South African horticulturists have worked out a method of propagating papaya (papaws) from cuttings. This now means that selected plants can be mass-produced and the variability, fruit size and quality so often encountered in most papaya plantations can be eliminated by the production of cuttings.
Near Pieter Maritzberg, uniform, good-quality papaw fruits, produced on plants propagated vegetatively by cuttings, have brought returns as high as R15,000 per hectare for growers.
The variety 'Hortus Gold' is a female plant which has been vegetatively propagated by rooting leafy cuttings under intermittent mist with a bottom heat of 25°C.
For successful rooting of leafy cuttings, strict sanitation is essential, otherwise stem rots can kill the cuttings. The well-drained rooting medium must be sterilised by steam or chemicals between successive batches of cuttings.
Leafy cuttings are taken from young side shoots during the summer when the stem is still green. They normally take 4 to 6 weeks to develop roots.
Cuttings can also be taken in the spring and autumn, but the success rate is lower.
The technique is to take cuttings which are at least 20 cm long and at least 2 cm in diameter, and remove all leaves except the 3 to 4 developing ones with vertical leaf stalks. All other leaves are cut back leaving about 10 cm of the leaf stalk.
The reason for leaving the leaf stalks is to ensure that if bacterial infection occurs at the cut end of the stalk, it will not be able to progress far before natural abscission develops at the base of the petiole. By cutting the leaf stalks long, it prevents the chance of bacterial infection of the stem of the cutting.
After trimming the leaves, the base of the cutting is dipped in a root-promoting powder such as indole-butyric acid (IBA). A powder formulation of 1 percent IBA or a concentrated quick dip of the cutting in a 2000 to 4000 p.p.m. lBA in 5 percent ethanol gives good results.
Bottom heat at 25°C applied by electric heating cables beneath the rooting medium also hastens rooting.
Intermittent mist applied during the daylight hours keeps the leaves cool and turgid. This allows plants to photosynthesize carbohydrates while the roots are being incubated.
Once rooted, the cuttings are potted in small plastic bags with drainage holes, and are left under mist for about 10 days.
They are then hardened off in a shade house prior to transplanting to their permanent positions.
The rooted cuttings should be planted as deep as possible without covering the growing point with soil.
Additional Note: Kerevat Horticultural Research Station at Rabaul, P.N.G. is currently propagating papaws by the bud grafting technique. They graft selected good varieties on to local wild root stocks.
DATE: July 1982
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