CHAPTER ONE
INTRODUCTION
Fruits, due to their high moisture content and nutrient composition are very susceptible to attack by pathogenic fungi which in addition to causing rots may also produce mycotoxins which make them unfit for human consumption (Stinson et al., 1981; Philips, 1984; Moss, 2002). Postharvest diseases account for about 50% losses in fruits stored in poor storage conditions especially under high humidity. They pose a major problem to the agricultural industries (Agrios, 2005). Cucumber fruits are among the fruits susceptible to postharvest diseases caused by fungi under poor storage conditions.
Cucumber (Cucumis sativus L) is a member of Cucurbitaceae family (Saltveit, 1997). It is borne on indeterminate, tendril-bearing vines of subtropical and tropical origin (Robinson and Decker-Walters, 1997). Cucumis sativus, originated from Northern India. It is a quick growing vine crop that produces mature fruits within 2 months of planting. Healthy vines continue to produce marketable fruits for at least 4 weeks. The plant has large leaves that form a canopy over the fruit. The fruits are round to oblong or roughly cylindrical, with tapered ends, and may be as long as 60 cm in length and 10 cm in diameter (Miller and Wehner, 1989). Valenzuela et al, (2005) showed that the crop is widely grown because of its nutritional value.
1.1 Horticultural Maturity Indices
Cucumber fruits are harvested at various stages of development but when they are generally immature, at sizes ranging from 5 – 15 cm long before the seeds are fully enlarged and hardened (Tan, 1997). Firmness with external glossiness and formation of jelly-like material around the seeds are indicators of proper harvest maturity (Saltveit, 1997; National Agricultural Research Institute (NARI), 2004). Saltveit and McFeeters (1980) stated that straight, uniformly cylindrical fruits that are slightly tapered at both ends are of highest quality. Cucumbers contain over 90% water (NARI, 2004).
1.2 Taste of Cucumber
There appears to be variability in the human olfactory response to cucumbers, with the majority of people reporting a mild, almost watery flavour or a light melon taste, while a small but vocal minority having the opinion of a highly repugnant taste, some said almost perfume-like (Miller and Wehner, 1989).
Various approaches have been employed with regard to remove bitterness from cucumbers. Among these, are some very common and popular practices in India which include cutting off the ends of cucumber, sprinkling some salt, and rubbing the now-exposed ends of the cucumber with the cut-off ends until they frothed. Haung (2009) stated that one ought to peel a cucumber from the end that was once attached to the vine, in order not to risk spreading the bitterness throughout the cucumber.
1.3 Uses of Cucumber and it’s nutritional value
Cucumber is one of the most popular salad vegetables. It is served and eaten at home or in restaurants especially in fast food establishments. Fresh cucumbers are sliced and served in salads or as garnishes to add colour to the meal. The young fruits, usually of small-fruited cultivars, are pickled as gherkins, the smallest used for mixed pickles and small to medium sized fruits for dill pickles. Aboloma et al. (2009) stated that the seed kernels are occasionally eaten and yield edible oil. The young leaves are cooked as spinach in Indonesia and Malaysia (Anonymous, 2010). Cucumber gives relief from heart burn, acid stomach, gastritis and even ulcer. Daily consumption of cucumber juice helps control cases of eczema, arthritis and gout. Cucumber has been found to be beneficial for those suffering from lung, stomach and chest problems (Bates et al., 1990). Cucumber is an excellent source of silica, which is a trace mineral that contributes to the strength of connective tissue in the human body (Brown, 2008).
1.4 Diseases of Cucumber
Cucumber fruits grown for the production and processing industries are seriously affected by several diseases. For example, powdery mildew and scab cause losses of 45% in field cucumbers, and scab reduces both quality and shelf-life (NARI, 2004). Although, an accurate estimate is difficult to obtain, the annual crop loss is probably between 20 and 30%. In addition, the diseases that affect cucumbers also affect other crops as melons, squashes, gourds, and pumpkins in the cucurbit family. A healthy high-quality crop can be produced only from cucumber plants that are free from diseases. Some of the diseases include:
1.4.1 Alternaria Rot
Alternaria rot, caused by the fungus Alternaria alternata, is a common soil-borne pathogen that causes post harvest fruit rot of cucumbers. Fruits which have been stored for extended periods and those damaged by chilling injury are highly susceptible to Alternaria infection. Infection typically begins in injured areas or natural openings (lenticels) in the pericarp. Symptoms are circular to oval lesions on the cucumber surfaces that are bleached or light brown in colour. The lesions soon become sunken and under humid conditions are rapidly covered by a dark mould, identified as A. alternata (NARI, 2004).
