A review of the development, production and post harvest requirements of Gerberas

1.0 Introduction:

Gerberas (also known as the Transvaal or Barberton Daisy) were discovered in the early 1880’s and have been popular with plant breeders ever since (Kessler, 1999). They are grown world wide and available all year round as cut flowers, pot plants and bedding plants, making them extremely versatile for many different markets. As cut flowers they are extremely popular as they are high value and available in over 200 different varieties (Flowers and Plants Association, 2007). They also have a long vase life, and cope well with transportation, which makes them suitable for domestic and export markets (Nair, 2003). Many improvements have been made over the years and most of the modern breeding work has come from the Netherlands where Gerberas were the fifth most popular flower to come out of the Dutch auctions in 2003 (Flower Council of Holland, 2003).

2.0 Market:

Gerberas are very popular for use in bouquets in supermarkets and florists, but obviously in varying quantities. A packager for a supermarket will require a large number of the same colour Gerbera, with the same stem length and flower size, to put in the mixed bouquets, which are then distributed throughout supermarkets, petrol stations and other similar outlets. The flowers for these outlets usually come with a guaranteed vase life so it is essential that the flowers are in the best possible condition. Florists operate on a much smaller scale, so possibly the best solution for them is the mixed boxes of Gerberas, where a range of colours are packaged together. Florists would also be able to use the more unusual varieties of Gerbera, such as the Gerondo(r) (figure 1) or the Pomponi (figure 2) in specialist arrangements.

Figure 1: Gerbera Gerrondo(r) Figure 2: Gerbera Pomponi Sponge Bob.

Source: Flower Council of Holland (2005) Source: Bruffin (2007)

3.0 Production:

Most Gerberas are grown under protection even in warmer climates such as South Carolina in the USA where there is demand for Gerberas early in the year for Valentines Day (Dufault et al., 1990). In countries such as Japan, where the night temperatures are still relatively warm, Gerberas are grown in the ground (Roskam, 2000). Japanese growers buy in 90-95% of plants from Holland but are a lot fussier about quality than the Dutch and will reject any flower that is less than perfect (Roskam, 2000) whereas in the United Kingdom standards are not always so high. Robin Meek at Zwetsloots, Bedfordshire pointed out that flowers that don’t meet the top specifications in the United Kingdom will still be sold to cash and carry wholesalers and markets (personal communication, 30 November 2007). Gerbera production is becoming quite mechanised in countries that can afford the extra investment, to include irrigation systems, osmosis machines, feeding units, and pH-EC measuring equipment (Florist de Kwakel, 2004). This extra cost is obviously justified with the prospect of higher production and therefore higher value crops.

3.1 Propagation:

* Seed: Gerberas have large seeds, which germinate at about 70% under suitable environmental conditions (Rogers and Tjia, 1990). Plants are genetically varied so Gerbera produced from open pollinated seed are unlikely to be similar, which is no good for commercial production. F1 hybrid seed can be a solution to this problem and are produced by a number of seed companies with a reasonable degree of success. An advantage of the F1 Hybrid seed is the relatively low cost for each propagated plant and the ability to produce unlimited quantities of any particular cultivar.

* Division: Gerberas have a crown composed of many short leafless rhizomes, which bear vegetative buds and may be easily propagated by division (Rogers and Tjia, 1990). However, many stock plants are needed for this method of propagation so it is not ideal for a large commercial business. There is also quite a high risk of infection by Phytophthora cryptogea (Crown Rot).

* Micropropagation: Micropropagation (or tissue culture) is the predominant method for commercial propagation of Gerberas as it produces uniform, vigorous, disease free plants. It is also possible to produce large amounts of plants in a short space of time, which is crucial with Gerberas as new varieties are constantly being bred.

3.2 Cultivation in soil:

A number of requirements need to be met if growing Gerberas in soil, such as:

* Soil structure: The soil should be airy and permeable, to allow plant roots to penetrate easily and to allow fast draining of water. If the soil becomes waterlogged the plant becomes more susceptible to fungal diseases. Substances such as perlite and rice chaff can be added to the soil to improve its structure, but care should be taken so that the pH and nutrient levels in the soil are not altered by this.

* Disease free soil: Sterilisation should take place to ensure that the soil is free from pests and diseases. This sterilisation used to be done with methyl bromide gas, but this is banned in most countries now. An alternative method is steam sterilisation, which is more expensive (Florist de Kwakel, no date [a]) but the risk of losing an entire crop outweighs the extra cost.

* Nutrition: Tests should be carried out on the soil to check for nutrient levels prior to planting in case any additional fertilisers or manures are required.

* Heating: Gerberas can be grown with or without heating, but yields have shown to be higher when the soil has been heated (Florist de Kwakel, no date [a]). The benefits of heating the soil are higher production in the winter months, faster production in the spring and a decrease of fungal diseases in the soil.

3.3 Cultivation in substrates:

There are many advantages of growing Gerberas in substrates rather than soil, and the main factor is that the crop is easier to control and manage. Plants are grown in pots of the substrate on bench systems (figure 3), which allows the working height to be determined. This makes the crop easier to harvest and maintain because the pots can be adjusted to the height of the workers. Transmission of pests and diseases is minimised as the plants are in separate pots and the media should be sterile to start with (Florist de Kwakel, 2004). A disadvantage of growing in substrates is the cost required to invest in this system and any necessary equipment required, such as feeding solution computers (Florist de Kwakel, 2004).

Figure 3: Bench System for Gerberas Source: Roskam (2007)

Peat: This is still widely used as a substrate for Gerbera production, but although it gives good yields (Florist de Kwakel, 2004), it does have its disadvantages. For instance, the structure of peat varies depending on where it has come from, so it will not always be reliable. There are the environmental issues as well, and some company policies require plants and flowers that have not been grown in peat. Peat is also tricky to irrigate and can either become too wet, or dry out and then take a long time to absorb water (Mathias, 2006).

Coir: Coir or coco substrate has become more popular in Gerbera cultivation because of its good stability and air/water ratio (Florist de Kwakel (no date [b]). Care should be taken to check the cleanliness of the product as it can contain elements such as Sodium, Chloride and Potassium. The coir is initially washed to remove these elements and all other tannins, which can be hazardous to plants. This also reduces the electrical conductivity from between 4-4.5 to 0.2 S/m (Mathias, 2006) which helps to reduce the amount of fertiliser required (Roberson, 2006).

In countries like Brazil, coir is an ideal substrate for Gerbera growers as there is a sustainable supply from the local area where coconuts are a typical crop. The coir also has a sufficient amount of Phosphorus present, which due to the natural weathering in tropical soils is not always available (Mathias, 2006). Coir allows good aeration between the roots which is essential for Gerbera growth and as the containers are raised from the ground, there is better ventilation, reduced use of fungicides and no need for weeding. Gerbera production in one particular Brazilian farm has improved by 20% since using coir, which has stabilised sales and allowed better planning of greenhouse labour (Mathias, 2006).

Rockwool: Dutch Gerbera growers have been experimenting with rock wool and have found that a combination of small cubes with a solid disc positioned on the top of the container produces positive results. This technique was developed in 2004, with an introduction to the commercial market in 2005. Benefits have included good rooting speed and distribution and excellent water drainage (FlowerTech, 2006).

3.4 Light Requirements:

Gerbera is as a quantitative short day plant and field trials by different growers have shown that most plants produce fewer flowers as soon as the day length is more than 11.5 hours (Wessels, 2006). Getting the right intensity of light is essential, as Gerberas require a high light intensity to produce a high number of good quality buds. If the light is too low, the plant will have stretched foliage and long weak flower stems, whereas if it is too high, the plant will be compact with the stems hidden in the foliage (Kessler, 1999). Shading can be used to reduce light levels and protect the plants from excessively high summer temperatures.

European countries producing Gerberas have shorter days, lower winter light and cooler temperatures than countries in America and Africa and so more energy for light and heat is used. It is possible to increase the production of some Gerbera varieties at times of the year when they are more expensive by lighting for longer day lengths, but the downside to this would be a noticeable dip in production when the day lengths are returned to normal (Wessels, 2006). Research is still being carried out to reduce this dip in production by using different intensities in light and trials with different cultivars

3.5 Harvesting:

The harvesting of most Gerbera flowers should occur when the second circle of disk florets shows pollen development (Rogers and Tjia, 1990), but there are some varieties, such as those which close at night, that can be harvested a bit later (Reid, 2004). Gerbera flowers have low energy reserves, so if picked any earlier than this the flower will not open fully (Roskam, 2007). The flowers should also be pulled from the base of the stem rather than cut as this causes less damage to the crown of the plant, reducing the risk of disease infection and is thought to encourage further flower production (Reid, 2004).

4.0 Pests and Diseases:

Gerberas can be affected by many pests and diseases, some of which are more serious than others and could jeopardise the entire crop. The risks to the crop could be failure to grow, distorted growth, or damage to foliage or flowers. As with all flowers grown for the cut flower market, it is vital for the appearance of the flower, stem and foliage to be as perfect as possible. If the crop is less than perfect, it is at risk of being rejected by buyers.

There are many pests that affect Gerberas, most of which can be treated with pesticides, sterilisation or integrated pest management methods, but early detection is vital to prevent a whole crop being destroyed. Pests such as Aphids, Whitefly, Red Spider Mite and Leaf Miners damage the leaves and stems initially and in severe infestations can colonise the flower. This could weaken the plant and reduce its productivity and vigour (Rogers and Tjia, 1990). Pests such as Cyclamen Mite, Strawberry Mite and Thrips cause damage to the flowers, which would usually end up with the entire crop being rejected. Larger pests such as mice, slugs and snails can also be a problem but regular checks of the area and setting traps can be a cheap and easy solution.

The following diseases are common in Gerbera production, but again can be prevented if the right methods are in place.

* Crown Rot: a serious wilting disease caused by Phytophthora cryptogea was initially a major problem as the pathogen is carried through the generations of plants when divided. However, the possibility of tissue culture has successfully controlled this disease. It also occurs when there has been a sudden drop in temperatures, so heating the soil and spraying with pre-heated water is a possible prevention (Florist de Kwakel, no date [a]).

* Botrytis: This fungal disease occurs when the relative humidity in the air is high and when there is little or no air circulation between the plants or flowers. It can be prevented by ensuring the crop is watered at soil level, air circulation around the crop is good, and the leaves of some plants can be thinned out if there is a lot of foliage.

5.0 Post Harvest Requirements:

Gerberas can have a vase life of up to two weeks (Terra Nigra, 2007a) if given the correct post harvest treatment. They are sensitive to gravity, light, and bacterial contamination, but are not affected greatly by exposure to ethylene (Reid, 2004). Ethylene was found to increase the respiration and ethylene production of Gerbera but does not reduce the vase life (ChiaHui et al, 2004).

Pests and Diseases:

Even after the flowers have been harvested, they are still susceptible to attack from pests and disease. A method that is used as a quarantine treatment is irradiation. This uses ionizing radiation such as cobalt/60 and X-ray to treat against pests such as scale insects and thrips, without reducing the quality of the Gerberas (Hara, 2005).

Botrytis is a disease that can affect Gerberas pre and post harvest and subsequent wastage can cause great financial losses all the way down the supply chain. If one flower in a mixed bouquet in a supermarket is affected, it will spread to the rest of the bouquet, leading to a severely reduced vase life. To minimise the risk of this disease spreading, the cool chain must be monitored all the way from the supplier to the retailer to avoid any sudden changes in temperature or humidity.

Conditioning:

When Gerbera flowers are pulled from the plant, the lower 2-5cm is woodier from the rest of the stem. This is called the ‘heel’ and should be removed before putting the flowers in water. This part of the stem has very narrow xylem vessels, which can reduce the transportation of water through the stem and result in a shorter vase life (Roskam, 2007). The water must always be clean as Gerbera stems can be easily blocked by the growth of bacteria, causing the flowers to droop. Bacteria prefer a slightly alkaline environment so adding Chlorine to the water lowers the pH and can also kill any bacteria already present (Florist de Kwakel, no date [a]). Gerberas take up water easier if a large portion of the stem is submerged in water (Roskam, 2007) and some companies have special baths designed for this (figure 4). The Gerberas are slotted in to cardboard trays which are attached to the top section of the bath and then lowered in to the water for a set amount of time depending on the variety (Baker 2005a). Pulsing Gerberas in a solution containing sucrose and silver nitrate is also beneficial and has been found to increase the vase life of some cultivars by up to three days (Nagaraja, et al, 2000)

Figure 4: Gerbera bath at Terra Nigra. Source: Baker 2005b

Packaging

There are a variety of different packaging methods available to growers depending on the size and fragility of the flower. The flowers of the Gerbera and mini Gerbera transport fairly well in flat boxes with the slotted cardboard inserts (figure 5), and the delicate petals are protected providing the boxes are not squashed or upturned in transit.

Figure 5: GERB-PAC(tm) system. Source: Ever-Bloom (no date).

Gerberas keep their appearance better if transported in water (Pagter, 2007) especially if the transport period between grower and retailer is several days. This can leave the flowers vulnerable to damage when being moved between lorries, aeroplanes and auction houses. The Gerona packing system (figure 6) has all the components needed to transport Gerberas safely to their destination. The bucket of water keeps them hydrated, with cardboard or plastic interiors to keep the flowers separated and supported and a cardboard collar to wrap around the flowers and bucket to minimise external damage to the petals.

Figure 6: Gerona Packaging System. Source: Pagter (2007)

It is important with Gerberas to support the stems during transit, as the flowers are heavy, especially with the fuller flowered varieties such as Gerrondo(r) and Pomponi. Another system to protect the flowers whilst being transported in water is with Gerbera cups (figure 7) or socks. Gerbera cups protect the delicate flowers whilst in transit and because of their lightweight nature, compared to boxes or cardboard flower racks, are said to reduce transport costs by up to 50% (FlowerTech, 2003). Machines have also been developed for larger scale businesses to attach the cup and therefore saving on labour costs (Flowertech, 2003). The plastic cups are perforated so that the flower stays ventilated, reducing the risk of Botrytis.

Figure 7: Gerbera Cups Source: Roskam (2007)

6.0 Development:

Due to the popularity of the Gerbera, new developments are appearing all the time to try to ensure the best possible crop is produced. This report has already mentioned examples with the production techniques, post harvest treatments and the packaging, but the main developments are with the different varieties. New varieties of Gerbera are being bred all the time and breeders not only try to come up with new colours and petal formations, but also to improve vase life, stem strength, and productivity. Gerbera specialists Terra Nigra have recently come up with a variety of Gerbera that has foliage on the stem of the flower, called Gerfolia(r) (figure 8).

Figure 8: Gerfolia(r) Source: Terra Nigra (2007b)

This will increase the value of the flower as it will reduce the need for extra foliage in bouquets and arrangements and will cut down on the bacterial pollution of the vase water, therefore extending the vase life. This variety is still on trial and is due to be introduced to the cut flower market some time in 2008 (Terra Nigra, 2007b).

As well as developing new varieties with interesting features like the Gerfolia(r), breeders are also cultivating varieties with resistant to particular diseases such as powdery mildew (Institute of Food and Agricultural Sciences, 2007).

7.0 Conclusion:

Breeders are constantly striving to produce Gerberas with a fast cropping period, long vase life, sturdy stem, high yields, interesting petal formation and colour that are easy to transport and meet the demands of the market. As with all areas of the floristry industry, the fashions change and what might meet the demands of the market at present will not necessarily meet the same criteria in the future. Growers and breeders will remain competitive in this market to always try and produce the most fashionable and high value flowers.