Altitudinally gradient -defined specific environmental conditions of Ziziphus spina Christi population in Aseer region could lead to genetic variations among population for adaptations, which in turn may affect metabolic pathway governing the plant phenotypic variations, chemical compound content and activity against pathogens, etc. To the best of our knowledge, no databases were found for the degree of genetic diversity of Z. spina-christi plants associated with altitudinal gradients. This study examined the degree of variations in deoxyribonucleic acid (DNA) polymorphism, leaves chemical compositions, antibacterial activities of various leaves extract against some human pathogenic bacteria for five natural populations of Z. spina-christi along an environmental and altitudinal gradient in Aseer Mountain, Saudi Arabia. The study area have been classified into five zones based on elevation above sea level, namely, low (Al-marbh population at 147 m), moderate (Raheb Valley population at 505m), high (Rakhma Valley population at1000 m and Dala Valley at1424 m) and very high (Abha population at 2227 m). The degree of genetic variability among the five populations was evaluated by random amplified polymorphic DNA (RAPD) and intersimple sequence repeats (ISSR) markers. The genetic similarity by...