Seed Production 91
8.2.1 Seed Production in Isolation
Under controlled conditions, it is possible to produce seed with 100% genetic purity
but it is a cumbersome job and may not be feasible for the majority of the growers.
Moreover, it requires manual labour with some technical knowledge and experi-
ence. Therefore, seed can also be produced in isolation which does not require any
elaborate process in crossing and selfing. The foundation and certified seeds are
generally produced following this method. Isolation distance is an important fac-
tor for pure seed production of different cultivars (Saran et al. 2014a). The isolation
distance may be kept at 1000–1500 m (Ram 1995). This distance depends upon the
locality and activity of vectors. For ensuring a definite demarcation line of isola-
tion in a locality, the simple method is transplanting of Washington or Homestead
variety as a gene marker. The purple colour of stem and petiole is a dominating
character in this variety. If the progeny of open pollinated plants do not produce any
purple-coloured plant, it means the isolation distance is correct. This distance may
be further increased if there are some purple-coloured plants found in the progeny. If
a suitable isolation is not available, seed can be produced in the middle of an orchard
of any crop like mango, litchi, sapota, ber or chestnut (Ram 1986a). These fruit trees
act as a physical barrier against cross-pollination with other varieties of papaya in a
locality. The seed in isolation generally produces 95%–99% pure seed depending upon
the local condition. The entire fruit of the orchard can be utilised for seed extraction.
This can be done where the market is available for cut fruits/pulp or a factory for the
processing purpose. The planting season may start from March to October in differ-
ent climatic conditions.
Sometimes, collar rot is noticed. The plants planted on raised beds or ridges help
to avoid the disease. It may be controlled with repeated sprays of Bordeaux mixture
(5:5:26). In areas susceptible to root rot, application of 1.0 kg lime and 100 g copper
sulphate in the pits is an effective preventive measure against this disease.
8.2.2 Seed Extraction and Storage
The fruits should be harvested when they start ripening or reach colour turning
stage (2%–4% ripening). Cut the fruits longitudinally and collect the seed care-
fully in a container with the help of spoon or knife (Figure 8.1). Fresh seeds put
overnight for fermentation followed by sarcotesta should be removed by rubbing
against gunny bags and finally washed in running tap water. After this, the seeds
are dried in shade till the moisture comes down to 8%–9%. After drying, the seeds
should be cleaned properly by removing the immature seed and other foreign
materials. The standard method of storing papaya seed is to keep it in a refrig-
erator at 5°C. However, papaya seeds are sensitive to low temperature storage.
Lipid crystallisation occurs at temperatures below −13°C to −15°C and seeds suf-
fer damage if subsequently imbibed without briefly raising seeds to around 45°C
to allow lipids to safely melt. The species-specific critical temperature seems to
be related to triacyglycerol composition. This facility may not be available every-
where. Therefore, the seed should be kept in airtight bottles or packed in polythene
bags and dry place under ordinary room temperature (Ram 1995). A standard