Berry genetics

The bramble (blackberry) picking planned for Saturday was cancelled due to 'weather', but H. still popped up with spring onions and carrots from her garden to augment the bowl of crudities for the sleepover. Weather looks better for picking today or tomorrow, when she has a spare hour. The picking grounds are secret, because I need as much jam from H's kitchen as I can provide ingredients for and scrounge.

Colin Tudge's 'Engineer in the Garden' has brought to my attention some idiosyncratic aspects of berry reproduction and genetics.

The Rubus genus (Rosaceae family) are excellent examplars of 'introgression', a preference for breeding outside their selves, which tends to also produce polyploidy, a multiplication of chromosomes. Examples of these are the berries we've collected for jam this month- rasps, tayberries, loganberries and tummelberries. And the red- and blackcurrants, too- all Rubus. Rubus species come with a basic half-set of 7 chromosomes, which through polyploidy are represented in diploid, tetraploid, hexaploid and octoploid forms in indigenous Taiwanese species. Half of these species and subspecies are called Focke, presumably after some collector, which amuses me.

Rubus are prone to accept pollination from outside populations, and develop anatomical and physiological barriers to prevent 'in-breeding'. Swedes, cabbages and rape (all Brassica) are all the same 'species' as per Mayr's definition- a practically interbreeding population. Brassicas are preferential outbreeders, and thus must be raised apart from each other in order to breed and seed true.

Polyploidy (multiplication of chromosomes) is an evolutionary event that happens rarely in mammals, but is fairly common in plants and instrumental in farming. The domestication of some of the most historically influential starch foods (wheat, maize) were dependent on polyploidy. I do recommend Tudge on the subject.