Practical aspects of a breeding program of asparagus based on in vitro anther culture

The in vitro anther culture technique has been applied in Italy during the last twenty-five years and has allowed to release commercially F1 all-male hybrids. Our experience proves that the strategy adopted during the in vitro work and the evaluation of doubled haploid clones (DH) and F1 all-male hybrids may play an important role. The best response to androgenesis was obtained from anthers of male plants grown in the field, flowering under long day light period and warm temperature (average 15/25degrees C night/day). The anthers containing the highest percentage of uninucleate microspores were the most responding, but all those wounded during excision proliferated somatic callus. Androgenetic embryoids were visible on the anthers after 30 to 40 days (not later) of culture as white spheres of about 1 mm diameter. Cytological observation evidenced that diploid and tetraploid level of androgenetic clones derived either from chromosome endoreduplication at the first mitosis in the microspore or from unreduced microspore. From 246,000 anthers cultured in vitro 2860 androgenetic clones were regenerated out of which 1658 were DH. In a soil naturally infected by Fusarium spp. 62 female and 55 male doubled haploid clones were selected. When these clones were recloned in vitro and replanted in the same soil, they showed the same phenotipic behaviour and percentage of dead plants. Out of 280 F-1 all-male two-way and three way hybrid tested in multilocation field trials, seven have been released commercially in 1993, but only two of these (Eros and Marte) at present are widely grown in Northern Italy. More recently three new hybrids (Italo, Ercole, Zeno) have been selected for improved yield earliness, resistance to rust and spear quality.