Effects of short-term storage on germinability of pistachio pollen

The effects of short‐term storage under room conditions (constant 25°C and 35% relative humidity), refrigeration (4°C) and freezing (‐20°C) on the germinability of pollen of pistachio, Pistacia vera L., were studied and the effects of desiccation and pollen age on its germinability were reassessed. It was found that: (1) weight loss as a result of desiccation was positively correlated with germinability; (2) pollen grains stored in room conditions only germinated after prehydration, which restored germinability even after 7 days of exposure; (3) refrigerated (4°C) pollen grains retained their germinability for at least a week; (4) frozen pollen grains irreversibly lost most of their germinability; (5) 2‐day‐old pollen grains, within the anthers, retained their germinability under room conditions. These findings will contribute to the improvement of pistachio pollen preservation and help to find a simple and inexpensive method for its short‐term storage, while retaining its germinability.     

Nutrient seed priming improves seedling development of maize exposed to low root zone temperatures during early growth

Low root zone temperature (RZT) in early spring is a major constraint for maize production in Central and Northern Europe. Nutrient acquisition, nutrient uptake and particularly root growth are severely reduced at low RZT and the consequences of these growth depressions are frequently not completely compensated until final harvest. Perspectives to overcome these limitations by seed priming treatments with different micronutrients (Fe, Zn, Mn) were studied with maize seedlings exposed to low RZT (12 °C).Model experiments were performed in nutrient solution and soil culture using rhizo-boxes with root observation windows under green house conditions. To observe effects on final grain yield, additionally two field experiments were conducted in 2010 and 2011. Nutrient seed priming resulted in a significant increase in seed contents of the respective nutrients, i.e. Fe (25%), Zn (500%) and Mn (800%). At low RZT, biomass production and total root length of maize plants were significantly increased after Fe and Zn + Mn priming treatments, both in nutrient solution and in rhizo-box culture. There was no prominent difference in shoot Fe, Zn, Mn and P concentrations but total shoot contents per plant were significantly increased after nutrient seed priming. Plant growth promotion and improved micronutrient status was detectable also under field conditions at 5 weeks after sowing. This offers perspectives for using micronutrient seed priming for improving early seedling development and plant nutrient status of maize under low temperature climatic conditions.     

Variance component estimations and allocation of resources for breeding sweetpotato under East African conditions

In Africa, average sweetpotato storage root yields are low and breeding is considered to be an important factor in increasing production. The objectives of this study were to obtain variance component estimations for sweetpotato in this region of the world and then use these to determine the efficiency of variety trials and breeding systems. From an incomplete series of variety trials in Kenya and Uganda (comprising 15 genotypes, three locations, two crop durations and three seasons) variance components were estimated ‐ using the REML method ‐ for the following traits: storage root yield, biomass production, harvest index, storage root dry matter and the Elston index which was used to aggregate all four traits. The storage root yield of clones across all 12 environments ranged from 15.2 to 33.0 t/ha. The variance components were significant for all traits, except the genotype by season interactions for storage root dry matter. The efficiency of selection systems was determined for total test capacities of 450 and 900 plots and using not more than five locations. Two‐stage selection was 17‐81% more efficient than one‐stage selection after two seasons of testing. Two‐stage selection was optimized under the restriction of using at least two locations at step 1. Trials with two locations and one replication at step 1 and five locations and two replications at step 2 were appropriate both for selecting for storage root yield and for simultaneously selecting for storage root yield, biomass production, harvest index and storage root dry matter content by using the Elston index. There are indications that such an allocation of resources for breeding sweetpotato is also appropriate for other regions in Sub‐Saharan Africa.     

The stage sensitivity of short‐term heat stress to lodging‐resistant traits and yield determination in canola (Brassica napus L.)

With the expected increase of abiotic stress under global climate change, significant research has been devoted to how abiotic stress will affect crop production. To date, there has been little research on the stage sensitivity of short‐term heat stress to crop lodging and yield determination in canola. This research was conducted in a controlled growth facility and aimed to examine root morphology, pod fertility, seed yield and crop lodging of two contrasting canola genotypes subjected to a short‐term heat stress (27.0/24.3°C, light/dark), imposed respectively at three growth stages, rosette vegetative stage (RVHT), early flowering stage (EFHT) and late flowering stage (LFHT), in comparison with non‐stressed control (CK) (23/17°C). The results demonstrate that heat stress imposed at RVHT and LFHT was less detrimental to seed yield and lodging resistance. However, EFHT showed significant adverse effects on both, which was further confirmed by redundancy analysis (RDA) and structural equation modelling (SEM). Compared with the CK, EFHT resulted in a yield loss of 43%, which was mainly due to poor pod fertility, less number of filled pods (?28%), decreased pollen viability (?38%) and a lower success ratio of filled pods (?29%). The taproot was found to be relatively tolerant to heat stress, but lateral roots were sensitive to heat stress at EFHT and LFHT. Root capacitance could be used as a non‐destructive method for evaluating lateral root morphology. Compared with the CK, EFHT displayed a high risk of stem lodging, as indicated by a 27% lower safety factor. This was mainly attributed to the reduced stem bending strength that was caused by the deterioration of stem mechanical properties under EFHT, as illustrated by SEM. Root lodging resistance was not altered by any stages of short‐term heat stress, as the taproot remained stable.     

The Impact of Temperature on Seedling Root Traits of European and Tropical Maize (Zea mays L.) Cultivars

Twelve European and twelve tropical maize cultivars were grown in polyethylene tubes under three temperature regimes (14/12 °C, 22/20 °C; 30/28 °C). The plants were harvested when the third leaf was fully expanded. The experiments were undertaken in order to: (i) study the general response of root traits of maize seedlings to chilly, temperate and very warm conditions and (ii) find out whether and how the geographical origin of the maize material modifies the results. The results may be summarized as follows: 1. The 22/20 °C temperature regime led to the highest shoot and root dry weight, the greatest total root length, the most apices and the greatest root surface area. However, the optimal temperature for these traits appeared to be either slightly higher or lower than 22/20 °C (optimal temperature for number of apices > shoot dry weight > root surface area > root dry weight). 2. The shoot: root dry weight ratio was almost the same at 14/12 °C and 22/20 °C but increased significantly at 30/28 °C. The root surface area: root dry weight ratio was optimal at 22/20 °C but extremely low at 14/12 °C. The production of apices per unit root dry matter was lowest at 14/12 °C and increased steadily at higher temperatures. 3. The root surface area: shoot dry weight ratio was low both at 14/12 °C and at 30/28 °C. This may indicate that mineral nutrient deficiency, as a result of undersized root systems, is most likely at extremely low and extremely high temperatures. 4. Low temperatures promoted the formation of seminal roots. 5. Temperature affected the dominance of the longest seminal root (= primary root). At 14/12 °C, the primary root was rather short as compared to the seminal roots of higher order. At 30/28 °C, however, the primary root was markedly longer than other seminal roots of higher order. 6. At 14/12 °C, the European cultivars produced more shoot and root dry matter, generated more apices and developed greater root surface area than the tropical cultivars. At 30/28 °C, the situation was reversed. This confirms that the response to different temperatures is modified by the geographical origin of the plant material.     

Water stress and warming impact nutrient use efficiency of Mombasa grass (Megathyrsus maximus) in tropical conditions

Temperature and other abiotic factors, such water and nutrient availability, play an important role for plants in response to the changing environments. At this regard, both warming and drought might affect the nutrient use efficiency (NUE) and growth of Megathyrsus maximus a C4 forage grass of high interest for cattle feeding. However, the nutrient requirements of this species under climate change are unknown. Therefore, we aimed to evaluate the individual and combined effects of two levels of temperature: ambient and elevated temperature (2°C above ambient temperature), and two levels of soil water availability: irrigated plants and non‐irrigated plants on accumulation of leaf nutrients, NUE and biomass production of M. maximus. Temperature control was performed by a temperature free‐air‐controlled enhancement (T‐FACE) system under field conditions. In general, we observed that warming under well‐irrigated conditions increased the leaf accumulation of most nutrients, improving the NUE of N, P, K, Ca, Mg, Cu, Mn and Zn. Plant growth was also enhanced under warming effects, with higher leaf dry mass accumulation and root development. Meanwhile, drought decreased NUE of K, Ca, B and leaf dry biomass, while root growth was stimulated. The combined effects of warming and drought on nutrient accumulation, NUE and plant growth tended to be greater than the individual effects expected from a single factor; thus, warming mitigated the negative impacts of individual drought. In summary, our findings suggest that warming and drought, both as individual and combined factors, will change the nutrient requirements of M. maximus in tropical ecosystems.     

Identification of simple sequence repeat markers for sweetpotato weevil resistance

The development of sweetpotato [Ipomoea batatas (L.) Lam] germplasm with resistance to sweetpotato weevil (SPW) requires an understanding of the biochemical and genetic mechanisms of resistance to optimize crop resistance. The African sweetpotato landrace, ‘New Kawogo’, was reported to be moderately resistant to two species of SPW, Cylas puncticollis and Cylas brunneus. Resistance has been associated with the presence of hydroxycinnamic acids esters (HCAs), but the underlying genetic basis remains unknown. To determine the genetic basis of this resistance, a bi-parental sweetpotato population from a cross between the moderately resistant, white-fleshed ‘New Kawogo’ and the highly susceptible, orange-fleshed North American variety ‘Beauregard’ was evaluated for SPW resistance and genotyped with simple sequence repeat (SSR) markers to identify weevil resistance loci. SPW resistance was measured on the basis of field storage root SPW damage severity and total HCA ester concentrations. Moderate broad sense heritability (H² = 0.49) was observed for weevil resistance in the population. Mean genotype SPW severity scores ranged from 1.0 to 9.0 and 25 progeny exhibited transgressive segregation for SPW resistance. Mean genotype total HCA ester concentrations were significantly different (P < 0.0001). A weak but significant correlation (r = 0.103, P = 0.015) was observed between total HCA ester concentration and SPW severity. A total of five and seven SSR markers were associated with field SPW severity and total HCA ester concentration, respectively. Markers IBS11, IbE5 and IbJ544b showed significant association with both field and HCA-based resistance, representing potential markers for the development of SPW resistant sweetpotato cultivars.     

Drought and heat stress reduce yield and alter carbon rhizodeposition of different wheat genotypes

Drought and high temperature are major environmental stress factors threatening wheat production during grain filling stage resulting in substantial yield losses. Four wheat genotypes (Suntop, IAW2013, Scout and 249) were planted under two temperature levels (25 and 30°C) and two water levels (15% and 25% soil moisture content). Wheat yield, leaf δ¹³C, plant rhizodeposition, shoot biomass and root traits were examined. Low moisture (drought stress) and high temperature (heat stress) decreased the grain yield of all wheat genotypes, in particular 249, while combined drought and temperature stresses had the most pronounced negative effect on plant biomass and grain yield. Decreasing soil water availability decreased the allocation of plant‐derived C to soil organic carbon (SOC) and to microbial biomass through rhizodeposition. Leaf δ¹³C decreased with increased yield, suggesting that higher yielding genotypes were less water stressed and allocated less C to SOC and microbial biomass through rhizodeposition. Wheat genotypes with lower root/shoot ratios and thinner roots were more efficient at assimilating C to the grain, while genotypes with higher root/shoot ratios and thicker roots allocated more C belowground through rhizodeposition at the expense of producing higher yield. Therefore, improving these traits for enhanced C allocation to wheat grain under variable environmental conditions needs to be considered.     

Genistein and Daidzein Concentrations and Contents in Seedling Roots of Three Soybean Cultivars Grown under Three Root Zone Temperatures

Daidzein and genistein are plant-to-bacterium signal compounds involved in soybean nodule formation. They can induce nod gens expression in Bradyrhizobium japonicum. The objective of this study was to determine whether the production of signal molecules was affected by low root zone temperatures (RZTs) in a manner that varied among soybean cultivars. Daidzein and genistein concentrations of soybean seedling roots were measured at three RZTs by high performance liquid chromatography (HPLC). The results indicated that daidzein content and concentration per plant were higher at 15 and 17.5°C than those at 25°C. AC Bravor had higher daidzein contents and concentrations than did Maple Glen and KG20. At 17.5°C. KG20 had higher genistein content and concentration levels than Maple Glen, and no difference existed for the two cultivars at 15 and 25 C. Daidzein contents and concentrations of Maple Glen and AC Bravor increased with harvest time. However, for cultivar KG20, the content and concentration decreased at 19 days after inoculation. Genistein contents and concentrations of the three cultivars increased under each RZT up to the last harvest. There was an interaction between soybean cultivar and RZT for root genistein and daidzein contents and concentrations. The content and concentration of daidzein in soybean seedling roots were much higher (more than five times) than those of genistein.     

不同时期干旱胁迫对甘薯内源激素的影响及其与块根产量的关系

在人工控水条件下, 以抗旱品种济薯21和不抗旱品种济紫薯1号为试验材料, 设置全生育期干旱胁迫(DS)、发根分枝期干旱胁迫(DS1)、蔓薯并长期干旱胁迫(DS2)、快速膨大期干旱胁迫(DS3) 4个处理, 全生育期正常灌水(WW)为对照, 研究其对甘薯内源激素及块根产量的影响。结果表明, 与对照相比, 2个品种不同年份的所有干旱胁迫处理的鲜薯和薯干产量均显著下降。其中, DS薯干产量减产幅度最大, 济薯21和济紫薯1号3年平均分别减产44.62%和56.21%; 其次是DS1, 减产32.03%和44.03%; 再次是DS2, 减产30.41%和39.39%; DS3的减产幅度最小, 为13.66%和17.88%。抗旱品种济薯21的减产幅度小于不抗旱品种济紫薯1号。干旱胁迫抑制了甘薯地上部生长及块根的形成和膨大, 两个品种的单株叶片数、蔓长、地上部干重、地下部干重和块根淀粉率, 与对照相比, 各时期均表现为, DS的减少幅度最大, 其次是DS1和DS2, DS3的减少幅度最小。不同时期干旱胁迫均引起叶片和块根中GA、IAA和ZR含量下降, ABA含量上升。地上部干重与叶片GA、IAA和ZR含量呈显著正相关, 与ABA含量呈显著负相关; 地下部干重与块根GA、IAA和ZR含量呈显著正相关, 与ABA含量呈显著负相关。总之, 不同时期干旱胁迫均导致甘薯产量下降, 且胁迫时间越早, 对甘薯内源激素和块根产量的影响越大, 发根分枝期是甘薯对水分最敏感的时期。     

The Effect of Exposure to Ascending/Descending Imbibition Temperatures in Saline Solutions on Shoot and Root Growth Allocation in Germinating Sorghum Seed

Sorghum (Sorghum bicolor L. Moench) seeds were examined to determine the influence of exposure to ascending and descending imbibition temperature regimes on plumule and radicle axes behaviour of seed after treatment. Treatments included soaking in distilled water, 4.5 % NaCl or 4.5 % KCl for 3 days at three ascending or descending temperatures ranging from 11 to 21 °C. Root growth was enhanced by descending temperatures (21, 16 and 11 °C) over the 3‐day period, whereas ascending temperatures (11, 16 and 21 °C) increased growth differences between shoots and roots. Shoot–root growth was affected by imbibition temperature to a greater extent than germination. However, seed soaking treatments in NaCl or KCl did not improve root or shoot growth, but did improve germination rates.     

结薯数差异显著的甘薯品种生长前期根系特性及根叶糖组分比较

选用结薯数差异显著的甘薯品种商薯19和济徐23,于2013年和2014年分别在大田和盆栽条件下调查生长前期根系生长发育情况,测定根叶糖组分,分析其变化规律及其与单株有效薯块数形成的关系。结果表明,与济徐23相比较,商薯19发根缓苗迅速,整个生长前期均较为侧重吸收根系建成,且秧苗栽后15 d和30 d地上部和整个根系生物量比值(T/TR)相似;而济徐23较早完成不定根的发生(秧苗栽后15 d)和不定根向块根的分化建成(秧苗栽后30 d),封垄期（秧苗栽后45 d）具有较小的地上部和块根生物量比值(T/SR)。2个品种在生长前期根叶中蔗糖、己糖代谢和贮藏糖类多聚物的形成具有显著差异,其中商薯19整个生长前期比济徐23的根系蔗糖/己糖比率显著低,在块根分化建成过程中根叶间具有较高的蔗糖浓度梯度,且根系中存在2种低果聚糖(蔗果三糖和蔗果四糖),秧苗栽后30、45 d叶片淀粉含量显著低;而济徐23在块根分化建成过程中根系仅有蔗果四糖,且与商薯19比,封垄期根系蔗糖/可溶性总糖比率相似而根系蔗糖/淀粉比率显著低。2013年和2014年的大田试验均表明,封垄期商薯19具有显著多的单株有效薯块数和显著高的单株有效薯块鲜重(F=10.71,P=0.0170;F=13.97,P=0.0212),而收获时商薯19具有显著多的单株有效薯块数和显著高的块根产量(F=353.89,P<0.0001;F=88.94,P<0.0001),济徐23具有显著高的平均单薯鲜重(F=10.32,P=0.0124)。     

The effects of ethylene, 1-MCP and AVG on sprouting in sweetpotato roots

Exogenous ethylene is commonly used as a commercial sprouting inhibitor of potato tubers. The role of ethylene in the control of sprouting of sweetpotato roots, however, is not known. The aim of this study was to investigate the role of ethylene in control of sprouting in sweetpotato roots by observing the effect of an ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), and the ethylene antagonist, 1-methylcyclopropene (1-MCP), in the presence and absence of exogenous ethylene on root sprouting and associated sugar accumulation. Continuous exposure to 10 μl L⁻¹ ethylene, 24 h exposure to 625 nl L⁻¹ 1-MCP or dipping in 100 μl L⁻¹ AVG all inhibited sprout growth in sweetpotato roots of two varieties over 4 weeks of storage at 25 °C. The observations that both ethylene on its own and 1-MCP, which inhibits ethylene action, inhibit sprout growth indicate that while continuous exposure to exogenous ethylene leads to sprout growth inhibition, ethylene is also required for sprouting. In potato tubers ethylene is required to break dormancy, while continuous exposure inhibits sprout growth.Monosaccharide concentrations in ethylene, 1-MCP or AVG treated roots were lower than in untreated roots, and for ethylene treated roots this was associated with higher respiration rates. This is consistent with the activation of some additional process by ethylene which uses energy through sugar metabolism. 1-MCP and AVG both inhibited this increase in respiration rate and counteracted the decrease in monosaccharide concentrations. 1-MCP presumably counteracts the ethylene stimulation of this process, while the effect of AVG is attributed to its possible inhibitory effects on protein synthesis.     

Root Growth Inhibition and Lignification Induced by Salt Stress in Soybean

Salt stress was evaluated on root growth, enzyme activities (phenylalanine ammonia‐lyase or PAL and soluble plus cell wall‐bound peroxidase or POD), hydrogen peroxide (H₂O₂) production, total phenolic content and lignin content and composition in soybean (Glycine max L. Merrill) roots. Three‐day‐old seedlings were cultivated in half‐strength Hoagland’s solution (pH 6.0), with or without addition of 50–200 mm of NaCl, into a growth chamber (25 °C, 12/12 h light/dark photoperiod, irradiance of 280 μmol m^?2 s^?1) for 24 h. In general, root length and fresh and dry weights decreased after NaCl treatment. PAL activity decreased, soluble and cell wall‐bound POD activities increased, and H₂O₂ content significantly decreased after NaCl exposure. Consequently, total phenolic and lignin contents and p‐hydroxyphenyl (H) and syringyl (S) monomers of lignin increased in NaCl‐treated roots. Altogether, these results suggest that the effects caused by NaCl may be owing to the enhanced lignin production that solidifies the cell wall and restricts root growth.     

Influence of High Shoot and Root-Zone Temperatures on Growth of Three Wheat Genotypes during Early Vegetative Stages

High temperatures, whether of shoot or root, are reported to affect shoot and root growth of various plant species. The scanty information available on the differential response of wheat genotypes to high shoot and root‐zone temperatures triggered this investigation to study the response and adaptation of shoot and root growth of three wheat genotypes to high shoot and root‐zone temperatures during early growth stages. Three wheat genotypes; Fang (heat tolerant), Siete Cerros (heat sensitive) and Imam (recent cultivar adapted to a hot irrigated environment) were grown in soil and hydroponically. Three shoot/root‐zone temperatures (23/23, 23/35 and 35/35 °C for the soil experiment and 22/22, 22/38 and 38/38 °C for the hydroponic experiment) were applied at three‐leaf growth stage. High root‐zone temperature alone or combined with high shoot temperature reduced xylem sap flow rate, root dry weight, root length and root/shoot ratio. Unexpectedly, shoot fresh and dry weights and relative growth rate (RGR) were not significantly affected by the high root‐zone temperature except for the susceptible genotype, Siete Cerros, after prolonged exposure in the hydroponic experiment. In contrast, high shoot/root‐zone temperature significantly reduced shoot fresh and dry weights from as early as the first week of the hydroponic experiment. The 38/38 °C treatment also caused significant reduction in RGR and net assimilation rate during the first 2 weeks, but no significant differences were found during the last 2 weeks compared with 22/22 °C. Interesting responses were observed among genotypes in terms of shoot and root dry weights and root/shoot ratio at 38/38 °C treatment. The heat‐sensitive Siete Cerros showed the least reduction in these traits during the first 2 weeks while the heat‐tolerant Fang and Imam responded by greatly reducing their shoot and root weights. The situation was almost reversed with the duration of treatments such that Siete Cerros became the most affected genotype while Fang and Imam were better adapted to high shoot/root‐zone temperature. Specific root weight was the exceptional trait that increased under high temperature treatments. Results indicate that despite the reduction in root length and weight observed under high root‐zone temperature, shoot growth was not much affected suggesting that the use of suitable cultivar coupled with proper management could alleviate most of high root‐zone temperature effects during early growth stages.     

Effects of Salt Stress on Some Physiological and Photosynthetic Parameters at Three Different Temperatures in Six Soya Bean (Glycine max L. Merr.) Cultivars

The effect of NaCl (?0.1, ?0.4 and ?0.7 MPa) on some physiological parameters in six 23‐day‐old soya bean cultivars (Glycine max L. Merr. namely A 3935, CX‐415, Mitchell, Nazl?can, SA 88 and Türksoy) at 25, 30 and 35 °C was investigated. Salt stress treatments caused a decline in the K⁺/Na⁺ ratio, plant height, fresh and dry biomass of the shoot and an increase in the relative leakage ratio and the contents of proline and Na⁺ at all temperatures. Effects of salt stress and temperature on Chl content, Chl a/b ratio (antenna size) and qN (heat dissipation in the antenna) varied greatly between cultivars and treatments; however, in all cases approximately the same qP value was observed. It indicates that the plants were able to maintain the balance between excitation pressure and electron transport activity. Pigment content and the quantum efficiency of photosystem II exhibited significant differences that depended on the cultivar, the salt concentration and temperature. The cultivars were relatively insensitive to salt stress at 30 °C however they were very sensitive both at 25 and 35 °C. Of the cultivars tested CX‐415 and SA 88 were the best performers at 25 °C compared with SA 88 and Türksoy at 35 °C.     

1H-NMR Method Enables Early Identification of Degeneration in the Quality of Sweet Potato Tubers

In sweet potato tuber, which is a tropical plant, long‐term storage leads to loss of water and carbohydrate, thus water mobility was investigated using ¹H‐NMR spectroscopy. Electrolyte leakage indicated that tubers stored at 15 °C for 1 year were partly injured and that frozen‐thawed tissues were dead. Nuclear magnetic resonance (NMR) spin–lattice relaxation time (T₁) and spin–spin relaxation time (T₂) clearly increased with the duration of storage, whereas these values decreased in the dead tissues. Furthermore, Arrhenius plots for T₁ and T₂ were determined at temperatures ranging from 20 to 0 °C in 2.5 °C steps. In the fresh tubers, a strong converse temperature dependency was shown in the T₂ measurement. On the contrary, there was no temperature dependency in the T₂ of the dead tissues. Thus, the existence of inverse temperature dependency reflected tissue viability. Additionally, any change in the T₂ of the fresh tubers occurred at about 14 °C, which virtually coincided with the storage temperature of 15 °C. The slope change in T₂ might have responded to a physiological change as a primary event. In conclusion, monitoring water status by NMR could provide early identification of changes in the quality of post‐harvest crops; this method shows great promise for use in environmental‐stressed crop yield research.     

甘薯根系生物学性状的相关性、主成分和灰色关联度分析

为研究甘薯根系生物学性状的内在关系,了解其形成和分化规律,为甘薯标准化栽培和新品种培育提供理论支撑。试验通过温室水培和田间调查相结合的方式,利用统计学方法研究了10个甘薯品种的根系性状。栽后10天,甘薯苗期根系的投影面积、表面积、平均直径和体积等形态性状贡献率最高且达80.56%;栽后20天,根平均直径的贡献率最高且达27.79%。收获后,单株块根总鲜重与倒三节、倒二节块根重量呈极显著正相关,与商品薯数呈显著正相关,与倒二节块根数呈显著负相关,与倒三节块根重量关联系数最高且达0.6595。在栽后15天,苗期根系的投影面积、表面积和体积与单株块根总鲜重之间呈显著负相关;而在栽后25天,苗期根系干重与单株块根总鲜重之间呈显著正相关,苗期根干重、根体积、根长和根平均直径等性状与单株块根总鲜重关联度较大。栽后10天和20天可能是甘薯根系生长、分化的重要时间节点,节间长度和栽插深度影响产量形成,苗期根系生物学特性与收获后块根产量之间有直接关系。     

腐植酸提高食用型甘薯块根可溶性糖含量的生理基础

选用典型的食用型甘薯品种北京553,设置施用腐植酸和对照处理,于2008-2009年2个生长季在山东农业大学农学试验站进行试验。在甘薯块根膨大过程中定期取样,测定块根可溶性糖和淀粉含量及相关酶活性、功能叶蔗糖含量及相关酶活性变化。结果表明, 与对照比较,施用腐植酸显著提高了功能叶磷酸蔗糖合酶活性和蔗糖含量,生育期内平均增幅分别为30.90%和9.48%,显著降低了块根蔗糖合酶活性,平均降幅为11.04%,促进了蔗糖、果聚糖等在块根中的积累;同时,施用腐植酸还显著提高了块根中淀粉酶活性,α-淀粉酶和β-淀粉酶平均增幅分别为11.33%、15.70%,促进了后期葡萄糖、果糖等在块根中的积累。在甘薯收获期,块根可溶性总糖含量提高了15.49%、淀粉含量降低了3.56%。总之,施用腐植酸能够增加块根中蔗糖的供应量、抑制可溶性糖向淀粉转化、促进淀粉水解,这些是提高块根可溶性总糖含量的生理基础。     

Root-mediated Allelopathic Interference of Nettle-leaved Goosefoot (Chenopodium murale) on Wheat (Triticum aestivum)

A study was conducted to determine the potential and nature of root‐mediated allelopathic interference of Chenopodium murale on wheat. Early growth of wheat reduced significantly in agar medium where C. murale seedlings were previously growing as well as in rhizosphere soil of C. murale. The reduction in wheat growth was due to the presence of inhibitory metabolites released by roots of C. murale in the growth media. Even the soil incorporation of root residues also reduced the wheat growth in terms of seedling length and seedling dry weight. Only a partial amelioration in growth inhibition occurred upon charcoal supplementation or nitrogen fertilization in these amended soils. Root residues did not reduce the available nutrients in the soil, which was rather nutrient rich. These results indicated the definite role of allelopathy of C. murale roots in retarding wheat growth. Root amended soils contained significantly higher amount of phytotoxic phenolics as the putative allelochemicals, which were ferulic acid, vanillic acid, p‐coumaric acid and benzoic acid. The study concluded that C. murale roots and their exudates exerted allelopathic effects on wheat by releasing water‐soluble phenolic acids as putative allelochemicals in soil.