ارزیابی تحمل تنش خشکی در اینبرد لاین‌های ذرت (.zea mays l)

به‌منظور ارزیابی تحمل تنش خشکی در اینبرد لاین‌های در حال خلوص ذرت، دو آزمایش جداگانه با تیمارهای آبیاری کامل و تنش خشکی (به‌ترتیب آبیاری پس از 50 و 90 میلی‌متر تبخیر از سطح تشتک تبخیر) به مدت دو سال (1402-1401) در موسسه تحقیقات اصلاح و تهیه نهال و بذر در کرج اجرا شد. آزمایش به‌صورت طرح آلفا لاتیس 7×6 روی 34 اینبرد لاین در حال خلوص در مرحله s4-s5، شش لاین خالص مناطق معتدله و دو لاین شاهد (mo17 و b73) با دو تکرار به اجرا درآمد. نتایج نشان داد که تنش خشکی اثر معنی‌داری بر خصوصیات فنولوژیکی ژنوتیپ‌های ذرت داشت. در شرایط آبیاری کامل، تعداد روز تا ظهور گل تاجی در لاین‌های ذرت بین 69.2 تا 80.7 روز متغیر بود، درحالی‌که در شرایط تنش خشکی این دامنه به 71.7 تا 84.7 روز افزایش یافت. تعداد روز تا گرده‌افشانی در شرایط آبیاری کامل بین 71.3 تا 83.1 روز بود و در شرایط تنش خشکی این دامنه از 75.1 تا 88.9 روز افزایش یافت. تنش خشکی باعث کاهش معنی‌دار ارتفاع بوته، وزن هزار دانه، تعداد دانه در بوته و وزن حجمی دانه (وزن هکتولیتر) اینبرد لاین‌های ذرت شد. در تیمار آبیاری کامل، ژنوتیپ‌های 19 و 2 به‌ترتیب بیشترین و کمترین (431 و 237 گرم) وزن هزار دانه را داشتند. در تیمار تنش خشکی، ژنوتیپ‌های 36 و 12 به‌ترتیب بیشترین و کمترین (349 و 190 گرم) وزن هزار دانه را داشتند. بیشترین عملکرد دانه در تیمارهای آبیاری کامل و تنش خشکی (به‌ترتیب 10530 و 7222 کیلوگرم در هکتار) در لاین 35 ثبت شد. بیشترین مقدار بهره‌وری آب در تیمار آبیاری کامل (1.75 کیلوگرم بر مترمکعب) و در تیمار تنش خشکی (1.16 کیلوگرم بر مترمکعب) نیز در لاین 35 به‌دست آمد. لاین‌های 35، 27، 6، 31، 15، 24، 32، 33 و 28 به‌ترتیب به‌عنوان ژنوتیپ‌های امیدبخش برتر در شرایط تنش خشکی و لاین‌های 35، 6، 32، 31، 15 و 33 به‌ترتیب به‌عنوان ژنوتیپ‌های امیدبخش برتر در شرایط آبیاری کامل شناسایی شدند. نتایج نشان داد که لاین 35 برتری قابل‌توجهی در عملکرد دانه و بهره‌وری آب در هر دو شرایط بدون تنش و تنش خشکی داشته و به‌عنوان ژنوتیپ برتر همراه با سایر ژنوتیپ‌های منتخب، برای تولید هیبریدهای متحمل به تنش خشکی در برنامه‌های به‌نژادی ذرت قابل استفاده خواهد بود.

evaluation of maize (zea mays l.) inbred lines for drought stress tolerance

introduction: in dry and semi-arid climatic conditions of iran, drought stress is one of the major limiting factors for grain yield in maize (mahrokh et al., 2021). as one of the most important cereal crops in ensuring food security and feeding the growing global population, maize holds significant importance. however, due to its high sensitivity to water deficit, its grain yield is considerably reduced under drought conditions. therefore, identifying and selecting drought-tolerant genotypes with acceptable yield performance is of paramount importance. the objective of this experiment was to evaluate maize inbred lines under normal irrigation and drought stress conditions. the effect of drought stress on phenological, morphological, grain yield, yield components and irrigation water productivity was assssed. the drought-tolerant genotypes were selected for being utilized in maize breeding programs.materials and methods: the experiment was conducted as an alpha lattice design (7×6) with 34 maize inbred lines (at the s4–s5 stage) sourced from the country's hot and dry regions, supplemented with six inbred lines from temperate regions and two check lines (mo17 and b73). the experiment was arranged in two replications and six incomplete blocks per replication, with seven entries per block, under two irrigation regimes (normal irrigation and drought stress) in two growing seasons (2022 and 2023) at the seed and plant improvement institute, karaj, iran. in the normal irrigation treatment, irrigation was applied after a cumulative evaporation of 50 mm from a class a evaporation pan, while in the drought stress treatment, irrigation was applied after 90 mm evaporation from a class a evaportation pan. days to tassel emergence, days to pollination, days to silk emergence, anthesis-silking interval (asi), plant height, number of leaves per plant, ear length, ear diameter, number of grains per plant (gpp), 1000 grain weight (tgw), grain yield, grain moisture content, hectoliter weight, and irrigation water productivity (wp) were measured during growing seasons and after harvest. results: drought stress had significant impact on all phenological characteristics of maize inbred lines. under normal irrigation conditions, the mean days to tassel emergence varied from 69.2 to 80.7 days, while under drought stress this period increased to 71.7–84.7 days. similarly, days to pollination under normal irrigation conditions ranged between 71.3 and 83.1 days, and under drought conditions, this period extended from 75.1 to 88.9 days. line 10 showed the shortest duration days to pollination, while line 19 had the longest. drought stress significantly reduced plant height, tgw, gpp, and hectoliter weight. under normal irrigation, line 19 and 2 had the highest and lowest tgw (431 and 237 g, respectively). however, under drought stress conditions, line 36 had the highest tgw (349 g), and line 12 the lowest (190 g). line 35 produced the highest grain yield with 10530 kg.ha-1 under normal irrigation and 7222 kg.ha-1 under drought stress. this line also had the highest wp under normal irrigation conditions (1.75 kg.m-3) and under drought stress (1.16 kg.m-3).conclusion: the results of this experoiment demonstrate that the responses of maize inbred lines to normal irrigation and drought stress conditions were complex and multidimensional. the observed delays in flowering stages under drought stress, along with significant reductions in tgw, gpp, and wp, indicated the negative impact of water deficit on growth and reproductive processes in maize inbred lines. however, the considerable genetic variation among the evaluated inbred lines provides a solid foundation for selecting and incorporating desirable genes, such as high grain yield and enhanced drought tolerance, in breeding programs. inbred lines 35, 27, 6, 31, 15, 24, 32, 33, and 28 were identified as the promising lines under drought stress, while inbred lines 35, 6, 32, 31, 15, and 33 were deemed suitable under normal irrigation conditions. overall, inbred line 35 performed superior for both grain yield and water productivity under both conditions, and could be utilized for development of drought-tolerant hybrids in maize breeding programs.