Impact of climate change on crop adaptation : current challenges and future perspectives

Climate change (i.e. changes in rainfall pattern and temperature) is a global issue affecting all regions and almost all sectors of life. This paper reviews the impact of climate change on crop adaptation and highlighted the recent advances used against these abiotic stresses. Reports have predicted agriculture is most vulnerable sector to climate change. The increasing climate variability has serious threats to crop adaptability and availability. Thus, climate change has threatened the food security. Therefore coping strategies to mitigate the threats to food security are matter of urgency. This can help to mitigate the impact of climate change on crop adaptation. The feasible adaptation practices that could be adapted include sowing time adjustments, stress tolerant varieties and short duration cultivar. The government and policymakers should support sustainable agriculture, farming practices and new technologies. The use of new genetic engineered methods can help to produce more transgenic plants against these environmental extremes.


Introduction
Fluctuations in temperature and rainfall pattern are evident in many regions around the globe.Scientific research provides evidence of increase in temperature from 2-4.5 ºC during 21 st century.During last three decades temperature has been increased at the surface of the earth than earlier decades since 1850.The period from 19 th century to 21 st century is probably the warmest era of the last fourteen centuries due to solar radiations (IPCC-2014).Uncertain and uneven distribution of rainfall not only creates a flooding devastation but also become cause of longer dry spells and eventually drought conditions [1].Climate change is a serious issue all over the world; it has not only affected plants but has impacts on almost all areas of life (animal, fishes and human being, etc.).Research showed that developed countries have more severe (8-11 %) threats due to climate change than developing countries [2].Natural disasters in North America, Central America, and the Caribbean revealed vulnerabilities of farming community to extreme weathers.

Stresses produced due to climate changes and its impacts on crops adaptation
The effects of abiotic stresses on crop adaptation and production have been observed due to fluctuation in climatic conditions [10].Plants abiotic stresses are produced due to abiotic factors.These factors include extreme levels of temperature (heat or cold stress), light, radiations, water (flooding and drought stress), chemicals (metals and pH), and gaseous contaminants (ozone, sulfur dioxide).Heat and drought are frequently occurring stresses under field conditions, have a substantial impact on the performance of plants and their offspring's and can permanently plague plants Although in some areas of the world located within the northern widths above 55 ºC climate changes will have positive effects on agricultural production but many plants especially native to warm habitat suffer from negative impacts of these changes.Extreme events takes place during the summer season are serious threats for crop adaptation and production for instance wheat plant reduces its period of planting to flowering and emergence to flowering due to rise in temperature, evaporation and transpiration.Rise in 1 ºC of temperature leads to a reduction of 5 days flowering.Period of grain filling is also effected due to rise in temperature eventually leads to biomass reduction [7].
For example, after wheat rice is the second major staple food crop and is economically important crop for Pakistan.Production of rice was increased 4.33 % with 3 ºC increase in temperature.However, 5.71 % and 15.26 %, reduction in crop production was observed due to increase in precipitation (during September-October) by 5% and 15% respectively [14]

Strategies to cope with this climate change
Changing climatic conditions have impact on food security from the local to global level.Climate change threatening the food security which is not a new issue.However, previously no attention was paid to mitigate this issue.But now climate change adaptation strategies are a matter of urgency.For adaptation of crop in changing climatic conditions following strategies are needed.

Cultural practices
A few studies conducted to understand the farmer's managing strategies to mitigate climate hazards for crop adaptation.The coping strategies of farmers in eastern Uttar Pradesh, India that mitigate or minimize stressful events (temperature and rainfall) include change in timing of sowing and harvesting, use of short duration cultivar, inter cropping, change in cropping pattern, use of ground water for irrigation and agroforestry.All these practices are useful to reduce the effects of climate change on crop adaptation [28].Some adaptation practices such as sowing time adjustments, adopted drought tolerant varieties, and shifted to new crops are very useful for crop adaptation in four provinces (98 % of country's land area) of Pakistan.8-13 % higher food security level and reduced exposure to weather risks are observed by adapting these practices at farm level [29].Application of nitrogen fertilizer is very important mitigation option and helps in adaptation of plants to global warming.It is an indirect energy source and is important to maintain soil fertility and to increase crop adaptability and yield.Thus, the role of fertilizer in feeding the world is incontrovertible

Conclusion
High temperature and rainfall irregularities are a key indicator of climate change.The Whole world is going to be effected by climatic changes.Arid areas are more vulnerable to increasing temperature and drought stress.Climate changes causing both positive and negative impacts on crops but negative impacts are more common than positive impacts.Disequilibrium taking place in agricultural productions cannot be eliminated easily.How many efforts and time it would take to eliminate this issue is not clear.Therefore emphasizing is given to manage agricultural productions in the drought and high temperature.Dissemination of new cultural techniques, adapted cropping patterns and conventional and nonconventional methods for improvement of crop varieties would be the suitable derivatives of fundamental change required in the agriculture sector.New crops with increased heat and drought tolerance will help to reduce potential risks.Awareness is necessary for a significant response, which ultimately depends on knowledge and experience.Agriculture extension services, sending farmers' climate information and farmers together in forming communication are for increasing crops adaptation to climate change.Policies for increasing farmer flexibility would also allow farmers to manage modern climatic conditions.However, we need to develop more stable genetic engineered crops in near future through novel CRISPR/Cas9 methods against environmental extremes.
[11].Plants production depends upon range of temperature around the plants of each species; because plants require optimum range of temperature for their production and adaptation.Impact on plant phenology due to change in temperature are equally significant [12].Heat stress reduces grain yield and grain-filling period, frost causes sterility and abortion of grains [13] and drought stress adversely affects the physiology, morphology and biology of plants [9].

Table 1 . Impacts of climate change on four major crops of Pakistan during 2014-15 Ali et al. [16]
.Ali et al. [16]studied the impacts of climate change on four major crops of Pakistan presented in (Table1).