Eggplant or aubergine is a species of nightshade grown for its edible fruit. This black beauty is a good source of dietary fibre, vitamins and minerals and often substituted for meat.
By STEVEN CARRUTHERS
Eggplant (solanum lemongena), also called aubergine, melongene, guinea squash, garden egg and bringal, belongs to the nightshade family and is closely related to potato, tomato and pepper. Colloquially, they are sometimes known as black beauties. In Australia and North America, the common name is eggplant, while in the United Kingdom and France it is known as aubergine.
Eggplant is a tender, frost-intolerant perennial grown as an annual. The flavour depends on the method of cooking and has been described as a mild flavour, similar to that of fried oysters. The taste has also been compared to squash mixed with a mild cucumber. Eggplant is often substituted for meat because of its meaty texture.
Eggplant is an excellent source of vitamin C and moderate source of potassium, iron, niacin and folate. Folate is an important B-complex vitamin used to prevent birth defects such as spina bifida. Folate has also proved beneficial for people with heart disease, cervical dysplasia, chronic fatigue, depression and HIV infection. Eggplants do not contain any fat, cholesterol or sodium.
Eggplant is a smooth and shiny-skinned vegetable with a creamy white, pithy interior with small brown seeds throughout the flesh. Although there is only one species, there are a number of different varieties and, indeed, the name ‘eggplant’ was derived from a variety with small, white, egg-shaped fruit. Other varieties can be pear-shaped, rounded or elongated (cucumber-style). Depending on variety, colours range from a deep purplish black through to pale green to yellow and white. These days, the most popular variety is the large, purple-black, pear-shaped fruit. Some varieties have been bred for early cropping and others for colder regions. Local advice from seed companies should be sought on the most suitable type to grow in a particular locality.
In 2013, global production of eggplant was 49.4 million tonnes, with 57% of output coming from China, followed by India with 27% of total world production. Other major producers are Iran, Egypt and Turkey.
Eggplant is a warm-season crop that produces best in hot, sunny weather. Most commercial crops are grown outdoors; however, more and more interest is being shown in greenhouse production. The manipulation of the growing environment, which the greenhouse offers, translates into slightly higher yields, easier pest and disease control and, ultimately, higher profits due to predictability and premium fruit.
Eggplants have a woody stem and large, fleshy leaves. They are mostly self-supporting, though tying is necessary to prevent the stem from collapsing when bearing the weight of fruit.
Plants have a dominant growing point, although side-shoot development can be quite powerful and can be used to divide the plant or to train it into a particular shape. These side-shoots may develop at the axils of all leaves, but their strength will be determined by the maturity of the plant and the amount of fruit that is being carried. Fruit set does not rely on pollination, as eggplants are parthenocarpic.
Eggplants usually take 14-16 weeks to bear fruit, varying somewhat according to climate, variety and the number of stems per plant. The more stems on a plant, the more fruit it will bear, however, there is the disadvantage of lower yield per space over time.
It is important to be aware of the factors which assist in fruit setting—flower strength and day/night temperatures are two of the main variables. The larger the flower when it opens, the faster fruit development occurs and thus, the larger the fruit at harvest time. In terms of temperature, a 5 degree C (9 degree F) difference between the mean day and night temperatures signals to the plant an end to its annual growth cycle, and promotes quick fruit setting. Equal day and night temperatures can completely halt fruit development.
Eggplant requires a long growing season, depending on variety and environmental conditions, so transplants are most commonly used. Seeds are usually started in a greenhouse or on hotbeds, sown in shallow flats 9-10 weeks before transplanting. Constant temperatures must be maintained, because young plants are easily checked by cool temperatures or draughts. Transplants grown in the greenhouse should be kept at 21- 27 degrees C (70-80 degrees F) during the day, and 18-21 degrees C (64-70 degrees F) at night. After transplanting, the optimum daytime temperatures are 24-30 degrees C (75-85 degrees F), and 18-24 degrees C (65-75 degrees F) at night. Eggplants are even more sensitive to cold than tomatoes or peppers and will be injured by temperatures below 18 degrees C (65 degrees F).
Seedlings should be raised on a relatively weak nutrient solution of 1 mS. As plants increase in size, so should the nutrient increase in strength.
In soil, eggplants prefer a well-drained sandy loam rich in organic matter, and a pH between 5.5 to 6.5. Crops are side-dressed frequently with nitrogen, phosphorus and potash, especially when plants begin to bloom. The use of plastic mulch can increase the yield by helping to warm the soil, by conserving moisture, and by controlling weeds.
In commercial hydroponics, rockwool and cocopeat are popular growing media used for eggplant production. The most common system used in the Sydney region is in 20-litre black plastic bags containing a commercial potting mixture, one plant per bag. The bags are placed on raised beds covered with black plastic and irrigated by one dripper per bag. The drippers provide both water and plant nutrients.
Eggplant seeds can be started in propagation cubes placed on a propagation mat for 16 days under a 1,000 Watt HPS light (around 800 footcandles) for 18 hours/day. On the 16th day, seedlings can be transplanted into larger rockwool propagation cubes then placed on rockwool slabs with two plants/slab. Support strings should be installed early when the plants are about 20 cm (eight inches) tall. Thereafter, support clips can be installed about every 25 cm (10 inches).
Some growers maintain three branches per plant on separate strings with a maximum of three fruit per branch. Flowering and fruit set begin 6-8 weeks after transplanting. It takes three or more weeks before the fruit reaches marketable size of between 10-15 cm (4-6 inches) diameter. Fruits should be harvested before they reach full maturity.
Cultivating eggplants is much less work than tomatoes.
The feeding regime for eggplant depends on a number of factors, including humidity, temperature, light intensity, type of media, and average volume of growing medium per plant. It is a relatively heavy feeder and a mature plant will like a strong nutrient solution, between 2.2 and 3.5 mS, and a pH between 5.8 and 6.2. The EC can and will vary according to different environmental conditions, and it is good management practice to regularly test the run-off for pH and EC.
If all goes well with the crop, a yield of 40 eggplants per square metre, weighing 300-350 grams can be achieved. Although eggplants are ready to harvest once the skin turns glossy, they are tastiest when picked young. Once the outside skin turns dull, it is past its prime. Over-mature fruits are spongy and seedy and may be bitter—salt removes some of the natural bitterness in cooking.
Fruit should be harvested before maturity, using a knife or pruning shears (rather than breaking or twisting the stems), cut from the vine about 25 mm (one-inch) above the calyx. Many eggplant varieties have small prickly thorns on the stem and calyx, so exercise caution or wear gloves when harvesting. The large (usually green) calyx should be attached to the fruit. Fruits should be wiped clean or washed after harvest to enhance their glossy appearance. The fruit must be handled carefully so that the spines on the calyx do not pierce their delicate skins during packing and transport to market.
Eggplant can be stored for up to one week at a temperature of 8-15 degrees C (46-54 degrees F). Below 8 degrees C, eggplants will develop chilling injury symptoms including pitting and decay. Humidity should be kept at around 80-90% to avoid excessive water loss and fruit spoilage.
Pest and diseases
Eggplants are particularly prone to Botrytis infection on the calyx between the petal ring and the fruit, which holds water, providing ideal conditions for infection. Removal of the petal ring once fruit starts to develop will help reduce the risk of Botrytis.
Verticillium wilt is also a serious disease in eggplants. Although it is primarily a soilborne fungus, it can infect eggplants grown hydroponically if proper management and sanitation practices are not adhered to. Remove and destroy entire infested plant.
Fusarium wilt is another soilborne fungus, where wilting progresses from lower to upper leaves, followed by collapse of the plant. As for Verticillium, remove infected plant material. Growers should also check with their seed supplier for Verticillium and Fusarium-resistant varieties.
Eggplant is a delicacy for insects, with aphids and spider mites the main culprits. With regard to the former, the presence of ants may be an early indication of aphids in the greenhouse. Other pests include tomato russet mites and leaf-eating ladybirds. On flowers, tomato caterpillars, eggplant caterpillars, fruit flies, aphids and looper caterpillars are problem pests.
Biocontrols for aphids include ladybugs and Aphidius colemani [a parasitic wasp for green peach) and Aphelinus abdominalis [a parasitic wasp for potato aphid]. Other Integrated Pest Management (IPM) strategies that may be helpful to control aphids include planting alliums such as garlic, chives, anise and coriander, as well as nasturtiums and petunias. Yellow sticky traps, or yellow dishes containing soapy water are other pest management strategies. Soap sprays and mint tea spray are also highly effective, and lacewings will eat 100 aphids per day.
Spider mites live on the underside of leaves and thrive in hot, dry conditions. Try lightly spraying the undersides of leaves with water daily. Sulphur is another management strategy for spider mite infestations.
Eggplant is the only member of the Solanaceae family to come from the eastern hemisphere, thought to have been first cultivated in India some 4,000 years ago. One of the oldest references to eggplant occurred in China in the 5th century, when it was recorded on a scroll that Chinese ladies of fashion made a black dye from eggplant to stain their teeth which, after polishing, shone like silver.
Little is known about eggplant in the ancient Mediterranean world. It was introduced into Spain and North Africa in the Middle Ages by Arab traders. Spanish explorers then carried it to the New World. It did not arrive in France as the glorious aubergine (from the Arabic al-badhinan) until the 17th century. In the Americas, Thomas Jefferson grew eggplant he obtained from France in his garden at Monticello in Virginia. Today, the heirloom garden there continues to grow an all-white, prickly variety.
The Turks are said to have 1,000 recipes for eggplant, and regularly cook about 40. Greeks, Egyptians and other peoples of Europe and the Middle East also feature the eggplant as daily fare. Southern Italians revel in eggplant parmigiana, while the French of the South favour ratatouille, a vegetable stew. Spicy eggplant dishes abound in the plant’s home country of India, as well as in China and Thailand. Ω
PH&G April 2016 / Issue 166