Genotypic Variation In Response Research Articles

Genotypic variation in response to salinity in a new sexual germplasm of Cenchrus ciliaris L.

As part of a breeding program for new salt-tolerant sexual genotypes of Cenchrus ciliaris L., here we evaluated the salt-stress response of two new sexual hybrids, obtained by controlled crosses, at seedling and germination stages. A seedling hydroponic experiment with 300 mM NaCl was performed and physiological variables and growth components were evaluated. While salt-treated sexual material did not show a decrease in productivity with respect to control plants, a differential response in some physiological characteristics was observed. Sexual hybrid 1-9-1 did not suffer oxidative damage and its proline content did not differ from that of control treatment. By contrast, sexual hybrid 1-7-11 suffered oxidative damage and accumulated proline, maintaining its growth under saline stress. At the germination stage, sexual hybrid 1-9-1 presented the highest Germination Rate Index at the maximum NaCl concentration assayed, suggesting an ecological advantage in this genotype. These new sexual resources are promising maternal parental with differential response to salt and could be incorporated in a breeding program of C. ciliaris in the search of new genotypes tolerant to salinity.

Screening for Sugarcane Brown Rust in the First Clonal Stage of the Canal Point Sugarcane Breeding Program

Sugarcane (Saccharum spp.) brown rust (caused by Puccinia melanocephala Syd. & P. Syd.) was first reported in the United States in 1978 and is still one of the great challenges for sugarcane production. A better understanding of sugarcane genotypic variation in response to brown rust will help optimize breeding and selection strategies for disease resistance. Brown rust ratings were scaled from non-infection (0) to severe infection (4) with intervals of 0.5 and routinely recorded for genotypes in the first clonal selection stage of the Canal Point sugarcane breeding program in Florida. Data were collected from 14,272 and 12,661 genotypes and replicated check cultivars in 2012 and 2013, respectively. Mean rust rating, % infection, and severity in each family and progeny of female parent were determined, and their coefficients of variation (CV) within and among families (females) were estimated. Considerable variation exists in rust ratings among families or females. The families and female parents with high susceptibility or resistance to brown rust were identified and ranked. The findings of this study can help scientists to evaluate sugarcane crosses and parents for brown rust disease, to use desirable parents for crossing, and to improve genetic resistance to brown rust in breeding programs.

In vitro somatic embryogenesis and plantlet regeneration from immature male inflorescence of adult dura and tenera palms of Elaeis guineensis (Jacq.).

We report here a method for plant regeneration through somatic embryogenesis from explants collected from immature male inflorescence of adult oil palm cultivated in India. Callus induction was successful from tissues of immature male inflorescence collected from both dura and tenera varieties of oil palm. A modified Y3 (Eeuwens) media supplemented with several additives and activated charcoal (3%) were used for the experiments. Out of four different auxin treatments, 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid (picloram) produced maximum callus induction (82%) and it was not significantly different from 2,4-dichlorophenoxyacetic acid (2,4-D) and a combination of 2,4-D + picloram. The callus induction obtained with auxin α-naphthalene acetic acid was only 54% and it was significantly low as compared to the other treatments. Highest embryogenesis was obtained with a combination of 2,4-D + picloram (4.9%) followed by picloram (3.4%). Genotypic variation in response to the same auxins was observed both for callus induction and embryogenesis. Callus induction and embryogenesis ranged from 42 to 72% and 6.8 to 9.35%, respectively in tenera. The formation of embryogenic calli was marked by the appearance of white to yellowish globular or nodular structures which subsequently formed clear somatic embryos. Somatic embryogenesis was asynchronous and at one time we could find different stages of embryogenesis like the globular, torpedo and the cotyledonary stages. The somatic embryos when exposed to light in the same basal media along with 6-benzyladenine (18 µM), abscisic acid (3.78 µM) and gibberellic acid (5.78 µM) regenerated into plantlets. To the best of our knowledge this is the first report o f callus induction and somatic embryogenesis from immature male inflorescence of oil palm.

栽植密度を用いた大気CO_2上昇下で高い生産性を示すコムギ品種の選抜方法 : 北海道の春播性コムギの疎植応答における品種間差異(2ヶ年の結果)(平成27年度年次講演会一般公演)

栽植密度を用いた大気CO_2上昇下で高い生産性を示すコムギ品種の選抜方法 : 北海道の春播性コムギの疎植応答における品種間差異(2ヶ年の結果)(平成27年度年次講演会一般公演)

Physiological and Growth Responses of Sugarcane Genotypes to Nitrogen Rate on a Sand Soil

AbstractYields of sugarcane (a complex hybrid of Saccharum spp.) in FL, USA, are lower on sand soils than on organic (muck) soils. Nitrogen (N) supply may limit sugarcane growth and yields on these sand soils. A 2‐year pot study was conducted to determine sugarcane genotypic variation in response to N rate on a sand soil. Treatments included four N rates (0, 75, 150 and 225 kg ha−1) and three sugarcane genotypes (CP 80‐1743, CP 01‐2390 and TCP 87‐3388). Nitrogen fertilizer was equally split and applied at about 55 and 125 days after planting (DAP) for each treatment. During the experiment, the number of nodes and length of the primary stalks and tillers were recorded. Leaf relative chlorophyll (soil plant analysis development (SPAD)) and net photosynthetic rate (Pn) were measured biweekly. All plants were harvested at 183 DAP to measure green leaf area (GLA), shoot biomass accumulation and partitioning, and fertilizer N use efficiency (NUE). Genotypes differed significantly in leaf SPAD, Pn, GLA, and shoot biomass accumulation and partitioning. CP 01‐2390 had the highest leaf Pn and shoot biomass, and CP 80‐1743 had the lowest GLA, shoot biomass and NUE among genotypes. Nitrogen rate affected leaf SPAD, GLA, shoot biomass and NUE, but had much less effect on leaf Pn. Green leaf area and biomass increased with increasing N rates. Our results suggest that a two‐pronged approach, selection of genotypes with high NUE while working to optimize N rates and delivery can improve sugarcane yields on sand soils.

Adaptive phenotypic plasticity and local adaptation for temperature tolerance in freshwater zooplankton

Many organisms have geographical distributions extending from the tropics to near polar regions or can experience up to 30°C temperature variation within the lifespan of an individual. Two forms of evolutionary adaptation to such wide ranges in ambient temperatures are frequently discussed: local adaptation and phenotypic plasticity. The freshwater planktonic crustacean Daphnia magna, whose range extends from South Africa to near arctic sites, shows strong phenotypic and genotypic variation in response to temperature. In this study, we use D. magna clones from 22 populations (one clone per population) ranging from latitude 0° (Kenya) to 66° North (White Sea) to explore the contributions of phenotypic plasticity and local adaptation to high temperature tolerance. Temperature tolerance was studied as knockout time (time until immobilization, T(imm)) at 37°C in clones acclimatized to either 20°C or 28°C. Acclimatization to 28°C strongly increased T(imm), testifying to adaptive phenotypic plasticity. At the same time, Timm significantly correlated with average high temperature at the clones' sites of origin, suggesting local adaptation. As earlier studies have found that haemoglobin expression contributes to temperature tolerance, we also quantified haemoglobin concentration in experimental animals and found that both acclimatization temperature (AccT) and temperature at the site of origin are positively correlated with haemoglobin concentration. Furthermore, Daphnia from warmer climates upregulate haemoglobin much more strongly in response to AccT, suggesting local adaptation for plasticity in haemoglobin expression. Our results show that both local adaptation and phenotypic plasticity contribute to temperature tolerance, and elucidate a possible role of haemoglobin in mediating these effects that differs along a cold-warm gradient.

Oilseed rape (Brassica napus L.) genotypic variation in response to boron deficiency

Boron efficiency of 16 oilseed rape genotypes was tested using both hydroponic and pot-soil growing techniques. From the nutrient solution experiment (0.1 and 10 µM B), 4 representative contrasting genotypes were selected based on relative root and shoot growth. These were then grown in pots with low-B soil (0.25 mg kg^{-1}). From the nutrient solution experiment, 2 genotypes selected as B-inefficient did not show any growth disorders, and the concentration of B in the shoots was above critical. Furthermore, 4 contrasting genotypes were subjected to the stable 11B isotope-enriched uptake solution for 6 h to verify possible low B-induced active uptake by roots and xylem loading of B. The concentration of 11B in either root cell sap or xylem exudate was higher than in the external nutrient solution, which indicated the presence of low B-induced active uptake for all tested genotypes, and, to some extent, their efficiency with low B. In conclusion, a combination of different growing techniques under controlled environmental conditions together with different parameters including relative root and shoot weight, shoot B concentration, and B uptake provided reliable B efficiency results in oilseed rape genotypes.

Genotypic variation in response to low boron in eucalypt clones

Eucalypts are increasingly important in the tropics for meeting growing demand for timber, wood chips, paper pulp and biofuel. Many new plantations are planted on low boron (B) soils, with adverse effects on plant growth and productivity. Two experiments in sand culture with different levels of added B, from 0 to 10 μM B, examined the effect of B deficiency on growth, wood yield and morphology of fibres of three commercially available eucalypt clones: K7 (Eucalyptus camaldulensis × E. deglupta), K51 (E. brassiana × E. grandis) and K57 (E. camaldulensis). In plant height, dry weight and wood production, K7 was more tolerant of B deficiency, but K57 and K51 were more responsive to increasing B. At the level of B that depressed growth by up to 54% and wood yield by up to 65%, no significant effect of B deficiency was observed on fibre morphology. However, as the wood:shoot ratio in K51 and K57 increased with increasing B, there is a possibility that B has a direct effect on wood production in some genotypes, in addition to an indirect effect via better growth. These results indicate that attention to B nutrition in eucalypt plantations would be beneficial to plant growth and productivity before effects of B on individual wood fibres becomes detectable. Selection for B-efficient genotypes could be useful for plantations on low B soils, and the full potential of sites where B is not limiting could be better realised with B-responsive genotypes.

A new QTL for resistance to Fusarium ear rot in maize

Understanding the inheritance of resistance to Fusarium ear rot is a basic prerequisite for an efficient resistance breeding in maize. In this study, 250 recombinant inbred lines (RILs) along with their resistant (BT-1) and susceptible (N6) parents were planted in Zhengzhou with three replications in 2007 and 2008. Each line was artificially inoculated using the nail-punch method. Significant genotypic variation in response to Fusarium ear rot was detected in both years. Based on a genetic map containing 207 polymorphic simple sequence repeat (SSR) markers with average genetic distances of 8.83cM, the ear rot resistance quantitative trait loci (QTL) were analyzed by composite interval mapping with a mixed model (MCIM) across the environments. In total, four QTL were detected on chromosomes 3, 4, 5, and 6. The resistance allele at each of these four QTL was contributed by resistant parent BT-1, and accounted for 2.5-10.2% of the phenotypic variation. However, no significant epistasis interaction effect was detected after a two-dimensional genome scan. Among the four QTL, one QTL with the largest effect on chromosome 4 (bin 4.06) can be suggested to be a new locus for resistance to Fusarium ear rot, which broadens the genetic base for resistance to the disease and can be used for further genetic improvement in maize-breeding programs.

DROUGHT STRESS: Physiological Basis for Genotypic Variation in Tolerance to and Recovery from Pre‐flowering Drought in Peanut

AbstractDrought during the pre‐flowering stage can increase yield of peanut. There is limited information on genotypic variation for tolerance to and recovery from pre‐flowering drought (PFD) and more importantly the physiological traits underlying genotypic variation. The objectives of this study were to determine the effects of moisture stress during the pre‐flowering phase on pod yield and to understand some of the physiological responses underlying genotypic variation in response to and recovery from PFD. A glasshouse and field experiments were conducted at Khon Kaen University, Thailand. The glasshouse experiment was a randomized complete block design consisting of two watering regimes, i.e. fully‐irrigated control and 1/3 available soil water from emergence to 40 days after emergence followed by adequate water supply, and 12 peanut genotypes. The field experiment was a split‐plot design with two watering regimes as main‐plots, and 12 peanut genotypes as sub‐plots. Measurements of N2 fixation, leaf area (LA) were made in both experiments. In addition, root growth was measured in the glasshouse experiment. Imposition of PFD followed by recovery resulted in an average increase in yield of 24 % (range from 10 % to 57 %) and 12 % (range from 2 % to 51 %) in the field and glasshouse experiments, respectively. Significant genotypic variation for N2 fixation, LA and root growth was also observed after recovery. The study revealed that recovery growth following release of PFD had a stronger influence on final yield than tolerance to water deficits during the PFD. A combination of N2 fixation, LA and root growth accounted for a major portion of the genotypic variation in yield (r = 0.68–0.93) suggesting that these traits could be used as selection criteria for identifying genotypes with rapid recovery from PFD. A combined analysis of glasshouse and field experiments showed that LA and N2 fixation during the recovery had low genotype × environment interaction indicating potential for using these traits for selecting genotypes in peanut improvement programs.

Evaluation of seedling survivability and growth response as selection criteria for breeding drought tolerance in wheat

Detection of genotypic variation in response to water stress at seedling stage could help in escalating selection intensity in breeding drought tolerant varities. Nine genotypes were tested for seedling survivability under drought stress. Four genotypes, i.e. ‘Sarsabz’, ‘Sitta’, ‘Fareed’ and ‘FD-83’, showed complete survival on resumption of irrigation after drought stress. These genotypes were late dying as they withered slowly under drought. Percent wilting and percent survival on resumption of irrigation were negatively correlated. Six genotypes were selected on the basis of seedling survivability (late and early dying) and evaluated for seedling growth response under drought. Root length and dry weight increased significantly under stress in ‘Sitta’, ‘FD-83’ and ‘Fareed’. Drought stress also increased the root-to-shoot length ratio in ‘FD-83’ and ‘Fareed’. However, seedling fresh and dry weight significantly reduced in ‘Nesser’ and ‘Inqalab-91’ under stress. In ‘FD-83’, seedling fresh and dry weight increased over control under stress. Results indicated that seedling survivability, root-to-shoot length ratio, root length and dry weight were most important traits for screening drought tolerance at seedling stage. On the basis of these indices, ‘Sitta’, ‘Fareed’ and ‘FD-83’ were classified as drought tolerant, ‘Sarsabz’ and ‘Nesser’ as moderately tolerant and ‘Inqalab-91’ as sensitive genotypes. Collectively, results suggested that selection by combining seedling survivability, growth response, RWC and leaf water potential can be efficiently used for rapid evaluation of drought tolerance in wheat breeding.

Genotypic Variation in Responses of Citrus spp. to Arbuscular Mycorrhizal Fungi

Thailand is part of Southeast Asia that covers the center of diversity of citrus species, where various species of thegenus are widely grown. One of the most common is tangerine (Citrus reticulata), which is commonly grown bygrafting on rootstocks of different tangerine varieties or other citrus species. The objective of this study is to investigateresponses of some Citrus spp. seedlings to arbuscular mycorrhizal (AM) fungi, and thus their potential as rootstocks.The experiment was done with four tangerine varieties, Cleopatra, Fremont, Ocean and Sainamphung; and four othercitrus species, lime (C. aurantifolia), pomelo (C. maxima), sweet orange (C. sinensis) and Troyer citrange (Citrussinensis????Poncirus trifoliata), in pots for five months. Roots of non-inoculated plants were not infected with AM fungi,while inoculated plants were heavily infected with AM fungi, and contained 14-28 AM spores per 10????g of rhizospheresoil. Most of the citrus responded positively to AM fungi, but with different magnitudes among the varieties and species.Lime and pomelo seedlings were fast growing compared to other citrus species. Total dry weight and N, P, K and Mgcontents were increased most strongly by AM fungi in lime, pomelo and tangerine varieties Ocean, Fremont andSainamphung, but little or none in Cleopatra, Troyer and sweet orange. Lime was the most outstanding in the responseto AM fungi, followed by Ocean tangerine and pomelo. The potential of lime, pomelo and Ocean tangerine as rootstockfor tangerine should be further investigated.

Involvement of lignification and membrane permeability in the tomato root response to boron toxicity

To gain an insight into the role of lignification and membrane permeability in the root response to boron (B) toxicity, lignification-related enzymes and a number of physiological and oxidative stress parameters were analyzed in two tomato (Solanum lycopersicum L.) cultivars (Kosaco and Josefina) subjected to 0.05 (control), 0.5 and 2mM B during 16 days. 2mM B supply inhibited root growth and increased the root B concentration in both tomato cultivars. Although excess B increased the hydrogen peroxide (H2O2) concentration in Kosaco, no major changes were observed in other oxidative-stress-related parameters. High levels of B supply also induced higher lignin deposition in Kosaco roots but did not in Josefina ones. The latter result was associated with an increase of the polyphenol oxidase (PPO), guaiacol peroxidase (GPOX) and soluble syringaldazine peroxidase (SPOX) activity in Kosaco roots. Boron toxicity did not induce lipid peroxidation but increased the leakage of K+ and the passive efflux of B in tomato roots. We conclude that high concentrations of B do not cause major oxidative or membrane damage in tomato roots. The data also indicate that high levels of B supply induce a higher lignin deposition in Kosaco roots but not in Josefina ones. This phenomenon suggests that lignification is not an essential factor reducing root growth in tomato plants, however, it proves that exist a high genotypic variation in response to excess B at root level.

Genotypic Variation in Responses of Cassava (Manihot esculenta Crantz) to Drought and Rewatering: Root System Development

Soil moisture condition is a major factor that affects root system development and thus, crop production. This study aimed to evaluate genotypic variations of cassava in root system structures and their responses to different soil moisture conditions by examining various root traits including production and elongation of adventitious roots and their laterals. Four pot experiments were conducted and different genotypes of various backgrounds were grown under well-watered, droughted, droughted to rewatered conditions. One field experiment was also conducted with selected genotypes till maturity. Results showed that substantial genotypic variations exist in root system structure, and the effects of the soil moistures were significant for most of the root traits. The principal component analysis (PCA) showed that the lateral root development mainly accounted for the variations in root system structure regardless of soil moisture conditions. The PCA on the differences between droughted and well-watered control, and droughted-rewatered and the control further indicated that the branching ability of adventitious roots was mainly responsible for the root system responses to drought as well as rewatering. Genotypic ranking in root system responses to drought was almost consistent among the pots and field experiments. Genotypicvariations in rooting depth were relatively small while those in horizontal spread were apparent in the field experiment.The ability to maintain adventitious root elongation under drought, resulting in relatively large horizontal spread of root system and to recover sharply from drought by lateral root branching may be related to good growth and yield performance under field.

Elevated CO2 will not select for enhanced growth in white spruce despite genotypic variation in response

The effect of elevated atmospheric CO 2 on plant growth has been well-documented in the literature. However, few studies have quantified intra-specific genetic variation in growth response, and the potential for natural and artificial selection to act upon this variation. This study examined intra-specific variation in growth response to elevated CO 2 in 29 genotypes of white spruce ( Picea glauca ), a widely distributed and economically important species of the boreal forest region in North America. Trees were exposed to either ambient (370 μL L −1 ) or twice-ambient CO 2 (740 μL L −1 ). The opportunity for selection (i.e. the relative variation in fitness) was determined at low and high CO 2 levels with size as a measure of fitness and heritability of this variation determined. There was considerable variation among the genotypes in size and response to elevated CO 2 . The increase in mass at elevated CO 2 ranged from 23% to 108% depending upon genotype. In spite of this variation, the genetic correlation between the two environments approached unity, as genotype variance was much greater than the genotype×CO 2 variance. Elevated CO 2 had no effect on heritability of the size-related traits we examined, and either had no effect on opportunity for selection, or decreased it. We conclude that selection at elevated atmospheric CO 2 is unlikely to increase mean plant size in white spruce beyond that observed for present day populations grown at elevated CO 2 , despite the substantial genetic variation in CO 2 response displayed by this species. Der Effekt einer Erhöhung des atmosphärischen CO 2 -Gehaltes auf das Pflanzenwachstum ist in der Literatur gut dokumentiert. Es gibt jedoch wenige Untersuchungen, die eine intraspezifische genetische Variation in der Wachstumsreaktion und die Möglichkeiten einer artifiziellen oder natürlichen Selektion, die auf dieser Variation beruht, quantifizieren. Diese Untersuchung betrachtete die intraspezifische Variation in der Wachstumsreaktion auf erhöhte CO 2 -Gehalte von 29 Genotypen der Weißfichte ( Picea glauca ), einer weit verbreiteten und ökonomisch bedeutenden Art der borealen Waldregion in Nordamerika. Die Bäume wurden einer Umgebung mit einfachem (370 ìL L −1 ) oder doppeltem (740 ìL L −1 ) CO 2 ausgesetzt. Die Möglichkeit einer Selektion (d. h. die relative Fitness) wurde für die niedrigen und hohen CO 2 -Gehalte bestimmt, indem die Größe als ein Maß für die Fitness und die Erblichkeit dieser Variation bestimmt wurde. Es gab eine beträchtliche Variation zwischen den Genotypen in der Größe und der Reaktion auf erhöhte CO 2 -Gehalte. Die Massenzunahme bei erhöhten CO 2 -Gehalten variierte zwischen 23% und 108% in Abhängigkeit vom Genotyp. Trotz dieser Variation näherte sich die genetische Korrelation zwischen den beiden Umwelten der Eins, weil die Genotypenvarianz sehr viel größer als die Varianz Genotyp×CO 2 war. Ein erhöhter CO 2 -Gehalt hatte keinen Effekt auf die Erblichkeit der untersuchten größenbezogenen Eigenschaften, und hatte entweder keinen Effekt auf die Möglichkeit einer Selektion oder verminderte ihn. Wir schließen daraus, dass es unwahrscheinlich ist, dass eine Selektion bei erhöhtem CO 2 -Gehalt die mittlere Baumgröße der Weißfichte über diejenige der heutigen Populationen, die bei erhöhtem CO 2 -Gehalt wachsen, erhöht, obwohl es eine deutliche genetische Variation in der Reaktion auf CO 2 bei dieser Art gibt.

Influence of Silicon on Sunflower Cultivars under Drought Stress, I: Growth, Antioxidant Mechanisms, and Lipid Peroxidation

: Understanding plant responses to drought stress is essential, and there is a need to know possible physiological mechanisms of damage and drought avoidance for the genetic improvement of crops. Therefore, we investigated the effects of silicon (Si) on shoot and root growth, leaf relative water content (RWC), stomatal resistance (SR), lipid peroxidation (MDA), membrane permeability (MP), proline and hydrogen peroxide (H2O2) accumulation, nonenzymatic antioxidant activity, and the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of 12 sunflower cultivars grown under drought conditions. Silicon applied to the soil counteracted the deleterious effects of drought in 6 of the 12 sunflower cultivars. In general, SR and H2O2, proline, and MDA content were increased in all the cultivars under drought stress. However, application of Si decreased their levels and alleviated membrane damage (MP) significantly by increasing leaf RWC. The CAT activity was significantly decreased by drought stress, but supplemental Si increased it. In general, SOD and APX activities of the cultivars were increased by drought and decreased by application of Si. The nonenzymatic antioxidant activity of the cultivars was significantly increased by Si under drought stress. Based on the present work, it can be concluded that applied Si alleviates drought stress in sunflower cultivars by preventing membrane damage, although the cultivars showed genotypic variation in response to applied Si.

QTL mapping of resistance to Fusarium ear rot using a RIL population in maize

Fusarium ear rot is a prevalent disease in maize, reducing grain yields and quality. Resistance breeding is an efficient way to minimize losses caused by the disease. In this study, 187 lines from a RIL population along with the resistant (87-1) and susceptible (Zong 3) parents were planted in Zhengzhou and Beijing with three replications in years 2004 and 2006. Each line was artificially inoculated using the nail-punch method. Significant genotypic variation in response to Fusarium ear rot was detected in both years. Based on a genetic map containing 246 polymorphic SSR markers with average genetic distances of 9.1 cM, the ear-rot resistance QTL were firstly analyzed by composite interval mapping (CIM). Three QTL were detected in both Zhengzhou and Beijing in 2004; and three and four QTL, respectively, were identified in 2006. The resistant parent contributed all resistance QTL. By using composite interval mapping and a mixed model (MCIM), significant epistatic effects on Fusarium ear rot as well as interactions between mapped loci and environments were observed across environments. Two QTL on chromosome 3 (3.04 bin) were consistently identified across all environments by the two methods. The major resistant QTL with the largest effect was flanked by markers umc1025 and umc1742 on chromosome 3 (3.04 bin), explaining 13–22% of the phenotypic variation. The SSR markers closely flanking the major resistance QTL will facilitate marker-assisted selection (MAS) of resistance to Fusarium ear rot in maize breeding programs.

Genotypic Variation in the Response of Rice (Oryza sativa L.) to Increased Atmospheric Carbon Dioxide and its Physiological Basis

AbstractIncreasing atmospheric carbon dioxide concentration (Ca) is one aspect of global change that will have a significant impact on the productivity of agricultural crops. Crop yields have been shown to increase with increasing Ca. The magnitude of yield response to increased Ca could vary depending on genotypic and environmental factors. The objective of this study was to determine the genotypic variation of yield response and its physiological basis in rice (Oryza sativa L.) through an initial varietal screening using 16 genotypes. The genotypes were grown under two concentrations of Ca, i.e. 370 ± 28 (ambient) and 570 ± 42 (elevated) μmol mol−1, in open top chambers under lowland field conditions at the Rice Research and Development Institute in Sri Lanka (7°50′N, 80°50′E) from May to August 2001 (yala season) and from November 2001 to March 2002 (maha). Ca within chambers was maintained around target concentrations by a computer‐based real‐time data acquisition and control system. There was significant variation between genotypes in the response of yield to elevated Ca, with absolute increases up to 530 g m−2 in yala and 347 g m−2 in maha. In relative terms, percentage yield increases from ambient to elevated Ca ranged from 4 % to 175 % in yala and from 3 % to 64 % in maha. Genotypic variation in yield showed significant positive correlations with light‐saturated net photosynthetic rate of the flag leaf during the grain‐filling stage. This indicated that increased assimilate supply and its genotypic variation contributed to the observed genotypic variation in yield response to elevated Ca. Furthermore, the capacity to develop a larger reproductive sink through increased panicle number per m2 and increased number of grains per panicle contributed to greater yield at elevated Ca. There was a significant genotype × season interaction with genotypes responding differentially to increased Ca in the two seasons. This was mainly due to inter‐seasonal variation in incident radiation during the grain‐filling stage. Our results demonstrate the significant genotypic variation that exists within the rice germplasm, in the response to increased Ca of yield and its correlated physiological parameters. A subset of genotypes from screening trials such as the present study can be used for more in‐depth analysis of the influence of elevated Ca on processes responsible for yield determination in rice and for molecular studies to elucidate the genetic basis of the response to increased Ca. This could pave the way for breeding genotypes which are more productive in a future high CO2 environment, provided that genotypes with greater flexibility in their physiology are selected to counter the genotype × environmental interaction.

QUANTITATIVE GENETIC ANALYSIS OF PLANT GROWTH: BIASES ARISING FROM VEGETATIVE PROPAGATION

Propagation through vegetative cuttings is a widely used technique that may bias estimates of genetic and environmental effects on plant growth. Leafy stem cuttings from 210 genotypes from eight populations of Salix pulchra were rooted and raised at three levels of nitrogen availability. Cuttings showed a complex suite of responses to vegetative propagation. Population and/or genotypic variation in response to vegetative propagation was observed in (1) retention of leaves during rooting, (2) date that cuttings resumed shoot growth after rooting, and (3) the frequency of cuttings that remained shoot dormant throughout the experiment. Nitrogen treatments also caused different responses to vegetative propagation, influencing date that cuttings resumed shoot growth and frequency of shoot dormancy. Because each of these responses had a direct effect on final plant size, I concluded that final size was a product of both differences among genotypes and treatments in plant growth rate, as well as genotype- and treatment-specific responses to vegetative propagation. This study shows that plant growth experiments can be designed to quantify responses to vegetative propagation and statistically remove these artifacts of propagation from estimates of genetic and environmental effects on plant growth.

QUANTITATIVE GENETIC ANALYSIS OF PLANT GROWTH: BIASES ARISING FROM VEGETATIVE PROPAGATION

Propagation through vegetative cuttings is a widely used technique that may bias estimates of genetic and environmental effects on plant growth. Leafy stem cuttings from 210 genotypes from eight populations of Salix pulchra were rooted and raised at three levels of nitrogen availability. Cuttings showed a complex suite of responses to vegetative propagation. Population and/or genotypic variation in response to vegetative propagation was observed in (1) retention of leaves during rooting, (2) date that cuttings resumed shoot growth after rooting, and (3) the frequency of cuttings that remained shoot dormant throughout the experiment. Nitrogen treatments also caused different responses to vegetative propagation, influencing date that cuttings resumed shoot growth and frequency of shoot dormancy. Because each of these responses had a direct effect on final plant size, I concluded that final size was a product of both differences among genotypes and treatments in plant growth rate, as well as genotype- and treatment-specific responses to vegetative propagation. This study shows that plant growth experiments can be designed to quantify responses to vegetative propagation and statistically remove these artifacts of propagation from estimates of genetic and environmental effects on plant growth.