Introduction:

Enhancing genetic gains in rice production to meet the demands of a growing population is imperative. However, conventional breeding methods fall short due to longer generation times and seasonal constraints. In a recent study titled “ SpeedFlower : a comprehensive speed breeding protocol for indica and japonica rice” researchers thoroughly investigated the Effect Of Led Grow Lights on Speed breeding of Indian rice varieties.
Meeting the escalating demands for rice amidst population growth necessitates a significant increase in genetic gains. Speed Breeding (SB) emerged as a promising solution, offering accelerated breeding cycles regardless of environmental factors.

Outcomes

Optimization of Robust SB Protocol

The journey to develop Speed breeding of rice involved meticulous experimentation to fine-tune growth parameters for optimal rice production. Understanding rice growth stages was paramount, with focus areas including vegetative, reproductive, and maturation phases. Key parameters such as light spectrum, intensity, photoperiod, and early germination were meticulously studied and integrated into the Speed Breeding protocol. The protocol's versatility was demonstrated across various rice varieties, from indica to japonica, spanning different maturity durations.

Ratios of Spectrum and Intensity Affect Flowering Duration

The study examined the impact of different combinations of light spectrum and intensity, as well as durations of a long photoperiod, on the flowering duration of various rice varieties.

Effect of Light Spectrum and Intensity on Flowering Duration

● Early-duration varieties CO-51 and IR64 flowered at 60 and 62 days, respectively, in the SB facility with a spectrum ratio of 2R > 1B and an intensity of 800 µmol/m2/s, compared to 87 and 84 days in the field.
● DRR Dhan 44 flowered at 63 days in the SB facility with the same light combination, compared to 93 days in the field.
● Medium-duration variety Sarjoo-52 exhibited flowering between 60 and 64 days under all three spectrum ratios and at an intensity of 800 µmol/m2/s, compared to 93 days in the field.
● Late-duration varieties Swarna and Samba Mahsuri showed varying responses to intensity, with Swarna flowering early at approximately 74-75 days under both 400 and 800 µmol/m2/s intensities with a 2R > 1B spectrum ratio, while Samba Mahsuri showed flowering within a range of 66–70 days across the entire spectrum and at both low and high intensities.
● Landrace Black rice flowered at 49 days with a 2R > 1B spectrum ratio and an intensity of 800 µmol/m2/s, compared to 108 days in the field.
● Kalanamak exhibited early flowering ranging from 76 to 81 days under all three spectrums at an intensity of 800 µmol/m2/s, compared to over 130 days in the field.
● Japonica rice Gedonzipetan flowered at 69–72 days under the 2B > 1R/1R = 1B spectrum and in 76 days under 2R > 1B
spectrum at both intensities, while Betagomblin exhibited early flowering (58 days) under a 2R > 1B spectrum ratio at an 800 µmol/m2/s intensity. In field conditions, Gedonzipetan and Betagomblin took 84 and 91 days, respectively, to flower

Effect of Long Photoperiod on Flowering Duration

● Different durations of a long photoperiod (20, 22, and 24 hours) for the initial 6, 9, 12, and 15 days influenced flowering duration in rice.
● Early flowering was observed in various varieties under different combinations of long-day photoperiods, with CO-51, DRR Dhan 44, and Sarjoo-52 flowering at 55, 53, and 55 days, respectively, when exposed to a 24-hour long-day photoperiod for the initial 15 days.
● IR64 exhibited early flowering in 50 days at a 22-hour long-day photoperiod for the initial 15 days.
● Swarna showed early flowering between 55 and 56 days when exposed to both 22 and 24-hour long-day photoperiods for the initial 15 days.
● Kalanamak and black rice exhibited early flowering in various combinations of long-day photoperiods, with Kalanamak flowering at 50–51 days with a 24-hour long-day photoperiod for the initial 9 and 12 days and black rice flowering between 45 and 52 days in all possible combinations.

Overall, the results suggest that a high red-to-blue spectrum ratio (2R > 1B) and high light intensity (800 µmol/m2/s) are optimal for growing a heterogeneous population in the SB facility. Additionally, a 24-hour long-day photoperiod for the initial 12–15 days is superior for inducing early flowering in a heterogeneous population.

Initial Long-day Photoperiod Controls Plant Growth and Flowering Duration

Fine-tuning photoperiod duration during specific growth stages proved pivotal in synchronizing flowering and accelerating generational advancement. Through meticulous experimentation, an optimal 24-hour long-day photoperiod during the initial vegetative phase emerged as a key driver for early flowering across diverse rice genotypes.

Speed Breeding Advances 4–5 Generations of Rice per Year

The culmination of extensive research and optimization efforts resulted in the development of Speed Breeding, a game-changer in rice breeding. This protocol, characterized by its efficiency and universality, enables the rapid advancement of multiple rice generations per year, fostering unprecedented gains in genetic improvement.

References

SpeedFlower : a comprehensive speed breeding protocol for indica and japonica rice available at https://www.researchgate.net/publication/376379495_
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