Boron Concentration Affects In Vitro Pollen Germination and Tube Growth in Kiwifruit (Actinidia deliciosa) Cultivar 'Matua'

The effect of varying boron (B) concentrations on in vitro pollen germination and tube growth of 'Matua' kiwifruit was evaluated. Five concentrations of boric acid (H3BO3): 0, 25, 50, 100 and 500 mg L-1, were added to the germination media, prepared with 5% sucrose and 2% agar. 'Matua' pollen was placed on the agar media and incubated in Petri dishes at 20 degrees C for 48 h, with germination evaluated after 24 h. Pollen incubated at concentrations of 25 and 50 mg L-1 boric acid showed 67.5 and 73.5% of pollen germination, respectively. Significant reductions in pollen germination, 24.0 and 22.7%, were observed at B concentrations of 100 and 500 mg L-1, respectively. In the media prepared without B, only 16.7% germination was observed. After 48 h of incubation, in media prepared with 25 and 50 mg L-1 of boric acid, pollen tube lengths reached 53.2 and 66.7 mu m, respectively, being significantly longer than those incubated in 100 and 500 mg L-1 B media (27.2 and 22.4 mu m, respectively), and the 0 mg L-1 B media, where pollen tube length reached only 18.3 mu m. It can be concluded that boric acid concentrations 100 mg L-1 or higher in the growing media reduce 'Matua' pollen germination and tube growth.