Effect of soil moisture at different temperatures on Rhizoctonia root rot of wheat seedlings

The effect of soil moisture at different temperatures on root rot of wheat seedlings caused by Rhizoctonia solani AG-8 was studied in temperature controlled water tanks under glasshouse conditions. Four moisture levels (15, 30, 50 and 75% of soil water holding capacity at saturation which were equal to –10, –7, –5 and –3 kPa, respectively) were tested in tanks maintained 10, 15, 20 or 25 °C. The role of microbial activity in the effect of soil moisture and temperature on disease severity was also studied by including treatments of steam treated soil. Results showed that at soil moisture levels optimum for plant growth (50 and 75% WHC) disease was more severe at a lower temperature (10 °C), but under relatively dry conditions (15% WHC) disease levels were similar at all temperatures tested. In warm soils (20 and 25 °C) at high soil moisture levels (50 and 75% WHC), disease was more severe in steam treated soil than in non-steam treated soil, indicating that the suppression of disease in natural soil under these conditions was associated with high soil microbial activity.     

自然林下与田间根腐三七根际微生物群落特征及比较分析

【背景】三七根际微生物群落特征与其土传根腐病害密切相关,而针对自然林下根腐三七的相关研究鲜见报道。【目的】比较分析自然林下与田间根腐三七根际土壤微生物群落的组成特征,结合土壤理化性质与酶活性分析,为三七根腐病害防治与仿野生栽培提供科学依据。【方法】采集自然林下与田间根腐三七根际土壤,利用高通量测序技术,分析土壤细菌与真菌群落的物种组成与多样性,并测定土壤理化性质和酶活性。【结果】自然林下与田间根腐三七根际土壤中细菌和真菌群落组成具有明显差异,自然林下根腐三七根际土壤中担子菌门(Basidiomycota)、酸杆菌门(Acidobacteria)和疣微菌门(Verrucomicrobia)的相对丰度较高,而田间根腐三七根际土壤中子囊菌门(Ascomycota)、变形菌门(Proteobacteria)和绿弯菌门(Chloroflexi)的相对丰度较高。在属分类水平,镰刀菌属(Fusarium)是自然林下根腐三七根际土壤中的优势菌群,相对丰度为17.30%,而癣囊腔菌属(Plectosphaerella)是田间根腐三七根际土壤中的优势菌群,相对丰度为22.55%;Candidatus Ba...     

Comparison of APRI and Hydrus-2D models to simulate soil water dynamics in a vineyard under alternate partial root zone drip irrigation

Alternate partial root zone irrigation (APRI) is a new water-saving irrigation technique. It can reduce irrigation water and transpiration without reduction in crop yield, thus increase water and nutrient use efficiency. Understanding of soil moisture distribution and dynamic under the alternate partial root zone drip irrigation (APDI) can help to develop the efficient irrigation schemes. In this paper, a two-dimensional (2D) root water uptake model was proposed based on soil water dynamic and root distribution of grape vine, and a function of soil evaporation related to soil water content was defined under the APDI. Then the soil water dynamic model of APDI (APRI-model) was developed based on the 2D root water uptake model and soil evaporation function combined with average measured soil moisture content at 0–10 cm soil layer. Soil water dynamic in APDI was respectively simulated by Hydrus-2D model and APRI-model. The simulated soil water contents by two models were compared with the measured value. The results showed that the values of root-mean-square-error (RMSE) range from 0.01 to 0.022 cm³/cm³ for APRI-model, and from 0.012 to 0.031 cm³/cm³ for Hydrus-2D model. The average relative error between the simulated and measured soil water content is about 10% for APRI-model, and from 11% to 29% for Hydrus-2D model, indicating that two models perform well in simulating soil moisture dynamic under the APDI, but the APRI-model is more suitable for modeling the soil water dynamic in the arid region with greater soil evaporation and uneven root distribution.     

Biochar effect on severity of soybean root disease caused by <Emphasis Type="Italic">Fusarium virguliforme</Emphasis>

Background and aims

Biochar is known to decrease soil bulk density, increase nutrient and water retention, and to suppress certain soil-borne pathogens. The aims of our glasshouse and field experiments were to; 1) determine whether biochar amendments impact the severity of soybean root rot caused by Fusarium virguliforme; 2) to determine if biochar reduces severity of root rot by changes in physicochemical properties of soil; 3) whether biochar induces systemic resistance to root rot in soybean plants.

Results

Results of the first glasshouse pot study indicate that biochars differ significantly in their effect on root rot caused by F. virguliforme, as two of eight biochars significantly suppressed root rot severity. Results for the second glasshouse pot study indicate that disease suppression was not related to changes in soil physicochemical properties (bulk density, soil moisture, soil pH). A third split-root experiment provided no evidence that biochar amendments are capable of inducing systemic resistance in soybean plants. Results of the small plot experiment proved that biochar was effective at reducing visual above ground symptoms of SDS, but did not affect soybean grain yields.

Conclusions

Both systemic and indirect effects of biochar on SDS root rot severity have been eliminated in the present study; further research is needed to determine whether suppression of root rot severity is related to changes in soil microbial communities induced by biochar.

     

Biological Control of Fusarium oxysporum f.sp. asparagi by Applying Non-pathogenic Isolates of F . oxysporum

Root rot severity of asparagus plants grown in sterilized field soil inoculated with Fusarium oxysporum f . sp . asparagi (Foa) was reduced by more than 50% when the soil was precolo nized by each of 13 non - pathogenic (np) isolates of F. oxysporum originating from asparagus roots or field soils . In a greenhouse experiment , application of six np isolates to naturally infested field soil was followed by a 23 - 49% decrease of disease severity , depending on the isolate . One of them , Fo47 originating from Fusarium suppressive soil in France , was applied to field plots infested with Foa . Foa root rot was not suppressed in asparagus plants grown for 1 year in these plots . Pathogenic and np isolates extensively colonized the root surface and isolates of both types infected the roots of asparagus plants grown in sterilized field soil , with significant differences among the np isolates . Inoculation of sterilized field soil with np isolates reduced germination of Foa chlamydospores by 43 - 64% depending on the isolate used . It is concluded that np isolates of F. oxysporum can suppress asparagus root rot caused by Foa in naturally infested field soil . The differences for root colonization capacity among the np isolates imply that selection for this trait might reveal isolates that perform better under field conditions .     

干旱胁迫下尖果沙枣幼苗的根系活力和光合特性

以尖果沙枣1年生实生苗为材料,研究了自然干旱时不同土壤相对含水量对幼苗叶片细胞质膜相对透性、叶片相对含水量、根系活力、光合色素含量和光合参数等指标的影响.结果表明:土壤相对含水量从70%(CK)降到40%时,幼苗根系活力和净光合速率均逐渐上升并达到最大值,分别为1178μg.g-1.h-1和21.9μmol.m-2.s-1;光合色素含量稳步上升;蒸腾速率和水分利用效率均保持稳定;叶片细胞质膜相对透性保持较低水平.土壤相对含水量从40%降到20%时,幼苗叶片相对含水量仍在50%以上,叶片细胞质膜相对透性仍保持较低水平;根系活力和光合色素含量仍较高;但其他光合参数开始缓慢下降.土壤相对含水量从10%降到5%时,幼苗叶片细胞质膜相对透性急剧上升;叶片相对含水量、根系活力、总叶绿素含量、光合参数均极显著下降;而土壤相对含水量为10%时幼苗表现出最高的水分利用效率.尖果沙枣土壤相对含水量最好控制在40%~50%,其1年生实生苗的永久萎蔫系数为4.3%(土壤相对含水量).     

连作花魔芋软腐病株与健株根域丛枝菌根真菌群落多样性

【目的】解析不同连作年限花魔芋软腐病株、健株根域的丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)群落多样性。【方法】使用AMF 18S SSU rRNA基因特异引物AMV4.5NF/AMDGR对正茬及连作2年和3年的软腐病株、健株魔芋根系和根际土壤DNA扩增建库,通过高通量测序和生物信息学分析探究魔芋软腐病与其根域AMF群落多样性的关系。【结果】魔芋根系具有明显的AMF菌丝、泡囊和丛枝等结构。在相同连作年限条件下,健株根系AMF总侵染率、侵染强度和孢子密度均显著高于病株(P<0.05);在不同连作年限条件下,病株根系AMF总侵染率和侵染强度随连作年限延长而降低。从所有样品中共鉴定到9属53种AMF,其中有49个已知种和4个新种。球囊霉属(Glomus)和类球囊霉属(Claroideoglomus)是AMF群落的优势属,其AMF种分别占总AMF种数的41.5%和26.4%;丰度最高的Paraglomus sp.VTX00308是所有样品的共有种。连作、软腐病及二者的交互作用显著影响根系AMF群落的Shannon指数和Simpson指数及根际土壤AMF的Chao1指数(P<0.05)。通过丰度差异分析发现6个在连作软腐病发生后丰度差异显著的AMF种(P<0.05);NMDS分析表明,不同连作年限的魔芋软腐病株与健株之间的根域AMF菌种组成、相对丰度和群落结构存在差异。相关性分析表明,软腐病发病率和病情指数与魔芋根系和根际土壤AMF的Shannon指数、根系AMF的Chao1和Simpson指数以及AMF总侵染率、侵染强度和孢子密度极显著负相关(P<0.01)。【结论】比对健株,连作魔芋软腐病株根际土壤AMF孢子密度以及根系AMF侵染率、种数和多样性均降低,其群落结构显著改变。     

逐步失水过程中绿竹光响应进程及其拟合

利用便携式光合测定系统Li-6400,在人为浇水至土壤水分饱和后的自然耗水过程中,分析2年生绿竹盆栽苗叶片在连续多级土壤水分下的光合作用光响应过程.结果表明: 在土壤相对含水量53.5%～95.6%条件下,绿竹光合作用光响应过程不会受到明显的强光抑制,且在相对水分亏缺条件下(53.5%～69.6%)达到更高的光合作用水平,而在严重水分亏缺后(土壤相对含水量≤33.6%)产生明显光抑制.在对绿竹叶片逐步失水过程的光响应拟合中,直角双曲线模型对净光合速率(P_{n max})的拟合值远高于实测值;直角双曲线模型、非直角双曲线模型和指数模型3种模型拟合的光饱和点(LSP)远低于实测值.在严重水分亏缺阶段,3种模型对光响应曲线拟合存在较大误差.气孔限制值(L_s)及瞬时水分利用效率(WUE_inst)具有相似的阈值响应过程,表现为随着土壤相对含水量减少而先增大后减小,且最大值出现在53.5%～69.6%条件下,这一结果与光合作用光响应过程取得P_{n max}的土壤相对含水量范围相同,具有一定的表征意义.绿竹旱涝管理最佳的土壤相对含水量为53.5%～69.6%,较高土壤含水量下(69.6%～95.6%)绿竹也有良好的光合表现.直角双曲线修正模型对绿竹在相对含水量为23.1%～95.6%条件下的光合作用光响应过程拟合较好,而其余3种模型均有局限性.     

不同抗旱性花生品种的根系形态发育及其对干旱胁迫的响应

为明确不同抗旱性花生品种的根系形态发育特征,探讨其根系形态发育特征对不同土壤水分状况的响应机制,在防雨棚旱池内进行土柱栽培试验,研究抗旱型品种“花育22号”、“唐科8号”和干旱敏感型品种“花育23号”3个不同抗旱性花生品种根系形态发育特征及其对干旱胁迫的响应.结果表明:抗旱型品种根系较发达,具有较大的根系生物量、总根长、总根系表面积.干旱胁迫使抗旱型品种根系总表面积和体积增加,而干旱敏感型品种则相反.干旱胁迫显著增加抗旱型品种“花育22号”20 cm以下土层内根长密度分布比例及根系表面积和体积,但“唐科8号”相应根系性状仅在20-40 cm土层内增加;干旱胁迫使干旱敏感型品种“花育23号”40 cm以下土层内各根系性状升高,但未达显著水平且其深层土壤内各根系性状增加幅度小于“花育22号”.花生根系总长、总表面积及0-20 cm土层内根系性状与产量间呈显著或极显著正相关.土壤水分亏缺条件下,花生主要通过增加深层土壤内根长、根系表面积和体积等形态特性,优化空间分布构型,以调节植株对水分的利用.     

The Role of Phytophthora cryptogea and Waterlogging in Root Rot Kiwifruit

A 48 h or 96 h period of waterlogging induced a partial rotting of the root system of 18 month old potted kiwifruit cuttings. However, root regeneration compensated for the loss of damaged roots and the plants remained healthy. Inoculation with Phytophthora cryptogea under low soil moisture conditions caused a small amount of root rotting (11 %) and regeneration of the roots occurred. Root rot was significantly increased when inoculations were combined with extended periods of waterlogging. Root rot incidence was highest (89 %) in inoculated plants exposed to periods of 96 h waterlogging. Regeneration did not occur with any of these plants and consequently, the shoot systems were severely damaged.     

Effects of oxygen on aerobic solid-state biodegradation kinetics

Oxygen is a critical control variable for composting and other solid-state biodegradation processes. In this study we examined the effect of varying oxygen concentrations (1%, 4%, and 21% O2 (v/v)) on biodegradation kinetics under different substrate (sewage sludge and synthetic food waste), temperature (35, 45, 55, and 65 degrees C), and moisture (36-60% H2O) conditions. Three forms of a saturation or Monod-type model and one form of an exponential model were evaluated against data from extensive experiments under carefully controlled environmental conditions. The exponential model performed well at temperatures from 35 to 55 degrees C but had problems at higher temperatures. The Monod-type models yielded the best fit based on R2 values. Multiple linear regression was used to express the oxygen half-saturation coefficient as a function of temperature and moisture. For a modified one-parameter saturation model the half-saturation coefficient varied from -0.67% to 1.74% v/v O2 under the range of conditions typical of composting systems. While the positive correlation of biodegradation rate with oxygen concentration reported by previous researchers held true for temperatures below 55 degrees C, an inverse relationship was found at 65 degrees C. Although this study did not directly examine anaerobic conditions, the results under microaerophilic conditions suggest oxygen may not offer kinetic advantages for extreme thermophilic biodegradation processes.     

Macropore sheath: quantification of plant root and soil macropore association

Plants require roots to supply water, nutrients and oxygen for growth. The spatial distribution of roots in relation to the macropore structure of the soil in which they are growing influences how effective they are at accessing these resources. A method for quantifying root-macropore associations from horizontal soil sections is illustrated using two black vertisols from the Darling Downs, Queensland, Australia. Two-dimensional digital images were obtained of the macropore structure and root distribution for an area 55 × 55 mm at a resolution of 64 μm. The spatial distribution of roots was quantified over a range of distances using the K-function. In all specimens, roots were shown to be clustered at short distances (1–10 mm) becoming more random at longer distances. Root location in relation to macropores was estimated using the function describing the distance of each root to the nearest macropore. From this function, a summary variable, termed the macropore sheath, was defined. The macropore sheath is the distance from macropores within which 80% of roots are located. Measured root locations were compared to random simulations of root distribution to establish if there was a preferential association between roots and macropores. More roots were found in and around macropores than expected at random. This revised version was published online in June 2006 with corrections to the Cover Date.     

青稞根腐病对根际土壤微生物及酶活性的影响

选取甘肃省卓尼县青稞种植区为研究地点,调查青稞根腐病的发病情况,并分别采集其健康植株和发病株根际的土壤,对比分析其土壤微生物生物量(碳、氮、磷)、微生物数量(细菌、真菌、放线菌)以及过氧化氢酶、蔗糖酶、脲酶、碱性磷酸酶、纤维素酶5种酶活性。结果发现,研究区10个采样点均有青稞根腐病的发生,发病率在5%—20%之间,不同地点发病率不同。根腐病的发生,会显著影响青稞根际微生物生物量,导致微生物生物量碳、氮、磷的含量发生变化,其中微生物生物量氮和磷含量整体降低,且不同采样点微生物量不同。土壤微生物数量总体呈现细菌放线菌真菌的趋势,但不同微生物对根腐病发病的响应不同,细菌和放线菌数量因根腐病的发生而减少,真菌的数量则增多;不同采样点土壤微生物数量不相同,细菌和真菌呈现区域性特征,放线菌的数量不呈现地域性。根腐病的发生还造成土壤酶活性的改变,其中蔗糖酶、脲酶、磷酸酶的含量因根腐病的发生而降低,而纤维素酶则升高,过氧化氢酶的变化没有规律。总而言之,根腐病的发生会使青稞根际土壤微生物组成发生改变,碳、氮、磷等物质代谢受到抑制,而能量代谢发生紊乱。因此,研究和防治青稞根腐病就必须重视土壤微生物及土壤酶的作用。     

Quantifying the effect of soil moisture content on segmenting root system architecture in X-ray computed tomography images

Aims

A commonly accepted challenge when visualising plant roots in X-ray micro Computed Tomography (μCT) images is the similar X-ray attenuation of plant roots and soil phases. Soil moisture content remains a recognised, yet currently uncharacterised source of segmentation error. This work sought to quantify the effect of soil moisture content on the ability to segment roots from soil in μCT images.

Methods

Rice (Oryza sativa) plants grown in contrasting soils (loamy sand and clay loam) were μCT scanned daily for nine days whilst drying from saturation. Root volumes were segmented from μCT images and compared with volumes derived by root washing.

Results

At saturation the overlapping attenuation values of root material, water-filled soil pores and soil organic matter significantly hindered segmentation. However, in dry soil (ca. six days of drying post-saturation) the air-filled pores increased image noise adjacent to roots and impeded accurate visualisation of root material. The root volume was most accurately segmented at field capacity.

Conclusions

Root volumes can be accurately segmented from μCT images of undisturbed soil without compromising the growth requirements of the plant providing soil moisture content is kept at field capacity. We propose all future studies in this area should consider the error associated with scanning at different soil moisture contents.     

三峡库区森林土壤大孔隙特征及对饱和导水率的影响

土壤大孔隙是土体内孔径较大能优先传导水分的根孔、洞穴或裂隙,大孔隙内优先流的产生是土壤水分运动研究由均衡走向非均衡的标志。利用原状土柱的水分穿透试验,对三峡库区山地不同林型覆盖下土壤的大孔隙结构进行了研究,分析了温性阔叶林棕壤、针阔混交林黄棕壤、暖性针叶林黄壤及弃耕草地剖面内大孔隙的剖面分布特征及其对土壤饱和导水率的影响。结果表明:研究区内森林土壤的大孔隙当量孔径在0.3—3 mm之间,占土壤总体积的0.15%—4.72%。大孔隙中孔径0.3—0.6 mm的大孔隙密度最大,占大孔隙总数量的72.2%—90.4%;而孔径1 mm的孔隙仅占大孔隙总数量的1.26%—8.55%。土壤大孔隙密度和大孔隙面积比的顺序为:温性阔叶林棕壤针阔混交林黄棕壤针叶林黄壤弃耕坡地。各孔径段的大孔隙密度在不同样点均呈现A层-B层-C层逐渐减小的趋势,大孔隙密度与有机质含量呈显著正相关关系。土壤饱和导水率与不同孔径大孔隙的密度、面积比均成显著正相关关系,孔径1mm的大孔隙仅占大孔隙总数量的1.26%—8.55%,但决定了饱和导水率84.7%的变异。此外,森林土壤饱和导水率与各土壤层的有机质含量成显著正相关关系,有机质的增多有利于改善土壤的入渗性能。     

The influence of growth stages on cassava tuberous root rot in different ecological environments

A multilocational field experiment to determine the influence of cassava growth and development on tuberous root rots in Onne and Sabongidda-Ora humid forests and in the Ibadan derived savanna of Nigeria was carried out from June 2003 to November 2005. Healthy cassava stems of TME-1 (local), TMS 30572 and TMS 4 (2) 1425 (both improved) were planted in a randomised complete block design with three replications. The experiment was repeated and the data collected were statistically analysed using the general linear model statistical procedures with the SAS system for Windows. Experimental result showed tuberous root rot incidence and severity to be pronounced at 12 months after planting in Onne and Sabongidda-Ora humid forests but less at the Ibadan derived savanna. Local TME-1 variety had the highest root rot incidence of 53% and severity of 21% while improved TMS 4(2)1425 variety had the least root rot incidence and severity at 0% each.     

连栽桉树人工林土壤大孔隙特征及其对饱和导水率的影响

速生人工林多代连栽容易导致土地水源涵养能力下降。土壤大孔隙以优先流的形式补充地下水,是定量研究土壤水分运动的重要指标。以连栽1-4代桉树人工纯林为研究对象（记录为Ⅰ、Ⅱ、Ⅲ、Ⅳ）,采用水分穿透曲线法,绘制水分穿透曲线,结合Poiseulle方程计算出大孔隙数量、半径及饱和导水率等指标,对土壤大孔隙特征及其对饱和导水率的影响进行研究。结果表明：（1）桉树人工林土壤的出流速率总体表现先匀速增加后趋于稳定,稳定出流速率总体表现为I > II > III > IV。（2）大孔隙半径范围在0.3-1.5 mm,主要集中于0.4-0.6 mm,随土层深度增加显著减小（P<0.05）。大孔隙数量范围在3.56×10⁴-4.81×10⁵个/m²。随着连栽代次的增加,大孔隙孔径范围变小,同一孔径范围的大孔隙数量减少。土壤容重与大孔隙特征呈极显著负相关关系;有机质含量与大孔隙特征呈极显著正相关关系。（3）各样地土壤饱和导水率范围在0.41-4.50 mm/min,并随着连栽代次增加而降低。将大孔隙的总数量、平均体积与土壤饱和导水率进行线性拟合,拟合方程为：y=ax+b=,（R²>0.66）。综上,随着桉树人工林连栽代次的增加,土壤大孔隙孔径范围缩小、同等半径的大孔隙数量减少,饱和导水率降低,土壤入渗及导水性能减弱,容易造成水土流失。     

Integrated control of root rot and wilt disease of faba bean by soil amendment with suppressive compost in combination with seed coating with an antagonistic yeast

For this study, 21 isolates of fungi belonging to Rhizoctonia and Fusarium genera were isolated from the diseased faba bean plants, obtained from the different localities in Assiut governorate, showing root rot and wilt symptoms. The isolates proved to be pathogenic on Masr 1 faba bean cultivar under greenhouse conditions. F. oxysporum isolates caused wilt disease; however, the isolates of R. solani and other Fusarium species caused root rot. The virulence of isolates on the tested faba bean cultivar was different. The highly pathogenic isolates of these fungi were employed in this study. The effect of soil amendment with Planta Rich and Rich Composts (CMs) alone or in combination with seed coating by the antagonistic yeast Pichia guilliermondi before sowing on the severity of Rhizoctonia and Fusarium root rot and Fusarium wilt of faba bean was tested under greenhouse and field conditions. The tested isolates of yeast proved to be highly antagonistic to the pathogen in vitro. The test rates of CMs were equivalent to 2, 7, 10 and 14 ton/feddan in the greenhouse and 7 and 10 t/feddan in the field conditions. Uncomposted soil was used as a control. The results showed that the tested CMs have a suppressive effect on the severity of root rot and wilt diseases of faba bean under greenhouse and field conditions. The application of CMs (Planta Rich and Rich) alone at the rates equivalent to 2, 7, 10 and 14 t/feddan in greenhouse and 7 and 10 t/feddan in the field conditions to the soil infested with the tested pathogens reduced percentage of the tested diseases compared with uncomposted soil. Combined CMs treatments with yeast seed treatment increased the suppressive effect of CMs on the disease severity.     

Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings

The effect of different soil textures, sandy (97.5% sand, 1.6% silt, 0.9% clay), loamy sand (77% sand, 11% silt, 12% clay) and a sandy clay loam (69% sand, 7% silt, 24% clay), on root rot of wheat caused by Rhizoctonia solani Kühn Anastomosis Group (AG) 8 was studied under glasshouse conditions. The reduction in root and shoot biomass following inoculation with AG-8 was greater in sand than in loamy sand or sandy clay loam. Dry root weight of wheat in the sand, loamy sand and sandy clay loam soils infested with AG-8 was 91%, 55% and 28% less than in control uninfested soils. There was greater moisture retention in the loamy sand and sandy clay loam soils as compared to the sand in the upper 10–20 cm. Root penetration resistance was greater in loamy sand and sandy clay loam than in sand. Root growth in the uninfested soil column was faster in the sand than in the loamy sand and sandy clay loam soils, the roots in the sandy soil being thinner than in the other two soils. Radial spread of the pathogen in these soils in seedling trays was twice as fast in the sand in comparison to the loamy sand which in turn was more than twice that in the sandy clay loam soil. There was no evidence that differences among soils in pathogenicity or soil spread of the pathogen was related to their nutrient status. This behaviour may be related to the severity of the disease in fields with sandy soils as compared to those with loam or clay soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rhizosphere soil aggregation and plant growth promotion of sunflowers by an exopolysaccharide-producing Rhizobium sp. strain isolated from sunflower roots

Root-adhering soil (RAS) forms the immediate environment where plants take up water and nutrients for their growth. We report the effect of an exopolysaccharide (EPS)-producing rhizobacterium (strain YAS34) on the physical properties of sunflower (Helianthus annuus L.) RAS, associated with plant growth promotion, under both water stress and normal water supply conditions. Strain YAS34 was isolated as a major EPS-producing bacterium from the rhizoplane of sunflowers grown in a French dystric cambisol. Strain YAS34 was assigned to the Rhizobium genus by 16S ribosomal DNA gene sequencing. Inoculation of sunflower seeds and soil with strain YAS34 caused a significant increase in RAS per root dry mass (dm) (up to 100%) and a significant increase in soil macropore volume (12 to 60 microm in diameter). The effect of inoculation on sunflower shoot dm (up to +50%) and root dm (up to +70%) was significant under both normal and water stress conditions. Inoculation with strain YAS34 modified soil structure around the root system, counteracting the negative effect of water deficit on growth. Using [(15)N]nitrate, we showed that inoculation made the use of fertilizer more effective by increasing nitrogen uptake by sunflower plantlets.