Pollen viability was assessed by gentle squeezing of pollen grains from harvested anthers into a drop of 4% (w/v) sucrose solution on a glass slide. One drop of a 0.005% (w/v) aqueous solution of FDA was added. The preparation was examined after 5 min by fluorescence microscopy. Fully rounded, strongly fluorescent pollen grains were considered viable, whereas lightly fluorescent, dimorphic grains were considered non-viable. A minimum of 500 pollen grains per plant and JO plants per treatment were assessed and the percentage viability determined