Selection for aluminium tolerance in embryogenic lines of Citrus sinensis L. and C. aurantium L.

Abstract

The Citrus cultivars 'Amargo' and 'Pineapple' produce embryogenic cultures on two types of sugars, galactose and lactose. Two percent lactose is optimal for both cultivars; embryogenic callus is produced 8-10 weeks after inoculation. Whereas 2% galactose is optimal for 'Amargo', it is 3% for 'Pineapple'. Three types of embryos are recognized: whitish, greenish and heart shaped. In 8 to 10 week old cultures we do also observe a black spotted type of embryos. A high percentage of plant conversion for both cultivars is observed on a medium containing 30 mg/l of adenine and 2 mg/l of GA3 for 'Amargo'; for 'Pineapple' it is necessary to add BA. We tested two techniques for selection of Al-tolerant lines: one on stagnant liquid medium, and another on shaken liquid medium. The second technique gives a more serious selection pressure; there are almost no surviving calli. In 'Amargo' more calli survived than in 'Pineapple'. Selected calli had to be subcultured nine times to determine their stability. Four callus types of the two cultivars grew normally on selective media containing 0, 400, 1000 or 2000 mumol of aluminium.