Morpho-physiological Characters Contributes to Patience
Of Extraordinary Temperature in Tomatoes.
Muhammad Saeed1, Rashad Mukhtar Balal1, Muhammad Adnan Shahid1,3, Muhammad Zubair1 and Mujahid Ali2
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.
Tomato (Lycopersicon esculentum L.) is one of the most important edible vegetable belonging to familysolanaceae, which is also entitled as night shade family (Rudich, 2004). Around 500 B.C tomato was grown by the indians in past before the entrance of spaniards while it is inhereted from south America (Rudich and Atherton, 1986). After potato, tomato is considered as utmost significant vegetable due to great economical and commercial advantages. It is a warm season crop reasonably resistant to heat and drought and grown under wide range of soil and climatic conditions in all over the world as well as in Pakistan. It provides substantial nutritional consumption of vitamins A, C, essential mineral and nutrients as well as lycopene, a key constituent of red tomatoes with antioxidant properties which decreases some cancers risk (Rick, 1980; Giovannucci, 1999). It is used as vegetable in variety of ways for culinary purposes. Moreover, they are further supplied for processing products like ketchup, paste, pizza, and sauce etc. In Pakistan tomato is vital ingredient of every main course cooked food menu with dealings to its other uses (Shashikanth et al.,2010).
In Pakistan tomato is cultivated an area of 1689 hectares with an average net production of 142113 tons. The leading province is Punjab with total production of 94549 tons (Fruit, vegetables and condiments statistics of Pakistan, 2016-17). Tomatoes are very widespread vegetable cultivated almost everywhere in the world due to an opulent source of nutrients and multipurpose vegetable using in all food menu. The top producer countries of tomatoes are China, India, America, Turkey, Egypt, Iran, Spain, and Italy (Anonymous, 2003). Tomato plant is a non-woody herb, having alternate leaves, with flowers in cluster forms that are situated on the stems among the nodes. Tomato plants have special type of fruits classified as called berry with fleshy placenta and seeds are numerous in number having minute kidney shaped structure enclosed with tiny inflexible hairs. However skin colour of tomato varies among different cultivars due to the deposition of cutin on tomato fruits (Rudich, 1986).
Tomato plants are grouped as vines, primarily recumbent, naturally rising 10 cm (6 ft) or more above the earth if sustained, even though vertical bush cultivars have been produced, commonly 100 cm (3 ft) tall or littler. Tomatoes are two types according to growth and fruiting manner. Indeterminate categories consists of tender types tomato plants which are perennials, however disappearing year after year in temperate weathers (they are formerly instinctive to hot uplands), while they can survive up to three years in a conservatory like growth chamber and sheet houses in selected regions. Another kind of tomato is determinate types which basically complete their life cycle in a year almost in all-weather environments (Peet, 2009).
Tomato plants are dicots, which later on turn into successions of branching twigs, with a terminal bud at the tip that ensures the obtainable developing phases of tomato plants. When the tip ultimately stopovers rising, may be due to trimming or blossoming, adjacent buds proceeds and develop into other, entirely efficient creepers (vines). The vines of tomatoes are characteristically pubertal and enclosed with delicate tiny hairs. These hairs enable the vining progression, spinning into roots whenever the plant is in dealings with the land and dampness, particularly if the vines assembly to its actual root has been harmed or going to disengaged (Seung et al., 2008). Tomato is a self-pollinated plant. Tomato crop is sensitive to extreme temperature stresss, particularly the bulky fruited renewed varieties. Maximum nocturnal time temperature may result to decrement the fruit set of minor and seedless fruit development. Optimal temperature for fruit set is 25-30 (Anon, 2008).
Under extreme temperature conditions, all crop plants produce set of heat shock protein to some extent (Nover, 1991). They are indulged to defend the cells from injury of heat and similarly aid the organism in regulation of capabilities and gradually healing or recovery for normal status (Nover & Scharf, 1997). In recent time there are various limitations to crop productivity such as fluctuations in climate, raising temperature, uneven rainfall and extreme weather conditions are the most threating constressts that reduce the yield and output of crops. Productions of reactive oxygen species in plants are boosted by extreme temperature when it crosses critical threshold level which adversely affect the metabolism of a plant that brings harmful changes and damage the bio-molecules harms membranes and can vitiate lipids and proteins (Anjum et al., 2014).
The term heat stress is defined as when the temperatures are hot enough than normal temperature it cause an array of morphological, physiological and biochemical changes in plants, which result to affect the growth and development of a plant that may lead to a drastic reduction in economic yield (Rampino et al., 2009). Heat stress is a severe constresst to sustainable crop production in many countries including Pakistan across the globe and it is concluded that stress of high temperature in agricultural crops consequences in high crop losses (Vollenweider & Goerge, 2005). Heat stress can cause quite noticeable changes including blazing of leaves and shoots, other disorders like sunburn on leaves, branches and stems, including leaf agedness and shedding, fruit staining and decrement of yield (Guilioni et al., 1997). Heat stress can be mitigated by various approaches, through thermo-tolerance, genetic approach and metabolite adjustment protectant (Hall & Ismail, 1999).
For mitigation and tolerance of heat stress various approaches such as compatible osmolytes and production of heat shock proteins are the aspects that normalize membrane volatility and stimulate the antioxidative systems to salvage the reactive oxygen species (Kumar et al., 2012). Proline is well known osmoprotectant and chief osmolytes. It is proteinogenic amino acid. It is essential for primary metabolism in plants. It helps to sustain cell turgor, minimizing the damage caused by oxidation and alleviate subcellular structure and biological membranes (Samuel et al., 2000). During abiotic stresses like saline regime, deficit water condition, drought, heat stress, the accumulation of osmolytes such as proline (Pro) has been identified in the plants. Exogenous application of these osmolytes play significance role in heat sensitive plants as they lack the capability to accumulate these substances, hence heat tolerance can be mitigated through this way(Jain et al., 2009). The foliar application of proline ameliorates the growth endurance and restresst of widespread plants under various stress conditions (Ashraf & Foolad, 2007).
The primary function of proline is to alleviate the denatured structure of protein and avoiding accumulation during turn up (Samuel et al., 2000). Besides this proline under stress conditions has a significant role in the maintenance of the mitochondrial electron transport system and other proteins associated to photosynthesis, creating a linkage to improved photosynthetic yield (Abraham et al., 2010). Proline accumulation during scarcity of water plays important role to conserve cell turgidity and over transpiration of water hence developed and boosted the osmotic adjustment ability of the plant during deficit water conditions (Khan et al., 2015). Proline improved the morphological and physiological parameters of rice plant and also brings healthier alteration in their environment which improves its development and productivity (Ashraf et al., 2007).
However in the recent periods it has been documented from different investigations that exogenous application of proline as an osmo-protectant role has beneficial impact on the plants that grow in abiotic stress conditions. During abiotic stress including heat stress the accumulation of osmolytes such as proline, glycine betaine and trehalose is a notable phenomenon in the plants. The exogenous application of these osmolytes plays significance role in heat sensitive plants as they lack the capability to amass these substances, hence heat tolerance can be mitigated this way(Jain et al.,2009). The foliar application of proline relieves salinity and boosts the production as a short term and cost-effective method (Ashraf, 2007). It is concluded that in abiotic stress like salinity and as well as heat stress the exogenous application of proline resulted to improve dry weight and maximize the free proline content in alfalfa (Hayat et al., 2012). Thus by opting foliar application of proline as a short term and feasible tactic and considering tomato as an important horticultural crop an experiment wasscheduled to apply proline on tomato plants under heat stress conditions to improve its growth and heat tolerance potential and also to determine the best suitable concentration of proline that gives the better response against the heat stress. To govern the morpho-physiological characters that contributes to tolerance of high temperature in tomatoes.