Resistance to Asparagus virus 1 in the Wild Relative Asparagus amarus
Five asparagus cultivars, three breeding lines and the wild relative Asparagus amarus were tested for natural infection by Asparagus virus 1 (AV-1) in experimental fields at two locations over 3 and 4 years, respectively. In the first year after re-planting the annual crowns in the field, more than 90% of tested plants of cultivars were infected by AV-1. In the third and fourth year, 100% of tested plants of cultivars were AV-1 infected. In comparison, all plants of the wild relative A. amarus were completely free of AV-1, suggesting a high level of resistance. Additionally, 1-year-old glasshouse-cultivated plants of A. officinalis and A. amarus were placed in an AV-1 provocation cabin under field conditions. Seven months later, 100% of the A. officinalis plants showed a high virus concentration in ELISA, whereas no AV-1 was detectable in the A. amarus plants. This result was confirmed by highly sensitive AV-1-specific RT-PCR. To exclude vector resistance, the feeding behaviour of green peach aphid Myzus persicae was tested over 12 h using the electrical penetration graph method. Both asparagus genotypes were accepted by the aphids as potential hosts, but the feeding time was significantly longer on A. amarus. A genetic distance analysis of the various cultivars of Asparagus officinalis and selected wild relatives of the JKI collection was carried out, resulting in a clear discrimination of cultivars and wild relatives, especially A. amarus. The potential breeding value of the putative resistance carrier is discussed.