Screening for Halosulfuron Tolerance and Identifying Ethylene Response Genes in Sweetpotato[Ipomoea Batatas (Lam) L.]

Weeds cause significant yield loss in sweetpotato. Post-emergent herbicides cause damage to sweetpotato plant, which necessitates development of herbicide tolerant sweetpotato. An optimal tissue culture system is a prerequisite for in vitro screening of herbicide tolerant sweetpotato. Three Louisiana cultivars, ‘Beauregard’, ‘Orleans’, and ‘LA 07-146’, were tested to develop an efficient callus induction and plant regeneration system. 2, 4-D @ 0.23 µM was ideal for ‘Beauregard’ and ‘Orleans’ callus induction and 0.45 µM 2, 4-D for callus induction in ‘LA 07-146’. Phytohormone-free media was found suitable for regeneration. Plants were regenerated from callus tissues that survived in vitro with 2 µM, 6 µM, 8 µM and 10 µM of halosulfuron methyl (active ingredient of herbicide Sandea®). The culture conditions identified through this study have applicability to wide use in somaclonal selection in sweetpotato. Adventitious root emergence from original cuttings of sweetpotato marks the initial phase of storage root development. A better understanding of the mechanism of adventitious rooting in sweetpotato will be of immense importance to strategize breeding efforts to maximizing its marketable yield. In the present study, role of ethylene in adventitious rooting was investigated by application of 3.8 ppm of 1-mcp to two sweetpotato cultivars, ‘Beauregard’ and ‘Evangeline’, known to have contrasting adventitious rooting in response to 1-mcp. Sequencing of suppression subtractive hybridization libraries from both cultivars indicated that genes involved in the cell wall and sugar biosynthesis pathway were differentially expressed by exogenous application of 1-mcp. Two component response regulator, fructose bisphosphate aldolase and arabinogalactan, were present in both cultivars. However, their expression pattern varied at different time points between ‘Beauregard’ and ‘Evangeline’. Genes coding for ascorbate oxidase and oxysterol-binding protein were upregulated in ‘Beauregard’ whereas two-component response regulator was upregulated in both ‘Beauregard’ and ‘Evangeline’. Except for a slight upregulation of fructose-bisphosphate aldolase in ‘Beauregard’ and arabinogalactan in ‘Evangeline’ at 12 h time point, both genes showed downregulation in both cultivars at all other time points. Most of the differentially expressed genes were shown to be involved in ethylene signaling. This study confirmed previous results that ethylene is involved in adventitious rooting in sweetpotato