اثر تنش خشكي بر شاخصه هاي رشد و صفات مورفولوژيك دو اكوتيپ سير (.Allium sativum L) در تراكم هاي كاشت متفاوت

Effect of Drought Stress on Growth and Morphological Characteristics of Two Garlic (Allium sativum L.) Ecotypes in Different Planting Densities

كمبود آب يكي از مهم ترين عوامل محدود كننده رشد و عملكرد محصولات مي باشد. به منظور بررسي اثر تنش خشكي و تراكم كاشت بر شاخص هاي فيزيولوژيك رشد و صفات مورفولوژيك دو اكوتيپ سير (Allium sativum L.)، آزمايشي مزرعه اي به صورت اسپليت- فاكتوريل در قالب طرح بلوك هاي كامل تصادفي با سه تكرار در مزرعه اي واقع در جنوب شرقي شهرستان سمنان در سال زراعي 91-1390 اجرا شد. سه سطح تنش خشكي (100، 80 و 60 درصد نياز آبي)، به عنوان عامل اصلي و تركيب سطوح فاكتوريل شامل تراكم در سه سطح ( 30، 40 و 50 بوته در متر مربع) و اكوتيپ در دو سطح طرود و طبس به عنوان عامل فرعي در نظر گرفته شدند. حداكثر شاخص سطح برگ، حداكثر تجمع ماده خشك، حداكثر سرعت رشد محصول و حداكثر سرعت اسيميلاسيون خالص در شرايط 100 درصد نياز آبي به ترتيب برابر با 537/5، 53/387 گرم در متر مربع، 47/10 گرم بر متر مربع در روز و 92/4 گرم بر متر مربع برگ در روز بود كه اين مقادير با اعمال تنش خشكي در تيمار 80 درصد نياز آبي به ترتيب به طور معني داري به مقادير 745/3، 60/262 گرم در متر مربع، 31/6 گرم بر متر مربع در روز و 71/3 گرم بر متر مربع برگ در روز كاهش يافت. حداكثر سرعت رشد محصول در اكوتيپ طرود بيشتر از اكوتيپ طبس بود اما تعداد برگ و حداكثر تجمع ماده خشك در اكوتيپ طبس بالاتر بود. با اعمال و تشديد تنش خشكي، ارتفاع بوته در اكوتيپ طرود به طور معني داري كاهش يافت، اما اعمال و تشديد تنش، در ارتفاع اكوتيپ طبس تاثير معني داري نداشت. حداكثر سرعت رشد نسبي در اكوتيپ طبس در سطوح مختلف تنش خشكي تفاوتي نشان نداد، اما در اكوتيپ طرود با افزايش تنش در آبياري 60 درصد نياز آبي، افزايش معني داري در اين ويژگي مشاهده شد. اثر تراكم كاشت بر حداكثر شاخص سطح برگ، حداكثر تجمع ماده خشك، حداكثر سرعت اسيميلاسيون خالص معني دار بود. بيشترين مقدار حداكثر شاخص سطح برگ (017/5) و حداكثر تجمع ماده خشك (57/358 گرم در مترمربع) از تراكم 50 بوته در متر مربع حاصل گرديد. اعمال تنش خشكي، حتي در سطح خفيف تر آن و در مقدار آبياري 80 درصد نياز آبي، سبب كاهش بخشي از ويژگي هاي رشدي مورد ارزيابي گياه سير گرديد و در مجموع ويژگي هاي رشدي دو اكوتيپ در شرايط تنش بر ديگري برتري چشمگيري نداشت. تراكم كاشت بالاتر به سبب حضور سطح فعال فتوسنتز كننده بيشتر در واحد سطح، سبب افزايش تجمع ماده خشك در واحد سطح گرديد.

Introduction: Plants may be exposed to various stresses and water deficit is the most important limiting factor of growth and yield in many parts of the world and Iran. Stress induced growth decrement can be because of cell development decrease due to decrement of turgor pressure and meiosis and photosynthesis decrease due to stomata closure. Determination of desired planting density is one of the success factors of plant growth and production. Garlic (Allium sativum) has been an important medicinal plant over centuries in human life. According to the importance of medicinal plants and studying the effects of drought stress on them، the goal of this research is to investigate the effect of drought stress and planting density on growth and morphological characteristics of two ecotypes of garlic and determining the preferable ecotype and density from the perspective of these traits. Materials and methods: This experiment was performed in 2012 in a farm in south east of Semnan. It was conducted on a split-plot factorial arrangement based on randomized complete blocks design with three replications. Three levels of drought stress with 60، 80 and 100 percent of crop evapotranspiration (ETc) were the main plot factors and factorial combination of three planting density (30، 40 and 50 plants.m-2) and two ecotypes of Tabas and Toroud were the levels of sub plot factors. To estimate water requirement of garlic، daily measured meteorology parameters of Semnan synoptic station were used and water requirement was calculated based on FAO-56 instructions. From mid-January، the sampling of leaf area، bulb and leaf fresh and dry weight was started with destructive method every other week and continued until middle of Jun. three plant were selected randomly from each plot in each turn. From middle of May، height and number of leaves were measured. Leaf area measurement was done by leaf area meter (Delta-T). To estimate growth indices، dry weight of aerial and underground organs and leaf area from measured samples of treatments were used. Results and Discussion: The results showed that the highest value of maximum leaf area index (LAI)، maximum total dry matter accumulation (TDM)، maximum crop growth rate (CGR) and maximum of net assimilation rate (NAR) were observed at 100% ETc with the value of 5.537، 387.53 gr.m-2، 10.47 gr m-2day-1 and 4.92 gr.m-2leaf.day-1 respectively; and by applying the irrigation treatment of 80% ETc these values decreased to 3.745، 262.60 gr.m-2، 6.31 gr.m-2day-1 and 3.71 gr.m-2leaf.day-1 respectively. Drought stress can decrease cell development and division and plant photosynthesis، and thus، it can decrease leaf area index and consequently decrease light absorption، photosynthetic area، dry matter and crop growth rate. Difference between ecotypes in terms of number of leaves، maximum total dry matter accumulation and maximum crop growth rate was significant. Maximum crop growth rate (CGR) in Toroud ecotype was higher than Tabas ecotype but number of leaves and maximum concentration of total dry matter (TDM) in Tabas ecotype were higher than corresponding values in Toruod ecotype. The effect of planting density on maximum leaf area index (LAI)، maximum total dry matter (TDM) and maximum net assimilation rate (NAR) was significant. The highest value of maximum leaf area index (5.017) and maximum total dry matter (358.57 g.m-2) concentration were obtained from 50 plant.m-2 density. The highest value of maximum net assimilation rate (4.61) was obtained from 30 plant.m-2 density. It could be because of having leaves exposed to more light and less shading. Conclusion: Applying drought stress at the irrigation treatment of 80% ETc decreased studied growth characteristics of garlic. Therefore، it is recommended that garlic should be avoided from facing drought stress and its water requirement must be met as much as possible. In general، under drought stress، two studied ecotypes did not have any preference related to the studied growth characteristics. Higher planting density، due to higher active photosynthetic area over unit area، increased the dry matter in unit area.