Breeding guar [Cyamopsis tetragonoloba (L.) Taub]: A variety compendium of a multifaceted industrial crop for resource-constrained scenario in India.

Guar is an annual, multifaceted, short-day, edible nutritious legume with immense industrial value due to the galactomannan-rich gum isolated from its endosperm. Natural adaptation to limited water and low input cost cultivation makes it the preferred rainfed crop choice for resource-constrained, environments with marginal barren lands in the arid region of Rajasthan, Haryana, and Gujarat. India currently maintains over 3981 indigenous and 31 exotic collections. USDA, ARS, and Plant Genetic Resource Conservation Unit similarly maintain 1298 guar accessions. Natural variability for economic, industrial traits, and mutagenesis-induced variability have been intensively explored and inducted into the guar genetic improvement program. Restricted primary and secondary gene pool diversity, coupled with a petite cleistogamous flower, guar's genetic improvement through inter-specific hybridization has met only limited success. Genetic improvement has been carried out for photo-insensitivity, non-shattering pods, earliness, synchronized maturity, bold seeds, high gum content, determinate growth habit, non-lodging, plant height, resistance/tolerance to Alternaria leaf spot, bacterial blight, powdery mildew and to develop resource-efficient genotypes which could perform well in resource-constrained scenarios such as salinity, extremely high temperature, and drought stress. Genetic improvement programs have been carried out in three segments for breeding guar i.e. for 'grain type' with non-shattering grain, determinate growth habit with dwarf plant type with enhanced glucomannan-rich seed gum. Breeding 'vegetable type' guar with all node clusters bearing ability, high clusters number with long pods, and as 'fodder type' with non-pubescent leaves with basal branched habit and delayed flowering. Continued strategic breeding efforts have significant achievements producing more than 86 guar varieties in the last 66 years of which 58 varieties were developed at India's ICAR six prime institutions. Whole genome sequence assembly (550.31 Mb) guided elucidation of guar gum biosynthesis pathway genes and genotype selection to create efficient high gum guar genotypes development through targeted trait breeding with emphasis on seed size, type, and yield is the need of the hour. This review focuses on the global state of the art in the guar varietal improvement program (India and other parts of the globe), the available spectrum of varieties for global guar market stakeholders, challenges, and the constraints that need to be addressed by the guar breeders to meet consumer demands of specific market niches of grain, fodder, and vegetable type guar varieties steering the varietal improvement program in guar. [Display omitted] • Grain, fodder, vegetable, guar varieties compendium. • Guar varietal improvement breeding history, targets, leads. • Resource for global guar market stakeholders. [ABSTRACT FROM AUTHOR]