کمّی‌سازی نمو برگ در ارقام مختلف گندم: i- تولید و زوال برگ‌های ساقه اصلی در شرایط مزرعه

یکی از اجزای اصلی مدل‌های شبیه‌سازی رشد گیاهان زراعی، نمو سطح برگ است که اثر بسیار مهمی روی فتوسنتز و تعرق گیاهی دارد. نمو سطح برگ شامل ظهور برگ‌های جدید، توسعه برگ‌های سبز شده و پیری برگ‌های مسن است. به منظور تعیین پارامترهای مربوط به تولید و زوال برگ در ارقام گندم دو پژوهش مزرعه‌ای در مزرعه تحقیقاتی دانشگاه آزاد اسلامی واحد رامهرمز در قالب طرح بلوک‌های کامل تصادفی در طی دو سال زراعی 86-1385 تا 87-1386 اجرا شد. ارقام مورد استفاده شامل اترک، بیات، چمران، چناب، دز، اینییاء، کویر، مرودشت، شیراز، استار، شوا-مالد (کرخه)، ویریناک، یاواروس، زاگرس و لاین s78-18 بودند. آزمایش در شرایط عدم محدودیت آب و مواد غذایی انجام گرفت. برای توصیف تغییرات تعداد برگ در ساقه اصلی در مقابل درجهروز رشد از یک مدل دو تکه‌ای استفاده شد. نتایج نشان داد که تولید برگ در ساقه اصلی با دریافت 108/5 درجهروز رشد پس از کاشت در ارقام گندم آغاز شد و به‌صورت خطی و با سرعت متوسط 0/012 برگ بر درجه-روز رشد (فیلوکرون 83 درجه-روز رشد) افزایش یافت. زمان توقف تولید برگ با توجه به اختلاف معنی‌دار بین ارقام در دامنه‌ی 737/5 تا 856/5 درجه-روز رشد زمانی که بوته حدود 109 برگ در ساقه اصلی داشت، اتفاق افتاد. پیری برگ در ساقه اصلی زمانی آغاز شد که ساقه اصلی دارای 64 برگ بود و پس از این مرحله به ازای هر واحد افزایش در درجه-روز رشد، 0/00065 از برگ‌های ساقه اصلی زوال یافتند. روابط به‌دست آمده از این مطالعه را می‌توان در مدل‌های شبیه‌سازی گندم استفاده کرد.

Quantifying Leaf Development of Different Wheat Cultivars: I Production and Senescence of Main Stem Leaves in the Field

<strong >Introduction </strong > A major component in a crop growth model is leaf area development, which has crucial influence on photosynthesis and transpiration. Leaf area development involves the appearance of new leaves, expansion of the newly emerged leaves and senescence of old leaves. Modeling of the leaf growth has been extensively studied in many crops including cereals. Methods of predicting leaf area development are diverge from those dealing with the individual component processes of leaf growth viz. leaf appearance, leaf expansion and leaf death to the models predicting leaf growth at the whole plant or whole crop levels. Leaf appearance and expansion are most sensitive growth processes to environmental conditions and their dependence on temperature revealed in a range of cereals including wheat and barley and legumes including cowpea and soybean. Effects of temperature on leaf appearance rates are usually quantified using some form of thermal time. Air temperature above the canopy has most frequently been used to calculate thermal time. Genetic differences in senescence have also been reported among crop genotypes. Quantitative information regarding leaf area development in wheat especially in environmental conditions with high temperatures for the purpose of crop modeling is scarce. Furthermore, genotypic variations have not been evaluated. Therefore, the goal of this research was to determine parameters related to leaf production and senescence in wheat cultivars in warm environmental conditions. <strong >Materials and Methods </strong > The aim of this study was to quantify leaf production and senescence of 15 different wheat cultivars. Two field experiments with 15 wheat cultivars (Atrak, Bayat, Chamran, Chenab, Dez, Ineia, Kavir, Marvdasht, Shiraz, S7818, Yavaroos and shovaMald) were conducted at the research farm of the Islamic Azad University of Ramhormoz Branch, southwestern of Iran in 20056 and 20067 using a randomized complete block design with four replications. The relationship between main stem leaf numbers (HS) versus degreedays was described using bilinear regression model. <strong >Results and Discussion </strong > The results indicated that leaf production on main stem started with receiving 108.5 degreedays after sowing. The leaf appearance rate and along with it phyllochron had no significant across all data. Mean leaf appearance rate ranged from 0.0047 to 0.0082 leaf/˚Cd. At 13 out of 15 cultivars. The cession time (degreedays) of effective leaf production on main stem was not significantly different and ranged from 831.0 to 852.0 ˚C d. Leaf senescence on the main stem started when the main stem had about 46 leaves and proceeded at a rate of 0.065 % per each unit increase in degreedays. The relationships found in this study can be used in simulation models of wheat. <strong >Conclusions </strong > Based on results, there was no significant difference between wheat cultivars in terms of parameters related to leaf production and senescence on main stem except the time of cessation of the linear increase in leaf number on main stem. The relationships presented in this study describe leaf production and senescence under wellwatered condition and reflect the effects of carbon and nitrogen availability and remobilization under these conditions. However, they do not account for the effects of shortage of carbon, nitrogen or water on leaf development. Other relationships are required to predict these effects.