Towards Sclerotinia resistance: somatic hybridization between wild and cultivated sunflower

Abstract

The use of interesting characteristics from wild Helianthus species in sunflower breeding is limited by poor crossability or sterility of interspecific hybrids. Somatic hybridization by protoplast fusion is an efficient method for overcoming crossing barriers and increasing of the genetic variability of the plants. Protoplasts obtained from leaf mesophyll of Sclerotinia sclerotiorum-resistant accessions of Helianthus maximiliani and Helianthus mollis and etiolated hypocotyls of inbred lines PH-BC1-91A and Ha-74A were purified by floating on Ficoll. Prior to electrofusion wild species protoplasts were irradiated with UV light with the aim of inactivating a part of their genome. Fusion products were embedded in agarose droplets and subjected to different regeneration protocols. The best results were obtained with the protocol of Trabace et al. (1995). Developed microcalluses were released from the agarose and transferred to solid media. Shoot regeneration was achieved by culture of calluses on regeneration medium containing 2.2 mgL-1 BAP and 0.01 mgL-1 NAA (Krasnyanski et al., 1992). During the culture, calluses were treated with a high concentration of 2,4-D for a limited period. Studies at the molecular and morphological level showed that obtained plants were somatic hybrids.