Response of Indoor-Grown Cassava to Water Deficits and Recovery of Leaf Water Potential and Stomatal Activity after Water Stress

Wilting of the leaves occurred in acropetal succession at leafwater potentials between –0.9 and –1.1 MPa. Onlysevere water stress caused the discoloration and abscissionof the basal leaves. Leaf resistance was independent of leafwater potential above –0.5 MPa but increased as the potentialdropped below this value. When the stressed plants were rewatered,leaf water potentials recovered rapidly within the first h.Subsequently, the rate of recovery declined gradually. The maximumvalue of leaf water potential after rewatering was dependenton the severity of the water stress.     

Influence of Rate of Development of Leaf Water Deficits upon Photosynthesis, Leaf Conductance, Water Use Efficiency, and Osmotic Potential in Sorghum

This study reports the effect of rate of development of leaf water deficits in soil-grown sorghum (Sorghum bicolor) on the relationship of net photosynthesis, leaf conductance, and water use efficiency to leaf water potential, and on the degree of solute accumulation (osmotic adjustment). Recovery of these processes on rewatering, and responses during a second stress cycle were also studied. The most rapid rate of stress (1.2 MPa day^?1) resulted in no solute accumulation and the lowest rate of net photosynthesis and leaf conductance for any given leaf water potential during stress. Stress at 0.7 and 0.15 MPa day^?1 led to equal solute accumulations of approximately 0.6 MPa, but net photosynthesis, leaf conductance, and water use efficiency at a given leaf water potential were lower with the faster rate of stress (0.7 MPa day^?1). Additionally, leaf conductance at a given leaf turgor potential was lowest at the 1.2 MPa day^?1 stress rate, slightly higher at the intermediate rate of stress, and clearly highest at the slowest rate of stress. Recovery of both net photosynthesis and leaf conductance upon rewatering was rapid, taking less than 3 days, but full recovery of osmotic potential took between 6 and 11 days. One slow stress cycle had no influence on relationships during a second cycle. The concept of a threshold leaf water potential for stomatal closure is discussed and the conclusion reached that stomatal closure occurs slowly over a wide range of leaf water potential (> 1.0 MPa), the range being greater for slower rates of stress.     

Leaf Response to Water Deficits in Soybeans

Soybeans [Glycine max (L.) Merrill cv. Wayne] plants were subjected to an extended drying cycle in the field to investigate the leaf sensitivity to water deficits. Soybeans in irrigated plots were superior to those in non-irrigated plots in the average size and number of leaflets per plant. Apparent differences in the leaf area distributions in the canopy seemed to be mediated by moisture stress effects associated with leaf senescence and light penetration in the lower depths of the canopy. A major decrease in leaf enlargement occurred near a leaf-water potential of -8 bars, and at - 12 bars, the growth was completely halted. Similar decreases were observed at a stomatal conductance of 0.4 cm/s and at 0.2 cm/s no enlargement was observed.     

两个荔枝品种的叶面积与叶重量估测模型

以‘黑叶’和‘怀枝’2个荔枝品种的成熟叶片为材料,对叶周长、叶长、叶宽、叶长宽乘积与叶面积、叶重量之间的相关性进行回归分析。结果表明,‘黑叶’和‘怀枝’均可通过叶周长、叶长、叶宽和叶长宽乘积进行叶面积估算,其中以叶长宽乘积的估算效果最好;‘黑叶’可通过叶周长、叶长、叶宽、叶长宽乘积和叶面积估算叶重量,其中以叶长指标的估算效果最佳;‘怀枝’基于上述5个叶形指标进行的叶重量估算效果不佳。     

Leaf Area and Absolute Leaf Water Content

Leaf area was found to be an almost linear function of absoluteleaf water content (that is fresh weight—dry weight) forseveral dicotyledonous genotypes. A closely similar relationshipheld for a given genotype in the same rooting medium despiteincreasing plant size and different treatments which resultedin leaves which were sometimes morphologically dissimilar andoften substantially different in specific leaf water contents(water/dry matter). The usefulness of the linear relationshipfor estimating leaf area in growth studies is noted.     

Interrelationship between Leaf Gas-Exchange Characteristics,Area Leaf Mass,and Yield in Soybean (Glycine max L. Merr) Genotypes

Variability in leaf gas-exchange traits in thirteen soybean (Glycine max L. Merr) genotypes was assessed in a field experiment conducted at high altitude (1 950 m). Leaf net photosynthetic rate (P ^N) exhibited a high degree of variability at all the growth stages studied. P _N and other gas-exchange parameters exhibited a seasonal pattern that was similar for all the genotypes. P _N rate was highest at seed filling stage. P _N was positively and significantly associated with aboveground dry matter and seed yield. The area leaf mass (ALM) exhibited a strong positive association with leaf P _N, aboveground dry matter, and seed yield. The positive association between ALM, P _N, and seed yield suggests that this simple and easy to measure character can be used in breeding programmes as a surrogate for higher photosynthetic efficiency and eventually higher yield.     

Diversity,Distribution and Effects on Cassava Cultivars of Cassava Brown Streak Viruses in Malawi

Cassava brown streak disease (CBSD) has emerged as a major threat to cassava (Manihot esculenta) in eastern and southern Africa. CBSD was first reported in Malawi in the 1950s, but little data on the distribution and epidemiology of the disease are available. A diagnostic survey was therefore conducted in Malawi to determine the distribution, incidence and diversity of viruses causing the disease, and to characterize its effects on local cassava cultivars. Diagnostic tests confirmed the presence of cassava brown streak viruses (CBSVs) in 90% of leaf samples from symptomatic plants. Average CBSD foliar severity was 2.5, although this varied significantly between districts. Both Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) (genus Ipomovirus, family Potyviridae) were detected from sampled plants. UCBSV was widespread, whereas CBSV was detected only in the two most northerly districts. The average abundance of the whitefly vector (Bemisia tabaci) was 0.4 per plant, a low value that was partly attributable to the fact that the survey was conducted during the cool part of the year known to be unfavourable for B. tabaci whiteflies. Spearman's correlation analyses showed a positive correlation between CBSD foliar incidence and CBSD severity and between CBSD severity and CBSD stem incidence. Of the 31 cassava varieties encountered, 20–20 was most severely affected, whilst Mtutumusi was completely unaffected. Although data from this study do not indicate a significant CBSD deterioration in Malawi, strengthened management efforts are required to reduce the current impact of the disease.     

回归方程法测定两个龙眼品种叶面积研究

以‘储良’和‘石硖’2个龙眼品种的成熟叶为材料,对叶片的周长、长、宽、长/宽、宽×宽、长×长、长×宽等指标与叶面积的相关性进行分析,建立9种模拟回归方程。结果表明,‘储良’和‘石硖’的叶面积均可用叶片的周长、长、宽、长/宽、宽×宽、长×长、长×宽等指标进行估算,基于叶长×叶宽建立的9种叶面积回归方程R2均最高,拟合效果最好,且相关性最大,因此叶片长×宽可作为龙眼叶面积估测的首选指标。基于叶长×宽建立的9个回归方程中,一元线性方程、二次方程、三次方程、幂函数能较好拟合,其中以幂函数估算的精度最高,较适合用来估测龙眼的叶面积。‘储良’和‘石硖’叶面积对应的较为精准的叶面积幂函数方程分别为:y=0.751x1.006和y=0.986x0.973。最适合两个龙眼品种的总叶面积幂函数方程为y=0.869x0.988。     

Incidence of Three Major Cassava Diseases on Local Susceptible Cassava Cultivars at Three Planting Dates

Incidence of African cassava mosaic (ACMD), cassava bacterial blight (CBB), and cassava anthracnose (CA) on local susceptible cassava cultivars planted in December, February, and April was investigated. December cassava planting had a higher incidence of ACMD, CBB, and CA diseases compared with February and April plantings. CA seemed to be more prevalent at an older stage (8 months old) of plant growth. April planting had significantly lower incidence of major cassava diseases, and higher mean tuber, yield than the same cassava cultivars planted earlier. The length of exposure of cassava plants to the inocula and/or to the vector during the rainy season determines the occurrence of diseases. In the absence of resistant cassava cultivars and through, partial disease escape of susceptible cultivars from ACMD, CBB, and CA, planting the same cultivars in April can still produce a profitable cassava crop.     

Control of Plant Water Deficits Using the 'Snow and Tingey System' and Their Influence on the Water Relations and Growth of Sunflower

A system, designed by Snow and Tingey (1985) for ‘subjectingplants to reproducible water stress levels for extended periodsof time’, is considered. Modifications are also outlinedwhich enable water table heights to be maintained without theneed for complex float chambers. Sunflower plants (Helianthus annuus L. cv. Frankasol) were grownusing the system and these were either ‘well-watered’or subjected to water deficits. The temporal development ofwater deficits was closely monitored by regular psychrometricmeasurements of leaf water potential. Diurnal stomatal behaviour,mid-day abaxial stomatal conductance, and photosynthetic assimilationrates were also determined throughout the experiment, with growthanalysis at the end. A reduction in stomatal conductance occurred within 2–4d after the onset of a restriction in water supply. Data fromboth viscous flow and diffusion porometry suggested that stomatalclosure apparently began without a fall in bulk leaf water potential.Leaf water potentials of plants with a restricted supply ofwater did, however, subsequently decline during the early partof the experiment reaching values as low as –0.99±0.07 MPa after 14 d. No further reduction in bulk water potentialwas observed after a further 5 d, suggesting that a steady-statehad been reached. Corresponding values of leaf water potentialfor well-watered plants were about –0.60 ± 0.04MPa. Biomass determinations indicated the potential for quantifyingthe effects of water deficits, of controlled magnitudes, onrates of leaf production and expansion. However, the possibilityof physical limitations of root development—imposed bothby the plant container and also by the imposition of restrictedwater supplies—must be carefully considered when planningexperiments with this system.     

生长期对不同品种(系)木薯品质特性的影响

本文研究了不同生长期对不同品种(系)木薯含粉率、氢氰酸和单宁含量等品质特性的影响.结果表明,随着生长期的延长,木薯含粉率呈现先增加后下降的趋势,氢氰酸和单宁含量的变化趋势因品种(系)而异.品种南植在生长7个月收获时,木薯淀粉含量高,氢氰酸和单宁含量较低,品种D、SC和ZM在生长9个月收获时,木薯淀粉含量高,氢氰酸和单宁含量较低,因此适合食品用淀粉的深加工;品种C和E在生长8个月收获时,淀粉含量高,但氢氰酸和单宁含量也较高.本研究探明了不同生长期和品种对鲜木薯含粉率、单宁和氢氰酸含量的影响,为合理选择生长期和木薯品种提供理论支撑.     

The Relative Resistance of Cassava Cultivars to African Cassava Mosaic Disease (ACMD) as Determined by Two Methods: Rank-Sum and the Area Under the Disease Progress Curve

Twenty-five newly bred improved cassava cultivars, twenty-three improved from the International Institute of Tropical Agriculture and two local cultivars were evaluated for their relative resistance to African cassava mosaic begomovirus disease (ACMD) at Ibadan, in an area of high disease pressure representative of the forest/savanna transition zone of Nigeria. These cultivars were exposed to natural infection by the viruliferous whiteflies ( Bemisia tabaci Gennadius) and the disease incidence (DI) and index of symptom severity (ISS) were assessed for all clones. Results for the Rank-sum (i.e., sum of ranks for DI and ISS for each cultivar) and the area under the disease progress curve (AUDPC) were used to assess the relative resistance of the cassava clones. Those that showed low Rank-sum and AUDPC values were rated 'moderately resistant (MR)', 'resistant ( R )', and 'highly resistant (HR)' to ACMD depending on their respective values and deviation from the mean distribution curve. Clones M94/0121 and 94/0239 were rated HR under the two methods. Clone M94/0583 was rated HR under the AUDPC with a deviation from the mean distribution curve of m 2.00 while it was rated R under the Rank-sum method with a deviation from the mean distribution of m 1.99. Also plants of clones ISU and TMS 30572 were rated highly susceptible (HS) under both methods. Clone TME-1 was intermediate between Moderately resistant (MR) and Moderately susceptible (MS) under the AUDPC method with a deviation from the mean distribution of 0.00 but observed to be MS under the Rank-sum method with a deviation of + 0.2. The two methods of evaluation gave similar results as revealed by Spearman rank correlation ( r equals; 0.99, P <0.01). However, the AUDPC method is less cumbersome compared to the Rank-sum method. None of the clones was observed to be immune to the disease.     

水葫芦叶蛋白开发研究现状及发展趋势

本文概括了水葫芦叶蛋白开发研究现状,包括水葫芦叶蛋白的营养价值、提取工艺、毒性和功能性质评价。并预测了水葫芦叶蛋白研究的发展趋势。     

Cell Membrane Stability and Leaf Surface Wax Content as Affected by Increasing Water Deficits in Maize

A field experiment was conducted with a water-stressed treatmentand well-watered control using eight maize (Zea mays L.) cultivars.Effects of water deficits on cell membrane stability (CMS) measuredby the polyethylene glycol (PEG) test, leaf surface wax content,and relative growth rate were investigated. Cytoplasmic lipidcontent was also analysed. Cell membrane stability and leaf surface wax content increasedwith the degrees of stress. Tolerance to drought evaluated asincrease in CMS under water deficit conditions was well differentiatedbetween cultivars and was well correlated with a reduction inrelative growth rate under stress. A negative correlation wasfound between percentage injury in the PEG test and leaf surfacewax content. High phospholipid contents were observed in tissuesof drought tolerant cultivars under water deficit conditions. Key words: Cell membrane stability, cytoplasmic lipid, drought tolerance, leaf surface wax, relative growth rate     

Somatic Embryogenesis from Clonal Leaf Tissues of Cassava

Leaf lobes were isolated from palmate leaves of clonal cassava(Manihot esculenta Crantz) material growing in vitro or in glasshouseconditions and subjected to a two-stage culture procedure involvingincubation on Murashige and Skoog (MS2) basal medium supplementedwith 2–12 mg l^–1 2,4-D for 20 d (Stage I) beforetransfer to MS2 basal medium supplemented with 0.01 mg l^–12,4-D and 0.1 mg l^–1 6-benzylamino purine (BAP) (StageII medium). Embryogenetic tissues, foliose structures and somatic embryosdeveloped from leaf lobes at all Stage I 2,4-D concentrations,except on those explants isolated from shoot-tip cultures incubatedon MS2 basal medium supplemented with 0.1 mg l^–1 NAA and1.0 mg l^–1 BAP. Leaf lobes isolated directly from glasshouse plants showed optimalembryogenetic competence when subjected to a Stage I cultureperiod of 17 d, although foliose structure initiation was optimalwith shorter Stage I durations. Leaf lobes of 2–4 mm lengthand those isolated from phyllotaxic leaf numbers 4 and 5 showedthe greatest embryogenetic competence. Manihot esculenta, cassava, somatic embryogenesis, tissue culture, morphogenetic competence     

木薯商业品种的指纹图谱构建

利用SSR分子标记技术构建10个木薯商业品种的指纹图谱。通过基因组多态性分析,从已定位于木薯连锁群的44对SSR引物中筛选到22对扩增效果好的引物,经统计分析发现,用其中4对引物ssry-13、ssry-19、ssry-23和ssry-45的组合能够建立该组木薯商业品种的指纹图谱,品种鉴定的置信概率达到99.9985%。     

Effects of Water Deficits on Carbon Assimilation

This review focuses on the effects of water deficits on photosynthesisand partitioning of assimilates at the leaf level. It is nowestablished that the rate of CO₂ assimilation in the leavesis depressed at moderate water deficits, mostly as a consequenceof stomatal closure. In fact, depending on the species and onthe nature of dehydration, carbon assimilation may diminishto values close to zero without any significant decline in mesophyllphotosynthetic capacity. This remarkable resistance of the photosyntheticapparatus to water deficits became apparent after the measurementof photosynthesis at saturating CO₂ concentrations was madepossible. Whenever light or heat stress are superimposed a declinein mesophyll photosynthesis may occur as a result of a ‘down-regulation’process, which seems to vary among genotypes. A major secondaryeffect of dehydration on photosynthetic carbon metabolism isthe change in partitioning of recently fixed carbon towardssucrose, which occurs in a number of species in parallel tothe increase in starch breakdown. This increase in compoundsof low molecular weight may contribute to an osmotic adjustment.Controlling mechanisms involved in this process deserve furtherinvestigation. Key words: Carbohydrates, carbon partitioning, heat stress, photoinhibition, photosynthetic capacity, stomatal limitation, water deficits     

Water Stress and Leaf Growth of Field Beans (Vicia faba L.) in the Field: Leaf Number and Total Leaf Area

The leaf area growth of field beans grown under covers in thefield was measured non-destructively on plants subjected tothree different degrees of soil water stress by means of dryingcycles of different lengths in 1974 and 1975. After a periodof 46 days the total leaf area of the well-watered plants wasabout double that of the non-watered ones. The total leaf areaat the final-sampling and the mean plant water potential duringthe observation period were linearly related with highly significantcorrelation coefficients (0·96 in 1974 and 0·86in 1975). The differences between treatments in total leaf areawere mainly produced by the mechanisms determining leaf sizerather than those associated with leaf production and maintenance,namely leaf production, unfolding and death. In neither yearwas leaf production or unfolding sensitive to water stress beforeflowering. Plant water potential () exerted a cumulative longterm effect on these two mechanisms. The threshold values of for reducing the rates of leaf production and unfolding weremore negative in the drier year (1975). Leaf death was affectedby drought earlier than leaf production and unfolding. Vicia faba, field bean, water stress, leaf area     

Evaluation of Cassava Cultivars for Resistance to Cassava Mosaic Disease and Yield Potential in Central African Republic

Eleven cassava genotypes were tested against cassava mosaic disease (CMD) and compared to a local susceptible cultivar in field conditions from June 2011 to July 2012 in Central African Republic (CAR) at two sites representative of the savanna (Damara) and forest (Pissa) zones of the country. The mean number of whiteflies observed on plants varied among genotypes within each site, but was found nearly three times higher at Damara than at Pissa, resulting in a CMD incidence nearly five times higher at Damara than at Pissa. However, no relation was observed between the number of insect on the plants and the level of susceptibility/resistance of the genotypes. The difference of disease pressure between the two sites revealed high level of resistance in several genotypes, while some other ones indicated rather only a partial resistance. Nevertheless, none of the genotypes tested was found immune, in the end, the virus being detected at least in one site in every genotype, including those ones presenting no symptoms in both sites. The impact of CMD on yield components was assessed on the local susceptible check and three partially resistant genotypes, showing that the disease has no significant effect on the tuberous roots number as well as their weight in both sites. The yield potential varied among different genotypes and between the two sites, the mean number of tuberous roots as well as their mean weight being higher in Damara than in Pissa. This study identified highly resistant genotypes such as ‘Gabon’ that performed well in both sites, and ‘91/02322’ that was symptomless and presented a yield potential equivalent to the local check. These genotypes could be distributed to growers with the main advantage to be resistant to CMD and, therefore, reducing the risk to spread sources of inoculum all over the cassava cropping areas in the country.