چكيده فارسي :
بمنظور بررسي اثر تأخير در كاشت برخصوصيات زراعي و ميزان افت عملكرد دانه كلزا در مازندران، ده ژنوتيپ كلزا در قالب طرح بلوك‌هاي كامل تصادفي در دو آزمايش جداگانه شامل شرايط مطلوب (25 مهرماه) و كشت تأخيري(25 آبان ماه) طي دوسال زراعي 92-1390 در ايستگاه تحقيقات زراعي بايع كلا مورد ارزيابي قرار گرفتند. در اين مطالعه مراحل فنولوژيك، ارتفاع بوته، اجزاي عملكرد و عملكرد دانه مورد ارزيابي قرار گرفتند. ژنوتيپ هاي مورد بررسي از نظر كليه صفات به استثناء وزن هزاردانه در تاريخ كاشت مطلوب داراي تفاوت ژنتيكي معني‌داري بودند. تأخير در كاشت منجر به كاهش معني‌دار تمامي صفات مورد بررسي به استثناء وزن هزار دانه شد. در بين مراحل فنولوژيك، بيشترين و كمترين افت ناشي از تأخير در كاشت به ترتيب مربوط به طول دوره گلدهي و تعداد روز تا رسيدگي بود. ميزان افت تعداد خورجين در بوته و عملكرد دانه نيز به ترتيب برابر 0/23 و 0/38 بود. همبستگي مثبت و معني‌دار عملكرد دانه با صفات تعداد روز تا شروع گلدهي و تعداد خورجين در بوته در هر دو تاريخ كاشت نشان دهنده آن است كه تغيير در صفات مزبور نقش بارزي در عملكرد دانه خواهد داشت. در اين بررسي ژنوتيپ‌هاي ظفر (G10)، Zabol-0 (G2) و (Safi6 (G5 به ترتيب با عملكرد دانه 3142/3، 2979/4 و 2967/3 كيلوگرم در هكتار در شرايط كاشت مطلوب و همچنين 1890/2، 1905/7 و 1784/7 كيلوگرم در هكتار در شرايط كشت تأخيري از عملكرد دانه بالايي برخوردار بوده و در هر يك از دو تاريخ كاشت در گروه آماري يكسان قرار گرفتند.
چكيده لاتين :
Introduction: Rapeseed (Brassica napus L.) is considered to be one of the important oil crops that possess a balanced fatty acid composition. All crop physiological functions are affected by day length, temperature and other environmental factors that are collectively influenced by planting date, which in turn impacts yield and yield components (Rameeh, 2014). The potential yield of rapeseed is determined at flowering stage, which indicates that there is a relationship between vegetative phase prior to flowering stage and potential flower production as well as yield components (Mendham et al., 1981). Determining a suitable planting date plays an important role in the co-occurrence of plant growth stages with the desired environmental conditions, which can result in maximum yields. This means that the coordination of plant growth and optimal environmental conditions can be achieved if the possibility of the occurrence of unfavorable environmental conditions such as freezing or drought is minimized from flowering till maturity stage, and favorable conditions i.e. solar radiation, temperature and humidity reach their optimum when plant is at pod and grain formation stages (Whitfield, 1992). Delayed sowing of rapeseed causes the reproductive stage to coincide with high environmental temperatures, resulting in the increased respiration of the photosynthetic organs, which consequently leads to decreased photosynthetic reserves, reduced grain weight and eventual decline in the yield. Coffelt and Adamsen (2005) showed that the delayed planting of spring rapeseed shortened the length of time required for vegetative and reproductive growth, leading to reduced grain yield. The aim of this study was to evaluate the effects of late planting on phonological stages and yield components and thus ultimate yield of newly released rapeseed lines under Mazandaran climatic conditions. Materials and Methods: Ten rapeseed genotypes were studied based on a ran domized complete block design in two separate experiments at two planting dates including optimum (16 Oct.) and late (15 Nov.) planting dates during the years 2011-2013 at Baykola Agriculture Research Station. The rapeseed genotypes consisted of 9 promising lines; G1: RGS003 ،G2 :Zabol ،0-G3 :Zabol،15-G4 :Safi7، G5 :Safi6 ، G6 :Safi5، G7 :Safi31 ،G8 :S8-401 ،G9:L7 along with the local variety Zafar( G10 )as check .Zafar and RGS003 are the most prevalently grown genotypes in the region .The other genotypes were the F6 generation from the domestic breeding .Each experimental plot comprised 4 rows of 5 cm long and 30 cm apart. The phonological stages measured for each genotype throughout the growing season included days from planting to flowering initiation and termination ,flowering duration and days to physiological maturity .To determine plant height and yield components ,ten plants were randomly selected from each plot and then average height of plant ,number of pods per plant ,number of grains per pod and-1000 grain weight were recorded .To measure grain yield ,plants were harvested from a two square meter area of two middle rows of each sub -plot after eliminating edge rows as margin effects .The grain yield was transformed to kg ha-1. Following combined analysis of variance, the means comparison was performed using the least significant difference (LSD) test. All statistical analyses were carried out using SAS software (SAS Institute INC., 2004). Results and discussion: The results revealed that the effects of year, planting date and genotypes were significant, demonstrating that the measured traits were responded differently to the variations in the experimental factors. The significant interaction effect of year x genotype was indicative of the extent of the changes in the studied traits over two years of the experiment. The ranks of genotypes for the experimental traits were similar over the 2-year period of the study (Table 1). Days to flowering initiation amongst the genotypes at the optimum planting date varied from 121.6 to 131 days, which respectively belonged to G9 and G10 genotypes. The variation in this trait at the delayed planting date for these genotypes was from 103.7 to 109.8 days (Table 2). Delaying planting date by one month caused a significant reduction in days to flowering initiation which averaged from 18.5 to 0.15 days across the genotypes (Table 3). These results are in agreement with those of Shirairad et al. 2014 who showed that late cropping was associated with the accelerated flowering initiation and the reduced days to flowering as well as the decreased days from flowering to maturity in winter rapeseed. The positive significant correlation of days to flowering initiation with plant height, number of pods per plant and 1000-grain weight at the optimum planting date showed that increased number of days till flowering enhanced plant vigor and produced higher yield components (Table 6). Grain yield was positively correlated with days to flowering initiation and number of pods per plant at both planting dates, indicating that any variation in these traits produced considerable effects on grain yield. In this study, under optimum and delayed planting conditions, Zafar (G10), Zabol-0 (G2) and Safi6 (G5) had high mean values of grain yield and were therefore classified in the same statistical group at both planting dates (Table 4). Conclusion: In general, delaying planting date by one month led to significant reduction in all the experimental traits except for 1000-grain weight. Of the phonological stages, the most and least affected traits were, respectively, flowering duration and days to maturity. Among the yield components, a positive significant correlation was found between pods per plant and grain yield, reflecting the importance of pods per plant in determining yield. Keeping in view the fact that plant height and most of the yield components were depressed as a result of the late planting, average yield of the investigated genotypes decreased by 1021 kg/ha-1 or 38 % relative to the optimum planting date.
