Breeding asparagus varieties resistant to Phytophthora

Phytophthora rot affects asparagus production in Europe, North America, South America, Australia and New Zealand. Several species of Phytophthora attack asparagus, including P. megasperma, P. megasperma var. sojae, P. cryptogea, P. cactorum and P. richardiae. No cultivars of asparagus are resistant to Phytophthora rot. This disease causes establishment failures, reduced yields and post-harvest losses. In wet seasons plant losses as high as 80% have been recorded in young blocks. Yields can be increased between 40 and 70 % when the disease is controlled with fungicides. Our aim is to produce cultivars of asparagus that have durable resistance to the main Phytophthora spp. that cause disease on asparagus. A recurrent selection process has been used to develop durable resistance to a mixture of virulent Phytophthora isolates. Resistant plants identified in both a greenhouse screening procedure and a field disease nursery were randomly mated, and the progeny were evaluated for resistance to Phytophthora rot. After several cycles of selection, Phytophthora- resistant plants were crossed with plants with good general combining ability for yield and quality. 123 Phytophthora-tolerant experimental hybrids were evaluated in replicated field trials for yield and quality. Several Phytophthora-tolerant hybrids have been identified with yield and quality equal to or better than the standard cultivars "UC 157" and "JWC1". Meristem culture and PCR-based detection of Asparagus Virus 2 has been used to multiply virus-free parents of the best hybrids in preparation for establishing hybrid seed blocks.