Hops are dioecious, which means there are male and female plants. Only the mature, unfertilised cones of the female plants are harvested for use in beer, as they produce the yield of acids and essential oils that brewers value for their bittering and aromatic properties. Male plants are used when hop breeders wish to cross varieties and develop new cultivars. The resulting hop seedlings can include male, hermaphrodite and female plants.
HPA have been collaborating with a host of institutions to advance Diversity Arrays Technology (DArT) molecular marker technology that will allow hop breeders to identify desireable sex phenotypes earlier in the growth cycle than ever before. This technology will not reduce the time it takes to create, identify and develop a new cultivar. But it will allow us to remove non-target sex phenotypes from the nursery, rather than deploying plants in-field for a minimum of 6 months before being able to determine their sex phenotype. As a result, in-field trials will be more efficient in evaluating individual plants and crossing success.
The research was undertaken by scientists at the Slovenian Institute of Hop Research and Brewing, who selected male specific DNA sequences from an international hop industry DArT collaboration to evaluate their suitability for determining the sex phenotype among seedlings. Nine male specific DArT markers showed complete linkage with the male sex phenotype in three crossing families. Following optimisation, four were successfully converted from DArT to Polymerase Chain Reaction (PCR) markers. From 197 seedlings, there was variable correlation with sex phenotypic data for the individual PCR marker amplifications. By integrating the different markers into a single ‘multiplex’ reaction, they achieved a 100% positive correlation with sex phenotypic data.
To apply this technique to hop breeding program operations it needs to be accurate, fast and cost efficient since it would involve screening hundreds or even thousands of seedlings. To develop a fast and low-cost method, a crude sample DNA extraction technique followed by multiplex PCR was evaluated in 253 seedlings from 14 segregating populations, with no loss of accuracy. The study describes, for the first time, the routine application of molecular markers linked to male sex phenotypes in an intensive Slovenian hop breeding program. The methods described could be employed for screening of sex phenotypes at the seedling stage in other hop programs worldwide, thereby saving resources for desirable female plants.
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