الفهرس 
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Abstract
Potato is the world‘s fourth-largest food crop following rice, wheat and maize. The
global annual diet for a person included about 33 kg of potato. Potato was introduced
outside the Andes region-where it was domesticated for 7000 years- four centuries ago,
and has become an integral part of much of the world‘s cuisine. The world production of
potatoes in 2010 was about 324 million tones. Just over two thirds of the global
production is eaten directly by humans with the rest being fed to animals or used to
produce starch. Egyptian potatoes are cultivated in three growing seasons, summer, fall
(Nili) and winter in the period from the early of September to the end of February and
harvest time starts from the beginning of December until the end of May.
Late blight, caused by the oomycete Phytophthora infestans (Mont.) de Barry, is
the main disease of potato and an important disease of tomato worldwide. In addition to
potato and tomato, the pathogen attacks a broad range of plants in the Solanaceae family.
During favorable conditions, the pathogen can wipe out all entire plants in the field in a
few days resulted 100% yield losses. Although it represent an extremely important threat
to potato cultivation in Egypt, but less is known about the local population characteristics
of the pathogen so far.
To have a better understanding of this disease, a series of studies were carried out
on the pathogen population in Egypt including isolate identification via classical and
molecular biology tools, sensitivity of some Egyptian potato cultivars and fungicides
application as disease control measures.
Following are the most important results of the current study:
1. The initial symptoms of late blight disease observed during the middle of
November. The disease attacks all foliar parts of potato plants under favorable
conditions and easily destroy a whole potato field within two weeks.
2. Occurrence of potato late blight disease was monitored on plants from different
cultivars grown in commercial fields at different eleven governorates during 3- year periods 2014, 2015 and 2016. These governorates were Minufiya (Tamaly, Shama,
Gezie, Menouf, Shanshour, Khamseen, Kafr elashry, Barheem, Megeiria, Kafr
dawod, Shebien El-Kom, Nader, Kamshoch, Ashmoun, Teta and Hamoul), Behira
(Kom Hamada, Markzbadr, Nubariya, Elbostan, Tawfykia, Wady El-Netroon, El-
Khawaled and Khefog), Gharbiya (Kafr El-Zayat and El-Mahalla El-Kubra), Kafr
el-Sheikh (Sakha, Balteem, Tayifa, Keleen, Marazika and Dokmeira), Qaliobia
(Kaliob and Elkanater), Dakahliya (Manakhla, Diast, Roda, Berkash, Hodmeaidy
and Shirbin), Sharkyia (Salhia), Fayoum (Yossefelsedek, Rawan and Hanahabeeb),
Ismailia (Kasaseen), Beni Suef and Giza (Badrasheen).
3. During the growing seasons 2014, 2015, and 2016; a collection of 176, 134, and
109 isolates of Phytophthora infestans had been isolated, respectively from infected
potato samples in a conclusion of 419 isolates were collected and isolated during
these three seasons and Behira governorate has the highest values of disease
severity (80%) compared to other governorates; followed by Gharbiya governorate
(75%), Minufiya governorate (65%).
4. Isolates varied morphologically in different characteristics such as in mycelium
color and colony structure, producing sporangia on either rye or pea agar natural
media but more sufficiently abundant on the first one.
5. Mating type testing of 250 isolates showed that; 150 isolates, which were tested
during 2014 growing season, belonged to A1 mating type. In the next season, the
percentage of A2 was 15.9% while A1 was 84.13 %, and there was absence in the
presence of self-fertile isolates during these seasons.
6. Response to metalaxyl was determined for 63 isolates in vitro on pea agar amended
with 5 and 100 ppm metalaxyl. Most of A1 isolates were intermediately resistance
to metalaxyl while most of A2 isolates were (resistance) to metalaxyl. The
proportion of isolates resistant to metalaxyl was already high (42.9 %), were (41.3
%) classified as intermediate resistant and (15.8 %) were sensitive to metalaxyl and
there is no genetic linkage between mating type and fungicide resistance.
. B.K.26.4.14 (which was came from Komhamada, Beheira governorate) was
significantly the most aggressive isolate for the pathogenicity test with an LSD (0.05)
(71.7%) followed by G.Z.11.7.14 (Kafr el-Zayat- Gharbia governorate) LSD (0.05)
(54.1%), M.M.2.13.14 (Menouf- Minufiya governorate) LSD (0.05) (44.2%).
8. When we tested the isolates sensitivity to metalaxyl, we found that B.K.26.4.14
isolate was resistant while G.Z.11.7.14 isolate was intermediate-resistant,
M.M.2.13.14 isolate was sensitive to metalaxyl, and this supported the results
obtained from the pathogenicity test.
9. Genotyping of 30 collected purified isolates were analyzed with twelve SSR
markers in a multiplex PCR. Results revealed that all Egyptian isolated belonged to
the European clonal lineage named 23-A1 and differences in allele sizes at 12 loci
discriminated 30 isolates to 16 sub clones.
10. 14 sub-clones out of the 16 discovered sub-clones were only excisted in Egypt and
Tunisia and hadn,t discover in any other location in the world (personalcommunication
with Prof. Dr. David E. L. Cooke through Shreif El-Ganainy),
which indicates that mutation rate in this lineage is high.
11. This sub- clonal lineage may have been generated under Egyptian pressure
selection conditions and we noticed that it is tolerant to high temperature because
there were many outbreaks observed in May while temperature ranged from 25-
32˚C. The findings in the current study widen our understanding of the diversity in
the 23-A1 lineage, which is critical in late blight disease management.
12. Santana tubers were significantly the most susceptible cv. with average of LSD (0.05)
(13.4%), while Cara tubers were significantly the most tolerant cv. With an average
(1.2%) and 23- A1- 40 isolate (from Gharbia governorate), was significantly the most
virulent isolate on tubers infection with an average (13.87%).
13. A collection of eight active ingredients that are belonged to different fungicide groups
were tested in vitro for their effect on the pathogen mycelium growth reduction. All
active ingredients treatments significantly reduced the mycelium growth. Cymoxanil
and propamocarb hydrochloride have the highest effect on the mycelium growth inhibition with an average of LSD (0.05) (6.7, 6.8%, respectively), while, fluazinam and
mancozeb have the less effect compared to other active ingredients used in this
experiment (LSD (0.05) 12.25, 12%, respectively).
14. Twenty-three fungicides were evaluated for their efficacy against late blight
disease under naturally infected field. All tested fungicides were able to reduce the
pathogen growth to different extents when applied them prior to the establishment
of infections (as protective treatments). Triomax was the most effective fungicides
with an average (LSD(0.05) 3.33%); while, Zignal and Nando have the less effect on
reducing the disease severity with an average (10.67, 10%, respectively).
15. No significant differences in the mean final late blight score among the contact
fungicides i.e., Manfil, Kopar, Koma and Kaiman, which disease severity score
ranged from 6.33 to 8.33% and mixtures of contact and trans-laminar active
ingredients reduced late blight severity more than contact fungicide with one active
ingredient.
16. We recommend that the perfect programme to reduce the losses resulted by this
disease especially after the current study had proved the presence of many isolates
adapted to unsuitable environmental conditions and developed resistance against
the used fungicides, so, we must take essential precautions before planting, plant
high tolerant cultivars such as Cara and Spunta and when the cultivated plants
reached 35-40 days, we must spray them with recommended fungicides as a
protective treatment before the establishment of the infections.