اثرات تنش خشكي بر مراحل رويشي و زايشي در هيبريدهاي جديد ذرت دو منظوره

Effects of Drought Stress on Vegetative and Reproductive Stages of Forage and Kernel Corn Hybrids

به‌منظور بررسی اثر تنش خشكی بر مراحل رویشی و زایشی بر 14‌هیبرید ذرت، آزمایشی به‌صورت كرت های خردشده در قالب طرح بلوك‌های كامل تصادفی با سه‌تكرار در مزرعه پژوهشی موسسه تحقیقات اصلاح و تهیه نهال و بذر كرج طی سال 1388 اجرا‌گردید. عامل اصلی شامل سه‌سطح آبیاری نرمال، تنش ملایم و تنش شدید (به‌ترتیب آبیاری پس از 70، 100 و 130‌میلی‌متر تبخیر تجمعی از تشتك‌تبخیر كلاسA ) و عامل فرعی نیز شامل 14‌هیبرید ذرت شامل 11‌هیبرید جدید و سه‌هیبرید شاهد (KSC704, KSC720, KSC700) بود. در این آزمایش عملكرد دانه در هكتار، عملكرد علوفه خشك در هكتار، تعداد روز تا زمان گرده‌افشانی، تعداد روز تا ظهور تارهای ابریشمی، فاصله زمانی گرده‌افشانی تا ظهور كاكل، طول بلال، قطر بلال، تعداد بلال در بوته، تعداد دانه در ردیف و تعداد ردیف دانه در بلال اندازه‌گیری و محاسبه شد. نتایج نشان‌داد كه تفاوت هیبریدها از نظر تعداد روز تا گرده‌افشانی، تعداد روز تا ظهور تارهای ابریشمی و فاصله زمانی گرده‌افشانی تا ظهور كاكل، طول بلال و تعداد ردیف دانه در بلال در سطح احتمال یك‌درصد و در تعداد ردیف دانه در بلال و عملكرد علوفه خشك در سطح احتمال پنج‌درصد معنی‌دار بودند، در‌حالی‌كه بین هیبریدهای مورد‌مطالعه اختلاف معنی داری از لحاظ عملكرد دانه، تعداد بلال در بوته و قطر بلال مشاهده نگردید. اثر متقابل هیبرید و رژیم های آبیاری به‌جز طول بلال برای هیچ‌یك از صفات دیگر معنی‌دار نبودند كه بیان‌گر واكنش مشابه هیبریدهای مورد‌مطالعه نسبت به شرایط رژیم های آبیاری اعم الشده می‌باشد هم‌چنین كلیه صفات مورد‌بررسی به‌جز تعداد بلال در بوته به تنش خشكی واكنش نشان‌داده و اختلاف آن‌ها در سطح احتمال یك‌درصد معنی‌دار بود. افزایش دور آبیاری از تیمار آبیاری نرمال به تنش شدید باعث كاهش عملكرد دانه و عملكرد علوفه خشك به‌میزان 32‌درصد و 44‌درصد شد. هیبرید شماره 4 (KSC700) با عملكرد دانه (12961‌كیلوگرم در هكتار) و عملكرد علوفه خشك (15565‌كیلوگرم در هكتار) به‌عنوان بهترین هیبرید بود كه می‌توان بالا‌بودن عملكرد در این هیبرید را به طولانی‌تر بودن دوره رشد آن نسبت‌داد كه زمان بیش‌تری را برای تولید و تجمع مواد در اختیار گیاه قرار می‌دهد.

<strong > Introduction </strong > Maize is one of the most important cereals which its global production is severely affected by drought in many parts of the world. One of the best ways of water management on field is to choose the proper variety which could be chosen indirectly by the traits affecting the grain yield. <strong > Materials and Methods </strong > In order to study the effect of drought stress in vegetative and reproductive stages in 14 corn hybrids, an experiment was conducted at the experimental field of Seed and Plant Improvement Institute of Karaj, in 2009. The Research Station located in 50°, 55´ eastern latitude and 35°, 47´ northern longitude with 1254 height above mean sea level (AMSL). The soil texture of the location was loam-clay with pH= 7.5 and the Electrical Capacity (EC) = 0.7 dsm-1. The experiment was carried out using split-plot in a randomized complete block design (RCBD) with three replications. The main plots consisted of three levels of irrigation regimes (irrigation after 70, 100 and 130 mm cumulative evaporation from evaporation pan class A) and sub-plots included 14 new corn hybrids Includes eleven new hybrids such as (K47/2-2-1-4-1-1-1×MO17، K3653/2×K19، KLM76004/3-2-1-1-1-1-1-1×K3545/6، K3653/2×MO17، K74/2-2-1-2-1-1-1-1×K3545/6، K47/3-1-2-7-1-1-1×MO17، K47/2-2-1-2-2-1-1-1×K3544/1، KLM76004/3-2-1-1-1-1-1-1×K3544/1، K47/2-2-1-2-1-1-1-1×K3544/1، KLM77029/8-1-2-3-2-3×MO17 and KLM76005/2-3-1-1-1-1×MO17) and three hybrid control (KSC704, KSC720, KSC700). Irrigation time was determined using daily evaporation rate of standard class A evaporation pan. To determine the volume of water per irrigation, a sample of each plot from depth of root development was prepared before irrigation. The samples were kept in oven 80°C for 24 hours. The weight of soil moisture content was calculated and the volume of water per irrigation was calculated using equations 1 and 2. 1: H = ρb (F.C - m) D 2: V = H × A Where H is the water height in the plot, ρb is soil bulk density, F.C is the moisture level at field capacity, m is plot moisture mass desired at irrigation time, D is the root development depth, V is the volume of irrigation water in the plot, and A is the plot area. From each plot 10 plants were randomly selected to determine traits such as dry forage yield per hectare. In this experiment kernel yield per hectare, Dry forage yield per ha, Number of days until to pollination, number of days until silk emergence cords and period of pollination until silk emergence, ear length, ear diameter, number of ear in corn, number of kernels per row and number of rows per ear measured and calculated. <strong > Results and Discussion </strong > The results showed that hybrid differences in terms of number of days until the pollination, number of days until silk emergence cords, period of pollination until silk emergence and ear length was significant at 1% probability level. No significance differences were observed between hybrids for kernel yield, total number of kernels per ear, number of ear in corn and ear diameter. Hybrid and irrigation regimes interactions were not significant for any of the traits except for ear length that represent the same reaction of hybrids to the irrigation regimes. Evaluation of dry forage showed significant difference between years (P <0.01). Means comparison of the years showed that dry forage yield was lower in the first year (Table 3). Interaction effect of irrigation regimes × year was significant and statistically caused non-significant difference for dry forage yield in the irrigation regimes. This difference could be due to low ability of hybrids in uptake, transport and food construction during water shortages that led to reduce dry matter accumulation. Dry weight loss and reduce of photosynthetic materials due to water limitation have also been reported by other researchers. There were no significant difference among hybrids, but the highest amount of dry forage yield was in hybrid 8 and the lowest was in hybrids 3, 5, 10 and 11. Also, all the traits except number of ear per plant were affected by drought stress that caused significant difference (P <0.01) among hybrids. Changing irrigation regimes from normal to severe stress conditions decreased grain yield and dry forage yield by 32% and 44%, respectively. <strong > Conclusions </strong > Hybrid KSC700 determined as more tolerant (12961 and 15565 kg ha-1 grain yield and dry forage yield, respectively). Higher yield of KSC700 can be attributed to its long growth stage; therefore, the hybrid had more time for production and accumulation of assimilates.