Genetic Engineering of Sunflower (Helianthus annuus L.) for Important Agronomic Traits

Abstract

Sunflower assumes importance both as an oilseed crop and for confectionery purpose, and the breeding programmes for both these types run in parallel. Genetic improvement programmes are mostly based on traditional breeding and introgressive breeding approaches. Sunflower is one of the crops that has been greatly benefitted through interspecific hybridization for several traits such as cytoplasmic male sterility, seed quality traits, and resistance to biotic and abiotic stresses. However, continuous cultivation of the crop, changing climatic conditions, emerging new diseases, evolution of new races of the pathogens, and changing pest scenario demand intensive efforts at genetic upgradation of the crop. Despite the existence of ~50 Helianthus species of varying plant habits (annual, perennial) and ploidy levels (diploid, tetraploid, hexaploid), introgression for some of the agronomically desirable traits into cultivar germplasm is hampered by either lack of resistance in the wild species or the ploidy differences and the associated chromosomal imbalances leading to sterility. Hence, intervention of biotechnological tools is required for introgression of beneficial traits into cultivated sunflower. Application of genetic engineering tools in sunflower is limited by several problems associated with tissue culture-based shoot regeneration. Nevertheless, attempts have been made to establish the protocols for genetic transformation predominantly through Agrobacterium-mediated methods using explants with pre-existing meristems as target tissues. Most of the published reports (~75%) are on optimization of variables for obtaining a high frequency of transient gene expression while the studies on introgression of desirable attributes are mainly focused at enhancing resistance to biotic and abiotic stresses. Field testing of the transgenic events and intellectual property protection of the protocols is essentially from the private firms. This chapter provides an overview of the challenges associated with the development of tissue culture and transformation protocols and the present status of transgenic development in sunflower.