Okra physiological in nature (Vanangamudi, 2006). Metabolism that occurs

Okra Abelmoschus
esculentus (L.) Moench is an important vegetable crop in Bangladesh. The
yield is low compared to other okra growing countries of the world. Among
various constrains unavailability of quality seeds and diseases are mainly
responsible for low yield of okra (Rashid and Fakir, 2000). Generally the
quality seeds with higher germinability and greater vigor index are important
for better stand and higher yield. Use
of high quality seed of a high yielding variety and improved production
technologies ensure high yield and quality seed of okra. According to George (2009) use of quality seeds of high yielding
varieties may increase production up to 25-50 %.

Seed
invigoration implies to an improvement in seed performance by post harvest
treatment resulting in improved germinability, greater storability and better
performance. Invigoration treatment should bring about a qualitative
improvement in the seed, which should persist even after the treatment is
removed, and the treatments are basically physiological in nature (Vanangamudi,
2006). Metabolism that occurs during priming
is not enough to cause radicle emergence (McDonald, 2000). Rapid and
uniform field emergence is the essential prerequisite to increase the yield and
quality, ultimately profits in annual crops. Abbasdokht et al. (2004) reported
that high quality of germination in crops will result high yield. Uniformity
and percentage of seedling emergence of direct seeded crops have a direct
impact on final yield and quality, and are decided by the quality of seed used
for sowing and the environmental conditions prevailing during seedling
emergence. Water imbibition is the first step in seed germination. To combat
these problems, farmers pre-soak the seed in plain water for a few hours. But
this may cause seed damage in more than one ways. Of them, the major one is
that, excess water may be trapped in the area of embryonic axis, nodal zone and
cotyledons. This leads to suffocation due to deficient supply of oxygen
resulting in delayed and poor germination as well as weak seedling.  On the other hand priming for prolong period
will allow excess of water that may exceeds the quantity required for the
initiation of lag phase of germination and radicle protrusion will occur due to
which seed lose its desiccation tolerance thereby results in loss of seed
viability (Dekkers et al., 2015). So, aqueous solution of any chemical having
capability to supply O2 at the embryonic axis during seed imbibition
could be worthwhile measures. As such aqueous solutions of thiourea, H2O2
and polyethylene glycol (PEG) at varying concentration(s) and imbibition
period(s) have been found fruitful in various seeds, which improves germination
percentage, vigor index, reduces time to germinate and also increases early
seedling growth and field establishment. Priming
proved effective in improving percent germination and reducing the mean
germination time (MGT) as compared to unprimed seeds. Priming agents, its
osmotic potential and duration significantly affected germination percentage (Farooq
et al., 2005; Rahman et al., 2016). Primed seeds usually exhibit an
increased germination rate, greater germination uniformity (Basra et al., 2005; Arif et al., 2008)). Pre-soaking treatment of seed with thiourea
has been reported to enhance seed germination in onion, potato, ash gourd,
bitter gourd and ribbed gourd (Renugadevi, 1992). Pre-soaking seed treatment
with H2O2 is another effective invigoration treatment
used in groundnut (Lai, 1988; Rahman et al. 1997), pearl millet (Choi et al.
1989), and cotton seed (Bordovsky et al., 1991). The salt or polyethylene
glycol solution is used in order to control water uptake and prevent radical
protrusion (Bray, 1995). PEG is most commonly used because of its non toxic
nature and large molecular size which lowers water potential without
penetrating into the seeds during soaking. Okra (Abelmoschus esculentus L.) is planted by direct dibbling of seed in
the field during January to June, the driest period of the year in Bangladesh.
Hence, soaking its seed before sowing may be helpful. The present experiment
was conducted with the view to find out the effect of pre-sowing seed soaking
in aqueous solution of thiourea, H2O2 and polyethylene
glycol (PEG) to improve germination, field emergence and vigor of okra seeds.

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