Practice question

In sugar beet Beta vulgaris, yield comprises root biomass and sucrose percentage, traits influenced by cell size, leaf area, and breeding system efficiency. Diploid 2n=18, triploid 3n=27, and tetraploid 4n=36 have been evaluated extensively in European trials. Tetraploids display reduced fertility, irregular meiosis with quadrivalents, slower growth, and lower seed set, while diploids have normal fertility but smaller cells and less vigor. Triploid hybrid produced by crossing tetraploid female × diploid male combines benefits: increased cell volume and leaf vigor from polyploid gigas effect, improved root tonnage, and acceptable sucrose concentration, while maintaining reasonable fertility of hybrid seed production system using monogerm lines. Field trials consistently showed monogerm triploid hybrids outyield diploid open-pollinated and tetraploid varieties by 10-15% in root yield and provide better bolting resistance and uniformity. Hence commercial sugar beet industry transitioned to triploid monogerm hybrids in Europe and USA for optimum sugar output per hectare. Polyploid breeding also involves development of monogerm seed using genetic male sterility and cytoplasmic male sterility systems, facilitating hybrid seed production; triploid monogerm hybrids combine ease of precision planting, uniform emergence, and high sucrose yield desired by sugar factories processing beet roots industrially for sugar extraction.