Breeding strategies for atemoya and cherimoya

Current production of annonas in Australia is mainly based on atemoya (Annona squamosa x Annona cherimola) hybrids. Very little cherimoya (Annona cherimola) is grown. Fruit quality and/or yield of atemoyas and cherimoyas are highly variable. Consumer acceptance for the fruit could be markedly increased by improving both internal (seed number, flavour) and external (shape, blemish, symmetry) fruit quality characteristics.

A major breeding programme, funded by the Australian Custard Apple Growers Association, has been initiated. The objective of this breeding programme is to select new varieties of atemoya with smooth skin, symmetrical shape, low seed number (less than 10 seeds per 100 g of pulp), low susceptibility to blemish and high level of self-pollination, eliminating the need for labour intensive and expensive hand-pollination. The breeding programme is using a multi-pronged approach in achieving its breeding objectives. A conventional breeding programme using polycrosses of 11 of the best, advanced selections/cultivars (‘Hillary White’, ‘Martin’, ‘Paxton’, ‘MHRS Gold’, ‘MHRS Red’, ‘Palethorpe’, ‘R11-T3’; ‘R11-T4’; ‘R11-T6’; ‘Ruby Queen’, ‘Bullock's Heart’) has been initiated.

The breeding programme will also attempt to develop seedless cultivars by first producing tetraploids either through gamma irradiation or colchicine and then crossing to diploids to produce seedless triploids. Other approaches such as embryo rescue of crosses of reported seedless selections of A. cherimola and currently available seedless A. squamosa may also be feasible. The programme has introduced red and pink skin-coloured germplasm (A. reticulata, A. reticulata x A. cherimola hybrids) from Florida and crosses to transfer skin colour genes into the best of the Australian selections and varieties are currently being developed.