Psidium cattleianum
(strawberry guava)

P. cattleianum is naturalized in many tropical and subtropical countries after introduction as an ornamental or a fruit tree. It has invaded humid areas such as rainforests on tropical islands especially in the Pacific and Indian Oceans where it displaces native species and threatens their survival. It thrives in a large range of ecological conditions and reproduces efficiently by seeds and suckers. Once established, it forms dense stands. This species shows allelopathic activity and its fruits host fruit flies (Motooka et al., 2003). Seeds continue to be available via mail-order on websites or seed catalogues, and the species will likely spread further. 

P. cattleianum is native to south-east Brazil and northern Uruguay. It has been widely introduced and now can be found widespread throughout the tropics and subtropics and has become naturalized almost everywhere where it has been introduced, particularly in rainforests and on island ecosystems in the Indian and Pacific Ocean where it is often invasive. 

P. cattleianum is already present in many tropical and subtropical countries. Further spread is probable and relies on deliberate introductions as a rare plant by rare fruit enthusiasts and nurserymen, an ornamental or a fruit tree. Introduction by botanical gardens, research institutes or extension services is possible for the purpose of fruit tree collections or fruit tree trials. This is encouraged by the fact that P. cattleianum appears as a promising new fruit crop for humid areas (Normand, 2002b), and that seeds are available via mail order from seed catalogues and websites. The risk of accidental introduction is likely to be low.

P. cattleianum is found associated with different vegetation types, from dry grassland and scrub to tall native rainforest (Cadet, 1980; Jacobi and Warshauer, 1992). It forms dense monospecific stands, preventing the regeneration of other plants, in particular native species. Habitats include sub-montane rainforest, montane cloud forest, montane rainforest, moist tropical montane forest, riparian forest, tropical evergreen forest, deciduous woodland (oak), tropical montane savanna, lowland sub-tropical rainforest, scrubland, grassland, degraded forest, cultivation and agroforestry systems.

In its native range, P. cattleianum is a plant of forest edges, glades and rangelands in mesothermic humid areas with annual rainfall of at least 1000 mm, without a pronounced dry season and with possible frost at higher altitudes. It is found in disturbed areas and is considered as an anthropogenic pioneer (Salimon and Negrelle, 2001). In other areas, it has been introduced as an ornamental or as a fruit tree, and has spread from gardens and has become naturalized, the seeds being propagated by birds and mammals. It can become invasive in areas disturbed such as roadsides, wastelands, pastures, scrubs, forested land (Jacobi and Warshauer, 1992; Harrington and Ewel, 1997; Woodcock et al., 1999) and on areas disturbed by natural processes such as storms and lava flows (Strasberg, 1995). It also invades undisturbed native forests (Cuddihy and Stone, 1990; Huenneke and Vitousek, 1990; MacDonald et al., 1991). It forms dense monospecific stands, preventing the regeneration of other plants, in particular native species. 

P. cattleianum is not a weed of crops but is an invasive species which threatens native forests and forestry plantations, and which has invaded meadows and pastures crowding out desirable forage plants (Hosaka and Thistle, 1954).

Genetics

The basic chromosome number in the genus Psidium is x=11 (Atchinson, 1947) and P. cattleianum is highly polyploid. However, its chromosome number varies according to different authors. P. cattleianum var. cattleianum was found to be heptaploid (2n=77) (Hirano and Nakasone, 1969a; Srivastava, 1978; Singhal et al., 1985) or octaploid (2n=88) (Atchinson, 1947; Smith-White, 1948). P. cattleianum var. lucidum was found to be hexaploid (2n=66) (Hirano and Nakasone, 1969a) or octoploid (2n=88) (Atchinson, 1947). Aneuploidy has also been reported (Raseira and Raseira, 1996), and anomalies have been observed during meiosis and could be related to the high ploidy level (Singhal et al., 1985; Raseira and Raseira, 1996). For each botanical variety, the species shows very few variations among seedlings produced (Popenoe, 1920; Fouqué, 1972, Hoyos, 1989), which seems inconsistent with its high ploidy level. This suggests that P. cattleianum may be an autopolyploid (if hexaploid or octaploid); however, the unbalanced heptaploidy and the presence of many univalents and the absence of multivalents during meiosis suggest that the species may be an allopolyploid (Singhal et al., 1985). Further studies are needed on the genetics of P. cattleianum.

The two known botanical varieties appear to be sexually compatible as reciprocal crosses produced substantial fruit set (Hirano and Nakasone, 1969b) although it is not mentioned if the fruit contained viable seeds. However, no hybrids have been identified in natural populations where both varieties grow together, and also, both varieties are incompatible with P. guajava, P. guineense, P. cujavillus and P. friedrichsthalianum (Hirano and Nakasone, 1969b).

Physiology and Phenology

Fresh seeds germinate within 10–20 days (Sweet, 1986). Initial seed moisture is about 31% and they are desiccation-tolerant until 12% moisture. They survive exposure to liquid nitrogen when dehydrated below 19% moisture (Becwar et al., 1983). In vitro germination rates are high (60–80%) at 18–30°C (Becwar et al., 1983; Huenneke and Vitousek, 1990). Light does not seem necessary for germination and chilling prior to germination or scarification with sandpaper does not improve germination (Huenneke and Vitousek, 1990). Passage through the gut of feral pigs (Sus scrofa) has little effect on total germination but it shortens the time required for germination (Diong, 1982). Germination of seeds collected at different elevations (150–762 m) are significantly different, but unrelated to elevation or seed weight (Huenneke and Vitousek, 1990).

Germination in natural conditions is lower than in vitro. Seedling establishment appears to be independent of soil disturbance (Huenneke and Vitousek, 1990). Although seeds may retain their viability for up to a year in controlled conditions (Sweet, 1986), they must germinate quickly in natural conditions or they die, and potential recruitment may be concentrated in a 'seedling' bank rather than in a seed bank (Huenneke and Vitousek, 1990).

The aggressiveness of P. cattleianum in outcompeting native flora is partly related to a high relative growth rate which may be a consequence of a large physiological plasticity. As with other invasive plants, it is able to adjust its photosynthetic capacities across a wide range of light environments (Dulai et al., 1998; Pattison et al., 1998). Moreover, it utilizes resources (carbohydrates, nitrogen) more efficiently than do native species, with, for example, a lower cost of leaf construction (Baruch and Goldstein, 1999).

Flowering and fruiting begin two or three years after germination and establishment. P. cattleianum has generally one fruiting cycle per year, with vegetative growth at the end of the cool and dry season (winter), and fruiting during or just after the hot and humid season (summer). Little vegetative or reproductive activity occurs in winter. Vegetative and reproductive activity appears independent of elevation in the range 100–762 m (Huenneke and Vitousek, 1990; Normand and Habib, 2001a). The two botanical varieties seem to have the same phenological cycle, although P. cattleianum is not a photoperiodic species for growth (Broschat and Donselman, 1983). Temperature has a strong effect on shoot and fruit development (Normand and Habib, 2001a).

In cultivation, P. cattleianum has generally two production cycles per year (Teaotia et al., 1970; Raseira et Raseira, 1996). Normand and Habib (2001b) showed that nitrogen can trigger the growth of flowering shoots leading to fruit production which permits two to three harvests per year in orchards. Wild P. cattleianum growing on rich soils or on field margins can produce fruits several times a year and are efficient starting points for seed dispersal.

Reproductive Biology

P. cattleianum multiplies by seeds and by suckers. Relative abundance of seedlings and suckers varies among sites and both contribute to recruitment, but suckers are likely to have a greater ability than seedlings to grow and dominate the forest floor (Huenneke and Vitousek, 1990).

The two botanical varieties are considered self-compatible (Hirano and Nakasone, 1969b; Teaotia et al., 1970; Raseira and Raseira, 1996), although Chezhiyan (1988) found P. cattleianum var. lucidum self-incompatible. Normand (2002a) specified that P. cattleianum self-compatibility is partial, ranging from fully self-compatible to self-incompatible, and which varies among individuals. This partial self-compatibility affects the probability of the flower to set fruit and the number of seeds per fruit. These variables are higher with cross-pollination than with self-pollination (Raseira and Raseira, 1996; Normand, 2002a). Seeds appear necessary for the flower to set fruit and parthenocarpy does not occur in P. cattleianum. Among a P. cattleianum population, flowering is asynchronous between and within trees, though the latter being more pronounced than the former. Asynchrony between trees may be related to genetic or environmental factors (Normand and Habib, 2002; Normand et al., 2002). Anthesis generally occurs between 9 and 11 am. Stigmas may be receptive from anthesis until 24 hours later (Teaotia et al., 1970), or 12 to 48 hours after anthesis (Chezhiyan, 1988). Pollen grains are small, about 23 µm, yellowish in colour and triangular. In vitro pollen germination is low, 0-50% (Hirano and Nakasone, 1969b; Seth, 1970; Raseira and Raseira, 1996) and pollen fertility tested by acetocarmine is variable at 20–75% (Teaotia et al., 1970; Singhal et al., 1985). Under field conditions, the longevity of P. cattleianum var. lucidum pollen grains is short, about 8 hours, but it remains viable up to 90 days at 4.5°C and 0% relative humidity (Seth, 1970). Pollination is entomochorous and likely anemochorous. Bees are effective pollinators.

During a study on La Réunion, fruit set varied between plants, but the mean fruit set rate at the population level was high, 57–70%, and was not affected by elevation or year (Normand and Habib, 2001a). Fruit retention was high with only a few fruit dropping once fruit has set. Fruit production in wild stands is not documented. When cultivated, mean fruit production reaches 14.2 kg per tree, i.e. about 2300 fruit, 6 years after planting (Normand, 2002b). P. cattleianum fruit has a biphasic growth curve (Silva Galho et al., 2000; Normand, 2002a). Individual fruit weight at maturity is highly variable (1.0-22.9 g) and seed number and tree leaf:fruit ratio explain to a large extent this variability (Normand, 2002a). P. cattleianum fruit is climacteric (Akamine and Goo, 1979; Brown and Wills, 1983), with a shelf life no longer than two days at room temperature, though this can be extended up to 12 days when fruit are harvested at an appropriate stage of maturity and kept at 12–14°C (Paniandy et al., 1999).

Seeds are dispersed by birds (Cadet, 1980; Cuddihy and Stone, 1995) and by mammals, feral pigs in Hawaii and Mauritius and monkeys in Mauritius (Diong, 1982; Lorence and Sussman, 1988).

Environmental Requirements

P. cattleianum has a wide ecological plasticity with regard to temperature and soil, but it prefers humid climates with at least 1000 mm rainfall per year without a pronounced dry season, and thrives well in the rainfall range 1500-7000 mm per year. P. cattleianum is a subtropical species and does not tolerate very hot environments, it being the most cold-resistant Psidium species. In mountainous tropical islands, it is found between 0 and 1300 m elevation (Cadet, 1980; MacDonald et al., 1991; Jacobi and Warshauer, 1992) although it has also been found up to 2300 m in Antioquia, Colombia (Missouri Botanical Garden, 2007). It experiences light frost in mountainous areas of its native range (Pedrosa-Macedo, 2000) and can withstand frost as low as -4.4 to -6°C (Wutscher and Shull, 1975; Vogel, 1986) but may be killed below -7°C. P. cattleianum var. lucidum is not as cold-resistant and is found at lower elevations than P. cattleianum var. cattleianum.

P. cattleianum prefers acid soils and is not sensitive to soil structure. It can grow on shallow or infertile soils, if more slowly, but is a pioneer species on lava flows in Réunion (Strasberg, 1995). It does, however, requires a well drained soil and does not tolerate waterlogging (Gonçalves Salvador, 1986).

Associations

Mature P. cattleianum fruit are hosts for many different species of fruit flies: Anastrepha fraterculus (Raseira and Raseira, 1996) and A. suspensa (Nguyen et al., 1992), Bactrocera dorsalis (Vargas et al., 1990), B. curvipennis (Brun and Chazeau, 1986), Ceratitis capitata (Vargas et al., 1983) and C. rosa (Etienne, 1982; Normand et al., 2000). Feral P. cattleianum stands and scattered plants in gardens or wastelands are important reservoirs of fruit flies, pests of surrounding fruit crops (Vargas et al., 1983, 1990; Nguyen et al., 1992; Normand et al., 2000).

P. cattleianum has few natural enemies which influence growth and plant development. In its native range in Brazil, 133 species were found associated with P. cattleianum, but only 15 of them affected the plant, and only four of them seemed to be specific (Wikler et al., 1994). In countries where it has been introduced, few non-specific pests are recorded on P. cattleianum, including fruit flies, scale insects, beetles (Coleoptera) and thrips (Selenothrips) (Williams, 1984; Brun and Chazeau, 1986). P. cattleianum is resistant to the nematode Meloidogyne incognita (Nik-Masdek and Ahmad-Kamil, 1994), but may be sensitive to M. acrita and M. arenaria (Cuadra and Quincosa, 1982). No disease pathogens have been recorded on P. cattleianum, and it is known to be resistant to the rust fungus Puccinia psidii which affects P. guajava (Rayachhetry et al., 2001).

Environmental

• Amenity
• Landscape improvement

Fuels

• Fuelwood

General

• Ornamental

Human food and beverage

• Fruits

Materials

• Essential oils

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

Ornamental

• Seed trade

The use of remote sensing to map the introduction and spread of P. cattleianum in Hawaiian forests has been investigated (Barbosa et al., 2016). Use of airborne imaging spectroscopy followed by classification with a Biased Support Vector Machine framework is suggested as showing promise for detecting P. cattleianum invasion.

The common guava, P. guajava, cannot be confused with P. cattleianum because of its different tree habit, its tetragonal twigs and its non-waxy leaves with very apparent 12-20 pairs of ribs. P. guajava fruit are also larger than P. cattleianum fruit and the pulp colour varies from white to yellow and pink. Likewise, the uncommon P. friedrichsthalianum Ndz. and P. sartorianum Ndz. native to Central America cannot be confused with P. cattleianum as the former is a medium-sized tree (6-10 m) with tetragonal pubescent twigs and the latter is a large tree (12-15 m). More readily confused is P. guineense Swartz (=P. araça Raddi or P. molle Bertol.) which is also a shrub, but somewhat smaller than P. cattleianum (1-3 m, though sometimes to 7 m). The main differences are that P. araça twigs are compressed and generally pubescent, leaves are larger than those of P. cattleianum with lateral ribs prominent on the lower surface, and the fruit are smaller (1-2.5 cm in diameter).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

Control

P. cattleianum is a difficult species to control (MacDonald et al., 1991) and there is no effective control practice for large invaded areas. The control of naturalised populations must be approached with different techniques selected in the light of the specific circumstances in each case.

Cultural control

P. cattleianum is not subjected to a cultural control as it invades mainly non-agricultural areas. In pastures, it is not browsed by cattle.

Mechanical control

Except for young seedlings, hand pulling is not feasible due to the strong root system and the presence of suckers. Mechanical cutting of the stem leads to the development of abundant suckers from the stump and any mechanical control must be associated with chemical control to avoid resprouting.

Chemical control

P. cattleianum is resistant to many foliar-applied herbicides. It is also resistant to 2,4D (Anonymous, 1981), and picloram applied as granules on the soil or applied on the cut stump mixed with diesel oil gave less than 50% success (Devine, 1977), but picloram activity and absorption by P. cattleianum leaves is increased by ammonium sulphate (Wilson and Nishimoto, 1975). P. cattleianum is, however, sensitive to glyphosate, triclopyr and tebuthiuron. Good chemical control has been obtained with undiluted triclopyr amine, with undiluted triclopyr ester or undiluted glyphosate on cut stumps, or with tebuthiuron Motooka et al., 1983, 1989; Santos et al., 1989). Triclopyr is recommended because of its lack of mobility and relatively short half-life. However these treatments are labour-intensive and can be applied only on limited areas.

Biological control

No biological control agents have been released to date. Research has focused on the identification of potential biological control agents specific to P. cattleianum in its native range (Wikler et al., 1994). Two Hymenoptera, a species of Eurytoma and Haplostegusepimelas, lay eggs on growing twigs and affect plant growth and flowering (Wikler et al., 1996; Pedrosa-Macedo, 2000) and appear to be species-specific (although considered doubtful for H. epimelas), which is an essential requisite to protect the congeneric common guava and native Myrtaceae species (Gardner et al., 1995). Recently, a further species Tectococcus ovatus (Hemiptera: Eriococcidae) has proven to be specific to P. cattleianum and is considered suitable for release as a classical biological agent in Florida, USA (Wessels et al., 2007).

Public concerns have prevented the release of a biological control agent for P. cattleiana in Hawaii. Warner and Kinslow (2013) report that a local activist persuaded members of the public and elected officials to oppose the proposed release of an insect to control this invasive species.

Integrated Control

As feral pigs are effective dispersal agents in Hawaii, their control appeared to be the first step to control the spread of P. cattleianum. However, Huenneke and Vitousek (1990) put into perspective the role of pigs in germination and establishment and moreover, the control of pigs may be ineffective as birds and other mammals also disperse P. cattleianum seeds.

3/6/2015 Updated by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

27/11/2007 Updated by:

Nick Pasiecznik, Consultant, France