الفهرس 
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Abstract
The present investigation was carried out during 1992 and 1993
seasons at the Citrus Orchard of the Faculty of Agriculture, Moshtohor, to
study the chromosomal behaviour, pollen grains viability, fruiting and fruit
quality in orange cultivars: Khalily Red, Tuncy, Centennial and Valencia.
Also, Roga, Suckarry oranges and two sour orange cultivars i.e. Balady
and Brazellian to investigate only the chromosomal behaviour and pollen
grains viability.
the pollination treatments used in this study were as follows:
1- Open pollination (control).
2- Bagging only.
3- Emasculation and bagging.
4- Hand self pollination.
5- Cross pollination with Balady sour orange.
6w Cross pollination with Brazellian sour orange.
7- Cross pollination with Roga orange.
8- Cross pollination with Suckarry orange.
The histology of ovules fecundation and embryo development were
also studied among the first four orange cultivars mentioned previously, to
correlate these cultivars to fertility of each.
The results of these studies could be summarized as follows:
1- Cytological studies:
A~.Chromosomal behaviour.
I- The meiotic investigations of pollen mother cells showed that the
chromosome number in all tested cultivars: Khalily Red, Tuncy, Centennial, Valencia, Roga and Suckarry oranges as well as two sour
orange cultivars: Balady and Brazellian was 2n = 18. Thus, these cultivars
were normal diploids.
2- In meiotic studies, it was found that the haploid number of
chromosomes in all tested cultivars was n=9. 3- The chromosomal behaviour at meiosis in each of these cultivars
showed 9 bivalents at late diakinesis and metaphase I stages. There were
univalent chromosomes beside the bivalents in some pollen mother cells
(PMGs) in different proportions.
More PMC’s with univalents were observed in Centennial orange
cultivar and Roga orange pollinizer than those in the other cultivars.
4- Cytological studies indicated that Suckarry orange and Balady
sour orange cultivars showed more regular chromosomal behaviour than
other tested cultivars did.
B- Pollen grains viability:
1- The percentages of pollen grams stainability and germination
showed that the viability was highest in Suckarry orange and Balady sour
orange, whereas it was lowest in Centennial orange cultivar.
2- There was a positive correlation between the percentages of
stainable pollen grains and the percentages of germinated pollen grains.
3- It was found a negative correlation between the percentages of
PMGs with univalents and the percentages of stainable pollen grains.
4- As a result of these cytological studies, one might conclude that
Suckarry orange and Balady sour orange could be considered cytologically
stable cultivars and can be safely used in breeding programs for citrus
improvement.II-Studies on fruiting and fruit quality:
1- It was found from specific effect of orange cultivar that Tuncy
orange significantly gave the highest percentages of fruit set, remaining
fruits after June DROP and mature fruits (yield), in addition, significant
increase in the percentage of fruit juice content and an increasing in
T. S.S/acid ratio about three times as much as in fruits of three other
cultivars. Also, Tuncy orange showed the lowest acidity content with an
average of nearly one-third of that for three other cultivars. It significantly
gave the highest number of well developed seeds and the lowest number of
shrivelled seeds per fruit in comparison with three other cultivars. Also,
both Khalily Red and Valencia oranges had fruits of juice more richer in
their ascorbic acid content than both Tuncy and Centennial orange
cultivars. 2-1- Regarding the specific effect of different pollination treatments,
it was found that cross pollinations with Suckarry orange and Brazellian
sour orange pollen grains caused significantly the highest percentages of
fruit set, remaining fruits after June DROP and mature fruits.
Also, both pollinizers caused significant increase in fruit weight and
it’s juice content expressed as weight in gm. per fruit. The two pollinizer
significantly gave the highest number of well developed seeds and the
lowest number of shrivelled seeds per fruit when both were compared with
other pollination treatments. Cross pollination with Suckarry orange pollen
grains had significantly resulted in an increase in T.S.S/acid ratio and
reduced the total acidity and ascorbic acid contents, but the reverse was
true _by cross pollination with Balady or Brazellian sour orange, where
both pollinizers caused thickest peel.
2-2- Emasculation and bagging treatment did not give any fruits in
all tested orange cultivars. That means, all these cultivars could not
produce the parathenocarpic fruits.
2-3- It was found positive correlations between the percentages of
well developed seeds per fruit on one hand and the percentages of each
fruit set, remaining fruits after June DROP and mature fruits on the other
hand. The highest significant positive correlations were found in cross
pollinations with Balady and Brazellian sour orange followed by cross
pollination with Suckarry orange.
3- Concerning the interaction between investigated orange cultivars
and different pollination treatments, it was found that combinations
between Tuncy orange cultivar and cross pollinations with both Balady
and Brazellian sour orange significantly caused the highest percentages of
fruit set, remaining fmits after June DROP and mature fruits, in addition
significant increase in the percentage of fruit juice content and also, these
combinations significantly gave the highest number of well developed
seeds and the lowest number of shrivelled seeds per fruit in comparison
with those of combinations between other three orange cultivars and
remained pollination treatments. The combination between Tuncy orange
cutivar and Suckarry orange as pollinizer, caused the lowest value of total acidity content and the highest value ofT.S.S/acid ratio compared with
those of other combinations.
The combinations of both Khalily Red and Valencia orange
cultivars with different pollination treatments had significantly resulted in
higher ascorbic acid content, while the interactions between different
pollination treatments and both Tuncy and Centennial orange cultivars
produced fruits of poorer ascorbic acid conten Histological studies:
1- Histological investigations showed that the initiation of embryo sac
tookplace at the beginning of blooming in Khalily Red orange cultivar.
2- The embryo sac was completely differentiated and the two nucleate
stages could be detected at the ballon stage of Valencia orange cultivar
3- The Centennial orange cultivar showed the highest percentages of
degenerated ovules, where degeneration of ovules in all tested orange
cultivars was not observed within the first three days after treatments
with the exception of Centennial orange cultivar when it’s flowers were
bagged only or emasculated and bagged.
4- The percentages of deteriorated ovules increased for all different
pollination treatments within 7 to 30 days and reached to the maximum
at 45 and 60 days after pollination treatments.
5- The fecundation occurred within 7-10 days after pollination of different
orange cultivars.
6- The first divisions of free nuclear endosperm was noticed in the
fertilized ovules within 15-20 days after hand self pollination of Khalily
Red orange cultivar.
7_ The first divisions of zygote took place ’at 30 days after cross
pollination of Tuncy orange cultivar with Brazellian sour orange and
the endosperm remained in the nuclear state.
8- The adventitious embryos appeared at 45 days after cross pollination of
Tuncy orange cv. with Balady sour orange9- The sequent divisions of both sexual and adventitious embryos took
place at 60 days after cross pollination of Tuncy orange cultivar with
Brazelhan and Balady sour orange, respectively.
10- Further development of nuclear endosperm forming cellular endosperm
at 70 days after open pollination of Kha1ily Red orange cultivar.
11- The adventitious embryos developed to the main body with globular
shape at 80 days after cross pollination of Tuncy orange cultivar with Balady sour orange.
12- The embryos reached to the cotyledonary stage and cellular
endospenn began to disappear at 100 days after cross pollination of
Tuncy orange cultivar with Suckarry orange.
13- The various parts of the complete embryo were formed (hypocotyle,
radicle, cotyledons and plumule) and the seed coats were completely
differentiated at 120 days after cross pollination of Tuncy orange
cultivar with Brazelhan sour orange.
14- Cross pollination with Suekarry orange pollen grains grains gave the
lower percentages of deteriorated ovules and the high dimensions of
fertilized ones in both Valencia and Khalily Red orange cultivars
compared with those of other pollination treatments.
15- Cross pollination with Balady sour orange pollen grains gave the
lowest percentages of degenerated ovules and the higher dimensions of
fecund ones in Tuney orange cultivar, while cross pollination with
Roga orange pollen grains caused the low percentages of deteriorated
ovules and the highest dimensions of fertilized ones in Centennial
orange cultivar in comparison with other pollination treatments.