Growing seedless oranges involves several phases--mutation breeding, grafting, transplanting to soil and growing outdoors. In most cases, the mutation breeding phase happens in a laboratory by utilizing biochemistry in isolating mutagens with desirable traits found on the plant's DNA (deoxyribonucleic acid). Once the hybridization happens, citrus growers can purchase hybrid seedlings and increase their cultivars by using the grafting method.
Mutation breeding is a form of hybridization that refers to the development of new cultivars by producing and selecting new mutations. This type of breeding helps scientists isolate breeds that produce fewer seeds and fewer defects. The process includes selecting the target tissue from a healthy fruit to expose mutagenic agents, choosing the mutagen (an agent that induces mutation), exposing the tissue, propagating from exposed tissues, screening these plants for desired mutation and evaluating the selections.
Grafting is a method used by citrus growers to create new hybrids from a healthy, seedless fruit-bearing plant. Grafting combines the shoot-tip (donor), which is a small patch of bark containing a bud, and a rootstock (recipient). Place the rootstock through folded, perforated paper into the test tube containing liquid nutrient medium. This medium is a solution containing sucrose and vitamins. Use a razor blade sliver attached to a surgical handle to remove the shoot-tip from the citrus or orange plant. Use the blade to make an incision on the rootstock, and then insert the shoot-tip into the incision on the rootstock by connecting the cut surface of the shoot-tip to the cortex (outer part of a root) of the rootstock.
Within three to four weeks after grafting, small leaves from the shoot-tip will start to appear from the incision. Two to four expanded leaves are ready for transplanting to soil after four to six weeks of successful grafting.
The new growth from the graft should have at least two expanded leaves before transplanting to soil. A pot containing steam-sterilized artificial soil mix is an ideal medium for transplantation. Enclose the pots in polyethylene bags tied with rubber bands, and then place in a shaded temperature-controlled greenhouse. Keep the temperature of the greenhouse between 18 to 25 degrees C (64.4 to 77 degrees F). Open the bags after eight to ten days, and then remove the bags completely after another eight to ten days. The seedless orange seedling should grow under normal greenhouse condition until ready for planting outside.
Seedless orange trees, such as navel oranges, should be ready for transplanting when the root ball is strong enough, which is approximately two to four months after removing the plastic bag. Remove the tree from the container as soon as the hole is ready, and then use a gentle stream of water from the garden hose. Wash the artificial soil medium from around the root ball to expose the peripheral roots. The growth commences almost immediately after the outer roots get in contact with the soil of the planting site.