237 Yüzüncü Yıl Üniversitesi Tarım Bilimleri Dergisi (YYU Journal of Agricultural Science) http://dergipark.gov.tr/yyutbd Research Article (Araştırma Makalesi) Effects of Endophytic Bacteria on Some Physiological Traits and Nutrient Contents in Pepper Seedlings under Drought Stress** Aynur SADAK 1* , Ahmet AKKOPRU 2 , Suat SENSOY 3 1,3 Horticulture Sci., Institute of Natural Sciences, Van Yuzuncu Yil University, 65080 Van, Turkey 2 Department of Plant Protection, Agriculture Faculty, Van Yuzuncu Yil University, 65080 Van, Turkey 3 Department of Horticulture, Agriculture Faculty, Van Yuzuncu Yil University, 65080 Van, Turkey 1 https://orcid.org/0000-0002-5865-6497 2 https://orcid.org/0000-0002-1526-6093 3 https://orcid.org/0000-0001-7129-6185 Corresponding author's e-mail: aynuursadak@gmail.com Article Info Received: 29.12.2020 Accepted: 27.02.2021 Online Published 30.03.2021 DOI: 10.29133/yyutbd.849260 Keywords Drought, EB, Enzyme activity, Growth, Mineral matters, Pepper. Abstract: The present study was conducted to determine the effects of the endophytic bacteria (EB) on some physiological traits and nutrient contents in pepper (Capsicum annuum L.) seedlings grown under drought stress. The pepper cv. Mostar F1 and two EB isolates [Bacillus thurigiensis (CA41/1) and Ochrobactrum sp. (CB36/1)] were employed under drought stress condition. The first EB application was at a density of 10 8 CFU mL -1 as 10 mL plant -1 at the first cotyledon leaf stage and the second one was two weeks later. The seedlings were irrigated by gravimetric method on a regular basis every two days. Twenty days after EB application, irrigation was terminated completely in half of the applications in order to form drought stress for 7 days. Among the studied traits, membrane damage index, leaf relative water content, amount of malondialdehyde, catalase enzyme activity, ascorbate peroxidase enzyme activity, and the contents of some mineral elements (K, Ca and Mg) were significantly different in drought stressed seedlings compared the control (regularly irrigated) seedlings. EB (Especially CA41/1) had generally positive effects on most studied traits, whereas drought stress had generally negative effects on the mentioned traits. There might be a high potential of EB fighting against drought stress in pepper; however, one keeps in mind that there is variation in the performance of EB; therefore, the best EB combinations have to be determined even for cultivars in each plant species in future studies. Endofitik Bakterilerin Kuraklık Stresi Altındaki Biber Fidelerinin Bazı Fizyolojik Özellikleri ve Besin İçerikleri Üzerine Etkileri Makale Bilgileri Geliş: 29.12.2020 Kabul: 27.02.2021 Online Yayınlanma 30.03.2021 DOI: 10.29133/yyutbd.849260 Anahtar kelimeler Biber, EB'ler, Enzim aktivitesi, Büyüme, Öz: Bu çalışma, kuraklık stresi altında yetiştirilen biber (Capsicum annuum L.) fidelerinde endofitik bakterilerin (EB) bazı fizyolojik özellikler ve besin içerikleri üzerine etkilerini belirlemek amacıyla yapılmıştır. Mostar F1 Biber çeşidi, iki EB izolatı [Bacillus thurigiensis (CA41 / 1) ve Ochrobactrum sp. (CB36 / 1)] kuraklık stresi altında kullanılmıştır. İlk EB uygulaması, ilk kotiledon yaprağı aşamasında 10 mL/bitki olarak 10 8 CFU/mL yoğunlukta ve ikincisi ise iki hafta sonra yapılmıştır. Fideler, iki günde bir düzenli olarak gravimetrik yöntemle sulanmıştır. EB uygulamasından yirmi gün sonra, 7 günlük kuraklık stresi oluşturmak için uygulamaların yarısında sulamaya tamamen son verilmiştir. Çalışılan özellikler arasında, kuraklık stresi altındaki fidelerde kontrol (düzenli olarak sulanan) fideler ile karşılaştırıldığında, membran zararlanma indeksi, yaprak oransal su içeriği, malondialdehit miktarı, katalaz enzim aktivitesi, Yuzuncu Yil University Journal of Agricultural Science Volume 31, Issue 1, 30.03.2021