So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Salicylic acid in relation to other phytohormones in plant: A study towards physiology and signal transduction under challenging environment

Seed germination and seedling growth are the stages most sensitive to salt stress, which can induce ion-specific effects and oxidative stress. Although silicon (Si) has been known to improve plant defense systems against stressful-conditions, little is known about seed priming with Si and mechanisms of Si-mediated alleviation of salt stress in seedlings. To further the modulation of salt-stress responses and their relation with Si, seed priming with calcium silicate (0, 0.05 and 0.1 mM Ca2SiO4) was used in lettuce seeds to improve seedgermination and tolerance on subsequent salt-stress exposure (0 and 50 mM NaCl). The effect of Si-priming was assessed on germination, germination rate index and mean germination time and survival of seedlings in salt-stressful conditions supported by biochemical approach involving antioxidant responses. Overall results indicated that Si plays a role in alleviating the negative effects of salt stress by improving germination performance and displayed increased SOD, CAT and GR activities and reduced malondialdehyde and H2O2 contents. Thus, our findings demonstrate that seed-priming with Si is an efficient management technique thatcan be used to alleviate deleterious effects of salt-stressful on germination of lettuce seeds and enhance salt tolerance of seedlings due the increased activity of ROS- scavenging enzymes.

/pdf/salt-stress-alleviation-by-seed-priming-with-silicon-in-4g6sbvro4h.pdf

Salt stress alleviation by seed priming with silicon in lettuce seedlings: an approach based on enhancing antioxidant responses

This study was carried out to assess the role of elevated concentrations of boron in barley (Hordeum vulgare L. cv. Giza 123) growth and yield as well as to test the involvement of some plant growth modulators in counteracting the boron-mediated retardations to improve its tolerance. Barley grains were treated with B concentrations of 0, 0.5, 1.5, 3.0 and 6.0 mg L -1 (as boric acid). The alleviation of the growth inhibition in the presence of 3.0 mg L -1 B was investigated by adding the following growth modulators: glutamic acid (1 or 3 mM ), glycine (1 or 3 mM), ascorbic acid (2 or 5 mM), salicylic acid (1 or 5 mM) and calcium chloride (1 or 5 mM). Barley grains were cultivated and samples were collected at vegetative (22-day-old), flowering (45-day-old) and harvesting stages (92-day-old). At vegetative stage, the application of 0.5 mg L -1 boron significantly increased (P ≤ 0.05) shoot fresh weight by 1%. The addition of 0.5 and 1.5 mg L -1 boron significantly increased (P ≤ 0.05 and 0.01) growth parameters (shoot and root fresh and dry weights) by 5%, leaf area by 4.5% and 7%, Chl a and Chl b contents by 3% and 7% at vegetative and flowering stages, respectively, and yield by 5.5%, compared to non-boron treated barley. The inhibitory effects of boron on barley growth started at concentrations above 3.0 mg L -1 , causing decrease in all the measured parameters. The five tested growth modulators alleviated boron toxicity at 3.0 mg L -1 at the following sequence: salicylic acid (1 mM), calcium chloride 5 mM ≥, ascorbic acid (2 mM) ≥, glycine (1 mM) and glutamic acid (3 mM). The boron-alleviating efficiency of either 1 mM salicylic acid or 5 mM calcium chloride recommended their application when cultivating barley in boron contaminated soils.

/pdf/effect-of-elevated-boron-concentrations-on-the-growth-and-3k2gqqdgd5.pdf

Effect of elevated boron concentrations on the growth and yield of barley (Hordeum vulgare L.) and alleviation of its toxicity using different plant growth modulators

Most of plant growth regulators are known to alleviate negative effects of osmotic stress on crop growth. To evaluate the effects of cycocel (CCC), as a growth regulator, on crop seed germination, early growth, and vegetative growth under osmotic stress conditions, a study was conducted under controlled conditions. Six crops, wheat, barley, maize, sunflower, safflower, and rapeseed were grown under five osmotic potentials (0, as non-stress, −0.5, −1.0, −1.5, and −2.0 MPa), which were raised from seeds treated with three CCC concentrations (0, 2.5, and 3.5 g l−1). Reduced germination, seedling and vegetative growth as well as enhanced leaf free proline and chlorophyll content index were observed under osmotic stress. The extent of these changes depended on the type of the used crops. Priming with optimum CCC concentration mitigated to great extent stress-induced adverse effects on these crops. The positive effect of CCC priming on wheat, maize, and rapeseed was observed only at moderate osmotic levels, whe...

Impact of cycocel on seed germination and growth in some commercial crops under osmotic stress conditions

Nitrogen and Boron Interactional Effect on Growth and Shoot Nitrogen and Boron Content in Rice

یکی از راه های جبران کاهش عملکرد گندم در اثر تنش خشکی، به عنوان مهم‌ترین عامل محدودکننده عملکرد، می‌تواند کاربرد تنظیم کننده‌های رشد باشد. بدین منظور، تأثیر دو تنظیم کننده رشد سایکوسل و سالیسیلیک اسید بر عملکرد و اجزای عملکرد دانه دو رقم گندم روشن و یاواروس در شرایط متفاوت آبیاری (مطلوب، تنش ملایم و تنش شدید) در پژوهشی دو مرحله­ای در مزرعه تحقیقاتی (آزمایش اسپلیت فاکتوریل بر پایه طرح بلوک‌های کامل تصادفی) و گلخانه تحقیقاتی (طرح کاملا تصادفی) دانشکده کشاورزی دانشگاه شیراز در سال زراعی 89-1388 مورد بررسی قرار گرفت. نتایج این مطالعه نشان داد که تنش خشکی موجب کاهش شدید طول سنبله، تعداد دانه در سنبلک، تعداد دانه و سنبلک در سنبله، عملکرد دانه، عملکرد بیولوژیک و شاخص برداشت گردید. بیشترین و کمترین اثر خشکی به ترتیب مربوط به عملکرد بیولوژیک و وزن هزار دانه بود. کاربرد تنظیم کننده‌های رشد سبب افزایش طول سنبله، اجزای سنبله، وزن هزار دانه و عملکرد دانه گردید. کاربرد سالیسیلیک اسید با افزایش، و سایکوسل با کاهش عملکرد بیولوژیک همراه بود. سایکوسل همچنین شاخص برداشت را افزایش داد. پاسخ عملکرد و اجزای عملکرد دانه به تنش خشکی و کاربرد سایکوسل و سالیسیلیک اسید در رقم روشن نسبت به یاواروس بیشتر بود. به نظر می‌رسد که رقم روشن دارای عملکرد دانه بیشتر و رقم یاواروس دارای مقاومت بیشتری به تنش خشکی بود. اگرچه تنش خشکی موجب کاهش اغلب اجزای عملکرد گندم شد، لیکن تنظیم‌کننده‌های رشد موجب جبران بخشی از کاهش عملکرد ناشی از خشکی گردیدند؛ بنابراین، این تنظیم‌کننده‌های رشد به ویژه سایکوسل برای استفاده در شرایط تنش خشکی قابل توصیه می‌باشند.

http://escs.birjand.ac.ir/article_110_7eee9bb4bc16438ba13b64ac10c3d5e7.pdf

Yield and yield component responses of bread and durum wheat to pgrs under drought stress conditions in field and greenhouse

/pdf/evaluation-of-yield-yield-components-and-stress-tolerance-1s7eo7i0vm.pdf

Evaluation of Yield, Yield Components and Stress Tolerance Indices in Bread Wheat Cultivars at Post-anthesis Irrigation Cut-Off

Seed germination and early seedling growth are critical stages for plants establishment and production, particularly under salinity conditions. Exogenous application of silicon (Si) can enhance germination as well as seedling growth. In this experiment, the effect of priming with Si (0, 0.75, 1.5 and 2.25 mM sodium silicate) on seed germination and seedling growth under NaCl (0, 100 and 150 mM) conditions was studied in two wheat cultivars of Kavir (salt tolerant) and Shiraz (salt sensitive). The experiment was designed as a factorial based on completely randomized design with three replications in the laboratoryof college of Agriculture, Shiraz University, in 2012. Results showed that seed priming by Si improved germination percentage, germination rate, vigor index, shoot and root length and seedling dry weight in both stress and non-stress conditions. Moreover, Si increased K+ uptake and K+/Na+ ratio and decreased Na+ content of cultivars with the effect of 2.25 mM being more pronounced. On the contrary, salt stress reduced the above traits andK+ uptake and K+/Na+ ratio and increased mean germination timeand Na+ uptake in both cultivars with the negative effects of 150 mMNaCl being more severe. However, the tolerant cultivar (Kavir) accumulated less Na+ and more K+ and had greater K+/Na+ ratio compared to non-tolerant cultivar (Shiraz). Although the salinity adversely affected seed germination and seedling growth in both cultivars, Kavir (tolerant cultivar) was less affected. It was concluded that priming with Si may promote germination and subsequent seedling growth of wheat cultivars under salinity conditions by reducing Na+ in favor of K+ accumulation.

http://iar.shirazu.ac.ir/article_3712_e4d04e9ffdcbb83cdd766d29cb62a247.pdf

The effect of exogenous silicon on seed germination and seedling growth of wheat cultivars under salt stress conditions

/pdf/tthyr-slysylykh-syd-w-brsynwstrwyyd-dr-t-dyl-thrt-tnsh-aby-157w0d5zn6.pdf

یحیی امام

Papers

Nitrogen and Boron Interactional Effect on Growth and Shoot Nitrogen and Boron Content in Rice

Yield and yield component responses of bread and durum wheat to pgrs under drought stress conditions in field and greenhouse

Evaluation of Yield, Yield Components and Stress Tolerance Indices in Bread Wheat Cultivars at Post-anthesis Irrigation Cut-Off

The effect of exogenous silicon on seed germination and seedling growth of wheat cultivars under salt stress conditions

تأثیر سالیسیلیک اسید و براسینواستروئید در تعدیل اثرات تنش آبی در دو رقم گندم