Agriculture Reference
In-Depth Information
Table 6.2.
Mean germination time
a
(GT) and its standard deviation (SD) for natural
and drum-primed leek seed
b
sown under different temperatures and osmotic
potentials (from Rowse, 1996, Tables 4 and 6).
Osmotic potential (Mpa)
-0.1
-0.3
Temperature (°C)
Seed
GT
SD
GT
SD
5
Natural
19.33
3.90
29.66
8.19
Primed
c
1.08
1.02
2.89
2.49
15
Natural
3.41
0.92
5.18
1.44
Primed
c
0.75
0.34
0.74
0.40
a
Germination was tested on absorbent paper moistened with the PEG solutions.
b
Cv. 'King Richard'.
c
Undried primed seed.
7-14 days at 15°C at this moisture content to achieve maximum advancement
for leek and onion seed. Advancement is less for seeds held at lower moisture
content and was zero at 30% seed moisture content (Gray
et al.
, 1990b).
The advancement of germination that results from priming is greater for
slower-germinating seedlots (Drew
et al.
, 1997). Priming can increase the
percentage of normal seedlings that develop from the germinating leek seeds
provided the seeds are sown soon after priming (Drew
et al.
, 1997).
Primed seeds are normally dried after treatment for ease of handling and
distribution. About 1 day of the advancement gained from priming is lost while
the dried, primed seed rehydrates after sowing, but most of the decrease in time
to germinate and decreased spread of emergence is retained. Dried, primed seed
can be stored for some time, but long-term storage - e.g. greater than 100 days
at 10°C and 40% RH - resulted in an increasing percentage of abnormal leek
seedlings that failed to produce roots (Maude
et al.
, 1994).
Priming simply accelerates germination of seeds - the relative growth rate
after germination of seedlings from primed or unprimed seeds has been shown
to be the same for both onions (Ellis, 1989) and leeks (Brocklehurst
et al.
,
1984).
The volume and the number of cells per seed embryo do not change during
the priming of onion and leek seeds (Gray
et al.
, 1990b). DNA synthesis, of
which approximately 20% is DNA repair-type synthesis, occurs during priming
of leek seeds despite the absence of cell division (Ashraf and Bray, 1993). During
priming, overall DNA levels in leek seed embryos do not increase, but RNA levels
increase by 50-100% (Bray
et al.
, 1989; Clarke and James, 1991). In primed
leek seeds germinated at 15°C, after an initial lag of 6-12 h, DNA, RNA and
protein synthesis increases in seed embryos much faster than in unprimed seed.
Furthermore, seeds having a low rate of biosynthesis compared with more
'vigorous' seed during normal germination have rates of biosynthesis equal to
