Breeding paired crosses

The eggs/embryos can then be washed out of the breeding boxes, rinsed, and transferred to Petri dish(es) with embryo medium. In a healthy, productive colony, most clutches from pair crosses will comprise around 100-300 eggs, with the majority having been fertilized. 

FI hybrids, the first-generation cross between two inbred strains are isogenic but not homozygous and as such they do not breed true, i.e. FI s between any pair of inbred strains are isogenic, however, if interbred lead to highly variable phenotypes. 

There are three general approaches used in Jerusalem artichoke breeding (1) controlled crosses conducted under greenhouse conditions, (2) natural open-pollinated crosses using polycross nurseries, and (3) a variation of the latter where isolated pairs are allowed to cross in the field. Each method has its advantages and disadvantages. 

On the other hand, colchicine s ability to induce polyploidy can solve many important problems of plant breeding. Colchicine renders infertile hybrids fertile. For example, the maximum Fuchsia species are diploid or tetraploid. The cross between diploid and tetraploid results often in a triploid, which is mostly sterile because the process of meiosis requires the pairing of similar chromosomes and due to lack of mechanism to allow the alignment of three similar chromosomes. However, colchicine treatment produces fertile hexaploid plants. Breeding of triticale from wheat and rye shows similar problem wheat is typically tetraploid and rye is diploid, with the triploid hybrid being infertile. Here also, treatment with colchicine results in fertile hexaploid triticale. 

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