How to 'Speed Breeding' ?
Speed breeding techniques accelerate plant growth, flowering and seed maturation, reducing generation time by 5 compared to field conditions and by 2.5 compared to regular greenhouse. More and more breeding and plant research departments hasten their studies with this procedure. It consists in setting up a controlled environment that meets all the plant needs, and influence its growth at every stage of its development.
Thanks to the 2018 publication by Sreya Ghosh and al., we know today how to perform speed breeding at low cost. Their instructions describe precisely setup protocols on two scales: On the one hand, a growth cabinet of 8 plants, on the other hand a whole glasshouse.
"The procedures are flexible and can be tailored to fit a wide range of breeding or research objectives and crop species. By sharing these procedures, we aim to provide a pathway for accelerating crop research and breeding challenges." Ghosh, S et al.
Breeding techniques for faster plant growth
Most attempts to induce growth acceleration and early flowering consist in exerting physiological stress, by restricting plant growth area, nutrients, water access and/or expose the leaves to intense light.
Speed breeding combines some of these techniques in a specific protocol that avoids deficiencies and stress during the growth. Water and nutrients are supplied in good quantity and the excess of light and heat during daytime gets offset by cooler temperatures at night.
Extended photoperiod is the cornerstone to hasten plant growth, but latest studies show also how the importance of light spectrum, notably the positive effect of high levels of purple and red, with low levels of red to far-reds.
"Successful attempts [of] extended photoperiod to hasten plant growth [have been published] using spring wheat, barley, pea, chickpea, radish, alfalfa, canola, flax, arabidopsis, apple and rose." Ghosh, S et al.
Induce early flowering by speed breeding
On the contrary, seed ripening gets accelerated by higher temperature or water shortage, enabling harvest one week after seed have set in the plant.
Optimal values may vary by species, cultivar and planting conditions. The best results were observed with sowing at 1 000 plants/m², 22h of LED light at 22°C, 2h of night at 17°C, and the light spectrum displayed on the left: The fastest seed-to-flowering time was 24 days, for Spring Barley.
In addition to generation time acceleration, a near-simultaneous flowering is obtained, even between genotypes of different earliness. Very convenient for crossing programs !
“A higher temperature should be maintained during the photoperiod, while a fall in temperature during the dark period can aid in stress recovery.”
“After [the seeds have set in the plant], either increase the temperature or withhold water from the plant to hasten seed ripening.” Ghosh, S et al.
Benefits of speed breeding for plant research
Above all, short generations and high plant density reduce variety development time and accelerates research findings. In addition, the technique is rather affordable, notably with the use of LEDs that limit power supply.
Furthermore, speed breeding has little effect on seed quality or quantity, and even on phenotype: “traits such as loss of awn suppressor, dwarf genes, reduced glaucousness or progression of fusarium could be recapitulated under the speed breeding conditions” (Vayola).
on various plant densities enables to find the best compromise between quantity and maturation time.
“The 22h approach demonstrated to be suitable for accelerating research activities involving adult plant phenotyping, genetic structuring, molecular studies like gene transformation, [and] rapid generation advancement [in Wheat, barley]. It was further demonstrated to be suitable for rapid generation advancement for pea, B. distachyon, M. truncatula, canola and chickpea.” Ghosh 2018
To go further..
Speed breeding is a great opportunity for your research department but handling 5 times more generations is not a piece of cake !
5 STRATEGIES TO GET THE MOST OUT OF YOUR GENETIC VARIABILITY
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1. Ghosh, S., Watson, A., Gonzalez-Navarro, O.E. et al. 2018. Speed breeding in growth chambers and glasshouses for crop breeding and model plant research. Nat Protoc 13, 2944–2963 doi:10.1038/s41596-018-0072-z https://www.biorxiv.org/content/biorxiv/early/2018/07/16/369512.full.pdf
2. Watson, A., Ghosh, S., Williams, M.J. et al. 2018. Speed breeding is a powerful tool to accelerate crop research and breeding. Nature Plants 4, 23–29 doi:10.1038/s41477-017-0083-8 https://www.biorxiv.org/content/biorxiv/early/2017/07/09/161182.full.pdf
3. Hickey, L.T., N. Hafeez, A., Robinson, H. et al. 2019. Breeding crops to feed 10 billion. Nature Biotechnology 37, 744–754 doi:10.1038/s41587-019-0152-9 https://www.gwern.net/docs/genetics/selection/2019-hickey.pdf
4. Valoya article on The Role of LEDs in Speed Breeding https://www.valoya.com/the-role-of-leds-in-speed-breeding/ (LED supplier of the John Innes Centre)
5. D. J. O'Connor, G. C. Wright, M. J. Dieters, D. L. George, M. N. Hunter, J. R. Tatnell, and D. B. Fleischfresser. 2013. Development and Application of Speed Breeding Technologies in a Commercial Peanut Breeding Program. Peanut Science: July 2013, Vol. 40, No. 2, pp. 107-114. https://www.peanutscience.com/doi/pdf/10.3146/PS12-12.1
6. Croser, Janine S. et al. 2016. “Time to Flowering of Temperate Pulses in Vivo and Generation Turnover in Vivo–in Vitro of Narrow-Leaf Lupin Accelerated by Low Red to Far-Red Ratio and High Intensity in the Far-Red Region.” Plant Cell, Tissue and Organ Culture 127(3):591–599. Retrieved doi: 10.1007/s11240-016-1092-4 https://link.springer.com/article/10.1007/s11240-016-1127-x
7. Deitzer, G. F., R. Hayes, and M. Jabben. 1979. “Kinetics and Time Dependence of the Effect of Far Red Light on the Photoperiodic Induction of Flowering in Wintex Barley.” Plant Physiology 64(6):1015–21. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=543183&tool=pmcentrez&rendertype=abstract
8. Ugarte, Cristina Cecilia, Santiago Ariel Trupkin, Hernán Ghiglione, Gustavo Slafer, and J. J. Casal. 2010. “Low Red/far-Red Ratios Delay Spike and Stem Growth in Wheat.” Journal of Experimental Botany 61(11):3151–62. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892155/