Bridging the gap: tools for interspecific and intergeneric hybridization in ornamentals

In nature, interspecific gene introgression is one of the driving forces for plant evolution. Also, with regard to ornamental breeding, interspecific and intergeneric hybridization techniques are considered as the most important tools to increase genetic variation and are at the basis of many modern assortments. Crosses between different cultivated species or between cultivated species and their wild relatives are therefore widely attempted to introgress new desirable traits in cultivars. Here we review the interspecific and intergeneric incompatibilities that may occur and how an integrated approach can overcome particular hurdles. Chromosome doubling, embryo rescue, in vitro pollination, unreduced gamete induction etc. can circumvent prezygotic or postzygotic bottlenecks. Combining cytological knowledge (chromosome numbers, ploidy levels, genome sizes) and phylogenetic data can predict crossing efficiency or assist to make thoughtful decisions for cross combinations. Alternatively, protoplast fusion can be used as asexual crossing method. Genome editing systems might help in future to break through existing crossing barriers and to speed up breeding strategies which aim to introgress traits from wild germplasm in domesticated plants