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.

To create novel variants for morphological, physiological, and biotic stress tolerance traits, induced mutations were created using Ethyl Methane Sulphonate (EMS) in the background of Samba Mahsuri (BPT 5204), a popular and mega rice variety of India. A population derived from 10, 500 M₁ plants and their descendants were phenotyped for a wide range of traits leading to the identification of 124 mutants having variations in key agro-morphological traits, and 106 mutants exhibiting variation for physiological traits. Higher yield is the ultimate goal of crop improvement and we identified 574 mutants having higher yield compared to wild type by having better yield attributing traits. Further, a total of 50 mutants showed better panicle exertion phenotypes as compared to Samba Mahsuri leading to enhancement of yield. Upon rigorous screening for three major biotic stresses, 8 mutants showed enhanced tolerance for yellow stem borer (YSB), and 13 different mutants each showed enhanced tolerance for sheath blight (ShB) and bacterial leaf blight (BLB), respectively. In addition, screening at multiple locations that have diverse field isolates identified 3, 3, and 5 lines for tolerance to ShB, YSB and BLB, respectively. On the whole, 1231 desired mutant lines identified at M₂ were forwarded to an advanced generation (M₅). PCR based allele mining indicated that the BLB tolerant mutants have a different allele than the reported alleles for well-known genes affecting bacterial blight resistance. Whole genome re-sequencing revealed substantial variation in comparison to Samba Mahsuri. The lines showing enhanced tolerance to important biotic stresses (YSB, ShB and BLB) as well as several economically important traits are unique genetic resources which can be utilized for the identification of novel genes/alleles for different traits. The lines which have better agronomic features can be used as pre-breeding lines. The entire mutant population is maintained as a national resource for genetic improvement of the rice crop.

Aims: The aim of the present work was to generate complete panicle emergence mutants of Samba Mahsuri (BPT-5204), using the chemical mutagen, ethyl methane sulphonate (EMS) Place and Duration of Study: The field evaluation was carried out repeatedly in two locations at Indian Institute of Rice Research, Rajendranagar and at ICRISAT Patancheru Hyderabad. The duration of the study was three successive seasons in triplicates namely, june-2014, january-2015 and june-2015. Methodology: Seedlings of 28-30 days old were transplanted in 5 lines (each line containing 20 plants) into the field. The plant spacing was 20 cm by 15 cm with density of one hill. The field was irrigated throughout the experiment with average of 10 cm water above the soil level. Regular hand weeding was embarked upon to free the plant of inter specific competition. The phenotypic data was recorded for CPE mutants through visual assessment. The characteristics that required measurements were done according to the usual procedure. The Distinctness, Uniformity and stability of the CPE mutant lines have been recorded following (DUS) test guidelines by UPOV guidelines for rice (38) & Yoshida S (44). Results: The identified stabilized thirteen complete panicle emergence (CPE) mutants showed superior agro morphological characters, compared with wild type (BPT-5204). The mutants CPE-2 and CPE-3 took 100 days to flowering and CPE-4 and CPE-7 mutants showed superiority for panicle length, and CPE-5 exhibited good performance for grain yield. In correlation analysis CPE trait had a significantly positive correlation with PH and TGW and negative correlation with 50%DFF. The CPE mutants used in the present study exhibited variability for most of the studied traits. Significant variation was detected in the identified stabilized CPE mutants for plant height, panicle length, flag leaf length and width, 50% flowering, different grain types and 1000 grain weight. Conclusion: The present study discovered adequate genetic divergence in the thirteen stabilized CPE mutants for various qualitative and quantitative traits. The promising mutants identified during the current study have the potential to be used in future breeding programs for getting productive and quality results.