U. Ü. ZİRAAT FAKÜLTESİ DERGİSİ, 2017, Cilt 31, Sayı 2, 139-155 (Journal of Agricultural Faculty of Uludag University) Araştırma Makalesi Effect of Plant density and Bio–Fertilizer on some morphological traits, seed yield and Yield Components of Sunflower (Helianthus annus L.) Abdo B. FAKIRAH 1* , Mansoor A.H. AL-THOBHANI 2 , Mansour Mohmed AL-AQIL 3 1 Department of Agronomy and Pastures, Faculty of Agriculture, Sana'a University 2 Department of Horticulture and Forestry, Sana'a University 3 Chairman of Agricultural Research and Extension Authority * e-posta: ab.fakirah@yahoo.com Geliş Tarihi: 21.04.2017; Kabul Tarihi: 15.07.2017 Abstract: This study was carried out at the research farm, faculty of Agriculture Sana'a University during growing seasons of 2012 and 2013. The objectives were to study the effect of two plant densities (5.55, 11.11 plant m 2-1 ) and three levels of Bio-fertilizer fertilization (0, 2, 4 liter ha -1 ) and on the seeds yield, and it's components of Sunflower plant (Cultivar Euroflor). Experimental results showed variation of plant density effect on examined characters. Head seeds weight and seeds oil content (%) significantly higher with lower plant density (5.55 plant m 2 ) -1 during first and second seasons, respectively, while higher plant density (11.11 plant m 2 ) positively and significantly influenced on seeds oil % and seeds oil yield during 2012 season. The results showed that the 4 L ha -1 Bio-fertilizer level significantly exceeded other Bio-fertilizer concentrations (0 and 2 L ha -1 ) in its effect on seeds yield, head seeds weight, seeds number/plant, head diameter, seeds oil % and seeds oil yield during first season (2012). During second season (2013), the 4 L ha -1 Bio-fertilizer level also surpassed the other levels on each of weight of 1000 seed, leaves number/plant and seeds oil %. Significant interaction between Bio-fertilizer and plant density levels was observed on seeds oil % through first and second seasons. On other studied characters, except plant height, there were interactions only during the first season (2012). Keywords: Sunflower plant, Bio-fertilizer, plant density, Yemen. 139