تاثير تنش كمبود آب بر برخي از صفات فيزيولوژيك و مورفولوژيك آفتابگردان در تراكم هاي مختلف كاشت

Effects of Drought Stress on some Physiological and Morphological Characteristics of Sunflower (Helianthus annuus) at Different Planting Densities

This study was aimed to investigate the effects of drought stress on some physiological and morphological characteristics of two sunflower (Helianthus annuus) hybrids at different planting densities. Treatments were arranged in the form of a split factorial by randomized complete block design with three replicates. It was conducted at the Research Farm of the Tabriz Azad University in 2006. Experimental treatments consisted of two sunflower hybrids (Record and Azarghol) and four levels of the drought stresses (100%, 75%, 50%, 25% available moisture) and three levels of densities (80, 90 and 100 thousand plants ha-1). Stress was based on different levels of available moisture, and planting densities. The between row spacing was 60 cm and with in row spacing where 16, 18 and 20 cm for the three planting densities respectively. Results indicated that drought stress led to a significant decline in the number of seeds on the head, kernel weight, empty seed percentage, leaf area index (LAI), leaf relative water content (RWC) and harvesting index (P<0.01). Based on the correlation between attributes and seed yield, it was found that reduction in the value of aforementioned characteristics resulted in the decline of seed yield per plant. The results, also showed that under the stress of 75% available moisture, cultivars under study had the highest number of seeds on the head, while under the stress of 25% available moisture had the least empty seed percentage. Record had the highest harvest index under the stress of 25% available moisture at 80 thousand plants h-1 and Azarghol had the least harvest index under the stress of 50% available moisture at 100 thousand plants h-1(P<0.01). It was also revealed that increasing drought stress resulted in increased stomatal resistance in these two cultivars. Azarghol at 90 thousand plants h-1 and Record at 80 thousand plants h-1 demonstrated the highest seed yield per plant, respectively(p<0.01).