Development and diversity analysis of an hexaploid pre-breeding asparagus population with introgressions from wild relative species

The development of new asparagus (Asparagus officinalis L.) cultivars has been hindered by the lack of genetic diversity in the crop. The current study aims at generating novel plant material to widen the genetic base of the crop by using CWR (crop wild relatives). We have developed a hexaploid population of about 1000 plants with introgressions of four polyploid CWR species (A. maritimus, A. pseudoscaber, A. brachyphyllus and A. macrorrhizus). The population is the second generation from a first backcrossing using the landrace 'Morado de Huetor' as recurrent parent and was obtained in open pollination. The diversity of the population was analyzed by six EST-SSR (Expressed Sequence Tag-Simple Sequence Repeat) markers. A random sampling of 60 plants was used to estimate the genetic variability. The results were compared with data previously obtained from the parental collection, the landrace 'Morado de Huetor' and diploid current asparagus cultivars. The average PICm (polymorphic information content) value of the new population and 'Morado de Huetor' were similar (>0.8) and higher than the value observed in the diploid cultivars (0.61). At least 22.2% of the alleles detected in the hexaploid population were specific from the CWR species used in this study. Principal coordinate analyses (PCoA) revealed a clear genetic diversity differentiation between populations. The population of 1000 plants was evaluated for agronomic traits (earliness, stalk number, branching height and stalk thickness) for two years and we selected 80 plants to develop a breeding base population. Variation was significant for all traits (P<0.001). These 80 plants were also analyzed with the six EST-SSR markers and they conserve the variability present in the starting population. The results show an increase in the genetic variability and offer a new opportunity for asparagus improvement.