A proposed model for inheritance of primocane fruiting in tetraploid erectblackberry

Inheritance of the primocane-fruiting (PF) characteristic was studied in se edling populations of tetraploid (4x) blackberries (Rubus subgenus Rubus), Four selections (A-1836, A-593, A-830, and A-1680) and two cultivars ('Arap aho' and 'Shawnee') were used as parents in a full diallel crossing scheme. Selection A-593 was used as the main source for PP due to its origin ('Bra zos' x 'Hillquist, the latter an old PP cultivar). All parents except 'Shaw nee' have A-593 in their parentage; among the parents, only A-1836 fully ex presses PF, Selfing of A-1836 resulted in 100% PF offspring, indicating tha t A-1836 is homozygous for this trait. Selfing of A-593, A-830, and 'Arapah o' produced either a 35:1 or a 20.8:1 PP (floricane or summer-fruiting):PF segregation ratio, fitting a tetrasomic inheritance model under either rand om chromosome assortment (RCSA) or random chromatid assortment (RCTA), resp ectively, also suggesting that PF is controlled by a single recessive gene and that the parents are duplex (AAaa) for this trait. Selection A-1680 and 'Shawnee' selfed did not produce PF progeny, but when crossed with the nul liplex A-1836, gave a 27:1 FF:PF ratio, indicating RCTA and that they are t ripler (AAAa) for PF, According to these research, both gametic outputs (RC SA and RCTA) seem to operate in 4x blackberry. The intensity in expression of PF had a negative relationship with time to harvest, with those seedling s showing the highest PF scores producing a crop in early to mid-August. Th is knowledge will be helpful in implementing breeding strategies to produce PP blackberry cultivars.