Speed breeding and seed services

Speed breeding runs plants under an extended photoperiod — commonly around twenty-two hours of light — with controlled temperature, high plant density and harvest of immature seed, in order to turn over generations far faster than a field season allows. In spring wheat, barley, chickpea and pea it supports something like six generations a year against one or two outdoors.

Why the daylength works#

Two effects combine. The first is photoperiodic: in long-day species, extended light acts through the photoperiod pathway that promotes the florigen signal in the leaf, so flowering is induced earlier in the plant’s development. The second is simply arithmetic — a longer photoperiod raises the daily light integral, so the plant accumulates the assimilate needed to reach flowering in fewer days.

Harvesting seed before full maturity, and germinating it directly or after a brief drying, removes further weeks. Under single seed descent only one seed per plant is carried forward, so plants can be grown at high density in small containers and the whole population fits in a chamber.

The method is therefore not universal. Short-day species — rice, soybean and many sorghums — flower later under long days, and accelerating them means the opposite manipulation. Winter cereals must still receive their vernalisation, which cannot be compressed below the weeks of cold the requirement specifies. And plants grown this way are small and yield few, light seeds; they are a route to a genotype, not a source of agronomic data.

What it does not solve#

Genetic gain per year rises with selection intensity, with the accuracy of selection and with additive genetic variance, and falls with the length of the breeding cycle. Speed breeding acts on that last term and on nothing else. It does not make the ranking of candidates more accurate, it does not create genetic variance, and it does not tell a breeder which lines are worth advancing.

This matters because the traits that decide a variety — yield, standing ability, disease response, quality — cannot be evaluated in a growth chamber on a stunted plant. Speed breeding is consequently used where selection is not happening or is genotype-based: fixing lines by rapid inbreeding through the early filial generations, driving marker-assisted backcross programmes through their required cycles, bulking a population, or turning over generations ahead of genomic selection, which ranks on markers rather than on the plant in front of it. The field trials at the end are unchanged in number and duration, and they remain where the actual decisions are made.

Counter-season nurseries do the same thing geographically#

The older version of this service is a winter nursery: a breeding population is shipped to the opposite hemisphere and grown out of season, adding a generation a year. It is slower per cycle than a chamber but it produces field-grown plants with normal seed and, unlike a growth room, a real environment — at the cost of quarantine, phytosanitary certification and shipping delay. The two are complements rather than rivals, and both are logistics attached to a breeding programme rather than improvements to it.