الفهرس 
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Abstract
Potato (Solanum tuberosum L.) is the fourth most important food crop worldwide after wheat, maize, and rice. 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. Many factors can limit the production. One of the most important factors is late blight disease that caused by the oomycete pathogen Phytophthora infestans. During favorable conditions, the pathogen can wipe out all entire plants in the field in a few days resulted 100% yield losses. The current study was summarized in the followings:
1- The initial symptoms of late blight disease observed during period of this study in 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 six governorates during 3- year period 2010-12. These governorates were Minufiya (Menouf, Tamaly, Hamoul, Kamshoch, Nader, Fesha, Gezie, Shama, Shanshour, Teta, Barheem, and Alkam), Beheira (Elbostan, Al-Busayli, Komhamada, Markzbadr, Nubariya, and Tawfykia), Gharbia (El-Mahalla El-Kubra), Kafr el-Sheikh (Sakha), Qalubiya (Elkanater and Kaliob ) and Dakahliya (Shirbin).
3- During growing season of 2009/10, 2010/11, and 2011/12 a total of 53, 61, and 91 isolates of phytophthora infestans have been isolated respectively from infected potato samples.
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4- Mating type testing of each isolate showed that 57% of the isolates belonged to mating type A1, 35% belonged to mating type A2 and the rest 8% were self-fertile.
5- Response to metalaxyl was determined for 96 isolates in vitro on pea agar amended with 5 and 100 ppm metalaxyl. All A2 and S.F isolates were resistant (R) to metalaxyl while most of A1 isolates were sensitive to metalaxyl and some of A1 isolates were intermediately resistant.
6-Three different genotypes of phytophthora infestans belonged to the two dominant clones in Egypt were chosen for the evaluations of late blight resistance of thirty three commercial potato cultivars under green house conditions. The tested cultivars were Faluka, Arnova, Agria, Sofia, Arika, Zafira, Picasso, Provento, Fontana, Markies, Nieta, Lady Rossetta, Germindin, Seniora, Monak, Excellent, Stirling, Ditta, S.w, Kuroda, Diamant, Marijke, Mustang, Festival, Sante, Spunta, Armada, Ambition, Taloka, Cara, Billini, Valor, and Nicola. Results obtained revealed the followings:
(A)- Both isolates EG_5 and EG_76 were virulent on the 33 tested cultivars but differ in their aggressiveness while isolate EG-44 was not virulent on Zafira, Provento, Excellent, Srtirling, S.W, Kuroda, Sante, Cara, Billini, and Valor.
(B)- The most aggressive isolate was EG-76 then EG-5. Potato cultivars that may have general partially resistance to virulent isolates were Cara, Valor, Billini, Sante, Marijke, Kuroda, S.w, Ditta, Stirling, Excellent, and Nieta. Potato cultivars that showed moderately resistance were Fontana, Picasso, Arika, Markies, Monak, Provento, Zafira, Arnova, Ambition, and Taloka. The lowest resistant cultivars were Faluka, Diamant, Seniora,
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Germindin, Mustang, Nicola, Sofia, Lady Rossetta, Festival, Spunta, and Agria.
7- Virulence profiles of two different isolates, EG-96 (13-A2-84) which is the A2 dominant genotype in Egypt and EG-75 (23-A1-18) which is the A1 dominant genotype in Egypt were tested on 11 set of differential potato lines which each line in this set carried one known R gene and the cultivar Craig’s Royal that has no known R gene was used as a positive control.
8- Results obtained revealed that isolate EG-96 (13-A2-84) was virulent on the leaflets of 12 differentials. On the other hand, virulence profile was 1, 2, 3, 4, 5, 6, 7, 10, and 11 on whole plant. EG-75 (23-A1-18) Virulence profile was 1, 3, 4, 7, 10, and 11 in Detached leaflets and In whole plant was 1, 3, 4, 7, and 11. This means that R10 only triggered immunity in whole plant but it wasn’t able to recognize the pathogen invasion in detached leaflets
9- Late blight resistance of fourteen commercial potato cultivars was evaluated under naturally infested field. Initial symptoms were observed on Agria, Mondial, Spunta, Hermes, Markies and Lady Rosetta at the plant age of 40 days in January, 2012 where the weather conditions were favorable for the disease epidemic infection. At the end of season the least value of disease severity was observed in Cara, Valor, and Billini. AUDPC for Valor was close to AUDPC for Care and Burren and the highest value of AUDPC was recorded with cv. Mondial.
10- Twenty one fungicides were evaluated for their efficacy against late blight disease. The tested fungicides were Alectis, Rado Elnasr,
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Flash, Medomil, Triomax, Prove, Dithane M 45, Revus Top, Primozeb, Manfil, Winner, Rival, Chemotrobin, Achromorf MZ, Kastro, Metalman, Shirlan, Novicure, Protect Pro, Infinito, and Ranman. Results obtained revealed that all fungicidal treatments significantly reduced the incidence of foliage blight compared with the untreated control except Protect pro which foliar blight severity dramatically rose to 72%. Fungicides that contain mixtures of active ingredients were superior to other fungicides which contain only one active ingredient and Mixture of contact and translaminar active ingredients recued blight incidence more than contact fungicide with one active ingredient.
11- Genotyping of 85 collected purified isolates with 15 reference isolates were analyzed with twelve SSR markers in a multiplex PCR. Genotyping generated a dendrogram with two main clusters.
(A)-The first cluster contained the European lineage Blue13. Twenty one of isolates which belonged to this clone were A 2 and 8 isolates were self fertile. 3 distinct sub-clonal lineages were observed within this clone. 13_A2_5 and 13_A2_43 were first observed Netherlands and Germany in 2004 and then spread across North Western Europe and into North Africa. Dominant in Great Britain in 2006-09. Proven to be aggressive and fully resistant to metalaxyl. The third sub-clonal lineage, 13_A2_84 contained a new allele combination at Pi02 locus (266-272). This sub- clone was first observed in Egypt from 2010.
(B)- The second cluster contained all isolates which belong to 23-A1 Southern European lineage. First observed in Great Britain in 2007
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particularly prevalent on tomatoes in Italy and Greece and then spread to North – Europe possibly on small tomato plants. It is sensitive to intermediate resistance to metalaxyl. Ten sub- clonal lineages were detected in Egypt 23_A1_4, 23_A1_10, 23_A1_12, 23_A1_13, 23_A1_14, 23_A1_15, 23_A1_16, 23_A1_17, 23_A1_1, and 23_A1_19.
(c)- An unrelated isolate (EG-6) was detected with three alleles at loci Pi63 and SSR6. The D13 118 bp allele and SSR6 242 bp noted in this ‘misc’ isolate weren’t detected in two dominant Egyptian lineages. The origins of this isolate are not known but it may have been generated by sexual recombination.
12- Eighteen Egyptian isolates were screened for the presence or absence of five effector genes which condition the susceptibility or resistance of hosts with known R-genes. The PCR amplified effectors were sequenced to examine their function in more detail. Results obtained revealed the following:
(A)- The Avr1 and Avr2 genes were absent in 13-A2 isolates. Unexpectedly, in one 13-A2 isolate (EG-96) the avr2 gene amplified and showed similarities to the avr2-like gene with many SNPs discriminating the two sequences. Two non- silent SNPs and one silent SNP were observed in avr1 compared with the reference isolate T30-4. No SNPs were seen in avr2 except isolate EG-96 which had twenty five SNPs, ten of them were silent SNPs.
(B)- The Avr2-like was present in all testes isolates but absent in reference isolate T30-4. Thirty SNPs were detected, eight SNPs were silent.