruits which deserve to be grown in New Zealand.  Many of them have already been tried, but with mixed success.  With global warming and the additional protection afforded by relatively cheap plastic clad greenhouses the potential is excellent.  New Zealand's unique freedom from fruit fly might one day even open up a market for exporting tropical fruit to Japan!.  

Click on the link to read Part 1 of Dr Nichols article: news/post/tropical-fruit-crops–part-1-/

Reference

Carr., M K V  (2012)  “The water relations and irrigation requirements of pineapple (Ananas comosus var. comosus): A REVIEW”  Experimental Agriculture 48(04)

Fotheringham C (2021) “Growing interest in pawpaw exports” Cook Island News 26 May 2921.   

Gruda N S (2021)  “Advances in horticultural soilless culture”. Burleigh Dodds  424 pp.

Hueso, J J , Salinas, I, Pinillos, V & Cuevas, J  (2019)  “Papaya greenhouse cultivation in south-east Spain” . Acta Hort, 1250, 1,5

Nichols M A (2021).  “Going bananas”  Orchardist, 94 (2), 58-59.

Salakpetch, S (2008) “Cultural practises and physiology of some valuable tropical fruits in Thailand”. Acta Hort. 787, 231-239.

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Developing a Tropical Fruit Industry for the Domestic Market is Enhanced (Part 1)

By Dr Mike Nichols

There is little doubt that global warming is going to result in the warmer areas of New Zealand being able to seriously consider the economics of producing some of the tropical fruits we occasionally import or enjoy when overseas.  There is already an increasing interest in the growing of banana (see Nichols, 2021), and this will result in a growing interest in other tropical fruits such as pineapple, mango, papaya, lychee and perhaps even such “exotic” tropical fruits as rambutan, longan, mangosteen, and perhaps even durian.  There are of course, sound biosecurity reasons for limiting the importation of exotic fruits (eg fruit fly etc). 

Over the past 50 years there has been on going interest in the potential of growing tropical fruits in New Zealand.  These have been directed at the selection of areas where the microclimate was more suitable.  With the development of relatively cheap plastic greenhouses, and global warning, the prospect of developing a tropical fruit industry for the domestic market is enhanced.  

The downside is that to produce these crops affectively will require some form of protected cropping (greenhouses) and in some cases supplementary heating. 

There is a looming shortage of electricity in New Zealand for the future particularly as we move rapidly away from carbon dominated energy sources.  With the bulk of the population in the North Island and Manapouri sourced electricity for the foreseeable future committed to the aluminium smelter there is an urgent need for more environmentally friendly electrical generation in the North Island.  Of course, New Zealand has an advantage over many temperate countries, and that is access geothermal energy.  

The new development by Contact Energy of the Tauhara geothermal power project near Taupo, with it’s Geothermal Energy Park, may well provide this opportunity.  However, heating does not have to be geothermally based, in fact in the Netherlands growers are looking at the possibility of sourcing heating from only a few hundred metres below the soil surface, as the temperature rises by about 2°- 3° C per 100 m in depth.   This geothermal gradient is, however, not the same all over the world but can range from 1° to 5° C/100 m.   This type of system can almost be regarded as a heat pump, with warm air in the summer being pumped underground during the summer (to cool the greenhouse), and heat being extracted from the ground in the winter months.

Pineapples:

There is really nothing unique about the growing of pineapples in temperate countries.  Back in the 19th Century the rich and powerful in England grew pineapples in very well heated greenhouses (called pineries), essentially to demonstrate their affluence.  Currently, however, the majority of pineapples consumed in New Zealand are imported by sea from the Philippines, where they are grown by Dole in a massive plantation at Polomolok.  Because of this they must be harvested ahead of optimum maturity, and are a variety suited both for processing (canning) and for fresh market.

There are small areas of pineapples currently being grown in New Zealand, some in the field (where the microclimate allows), but essentially, I consider that pineapple production in New Zealand requires some form of protected cropping, as I noted during a visit to the Canary Islands (see photo) where the climate is a little bit warmer than Northland.  In fact pineapples would almost certainly respond to supplementary heating in the cooler parts of the year. 

Pineapple is, in fact a unique type of plant.  It has developed the ability to close its stomata on the leaves during the heat of the day, and only open them during the late afternoon and night, so as to reduce water loss by transpiration.  This, of course, prevents carbon dioxide being taken up by the plant for photosynthesis.  However, the pineapple has a unique system called  CAM photosynthesis  in which the stomata are open at night and carbon dioxide is converted into malic acid and stored in the plant cells, and converted into carbohydrate during the day time.  The plant also has the ability to store water in it’s succulent leaves and the leaf axiles.   Nevertheless, it would appear that pineapple will respond to irrigation, as root growth ceases at flowering, and water stress can reduce the number of fruitlets and fruit weight.

The main question then is whether for a high value greenhouse crop whether using hydroponics might be a better approach than a soil-based system.?  Certainly, the advantages of hydroponics over soil for the majority of high value greenhouse crops is clear. Whether the New Zealand public is prepared to pay extra for a fresher product, harvested closer to maturity (and therefore hopefully sweeter) only time will tell.

What is certain is that pineapples crop best in warm temperatures, and that New Zealand is really not warm enough for good production unless we take advantage of modern technology.

Canary Islands 

Part 2 of this article will be posted in the next edition of G2G.

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