Plant oil plays an important role in the agriculture industry due to its massive use in the food preparation and processing. Plant oil can be easily extracted and utilized so it is used for various industrial applications.
By Kiran Tariq, Warda Mustafa
Due to the rapidly increasing population, the demand of oil for food and feed is increasing in developing countries. Global vegetable oil requirement is expected to be doubled as compared to the current production by 2050. Various crops are used for oil extraction like soybean, rapeseed, groundnut and brassica. Among these crops, sunflower occupy the fourth position. It has a total oil production of 54,000 tonnes during the year of 2018-2019(USDA, 2019).
Nutritional profile of sunflower:
Sunflower is a crop of high potential. It can easily fulfill the oil requirements of the future. It has about 40-50% oil content and 23% protein along with vitamins A, B, E and K. Its oil is a light-colored premium oil and is considered healthy for heart patients. It has low cholesterol and high (90%) unsaturated fatty acids namely oleic (C18:1, 16-19%) and linoleic (C18:2, 68-72%) acids. The remaining 10% of its fatty acids are palmitic (C16:0, 6%), stearic (C18:0, 5%) and minor quantities of myristic (C14:0), myristoleic (C14:1), palmitoleic (C16:1), arachidic (C20:0) and behenic (C22:0) acids. Its oil is easy to refine, palatable and is a source of fat-soluble vitamins. Its oil is considered healthy and is used as a human food and in many products.
Factors affecting the oil quality:
Three factors determine the oil quality including Fatty acid composition, the distribution pattern of the fatty acids within the triacylglycerol molecule and the total content and composition of natural antioxidants especially tocopherols.
Standard sunflower oil:
Standard sunflower oil should have 11% saturated fatty acids, 20% oleic acid, 69% linoleic acid and 700 mg kg-1 tocopherol in which 95% are in the form of alpha tocopherol.
Biotechnological techniques for the improvement of sunflower:
There is a need to develop such varieties that can fulfill the requirements of standard oil. For this reason, various biotechnological tools and techniques are being used to get desired results along with breeding. Among these techniques tissue culture, genetic engineering, mutagenesis, genetic mapping and CRISPR/Cas are of great importance.
Losses in sunflower yield due to biotic stress:
Various biotic stresses (insect attack and fungal diseases) cause great damage to the sunflower affecting its yield and oil content. As wild species and more than 500 cultivated varieties suffer a great loss due to charcoal rot disease. Similarly, Alternaria blight causes 27-80% reduction in seed yield and 17-33% reduction in oil yield. Downy mildew causes 50% reduction in yield. In the UK, head rot causes 50% reduction in seed and oil yield. Various biotechnological techniques are being used to develop resistance against various biotic stress to overcome these losses.
Insect and fungal resistant transgenic sunflowers:
Cry1F gene provides resistance against sunflower looper and Virginian tiger moth. Cry1F gene (Bt gene) was isolated from Bacillus thuringiensis and was used to produce Cry1F-transgenic sunflowers. The transgenic plants showed resistance to larvae at the seedling and pre-flowering stages as compared to the control. Similarly, leptidopteran (moths) resistant transgenic Bt sunflower have been developed. Cry1Ac gene has the quality to produce Cry1Ac which is lethal to Lepidopteran larvae. So, the introduction of the Cry1Ac gene produced these resistant sunflowers. These transgenic plants produced more inflorescence with more mature seeds and more viable seeds per plant as compared to the non-transgenic plants. Introduction of wheat germin gf2.8 OXO gene to sunflower produced Oxo-transgenic sunflower. These sunflowers were resistant to a fungal disease head rot. Introduction of Lectin or proteinase inhibitor genes in sunflower provided resistance against insects.
Improvement of oil quality through Mutagenesis:
Physical or chemical mutagenesis was used to develop sunflower lines having increased levels of saturated fatty acid content of more than 25%. Two mutants, CAS-3 and CAS-5 have been developed. CAS-3 has a high amount of stearic acid and CAS-5 has a high amount of palmitic acid. CAS-12 mutants have a high amount of oleic and palmitic acid. Similarly, CAS-14 mutants have been developed which have 37% stearic acid. Ethylmethane sulfonate chemical mutagen was used to obtain M2 seeds from a single M1 plant which have 5-39% palmitic acid.
Sunflower oil with high palmitic acid:
A significant decrease in stearic acid content occurred in the seeds of transgenic plants having a coding sequence Δ9-stearoyl-(acyl carrier protein) desaturase. This sequence was incorporated from castor bean to sunflower. Some progenies showed an increase in palmitic acid content with a decrease in stearic acid content and some plants showed less than 10% fatty acid content. Introducing some other genes also caused a potential increase in oil quality.
Limitations in sunflower improvement:
There are some limitations of using these techniques. There is no efficient and reproducible protocol for transformation as stable transformation is yet time consuming in sunflower. Some approaches such as PEG-induced vector uptake are labor intensive. The limitation of regeneration systems has restricted the progress in its transformation. Lack of collaboration between plant breeders and biotechnologists is also a main reason for less improvement in sunflower oil content. But several studies are still conducted for the improvement of the yield and oil content of the sunflower.
There is a need to explore more efficient transformation protocols for developing transgenic sunflower having desired traits. Transgenic technology has a great role in sunflower breeding and is a promising technique to increase the yield, resistance against insect and fungal diseases and oil content. Discovery of unique genes from wild sunflower plants is necessary to broaden its genetic base. CRISPR/Cas technology would help us a lot in obtaining the desired results to meet the demand of a rapidly increasing population.