INTRODUCTION
There are two ‘distinct’ forms of passion fruit, the golden or sour passion fruit (Passiflora edulis f. flavicarpa) and the purple one (P. edulis f. edulis)Footnote 1. Both are believed to have originated on the edges of the tropical rainforests in South America (Brazil). The golden form is grown in the lowland tropics, while the purple form, together with their hybrids, is found in the subtropics and at high altitudes (up to 3000 m) in the tropics. After the ‘discovery’ of the ‘New World’ in 1492, the first plant of the Passiflora group to be named outside South America was grown in Spain in 1553 (Bernacci et al., Reference Bernacci, Soares-Scott, Junqueira, Passos and Melletti2008). The passion fruit then spread rapidly and, by the end of the 19th century, it was widely distributed throughout the tropics and subtropics within the latitude range 0–35° N and S. Currently, about 95% of passion fruit production is with the golden or yellow form (Joy, Reference Joy2010). In Australia, 95% of the planted area is with hybrid cultivars (Rigden, Reference Rigden2012a).
Reliable data on the current area and productivity of passion fruit are unavailable. von der Linden (Reference Von der Linden2007) has indicated how four South American countries, Brazil, Ecuador, Colombia and Peru dominate the world's processed pulp market. The structure of the industry varies from country to country. Brazil, for example, is both the largest producer and the largest consumer of fresh and processed passion fruit. It has been estimated by Joy (Reference Joy2010) (and others) that there are in total about 35,000 ha of passion fruit planted in Brazil, producing 480,000 t of fresh fruit, most of which is consumed within Brazil. With its numerous and extensive plantations, mainly in the provinces of Bahia and Sergipe, it accounts for 50–60% of the total world production (857,000 t of fresh fruit). According to Borges and Lima (Reference Borges, Lima and Johnston2007), the passion fruit in Brazil is cultivated predominantly in small orchards each one to four hectares in area. Among fruit crops, it is an attractive farming choice since it provides a fast economic return, with the income distributed reasonably evenly throughout the year (Bernacci et al., Reference Bernacci, Soares-Scott, Junqueira, Passos and Melletti2008).
Ecuador is the world's largest exporter of processed passion fruit – puree, juice and concentrate. The juice is high in vitamin C (30 mg/100 g). The fruit has been widely used in folk medicine in South America to treat a number of ailments, including anxiety (Zibadi and Watson, Reference Zibadi and Watson2004). Thousands of Ecuadorian farmers and their families depend solely on passion fruit cultivation and fresh fruit sales; fruit is delivered to collection centres where it is sold on to processors. By contrast, in Colombia and Peru, processing companies either buy from contract farmers with no intermediaries involved or use fruit from their own orchards (von der Linden, Reference Von der Linden2007).
Menzel and Simpson (Reference Menzel, Simpson, Schaffer and Andersen1994) have reviewed the physiology of passion fruit. This followed an earlier review by Menzel et al. (Reference Menzel, Winks, Simpson, Bose and Mitra1990). Morton (Reference Morton1987) has provided a detailed description of the culture of passion fruit. Similarly, Borges and Lima (Reference Borges, Lima and Johnston2007) have reviewed the Portugese literature (mainly) on the same topic. A detailed and comprehensive description of passion fruit, and its culture in India, can be found on the Internet (KAU, 2013). An attempt is made in this paper to synthesise the limited amount of research reported on the water relations of passion fruit, and to do this in practically useful ways. It follows the format used in previous reviews in this series, including those of other crops grown for their fruit, such as banana (Carr, Reference Carr2009), coconut (Carr, Reference Carr2011), Citrus spp. (Carr, Reference Carr2012a) and pineapple (Carr, Reference Carr2012b). It begins with a description of the stages of crop development in relation to water availability, followed by reviews of plant water relations, water requirements and water productivity, and irrigation systems.
CROP DEVELOPMENT
The phenology of passion fruit is covered in the sequence vegetative growth, flowering, fruiting and root growth. The visible symptoms of water stress are summarised.
Vegetative growth
Morton (Reference Morton1987) described the passion fruit vine as a shallow-rooted, vigorous, woody perennial climber, climbing by means of tendrils. In commerce, the vines are supported on wire trellises. Passion fruit vines are usually grown from seeds, but grafting onto yellow-form rootstocks is also practised. Planting densities are variable, typically 2.5 m or 3 × 3 m (1100–1300 plants ha−1), but in warm areas plants may be thinned after the first year to give a density of 700 plants ha−1. Leaves grow in a sigmoid pattern and, in a container experiment, an individual leaf reached a maximum area of 65 cm2 when well-watered over a period of 15–18 days (Turner et al., Reference Turner, Menzel and Simpson1996). Drying of the whole root system stopped leaf expansion after six days, but did not change the pattern of leaf expansion. Growth resumed after re-watering but the final size of the leaves was halved. A midday leaf water potential of −1.5 MPa was associated with a 50% reduction in the relative leaf expansion rate, while leaf production virtually ceased at leaf water potentials below −2.0 MPa. Leaf production is fastest at air temperatures in the range of 24–38 °C (Menzel and Simpson, Reference Menzel, Simpson, Schaffer and Andersen1994).
In detailed experiments the root-zone temperature was varied over the range 10 to 38 °C for a grafted hybrid cultivar. The critical lower and upper root-zone temperatures for vine extension, leaf area, leaf node and leaf production were identified as 20 °C and 35 °C (Menzel et al., Reference Menzel, Turner, Doogan and Simpson1994). Beyond these temperature limits the rates of growth were less than 90% of the maximum recorded. The corresponding temperatures for flower production were 20 °C and 30 °C, and for leaf and stem dry weight 18 °C and 34 °C, while maximum root dry weight occurred at 38 °C. The authors considered that productivity of passion fruit would be adversely affected in cool subtropical areas if the soil temperature at depths of 0.15 m was either below 20 °C or above 30 °C in the tropics.
Flowering
A single flower bud is borne at each leaf node on new growth. Cross-pollination is mainly by bees. Flower (golden) receptivity (for pollen) declines sharply after about 1400 h (Souza et al., Reference Souza, Pereira, Viana, Pereira, Amaral and Madureira2004). Rain within two hours of pollination prevents fruit set (Morton, Reference Morton1987). Pollen is ripe three to four hours before the stigmas are receptive. Most golden cultivars are self-incompatible, and need to be cross-pollinated. This is not the case with purple forms or hybrids. After a certain number of fruits (from 4 to 10) have set along a branch, a temporary cessation of new vegetative growth, flowering and fruit setting occurs. These processes do not commence again until the fruit is mature (Menzel et al., Reference Menzel, Winks, Simpson, Bose and Mitra1990). Flower buds are not initiated under dry conditions. Pruning once a year stimulates new growth, while regular watering keeps the vine flowering almost continuously. Pruning is not practiced in Australia because of its expense. Instead, growers replant an orchard when the vegetation becomes too dense, as this can lead to pest and disease problems (Rigden, Reference Rigden2012a).
Menzel et al. (Reference Menzel, Simpson and Dowling1986) showed in a glasshouse experiment in Australia how even mild water stress (soil water potential of −0.01 MPa) can reduce all aspects of vegetative growth of a hybrid passion fruit, including the number of leaf nodes. The number of flower buds and flowers was also reduced. Flower bud initiation is the most sensitive stage of development, while developing flower buds appear to acquire some resistance to desiccation. Moisture stress also reduced flower size, but did not lead to premature abscission (Menzel et al., Reference Menzel, Simpson and Dowling1986). Staveley and Wolstenholme (Reference Staveley and Wolstenholme1990), in a very similar experiment in South Africa (with purple passion fruit grafted on to P. caerulea (red rootstock)), came to many of the same conclusions. In addition, the number of days to first fruit set was reduced by soil water stress. Based on these observations, it was recommended that the soil water potential should be maintained above −0.02 MPa during the critical periods of flower differentiation and fruit set.
Fruiting
Plants start to bear fruit within six to eight months from field planting. The fruit matures 60–90 days from fruit set (Menzel et al., Reference Menzel, Winks, Simpson, Bose and Mitra1990). Harvesting occurs throughout the year, but yields vary month by month. For example, in Brazil, during a so-called normal year, peaks of production occur in October and November (spring) and again in April (autumn). Crop distribution is similar in Ecuador, but with a subsidiary peak in July/August. In Peru, there is one large peak from July to September (representing 50% of the annual crop) and a secondary peak between January and March (30%). In Colombia, the main harvesting season is in June and July, and also January (von der Linden, Reference Von der Linden2007). In Queensland, yield peaks occur from May to August and from December to February (Passionfruit Australia Inc., 2012). Fruit set on one branch is harvested over a two- to three-month period. The centre of the fruit is filled with a pulpy aril that surrounds numerous small black seeds. Each plant can produce 300–600 fruits per year. Although, for example, a fresh fruit yield of 60 t ha−1 is possible in Kenya, a good commercial yield is 20–30 t ha−1 (Samson, Reference Samson2003).
Roots
Although passion fruit is described as shallow-rooted by Morton (Reference Morton1987), there is little published evidence to support this view. According to KAU (2013), passion fruit has a superficial root system with 60% of the roots (by mass?) located within 0.30 m of the surface. According to Rigden (Reference Rigden2012a) roots extend to depths of >1 m in some soil types (e.g. Aflisols) in Australia, but in most soils roots are concentrated within 0.5 m of the surface. Root depth is limited in the field if plant roots are distorted when they reach the bottom of the nursery polybag. Most growers in Australia replant every two years, some every year, mainly to control pest, viral and fungal disease problems. This will limit the maximum rooting depth.
In two container experiments conducted in Australia, root growth was measured. In one experiment, although water stress reduced the absolute dry weight of roots, the proportion of plant dry matter translocated to the roots compared with the leaves and stems increased (Menzel et al., Reference Menzel, Simpson and Dowling1986). In the second experiment, in which the soil volume available for the roots to exploit was varied, shoot weight was correlated with root weight, but a smaller proportion of dry matter was allocated to roots as the root weight increased (Menzel et al., Reference Menzel, Turner, Doogan and Simpson1994). In a recent detailed review of 65 pot experiments (with different plant species), Poorter et al. (Reference Poorter, Bühler, van Dusschoten, Clement and Postma2012) showed clearly that pot size matters, and how important it was for researchers to identify the right size of pot to ensure that the results were not distorted by the influence of pot size on biomass production.
Visible symptoms of water stress
Menzel et al. (Reference Menzel, Simpson and Dowling1986) observed the following changes in appearance after the imposition of water stress on pot-grown passion fruit hybrids. Staveley and Wolstenholme (Reference Staveley and Wolstenholme1990) also recorded similar symptoms:
• Stems thinner.
• Tendrils shorter.
• Leaves and flowers smaller.
• Side shoots fewer.
• Young leaves become yellow-green.
• Mature leaves become dull grey-green.
• Basal leaves turn yellow and senesced prematurely.
• Newly developed axillary shoots die.
• Marginal and tip necrosis develop in the leaves.
• Terminal shoots, young leaves and tendrils wilt at midday.
• Guttation from glands on the leaf margins and from the floral bracts is reduced.
It is important to note that dry matter production is restricted long before these visible symptoms appear. Similarly, it should be remembered that symptoms of water stress develop much more quickly/suddenly in pot-grown plants than in similar plants growing in the field; there is also less time for the plants to adapt to the dry conditions.
Summary: plant development
1. Leaf production virtually ceases at a leaf water potential of −2.0 MPa, and expansion of new leaves is considerably reduced at −1.5 MPa.
2. A single flower bud forms at each leaf node of new growth.
3. Water stress reduces leaf and floral bud initiation.
4. Flower bud development and fruit set are less sensitive to water stress than leaf initiation.
5. Heavy rain at flowering prevents fertilization; the pollen grains on stigma burst on contact with water. Extended periods of rain result in poor fruit set.
6. Unevenness in crop distribution during the year may be linked to water stress and temperature variation.
7. There is little quantitative evidence to support the view that the passion fruit plant is shallow-rooted.
PLANT WATER RELATIONS
Apart from a series of pot experiments undertaken in Australia, very little research appears to have been reported on the water relations of passion fruit. Turner et al. (Reference Turner, Menzel and Simpson1996) demonstrated how, by drying half the root system, non-hydraulic root signals influenced leaf expansion rates and flowering of passion fruit. Leaf expansion was reduced by 26% compared with a well-watered control, and water use was reduced by 21–27%. By contrast, there was no effect on the leaf water potential or on net photosynthesis rates. Plants with half the root system dry flowered five to seven days earlier than well-watered plants but had the same number of open flowers one month after treatments ended. These results question the validity of scheduling irrigation on the basis of measurements of leaf water potential. In another pot experiment, Menzel et al. (Reference Menzel, Simpson and Dowling1986) found that there were only small changes in leaf conductance in passion fruit over a wide range of leaf water potentials (−0.5 to −2.6 MPa).
In Brazil, Gomes et al. (Reference Gomes, da Luz, dos Santos, Batitucci, Silva and Falqueto2012) compared the responses to dry conditions and subsequent recovery of two container-grown passion fruit cultivars (Yellow Master (FB200) and Maguary (FB300) in terms of chlorophyll a fluorescent transients (Fv/Fm and ABS/RC ratios). Using the JIP-test, this evaluation showed that the two one-year-old cultivars differed in the plasticity of their responses to drought and re-watering. FB200 plants had an advantage over FB300 plants in terms of their efficiency in utilizing energy.
Summary: plant water relations
1. A limited amount of research has been reported on the water relations of passion fruit. Most experiments published have used container-grown plants.
2. Some evidence suggests that partial root zone drying can influence leaf expansion and time of flowering independent of any direct hydraulic mechanism.
CROP WATER REQUIREMENTS
Advisory leaflets and other publications from Brazil indicate that the passion fruit does best where the annual rainfall is between 800 mm and 1700 mm, with mean air temperatures of 23–25 °C (cited by Borges and Lima, Reference Borges, Lima and Johnston2007). In São Paulo State, Brazil (22°43′ S 47°38′ W: alt. 576 m), Silva et al. (Reference Silva, Folegatti, Silva, Alves and Bonfin-Silva2007) successfully used the Bowen-ratio, energy balance method to monitor the water use of passion fruit (cv. IAC 275). In this subtropical humid location, with a dry winter, two row-orientations were compared, north–south and east–west. The plants, spaced 4 × 4 m, were supported on a vertical structure with a single wire 2 m above the ground surface. The crop was well irrigated. Measurements began about two months after transplanting. Over the 12-month (2003/2004) period of measurement, the average potential evapotranspiration rates (ETc) for both row orientations were statistically similar: namely, 4.1 mm d−1 (equivalent to 1500 mm a−1) and 3.5 mm d−1 (1300 mm a−1) for north–south and east–west orientations respectively. In five individual months (December, January and February, and July and August) ETc was greater in the north–south rows than the east–west. Peak rates of water use occurred in November (average 5.5 mm d−1) and December (5.8 mm d−1), both for the north–south row orientation, and the minimum rate of use was in July (2.0 mm d−1) in the east–west orientation. Unfortunately, no attempt was made to relate these ETc figures to estimates of reference crop evapotranspiration (ETo) to derive values for the crop coefficient (Kc).
In a lysimeter-based experiment with the yellow passion fruit in tropical Brazil (6°53′ S 36°02′ W; alt. 470 m), ETc rates during apical vegetative growth after transplanting averaged 2.8 mm d−1. These increased to 5.0 mm d−1 when the side branches were developing, and then to 5.7 mm d−1 when the plants were flowering and fruiting. When averaged across a number of ancillary treatments, the corresponding Kc values (based on a Penman–Monteith estimate of ETo) were c. 0.57, 0.90 and 1.10 respectively. Irrigating with saline water (4.5 dS m−1) reduced ETc rates by 18% during vegetative growth and by 8% when the plants were in flower and forming fruit. An organic mulch reduced total water use (ETc) by about 5% (Freire et al., Reference Freire, Cavalcante, Rebequi, Dias and Souto2011). In a similar lysimeter study again in Brazil, the values of Kc varied from 0.42 to 1.12 (Silva and Klar, Reference Silva and Klar2002).
De Souza et al. (Reference De Souza, Bezerra, Viana, Teófilo and Cavalcante2009) used the water balance approach to estimate the ETc rate of passion fruit in the Curu Valley in Brazil (3°45′ S 39°15′ W) over a ten-month period (2004/2005) together with the corresponding Kc values. Basing their measurements on a 0.6-m deep soil profile, ETc totalled 1500 mm in the 296 days (5.8 mm d−1) following transplanting. The Kc values for the same three-crop growth stages as defined above were 0.65, 1.13 and 1.25 (overall average value = 1.09), when based on ETo (Penman–Monteith), or 0.7, 0.9 and 1.1 (mean = 0.9) for a USWB Class A pan.
Summary
1. The ETc rates of up to 5.8 mm d−1 have been consistently measured in Brazil using three different methods: Bowen ratio, lysimeters and a soil water balance.
2. The Kc value, based on a Penman–Monteith estimate of ETo, varies with the stage of growth from about 0.6 during apical extension growth up to 1.10–1.25 in the reproductive phase.
3. The FAO Irrigation and Drainage Paper 56 does not mention passion fruit (Allen et al., Reference Allen, Pereira, Raes and Smith1998).
WATER PRODUCTIVITY
Water stress (unquantified) reduces the current crop and also the development of flowering shoots for the next crop. Cropping is less seasonal with irrigation. A few controlled irrigation experiments have attempted to quantify these responses, mainly in Brazil.
In Brazil (22°43′ S 47°38′ W), de Sousa et al. (Reference De Sousa, Folegatti, Frizzone, Corrêa and Eloi2003) studied the yield response of golden passion fruit to irrigation (and potassium). The four (drip) irrigation treatments were based on applying a fixed proportion (in theory, 0.25, 0.5, 0.75 and 1.0) of the potential water use (ETc) of a passion fruit plant as recorded in a drainage lysimeter (measuring 1.5-m deep × 1.23-m2 surface area). Supplementary watering was necessary from April to October, when the Eto rate varied between 1.8 mm d−1 and 4.4 mm d−1. The actual volume of water applied in a year ranged from 927 L plant−1 to 2706 L plant−1, a three-fold difference. As the vines were spaced 3.5 × 4.0-m apart (714 plants ha−1), 2706 L plant−1 equates to about 200 mm year−1. The (commercial) yield response to water appeared to vary with the level of potassium fertilizer applied: at least the fitted response curves as published had different shapes. But when averaged (crudely) over all five potassium treatments, the yields from the two extreme irrigation treatments (0.25 × ETc and 1.0 × ETc) were almost identical.
In what appears to be the same experiment, de Sousa et al. (Reference De Sousa, Frizzone, Folegatti and Viana2005) later reported the water use efficiencies (water productivities) for each treatment combination. Values ranged from 8 kg (commercial fruit) ha−1 L−1 in the wettest treatment up to 34 kg ha−1 L−1 in the least wet treatment. It does not appear to be possible to draw any practically useful conclusions from this experiment. Carvalho et al. (Reference Carvalho, Martins, Monerat and Bernado1999) had earlier reported the results of a similar 18-month duration experiment (with the yellow form) with variable amounts of water applied (six levels, from rainfall only up to 1.25 × ETo) in combination with potassium fertilizer at four rates from 76 up to 760 g (K+) plant−1 (as KCl). The highest yields of fruit were obtained from the 0.85 × ETo treatment combination (namely, 0.85 ETo with 434-g K+ plant−1).
Carvalho et al. (Reference Carvalho, Martins, Monerat and Bernado2000) reported on a similar experiment, again in Brazil, but this time with nitrogen and water as the two variables studied. There were six irrigation treatments: a rainfall only (control), together with the replacement of fixed proportions of ETo, namely from 0.25 to 1.25 times ETo. Because only graphs showing statistical relationships without any data points are presented, it is not possible to judge the quality of the results, and the validity of the conclusions.
In equatorial Kenya (alt. 2185 m), passion fruit is an attractive crop for small-scale farmers because it has good local and export markets and can be harvested throughout the year. Gaturuku and Isutsa (Reference Gaturuku and Isutsa2011) reported the results of an irrigation experiment in Kenya with purple passion fruit vines grown in a silt-clay soil under a rain-shelter. Water was applied at fixed weekly rates (2.5, 5, 10 and 20 L plant−1) for a period ending 56 weeks after planting. It is not explained why or how these rates were selected. At a spacing of 1.5 × 1.5 m, 20 L plant−1 equates to only about 1.2 mm d−1. After 56 weeks there was no difference in the cumulative number of fruits harvested between treatments (range, dry to wet, 200–228 fruit plant−1) but there were differences in the fresh weight of fruit (range 5050–6016 g plant−1). There was no effect of mulch (black plastic, wheat straw, bare soil) on the cumulative number or weight of fruit. Neither the irrigation treatments nor the mulches had any effect on the many attributes of fruit quality recorded. Given the small quantities of water applied, and the failure to interpret the data in ways that might be useful, it is not obvious what can be learnt from this experiment.
Over a three-year period (2005–2007), Srinivas et al. (Reference Srinivas, Sulladmath, Palanappan and Venugopalan2010) conducted a field (drip) irrigation experiment in Bangalore, India (13°58′ N; alt. 858 m). The two watering treatments compared were 25% and 50% replacement of evaporation from a USWB Class A pan, applied on a daily basis after allowing for rainfall. Seedlings (cv. Kaveri), 40 days old, were planted in the field at a spacing of 3 × 3 m and subsequently trained on to a bower. The first harvest was made 185 days after planting and harvesting continued for another 175 days, at intervals of eight to 10 days. After the first 20 harvests, a total of 361 fruits plant−1 had been harvested from the 50% replacement treatment compared with 305 fruits plant−1 from the 25% replacement (a reduction of 15%). The corresponding yields of fresh fruit were 23 and 19 kg plant−1 (−17%). In the second group of harvests (15 in total) fruit yields totalled 12 and 10 kg plant−1 respectively (−19%). Yield differences were mainly the result of differences in fruit number, not size. The yield figures are averaged over four fertilizer treatments. As there was no control – ‘dry’ – treatment, nor a well-irrigated treatment from which to set yield limits, no broad conclusions can be drawn from this experiment. The (recalculated) incremental water productivity, between the 50% and 25% replacement treatments (assuming that the term water-use means irrigation water applied), equated to 25 kg (fresh fruit) ha−1 mm−1 (irrigation).
Fruit cracking can occur during fruit development when heavy rain follows a period of dry weather. The fruit skin cracks because of abrupt changes in the pressure (turgor) potential in the skin of the fruit, and the sudden expansion of the fruit that follows. As the fruit grows, the cracks become corky. Irrigation can help to reduce the incidence of fruit cracking.
Summary: water productivity
1. A few worthwhile irrigation experiments with passion fruit have been reported.
2. There is a need to undertake realistic field-based research to quantify the yield responses of passion fruit to water.
3. The only (crude) estimate of (irrigation) water productivity for passion fruit is 25 kg (fresh fruit) ha−1 mm−1.
4. The crop is not included in the FAO Irrigation and Drainage Paper 66 (Steduto et al., Reference Steduto, Hsiao, Fereres and Raes2012).
IRRIGATION SYSTEMS
In Australia, an Enviroscan was used to monitor the irrigation of passion fruit with micro-sprinklers (Anon, 2010). At the commencement of measurements there was full trellis cover with a good fruit load. Probes were located along the plant line, and sensors were placed at depths of 0.1, 0.2, 0.3, 0.5 and 0.7 m. Over the spring and summer, and the early autumn period (2009/2010), crop water use ranged from 2.5 to 5.4 mm d−1, but declined to <1 mm d−1 in winter. In the sandy loam soil, the effective rooting depth was at least 0.7 m. The wetted diameter was 1.8 m, and the distribution uniformity from the micro-sprinklers was judged to be very good (>90%). The resultant Enviroscan graphs illustrating changes in soil water content over time at each depth, as well as daily totals of rainfall and irrigation, were informative.
In Queensland, Australia, irrigation is considered to be essential for growing high quality passion fruit. Growers are strongly encouraged to schedule irrigation scientifically. Soil water monitoring devices, such as tensiometers and gypsum blocks, as well as capacitance probes are recommended (Rigden, Reference Rigden2012b).
In Brazil (6°50′ S 38°19′ W; alt. 235 m), Soares et al. (Reference Soares, Carneiro, Gomes, Gheyi and Fernades2008) compared the responses of yellow passion fruit to supplementary irrigation with saline water at five levels of electrical conductivity ranging from 0.2 t to 5.0 dS m−1. Over a period of 10 months, there were no discernable adverse effects on any of the growth attributes measured, including yield. By contrast, Freire et al. (Reference Freire, Cavalcante, Rebequi, Dias and Souto2011) found that irrigating with water with an electrical conductivity of 4.5 dS m−1 for 150 d after transplanting reduced growth and water use compared with the control treatment (0.5 dS m−1).
Summary: irrigation systems
1. As with most fruit crops, micro-sprinklers and drip are the most effective and precise ways of irrigating passion fruit (combined with fertigation).
2. Beware of damaging the pollen during peak flowering with sprinkler irrigation, alternatively irrigate at night.
3. The Enviroscan is a useful way of monitoring soil water content.
4. There is a limited amount of information on the response of passion fruit to saline irrigation water.
CONCLUSIONS
In Australia, by 2010, there were about 300,000 vines planted, producing in excess of 3000 t of fruit annually. The industry is looking to expand and in 2010 published a Strategic Action Plan (Passionfruit Australia Inc., 2012). Some of the issues in that plan are highlighted here since they relevant to this paper:
• Potentially climate change and variability may impact the growing conditions in established production regions, leading to changes in productivity and business viability.
• Changes in available water for crop production; climate patterns and micro-climates that affect crop set and/or fruit quality; pest and disease pressures and a range of other factors have the potential to have a positive or negative impact on production.
• Optimal production capacity can be achieved through improved varieties; access to disease-free planting material and improved agronomic practices, including pest and disease, nutrition, canopy and irrigation management.
This review has highlighted at an international level the need to strengthen our scientific understanding of how passion fruit responds to its environment, in particular the role of water in its development and productivity. As an under-resourced, minority crop the way forward for the passion fruit industry must be through international cooperation on research topics of generic importance, including water.
Acknowledgements
I acknowledge with thanks the advice and help provided by Peter Rigden and Professor Robert Paull.
