Tamarind monograph.pdf - Crops for the Future

Mechanical scarification has also been effective in breaking the seed coat
dormancy. Scratching the region near the hilum on coarse sand paper or
nicking it with a knife increased the rate of germination (El-Siddig et al.,
2001). Scraping the seed coat by rubbing on a rough surface to facilitate
quick absorption of water also increases the rate of germination (Gunasena,
1999). Masano (1994) found that slicing off the end of the seed resulted in
increased germination.
Magehembe (1995) reported that seed germination could be enhanced by
sowing immediately after extraction and/or cleaning. However, some studies
(FAO, 1988) indicate that germination can be improved by storing the seed
for six months before planting.
Tamarind seed can germinate in the presence of low salt concentrations. In a
greenhouse experiment, the effect of 0, 30, 60 and 120 mM NaCl on
seedling emergence and early growth of tamarind was investigated (El-
Siddig et al., 2004 a). Results have shown that percent emergence and
seedling dry weight were not markedly affected by 30 mM NaCl, but
progressively stronger inhibitory effects were observed at 60 and 120 mM.
In another study, the effects of reduced water potential (0, -0.3, -0.6, -0.90 or
-1.30 MPa) generated by either NaCl or polyethylene glycol-6000 (PEG) on
water uptake and germination of tamarind seeds were investigated under
laboratory conditions (El-Siddig, et al., 2004 b). At each iso-osmotic
solution, PEG appeared to be more inhibitory to water uptake than NaCl,
especially at the lowest water potential (-1.2 MPa). At this water potential,
no germination was observed in both NaCl and PEG solutions. For the other
treatments, NaCl resulted in lower germination percentages than iso-osmotic
solutions of PEG. These results suggest that the main effect of PEG occurred
via an inhibition of water uptake, while the detrimental effects of NaCl may
be attributed mainly to accumulated toxic ions.
It is important to clean seeds when they are collected. Seeds often become
contaminated with fungi after collection and as a result tend to deteriorate if
stored in this condition. Sometimes seeds become contaminated with
pathogens whilst still in the pods on the trees. Seed borne pathogens can
affect germination and subsequent growth. Seed dressing with carbendazim
(Bavistin), dithane M-45 (Mancozeb), thyride (Thiram), copper oxychloride
(Fytolan) and an organo-mercury fungicide (Ceresan at 3 g kg -1 of seed
weight) have been recommended for control of seed borne fungi (Purohit et
al., 1996). However the use of these fungicides may be subject to local
regulations.
5.2.1.3 Seed sowing
Under natural conditions the seed pods fall from the trees and the seeds are
released following decomposition of the pods. These seeds germinate and
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