Agriculture Reference
In-Depth Information
at the two-leaf (cotyledonary leaves) stage. Seedlings grown in containers
should be hardened gradually in sunlight and fi eld-transplanted around 1.5-2
months after germination, at about 20 cm high. In fi eld planting up to 15-20
seeds are sown in each hole. Upon germination seedlings are thinned out to
leave fi ve or six seedlings to grow to fl owering. So many seeds are planted in
each hole to allow for birds and fi eld mice loss. At fi rst fl owering, a vigorous
plant of the desired sex is kept and the others removed.
Allan (1964) was the fi rst to report the success of propagating papaya by
cuttings. Large, leafy, lateral shoots that developed after winter were initially
used as cuttings for rooting under intermittent mist. In subtropical countries,
the cool winter checks growth and temporarily overcomes apical dominance,
resulting in the proliferation of lateral shoots. Availability of cuttings became
less season-dependent when they were induced from vigorous 1-2-year-
old trees by topping of the shoot terminus to remove the apical dominance.
The methods for induction and proliferation of suitable-sized lateral shoots
for cuttings were improved further with the application of cytokinin and
gibberellic acid mixtures. Vegetatively propagated papaya fl ower 1-3 months
earlier and are 30 cm lower bearing.
Scion shoots from cultivars 'Co-1' and 'Honey Dew' can be successfully
cleft-grafted on to uniformly established seedlings (Airi
et al.
, 1986). Patch and
T-budding can also be used, but the success rate is poorer than cleft grafting.
Field grafting can be used to replace female trees. The union is established
in about 2-3 weeks and the female tree is cut back to about 60 cm from the
ground.
The early success of
in vitro
propagation of papaya was limited because
the sex of the seedling plants used could not be ascertained. Later, Litz and
Conover (1978) reported successful regeneration of papaya plantlets by
culturing apices of mature, fi eld-grown papaya plants in modifi ed Murashige
and Skoog media. A fi eld trial of
in vitro
plantlets indicated that they
propagated true to sex without somaclonal reversion (Drew, 1988). Besides
greater uniformity, the other benefi ts were earlier bearing, lower bearing
height and improved yield.
Field preparation
Field preparation in many areas is poorly done due to lack of appropriate
equipment or rough terrain. Subsoiling or ripping down to 50 cm or more
is desirable on heavy or compacted soils so roots can penetrate deeply (see
Fig. 3.2). Subsoiling provides better drainage if done parallel to the contour
lines. Discing, levelling and furrowing follow standard practice. Planting holes
30-45 cm in diameter are best dug with a soil auger attached to tractors.
Raised beds are used if there is a chance of fl ooding (see Fig. 3.3).
