الفهرس 
Material and methodsOnly 14 pages are availabe for public view
 |  | from | 173 |  |  |
| | | from | 173 | | |
Abstract
136
SUM MAR Y
This research was conducted under laboratory and glass
house conditions through the Agricultural systems development
project. Ministry of Agriculture during 1988-1991.
Plant materials of seven potato varietieS namely Alfa,
Ca r a , Daimon t • Desi re, Founda 1, .Jae r l a and Spun ta previous 1y
proved to be infected with potato virus X were assi~ned as a
source of t Ls sue s in all experiments of this work except in
ca se of the tube rle r s forma t ion p races s, which was res t ric ted
for the va r-Le t i.e s Cara, Spunta and Foundal. The main results
could be s umna rized as follows:
1. Usinn the longer apical meristem i.e. 0.4 mm increased
survival percentage, number of developed plantlets and their
relative growth rate compared to those of the ah oc t e r ones i.e
0.2 mm, Howt~ver the used varieties were reacted differently
in thiS respect.
2. The percentage of PVX free plantlets resulting from
the small si~e apical meristem i.e 0.2 mmwas greater than
those from the large size ones i.e 0.4 mm. They were 47.4%
and 21.2% for these two lengths, respectively.
3. Depending on potato variety. the percentage of virus
free plantlet resulting from the small apical meristems
ranged from 25.0 to 66.7%. The opposites were ranged from
13.0-28.6% when using the large size apical meristems.
2. The excised meristem tips 0.4 mm long were died within
less than one week when exposed directly to 37”C. As a resul r .
--_ .. -
137
these meristem tips were replaced by’l em nodal cuttings
taken from in vitro plantlets original~y produced from 0.4 mm
apical meristems and grown on nutritive medium before the
thermal application.
5. Growth of different variety was varied in response to
heat treatmert. No clear effect was shown on the relative
growth rate (If Cara and Diamont varieties due to exposing the
nodel cu t t Lnc to 37°C for 2, 4 or 6 weeks • Increasing the
exposure perjod to 6 weeks resulted in the death of the nodel
cuttings as vre Ll. as the renewed growing shoot(s) of Desiree,
Fou ndal and ~Jaer-La va r i.e ti es. Rega rding Alpha and Spun t a , the
growth was reduced significantly due to increasing periods of
the thermal a ppLf.ca t t on ,
6. Reduction in the survivals as well as plantlets
developed from t he excised s hoot a pi ces ta ken f rom the renewed
growths, re p.ran t e d on the nutritive medium was more pronounced
especially a·:ter 4 and 6 weeks of heat treatment compared to
the control ,:pre-conditioning heat treatment).
7. The pe rcen tage of PVX free plan ts in crease d to 64% when
the exposure to 37°C was extended to 6 weeks compa~ed to 28.8%
in the contrll treatment. A significant difference was
recorded between the varieties in this respect.
8. Generally when heat treatments were prolonged up to 4
. or 6 weeks. the percentages of plantlets that freed from PYX
were ranged from 60.0% to 81.8% according to the variety.
9. The ligherconcentration of thiouracil i.e. 50, 100
and 150 ppm ,...,hen added to c uI tu re media had a poisonous and
------ -
138
lethal effect as all the nodal cuttings place in the presence
of these con:entrations died and did not performed any new
vegetative growths.
10. Altl0Ugh, nodal stem segment cultures were relatively
able to grow in the presence of the lower concentrations of
. t \ ’
thiouracil i.e 10, 20 and 30 ppm, bu tit was observed that this
growth in all tested varieties was significantly lower than
that in the con t roL treatment (without thiouracil).
11. Inc~easing concentrations of thiouracil in nodal
seg men t cu 1tu re media from 10 to 30 ppm resul ted in an obvious
reduction in both survivals and rooted plantlets that developed
from shoot a Jicies 1.0 mm long taken from shoot(s) that grew
du ring treatments.
12. The va rLe ties va ried in the i r res ponse to the
thiouracil t-eatment. For example, the percentages of developed
plantlets we-e ranged from 38.7% in Foundal variety {the lowest
rate) to 71.1% in Diamont one (the highest one).
13. No clea r di He rences in the numbe r of PYX free plan tlets
were recorded due to application of la, 20, or 30 ppm
thiouracil. However, percentage of such plant1ets would be
increased ,it being 46.~ (43/93) 57.8% (48/83) and 65.3%
(49/75) for o:hese three concentrations,.respectively compared
to 23.8 (36/:_5) in the control (without thiouracil).
14. In Founda1 variety application of 30 ppm resulted only
in four pLanr Le t s , ell were freed from PVX, .80 it was performed
100% freedom. However this percentage was varied and ranging
from 50.0-81 03% according to the cultivar.
139
15. Nodel stem segments incubated under darkness
condi tions showed highl y inc reases in .the a ve rage leng th of
its initiated shoot(s) and the number of roots especially in
the presence :Jf Gt\3. On the Con tra ry, a weak growth and a
reduction in the number of roots were recorded when incubation
was under con::inuous illumination con.ditions.
I
16. Shoot apicies from renewed growths during preViously
incubation under complete darkness +GA
3
lead to a great
reduction in the percentages of developed plantlets when
compared with that from pre-incubated under continuous light
condi t Lo ns , These we re 57.2% and 82.8% fa r the two trea tmen ts ,
respectively.
as a result of continuous illumination compared to COntinuous
17. PVX was eliminated from great numbers of plantlets
darkness With Or Without GA3 in the growth medium, these were
34/171, 29/119 and 35/147 PYX-free plantlets with correspond_
ing percentages of 19.9%, 24.4% and 23.8% for these three
variants I respec tively.
18. In Vitro microtuber productivity of both plantlets
either infected Nith or freed from PYX were established. The
compa ris on be twe’:!nboth was ve ry .conspicous • Elimina tion of
PYX lead to grea: increases in the total numbers of the
obtained microtut’ers, the means of microtuber weight and
diameter comparee to those produced from CUltures that
remained infected.
19. Bo t h si ze of microtubers and frequency of that have
diameter equal to or larger than 5 mm were greatly improved
by elimination of PYX in all tested potato varieties.
140
20. Potted potato plants arised from PVX-free plantlets
remained healthy even up to mare than’3 months after transplanting.
Tile contrast was in those arised from plantlets
previously p rove d to be PVX-infected. The same results were
observed when microtubers taken from cUltures free from Or
infected witr PVX was planted in pots.