Thesis (Ph.D)-Cairo University, 2025.

Bibliography: pages 139-156.

The apple (Malus domestica) is a fruit that is cultivated extensively and has
significant economic value worldwide. Soil salinization and drought consider to be
major threats to apple production in some regions. The study aimed to facilitate the
detection and selection of salt and drought stresses tolerance in apple (Malus domestica)
seedling clones through tissue culture technique. Open pollinated mature seeds of local
Egyptian ‘Balady’ apple were collected from ripped fruits of one tree and used as
establishment plant materials. Every surface-sterilized seed was cultivated
independently and assigned a distinct serial number. None of the micro-propagated
individuals was typically as compared to each other or with the mother-plant according
to similarity indices based on Inter Simple Sequence Repeats (ISSRs), where the most
dissimilar genotype to the mother-plant was MS5 represents 84.9% similarity. After
three consecutive subcultures, salt stress was achieved by adding different
concentrations of NaCl (0, 1000, 2000 and 3000 ppm) to the proliferation medium,
while stimulated drought stress by adding different concentrations of mannitol (0, 50,
100, 150 and 200 mM). The MS5 clone maintained relatively higher number of shoots,
average shoot height and fresh weight together up to 3000 ppm NaCl comparing to
other tested clones which indicated the superiority of MS5 clone under severe salt stress
conditions. A specific positive marker of 290 bp by HB12 ISSR exclusively detected in
the most salt-tolerant MS5 clone may support early selection for salinity tolerance. The
most salt-tolerant MS5 clone was characterized by the least average of reducing sugars
and total phenols accompanied by the minimum overall antioxidant activity, with
stimulated activities of superoxide dismutase (SOD), peroxidase (Px) and catalase
(CAT) antioxidative enzymes over control as affected by elevated salt concentration up
to 3000 ppm NaCl. Data of three common differentially expressed genes (DEGs)
revealed that, protein phosphatases PP2C-77a and ABA insensitive transcription factor
ABI5-5b were downregulated while serine/threonine-protein kinase SAPK3 was
overexpressed in MS5 genotype under severe salt stress conditions. The MS18 clone
was the most adversely affected by osmotic stress induced by mannitol additives
indicating its sensitivity to drought stress compared to other clones which responded to
drought at varying levels. Also, it was the most susceptible clone under saline
conditions, which indicates potential overlapping tolerance pathways of both
dehydration and salinity abiotic stresses. The study confirmed the viability of in vitro
screening for salt- or drought-tolerant genotypes within apple seedling populations.

باستخدام تقنية زراعة الأنسجة جمعت بذور ناضجة ملقحة تلقيحا حرا لتفاح "بلدي" المصري المحلي (Malus domestica) من ثمار شجرة واحدة واستخدمت كمواد نباتية تأسيسية. زُرعت البذوروتم تعيين رقم تسلسلي مميز لها. ولم تتماثل الأفراد المتكاثرة بدقة مع بعضها أو مع النبات الأم وفقًا لمؤشرات التشابه القائمة على التكرارات التسلسلية البسيطة (ISSRs)، و ثبت جدوى الفحص المختبري لتحمل الجفاف، ووجود نمط جيني عالي التحمل للملوحة بين شتلات التفاح. و امكان استخدام الفحص المختبري للجينات عالية التحمل لصفتي الملوحة و الجفاف بين مجموعات شتلات التفاح لانتاج شتلات تتحمل ظاهرتي الاجهاد البيئي الملوحة و الجفاف.

Issues also as CD.

Text in English and abstract in Arabic & English.