सब्जियों की वृद्धि और विकास में जलवायु कारकों की भूमिका

Environment is defined as surrounding or everything outside the plant which influence the life of plant e.g. temperature, rain, light, humidity and soil etc.

There are 3 major classes of environmental factors: Climatic factors like light, temperature, humidity, wind, rain and photoperiod, Topographic factors like Slope of particular place, altitude etc and Soil/Edaphic factors like soil pH, soil structure, texture, organic matter in soil

The geographic distribution, plant growth and development are largely influenced by environment. If any environmental factor deviates from optimum requirement, it results in hindrance of plant growth and development by various means.

For example, only plants requiring very small amount of water can live in deserts. The environmental stresses directly or indirectly leads to incidence of various plant growth affecting biotic or abiotic stresses.

1. Role of Temperature                       

Temperature does not supply energy to plants, but controls rate of chemical reactions. It controls the plant development including morphogenesis and plant quality. Temperature, diurnal temperature-alternating day and night temperature and optimum temperature range have close relationship between yield and quality of vegetables.

Effect of temperature on Plant Physiology

Temperature is most important factor for plant growth because it has unique regulatory influences. Different metabolic responses, enzymatic activity, membrane permeability, substrate concentration and cumulative reactions are influenced. Water uptake by root system also influenced.

Transpiration which is driving force for the water uptake within root system is a function of leaf temperature. Biochemical reactions and metabolic processes not take place at temperature less than freezing point of water.

At 35 ⁰C or above molecular structure of enzymes and protein system alters, stunting the growth processes.

At the constant temperature condition lower than required for a crop results low rate of photosynthesis, growth and yield. At constant high temperature than optimum for a crop promotes high photosynthesis, respiration and low yield.

At lower night temperature, absorption of water is high, low respiration, less carbohydrates used, more CHOs stored, turgur pressure of new cell increases leads to cell elongation and new cells are formed. High night temperature increases photosynthesis and respiration, decrease carbohydrates and growth is less.

Effect of temperature on different plant parts

Effect of temperature on seed germination-

Germination of seed of some of crop can occur at minimum temperature of 2⁰C (Onion). In pea, cole crops and carrot at minimum temperature of 5 ⁰C germination occur. In most of warm season vegetable seeds a minimum temperature of 15⁰C is required for proper germination.

As the temperature increases germination increases. Cucurbits do well at 35⁰C and maximum temperature range 35-40⁰C. In okra seed do not germinate at temperature < 17⁰C. Optimum temperature for germination of Okra is 29⁰C. Optimum temperature for germination in pea is 22⁰C. In tomato optimum temperature for germination is 24⁰C.

Effect of temperature on economic parts-

Development of economic part is highly depend on temperature on many crops e.g:

• In potato 20-24⁰C temperature is favourable for sprouting and initial growth. Best temperature for tuberization is 18-20⁰ at the temperature > 30⁰C, completely stop tuber formation.
• In onion formation of bulb favoured by high temperature 15.5-25⁰
• In sweet potato temperature < 20⁰C is critical for tuberization. More tubers are formed at 25-30⁰
• In carrot good root development occurs at 15.5-21.1⁰ At the high temperature roots become sturdy and the low temperature they become tapered.
• In cauliflower also curd formation is thermosensitive.

Effect of temperature on viability in storage-

temperature and moisture content of seed in combination determine the storage life of seed. If seed moisture is high, storage temperature will have to be low and vice versa. Under ordinary storage conditions i.e 26⁰C, moisture content of most of vegetable crops is 5-10%. If the temperature is 21⁰C, moisture is 7-10%. Moisture of seeds brought down to 6-7% by freeze drying and has 10 times more storage life than seeds stored by conventional methods.

2. Effect of Light on vegetables production

Light is an electromagnetic radiation which is a form of kinetic energy and its properties are studied in 2 aspects: particulate and electromagnetic aspect.

Particulate - According to particulate concept light came from sun in the form of tiny particles called photon or quanta.

Electromagnetic - According to this tiny photon exhibits the properties of wave.

Light is an integral part of photosynthetic reaction in that it provides energy for combination of CO₂ and H₂O in formation of first manufactured compound. So greater amount of light with other favourable conditions leads to greater photosynthesis, so amount of CHOs increases for growth of plants. Performance of crops is influenced by 3 aspects of life:

Effect of Light intensity:

Light intensity refers to number of photon falling in a given area or total amount of light which a plant receive. In general for any given location intensity vary with day, season and distance from equator. Also vary with dust particles and water vapour present in atmosphere, slope of length and difference in elevation.

Optimum light intensity is acquired by every crop and specified in foot candle or Lux for each crop. A range of 3000-8000 f.c. is required by crops like capsicum, cucurbit, egg plant and sweet potato. Cabbage and potato requires 2000-8000 f.c. of light intensity.

Effect of Light quality:

It refers to length of waves. The visible part of spectrum of electromagnetic radiation ranges from wave length 390 mu to 730 mu. The compositions of visible light affect photosynthetic activity.

Since chlorophyll has the capacity to absorb radiant energy particularly in blue light (430-470 mu) and red (650-730 mu) ranges, blue and red light affect the rate of growth as measured in terms of dry weight. It is observed that tomato plant grown in blue and red light produce greater dry weight.

Effect of Light duration (photoperiod):

The most important aspect of light linking development of some vegetables is their photoperiodic requirement. Light duration is shorter in winter than summer and varies with distances from equator. Beside accumulation of carbohydrates day length is often a deciding factor for flower induction in certain plants.

Based on responses to length of light period plants are classified into long day, short day and day neutral plants. If long day plants are grown in short day period they are with less accumulation of CHOs and proteins resulting in weak vegetative growth and non flowering. If short day plants are grown in long day period there will be abundant CHOS and protein resulting in vigorous plant growth and non flowering.

In cucurbits day length and intensity of light coupled with temperature are known to influence sex expression. In cucumber abundance of light tends to increase number of staminate flowers and decrease in light increases number of pistillate flowers. In general cucurbit under high temperature and long day tends plants to be staminate.

3. Effect of moisture on growth and development of vegetables

Moisture in atmosphere and soil affect seed germination, vegetative growth, flowering, fruit set, maturity, quality, seed production, disease and pest occurrence and seed viability and storage. Basically moisture is responsible for cell division and cell enlargement, maintenance of turgor.

• When abundant water is available and other factors of environment being favourable there will be rapid cell division and enlargement and it favours vegetative phase of growth.
• When moderate water supply, rate of cell division and plant growth decreases whereas CHOs accumulation increases and favouring reproductive phase.
• Humidity plays important role in incidence of pest and diseases, beside seed production and storage. Mildew is associated with dry weather but humid condition favours diseases like downy mildew in onion. Humidity and temperature in combination are well known to influence growth and reproduction of many vegetable crops. A cool humid place is good for cauliflower, cabbage, beet root, turnip especially for seed production.
• In cucurbits moist condition increase onset of flowering. Low humidity promotes appearance of staminate flowers and high humidity favours pistillate flowers.
• Dry weather with low humidity is favourable for seed maturity and harvesting of most of vegetable crops. 

Authors

Saurabh Singh^{1, 2*}, Reeta Bhatia¹, S.S. Dey²

¹Division of Floriculture and Landscaping, ICAR-IARI, New Delhi, India-110012

²Division of Vegetable Science, ICAR-IARI, New Delhi, India-10012

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