Abiotic stresses are one of the major constraints to crop production and food security worldwide. The situation has aggravated due to the drastic and rapid changes in global climate. Heat and drought stress are undoubtedly the two most important stresses having huge impact on growth and productivity of the crops. It is very important to understand the physiological, biochemical and ecological interventions related to these stresses for better management. A wide range of plant responses to these stresses could be generalized into morphological, physiological and biochemical responses. Interestingly, this review provides a detailed account of plant responses to heat and drought stresses with special focus on highlighting the commonalities and differences. Crop growth and yields are negatively affected by sub-optimal water supply and abnormal temperatures due to physical damages, physiological disruptions and biochemical changes. Both these stresses have multi-lateral impacts and therefore, complex in mechanistic action. A better understanding of plant responses to these stresses has pragmatic implication for remedies and management. A comprehensive account of conventional as well as modern approaches to deal with heat and drought stresses have also been presented here. A side-by-side critical discussion on salient responses and management strategies for these two important abiotic stresses provides a unique insight into the phenomena. A holistic approach taking into account the different management options to deal with heat and drought stress simultaneously could be a win-win approach in future.

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Crop Production under Drought and Heat Stress: Plant Responses and Management Options

Agriculture and climate change are internally correlated with each other in various aspects, as climate change is the main cause of biotic and abiotic stresses, which have adverse effects on the agriculture of a region. The land and its agriculture are being affected by climate changes in different ways, e.g., variations in annual rainfall, average temperature, heat waves, modifications in weeds, pests or microbes, global change of atmospheric CO2 or ozone level, and fluctuations in sea level. The threat of varying global climate has greatly driven the attention of scientists, as these variations are imparting negative impact on global crop production and compromising food security worldwide. According to some predicted reports, agriculture is considered the most endangered activity adversely affected by climate changes. To date, food security and ecosystem resilience are the most concerning subjects worldwide. Climate-smart agriculture is the only way to lower the negative impact of climate variations on crop adaptation, before it might affect global crop production drastically. In this review paper, we summarize the causes of climate change, stresses produced due to climate change, impacts on crops, modern breeding technologies, and biotechnological strategies to cope with climate change, in order to develop climate resilient crops. Revolutions in genetic engineering techniques can also aid in overcoming food security issues against extreme environmental conditions, by producing transgenic plants.

Impact of Climate Change on Crops Adaptation and Strategies to Tackle Its Outcome: A Review.

Inducing drought tolerance in plants: Recent advances

The growing human population and a changing environment have raised significant concern for global food security, with the current improvement rate of several important crops inadequate to meet future demand1. This slow improvement rate is attributed partly to the long generation times of crop plants. Here, we present a method called ‘speed breeding’, which greatly shortens generation time and accelerates breeding and research programmes. Speed breeding can be used to achieve up to 6 generations per year for spring wheat (Triticum aestivum), durum wheat (T. durum), barley (Hordeum vulgare), chickpea (Cicer arietinum) and pea (Pisum sativum), and 4 generations for canola (Brassica napus), instead of 2–3 under normal glasshouse conditions. We demonstrate that speed breeding in fully enclosed, controlled-environment growth chambers can accelerate plant development for research purposes, including phenotyping of adult plant traits, mutant studies and transformation. The use of supplemental lighting in a glasshouse environment allows rapid generation cycling through single seed descent (SSD) and potential for adaptation to larger-scale crop improvement programs. Cost saving through light-emitting diode (LED) supplemental lighting is also outlined. We envisage great potential for integrating speed breeding with other modern crop breeding technologies, including high-throughput genotyping, genome editing and genomic selection, accelerating the rate of crop improvement.

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Speed breeding is a powerful tool to accelerate crop research and breeding

Plant tissue culture has become one of the fundamental tools of plant science research. It is extensively employed in the production, conservation and improvement of plant resources. The presence of somaclonal variation in populations derived from tissue culture is affecting the use of tissue culture negatively and has remained a major problem. Conversely, it is a source of new desirable clones/variants with better agronomic traits. In this review, we summarize the possible causes, detection methods and desirability of variants. Somaclonal variation is one of the most researched and reviewed topics. Hence, we restricted ourselves to outlining various examples which may be used as important references for researchers who intend to identify and/or characterize somaclonal variants while using tissue culture for research and production. Emphasis is placed on the negative effects of somaclonal variation. However, this review also includes examples of some useful variants generated as a result of somaclonal variation.

Somaclonal variation in plants: causes and detection methods

Preface / Introduction / Reproduction in Crop Plants / Plant Genetic Resources-Origin, Conservation and Utilization / Genetic Basis and Application of Selection in Self-pollinated Crops / Mendelian Consequences of Planned Hybridization in Self-pollinated Crops / Quantitative Inheritance / The Analysis of Genotype-Environment Interactions / Application of Biometrical Genetics in Plant Breeding / Pedigree Method / Bulk Population Breeding Method / The Single Seed Descent Method / Backcross Method / Fertility Regulating Mechanisms / Genetic Basis of Hetrosis / Breeding for Hetrosis / Genetic Structure of Cross-pollinated Crops / Population Improvement in Cross Pollinated Crops / Population Improvement Methods / Synthetic and Composite Varieties / Breeding for Asexually Propagated Crops / Breeding for Resistance to Diseases and Insect Pests / Mutation Breeding / Polyploidy in Plant Breeding / Tissue Culture in Crop Improvement / Molecular Approaches to Crop Improvement / Genetic Transformation and Production of Transgenic Plants / Biometry in Relation to Molecular Biology in Plant Breeding/ Field Plot Techniques in Plant Breeding / Plant Breeder's Rights, Release and Multiplication of Varieties/ Glossary / Index

Principles and Procedures of Plant Breeding: Biotechnological and Conventional Approaches

Abiotic stresses present a major challenge in our quest for sustainable food production as these may reduce the potential yields by 70% in crop plants. Of all abiotic stresses, drought is regarded as the most damaging. The complex nature of drought tolerance limits its management through conventional breeding methods. Innovative biotechnological approaches have enhanced our understanding of the processes underlying plant responses to drought at the molecular and whole plant levels. Hundreds of drought stress-induced genes have been identified and some of these have been cloned. Plant genetic engineering and molecular-marker approaches allow development of drought-tolerant germplasm. Transgenic plants carrying genes for abiotic stress tolerance are being developed for water-stress management. Structural genes (key enzymes for osmolyte biosynthesis, such as proline, glycinebetaine, mannitol and trehalose, redox proteins and detoxifying enzymes, stress-induced LEA proteins) and regulatory genes, including de...

Biotechnology and drought tolerance

In the present study, in vitro selection technique using pathogen culture filtrate of Colletotrichum falcatum Went was employed with the aim to identify associations (if any), between selection at the cellular and plant level for red rot resistance in sugarcane (Saccharum sp.). Five to eight months old sugarcane calli of genotypes CoJ 88 and CoJ 64 were screened in vitro against pathogen culture filtrate for two selection cycles. Effect of pathogen culture filtrate on callus survival and/or proliferation was observed to be directly related to its concentration in the selection media. Calli survived and exhibited further proliferation at 5, 10 and 15% v/v pathogen culture filtrate concentrations whereas, at higher concentrations (20 and 25% v/v) proliferation was completely inhibited. Shoot regeneration percent was higher in calli selected on 5% pathogen culture filtrate concentration than those selected on 10 and 15% concentrations. In vivo screening of field transferred somaclones against two pathtypes (Cf 03 and Cf 08) showed considerable variation for red rot resistance. Somaclones regenerated from resistant and/or tolerant calli exhibited better resistance than the parental genotypes. The results indicated that in vitro selection for red rot resistance was effective and expressed when somaclones were screened in the field. This indicated a positive association between in vitro and in vivo methods of selection for disease resistance in sugarcane.

In vitro selection at cellular level for red rot resistance in sugarcane (Saccharum sp.)

Heat tolerant mutants were obtained in two commercial potato cultivars, `Kufri Jyoti' and `Kufri Chandramukhi' through in vitro mutagenesis of in vitro propagated plantlets. Gamma-irradiated (20 and 40 Gy) shoots were micropropagated for three cycles (M1V3). A large number of the micropropagated shoots produced microtubers at 28 °C. Microtubers induced at high temperature had distorted shape but showed normal germination in field. Under stress conditions of high temperature, the frequency of chlorophyll variants increased in the gamma irradiation-derived material, however, nearly 40% of the plants had normal leaf tissue, whereas control plants showed completely damaged leaves.

Induction of mutations for heat tolerance in potato by using in vitro culture and radiation.

While drought resistance is become of increasing importance in rice (Oryza sativa L.), selection under actual field conditions is tedious due to low heritability and time required. Selection in tissue culture is thought to be one way to improve selection efficiency, but this requires standardized protocols. Rice cultivars PAU 201 and PR 116 showed significant callus induction, but the capacity for callus induction and regeneration decreased under polyethylene glycol (PEG) (6000) stress in both cultivars. Calli were induced on semisolid Murahige and Skoog (MS) medium supplemented with 2.5 mg l-1 2, 4-dichlorophenoxy acetic acid (2,4-D) + 0.5 mg l-1 kinetin (kin) + 560 mg l-1 proline + 30 g l-1 sucrose + 8 g l agar-1. Embryogenic calli showed shoot regeneration on MS medium supplemented with 2.0 mg l-1 benzyl aminopurine (BAP) + 0.5 mg l-1 kinetin + 0.5 mg l-1 napthalene acetic acid (NAA) + 30 g l-1 sucrose + 8 g l-1 agar. Increased levels of PEG (6000) (0, 0.5, 1.0, 1.5, 2.0 %) were used to create water stress. There was reduction in callus induction ability and plant regeneration efficiency with increasing levels of PEG (6000) stress. These results indicated that PEG (6000) can be used as water stress creating agent under in vitro conditions and rice variety PR 116 was relatively tolerant to drought stress as compared to PAU 201. This study will serve as a base line for in vitro screening of drought tolerant transgenic rice.

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Satbir Singh Gosal

Papers

Principles and Procedures of Plant Breeding: Biotechnological and Conventional Approaches

Biotechnology and drought tolerance

In vitro selection at cellular level for red rot resistance in sugarcane (Saccharum sp.)

Induction of mutations for heat tolerance in potato by using in vitro culture and radiation.

In vitro screening of rice (oryza sativa l.) callus for drought tolerance