Pre- and Postharvest Factors Affecting Quality and Yield in Tomato

Tomato production in the world is nearly about 159 million tons

Tomato is one of the most important vegetable crop in the world and also widely cultivated in Pakistan. It is a self-pollinated crop and has a chromosome number of (2n=2x=24). It is used both for culinary as well as industrial purposes. Usama Yousaf & Poonum Rana Author

It has high nutritional value specifically vitamin A and C and relishing flavor. Tomato production in the world is nearly about 159 million tons and one fourth of this is processed for the industry, hence it becomes the highest processing vegetable in the world. In Pakistan also, it is a very economical crop and tomato production in Pakistan during year 2011 was 530 thousand tons. Pakistan not only produce for its own needs but also exports tomato and earns the capital. In the year 2009-10 Pakistan exported 5692 tons of tomato and earned 77 million rupees. Source (agricultural statistics of Pakistan). On an average 42% of tomato fruit is wasted globally due to pre- and postharvest losses. The following study is to indicate the factors involved in these losses and how to prevent these losses.

 It is grown in almost all the areas that have dry and warm temperature because wetness during the monsoon season is very damaging. In similar way in December it is highly damaged by the frost so in these seasons tomato gives dwindling supplies of its produce and fetches exceptionally high price in market. So suitable range required for this is 21-25°C and it requires fertile to sandy loam soil for good performance.

Tomato has some main issues in its production, firstly it is targeted by (TMV & TYLCV) secondly it is damaged by the pathogens and early and late blights and one of the most important is lack of availability of hybrids produced locally. All these factors reduce yield to greater extent so there is need to sort and identify those factors that play a crucial role in enhancing the yield of tomato. There are some important physical factors that can influence the quality and yield in tomato.

Fertilizer Use:

Researchers have identified that nutrition of plant is controlling the quality of its produce. Adequate quantity of a specified fertilizer at a particular time has a specific role for specific desired traits, for example a good supply of potassium chloride in tomato ameliorates the color and reduces the occurrence of yellow shoulder in tomato. Yellow shoulder is an atrophy in tomato that is identified by discoloration in stem scar. Deficiency of potassium chloride can also cause ripening abnormalities. In the same way an increased nitrogen supply can negatively affect the tomatoes in green house. Beyond a threshold value of nitrogen reduces many quality parameters as decline in sugar contents, total soluble solids and reduced flavor. On the other hand, reduced quantity of nitrogenous fertilizer as ammonium chloride can give improved flavor. In addition to these trace elements such as boron also has impact on different traits. The function of calcium application has recently been reported. It has role in prevention of many diseases and also cause decline in fruit firmness during ripening. It has also seen that spraying some salts of calcium on leaves of tomato can reduce the chance of powdery mildew. It can also help in tackling bacterial wilt when present in high quantities.

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Pruning:

Pruning has positive role in high yield because it reduces the competition between the flowers and fruits being developed. Pruning hence channelize the nutrients to fewer fruits which serves as sink and hence ameliorating the nutrition profile and fruit size of these clusters. Pruning clusters to three fruits is economically efficient and gives high marketable yield. However, pruning also affects other parameters of fruit development but that depends upon genotype of cultivar, fruit to leaf ratio, truss position and developmental stage of sink. Pruning increases the total soluble solids and the greater size of tomato which is in a specific size range gets higher demand and fetches more price.

Maturity Stage:

Tomato can be harvested at different stages as it is a climacteric fruit i.e. it continues ripening even after harvesting. The maturity stage is the descriptor of many traits related to quality. Tomato can be harvested at mature green, half ripen and mature red and each stage exhibits its own postharvest properties. Researchers have noticed that the shelf life of tomato is longest when it is harvested at green stage.

Cultivar Type:

The selection of cultivar to be used by grower is of prime importance. The choice of consumer should be priority and a cultivar having more number of desirable traits and long shelf life should be used. If poor cultivar used then low yield and quality resulting poor market acceptability. Cultivars have differences in color, size, flavor, texture and duration of storage. A tomato cultivar Roma VF seems to show higher sucrose content and lower weight loss in comparison to cultivar Marglobe.

Irrigation:

Water is crucial for proper growth and development of plants. Tomato is not drought tolerant plant it needs to be irrigated regularly for good crop yield. Water scarcity being very important burning issue in agriculture so it is required to develop and promote cultivars that can tolerate or give bumper yield even in deficiency of water. Many growers have developed strategies to minimize the water stress and maintain the yield. According to Mitchell water deficiency reduced water accumulation in fruit and yield of fresh fruit but at the same time it increased total soluble solids. Ismail reported that irrigating in morning after three days gives good yield than daily irrigation.

Postharvest Quality maintaining factors:

After harvesting many activities are taking place in the fruit. The climacteric burst of ethylene induces senescence and ripening of fruits and proper release of ethylene is necessary for good quality of fruit and for this reason many practices are done that control the activity of ethylene and hence controlling the fruit ripening and quality. Following are important factors that determine quality of tomato fruit after harvesting.

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Temperature:

Temperature plays key role in the maintenance of shelf life of tomato. If harvested fruit is kept at 20∘C then it is very effective in reducing all the metabolic activities involved in ripening and hence giving more time gap for handling the harvested produce. Generally, one-hour delay between harvesting and storing at cool temperature will lead to loss of shelf life to one day. In climacteric fruits rate of respiration and metabolic activities is related to environmental temperature. Higher temperature increases the respiration rate and metabolic activities resulting in increased CO2 production. High level of CO2 creates a stimulus for ethylene production and this ethylene in very little quantity can cause an enhancement in fruit ripening. Higher temperatures hence can lead to rapid degradation of quality of produce. Tomato can be stored at lower temperatures and quality parameters like Nutritional value, flavor, texture and aroma can be protected through cold storage. However, tomato being tropical fruit also damaged by very low temperatures. Temperature below 10°C can cause chilling injury in tomato. The signs of chilling injury include premature fruit softening, irregular color development, formation of pits, off flavor development, water soaked lesions, browning of seeds and high postharvest decay.

Relative Humidity:

The water loss from the fruit is dependent on the environmental humidity. At higher levels of humidity tomato fruit maintains fruit freshness, size, taste and appearance and reduction in humidity cause wilting, softening and juiciness occurs. Optimum relative humidity is 85-90%(v/v) for mature green tomatoes but very high levels to 100% are damaging. The storage of tomato in lower relative humidity cause higher moisture losses and result in shriveled fruits and very high moisture cause fungal and mold development.

Combination of Gases:

Different gases have different roles in fruit senescence and ripening and combination of gases can affect the storage life of fruits. The optimal combination for preventing senescence in tomato is 3-5%(v/v) O2,1-3% and 1-5% (v/v) for green and ripe fruit respectively for CO2 and 94-96%(v/v) of nitrogen is required. Carbon monoxide prevents the infestations of pathogens in fruit and also improves some quality traits. For instance, tomatoes stored in 5–10%(v/v) carbon monoxide with 4%(v/v) oxygen were found to have superior total soluble solids (TSS) and titratable acid (TA) profiles as compared to control samples stored in air. But use of these gases in fruit commodities is lethal for human health so it is avoided.

Calcium chloride application:

Calcium is present in many higher plants and in some plants its deficiency cause problems. In tomato calcium as a fertilizer gives very good yield. When applied after harvesting shows positive effect in ripening of many fruits and vegetables. Postharvest application of calcium chloride causes a reduction in respiration and ethylene and hence it delays senescence in tomato. External application maintains cell wall integrity and prevents from enzymatic degradation. The postharvest losses are also dependent on Physical handling of the produce, a rough handling has more losses than good and fine handling.

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