Heat stress is defined as an increase in environmental temperature even a threshold levels for a time which is sufficient to damage a crop. When plants grow and develop in extreme heat it can result of heat stress.
The main resource of heat stress is global warming which is also due to adaptations of growers produce their own feedbacks on climatic structure. There are many factors which effect directly and indirectly and lead to heat stress e.g. high temperature (increasing rate of global warming), changing in environment, water, low availability of nutrients, diseases, soil structure and air of zone.
Climate and plant
The most important factor which influence the crop suitability is a climate of particular area which increase or decrease the yield potential of crop and determined more than 50% of variation in crops because it have both types of effects on plants beneficial and become adverse when increase or decrease from limiting value. There are three values of temperature which are maximum temperature, minimum temperature and optimum temperature from which a crop best grow on only optimum value and both the other values decrease or stop the growth of crop. There are many types of abiotic stress which badly disturb the growth and development of agricultural crops which reduce economical yield and total biomass of the plant, in which heat is most important, major stress and basic problem of now a days, due to continue increasing rate of global warming over past 10,000 years which is openly effected to overall food security. In 2010, more than 20% of agricultural crops were effected by rise in temperature in Russia, which increase the rate of wheat up to 50% in international market.
Heat stress damage
Heat stress damage indirectly plants e.g. water deficits in crops due to highest evaporative demands and damage directly also which is more destroyable. Heat stress affects the plants when high temperature occur with critical crop growth stages and plants have not resistant against such a conditions in their structure, numerous fluctuations in agricultural crops which change their metabolic system cause many problems in crops e.g. seed injury, heat illness, necrosis, shoot and root growth inhibition, crop injuries, reproductive development decrease or stop, plants cannot produce flowers or if they produce flowers then they may not set fruits and seeds, rise in propagative development cause reduction in yield and also cause death of plants. According to calculated modeling an increase in temperature 3-4 ºC cause decrease in crop yield 15-35% in Africa and Asia and 25-35% in Middle East. It is setting up in 1993 by Farm and Ranch Safety and Health Association (FARSHA). Crop species and their variety have different sensitivity to heat. Winter season crops are more sensitive to heat than summer season crops.
High temperature can damage agricultural crops in different ways
- Excessive daytime heat or can be damaged by excessive night heat.
- Damaged by high air heat or also damaged by high soil heat.
- Reproductive stage damage or vegetative stage damage.
Cool Season Crops | Warm Season Crops | ||
Hordeum vulgare (barley), Oleracea (brassica), Brassica napus (canola), Vicia faba (fava bean), Linum usitatissimum (flax), Phaseolus vulgaris (bean), Solanum tuberosum (potato), Lensculinarus (lentil), Lactuca sativa (lettuce), Lupinus (lupine), Avena sativa (oat), Pisum sativum (pea), Raphanus raphanistrum (radish), Secale cereal (rye), Spinacia oleracea (spinach), Triticosecale (triticale), Brassica rapa (turnip), Vicia (vetch) and Triticum aestivum (wheat). |
| Gossypium (cotton), Vigna unguiculata (cowpea), Cucurbitaceae (cucurbits), Eleusine coracana (finger millet), Amaranthus hypochondriacus (grain amaranth), Phaseolus lunatus (lima bean), Zea mays (maize), Vigna radiate (mung bean), Pennisetum glaucum (pearl millet), Piper nigrum (pepper), Cajanus cajan (pigeon pea), Oryza sativa (rice), Sesamum indicum (sesame), Sorghum bicolor (sorghum), Glycine max (soybean), Helianthus annus (sunflower), Ipomoea batatas (sweet potato), Nicotiana (tobacco) and Solanum lycopersicum (tomato). | |
Table1. Cool and warm season annual crops which have different effects by temperature
Agricultural crops and their temperature requirement
All the agricultural crops require an optimum temperature for their best growth and development. If the temperature rise from this level cause many problems in crops. It also depend on variety and cultivar.
Table#2. Temperature requirement of various crops and its impacts.
Crop Name | Maximum Temperature (ºC) | Minimum Temperature (ºC) | Optimum Temperature (ºC) | Temperature impacts |
Sugarcane | 50 | 20 | 26-32 | Growth effected, yield decrease and effect on ripening. |
Cotton | 35 | 11 | 32 | Germination does not take place, imbalance between vegetative and reproductive growth, small boll. |
Tea | 32 | 12 | 20-30 | Growth stop, quality decrease and effect on flavor. |
Tobacco | 30 | 12 | 20-26 | Germination does not take place, stop growth and development |
Rice | 38 | 12 | 30-32 | Effect on growth, plant height increase and yield decrease. |
Maize | 47 | 10 | 18-27 | Poor emergence, silking delay and effect on female component. |
Potato | 30 | 10 | 8-26 | Lose ability to sprout, growth inhibited. |
Soybean | 28 | 10 | 21 | Reduce flowering, holes in foliage and effect on plant height. |
Pea | 28 | 7 | 12-21 | Abortion of buds and flowers, wilting, death, |
Wheat | 30-32 | 3-4 | 25 | Nutrients accumulation, booting stage late. |
Tomato | 35 | 10 | 18-26 | Poor fruit set, reduced fruit and misshapen. |
Pepper | 32 | 14 | 16 | Pollen sterility occurs, flowers may drop and poor fruit set. |
Solutions for crops to mitigate the temperature impacts
Global warming control
Global warming is a gigantic problem and carbon intensity, emission of greenhouse gasses and human activities are sources of global warming and numerous agricultural product leftovers are also a resource of global warming. So, through limited waste or management practices can control global warming which is continue increasing and in future can prove a giant threat for agricultural crops and worldwide nutrition security. Now, chief step which is adopted to decrease the activities which cause the source of global warming and would practice alternative source which have decent influence on the environment.
Growing chamber
Growing chamber or room are the rooms where crops are grown under controlled temperature. Application of these chamber or rooms, reducing the effect of heat on plants which are decidedly sensitive to heat.
Crop and field management
Selection of various type of crop, a number of verities, date of sowing and other agronomic management practices in field in response to an unvarying environment also influence by temperature and these have an imperative role in controlling heat stress in some areas. These tools does not decrease the temperature, but decrease the impact of seasonal temperature in some regions on agricultural crops. Heat stress cause drought in plants due to increase rate of evapotranspiration, so by use of water we can also decrease the impact of temperature on crops.
Heat resisting agents
Plants have also power to make their own plant protection by producing agents. Plants produce chemicals and also micro-organisms that improve the plant tolerance against heat stress. We should need to improve these chemicals by genetic engineering in those plants which are highly sensitive and grow in those areas which receive high temperature.
- A combination of humic acid and seaweed is beneficial for plants in heat stress. A plant hormone cytokinins is present in seaweed which motivate cell division so it increase the root and shoot growth in plants when apply with Humic acid.
- In the same way humic acid and fulvic acid can also be use, have many beneficial trace elements.
- Glycinebetaine is an organic solute which accumulate in plants by genetic engineering through a gene BADH (betaine aldehyde dehydrogenase) copied from spinach play imperative role in many plants during the growth of young seedlings against low temperature stress. It increases the heat tolerance in plants.
About Authors:
Arshad Ali1*, Sadaf Khan2 and Rashida Parveen1.
1Postgraduate Lab, Department of Agronomy, University of Agriculture, Faisalabad
2Taxonomy lab, Department of Botany, University of Agriculture, Faisalabad