Cultivation Of Strawberry In Pakistan
History of strawberry
Strawberry is a commercial fruit crop in Pakistan. Thousands years back, wild species of strawberries were consumed by human beings (Liston et al., 2014). In old poetry, strawberries were mentioned for medicinal use about more than 2000 years ago (Darrow, 1966). Strawberries were considered unfit for consumption in the dark ages (Hummer et al.,2009). Reference of developing a quality strawberry begins to be more prevalent by the 16th century. Botanists began naming the different species and people began using them because of their medicinal uses. Regular strawberry cultivation was started by the mid-16th century. Chandler plants were initially originated in California and cultivated in coastal states due to their high yielding quality (Hancock, 2008). The cultivar Chandler is widely popular in Southern California as well. The country which produces the strawberries at large scale is United State of America (USA), it produces about 1 million metric ton annually. The strawberry which is produced in USA is about 30% of total world production. In Pakistan, the strawberry was introduced in the beginning of 1980 in Khyber Pakhtunkhwa and called as ground mulberry (Rajwanaet al., 2017). After that, due to its awesome taste and qualities strawberry cultivation was also started in Sindh, Baluchistan, and Punjab.
In Pakistan the strawberry has been grown on 179 hectares and it produced 609 tonnes of fruits (GOP, 2016). Strawberry is broadly divided into many categories. Douglas and Toro are most apporiopiate for cultivation in southern areas of Pakistan. While, Chandler, Cruz, and Tufts are mostly suitable for cultivation in Islamabad areas. Whereas, Honeyo, Chander, Grolla and Corona are best suggested for Swat. In Pakistan strawberry is mostly grown in Swat, Charsadda, Haripur, Mardan, Abbottabad, and Mansehara, while it is also produced and cultivate in the some other areas of Pakistan which include Peshawar, Gujarat, Sialkot, Jhelum, Chakwal, Multan and Karachi (Khalid et al., 2013).
Taxonomy of strawberry
Strawberry (Fragaria ananassaDuch) is associated with Rosaceae family (Zebrowska and Hortynski, 2002). The genus Fragaria contains about 3000 species (Longhiet al., 2014). In Rosaceae family, the fruit species like peach (Prunuspersica), pears (Pyrus spp.), apple (Malusdomestica), roses (Rosa spp.) and strawberries (Fragaria ananassa) are important economically (Longhiet al., 2014). In Rosoidae subfamily the genus Fragaria belongs to the subtribeFragariinae (Potter et al., 2007). Fragaria genus contains twenty wild species (Rousseau-Gueutinet al., 2009; Staudt, 1999). Ichijima and Longly (1926) determined the ploidy level of Fragaria species which is di-to decaploids. Fragaria ananassa isoctoploid with 56 chromosome numbers.
Nutritional value
Strawberries are an excellent source of vitamin C,vatmin B6, minerals i.e manganese, copper, potassium, phosphorus, magnesium, iodine; foliate, biotin ,fiber and omega-3 fats (in the form of alpha-linoleic acid). Due to its high nutritional value strawberry fruit is hailed as “the Queen of fruits”. Strawberry fruit contains 32 calories, 0.67 g protein, 7.7 g carbohydrates; 0.3 g fat. It contains vitamin C 58.8 mg and manganese 0.56 mg. It is also a high quality fount of cellulose 2 g and also the major source of vitamin K 2.2 mg, potassium 153 mg, magnesium 13 mg, vitamin B6 0.05 mg, phosphorous 24 mg, niacin 0.39 mg, calcium 16 mg and thiamin 0.02 mg. It has anti-inflammatory properties and helps to fight against asthma and cancer. It contains flavonoids and ellagic acid which control cardiovascular health (Finn and Strik, 2008). Aroma of strawberry fruit is delineating as a composition of buttery, sweet, sour and taste (Zaharah and Singh, 2011). Distinctive aroma is due to the presence of volatile compounds and fewer than 0.01% of the fresh fruit markedly affects the fruit aroma (Buttery, 1981). Sweetness and bitterness of the mature strawberries are because of the sugars and acids which in mixture with aroma provide their taste (Liaoaet al., 2013).
In general, sweetness or tart of the fruits is affected by the total sugars content or by the sugar/acid ratio (Afonssiet al., 2010). In strawberry fruit total soluble solids are present in the form of carbohydrates which are related with fruit texture, color, aroma and flavor (Lima et al., 1999). Attractive color of strawberry fruit is due to anthocyanin that indicates the fruit maturation (Chitarra and Chitarra, 2005). Strawberries provide a rich variety of phytonutrients, including dozens of polyphenol antioxidants belonging to the following nutrient groups: flavonoids, phenolic acids, lignins, tannins, and stableness. Hereditary component and difference in atmosphere can affect the fruit attributes (Galletta and Himelrick, 1990). It has been reported by many researchers that genes are involved in internal changes of the fruit i.e. quality, taste, and flavor (Shaw, 1990; Pelayo-Zaldívaret al., 2005; Diamantiet al., 2009;Crespoet al., 2010). Pelayo-Zaldívaret al. (2005) reported that genotypic difference was more responsible than harvest date for variations for pH, titratable acidity, total soluble solids, sugars, and aroma compounds.
Gebauer and Schulze (2009) reported that in strawberry fruit, nutritional quality can be intended through cultivars which are being used by the farmers for production. However, Janagard et al. (2008) concluded that although genes are involved for genotypic changes in fruit attributes but harvesting time also plays a very vital role in affecting the strawberry fruit quality.
Strawberry cultivation
Strawberry fruit is popularly consumed worldwide. Fruit is cultivated in region known as “temperate region” i.e. Europe, North America and some parts of Asia. Cultivars of strawberry are widely different in color, shape, flavor, ripening season, degree of fertility and resistance to diseases. Almost about 200 ovule are present. Strawberries mostly vary in foliage, and some also vary in sexual organs development (Flecher, 1917). Commercially strawberries plants are multiplied through runners or as roots without soil. Its cultivation follows on two general models “Annual Plasticulture or “Perennial system of matted mounds. Off season strawberries are cultivated in greenhouse. Mostly in Pakistan strawberries are grown in northern areas where climate is cold and suitable for strawberry cultivation.
Now cultivation is being done in Punjab, Sindh and Baluchistan. Runners are purchased from Swat and transplanting is done very carefully. Different methods are used for strawberry cultivation. Soil health relates with nutrients availability. Good preparation of soil increase plant growth and minimizes stress. Minerals, organic matter, water and air are several components of soil. Different types of soil contain different minerals. A soil should have maximum air spaces. Oxygen is needed to survive and to perform proper functioning at root zone of plant. Carbon and other ions are available in the form of air to build up more complex compounds. Soil which has large particle size will have greater pore and provide more air, but such soils have less water holding capacity and more drought could happen in such kind of soils. On all kind of soils strawberry could be grown, these soils range from light sandy to clayey. Strawberries can be benefitted if grown on raised beds, whereas adding organic matter also improves the soil and aids drainage. Strawberry can suffer from deficiencies of iron and magnesium on calcareous soils, so that it is important to provide these elements as chilated compounds.
Salinity
Salt stress is one of the most damaging environmental factors which affects the plants health and yield (Flowers et al., 1997). Salinization is basically accumulation of salts in soil due to application of brackish water or because of insufficient drainage of water from sub-soil (Kanberet al., 1992). Soil salinity and sodicity issues are common in areas where rainfall is less and water is not much to remove the salts and excess sodium ions out of the land and the problem is increasing day by day in arid and semi-arid areas of world (Madidiet al., 2004). Almost 10% of the land is merely affected by different kinds of salts. The earth is covered with 954 million hectares of saline soils. These salt effected soils are present in the whole world. More than 80 million hectares of such soils are in Africa, 50 million hectares in Europe, 357 million hectares in Australasia, 147 million hectares in Central, North and South America. Similarly, a large bulk of about 320 million hectares of land in South and South East Asia is under the grip of salinity (Alamet al., 2000). The lands which are salt affected are not able to be cultivated and to grow any kind of crops. Excess amount of salt damages the plant growth and productivity. Salt stress inhibits cell enlargement and cell division, and also causes nutritional imbalance (Makhadmehet al., 2002).
Strawberry is among the crops that are very sensitive to salinity. The most dangerous factor which adversely affects the strawberry plant health and yield is salt stress (Flowers et al., 1997). The detrimental effects of high salinity on plants can be observed at the whole-plant level as death of plants and decrease in productivity. Many plants develop mechanisms either to exclude salts from their cells or to tolerate their presence within the cells (Greenway and Munns, 1980). The earliest response is a reduction in the rate of leaf surface expansion, followed by a cessation of expansion as the stress intensifies. Most commonly, high Na+and Cl-cause salt stress. Salt stress has threefold effects; it reduces water potential, causes ion imbalance or disturbances in ion homeostasis, and toxicity. This altered water status leads to initial growth reduction and limitation of plant productivity. Since salt stress involves both osmotic and ionic stress (Hagman and Murata, 2003; Hayashi and Murata, 1998), growth suppression is directly related to total concentration of soluble salts or osmotic potential of soil water (Tabatabaeiet al., 2008; Greenway and Munns, 1980).
Salt stress affects all the major processes such as growth, photosynthesis, protein synthesis, and energy and lipid metabolism. Elevated NaCl levels in the root medium reduce mineral nutrient assimilation, especially of K+and Ca2+, resulting in ion imbalances of K+, Ca2+and Mg2+compared to Na+(Gabr, 1999; Khan et al., 2000 ), as well as exert negative effects on enzymes and membranes. NaCl is the dominant salt present in salt affected soils and adversely affect rice growth and yield in these soils (Flowers, 2004). If too much amounts of sodium ions enters into a plant, it will accumulate to toxic levels in leaves causing sudden death of the cell and reduce photosynthetic rate, which further inhibit plant growth (Acharyet al., 2012).
Salt stress mainly occurs due to increase in Na+ and Cl- which cause reduction in plant growth and yield (Rahnama and Ebrahimzadeh, 2004). Excess of NaCl concentration adversely affects the metabolism, physiology and morphology of plants (Hilalet al., 1998). High level of salt moderately damages the strawberry crop (Mass and Hoffman, 1997, Anna et al., 2003). When salinity was applied through aerial parts of plant then, amount of Na increased in plant leaves (Turhan and Atilla, 2004). In strawberry salt increased the sodium (Na+) and chloride (Cl-) concentrations and decreased the potassium (K) and magnesium (mg) contents (Turhan and Atilla, 2004). Increase in salt accumulation of arable land is considered as most destructive factor which may cause up to 5 % losses by the middle of 21 century (Mahajan and Tuteja., 2005). Soil salinity gradually increases with the application of sulphate of potash (K2S04) fertilizer and saline irrigation water (Epstein et al., 1980).
Many plants are cultivated to satisfy the demands of growers, but abiotic stresses especially salinity pose a threat to the growth and crop yields (Qureshiet al., 2005). The damaging outcomes of salinity on plant growth are linked with oxidative stress (Marschner, 1995), low osmotic potential of the soil solution, specific ion effects, nutritional disequilibrium (Ashraf, 1994; Zhu, 2002) and inhibition of photosynthesis process (Kumar et al., 2000). The generation of reactive oxygen species (ROS) is well documented in many crop plants as a result of salinity (Bartoliet al., 2004). Excessive soil salinity causes reduced plant growth, poor stands of crops, low yield and stops the absorption of essential plant nutrients (Ashraf and Harris, 2004). Salinity restricts plants water up take ability (Munns, 2005) and declines root growth and elongation (Ashraf et al., 2005). Salinity caused reduction in root conductivity (Zekri, 1987) and significant a reduction was observed in seed yield per plant (Ashraf et al., 2005).
Salt tolerance at germination stage is an important factor and has effects on germination of seeds (Sharma et al., 2004). Salt stress adversely affects plant during its growth cycle but the most sensitive stage is germination which is badly affected by the salt stress (Javanet al., 1997). When plants were exposed to drought and salt stresses, decrease in protein content was observed in root and young and older leaves of many crop species (Dos Santos et al., 1999; Gilbert et al., 1998). The decrease in total soluble content was observed in tomato, rice, broard bean, and amaranth and brugiera plants under salt (NaCl) stress (Alamgir and Ali, 1999;Wang and Nil, 2000;Al-aghabaryet al., 2004; Parida and Das, 2005; Parvaiz and Satyavati., 2008). In the whole world, 953.63 million hectares of land is affected by salts. Pakistan contains 6.31 million hectares of salt affected land,in which 60% is saline sodic and 40% are saline. Punjab land covers 80% of the saline sodic (Khan, 1998). Most of the areas are not being cultivated because of salinity effect.
Salinity effects on plants
Hyperionic and hyperosmotic stress caused by increase in salt level could be due to fertilizer application or by irrigation of saline water. These affect the disinfection of metabolism, membrane injury and ultimately cause death of plant (Mahajan and Tuteja, 2005). Salt stress also affects the mineral and nutrient uptake by crop plants (Makhadmehet al., 2002). The salinity assists to decline the harvest yield and quality (Sairam and Tyagi., 2004). The accumulation of Na+ and Cl-cause to decrease of K+ level in roots and leaves. Under saline conditions, a huge amount of Na+ and Cl-were noticed in roots and leaves of okra plants (Shahidet al., 2011).The seeds of most of crops give maximum germination with distilled water and are highly sensitive to salt stress at their phases of germination and seedling emergence (Zehtab-Salmasi, 2008; Devkota and Jha, 2010; Al-Taisan, 2010). Salt stress adversely affects plants whole mechanism includinggermination, seedling development, vegetative and reproductive stages. It has been revealed through molecular and biochemical studies of salinity that salt stress gradually increases the reactive oxygen species which includes hydrogen peroxide (H202) and superoxide (O-2) (Tanou et al., 2009; Ahmed et al., 2010).
Excessive salt can reduce the uptake of nitrogen by plants (Pardossiet el., 1999; Silveriaet al., 2001; Wahid et al., 2004). Due to leaching, nitrogen losses are more in saline soils. Therefore these nitrogenous fertilizers are necessary to use in amount which fulfill the nitrogen requirement of plants (Yin et al., 2007; Abdelgadiret al., 2010). Salt stress also affects photosynthesis, chlorophyll and carotenoids contents (Parida and Das, 2005). It has also been reported by many researcher that salt stress adversely affects plant metabolism (Hilalet al., 1998)
Mitigation of adverse effects of salt stress
Mitigation is done to minimize the degree of loss and harm which occurred due to salt stress. Different methods are used to prevent plants from adverse effects of salts. Some common methods which are basically used for mitigation of salt stress are “leaching, flushing and scraping”. Naturally plants also have tolerance for stress that includes water transport, osmolyte biosynthesis and ion homoeostasis (Hasegawa et al., 2000). In recent decades, exogenous application of protectants such as plant hormones, polyamines, trace elements, antioxidants and osmoprotectanats have been found very effective for mitigation of salt stress (Hoqueet al., 2007; Ahmed et al., 2010; Azzedineet al., 2011; Hossainet al., 2011; Rawaia-Eidet al., 2011; Yusuf et al., 2012). Exploring suitable ameliorants or stress alleviant is one of the tasks for plant biologists. Some of the mechanisms adapted by plant during the stress are alterations in morphological and physiological processes (Zhu, 2001). Phytohormones play a vital role in the reduction of salt stress and several kinds of hormones have been used for alleviation of salt stress i.e. salicylic acid (SA), auxins, cytokinins and sodium nitroprusside (SNP) etc. All kinds of phytohormones significantly increase the growth and productivity of the plants. Best results have been recorded with SA and SNP (Lee et al., 2010). In our study we have also done mitigation with SAand (SNP).
Salicylic acid (SA) is a signaling molecule which creates tolerance in plants against various stresses (Horvath et al, 2007). SA has been recognized as a regulatory signal mediating plant response to abiotic stresses such as drought (Munne-Bosch and Penuelas, 2003; Chiniet al., 2004), chilling (Jandaet al., 1999; Kang and Saltveit 2002), heavy metal tolerance (Metwallyet al., 2003; Yang et al., 2003; Freeman et al., 2005), heat (Larkindale and Knight, 2002; Larkindaleet al., 2005) and osmotic stress (Borsani et al., 2001). SA boasts immune system of plants and built resistance towards stress. In coordination with jasmonic acid (JA) and absicic acid (ABA), SA plays a very vital role in various plant developmental processes. In stress, SA responses in dual way as to mitigate the adverse effects of salt and also to increase growth and development of that plant (Dezaret al., 2011). SNP is the source of nitric acid (NO). Nitric acid is a bioactive molecule having multifunctional role which increase plant proliferation and enlargement (Siddiquiet al., 2011).
Several ambition such as, heavy metals, drought, salt stress can be reduced through exogenous application of NO (Kopyra and Gwozdz, 2003; Siddiquiet al., 2011). SNP also plays a vital task in plant developmental processes i.e. germination, flowering and in fruit ripening (Guo and Craword, 2005). Significant alleviation in rice seedling has been observed by the application of SNP, a NO donor (Uchida et al., 2002). It has been described by Farooqet al. (2009) that NO modulates mechanism responsible for salt stress defiance. SNP is widely used as a Nitric oxide (NO) sponsor remedy inin vivo and in vitro studies (Butler and Megson, 2002; Roncaroliet al., 2005). In addition, NO also plays a very positive role in lignification (Fanourakiset al., 2013).
