Effect of endophytic fungi on growth, production and quality of watermelon under greenhouse conditions

Effect of endophytic fungi on growth, production and quality of watermelon under greenhouse conditions
Muhammad Awais Khan1, Rashad Mukhtar Balal1 , Muhammad Adnan Shahid1,3 , Muhammad Zubair1
, Mujahid Ali2 and Muhammad Wajid Khan1

1. Department of Horticulture, University College of Agriculture, University of Sargodha
2. Institute of Horticultural Sciences, University of Agriculture, Faisalabad
3. Horticultural Sciences Department, Institute of Food & Agricultural Sciences, University
of Florida, Florida, USA.
(Date of Submission: (27/10/2017)
Watermelon (Citrullus lanatus) is an annual crop belong to Cucurbitaceae family. Watermelon is cultivated on an area of 7.12% the world (FAO, 2017). The cultivated species are diploid with 22 number of chromosomes. This crop is native to tropical Africa (Carroll, 1988). It can also grow in dry areas and sandy of southern Africa especially in Kalhari desert. It has been cultivated on commercial level in more than 96 countries of the world including Pakistan. It is planted mid-December to March, and is harvested in May to July 15. The world production of watermelon is about 93.7 thousand million tons. China is the largest producer of the watermelon in the world with annual production of 66434289 metric tons (FAO, 2017). It is mostly used as a fresh fruit, across the world. It is rich of nutrients especially good source of carbohydrates, protein, dietary, fiber, sodium, vitamin A, niacin, pantothenic acid, thiamin, vitamin B6, vitamin C, calcium, magnesium, potassium and carotenoids etc. High water contents are present that are approximately up to 92 %. Texture of flesh is good and is very favorite for the people living in deserts as a thirst quenching fruit. It contains very high level of naturally produced lycopene that is considered as an antioxidant that helps the human body to fight against cancer and to prevent diseases. Lycopene is present only in selected vegetables and fruits and is considered very effective in trapping the cancer promoting against that are called as free oxygen radicals. High quantity of toxic matter is present in human body that is reduced by the action of antioxidants
present in watermelon, which results in the reduction of asthma attack. It is rich in vitamin C and beta carotene content and shows wonderful effects in term of quenching diseases. Its juice is an effective too in aiding the water elimination from the body, fluid retention, itchiness and skin blemish (NRC, 2012).
It requires warm climate and relatively long growing season. The potential of watermelon as a cash crop is much for the farmers especially those residing near the urban areas. Its vine has sprawling or climbing nature. Its leaves are large green with 3-5 deep lobes, flowers are with short pedicles. Fruit is medium to large having smooth skin and flesh color can be dark red, red and yellow. Seeds are oval to oblong with a white, gray, red or brown color (Dane and Lang, 2004). Watermelon is a climacteric fruit and is ripening begins with internal production of ethylene, which induces softening of cell walls, production of secondary compounds and changes in sugar content, texture, flavor and aroma of fruit. Orange and white to cream flesh type of watermelons are cultivated in some parts of the world and their flesh is used as vegetable for cooking purposes. Their seeds are also used for the preparation of snacks and sauces after grinding. Seeds are also consumed as source of fat and protein in the diet (Dane et al., 2007).

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Watermelon is monoecious as male and female flowers are produced on the same plant. Most of its species produces imperfect type of male and female flowers. At the beginning of flowering, male flower are produce at each node and female flower are produced approximately at every seventh node. Watermelon flowers are viable for only one day, so a sufficient population of pollinating insect are required daily during the flowering season. However under sufficient availability of pollinating agent watermelon flowers abort at an average 2-3 fruit should set per plant. Actual number of fruit set differs from variety to variety, environmental condition, culture practices, number of pollinating insects and number of irrigations (Arnold et al., 2003). The most common definition of endophytic fungi is that of Petrini (1991), “All organisms inhibiting plant organs that at some time in their life, can colonize internal plant tissues without causing apparent harm to the host”. Endophytic fungi are group of fungi that causes infections like asymptomatic infections on aerial tissues of different group of plants. The majority of fungal endophytes are ascomycetes and their anamorphs. Basidiomycetes and zygomycetes rarely are isolated as endophytes (Arnold et al., 2003; Petrini, 1991). Group of these fungi do not affect the plants communities too much. They are not harmful to plants. They provide resistance to plant against insects (Azevedo et al., 2000), fungal pathogens (Arnold et al., 2003). Endophytic fungi increase the plant ability to stand and continue its life cycle in harsh environments (Redman et al., 2002).

The colonization of endophytes and propagation and secondary metabolites which are present inside the plants may be important for above effects. These opinions’ shows that endophytic fungi may be used as biological agents for the control of insects and many diseases.
Moreover, the growers need high yielding and early maturing types of watermelon, which have maximum disease resistance and shelf life. Therefore, evaluation of newly released varieties and advance experimental breeding lines is extremely valuable for growers in the commercial watermelon industry. Furthermore, it is helpful for identifying potential of new cultivars and experimental breeding lines that may be adaptable to growing condition (McCann et al., 2007).
In watermelon, sensory evaluation criteria should be complemented with other parameters for the proper characterization of the product. This involves the determination of soluble solid contents, quantitative and qualitative determination of sugars and measurement of fruit firmness and internal color. The hybrid types of watermelon are mostly diploid and triploid. “Sugar baby” was reported to be the most successful diploid and open-pollinated cultivar. The F1 hybrid is developed from two inbred lines that have been self-pollinated for many generation and then crossed with the consistent sale of the seed to the grower (Messiaen, 2013).
Endophytic fungi live within a plant’s tissue without causing any disease symptoms or apparent injury to the host (Kogel et al., 2006). Older plant parts may harbour more endophytes than younger ones (Arnold et al., 2003). Almost all plant species (400,000) harbour one or more endophytic organisms (Tan and Zou, 2001) but only a small proportion, about 5 % of the existing fungal species are known (Hawksworth, 2001). Shiomi et al. (2006) reported that endophytic fungi are some of the most unexplored and diverse group of organisms that engage in symbiotic associations with higher life forms and may produce beneficial substances for the host crop. Therefore it will be of great necessity if more economically valuable endophytic fungi are identified. Endophytic microorganisms are associated with living tissues, and may in some way contribute to the wellbeing of the plant (Haggag, 2010). Endophytes may facilitate host plants to tolerate and withstand environmental stress such as drought (Malinowski and Belesky, 2000), as well as protect their hosts against pathogens and pests (Arnold et al., 2003 and Akello et al., 2007).

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