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Speed Breeding for Crop Improvement

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Interdisciplinary Approaches in
Agriculture and Forestry
Dr. Sandeep Rout, Dr. Udit Nandan Mishra, Mr. Rupak Jena

I
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 Speed Breeding for Crop Improvement
Tushadri Singh1, Ashish Sheera1, Kavita Raina1, Sandeep Rout2
1
Division of Plant Breeding and Genetics, Faculty of Agriculture, SKUAST-Jammu-180009, India
2
Faculty of Agriculture, Sri Sri University, Cuttack, Odisha-754006, India

Abstract
Speed breeding technique is deemed as the future of plant breeding. Speed breeding refers to a quick generation
advancement technology used for decreasing the time of seed to seed cycle, thereby shortening the otherwise traditionally
long life cycle of a crop plant. With the use of this technology, up to 6 generations per year for photo insensitive crops and
2-3 generations per year for other crops have been obtained. This method manipulates the photoperiodic conditions and
temperature requirements of crops grown in controlled poly houses. This method can accelerate crop breeding
programmes and in use with other modern technologies like genome editing and high throughput genotyping platforms
this technique can serve to breed new varieties at a much faster scale. This idea was originally conceptualized by NASA in
order to grow food at a faster pace in space. Whether speed breeding can be applied to a particular crop or not can be
checked by the help of Breeder’s equation. The core recipe of speed breeding involves manipulation of light, photoperiodic
regime, temperature, and humidity. This method has many applications like accelerated breeding, speeding up the process
of genomic selection, boosting transgenic and CRISPR pipelines, and to study physiological traits of importance in crop
plants.
Keywords: Generation advancement, photoperiodic conditions, photo insensitive, speed breeding
Introduction
Speed breeding is a smart and fast generation advancement technology which servesto shorten the traditionally
long breeding cycles, consequently accelerating the crop research programmes and cultivar development. This
unique method was originally conceptualized by US NASA in the 1980s for growing crops in space at a much
faster rate.
In conventional plant breeding, after making crosses between desired parents, selection and screening for the
desired traits along withgeneration advancement of the selected material is time consuming and thus 8-10 years
are required for development of new variety. This slow improvement rate is attributed partly to the long
generation times of crop plants. To increase productivity and stability of crops to meet the changing climatic
conditions, there is need to fast-track research and also increase the rate of cultivar development. The time needed
for generation of most crops poses a bottleneck in research and breeding programs thereby creating the need for
technologies which accelerate plant development process and hence, generation turnover. This major problem can
be conveniently overcome by use of speed breeding which involves quickening the breeding cycle from seed to
seed by manipulating the photoperiodic conditions along with environmental conditions like soil media
composition, temperature, spacing in the glass houses, all done to achieve rapid generation advancement.
First wheat variety which was developed through speed breeding was ‘DS Faraday’ by Lee Hickey. It has high
protein content, tolerant to pre harvest sprouting and has milling quality. The speed breeding technique has mainly
been used for purpose of research, but is now being widely adopted by the industries as well.
Speed breeding in completely controlled and enclosed growth chambers can be used for accelerating plant studies
and development, and can also complement in studying mutants and transformation studies.

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 Figure 1. 1st wheat variety ‘DS Faraday’ developed through Speed Breeding.
(Source: www.seednet.com.au)
In comparison to plants grown in field, by using simple techniques of extended photoperiodic conditions
(normally 22 hour light and 2 hour dark photoperiod) by using combination of light emitting diodes (LED) and
metal halides in temperature controlled growth chambers results in rapid advancement of generations. This has
been successfully used to achieve 6 generations per year in Hordeumvulgare (barley), Triticum durum (durum
wheat), Triticumaestivum(spring bread wheat), Cicerarietinum(chickpea), Pisumsativum(pea) and 4 generations
for Brassica napus (canola) as compared against 2-3 generations per year obtained through normal glasshouse
conditions. The plants obtained through speed breeding have normal developmental process, can be easily crossed
and have high seed germination.
Concept
Using controlled lighting and temperature control conditions plants complete their traditionally long breeding
cycle in relatively shorter time by decreasing their time to flower and obtaining seed set, thereby increasing the
number of generations obtained per year.
For example in Arabidopsis thaliana, by manipulating the ratio of plant hormones and photoperiod along with the
germination of immature seeds, 10 generations per year can be obtained by reducing the time to flowering to 20-
26 days. Similarly in case of barley (Hordeum vulgare) using the method of Single Seed Descent,by manipulating
the photoperiod, temperature, soil fertility and using techniques of immature seed germination and embryo rescue
9 generations per year can be obtained by decreasing the flowering time to 24-36 days.

290
 Figure 2. Comparison of number of generations of crops obtained per year through speed breeding (4-6
generations per year) versus glasshouse conditions (2-3 generations per year).
(Source:www.nature.com/natureplants)
Innovation of Speed Breeding
The need for growing crops in lesser duration in space was first conceptualized by scientists in US NASA. This
idea further inspired scientists in the University of Queensland and University of Sydney to engineer a platform
for speed breeding.

Figure 3: Speed Breeding in environment controlled chambers.

(Source: www.science.uq.edu.au)
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Speed breeding takes the advantage of an artificial environment with increased duration of light to create the
impression of longer daylight period to fasten the breeding cycles of the photo insensitive crops.This results in
early reproduction of the crops by making use of continuous light. The speed breeding experiments in wheat have
shown that comparison of quality and yield between plants grownunder controlled conditions and those grown in
regular glasshouse conditions was the same.
Breeder’s Equation
Whether speed breeding can be applied to a particular crop or not it can be decided by the breeder’s equation:

Rt =
Where,
Rtis genetic gain over time
i is selection intensity
r is selection accuracy
σais genetic variance
y is years per cycle
The genetic gain over time increases with increase in selection intensity, selection accuracy and genetic variance
and with decrease in years per cycle. An increase in selection accuracy increases phenotyping and reduces error.
Core Recipe of Speed Breeding
The main ‘recipe’ for setting up speed breeding conditions includes:
1. Light:the preferable light for use in speed breeding is one covering the Photosynthetic ally Active Radiation
(PAR) i.e. 400–700 nm with focus on red, far-red and blue range. This spectrum can be achieved by using
Light Emitting Diodes (LEDs), or a combination of LEDs and halogen lamps. Photosynthetic Photon Flux
Density (PPFD) of ~450–500 μmol/m2/s at plant canopy height is also recommended which can be adjusted at
slightly lower or higher levels according to need of crop.

2. Photoperiodic regime: A photoperiod of 22 hour light and 2 hour darkness in diurnal cycle of 24 hours is
ideal photoperiodic regime for speed breeding. Another alternative is continuous light but slight period of
darkness is known to improve the health of plant.

3. Temperature: Ideal temperature for each crop should be applied.During photoperiod higher temperature
should be maintained, while during dark period fall in temperature can help with stress recovery. Temperature
has a major impact on the rate of plant development; therefore generation time can be accelerated by elevating
temperature. However in some cases higher temperature may induce stress like conditions and affect
performance of plant.

4. Humidity: Control over humidity even in controlled environment chambers is limited, but 60–70% RH is
ideal for crop growth, this level can be modified according to type of crop. For crops more adapted to arid
conditions, lower humidity level is recommended.

292
 Figure 4. Temperature controlled glasshouses with supplemental lighting consisting of LEDs.
(Sources:www.plantekno.com , www.jic.ac.uk)
Procedure of Speed Breeding
A general procedure for low cost speed breeding in a homemade growth room design is as follows:
1. As an alternative to normally used Conviron BDW chamber, a room having insulated sandwich panelling
fittedwith seven LED light boxes (one light box per 0.65 m2) and a 1.5 horsepower inverter split system
domestic airconditioner can be used.
2. The lightquantity of PAR at bench height should range from210–260 μmol/ m2s1& at 50 cm above the pot
from 340–590 μmol/ m2 s1.The lights should be situated at a height of 140 cm above the bench. The room
should be able toaccommodate 90 pots of 20.3 cm.
3. Automatic wateringcan be achieved by using Irrigation Controller, having one solenoidper room and one
spike dripper per 20.3 cm pot.
4. Thehumidity conditions should be ambient.
5. The lighting should be enriched in the blue, red and far-red part of the spectrum. It should be set to 12 hour
photoperiod and 12 hour darkness for4 weeks and then slowly be increased to 18 hour photoperiod and 6 hour
darkness.
6. An air-conditioner can be used for regulation of temperature and set at 21°C during the photoperiod and 8°C
in darkness.
Speed breeding approach is ideally realized using Single Seed Descent method, particularly for cereal crops. By
increasing the sowing density in speed breeding, we can achive rapid cycling of many lines having healthy plants
and viable seed.
The plants grown under speed breeding reached anthesis in approximately half time as compared to those grown
in same conditions under glasshouse conditions. The above described procedure has been used for speed breeding
of wheat, barley, oat and triticale.
Harvesting of Immature Spikes
Under normal conditions 15 days are required for the storage of grains after harvest to decrease the moisture and
attain natural ripening. This process is forgone in speed breeding where the harvest of plants is done just two
weeks after anthesis when the spikes/pods are still green. They are then popped into hot air oven/dehydrator at
35°C for 3 days to fasten the maturity process artificially. The performance of the seeds obtained by such artificial
drying is same as those obtained by normal drying except for the decrease in weight of such grains obtained by
artificial drying. Such artificial drying accelerates the normal ripening process and this serves to save precious
time and obtain faster seed to seed cycle, the core of speed breeding.

293
 Figure 5. Comparison between normal seed ripening process (takes about 15 days) and harvesting
immature spikes and their subsequent drying in dehydrator (takes about 3 days)
(Source:www.nature.com/natureplants)
Applications of Speed Breeding
Applications of speed breeding are as follows:
1. Accelerating the crop improvement programmes by achieving upto 6 generations per year in photo insensitive
crops and 2-3 generations in case of photo sensitive crops.
2. Speeding up the process of genomic selection.
3. An ideal method for generating large breeding populations.
4. For boosting transgenic and CRISPR pipelines.
5. It can be extended to study physiological traits of importance in crop plants.
Limitations of Speed Breeding
Some major limitations of speed breeding are:
1. The early harvest of immature seeds before completing normal ripening process interferes with the
phenotyping of some seed traits.
2. There is no universal protocol of speed breeding because of diverse response of plant species to
photoperiodic conditions.
3. Differential responses of various plant species when exposed to extended photoperiodic conditions.
4. Initial investment of setup is high.
Conclusion
With the ever increasing population, by 2050 farmers will have to increase food production by 60-80% to feed the
potential 9 billion people. Another main issue which arises is that breeding programmes should be in tandem with
the changing climatic conditions and to achieve rapid results in both these respects, speed breeding is the way to
go. Speed breeding in combination with modern crop breeding technologies, including genome editing, genomic
selection and high throughput genotyping, can be a great asset in accelerating the rate of crop development. Speed
breeding can serve to enhance the plant growth by accelerating research program in terms of reducing the
breeding cycle of plant. In India, particular success has been seen in case of wheat in speed breeding which can be
extended to other crop varieties, and similar facilities can be set up for the faster development.

294
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