Simulating Organ Growth in Wheat Based on the Organ–Weight Fraction Concept

Abstract

Quantifying dry matter partitioning into individual organs of plants is a key component for simulating crop growth and yield formation. This study was undertaken to develop a dynamic module of biomass partitioning over the entire duration of growth in wheat. The partitioning fraction of shoot or root was defined as the fraction of its dry weight in plant biomass, and partitioning fraction of green leaf, stem or ear as the fraction of its dry weight in shoot mass of wheat. The functional relationships of the partitioning fraction with physiological development time for the entire growth period were established, in which harvest index (HI) regulated partitioning fraction of ear to shoot biomass as a genetic parameter. The dry weight of individual organ was the product of the respective partitioning fraction and plant weight or shoot weight. Test of the model with the field experiment data sets involving different sowing dates, plant densities and nitrogen fertilization strategies indicated a good agreement between the predicted and observed values.     

Decrease in sorghum grain yield due to the dw3 dwarfing gene is caused by reduction in shoot biomass

Positive correlations between plant height and grain yield have been reported for sorghum. The introduction of stay-green in sorghum, and the associated reduction in lodging, has opened the possibility to exploit this positive association. The aim of this study was to analyse the direct effects of the dwarfing gene dw3 (and therefore plant height) on shoot biomass, grain yield, and yield components in pairs of 3-dwarf genotypes and their isogenic 2-dwarf tall mutants. Isogenic pairs with different genetic backgrounds were grown in three field experiments under nutrient and water non-limiting conditions. Tall mutants were significantly taller and produced more shoot and stem biomass than their shorter counterparts. Generally, tall types yielded more grain than short types, but significant interactions between experiment, genetic background and stature affected the consistency of the results. dw3 only affected grain size and not grain number. Increased grain mass of tall types was associated with significantly greater stem mass per grain at anthesis and greater shoot biomass per grain accumulated between anthesis and maturity. The increased biomass of tall plants was therefore important for increased grain yield under optimum conditions. Potential implications of increased biomass production for drought adaptation are discussed.     

Contribution of contrasting plant hierarchies to the response to N fertilizer in maize

The typical size structuring process that occurs as a consequence of intra-specific competition in maize promotes the appearance of contrasting plant hierarchies (i.e. dominated and dominant individuals). This process may become more intense under low nitrogen (N) availability. The alleviation of plant competition by N addition may reduce plant yield variability through a differential response to N in individuals of contrasting hierarchies. In this work, the response to N of dominated and dominant plants from stands with contrasting N supply (0 to 140-200 kg N ha⁻¹) was examined on 11 experiments carried out in Paraná, Argentina (31°50′S; 60°31′W) in a broad range of growing conditions that included the variation of the year, genotype, plant population and sowing date. Our objectives were: (i) to evaluate the response to N in contrasting plant hierarchies of maize, (ii) to quantify the contribution of dominated and dominant plants to the response to N of the overall stand, and (iii) to study the effect of N on relationships between plant hierarchies and stand variability. Response to N of yield per plant was associated with biomass per plant in non-fertilized controls, tending to be higher in plants with low biomass. The response to N of yield per unit area (i.e., considering all individuals of the stand) was related to the response to N of dominant and dominated plants (P < 0.0001). However, at a higher level of response to N of grain yield per unit area (>50-60%), dominant plants had a considerable lower response than dominated plants, whereas at a lower level of response (<30%), the contribution of contrasting plant hierarchies was similar. In stands with similar plant biomass between hierarchies, the differences in the response to N between plant types tended to be negligible. The coefficient of variation of yield per plant was reduced (P < 0.05) by effect of N in 4 out of 11 experiments, although it tended to be consistently lower in fertilized treatments. When the differences between the biomass of dominated and dominant plants were ample we found the highest response to N at the stand level, as a result of the higher increase in grain yield per plant in dominated plants than in dominant ones. The response to N in each plant hierarchy was differentially associated with increases in shoot biomass, harvest index, kernel number per plant and kernel weight.     

A comprehensive study of plant density consequences on nitrogen uptake dynamics of maize plants from vegetative to reproductive stages

Nitrogen (N) use efficiency (NUE), defined as grain produced per unit of fertilizer N applied, is difficult to predict for specific maize (Zea mays L.) genotypes and environments because of possible significant interactions between different management practices (e.g., plant density and N fertilization rate or timing). The main research objective of this study was to utilize a quantitative framework to better understand the physiological mechanisms that govern N dynamics in maize plants at varying plant densities and N rates. Paired near-isogenic hybrids [i.e., with/without transgenic corn rootworm (Diabrotica sp.) resistance] were grown at two locations to investigate the individual and interacting effects of plant density (low—54,000; medium—79,000; and high—104,000 pl ha⁻¹) and sidedress N fertilization rate (low—0; medium—165; and high—330 kg N ha⁻¹) on maize NUE and associated physiological responses. Total aboveground biomass (per unit area basis) was fractionated and both dry matter and N uptake were measured at four developmental stages (V14, R1, R3 and R6). Both plant density and N rate affected growth parameters and grain yield in this study, but hybrid effects were negligible. As expected, total aboveground biomass and N content were highly correlated at the V14 stage. However, biomass gain was not the only factor driving vegetative N uptake, for although N-fertilized maize exhibited higher shoot N concentrations than N-unfertilized maize, the former and latter had similar total aboveground biomass at V14. At the R1 stage, both plant density and N rate strongly impacted the ratio of total aboveground N content to green leaf area index (LAI), with the ratio declining with increases in plant density and decreases in N rate. Higher plant densities substantially increased pre-silking N uptake, but had relatively minor impact on post-silking N uptake for hybrids at both locations. Treatment differences for grain yield were more strongly associated with differences in R6 total biomass than in harvest index (HI) (for which values never exceeded 0.54). Total aboveground biomass accumulated between R1 and R6 rose with increasing plant density and N rate, a phenomenon that was positively associated with greater crop growth rate (CGR) and nitrogen uptake rate (NUR) during the critical period bracketing silking. Average NUE was similar at both locations. Higher plant densities increased NUE for both medium and high N rates, but only when plant density positively influenced both the N recovery efficiency (NRE) and N internal efficiency (NIE) of maize plants. Thus plant density-driven increases in N uptake by shoot and/or ear components were not enough, by themselves, to increase NUE.     

Comparative toxicity of selected insecticides to pea plants and growth promotion in response to insecticide-tolerant and plant growth promoting Rhizobium leguminosarum

Laboratory and field/pot experiments were conducted to determine the effect of two insecticides, fipronil and pyriproxyfen, on growth, symbiotic properties (nodulation and leghaemoglobin content), amount of N and P nutrients in plant organs, seed yield and seed protein of pea plants. In addition, the role of the most promising fipronil and pyriproxyfen tolerant Rhizobium leguminosarum strain MRP1 having plant growth promoting traits such as, production of phytohormones and siderophores, was also assessed in the presence and absence of both insecticides. Generally, fipronil and pyriproxyfen at the tested rates (recommended and higher doses) decreased the growth of both R. leguminosarum inoculated or uninoculated pea plants. Of the various concentrations of the two insecticides, pyriproxyfen at all concentrations in general, showed comparatively more severe toxicity to pea plants by decreasing plant biomass, symbiotic attributes, nutrients (nitrogen and phosphorus) uptake, seed yield and grain protein over the uninoculated control. The sole application of 3900 μg pyriproxyfen kg⁻¹ soil (three times the recommended dose) showed the highest toxicity and decreased the root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, seed yield and grain protein by 20%, 27%, 25%, 29%, 15% and 2% respectively, compared to the control. Interestingly, when the inoculant strain MRP1 was used with any concentration of the two insecticides, it significantly (P ≤ 0.05) increased the measured variables (plant dry weight, nodule numbers, dry nodule biomass, leghaemoglobin, nitrogen and phosphorus uptake, seed yield and grain protein) when compared to the plants grown in sandy clay loam soils treated solely (without inoculant) with the same individual treatment of each insecticide. For instance, three times the recommended dose of pyriproxyfen with strain MRP1 showed a highest stimulatory effect and increased the root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, seed yield and grain protein by 108%, 124%, 119%, 153%, 112% and 6% respectively, compared to the plants grown in soil treated solely with three times the recommended dose of pyriproxyfen.     

Effects of Relative Light Intensity on the Growth,Yield and Curcumin Content of Turmeric (Curcuma longa L.) in Okinawa,Japan

Abstract

The effects of relative light intensity (RLI) on the growth, yield and curcumin content of turmeric (Curcuma longa L.) were examined in Okinawa, Japan. The plants were shaded with white nets with different mesh sizes for maintaining respective RLI. Five RLI, 100 (without shading), 82, 79, 73 and 59% in 2004?2005 and four RLI, 100, 68, 52 and 48% in 2005?2006 were evaluated. In the first experiment, plant height increased markedly, but the number of leaves and tillers, and SPAD value increased slightly in the plants grown at 59?82% RLI compared with control (without shading). Turmeric shoot biomass and yield increased significantly at 59?82% RLI and they were highest at 73% RLI in the first experiment. Curcumin content of turmeric increased markedly at 59?73% RLI as compared with the control in the first experiment. Similar results in plant growth, shoot biomass, yield and curcumin content were obtained in the second experiment, but the effects of RLIs were smaller than in the first experiment because of late planting. This study indicates that turmeric is a partial shade-tolerant plant that could be cultivated at around 59?73% RLI for higher yield and curcumin content in Okinawa. However, the degree of RLI required for better turmeric cultivation may vary with the place, year and irradiance level.     

手持式植物冠层光谱测定仪在黄淮海平原地区冬小麦氮肥精准管理中应用的初步研究

通过应用手持式植物冠层光谱测定仪对冬小麦Feekes6生育期的冠层归一化植被指数（NDVI）和地上部氮素营养状况的测定，探讨了NDVI与小麦氮素营养状况之间的关系，旨在为手持式植物光谱测定仪在黄淮地区冬小麦氮肥精准管理中的应用提供依据。结果表明。小麦冠层NDVI值与同一时期植物干重产量、地上部氮素积累量间存在显著相关性（P〈0．01）；同时。Feekes6生育期冬小麦冠层NDVI值与收获期籽粒产量、地上部氮素积累量、籽粒氮素积累量之间存在显著相关性（P〈0．01）。对于地上部氮素积累量、籽粒氮素积累量与Feekes6生育期NDVI的关系，不同类型的拟合方程对比表明，直线方程比多项式、幂、指数和对数方程拟合结果的显著性更高。Feekes6生育期的红光／近红外比值（Red／NIR）与Feekes6生育期、收获期的作物产量、氮素积累量间也存在显著相关性。本文还讨论了利用Feekes6生育期NDVI值预测出的Feekes6生育期和收获期的作物地上部氮素积累量之差来计算冬小麦氮素追施量的方法。以上结果表明,黄淮海平原地区冬小麦Feekes6生育期冠层NDVI值和Red／NIR值可用于冬小麦的氮素精准管理。     

Evaluation of the yield potential and physicochemical properties of the biomass of Salix viminalis × Populus tremula hybrids

This study presents the characteristics of four Salix viminalis × Populus tremula hybrids, produced for the first time in the world grown in a three-year field experiment. Shoot weight per plant and major biomass yield components, including plant height, number of shoots per rootstock and shoot diameter, were determined. The infection severity caused by leaf rust (Melampsora sp.) was also evaluated. The biomass of three-year-old hybrid plants was subjected to chemical analyses and calorimetric tests to determine the energy value of biomass as solid fuel. Among the studied genotypes the highest yield was achieved by one of the studied hybrids. Its biometric parameters did not differ significantly from the standard genotype, and they were superior to the parameters of the maternal form. All Salix × Populus hybrids were more susceptible to rust infections than their maternal form and one hybrid was more resistant to infections caused by fungi of the genus Melampsora. Two hybrids have optimal biomass parameters as regards both calorific value and amount of carbon, hydrogen, sulfur and nitrogen.     

基于连续投影算法和光谱变换的冬小麦生物量高光谱遥感估算

为探索基于全波段冠层高光谱以及变换光谱的冬小麦地上部生物量的遥感估算方法,以2016、2017年冬小麦田间试验为基础,通过对冠层光谱和地上部生物量的相关性分析,筛选拔节期、抽穗期的冬小麦冠层光谱、一阶导数光谱、对数变换光谱和连续统去除光谱对地上部生物量的敏感波段,并结合偏最小二乘法(PLS)分别建立拔节期和抽穗期基于SPA算法的冬小麦地上部生物量估测模型,再与基于任意两波段组合的最佳归一化光谱指数、比值光谱指数、差值光谱指数和已报道光谱指数的冬小麦地上部生物量估测模型进行比较。结果表明：(1)SPA算法较好地利用了全波段冠层光谱信息,并显著降低了光谱维度,不同变换光谱的地上部生物量敏感波段个数在4~14之间;(2)拔节期和抽穗期冠层光谱与地上部生物量的相关性高于开花期和灌浆期,各生育时期一阶导数光谱与地上部生物量之间的相关性优于连续统去除光谱、对数变换光谱和光谱指数;(3) 利用抽穗期一阶导数光谱敏感波段建立的预测模型和验证模型达到了较高的精度,其预测模型的决定系数和均方根误差分别为0.78和0.87 t·hm^-2,验证模型的决定系数和均方根误差分别为 0.84和0.69 t·hm^-2,预测相对偏差为2.74。这说明,抽穗期是估算地上部生物量的最佳生育时期,且基于冠层一阶导数变换光谱,结合连续投影算法和偏最小二乘回归方法所构建抽穗期地上部生物量估算模型具有最优的精度和预测能力,可用于地上部生物量的定量估算。     

Examining the impact of shade on above-ground biomass and normalized difference vegetation index of C3 and C4 grass species in North-Western NSW,Australia

Previous investigations have detected a directional trend in the normalized difference vegetation index (NDVI) of pastures around scattered paddock trees and identified shade from the tree as the most likely causal factor. This study uses a field experiment to quantify the effect of varying levels of shade on the above-ground biomass and NDVI of three grass species native to Australia (Microlaena stipoides, C₃, shade tolerant; Austrodanthonia richardsonii, C₃, prefers full sunlight, and Chloris ventricosa, C₄, prefers full sunlight) in different seasons. The study demonstrates that shade had little influence on the above-ground biomass of C₃ species but significantly reduced biomass in the C₄ species. Until early winter, the NDVI of each species was generally significantly higher in all shaded treatments than in the no-shade treatment. This suggests that shaded plants retained a higher proportion of green biomass and/or changed leaf shape, increased leaf area and chlorophyll content. Regardless, although not proven in this experiment, it is likely shade prolonged the retention of green plant material into mid to late winter. Overall, this experiment explains the directional trends in NDVI around scattered trees found in previous work and suggests that shade from scattered trees prolongs green pasture production in a range of native grass species, without loss of C₃ pasture biomass.     

Development and growth of two Lesquerella species grown under different temperatures during the reproductive period

The genus Lesquerella is a promising source of hydroxy fatty acids (HFA). Several species such as Lesquerella fendleri and Lesquerella mendocina are candidate crops for arid and semi-arid cropping systems. Several reports are available on the environmental effects on growth and yield in Lesquerella, but information on the effect of temperature on plant growth and development specifically during the reproductive period in Lesquerella is limited. The objective of this work was to determine the effect of two contrasting thermal regimes after flowering on time to maturity, plant growth and biomass allocation to the different organs in L. fendleri and L. mendocina. A greenhouse experiment was conducted with plants grown at a range of 11–23 °C during the vegetative phase. After this stage, 50% of the plants of each species remained under the same temperature regime until maturity, whereas the other 50% was transferred to another module subjected to a range of 17–31 °C until maturity. The duration of the reproductive phase was reduced by 23 days in plants of both species in the 17–31 °C treatment compared to those at 11–23 °C, although no differences were observed when the length of the reproductive phase was measured in thermal-time units. Total plant biomass for both species was 20% greater in the 11–23 °C treatment. In L. fendleri, this increment occurred due to more vegetative shoot biomass, whereas in L. mendocina it was associated with greater reproductive and root biomass. No changes in biomass allocation were produced by temperature in L. fendleri, while in L. mendocina the lower temperature regime increased allocation to the reproductive organs, at the expense of a lower allocation to vegetative shoot. These results could be used to predict the specific temperature effects after flowering on yield under field conditions, and suggest that L. mendocina might be a promising perennial alternative for cooler sites.     

基于NDVI的滴灌春小麦氮肥分期施用推荐模型

为探讨利用冠层光谱数据实现滴灌春小麦推荐追施氮肥的可行性,利用手持主动遥感光谱仪(Greenseeker)测定了滴灌春小麦各生育时期的冠层NDVI值,分析其与滴灌小麦不同时期追施氮肥效应的关系.结果表明,从拔节期到乳熟期NDVI值与春小麦出苗后天数可用一元二次函数拟合,模型精度较高,R2均大于0.91;拔节期、孕穗期、抽穗期和灌浆期的冠层NDVI值与施氮量之间呈极显著线性相关;利用一元二次模型拟合出施氮量与产量之间的关系,得出实现最高产量7 393 kg·hm-2下的施氮量为289kg·hm-2,实现最佳经济产量7 378 kg·hm-2下的施氮量为265 kg·hm-2;拔节期、孕穗期、抽穗期和灌浆期的NDVI临界值分别为0.715、0.792、0.887和0.911;根据各生育时期NDVI值与施氮量的关系,建立了氮肥推荐模型,并且根据模型计算出滴灌春小麦各生育时期NDVI值对应的氮肥追施推荐用量表.     

利用有效积温提高冬小麦估产精度的研究

为探索如何利用冬小麦生长过程中的积温信息来提高遥感估产的准确性,以2009-2010和2012-2013年2个冬小麦生长季的田间试验数据为基础,利用有效积温和植被指数(NDVI)构建冬小麦当季估产指数INSEY(In-season estimate of yield)和INSEY-CGDD(In-season estimate of yield-cumulative growing degree days),分别用NDVI、INSEY和INSEY-CGDD与实测产量建立估产模型,并比较分析3类估产模型的精度。结果表明,3个变量与实测产量均成指数关系,其中INSEY-CGDD模型的精度最高(R2=0.59),预测能力最优,其次是INSEY模型(R2=0.55);而NDVI模型的精度最低(R2=0.35),预测能力最差。因此,在冬小麦估产模型中引入有效积温调整参数,可有效提高遥感估产模型精度。     

Effects of enhanced ultraviolet-B radiation on crop structure,growth and yield components of spring wheat under field conditions

Spring wheat (Triticum aestivum) was grown in the field for two consecutive seasons under ambient and supplemental levels of ultraviolet-B (UV-B, 280–315 nm) radiation to determine the potential for alterations in community structure, developmental stages, growth and yield components. The supplemental UV-B radiation simulated depletions of 12, 20, or 25% stratospheric ozone. Spring wheat is a potentially UV-B sensitive species, showing the greatest sensitivity to UV-B radiation at 5.31 kJ m⁻². Delays in development and decrease in plant height were observed at early tillering stage under UV-B treatment, and slowly exacerbated during further development. UV-B radiation changed crop structure, by decreasing the total number of tillers produced and increasing dead shoot number, resulted in fewer head-bearing shoots at ripening stage, and decreased biomass and yield. UV-B radiation decreased the area of the last leaf and leaf area index, but increased specific leaf weight. UV-B radiation inhibited biomass accumulation and altered the patterns of biomass partitioning; these effects might be correlated with yield. Decreases in yield were the result of significant reductions in spike number, grain number per spike and thousand grain weight under UV-B. Generally, the effects of UV-B radiation on developmental stages and crop structure were the most important, they might change the other characteristics of spring wheat crop. The responses of spring wheat crop to enhanced UV-B radiation were assessed, decreases in some crop characteristics caused by a 10 or 20% global ozone depletion were predicted. Ozone depletion had the greatest decrease in yield and the least reduction in plant height.     

Relationship between Shoot Elongation and Dry Matter Weight During Submergence in Oryza sativa L. and O. glaberrima Steud. Rice Cultivars

Abstract

Rice plants are damaged by flash floods with a rapid increase in water level caused by a heavy rain. However, rice plants cope with the flash floods either by an “escape strategy” involving rapid shoot elongation or by a “quiescence strategy” involving surviving under water with minimal activity. As we found in previous experiments, Saligbeli cultivar adapted well to flash floods through rapid shoot elongation. To understand the vigorous growth process during submergence, we studied the relationship between shoot elongation and changes in dry matter weight (DMW) during submergence. O. glaberrima Steud. cv. Saligbeli and O. sativa L. cv. Ballawé and IR 49830-7-1-2-2 were used. Saligbeli and Ballawé exhibit shoot elongation, and IR 49830-7-1-2-2 exhibits flash-flood tolerance due to the presence of the Sub-1 gene. Twelve-day-old seedlings were submerged for 7 days and the plant length and DMW were measured. The plant length ratio of submerged to control plants in Saligbeli was higher than that of other cultivars during 2-6 days of submergence but IR 49830-7-1-2-2 shoot elongation was inhibited by submergence. In all three cultivars, the elongation of the developing leaf sheath conferred shoot elongation during submergence. The plant length of all submerged plants showed a strong positive correlation with DMW of the leaves developed during submergence. Submerged Saligbeli and Ballawé showed strong negative correlations between DMW of the leaves developed before and during submergence (r = –0.786 for Saligbeli and –0.772 for Ballawé , P < 0.05), suggesting that the enhancement of shoot elongation during submergence is accomplished by using dry matter of the leaves developed before submergence. However, the correlation was not observed in the submerged IR 49830-7-1-2-2. Further details from studies using isotopes are also needed to understand the plant growth during submergence.     

Tolerance to Fusarium wilt and anthracnose diseases and changes of antioxidative activity in mycorrhizal cyclamen

Mycorrhizal associations imply a remarkable reprogramming of functions in both plant and fungal symbionts. This consequent alteration on plant physiology has a clear impact on the plant responses to biotic stress management. As a consequence, a pot experiment was conducted to study the interactions between the arbuscular mycorrhizal fungus (AMF) Glomus fasciculatum and the two pathogens Fusarium oxysporum and Colletotrichum gloeosporioides and subsequent effect on growth, disease tolerance and the changes in antioxidative ability in cyclamen plants under growth chamber condition were investigated. At plant maturity, inoculation with F. oxysporum and C. gloeosporioides, responsible for Fusarium wilt and anthracnose of cyclamen respectively, significantly reduced shoot and root dry weights, increased both the disease incidence percentage and showed lower antioxidative activity viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), ascorbic acid (AA) and polyphenol contents in plants. In contrast, the growth response and biomass production of cyclamen plants inoculated with AMF was significantly higher than the nonmycorrhizal control plants, both in the presence and absence of the pathogens. Mycorrhization enhanced plants to reduce the Fusarium wilt and anthracnose incidence compared to nonmycorrhizal controls. In every case, without and with pathogen association, plants inoculated with AMF increased the antioxidant (SOD, APX, AA and polyphenol) production compared to control plants. The results demonstrate that AMF have the ability to induce resistance against Fusarium wilt and anthracnose in cyclamen by increasing the antioxidative activity in plants, which promoted plant growth, biomass production and drastically reduced the disease incidence in cyclamen.     

夏玉米长势卫星遥感动态监测指标研究

通过野外样点布设获取地面农学参数平均株高、群体密度、干物重和叶面积指数,经过频数统计分析,获得夏玉米一、二、三类苗苗情农学指标。结合MODIS遥感数据,进行农学参数和归一化植被指数(NDVI)的相关分析,结果显示,NDVI和平均株高、叶面积指数以及生物量都呈显著正相关,其中NDVI和叶面积指数关系最为显著(各生育期R2>0.623),因此可通过建立叶面积指数和NDVI的关系确定夏玉米长势遥感指标,为大面积遥感监测夏玉米长势提供科学依据。     

Utilization of potatoes for life support systems in space. I. Cultivar-photoperiod interactions

The productive potential of potatoes (Solanum tuberosum L. cvs. Norland, Superior, Norchip, and Kennebec) was assessed for life support systems being proposed for space stations and/or lunar colonies. Plants were grown in walk-in growth rooms for 15 weeks at 20 C under 12-, 16- and 20-h photoperiods of 400 μmol m^t-2s^t-1 photosynthetic photon flux (PPF). Norland yielded the greatest tuber fresh weight, producing 2.3, 2.4, and 2.9 kg/plant under 12-, 16-, and 20-h photoperiods, respectively. The respective yields for the other cultivars under 12-, 16-, and 20-h were: Superior, 1.9, 1.5, and 1.8 kg/plant; Norchip, 1.8, 1.4, and 2.0 kg/plant; and Kennebec, 2.3, 0.2, and 0.8 kg/plant. Shoot and total plant biomass increased with lengthening photoperiods except for Kennebec, which showed increased shoot growth but no change in total growth with the longer photoperiods. Kennebec shoot growth under the 20-h photoperiod, and to some extent under 16-h, was noticeably stunted with shortened internodes. In addition, leaves of these plants showed mild chlorosis with rusty “flecking” of the surfaces. The harvest index (ratio of tuber yield/total biomass) was highest for all cultivars under the 12-h photoperiod, with a maximum of 0.69 for Norland. Similarly, the tuber yield per input of irradiant energy also was highest under 12-h for all cultivars. The tuber yield expressed on an area basis for the highest yielding treatment (Norland under 20-h) equaled 2.2 kg dry matter m^t-2. Over 15 weeks this equates to a productivity of 20.7 g tuber dry matter m^t-2 day^t-1. Assuming 3.73 kcal per g tuber dry matter and a daily human dietary requirement of 2800 kcal, then 36 m² of potatoes could supply the daily energy requirement for one human. Potential for increasing productivity is discussed.     

Biomass distribution,maturity acceleration and yield in drought-stressed common bean cultivars

Common bean (Phaseolus vulgaris L.) is an important food crop grown under rainfed conditions in Latin America where drought is a major limiting factor for production. The objective of this study was to assess the role of phenological adjustment and shoot biomass distribution on seed yield of drought-stressed common bean. Four cultivars differing in growth habit, gene pool origin, and contrasting responses under drought, were tested during 2001 at two locations in Mexico: Cotaxtla, Veracruz (lowlands) where the effect of terminal drought (TD) (end-of-season) was evaluated, and Texcoco, State of Mexico (highlands), where the effects of intermittent and terminal drought were evaluated. Seed yield, plant shoot biomass, and days to flowering and to physiological maturity were recorded. Leaf relative water content (RWC) was recorded after the onset of the intermittent drought (ID) treatment in Texcoco. The drought intensity index was 0.37 in Cotaxtla compared to 0.49 and 0.58 under TD and ID, respectively in Texcoco. Days to flowering and to physiological maturity showed a negative and significant relationship with seed yield. Under drought stress, a significant reduction in the harvest index was observed in susceptible cultivars. All cultivars showed higher values of shoot biomass accumulation, pod and seed number, seed weight and RWC at the basal nodes of the plant across locations and moisture treatments. Cultivar Pinto Villa exhibited the highest biomass accumulation and seed yield across treatments and locations. Significant reduction in number of days to maturity was observed under drought, mainly in resistant cultivars, Pinto Villa and G4523. Maturity acceleration, coupled with a high seed filling rate, contributed to lessen the impact of drought stress in resistant common bean cultivars.     

Effect of lowering the root/shoot ratio by pruning roots on water use efficiency and grain yield of winter wheat

A pot and a field experiment were conducted to assess the effects of root/shoot ratio (R/S) on the water use efficiency (WUE) and grain yield of winter wheat. The R/S was regulated by pruning the roots during the stem elongation stage, resulting in reduced root systems of the plants. At the heading stage, the root dry weight of root-pruned plants was less than that of intact-root plants, but their R/S was similar to that of intact-root plants under both experimental conditions. After tiller pruning, the R/S of root-pruned plants was significantly lower than that of intact-root plants (p < 0.05). Root pruning reduced the rate of leaf transpiration and lowered the number of tillers per plant (p < 0.05) during the vegetative stage. As a result, root-pruned wheat showed reduced water use when compared to intact-root plants before heading (p < 0.05). At anthesis, there was no significant difference in transpiration between plants with intact roots and those with pruned roots in the pots. However, under field conditions, transpiration of root-pruned plants was significantly higher than that of intact-root plants at anthesis. Additionally, at anthesis root-pruned plants had a higher rate of leaf photosynthesis and lower rate of root respiration, which resulted in a significantly higher grain yield at maturity when compared to plants with intact roots. Under both experimental conditions, there were no significant differences in shoot dry weight per plant between root-pruned and intact-root plants grown in monoculture. When root-pruned plants were grown with intact-root plants, the root-pruned wheat was less productive and had a lower relative shoot dry weight (0.78 and 0.86, respectively) than the intact-root plants (1.24 and 1.16, respectively). These results suggest that plants with pruned roots had a lower ability to compete and to acquire and use the same resources in the mixture when compared with intact-root plants. Root pruning improved the WUE of winter wheat under both experimental conditions. This suggests that appropriate management for the root system/tillers in wheat crops can be used to increase grain yield and water use efficiency. Specifically, lowering the R/S improved the grain yield and WUE of winter wheat significantly by lowering its competitive ability and improving root efficiency. Therefore, drought-resistance breeding to improve the grain yield and WUE, at least for wheat, should be made by targeted selection of less competitive progeny with a small R/S for cultivation in arid and semiarid areas.