Seed Production 93
8.4.1 Seed Viability
Papaya seed survives for a short period of time under ambient conditions. The seeds
show an orthodox storage behaviour (Ellis 1984) in which they withstand desicca-
tion and extend longevity at lower temperatures. Papaya seeds are susceptible to
chilling temperatures and are killed when stored at zero or subzero temperatures.
Therefore, the seeds are considered intermediate between recalcitrant and orthodox
attributes. Seed moisture content is very crucial in papaya seed storage. Higher seed
moisture content injures the seed life and rapidly reduces seed viability during stor-
age. Harrington (1972) found that papaya seed longevity decreases by one-half for
every one percent rise in seed moisture content, and that it well maintains at the
range of 5%–14% moisture content. Seed moisture of 5%–7% is ideal for safe stor-
age of papaya seeds. In general, the moisture content of seed increases with a rise
in relative humidity level, and absorption depends on the surrounding temperatures.
Papaya seeds deteriorate rapidly at higher storage temperatures and relative humid-
ity. Fresh seeds give higher germination rate and seedling vigour that will decline
with increase in the storage time. Zulhisyam et al. (2013) reported that the seeds with
6%, 8% and 10% moisture contents using silica gel are stored at 0°C, 4°C and 28°C,
respectively, for three months. Seeds containing 6% moisture content and stored at
0°C gave higher percentage of germination, lower dormancy and lower seed death
compared to the seed of the other storage conditions. The result suggested that such
a condition was the best for papaya seed storage. Seeds containing 10% moisture
content and stored at 28°C is not recommended for papaya seed storage because seed
deterioration rate under such a condition was higher.
The effect of seed moisture, packaging materials and storage temperature on seed
viability during storage was investigated in three varieties of papaya. The seeds were
dried to various moisture levels, packed in polythene cover (700 gauge), aluminium
poly pouches and butter paper bags and stored under controlled (15°C and RH 30%)
and ambient conditions. The observations on seed germination and seedling vigour
were recorded at 3-month intervals for 24 months. The results revealed that the
seeds could be stored without any decline in viability and vigour for 24 months at
15°C irrespective of variety, packaging materials and seed moisture levels. However,
under ambient conditions, the seeds of Surya could maintain high viability upto 15
months of storage, whereas Co-2 and Co-7 could maintain viability (>75%) upto 24
months with little decline in seed vigour. Among the packaging materials, poly-lined
aluminium pouches were found to be better and the seed moisture (5%–10%) had no
marked effect on viability (Yogeesha et al. 2008).
The seed is enclosed in a gelatinous sarcotesta (aril or outer seed coat), which
is formed from the outer integument. Papaya seed germination is slow, erratic and
incomplete. While the sarcotesta can delay germination, dormancy is also observed
in seeds from which the aril has been removed. Several attempts have been made
to overcome dormancy and improve papaya seed germination. Treatments such as
removing sarcotesta, presoaking in water or water leaching promote Carica spp. ger-
mination. Seeds germinated poorly at 25°C in the presence of gibberellin (GA 4 + 7 ) or
following matriconditioning at 25°C for four days. However, a combined treatment
of matriconditioning and GA 4 + 7 for four days synergistically promoted germination