An in vitro screening system to assess aluminum toxicity in sugarcane (Saccharum spp.) cultivars

Mutagenic breeding is an approach being developed especially for those characteristics that are not inherited through conventional genetic hybridization. Soil acidity and aluminum (Al3+) toxicity limit sugarcane production, particularly in leached soils in the coastal cultivation regions in South Africa. An in vitro screening procedure was developed based on plantlet re-rooting in Al3+-containing medium to select putative Al3+ tolerant variants produced by induced mutagenesis. A preliminary test did not show any difference among three cultivars in their ability to re-root in the presence of Al3+. Subsequent work focused on Saccharum sp. ‘NCo376’ and two Al3+ concentrations (15 and 45 mM), representing LC50 and LC90 re-rooting inhibition. In an attempt to increase the stringency of the selection conditions, the possible effects of inorganic nitrogen (N) forms in the culture media on Al3+ toxicity were investigated. The form of N affected root regrowth and citrate exudation. Sugarcane plantlets showed an uptake preference for ammonium (NH4+) over nitrate (NO3−), and 10 and 20 mM NH4+ appeared to alleviate Al3+ toxicity compared with NO3−. Although in agricultural soils NO3− is the dominant form of N, it can readily leach into the sub-soil, in which deep roots encounter Al3+ toxicity in the presence of NO3−. Therefore, the ability to withstand the toxic effects of Al3+ in the presence of NO3− could be beneficial for N use efficiency and access to water at depths during drought.