Effect Of Climate Change On Rice: Challenges And Mitigation Through Plant Breeding





Science, 25 Aug - 2017 ,

Effect Of Climate Change On Rice: Challenges And Mitigation Through Plant Breeding
Credit: pixabay.com

More than 50 per cent of the world population depend on rice for their survival. It feed 4 billion people i.e 56% of world population. Rice is the main staple food of India and the world.

More than 50 per cent of the world population depend on rice for their survival. It feed 4 billion people i.e 56% of world population. Rice is the main staple food of India and the world. The Goal of United Nations is to reduce poverty, hunger and malnutrition of the world. This was the main reason for the United Nation for the announcement of 2004 as the “International Year of Rice”. Rice is grown by 144 million farm families i.e. 25% of the world farmers.

Harvested from 166 million Hectare i.e 10% of the world crop land. Rice is the source of more than 500 calories per person per day for over 4 billion people (FAOSTAT 2016). Climate change is estimated to affect 20 million hectares of the world’s rice-growing area adversely, mainly in India and other Asian countries. It is forecasted by the International Food Policy Research Institute that by 2050, the rice prices will increase between 32% and 37% as a result of climate change due to the reduction in rice productivity by 14% in South Asia, 10% in East Asia and the Pacific and 15% in sub-Saharan Africa. Global population is predicted to rise to over 9 billion by 2050, which will lead to a 25% increase in the demand for rice.

Factors affecting climate change

Evidence of climate change that affect the productivity of rice mainly in Asian countries such as

(1) Increase in temperature,

(2) Irregular rainfall, more water demand,

(3) Attack by known and new pest and diseases,

(4) Plant Breeding Impact,

(5) Emission of methane from rice fields and

(6) Natural disasters such as heat waves, salinity, prolong drought period and floods brought about        by climate change.

Global Warming

Increase in the average temperature of the earth’s atmosphere and oceans can cause global warming. Increase in the temperature of earth surface due to trapping of heat from the sun by the green house gases such as carbon dioxide, water vapour, nitrous oxide and methane. Rice production is one of the major contributors of green house gas like Methane. These gases trap the heat coming from the sun, and not revert back into the space, which cause rise in the temperature of earth surface. The increase in temperature of earth surface results in climate change and altered the weather pattern. In 2001, the ‘UN-sponsored Intergovernmental Panel on Climate Change’ reported that worldwide temperatures have increased by more than 0.6°C in the past century and estimated that by 2100, average temperatures will increase by between 1.4°C and 5.8°C (Nguyen, 2005). And this uncertain climate change leads to outbreaks of harmful insect pest and diseases. That has greater harmful impact on agriculture, forestry and ecosystems .The increase in temperature also disturb the normal livelihood of people, animals and plants.

Rice Productivity and Global Warming

High carbon dioxide concentration in the atmosphere and rising temperature makes rice crop to increases temperatures would decrease the rice production globally (Nature climate change). As rice is C3 crop is less efficient in CO2 fixation than C4 crop. Both lowland and upland rice cultivation and rice production under slash-and-burn shifting cultivation results in the emission of methane and nitrous oxide gases and, thus, contributes to global warming. Green house gases like methane and Nitrous oxide, contributes to global warming with rise in temperature is emitted by both upland and lowland rice under slash-and-burn shifting cultivation. Moreover, many study revealed two major factors that greatly affect the productivity of rice, first, elevation in CO2 augment emission of methane from paddy crop, and second, increase in temperature caused a decline in rice production.  Rice cultivation is responsible for more than 10% of release methane from rice field. Since more than half of the worlds’ humanities are dependent on rice, the production systems for rice crop are, thus, vital for the reduction of hunger and poverty.

Temperature limit for growth of rice is 45°C and temperatures more than this will adversely affect its productivity. The temperature ranges for rice at different Phase after germination is 35–31°C whereas for ripening it is 20–29°C (Table 1). The temperature is one of the major factors that may affect and produce abnormal symptoms in rice (Table 2). Such uneven increase in temperature  during the crop growth period, notably during highly sensitive reproductive and early grain-filling phase of rice (Oryza sativa L.), leads to decreased biomass, grain production and quality.

Table: 1. Critical temperatures for the development of rice plant at different growth stages

 

Critical temperature

Growth stage

Low

High

Medium

Germination

16-19

45

18–40

Seedling Emergence

12

35

25-30

Rooting

16

35

25-28

Leaf Elongation

7-12

45

31

Tillering

9-16

33

25-31

Initiation of panicle primordia

15

-

-

Panicle Differentiation

15-20

30

-

Anthesis

22

35-36

30–33

Ripening

12-18

>30

20-29

Source: From Yoshida, S. 1978. Tropical Climate and Its Influence on Rice. IRRI Research Paper  

Series 20. Los Baños,  Philippines, IRRI.

Table: 2. Symptoms of heat stress in rice

Growth Stage

Symptoms

Vegetative

White leaf tip, chlorotic bands and blotches, white bands and specks, reduced tillering, reduced height

Reproductive anthesis

Reduce spikelet number, sterility

Ripening

Reduced grain-filling

Source: From Yoshida, S. 1981. Fundamentals of Rice Crop Science. Los Baños, Philippines,  IRRI. 269 pp.

Rice Productivity and Water Manage

Climate change is expected to affect water demand for rice via changes in rainfall regime, soil water balance, and evapotranspiration. Higher temperatures and increased variability of precipitation are predicted to increase water demand and could potentially require more irrigation in lowland rice-growing areas. The rice crop is affected both at the vegetative and reproductive stage due to a rise in temperature and, hence, productivity is also affected. The temperatures required at different crop growth phases are given in Table 1. High temperatures may result in various possible injuries to rice crops given in Table 2. High temperatures for 1–2 h at anthesis may result in sterility of the rice crop. The change of precipitation due to climate change has presented obvious regional trends. At the global scale, precipitation tended to increase in the high latitude regions of the Northern Hemisphere and in the tropical regions; while in the semi-tropical regions, the precipitation decreases over the past several decades.  

Drought effect on Rice

Drought is the most serious constraint and devastating for rice growing areas, affecting millions of land in Asian countries. In some states in India, drought is expected to be more frequent especially in north-eastern India, Jharkhand, Orissa and Chhattisgarh. Moreover drought caused yield loss of more than 35 %. Drought affected more than half of India’s crop land and led to a huge loses in crop production during 1987 and 2002-2003. Rice is particularly very much sensitive to moisture stress. Drought severely causes poor germination, reduced tillering, low spikelet fertility or creates sterility in flower, reduced plant height, degrade seed quality, create chalkiness and delays flowering. That finally affects the yield or economic loss. Respiration rate increases due to rise in temperature, that’s cause rice less productive. It is expected to fall crop yield significantly due to increase in temperature by 2050s.

Flooding and Salinity effect on Rice Productivity

Flooding is a serious hindrance to rice production, mostly in rainfed lowland areas of the globe. The flooding especially found in deltas and major river basins of tropics that has provided the sustenance for the rice production. Moreover, flooding also a cause of yield fluctuations because of unpredictable rainfall patterns and unsteady drainage of most of the rice fields. This results in overabundance water in these fields for varying depths and periods. The flooding is categorized into four types depending on the plant character and varietal types that are remodelled to the situations: (1) Flooding during germination (2) Flash flood (3) Stagnant flooding (4) Deeper stagnant flooding. Particular field, more than one of these situations can occur in the same season or in different seasons. Flooding can hit rice crops at any phase of growth. The chances of survival are extremely low when completely submerged during the crop’s vegetative stage. Submergence causes reduction in plant growth leading to the death of rice plant.

Major part of land suited to rice production in Asia and is currently not in use due to accumulation of high salt. Rise of temperatures due to Climate change prompt high evapo-transpiration rates leading to salt accumulation in rice fields. Rising sea levels brings salt water in land, which contributes to soil salinity. In Indian coastal areas, salinity affects more than hectares of land that can otherwise be used for rice cultivation. Effects of salt stress on rice are similar to those of drought leading to lower yields. It has been estimated through worldwide that more than 20% of total cultivated and 33% of irrigated agricultural lands are highly affected soil salinity. Moreover, the coverage of salinized areas are increasing at a steady rate of 10% annually for many reasons, including low precipitation, excessive evaporation, weathering of rocks, regular irrigation with salinized water, and improper cultural practices. It has been expected, due to the unpredictable climate, more than 50% of the well suited land for rice farming would be salinized by the year 2050.  Rice is highly sensitive to salt stress in its early growth stage, this poses a major problem to rice farmers because transplanted seedlings may all die and establishing a sufficient crop stand becomes very difficult. Salt stressed soils are known to suppress the growth of plants.  Rice crops grown on saline soils suffer on an account of high osmotic stress, nutritional deficiency and toxicities, poor soil physical properties and low crop productivity. Rice is especially susceptible to salinity during two periods of its growth phase. The first phase is the seedling stage and the second is few days before panicle excertion and it ends with flowering, and poor maturation.

Biotic stresses affecting Rice: Disease and Insect

One of the major challenges in rice production are outbreaks of new insect pest and diseases. A part of the biotic stresses insect pests leads to damage about 10-15% yield losses. The average yield losses in rice have been estimated to vary between 21-51 per cent. The key pest in paddy crop causing 25-30%, 10-70% and 15-60% yield losses, were yellow stem bore, plant hoppers and gall midge respectively. At National level, stem borers accounted for 30% of the losses while planthoppers (20%), gall midge (15%), leaf folder (10%) and other pests (25%). The incidence of insect pests and resultant yield losses vary depending upon the age of crop.  Study conducted by the International Rice Research Institute (IRRI), it was found that, on average, farmers lose 37% of their rice yield to pests and diseases, and that these losses can range between 24% and 41% depending on the production situation.

Strategies for mitigating effects of global warming on rice production

Climate change of course is not only something that’s happening in India. It is recognized as a global problem and requires a global solution to mitigate the driving greenhouse gas emissions with the increasing likelihood that the accumulating greenhouse gases will change the climate, a consensus has emerged in the international community over the need to stabilize GHG atmospheric concentrations and provide long-term solutions to climate change problem. There are several options available to reduce methane emissions from rice agriculture. The management practices such as mid-season drainage and using alternative fertilisers as well as switching to more heat-tolerant rice varieties and adjusting sowing dates are some of the measures suggested to reduce the methane emissions.

Impact of climate change can also be tackled by the new techniques of plant breeding and genetics. It may also be controlled by adopting proper strategies and policies of different countries. A proactive approach may save the rice production, as well as help in reducing emissions of greenhouse gas ‘methane’ from rice cultivation. Improvements in irrigation systems, water harvesting techniques, and more-efficient agricultural water management can reduce the risk of loss caused by drought.

The Challenges and mitigation through Plant Breeding

1. To develop and release new rice cultivars with better adaptation to high temperature and other climatic stresses. Drought-tolerant varieties which have been released in several countries and are now being planted by farmers. These include Sahbhagi Dhan in India, the Sahod Ulan in the Philippines, and the Sookha Dhan and tarharra-1 varieties in Nepal.

2. Submergence tolerance of rice crop plants has substantially been improved by introgressing the “Sub1” gene by MABB into popular rice cultivars in many rice-growing areas in Asian countries that favour resistance to submergence for up to 12-14 days. Flood-tolerant varieties that have been released and are now being planted include Swarna Sub1 in India, Samba Mahsuri in Bangladesh, and IR64-Sub1 in the Philippines. These are improved through Marker assisted backcross breeding method. Numerous drought tolerance varieties released in 2009  with yield advantage of 1-3.5 t/ha.

3. With the new techniques of plant breeding and genetics several cultivars of salinity and alkalinity tolerant cultivars released in India and Bangladesh. These include CR Dhan 405”Luna Sankhi”, CR Dhan 406”Luna Barial” and CSR43 ( Sodic Soil tolerant) released in India. Tolerant cultivars released in Bangladesh include BRRI dhan 47, BRRI dhan 53, BRRI dhan 54, BRRI dhan 8 and BRRI dhan 61.

4. Several Insect Pest and disease resistant variety have been developed to overcome the loss caused by the attack of biotic stresses.

5. Conversion of C3 rice to C4 rice by the application of genetic engineering, that may overcome the problem of loss caused by rise in CO2 level in the atmosphere. As C4 plant has high efficiency to extract CO2 from the atmosphere because C4 plant have PEP case enzyme to produce first stable product of 4 carbon compound i.e malic acid. Work is being going on to integrate the C4 photosynthesis system into rice at IRRI since 2012.


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