Exploitation of Heterosis in Pearl Millet: A Review

Abstract

The phenomenon of heterosis has fascinated plant breeders ever since it was first described by Charles Darwin in 1876 in the vegetable kingdom and later elaborated by George H Shull and Edward M East in maize during 1908. Heterosis is the phenotypic and functional superiority manifested in the F1 crosses over the parents. Various classical complementation mechanisms gave way to the study of the underlying potential cellular and molecular mechanisms responsible for heterosis. In cereals, such as maize, heterosis has been exploited very well, with the development of many single-cross hybrids that revolutionized the yield and productivity enhancements. Pearl millet (Pennisetum glaucum (L.) R. Br.) is one of the important cereal crops with nutritious grains and lower water and energy footprints in addition to the capability of growing in some of the harshest and most marginal environments of the world. In this highly cross-pollinating crop, heterosis was exploited by the development of a commercially viable cytoplasmic male-sterility (CMS) system involving a three-lines breeding system (A-, B- and R-lines). The first set of male-sterile lines, i.e., Tift 23A and Tift18A, were developed in the early 1960s in Tifton, Georgia, USA. These provided a breakthrough in the development of hybrids worldwide, e.g., Tift 23A was extensively used by Punjab Agricultural University (PAU), Ludhiana, India, for the development of the first single-cross pearl millet hybrid, named Hybrid Bajra 1 (HB 1), in 1965. Over the past five decades, the pearl millet community has shown tremendous improvement in terms of cytoplasmic and nuclear diversification of the hybrid parental lines, which led to a progressive increase in the yield and adaptability of the hybrids that were developed, resulting in significant genetic gains. Lately, the whole genome sequencing of Tift 23D2B1 and re-sequencing of circa 1000 genomes by a consortium led by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) has been a significant milestone in the development of cutting-edge genetic and genomic resources in pearl millet. Recently, the application of genomics and molecular technologies has provided better insights into genetic architecture and patterns of heterotic gene pools. Development of whole-genome prediction models incorporating heterotic gene pool models, mapped traits and markers have the potential to take heterosis breeding to a new level in pearl millet. This review discusses advances and prospects in various fronts of heterosis for pearl millet.

Pearl Millet: A Climate-Resilient Nutricereal for Mitigating Hidden Hunger and Provide Nutritional Security

“…Now it is being cultivated over 30 million ha worldwide, with the majority of the crop grown in Africa (>18 million ha) and Asia (>10 million ha) (Raheem et al, 2021 ). Around 90 million people in the Sahelian region of Africa and northwestern India consume pearl millet grain as a staple food (Srivastava et al, 2020b ). Jukanti et al ( 2016 ) have reviewed the origin and evolutionary history of pearl millet.…”

“…Various molecular markers and genomic tools have been developed and applied for QTLs/genes identification, genetic diversity, and MAB to enhance pearl millet breeding by exploring its genetic potential at the molecular level (Serba and Yadav, 2016 ; Anuradha et al, 2017 ; Bollam et al, 2018 ; Kumar et al, 2018 ; Singhal et al, 2018 ; Ambawat et al, 2020 ; Srivastava et al, 2020a , b ). Various molecular markers developed for pearl millet include restriction fragment length polymorphism [RFLP (Liu et al, 1994 )], random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism [AFLP (Devos et al, 1995 )], sequence-tagged sites [STSs (Allouis et al, 2001 )], simple sequence repeat [SSRs (Qi et al, 2004 ; Meena et al, 2020 ; Srivastava et al, 2020a )], single-stranded conformation polymorphism-SNP [SSCP-SNP (Bertin et al, 2005 )], expressed sequence tag-derived simple sequence repeats [EST-SSRs (Senthilvel et al, 2008 ; Rajaram et al, 2013 )], DArT array technology [DArTs (Senthilvel et al, 2010 ; Supriya et al, 2011 )], conserved intron-specific primers [CISP (Sehgal et al, 2012 )], and single nucleotide polymorphisms [SNPs (Sehgal et al, 2012 )].…”

Genetic Gains in Pearl Millet in India: Insights Into Historic Breeding Strategies and Future Perspective

“…This involved both cytoplasmic and nuclear diversification of parental lines. In addition to A1 CMS source (Burton, 1965 ), A2, A3 (Athwal, 1961 , 1966 ), A4 (Hanna, 1989 ), and A5 sources (Rai, 1995 ) were reported. Extensive characterization of these sources established instability of A2 and A3 sources, whereas A4 and A5 were found as more promising (Rai et al, 1996 ).…”

“…Many traits of agronomic importance have been mapped related to diseases, terminal drought, grain and fodder quality, combining ability loci, and heterotic gene pools (Kumar et al, 2018 ; Basava et al, 2019 ; Gupta et al, 2020 ; Srivastava et al, 2020a , b ) with SSR and SNP markers. The available QTLs can also be remapped using the currently available SNP-based high-throughput genotyping systems.…”

“…The available QTLs can also be remapped using the currently available SNP-based high-throughput genotyping systems. This will allow integration into the modern breeding pipelines using high-throughput genotyping platforms available currently in pearl millet (Srivastava et al, 2020a , b ). Furthermore, with the availability of reference genome sequence, large-scale whole-genome resequencing data, cost-effective genotyping platform, and precise phenotyping platforms (see later), it has become possible now to map breeding-related traits in a fast manner (Bohra et al, 2020 ).…”