Propagation and Layout 69
acid (NAA) (Ahmad and Anis 2007; Anandan et al. 2011). Combination of BAP
and NAA (5.0 μM each) was found best medium composition and gave optimum
response for shoot induction along with the highest number of shoots or explants.
Maximum shoot elongation was observed at 1.5 μM gibberlic acid (GA 3 ) concentra-
tion. Induction of rooting was found to be an extremely difficult process in papaya.
Hence, different hormonal combinations were tried to find a suitable media for
rooting. Half-strength MS medium without any growth regulator (control) failed to
induce root formation even after 4 week. Elongated (60.25%) shoots were rooted on
MS medium containing 2.5 μM indole-3-butyric acid (IBA) within 3 weeks after
sub-culturing (Anandan et al. 2011). The in vitro-raised plantlets were successfully
hardened in greenhouse with 72% survival rate (Figure 5.1). Under Indian condi-
tions, this technique failed due to lack of properly standardised techniques, quality
laboratory facilities and high cost of production. Due to which the farmers are not
getting tissue-cultured plants of papaya today.
5.1.5 Conventional Propagation
Even though scion grafting and rooting of cuttings (Allan and MacMillan 1991)
are possible, these methods are not routinely used for commercial papaya propa-
gation. Propagation of papaya is mostly through seeds. Farmers, generally, collect
fruits of good quality from their orchards and extract seeds for subsequent plantings.
Numerous black seeds, enclosed in a gelatinous aril, are attached to the wall of the
ovary in five rows.
The papaya seeds are very costly as they are produced under controlled con-
ditions to maintain their genetic purity. Though, lots of problems are associated
with seeds like, poor seed germination, poor seedling vigour, etc. under ex-situ
condition, yet papaya seeds possess the highest viability and vigour at physiological
maturity. Seed quality deterioration sets in early after extraction, resulting in low
germination and seedling vigour. The subsequent reduction in seed germination
after storage is also very fast due to accumulation of inhibitors in sarcotesta (Rayes
et al. 1980). Higher the moisture content of the seeds along with high tempera-
ture of storage environment, the quicker is the loss of viability. Seed ageing causes
gradual decline in all vital cellular components thereby, causing progressive loss of
viability. The lipid auto-oxidation has also been suggested to be one of the causes of
seed ageing. Seed deterioration leads to reduction in seed quality, performance and
stand establishment. The priming with 1000 ppm GA 3 and 1 M KNO 3 in fresh and
accelerated aged seeds showed significant improvement in seed quality parameters.
Papaya seeds germinated poorly at 25°C in the presence of gibberellin (GA 4 + 7 ) or
following matriconditioning at 25°C for 4 days. However, a combined treatment of
air-conditioning and GA 4 + 7 for 4 days synergistically promoted germination and
seedling emergence. Drying the seeds after conditioning reduced the percentage
of seedling emergence in the combined treatment involving 400 μM GA 4 + 7 on ly.
Combining matriconditioning with 100 or 200 μM GA 4 + 7 could effectively reduce
germination time, improve seedling emergence and is recommended as a standard
procedure for testing papaya seed germination. The seedling vigour index was sig-
nificantly higher in seeds treated with GA 3 at 100 ppm for 36 h whereas lower in