Onion and sunflower show:
Onion Allium cepa and sunflower Helianthus annuus exhibit relatively low inbreeding depression compared to highly sensitive cross-pollinated crops. Genetic basis involves fewer lethal equivalents and prevalence of additive gene action for bulb weight and head diameter. Upon selfing, reduction in size about 10 to 20 percent observed, plants retain viability, flowering and seed set adequate for line maintenance. Low depression suggests partial self-compatibility evolved, some purging during domestication and reliance on additive QTL not strongly influenced by dominance. Breeding exploits this tolerance: inbreds developed through mass selection combined with one or two generations of selfing used as parents for open-pollinated synthetics and hybrids. Management still requires monitoring vigor loss but less intensive than high depression crops necessitating mild inbreeding and larger population size. This understanding supports competitive exam preparation for NEET, GATE and CSIR NET concepts linking genotype with phenotype through molecular pathways involving transcription factors, hormones and metabolic enzymes that regulate development, adaptation and reproductive biology in applied breeding programs.
Ref: FSS e-courses Onion breeding depression; Janick Encyclopedia Sunflower; Singh BD Table depression categories.