Artificial hybridization techniques in small millets—A review

Abstract

Small millets are nutri-rich, climate-resilient food and fodder crops. They include finger millet, proso millet, foxtail millet, little millet, kodo millet, browntop millet, and barnyard millet. They are self-pollinated crops and belong to the family Poaceae. Hence, to widen the genetic base, the creation of variation through artificial hybridization is a prerequisite. Floral morphology, size, and anthesis behavior cause major hindrances in recombination breeding through hybridization. Manual emasculation of florets is practically very difficult; therefore, the contact method of hybridization is widely followed. However, the success rate of obtaining true F1s is 2% to 3%. In finger millet, hot water treatment (52°C) for 3 to 5 min causes temporal male sterility. Chemicals such as maleic hydrazide, gibberellic acid, and ethrel at different concentrations aid in inducing male sterility in finger millet. Partial-sterile (PS) lines developed at the Project Coordinating Unit, Small Millets, Bengaluru are also in use. The percent seed set in crosses derived from PS lines ranged from 27.4 to 49.4, with an average of 40.10%. In proso millet, little millet, and browntop millet, apart from contact method, hot water treatment, hand emasculation, and the USSR method of hybridization are also followed. A newly developed modified crossing method known as the Small Millets University of Agricultural Sciences Bengaluru (SMUASB) method in proso and little millets has a success rate of 56% to 60% in obtaining true hybrids. Hand emasculation and pollination under the greenhouse and growth chamber in foxtail millet with a success rate of 75% seed set is suggested. In barnyard millet, hot water treatment (48°C to 52°C) for 5 min followed by the contact method is often practiced. Kodo millet being cleistogamous, mutation breeding is widely followed to create variation. Most commonly, hot water treatment is followed in finger millet and barnyard millet, SMUASB in proso, and little millet. Although no specific method is suitable for all small millets, it is essential to identify a trouble-free technique that produces maximum crossed seeds in all the small millets.

Finger millet: a hero in the making to combat food insecurity

“…Cross-pollination is difficult because the anthers dehisce before the flower opens (typically between 1 and 5 am) and pollen viability only lasts for about 20 min (Dodake and Dhonukshe 1998 ). Because of the small size of the flowers, emasculation is typically done by hot water treatment after which the emasculated panicle and a pollen donor panicle are tied together and covered with a bag (Nagaraja et al 2023 ; Raj et al 1984 ). Successful F 1 hybrids are often identified using morphological markers, although the use of molecular markers is becoming more prevalent.…”

Finger millet (Eleusine coracana) improvement: Challenges and prospects—A review

“…Widening the genetic base of finger millet through artificial hybridization presents a critical challenge due to the floral biology (e.g., cleistogamous flower, small florets and poor synchronization of anthesis) (Nagaraja et al, 2023;Owere et al, 2016). Controlled crosses are the main approach in finger millet breeding programs, especially for genotypes with dominant traits (Owere et al, 2016).…”

“…However, this method had a limited success rate (2% to 3%), necessitating alternative approaches (Nagaraja et al, 2023). Treating flower buds with hot water (e.g., 52 C, 3-5 min) and synthetic chemicals such as maleic hydrazide, gibberellic acid and ethyl induce temporary male sterility in finger millet (Nagaraja et al, 2023). Molecular markers have been used to assess emasculation efficiency and identify the true hybridity of crosses in finger millet.…”