ارزيابي واكنش عملكرد و اجزاي عملكرد ژنوتيپ‌هاي گندم نان (.Triticum aestivum L) نسبت به تاريخ كاشت به‌موقع و ديرهنگام

Evaluating the response of yield and yield components of bread wheat (Triticum aestivum L.) genotypes to normal and late seeding dates

افزايش عملكرد در گندم مستلزم شناخت روش‌هاي مديريتي مناسب است. از جمله مهم‌ترين آنها معرفي ارقام جديد و تاريخ كاشت مناسب مي‌باشد. به منظور مطالعه واكنش عملكرد و اجزاي عملكرد گندم نان نسبت به دو تاريخ كاشت به موقع و ديرهنگام آزمايشي در ايستگاه تحقيقات كشاورزي گرگان وابسته به مركز تحقيقات كشاورزي و منابع طبيعي استان گلستان در سال زراعي 1394-1395 انجام شد. اين بررسي در دو آزمايش جداگانه انجام شد. هر آزمايش در سه تكرار شامل نه ژنوتيپ گندم بود. آزمايش اول در تاريخ 15 آذر (به موقع) و آزمايش دوم 15دي (ديرهنگام) بود. نتايج تجزيه واريانس نشان داد كه اثرات تاريخ كاشت بر روي ارتفاع بوته، روز تا گلدهي، روز تا رسيدگي، تعداد سنبله در مترمربع، عملكرد دانه، عملكرد بيولوژيك و شاخص برداشت معني‌دار بود. همچنين اثرات متقابل تاريخ كاشت × ژنوتيپ‌هاي مورد بررسي بر روي همه صفات مورد بررسي معني‌دار گرديد. نتايج نشان داد كه با تأخير در كاشت ميانگين درجه روز رشد تجمعي از كاشت تا رسيدگي فيزيولوژيكي كاهش يافت به طوري كه در تاريخ كاشت به موقع 2283 درجه-روز رشد دريافت نمود كه اين درجه روز رشد توانست 3783 كيلو گرم در هكتار دانه توليد كند. تاريخ كاشت دوم مقدار 697 درجه روز رشد كمتر دريافت كرد و كاهش ماده خشك به ازاي هر روز تأخير در كاشت 57/1 كيلو گرم در هكتار بود. بررسي عملكرد دانه نشان داد كه بيشترين عملكرد دانه (3784 كيلوگرم در هكتار) در همه ژنوتيپ هاي مورد بررسي از تاريخ كاشت به موقع (15 آذرماه) به دست آمد و همه ژنوتيپ هاي مورد بررسي در هر دو تاريخ كاشت از نظر عملكرد دانه بالاتر و يا هم رديف (در يك گروه آماري) با رقم شاهد (گنبد) قرار گرفتند.

Introduction: According to the latest statistics by the Ministry of Jihad-e- Agriculture of Iran (2016), the total cultivation area for crops in Iran is 11.3 million ha, of which, 8.17 million ha are dedicated to cereal production where wheat has a share of 63.17 % and the total land area under wheat cultivation in Golestan province is 357 thousand ha. Seeding date is one of the most important management factors in determining yields of crop plants. The purpose of the selection of suitable seeding dates is to find a time period during which the favorable environmental conditions for crop emergence, establishment and vegetative development are pervasive and none of these stages are faced with unfavorable environmental conditions (Khajehpour, 2001). Planting date, particularly in areas with environmental constraints such as extreme mid-summer heats, and early or late season cold snaps, is an important decision-making management consideration in crop production. Often with a change in planting date, ambient and soil temperature will vary, which in turn can cause different plant responses at various growth stages (Tomar et al., 1993). As previously stated, Golestan province is a major cultivation area for bread wheat and the introduction of new cultivars is of the research priorities in the province. Thus, this experiment was conducted to assess the response of yield and grain yield components of bread wheat promising lines to normal and delayed seeding dates. Materials and Methods: The investigation was carried out at Gorgan Agricultural and Natural Resources Research and Education Center in 2015-2016 growing season as two separate experiments based on completely randomized block design. The first experiment was the normal seeding date (December 6th, 2015) of 8 wheat promising lines along with Gonbad cultivar as check. The second experiment was the late seeding date (January 5th, 2016) of the same lines and check cultivar. Seeding rate in all experimental plots was 350 seeds/m2. The plot area was 7.2 m2 and consisted of six rows of 6 m long and 20 cm distance among rows. The plants were supplied with adequate rates of fertilizers based on the soil analytical results in the both experiments. Among the measurements included in this study were growing degree days (GDD), yield components, harvest index, days to anthesis and physiological maturity.Results and Discussion: The results of analysis of variance showed that the effects of seeding date were significant on plant height, days to anthesis, days to physiological maturity, number of spike/m2, grain yield, biomass and harvest index. Also the interaction effects of seeding date × genotype were significant in the all investigated traits (Table 4). The delayed cropping was associated with the increased minimum and maximum air temperature (Table 2), which resulted in decreased days to anthesis and maturity (Table 5). The greatest grain yield reduction was observed at late seeding date (Table 6). Since late seeding encountered long and hot summer days, conducive time period for the vegetative growth of wheat shortened as compared to normal planting, leading to decreased plant height. The rise in plant height at normal or early planting dates could be explained by the enhanced allocation of nutrients to shoot since the time period for plant growth is increased under these sowing conditions (Rabiee, 2015). With delay in seeding date, average accumulated GDD from sowing to physiological maturity decreased. Under normal planting date with an average air temperature of 14 °C, the GDD accumulation was 2283, and as a result, the wheat cultivars were able to produce 13659 kg. ha-1 of dry matter and 3783 kg. ha-1 of grain yield. In contrast, under late planting date with an average air temperature of 11 °C, 1856 GDD were accumulated, which led to the production of 6521 kg. ha-1 of dry matter and 2070 kg. ha-1 of grain yield by the wheat plants. This indicates that late planting accumulated 697 less GDD than normal planting, which resulted in a decline of 1713 kg. ha-1 in dry matter production. Normal planting date produced the highest grain yield (3784 kg. ha-1). The wheat cultivars under both late and normal planting conditions were classified in the same statistical group as check (Gonbad) in terms of grain yield performance.