Strawberry

Strawberry is scientifically known as Fragaria x ananassa. Breeding between two American species, Fragaria chioensis and Fragaria virgiana resulted in a hybrid plant, the cultivated strawberry. The cultivated strawberry originated from hybridizing two American species, Fragaria chilioensis Duch. and Fragaria virginiana Duch. Strawberries can be diploid, tetraploid, hexaploid, octoploid, and decaploid. The woodland strawberry, F. vesca, and most native species worldwide are diploid. They range from dioecious to hermaphroditic and self-fertile to self-incompatible. Three known tetraploids are Fragaria moupinensis, Fragaria orientalis, and Fragaria corymbosa. F. moschata is a hexaploid strawberry and is known for its musky flavour. F. chiloensis and F. virginiana are octoploid, with their flowers mostly being dioecious, although some are hermaphroditic. Nowadays, all the cultivated varieties of strawberries are octaploid (2n = 8x = 56) in nature. Over twenty species and six hundred varieties of strawberries vary in color, flavor, size, and texture.

Strawberry is a small fruit, but for quality and higher production, many nutrients are required for efficient nutrient management. It is the most popular berries in the world and a small fruit belonging to the family Rosaceae, which has acquired significant prominence among fruits and is now classified as a functional food offering multiple health benefits beyond essential nutrition with antioxidant and antihypertensive properties. The name ananassa means ‘pineapple-flavored’, a curious description for the modern, large-fruited garden strawberry that arose from crossing American species. The biggest strawberry producer in the world is China, followed by the United States of America. Strawberries have acquired significant prominence among fruits produced and consumed in the United States: fourth highest in production, following grapes, oranges, and apples, and fifth highest in consumption, preceded by bananas, apples, oranges, and grapes.

Cultivation and horticultural practices

Cultivated strawberry (Fragaria x ananassa Duch) is one of the legendary fruits in temperate countries. However, it can also be grown in tropical highland areas and sub-tropical climatic conditions. It is the most straightforward fruit to grow in the kitchen garden, in decorative pots, hanging baskets, and in flat or raised beds and protected structures. It is paid back within six months after planting. The high demand for organic berry fruit plants has increased in the last decades, making strawberry cultivation a very demanding enterprise.

Strawberries can be propagated through sexual and asexual reproduction. The seeds outside a strawberry are the fruits, each containing a single seed. Seed propagation is widespread and limited for raising hybrid populations. However, strawberry seeds have a very poor germination rate due to certain inhibitory substances in the fruit. Vegetative propagation of strawberries can be conducted by stolons or by crown division.

In addition to crowns, known as compressed stems, strawberry plants can produce runners, known as stolons. Stolon is an elongated, two-node, vegetative, axillary shoot that supports the rosettes (ramets) until it is completely on its roots. Different strawberry cultivars vary widely in their ability to produce runners, with day-neutral types typically making fewer runners than short-day types. Daughter plants arise from these runners, which is how the strawberry cultivars are clonally propagated.

Stolon functions not only to form new plants but also to support the ramet until it is entirely independent of its roots, which sometimes happens only after the ramet is completely developed or never. Furthermore, strawberry is widely cloned through micropropagation as the technique produces healthy and true-to-type materials with higher running capacity than conventional seedlings.

Proper plant nutrition is crucial for good plant health, high productivity, and fruit quality. Calcium fertilizers are used in strawberry plantations as they positively affect berry firmness, rot resistance, and storage quality. For berry formation, higher amounts of phosphorus and potassium are required. Then, nitrogen is found to increase the fruit size and quality. Micronutrients like copper, iron, manganese, molybdenum, silicon, and zinc. Copper plays a role in the fixation of nitrogen, which indirectly aids in improving fruit quality and size.

Strawberry is a permanent herbaceous plant with an adventitious root system, and most of the roots are confined on the top surface soil and are very sensitive to nutrient fluctuation. Strawberry can be cultivated in a wide range of soil varying from light sand to heavy clay but grows best in humus-rich light porous soil. It has ovate leaflets that are glaucous above and white beneath. Various strawberry cultivars have been developed to suit different climatic conditions.

Strawberries can be roughly categorized into two groups; seasonal flowering strawberries, also called June-bearing or once-flowering plants, and perpetual flowering types, called everbearing, remontant, repeat flowering or day-neutral plants in different reports. Environmental responses of different types have been studied for decades in both garden strawberry and woodland strawberry, and various responses have been reported in different cultivars and genotypes.

The flowers of strawberries are usually self-fertile, in which each pistil will develop into a single-seeded fruit known as achene after successful self-pollination and fertilization. Many Fragaria species are dioecious. However, hermaphrodism is also present and ranges in expression from plants with entire cymes that are completely self-fertile to plants where individual flowers are occasionally self-fertile. The control of flowering is one of the critical processes that determine the ability of the species to adapt to different climates and growing conditions.

Generally, a high growth rate of strawberries is maintained at a day temperature of twenty-two to twenty-three degrees Celsius. Strawberry is a short-day plant, which requires exposure to about ten days of less than eight hours of light for flower bud differentiation. Strawberry varieties have characteristics of temperature-day length responses, which determine their regional adaptation. Everbearing strawberry varieties are considered long-day plants and form flower buds in the long days of summer with more flower buds at seventeen hours per day than at fifteen hours and relatively few at eleven or thirteen hours. In typical temperate areas such as extreme cool areas, strawberry plants remain dormant during winter, and low temperatures are required to break their dormancy.

Traditionally, three systems are now used to grow strawberries: traditional matted row, annual hill, and all synthetic. Traditional matted row employed the fields that generally last three years and sometimes more than three years. The third option usually involves the cultivation of buckets, peat bags, or the nutrient film technique (NFT). It is now programmable culture systems for larger fruits and higher yield per unit area. Nowadays, strawberries are produced through a soilless cultivation system, performed under greenhouses or plastic tunnels to protect fruits from adverse weather conditions. Some planters grow the strawberries in a container in a controlled environment.

Artificial light, such as light-emitting diodes (LED) in protected growing conditions, is also used to affect relevant aspects of crop physiology, such as the transition phase between vegetative and reproductive growth in strawberries by means of different durations of the photoperiod. Moreover, not only the photoperiod but also different light wavelengths (monochromatic lights) have been found to control flower differentiation in strawberries. The choice between the three systems is first related to farming intensity and labor organization, then to economic-technical factors and finally to market demand. However, it is always influenced by environmental conditions. Continuous light with blue LEDs or white fluorescent lamps can shorten the nursery period by approximately twenty days and improve fruit production efficiency over standard cultivation conditions.

White strawberries

The most luxurious strawberry in the world is the white strawberry from Japan. It is white inside and out. They are bred to be bigger, softer, and even sweeter than an average strawberry. Yasuhito Teshima breeds the white strawberry through crossbreeding on different kinds of strawberries. It is commonly called a white jewel, also known as Shiroi Houseki. The strawberry is white because growers like Teshima cut down on sunlight, which reduces anthocyanin levels, which involved ten years of experimentation and research. Even after his many years of conducting experiments on strawberries, only ten percent of them turn out white, and only a few of these are completely pale.

When a white jewel is fully developed, it will not turn red, even under direct sunlight. Often described as sweet-smelling with soft skin, the taste is reportedly comparable to fresh pineapple. After a few seconds, the flavour turns less tropical and more like candy, but not in an overpowering way. It is pricey due to several factors, such as the years spent breeding them, low yield rate, labor-intensive growing process, and space. That is why they are rare in the market.

Disease, pest, and postharvest management

Strawberry is a soft, easily perishable fruit characterized by a limited postharvest life, mainly because of fungal decay, firmness, weight loss, loss of brightness, and color darkening. To prolong the postharvest life of strawberries, one must use the most suitable cultivars and design storage conditions so the product can be optimally protected. Humidity is the most important factor regulating the occurrence of gray mold. Frequent rains induce maximum disease incidence. Furthermore, it seems that these conditions must be maintained for more than twenty-eight hours for an epidemic development of the disease.

Several soil pathogens damage strawberry roots, resulting in vigor declines and, ultimately, death. Fungal diseases of strawberries are important worldwide and occur in all parts of the plant, including flowers, fruit, leaves, crowns, and roots. Botrytis gray mold rot, caused by Botrytis cinerea Pers. ex Fr., is a vital fruit rot wherever strawberries are grown. Strawberry leaf spot, caused by Ramularia tulasnei Sacc. (Sexual stage Mycosphaerella fragariae Tul.), is a common disease of strawberries. The disease is less severe today than it used to be because plant breeders have incorporated resistance into some current cultivars.

Colletottichum fragariae Brooks causes anthracnose fruit rot on strawberries. It is characterized by dark brown, circular, sunken, firm rot lesions that usually turn black after a few days. The lesions occur anywhere on the ripe fruit. Two or more lesions may coalesce and are occasionally covered by masses of buff-colored spores. Besides, powdery mildew of strawberries is caused by Sphaerotheca macularis (Wallr. ex Fr.) Jacz. f. sp. fragariae, has been reported in most areas where strawberries are grown. Red stele, caused by Phytophthora fragariae Hickman, is a severe economic disease in almost any area with wet winters and soils having poor internal drainage.

Furthermore, crown rot (vascular collapse) and leather fruit rot are caused by Phytophthora cactorum (Leb. & Cohn) Schroet. Crown rot is characterized by an intensive browning and eventual disintegration of the vascular tissues of the crown. The leather-rot strains of the fungus can infect fruit at any stage of development. On green fruit, diseased areas are dark brown or green and have brown margins. Verticillium wilt, caused by Verticillium dahliae Kleb., occurs throughout the temperate zones of the world wherever strawberries are grown.

Black root rot is a complex disease characterized by feeder rootlet killing, deterioration, blackening of the primary root system, and decline in vigor and productivity of the plants. Several fungi such as Ceratobasidium sp., Idriella lunata Nelson et Whihelm, Pythium ultimum Trow, Pythium irregulare Buis, and various other Pythium spp., Pyrenochaeta spp., Cylindrocarpon destructans, and Fusarium spp., have been reported to be involved in the black root rot disease. Protective fungicidal sprays are helpful for the control of gray mold fruit rot during periods of moderate disease incidence. During continuous rainfall, however, managing the disease is almost impossible.

There is the need to control two major strawberry pests, aphids and mites, obtained by distributing two predators, Chrysoperla carnea and Phytoseiulus persimilis, as biological control. Flower thrips (Frankliniella spp.) have become a significant problem, particularly in areas with mild winter conditions or growing day-neutral varieties, where flowers are present over a long period. Biological control of this and other flower pests such as Lygus spp. are difficult. Soil fumigation is a standard practice where the strawberries are grown as an annual crop to control weeds and some soil diseases and pests, which has been fundamental to the success of the modern strawberry industry.

Strawberry is ready for harvest four to six weeks after full blossoming. The “pick your own” method of harvesting has become a choice for growers as well as consumers. The growers usually sell their produce by weight instead of volume with standard capacity containers to discourage unspecified harvesting containers being brought by the consumers. The time between first and full bloom may be ten to twelve days. The berries are picked with the cap and stem attached to retain their firmness and quality. The harvesting generally lasts up to three weeks.

Then, the fruits should be sorted carefully, and any fruits with a fungal infection, lesions, or injuries must be discarded. Good temperature management is essential in reducing strawberry deterioration and maximizing postharvest life. The best way to delay spoilage is to quickly remove field heat and maintain the berries at a temperature close to zero degrees Celsius. Deterioration of the ripe strawberry is enhanced by high fruit temperature, which hastens metabolic activities, decay development and internal breakdown. In addition, failure to maintain production at a low temperature during handling, storage, and transportation results in loss of quality and marketable produce. Therefore, rapidly removing field heat within one hour of harvest is essential. It is important to begin cooling within an hour of harvest to avoid loss of quality and reduced amount of marketable fruit.

Postharvest treatment with calcium chloride increases the percentage of bound calcium in the cell wall, while preharvest sprays lead to more incredible vitamin C content, increase in total calcium, reduction in polygalacturonase and increase in pectin methylesterase activities. Preservation of fresh produce through edible coatings has been achieved in several items of perishable produce. The edible coating significantly prevents weight loss and decay, maintains firmness, delays alteration of color (redness) and total soluble solids content and improves the quality and storage features of the strawberries. Heat treatments have been applied in postharvest technology of fruits for insect disinfestation, decay control, ripening delay and modification of fruit responses to other stresses.

In addition, a chemical, 1-Methylcyclopropene is a competitive inhibitor of ethylene action, binds to the ethylene receptor to regulate tissue responses to ethylene, and has been found to reduce respiration. Carbon dioxide shocks could be an alternative to conventional controlled atmosphere storage of strawberries. Self-produced carbon dioxide from film-packed strawberries, when retained within the package, has been found to delay fruit softening and colour development with a significant reduction in decay. Strawberry is highly susceptible to attack by microbial organisms causing various diseases and fruit decays.

Besides, the interest in using a high oxygen atmosphere in postharvest research has sprung from the knowledge that these conditions are detrimental to the growth of a few specific groups of bacteria and fungi. Ozone has been used as an alternative to chlorine because of its better efficacy against many microorganisms. Besides, ozone leaves no toxic residue on the treated fruits, unlike chlorine. Ultrasound technology to maintain the quality of fruit and vegetables has gathered momentum in recent years. Ultrasound improves not only microbial safety but also the physical and chemical properties of the products. The strawberries are packed in plastic punnets and placed in corrugated fiber trays. The punnet-filled trays should be kept in shade or shelter to reduce water loss from the berries.

Nutritional facts

Strawberry is a rich source of a wide variety of nutritive compounds such as sugars, vitamins, minerals, and fiber, as well as non-nutritive, bioactive compounds such as flavonoids, anthocyanins, phenolic acids, carotenoids, phytosterols, and triterpene esters, which plays a synergistic role in its characterization as a functional food. Strawberry contains ellagitannins or ellagic acid, one of the primary sources of ellagic acid in our diet. Strawberries were recently included among the hundred wealthiest sources of dietary polyphenols and further secured a ranking on the list of eighty-nine foods and beverages, providing more than one-milligram total polyphenols per serving. It is a healthy food choice as low in total calories, with one hundred gram serving providing only thirty-two kilocalories. It has fructose contents that may contribute to blood sugar level regulations by slowing digestion.

Volatile chemicals are responsible for the aroma and contribute to the flavor of fresh strawberries. Fresh strawberries produce numerous volatile compounds that can be three hundred and sixty compounds that have been isolated, including esters, aldehydes, ketones, alcohols, terpenes, furanone, and sulfur compounds. Ellagic acid and ellagitannins have been reported as significant contributors to the antioxidant and anticarcinogenic effects of strawberries. Anticarcinogenic effects of strawberries are mediated mainly through the detoxification of carcinogens, scavenging of reactive oxygen species, and the decrease in oxidative DNA damage. Many studies have found that it helps prevent inflammation, oxidative stress, cardiovascular disease, certain cancers, and obesity.

Cultivar differences have accounted for variations in total polyphenols, anthocyanins, or folate content in strawberries grown in Europe or the United States. Anthocyanins are the most prevalent phenolic compound found in the outer cell layers of various fruits, constituting up to forty percent of total phenols in some strawberry cultivars. In cultivated strawberries, the major flavonols are quercetin and kaempferol. Furaneol is a crucial component of the fragrance of strawberries as they are used widely in various manufacturing, including foods, beverages, confections, perfumes, and cosmetics.

Strawberry fruit is greatly appreciated by everyone irrespective of age group for its flavour, attractive red color, juicy texture, and sweetness. Besides, the fruit is rich in fiber, folic acid, vitamin C, protein, minerals, phosphorus, potassium, calcium, iron, phenolics, and flavonoids. Its attractive red color is due to the high content of polyphenolic compounds, specifically anthocyanins, the type of polyphenols quantitatively most important in strawberries. While consumption of fresh strawberries is more prevalent than frozen berries, the US market of both new and frozen strawberries includes imports of the berry crop from Mexico, Chile, and China. Favorite uses of fresh strawberries include sliced cakes, breakfast cereal, and salads (mixed fruit and green) and dipped whole in melted chocolate.

Strawberries, in addition to the fresh or frozen forms, are also commercially available as processed products, such as ice cream, jams, juices, fruit leather, nectar, puree, dried re-hydrated with yogurt, as well as bakery products and are extensively used in North American cuisine as a popular berry ingredient. Moreover, strawberries can be consumed in fried and preserved form through sun drying. Stage of ripeness, age of plants, quality of ground, and genotype of variety are known to affect the quantitative variations in sugar and acids in strawberries. The hedonic test is one of the sensory analyses in which consumers were asked to express their ‘liking’ of the strawberry samples on a scale of zero to one hundred. Analytical sensory tests will be conducted with a trained expert panel. An instrument called a refractometer is used to determine the mineral per sugar ratio and the acidity of the strawberry.

Allergy on strawberry

Some people experience an anaphylactoid reaction to eating strawberries. The most common form of this allergic reaction is oral allergy syndrome, but symptoms may also mimic hay fever, dermatitis, or hives and, in severe cases, may cause breathing problems.

This is because the allergen may be tied to a protein for the red anthocyanin biosynthesis expressed in the ripening of strawberries. The homologous protein known as Fragaria allergen1 is also found in birch pollen and apple, which people may also develop cross-reactivity to all three species. A white strawberry is an option for strawberry allergy sufferers as they lack a protein necessary for normal ripening by anthocyanin synthesis of red pigments.

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Wenyan Zhang