大豆生长及叶绿素荧光特性对铝胁迫的反应

采用溶液培养的方法，设置了不同的铝处理浓度和处理时间，对铝毒胁迫下的两个大豆品种（浙春2号、浙春3号）的根系生长和叶片的叶绿素荧光进行了研究。结果表明：铝抑制了大豆的根系干重、根系总长度、根系体积的增加。在高浓度的铝处理下，根系生长7 d后就受到了明显抑制。对茎叶干重的影响在14 d铝处理后才得到表现，茎叶部出现铝毒症状滞后于根部。根尖的根系活力在10 mg / L的铝浓度下有所增加，增强了根系吸收水分和矿质元素的能力。根系质膜透性随着铝处理浓度的增加而增大，在90 mg / L的铝处理下达到最大，植株受到严重伤害。低铝（10 mg / L）使大豆叶片的叶绿素含量少量增加，高铝（90 mg / L）胁迫叶绿素含量降低，且叶绿素a下降的幅度大于叶绿素b。荧光参数的研究表明，随着铝胁迫的增加，Fo下降，Fm、Fv / Fm增大，植株抵抗逆境的能力下降，光合电子传递减小，最终导致光合速率下降。两个大豆品种具有基因型差异，浙春2号比浙春3号更耐铝。     

Uptake and use efficiency of N, P, K, Ca and Al by Al-sensitive and Al-tolerant cultivars of wheat under a wide range of soil Al concentrations

The impacts of acidic soils and Al toxicity on wheat nutrient economy have been scarcely researched under field conditions even though these soils are widely spread in wheat production areas around the world. The main objective of this study was to quantitatively evaluate the element (N, P, K, Ca and Al) economy of an Al-sensitive and an Al-tolerant wheat cultivar growing under different soil Al concentrations at field conditions. To reach this objective, two field experiments were conducted in an Andisol in Valdivia (39°47′18″S, 73°14′05″W), Chile. Treatments were a factorial arrangement of: (i) two spring wheat cultivars (Al-sensitive, Domo.INIA and Al-tolerant, Dalcahue.INIA) and (ii) five exchangeable Al levels (0-2.7 cmol₍₊₎ kg⁻¹) with three replicates. At harvest, plant biomass was sampled and divided into 5 organ categories: ears, grains, blade leaves, stems plus sheath leaves and roots. The element content (N, P, K, Ca and Al) in each organ was measured to quantify element uptake and concentration, nutrient uptake efficiency (UPE) and nutrient utilization efficiency (UTE). Element uptake (N, P, K, Ca, and Al) was negatively affected by the increased soil Al concentration in above-ground and root biomass in both cultivars (R² = 0.61-0.98, p < 0.01), although clear differences were found between cultivars. On the contrary, the impact of soil exchangeable Al on the plant element concentration was minor, showing weak associations with soil Al levels. However, the Al concentration in above-ground tissues of the Al-sensitive cultivar was an exception because it increased exponentially with the Al soil concentration (R² = 0.96-0.99, p < 0.001). Nutrient uptake efficiencies, UPEs (N, P, K and Ca), were negatively affected by soil Al concentrations and were well described by linear equations in both cultivars (R² = 0.58-0.98, p < 0.05), with notable differences between them. Both nutrient uptake (capture) and UPE were the traits that best explained above-ground biomass production (R² = 0.82-0.99, p < 0.001, n = 20). Nutrient utilization efficiency, UTEs (N, P, K and Ca) responded more conservatively to the soil Al concentration, except for the Al sensitive cultivar under very high soil Al levels.     

铝胁迫下大豆根系分泌物对根际土壤的影响

以2个大豆品种（浙春2号和浙春3号）为材料，设置了4个铝浓度，分别在铝处理7d和14d时，测定大豆根系分泌物中的氨基酸、有机酸及可溶性糖，同时对大豆根际土壤的pH值、土壤酶和土壤呼吸速率进行分析。实验结果显示，虽然根系分泌物对根际土壤具有一定的酸化作用，但是随着铝浓度的升高，根系分泌物有使根际土壤酸碱度趋向平衡的效应。低铝浓度下，大豆根系分泌较多的可溶性糖和氨基酸，促使根际土壤酶活性的增强和土壤呼吸速率的提高，同时还可分泌较多的柠檬酸，与大豆的耐铝性相关。高铝浓度抑制主要根系分泌物的分泌，降低土壤酶活性和土壤呼吸速率；但高铝胁迫增加可溶性糖分泌量。实验结果表明，浙春2号大豆比浙春3号大豆耐铝；随着铝处理时间的延长，铝毒害作用明显。     

铝胁迫对大豆幼苗根系形态和生理特性的影响

采用砂培法研究了不同铝浓度条件下, 2个大豆品种(浙春3号和华春18)幼苗根系形态特征和生理特性的变化.结果表明:低浓度(50mg/L)的铝促进大豆根系长度、根系体积、根系表面积和根系活力的增加,降低根系细胞质膜透性,对大豆生长有一定的促进作用;高浓度的铝(5000mg/L)明显抑制根系长度的增长,使根系直径显著增大,降低大豆根系活力,使根系细胞质膜透性大大增加,明显不利于大豆的生长发育.2个大豆品种对铝胁迫存在着一定的差异,浙春3号对铝毒胁迫的耐受能力要强于华春18.     

Al toxicity effects on radiation interception and radiation use efficiency of Al-tolerant and Al-sensitive wheat cultivars under field conditions

Soil acidity and Al toxicity are highly extended in agricultural lands of Chile, especially where wheat is widely sown. To evaluate quantitatively the response of wheat biomass and its physiological determinants (intercepted radiation and radiation use efficiency) to Al toxicity, two field experiments were conducted in an Andisol in Valdivia (39°47′S, 73°14′W), Chile, during the 2005–2006 and 2006–2007 growing seasons. Treatments consisted of a factorial arrangement of: (i) two spring wheat cultivars with different sensitivity to Al toxicity (the sensitive cultivar: Domo.INIA and the tolerant cultivar: Dalcahue.INIA) and (ii) five exchangeable Al levels (from 0 to 2.7 cmol₍₊₎ kg⁻¹) with three replicates. Crop phenology and intercepted radiation (IR) were registered during the entire crop cycle, while 10 samples of above-ground biomass were taken at different stages between double ridge and maturity. Both biomass and leaf area index (LAI) were recorded in these 10 stages. Radiation use efficiency (RUE) was calculated as the slope of the relationship between accumulated above-ground biomass and accumulated photosynthetically active radiation intercepted by the canopy (IPARa). Crop phenology was little affected by soil Al treatments, showing only up to 17 days delay in the Al-sensitive cultivar under extreme Al treatments. Above-ground biomass at harvest was closely associated (R² = 0.92) with the crop growth rate but no relationship (R² = 0.14) was found between the crop cycle length. IPARa explained almost completely (R² = 0.93) the above-ground biomass reached by the crop at harvest under the wide range of soil Al concentrations explored in both experiments. On the other hand, a weaker relationship was found between above-ground biomass and RUE. The effect of soil Al concentration on IPARa was mainly explained by LAI as a single relationship (R² = 0.93) between IR (%) and LAI at maximum radiation interception showing a common light attenuation coefficient (k = 0.33).     

Adventitious root cultures of Castilleja tenuiflora Benth. as a source of phenylethanoid glycosides

Castilleja tenuiflora is a highly valued medicinal plant that grows in pine-oak woods in Mexico. In this study, we identified for the first time verbascoside and isoverbascoside as the major phenylethanoid glycosides (PhGs) in C. tenuiflora. These compounds have proven biological activities, including anti-inflammatory, antioxidant, and cytotoxic activities, which may be related to the traditional uses of this plant. We developed a reverse-phase high-performance liquid chromatography (RP-HPLC) procedure to analyze PhGs, and determined their concentrations in various different tissues of wild plants. Verbascoside accumulated mainly in roots and inflorescences (9.23 and 7.88 mg g⁻¹ dry biomass, respectively), while isoverbascoside accumulated mainly in the roots (7.13 mg g⁻¹ dry biomass). To provide an alternative source of material for production of bioactive compounds, we established in vitro adventitious root cultures in which roots were grown in B5 medium containing either 10 μM indole 3-acetic acid (IAA) or 10 μM α-naphthaleneacetic acid (NAA). The greatest dry biomass yield (30 g L⁻¹) was achieved at 30 days after transfer of roots into IAA-containing medium. The highest specific yields of PhGs were also obtained using this auxin; the maximum level of verbascoside was 14.62 mg g⁻¹ dry root biomass (438.6 mg L⁻¹) at 30 days after root transfer, and the maximum yield of isoverbascoside was 37.32 mg g⁻¹ dry root biomass (522.48 mg L⁻¹) at 23 days after root transfer. Adventitious root cultures of C. tenuiflora are a promising system for further studies on scale-up and phenylethanoid glycosides biosynthesis.     

Inhibitory effects of cover crop mulch on germination and growth of Stellaria media (L.) Vill., Chenopodium album L. and Matricaria chamomilla L.

Cover crops may suppress weeds due to their competitive effects and the release of inhibitory compounds. We examined the inhibitory influence of 11 cover crop mulches on the germination and growth of weed species (Stellaria media (L.) Vill., Chenopodium album L. and Matricaria chamomilla L.) in laboratory, greenhouse and field experiments. In the laboratory, cover crop extracts were tested in germination bioassays at six concentrations (0–500 mg ml⁻¹). The germination rate and root length (i) were measured 10 days after treatment (DAT). Pot experiments were carried out in the greenhouse to investigate the effects of cover crop mulch (ii) incorporated into the soil on weed germination and weed dry mass. Field trials measured the suppressive effects of cover crops and cover crop mixtures on weeds (iii). Correlations were determined between the experiments to quantify the competition and the biochemical effects of cover crops separately. Cover crop extracts at a concentration of 125 mg ml⁻¹ (i) significantly reduced the weed germination rate by 47% and the root length by 32% on average. M. chamomilla showed a lower susceptibility to the extracts of S. alba, R. sativus var. niger and H. annuus compared to C. album and S. media. The mulch-soil mixtures (ii) significantly reduced the germination rate by 50% and the dry mass by 47% on average across all three weed species, while M. chamomilla showed the highest tolerance to the mulches of V. sativa and A. strigosa. The correlation analysis revealed a strong positive correlation between extract toxicity and field weed suppression and, thus, indicated a high impact of the biochemical effects of the tested cover crops on weed suppression, especially for S. media and M. chamomilla.     

Evaluation of bioethanol production from five different varieties of sweet and forage sorghums (Sorghum bicolor (L) Moench)

Cultivars of sweet (Rio, M81E and Della) and forage sorghums (Tato and Thor) were planted in Northeast Mexico in order to estimate optimum harvesting time, sugar production, biomass composition and ethanol yields. The juices were characterized in terms of sugar composition, free amino nitrogen (FAN) and phenolics and then yeast (Saccharomyces cerevisiae)-fermented into ethanol. The cultivars yielded different volumes of sweet juice and total sugars. They also had different optimum harvesting times. Glucose was the most abundant sugar in raw juices, followed by fructose and sucrose. FAN concentration ranged from 19 to 36 mg L⁻¹ therefore, nitrogen supplementation was required for adequate fermentation. After 18 h fermentation, there were no differences in efficiencies among cultivars but the sweet sorghums yielded more ethanol Ha⁻¹ compared to the two forage sorghums (approximately 1000 L Ha⁻¹ versus 770 L Ha⁻¹). Della was the cultivar with the highest productivity with 1051 L Ha⁻¹ ethanol produced after the first cut.     

Efficacy and environmental fate of copper sulphate applied to Australian rice fields for control of the aquatic snail Isidorella newcombi

Copper sulphate pentahydrate (CuSO₄·5H₂O) is widely used for controlling Isidorella newcombi, an aquatic snail that causes substantial damage to rice crops in southeastern Australia. We conducted field trials on a Birganbigil clay loam soil that demonstrate high levels of efficacy against adult I. newcombi (95% mortality at 6.38 kg ha⁻¹ CuSO₄·5H₂O (1.14 mg Cu L⁻¹)). Dissolved copper fell below the detection limit (0.02 mg Cu L⁻¹) between 7 and 20 d after spraying at application rates up to 2.16 mg Cu L⁻¹ (12 kg ha⁻¹ CuSO₄·5H₂O). Total copper concentrations in the water column fell below the detection limit (0.007 mg Cu L⁻¹) 7–12 d after spraying at initially applied concentrations of 0.52–1.12 mg Cu L⁻¹, but remained detectable (0.01–0.02 mg Cu L⁻¹) until 30 days after spraying (the conclusion of monitoring) when applied at higher initial concentrations (1.18–2.16 mg Cu L⁻¹). There was a strong positive correlation (r² = 0.90, P < 0.001) between copper application rate and copper concentrations in surface sediments 30 d after spraying. Bioassays with immature snails using three different test soils beneath irrigation water showed that underlying soil type strongly influenced the response of snails to applied copper, with significant (P < 0.05) differences between LC₉₀ values which ranged from 0.41 to 1.04 mg applied Cu L⁻¹. Laboratory studies showed that dissolved copper concentrations remained significantly higher (P < 0.05) in the water column above the soil that had the most deleterious effect on copper toxicity. Dissolved organic carbon concentrations were significantly (P < 0.05) higher in both this soil and in the overlying water in the corresponding bioassay system, and correlated more closely with LC₉₀ values than other water chemistry parameters such as total hardness. Our results support the ongoing use of a variable copper application rate of 6–12 kg ha⁻¹ CuSO₄·5H₂O to allow for site-specific variations in efficacy, and suggest that variations in the release of dissolved organic carbon compounds from flooded soils may be a key factor moderating copper toxicity to I. newcombi in rice fields.     

Chitosan enhances withanolides production in adventitious root cultures of Withania somnifera (L.) Dunal

Calli were obtained from leaf, cotyledon and internode explants of in vitro-grown plants of Indian cultivar of Withania somnifera in MS medium supplemented with 2, 4-D (2.0 mg l⁻¹) and Kinetin (0.2 mg l⁻¹). The brown, semi-friable callus (500 mg FW) derived from leaf explants produced higher number of primary adventitious roots (9 roots/callus) in half strength MS medium fortified with IBA (0.5 mg l⁻¹) and NAA (0.1 mg l⁻¹). The primary adventitious roots with an inoculum mass of 15 g FW were cultured for 6 weeks in the same medium for secondary adventitious root proliferation. Elicitation of abiotic elicitor, aluminium chloride at 10 mg l⁻¹ at the end of 4 weeks culture with 4 h exposure time enhanced withanolides productivity. Under similar culture conditions, the biotic elicitor, chitosan at 100 mg l⁻¹ stimulated higher production of all withanolides when compared to aluminium chloride treatment. This is the first report on the use of callus-derived adventitious root culture for the enhanced production of withanolides upon chitosan elicitation.     

Wheat grain tissue proportions in milling fractions using biochemical marker measurements: Application to different wheat cultivars

Measurement of biochemical markers allows the quantification of wheat (Triticum spp.) grain tissue proportions in milling fractions. In order to evaluate the ability of extending this methodology to an unknown wheat grain batch, the variability of the markers in the different tissues was assessed on various wheat cultivars. Ferulic acid trimer amounts in the outer pericarp ranged from 0.97 to 1.67 μg mg⁻¹ (dm) with an average value equal to 1.31 μg mg⁻¹ (dm). Alkylresorcinols amounts in a composite layer, including the testa, the inner pericarp and the nucellar epidermis, ranged from 10.5 to 16.7 mg g⁻¹ (dm), with an average value equal to 14.0 mg g⁻¹ (dm). In the aleurone layer, phytic acid amounts ranged from 94.9 to 187.2 mg g⁻¹ (dm) with an average value equal to 152 mg g⁻¹ (dm) whereas, para-coumaric acid ranged from 0.08 to 0.29 μg mg⁻¹ with an average level of 0.18 μg mg⁻¹. In the embryonic axis, wheat germ agglutinin ranged from 879 μg g⁻¹ to 2086 μg g⁻¹ with an average value of 1487 μg g⁻¹. The impact of this variability on tissue proportion determination was evaluated and a strategy to decrease the prediction error was suggested. Percentages of the outer pericarp, intermediate layer (including the testa), aleurone layer and embryonic axis within grains were calculated and their variability discussed.     

Divergent selection at ultra-low plant density for seed protein and oil content within soybean cultivars

Soybean [Glycine max (L.) Merr.] seed is a major source of protein for animal feed and oil for human consumption. Selection within elite soybean cultivars for the improvement of agronomic and seed traits is assumed to be ineffective due to the belief that cultivars are highly homogeneous. Previously reported data suggest that latent variation among the single plant selections within a cultivar exists and that mechanisms that generate de novo variation may also be present. The main objective of this study was to perform divergent single-plant selection at ultra-low plant density and investigate the presence of genetic variation for seed protein and oil within three elite soybean cultivars. A secondary objective was to investigate the variation for fatty acid composition. In 1995, single plants from the three cultivars were grown in a honeycomb design using a plant-to-plant spacing of 0.9 m. A total of 333 plants from ‘Benning’, 392 plants from ‘Haskell’, and 371 plants from ‘Cook’ were evaluated. Divergent single-plant selection for protein and oil content was performed to select a total of 20 plants for high or low protein and 20 plants for high or low oil from each cultivar. The selected plants were further evaluated in replicated row-plot experiments for 3 years. Our results indicate that single-plant selection at low plant density was successful in discovering significant variation for seed protein and oil within each of the three soybean cultivars. For protein content, the magnitude of intra-cultivar variation between the highest- and lowest-protein lines averaged 19 g kg⁻¹ across the three cultivars and ranged from 13 to 24 g kg⁻¹. For oil composition, the magnitude of variation between the most divergent lines averaged 12 g kg⁻¹ across the three cultivars and ranged from 9 to 14 g kg⁻¹. Significant variation among the selected progeny lines was also discovered for specific fatty acid composition. The magnitude of intra-cultivar variation averaged from 6 to 29 g kg⁻¹ across the five fatty acids of soybean. The genetic variation discovered within the soybean cultivars is most likely due to latent variation and/or newly created variation. Our data provide evidence that single-plant selection at ultra-low plant density within elite cultivars can be effective in improving the seed composition of a soybean cultivar.     

不同耐铝大麦品种对铝锰互作胁迫的生理响应研究

铝（Al）和锰（Mn）是限制酸性土壤作物生长的两大主要因素。以耐铝性差异较大的两个大麦品种为材料,研究了不同处理对大麦生长、叶片功能和氧化胁迫指标的影响。结果表明,与对照相比,铝毒害导致大麦根长下降,根系干物质量降低,锰毒害显著降低植株株高和地上部干物质量,铝锰共存时锰加重大麦铝毒害。铝锰胁迫降低功能叶叶绿素含量和光合能力,复合处理下叶片功能指标下降幅度高于单独铝或锰处理。胁迫处理下叶片功能指标的下降幅度以叶绿素a含量和叶片蒸腾速率最明显。胁迫处理对铝敏感品种的生长和叶片功能毒害强于耐铝品种。铝锰胁迫引起大麦功能叶丙二醛（MDA）含量增加,过氧化物酶（POD）和 超氧化物歧化酶（SOD）活性增强,铝敏感品种增幅更大,复合处理时两品种叶片 MDA 积累量及铝敏感品种 POD 和 SOD 活性增幅显著高于单独铝或锰处理。     

Nutrient and assimilate partitioning in two tropical maize cultivars in relation to their tolerance to soil acidity

The use of Al-tolerant and P-efficient maize cultivars is an important component of a successful production system on tropical acid soils with limited lime and P inputs. Grain yield and secondary plant traits, including root and aboveground biomass, nutrient content and leaf development, were evaluated from 1996 to 2002 in field experiments on an Oxisol in order to identify maize characteristics useful in genetic improvement. Here we present the results of the 2002 trial and compare them with previous results. The aim of this experiment was to assess the effect of assimilate and nutrient partitioning on the growth and grain yield of two tropical cultivars having different Al tolerance (CMS36, tolerant, Spectral, moderately tolerant). The soil had an Al saturation of 36% in topsoil (pH 4.5) and >45% below 0.3 m depth (pH 4.2). Measurements made from emergence to grain filling included: root, stem and leaf biomass, P and N content, leaf area index (LAI), radiation use efficiency (RUE), soil available N and root profiles at anthesis. The experiments consisted of two P treatments, zero applied or 45 kg P ha⁻¹ (−P and +P). All the treatments received N and K fertilizers. In −P, root biomass and LAI at anthesis were twice as great in CMS36 as in Spectral. In +P the differences between cultivars were negligible. Roots were deeper in CMS36 due to its higher Al tolerance. Total biomass and grain yield were not strongly related to root biomass and LAI. Other factors such as the leaf biomass and the amount of nutrients per unit leaf area were highly correlated with RUE and biomass. In −P, Spectral had the same total biomass but a higher grain yield than CMS36 (2.1 Mg ha⁻¹ versus 1.5 Mg ha⁻¹). This was due to a higher leaf P content (+40%), a greater RUE (+74%), and a lower number of sterile plants. In +P, CMS36 had higher total biomass and grain yield (4.1 Mg ha⁻¹ versus 3.1 Mg ha⁻¹). This was due to its higher leaf P (+25%) and leaf N (+43%) contents, and an increased RUE (+130%) that were associated with higher P and N uptake. Our results indicated that although root tolerance to Al toxicity is necessary for good crop performance on acid soils, assimilate and nutrient partitioning in the aboveground organs play a major role in plant adaptation and may partially compensate for a lower root tolerance.     

Growth of the whole root system for a plant crop of sugarcane under rainfed and irrigated environments in Brazil

Sugarcane crops are managed over 8 million hectares in Brazil and future extensions might occur on less favorable lands where irrigation would be necessary to increase and stabilize yields. Root growth was studied by sequential soil coring under rainfed and irrigated conditions for one cultivar widely planted in Brazil. Root length densities (RLD) were measured 34, 49, 125, 179, 241 and 322 days after planting (DAP) down to a depth of 1 m. At the harvest (332 DAP), root intersects (a proxy for RLD) were counted on two vertical trench walls in each water supply regime, down to a depth of 6.0 m. The highest RLD in deep layers (below a depth of 0.6 m) were observed in the rainfed crop from 125 DAP onwards. By contrast, the highest RLD in the upper layers during dry periods were found in the irrigated crop. The maximum depth reached by roots at the harvest was little affected by irrigation: 4.70 m and 4.25 m in the rainfed and irrigated crop, respectively. About 50% of root intersects were observed below the depth of 1 m in the two water supply regimes. This pattern suggested a strong genetic control of root growth in deep soil layers. The total amount of root intersects 332 DAP was 49% higher in the rainfed crop than in the irrigated crop, and root distribution was more homogeneous. Mean root front velocity was about 0.5 cm day⁻¹ the first 4 months after planting and increased thereafter up to the end of the harvest (1.86 cm day⁻¹ and 1.75 cm day⁻¹ on average in the rainfed and the irrigated crops, respectively). Our study pointed out the necessity to take into account the development of sugarcane roots in deep soil layers to improve our understanding of net primary production control by water availability.     

Root Morphology and Anatomy Affect Cadmium Translocation and Accumulation in Rice

Paddy fields contaminated with cadmium (Cd) present decreased grain yield and produce Cd-contaminated grains. Screening for low-Cd-accumulating cultivars is a useful method to reduce the amount of Cd in the grains. The present study aimed to examine the roles of the root morphology and anatomy in Cd translocation and accumulation in rice plants. Twenty-two rice cultivars were used in the first experiment, after which two cultivars [Zixiangnuo (ZXN) and Jinyou T36 (JYT36)] were selected and used in subsequent experiments under hydroponic conditions. The results showed that there were significant differences in Cd concentrations in the shoots (ranging from 4 to 100 mg/kg) and the Cd translocation rates (shoot/root) (from 7% to 102%) among the 22 cultivars, and the shoot Cd concentration was significantly correlated with the Cd translocation rate of the 22 cultivars under 0.1 mg/L Cd treatment. Compared with cultivar ZXN, JYT36 had greater root Cd uptake and accumulation but lower shoot Cd accumulation and Cd translocation rate. The number of root tips per surface area of cultivar ZXN was greater than that of JYT36, while the average root diameter was lower than that of JYT36. Compared with ZXN, JYT36 had stronger apoplastic barriers, and the Casparian bands and suberin lamellae in the root endodermis and exodermis were closer to the root apex in both the control and Cd treatments, especially for suberin lamellae in the root exodermis with Cd treatments, with a difference of 25 mm. The results also showed that, compared with ZXN, JYT36 had greater percentages of Cd bound in cell walls and intracellular Cd but lower Cd concentrations in the apoplastic fluid under the Cd treatment. The results suggested that Cd translocation, rather than root Cd uptake, is a key process that determines Cd accumulation in the rice shoots. The root morphological and anatomical characteristics evidently affect Cd accumulation in the shoots by inhibiting Cd translocation, especially via the apoplastic pathway. It was possible to pre-screen low-Cd-accumulating rice cultivars on the basis of their root morphology, anatomical characteristics and Cd translocation rate at the seedling stage.     

Efficacy of azoxystrobin for the control of cucumber downy mildew (Pseudoperonospora cubensis) and fungicide residue analysis

During a five-year trial (2007–2011), the efficacy of azoxystrobin (Quadris, 250 g a.i. L⁻¹, Syngenta) in two doses (187.5 g a.i. ha⁻¹ and 250 g a.i. ha⁻¹) and chlorothalonil (Bravo 720-SC, 720 g a.i. L⁻¹, Syngenta) at a rate of 1.44 kg a.i. ha⁻¹ was tested for the control of cucumber downy mildew (CDM). Cultivars that were susceptible or resistant to CDM (Regal and Haros, respectively) were tested for their response to fungicide applications. Differences in both disease severity and yield of the cultivars among resistance levels and fungicide treatments were observed. A highly significant and negative correlation was obtained between AUDPC and yield. Higher yields can be achieved by planting more resistant cultivars in combination with lower doses of fungicides. This is an indication that CDM contributes significantly to yield losses in cucumber production in Serbia. While monitoring the degradation of azoxystrobin residues, a decrease in residue levels to 1.0 mg kg⁻¹ below the maximum residue level (MRL) was observed at the end of the pre-harvest interval (PHI).     

Regeneration in Jatropha curcas: Factors affecting the efficiency of in vitro regeneration

Factors influencing in vitro regeneration through direct shoot bud induction from hypocotyl explants of Jatropha curcas were studied in the present investigation. Regeneration in J. curcas was found to be genotype dependent and out of four toxic and one non-toxic genotype studied, non-toxic was least responsive. The best results irrespective of genotype were obtained on the medium containing 0.5 mg L⁻¹ TDZ (Thidiazuron) and in vitro hypocotyl explants were observed to have higher regeneration efficiency as compared to ex vitro explant in both toxic and non-toxic genotypes. Adventitious shoot buds could be induced from the distal end of explants in all the genotypes. The number of shoot buds formed and not the number of explants responding to TDZ treatment were significantly affected by the position of the explant on the seedling axis. Explants from younger seedlings (≤15 days) were still juvenile and formed callus easily, whereas the regeneration response declined with increase in age of seedlings after 30 days. Transient reduction of Ca²⁺ concentrations to 0.22 g L⁻¹ in the germination medium increased the number of responding explants.Induced shoot buds, upon transfer to MS medium containing 2 mg L⁻¹ Kn (Kinetin) and 1 mg L⁻¹ BAP (6-benzylamino purine) elongated. These elongated shoots were further proliferated on MS medium supplemented with 1.5 mg L⁻¹ IAA (indole-3-acetic acid) and 0.5 mg L⁻¹ BAP and 3.01-3.91 cm elongation was achieved after 6 weeks. No genotype specific variance in shoot elongation was observed among the toxic genotypes except the CSMCRI-JC2, which showed reduced response. And for proliferation among the toxic genotypes, CSMCRI-JC4 showed highest number of shoots formed. Among the rest, no significant differences were observed. The elongated shoot could be rooted by pulse treatment on half-strength MS medium supplemented with 2% sucrose, 3 mg L⁻¹ IBA (indole-3-butyric acid), 1 mg L⁻¹ IAA, 1 mg L⁻¹ NAA (α-naphthalene acetic acid) and subsequent transfer on 0.25 mg L⁻¹ activated charcoal medium. The rooted plants could be established in soil with more than 90% success. No significant differences were observed in rooting of shoots in the different toxic genotypes. However, rooting response was reduced in non-toxic genotype as compared to toxic genotypes.     

Effect of Acid Aluminous Soil on Photosynthetic Parameters of Potato (Solanum tuberosum L.)

Potato is grown worldwide, in some cases in very acid soils. Aluminum (Al) is a major limiting factor for crop productivity in acid soils. Al toxicity was studied mainly on plant roots, while less attention was given to its effects on leaves. Al tolerance observed in solution cultures has rarely been correlated with Al tolerance in acid soils. Al tolerance was assessed in 12 potato cultivars grown in nutrient solutions containing 0, 25, and 50 μmol Al L^?1 by its relative root elongation (RRE). The effect of acid soil with high level of exchangeable Al on leaf mineral content, chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, water use efficiency (WUE), and light use efficiency (LUE) was studied on cultivars, with the greatest differences in RRE (cv. Tresor, 63.1 and 42.5% and cv. Canberra, 23.3 and 19.2%, for the 25 and 50 μmol Al L^?1 treatments, respectively), grown for 49 days after planting (DAP) in acid and limed soil. Growth in acid soil significantly reduced concentrations of nitrogen (?18.51%) and magnesium (?27.17%) in the leaves in cv. Canberra and concentrations of potassium and copper in both cultivars. Canberra grown in acid soil showed a significant decrease in chlorophyll content and photosynthetic rate, from 28 to 49 DAP, and in transpiration rate and LUE when averaged across all measurements, while cv. Tresor was not affected. Physiological disorders observed on leaves of plants grown in acid soil can be correlated with the differences in Al tolerance observed in nutrient solutions.