Poor Root System Research Articles

Grafting of Cannabis – The effect of the rootstock on vegetative and reproductive indices of the scion

Among the commercial cannabis varieties, some are high yielders but characterized by a relatively poor root system. Roots absorb water and minerals from the soil, enabling vegetative development that directly affects yield, as vigorous plants have more resources to support reproduction. Moreover, healthy foliage is a primary key to high assimilation rates, leading to better production of photosynthetic products, including cannabinoids and terpenes, which are the main active components of cannabis. We grafted a high-THC variety, named 'Freud Super-Ego' (FSE) onto three chemotypes of rootstocks: high-THC (T), high-CBD (C), and Balanced (B). All the rootstocks had significantly greater root biomass compared to FSE. All the grafting treatments significantly improved FSE's vegetative indices and yield. The best overall vegetative performance – height, stem circumference, number of mature leaves - was that of plants grafted onto the Balanced and high-CBD rootstocks, resulting in high yields as well. However, the greatest number of inflorescences was counted when FSE was grafted onto a high-THC rootstock. According to leaf mineral content analysis, the highest nitrogen and phosphorus levels were found in leaves of FSE grafted on the balanced rootstock. The cannabinoid content profile analysis revealed that all grafting treatments raised the THC level in FSE's inflorescences by 8–12 % in comparison to the non-grafted control, and the THC rootstock led to the highest THC level. The results indicate the importance of grafting in cannabis as a tool to increase the productivity and quality of the product.

Fusarium clavum causes sugar beet seedling root rot in Wyoming, USA

Seedling rot in sugar beet was observed at Snyder Farms, Wyoming, USA, in April 2022. The diseased seedlings exhibited water-soaked brown to blackish lesions in hypocotyls with poor root systems. Four fungal isolates were retrieved from the diseased samples, and their morphological features were found to be identical to those of previously reported Fusarium species. Artificial inoculation with isolates developed similar symptoms to those observed in the field samples. Based on morphological characteristics, pathogenicity assays, sequence homologies of the internal transcribed spacer, translation elongation factor (tef1α), largest subunit of RNA polymerase II (rpb2), β-tubulin (β-tub), and multilocus phylogenic analyses with tef1α and rpb2, the causal agent was identified as Fusarium clavum (F. incarnatum-equiseti species complex 5). This is the first worldwide report of sugar beet seedling rot caused by F. clavum, detected in Wyoming, USA. This finding will help to formulate effective management practices to manage the pathogen and prevent its widespread occurrence.

Root Niches of Blueberry Imprint Increasing Bacterial-Fungal Interkingdom Interactions along the Soil-Rhizosphere-Root Continuum.

Plant root-associated microbiomes play critical roles in promoting plant health, productivity, and tolerance to biotic/abiotic stresses. Blueberry (Vaccinium spp.) is adapted to acidic soils, while the interactions of the root-associated microbiomes in this specific habitat under various root microenvironments remain elusive. Here, we investigated the diversity and community composition of bacterial and fungal communities in various blueberry root niches (bulk soil, rhizosphere soil, and root endosphere). The results showed that blueberry root niches significantly affected root-associated microbiome diversity and community composition compared to those of the three host cultivars. Deterministic processes gradually increased along the soil-rhizosphere-root continuum in both bacterial and fungal communities. The co-occurrence network topological features showed that both bacterial and fungal community complexity and intensive interactions decreased along the soil-rhizosphere-root continuum. Different compartment niches clearly influenced bacterial-fungal interkingdom interactions, which were significantly higher in the rhizosphere, and positive interactions gradually dominated the co-occurrence networks from the bulk soil to the endosphere. The functional predictions showed that rhizosphere bacterial and fungal communities may have higher cellulolysis and saprotrophy capacities, respectively. Collectively, the root niches not only affected microbial diversity and community composition but also enhanced the positive interkingdom interactions between bacterial and fungal communities along the soil-rhizosphere-root continuum. This provides an essential basis for manipulating synthetic microbial communities for sustainable agriculture. IMPORTANCE The blueberry root-associated microbiome plays an essential role in its adaptation to acidic soils and in limiting the uptake of soil nutrients by its poor root system. Studies on the interactions of the root-associated microbiome in the various root niches may deepen our understanding of the beneficial effects in this particular habitat. Our study extended the research on the diversity and composition of microbial communities in different blueberry root compartment niches. Root niches dominated the root-associated microbiome compared to that of the host cultivar, and deterministic processes increased from the bulk soil to the endosphere. In addition, bacterial-fungal interkingdom interactions were significantly higher in the rhizosphere, and those positive interactions progressively dominated the co-occurrence network along the soil-rhizosphere-root continuum. Collectively, root niches dominantly affected the root-associated microbiome and the positive interkingdom interactions increased, potentially providing benefits for the blueberry.

PENGARUH EKSTRAK BAWANG MERAH (Allium cepa L.) DAN MEDIA TANAM TERHADAP PERTUMBUHAN STEK LADA (Piper ningrum L.)

This research is motivated by the increasing demand for Indonesian pepper. So that an effort is made to develop pepper by using seedling techniques by cuttings. The weakness of using cuttings lies in a poor root system so that the role of shallot extract is needed to stimulate root formation and the planting medium can also affect the growth of cuttings to improve seedling quality. This study aims to determine the effect of onion extract and planting media on the growth of pepper cuttings. The study used a Randomized Block Design (RBD) with a factorial pattern consisting of two factors. The first factor was the soaking time of shallot extract consisting of 3 levels, namely: K1 (without soaking), K2 (3 hours) and K3 (6 hours). The second factor is the composition of the planting medium with a volume ratio (soil, sand and manure) consisting of 4 levels, namely P1 (soil), P2 (2 soil: 1 sand: 1 manure), P3 (1 soil: 2 sand: 1 fertilizer). manure) and P4 (1 soil : 1 sand : 2 manure). The variables observed were shoot length, number of leaves, root length and wet weight. The results showed that the best interaction of soaking in shallot extract and planting medium was obtained in the K2P4 treatment, the best single effect in the soaking in shallot extract was obtained in the K2 treatment and in the planting medium was obtained in the P2 treatment.

Dynamics of growth parameters of Gentiana lutea L. in vitro plants under different lighting conditions

Aim. Study of the dynamics Gentiana lutea L. plant growth processes in vitro depending on the light regime changes of their cultivation in order to develop a scheme to increase their adaptive potential. Methods. Methods of plant cultivation in vitro, biometric method, as well as ANOVA variance analysis and middle group analysis in pairs using the Tukey test (Tukey test) were used. Results. It is shown that the cultivation of G. lutea plants in vitro using 25 W/m2 light flux intensity in the region of photosynthetically active radiation and the ratio of blue (Eb): green (Eg): red (Er) ranges = 41.8%: 42.7 %: 15.5% triggers non-specific photomorphogenesis reactions for intact plants, which lead to poor root system development, stem elongation, formation of small leaves with a thin leaf blade, overall low productivity and low adaptation potential of G. lutea plants to ex vitro and in situ conditions. Increasing the light flux intensity to 44 W/m2 and increasing the red wave proportion up to 20.3% allows not only to improve the bioproductivity of G. lutea plants which are cultivated in vitro, but also to increase the coefficient of microclonal reproduction without the additional use of exogenous growth regulators. The greatest growth of the aboveground and underground parts, increase in effective leaf surface are observed in vitro plants during cultivation at 135 W/m2 light flux intensity and spectral composition Eb: Eg: Er = 29.5%: 32.5%: 38.0%. Conclusions. It is possible to improve plant bioproductivity by changing the light conditions of plant cultivation in vitro, and, accordingly, to increase the adaptive potential to ex vitro and in situ conditions.
 Keywords: Gentiana lutea L., in vitro plants, light flux intensity, spectral composition, growth parameters.

English

Drought is one of major abiotic stresses that effect rice production. Roots play vital role in absorption of water and nutrients from soil contributing for drought tolerance. The present study quantified the effects of different irrigation intervals on root development and agronomical traits of three Egyptian rice cultivars, Giza177, Giza178, Sakha107, IET1444 as a popular drought tolerant and Moroberekan as control genotype. Irrigation treatments were imposed 15 days after transplanting and applied for every 4, 8 and 12 days during 2018 and 2019 rice growing seasons. The results showed the reduction in root architecture traits with prolonged irrigation intervals. A significant decrease in plant height, number of panicles plant-1, grain yield (t ha-1) and relative water content, while sterility (%) and water use efficiency significantly increased over irrigation intervals. The highly significant and positive correlation was found among grain yield and root:shoot ratio, relative water content and number of panicles plant-1, while the negative correlation was with root xylem vessel number and sterility. It was concluded that, the drought reduced the grain yield and its components due to poor developed root system. Moroberekan and IET1444 genotypes can be used as a donor parent for rice breeding program. Further studies are also required to identify factors that contribute to the high yield potential of both Giza178 and Sakha107 under different water stress condition. © 2021 Friends Science Publishers

Taxonomy and Grafting of Ornamental Cacti: A Review

Nowadays, cacti and succulents are widely utilized in landscaping. These plants suit very effectively for both indoor and outdoor decorations. The family Cactaceae comprises of 130 genera with 2000 species and this is primarily divided into three tribes namely: Pereskieae, Opuntieae and Cereeae. Cactus flowers are very attractive and are diverse in size, number, form and color. The nocturnal flowers are always white, with light-yellow or red tones, whereas diurnal flowers are white, purple, yellow-orange, red or green. Basically, an areole is a transformed axillary bud situated over a tubercle with spines and often with hairs and trichomes. Due to their low maintenance requirements and their ability to withstand harsh environments, cacti are extremely popular as ornamental plants across the planet. Cacti can be propagated by seeds, cuttings, offsets and grafts. Grafted cacti are now regarded as one of the most admired ornamental indoor plants worldwide. In cacti, grafting has become a commercial method of propagation to accelerate and hasten the growth rate of slow growing species, to ensure the survival of the plants with poor root system, to ensure the survival of genetic aberration of variegated and bright coloured cacti (red and yellow caps) that lack chlorophyll, to accelerate the growth of plants for commercial use, in order to keep cristate and monstrose forms look attractive. Successful grafts have been obtained when the species like Trichocereus spachianus, Trichocereus macrogonus, Trichocereus pachanoi, Hylocereus trigonus, Hylocereus undatus, Selenicereus grandiflorus, Opuntia bergeriana, Opuntia ficus-indica are grafted onto Nopalea spp. The exogenous application of IBA has a positive effect on the vegetative growth of grafted plants using (Gymnocalycium mihanovichii scion grafted onto Trichocereus spachianus rootstock.

Relationship of fertilizer and periodic drought on biomass allocation in greenhouse-grown sunflower

The objective was to analyze organ plasticity in biomass allocation in response to limited resources and its influence on commercial traits of potted sunflower production. Although drought dramatically increased net photosynthetic rate and water-use efficiency, total leaf area, leaf dry mass, and total dry mass with drought stress decreased at rates of 20.9, 21.8, 23.0, and 9.9%, respectively. Irrigation positively affected specific leaf area, stem mass fraction, and root mass fraction. Adversely, fertilizer had a negative effect on stem mass fraction, root mass fraction, and root/shoot ratio. Interestingly, leaf mass fraction was not affected by them. Drought and greater fertilizer amount promoted flower yield and maintained leaf mass fraction stability at the expense of stem and root production. This induced plants to produce a thin stem, poor root system, and weak lodging resistance despite high flower production. This could have significant economic consequences for commercial potted flower production.

English

Water deficiency has become a major issue threatening the sustainability of arable crops globally. This study was conducted to assess the effects of deficit supplemental irrigation (DSI) at different growth phases on the performance of different maize hybrids under semi-arid climate. The irrigations were skipped either at vegetative or reproductive stage, while a sufficient supplemental irrigation was taken as control in three maize hybrids i.e., P-30Y87, S-6621 and P-30Y58. The DSI at both growth phases significantly hampered root length and proliferation, crop growth rate (CGR), leaf area index (LAI) and relative water contents (RWC). The DSI applied at both growth phases reduced the grain yield and yield related attributes, but DSI at reproductive stage was more lethal. Hybrid P-30Y87 performed better under different irrigation treatments due to better root system, crop allometry and other yield related traits compared to other hybrids while hybrid P-30Y58 recorded the lowest crop yield due to poor root system. The lateral roots had positive correlation with grains cob-1 and water use efficiency, while positive correlation among root length and grain weight and yield was observed under DSI at both growth phases. In conclusion, DSI at reproductive stage severely hampers the maize productivity; however maize productivity under deficit irrigation supply can potentially be improved to some extent by using maize hybrids with better root system. The moisture deficiency at reproductive stage proved more lethal for maize productivity, while maize hybrids with better root system potentially evaded the adverse effects of moisture deficits under semi-arid climate.

Effects of tillage practices on root characteristics and root lodging resistance of maize

Lodging is an important adversity affecting maize yield and quality in the world, especially under dense populations. A field experiment was conducted with two hybrids, Xianyu335 (XY) and Jingdan28 (JD) to study the influence of tillage practices on root system characteristics and their relationships with lodging resistance. The tillage practices included direct seeding of maize into stubble (ST), direct seeding with hilling (STH), rotary tillage before seeding (RT) and rotary tillage with hilling (RTH); the hilling was done at the jointing stage. The RT significantly increased the soil water content, number of nodal roots, root length density, average root diameter, axile root/shoot (RS) ratio and root width, decreased the penetration resistance (PR), centre of gravity height and ear position coefficient of plants, and enhanced vertical root-pulling resistance and tensile force of individual aerial roots. The grain yield was also highest and root lodging rate lowest under TR, followed by ST. Although hilling at the jointing stage tended to increase root number, root length density and average root diameter within the 40cm depth, the RS ratio, root width and vertical root-pulling resistance decreased markedly, resulting to lower yields and poorer root-lodging resistance. The vertical root-pulling resistance was positively correlated with number of nodal roots and RS ratio, but negatively correlated with centre of gravity height of plants. The root lodging rate had weak positive correlation with PR which had significant negative correlation with number of nodal roots. This suggested that the poor root system of summer maize was the main reason of the weak root lodging-resistance and rotary tillage before seeding and direct seeding into stubble would be suitable practices for maize production while hilling could exacerbate root lodging and should be avoided. The knowledge obtained here will be useful for hybrid selection and improving cultural practices for enhancing the root lodging resistance of maize in rain and wind prone regions.

Identification of Putative Molecular Markers Associated with Root Traits in Coffea canephora Pierre ex Froehner.

Coffea canephora exhibit poor root system and are very sensitive to drought stress that affects growth and production. Deeper root system has been largely empirical as better avoidance to soil water limitation in drought condition. The present study aimed to identify molecular markers linked to high root types in Coffea canephora using molecular markers. Contrasting parents, L1 valley with low root and S.3334 with high root type, were crossed, and 134 F1 individuals were phenotyped for root and associated physiological traits (29 traits) and genotyped with 41 of the 320 RAPD and 9 of the 55 SSR polymorphic primers. Single marker analysis was deployed for detecting the association of markers linked to root associated traits by SAS software. There were 13 putative RAPD markers associated with root traits such as root length, secondary roots, root dry weight, and root to shoot ratio, in which root length associated marker OPS1850 showed high phenotypic variance of 6.86%. Two microsatellite markers linked to root length (CPCM13400) and root to shoot ratio (CM211300). Besides, 25 markers were associated with more than one trait and few of the markers were associated with positively related physiological traits and can be used in marker assisted trait selection.

Growth of ‘M9’ apple root in five Central Europe replanted soils

Soil sickness is a widespread problem in replanted apple orchards with a complex symptomatology and etiology influenced by soil and climate conditions. Consequently, a conclusive technical solution is still lacking for intensive apple orchards. The present work aims to analyze the morphological and functional changes occurring in the M9 apple root systems growing in pot filled with soil derived from five different European growing areas. For each growing area, the soil was collected from the apple orchard and used directly in the pot or gamma-ray sterilized before potting. Soil from a neighborhood fallow was also used as control for each growing area. In the non-sterilized replant soils plants developed poor root systems due to a limited biomass allocation. Fibrous roots production was particularly compromised. The roots had a smaller diameter and a lower ramification index. The root cell membrane integrity was also lower. Gamma-ray sterilized replant soils increased root growth, branching and cell integrity, while nearby fallow soil induced an intermediate root behavior. The magnitude of the symptoms showed a significant interaction between soil treatment and sampling site and root growth was correlated with the organic matter content in the soils.

Responses of Root Growth and Nitrogen Transfer Metabolism to Uniconazole, a Growth Retardant, during the Seedling Stage of Soybean under Relay Strip Intercropping System

Relay strip intercropping of soybean has been widely developed in the southwest of China to secure China's soybean production. However, due to the shading from maize, soybean plants are thin and have a poor root system. Uniconazole is a plant-growth retardant that could enhance root vigor; increase root length, root volume, and root dry weight; and affect nitrogen (N) metabolism. To understand the effects of uniconazole on the root growth and N-transfer metabolism of soybean seedlings under relay strip intercropping, the changes in some morphological characteristics of root, dry-matter weight, root vigor, nitrate (NO3 −)-N, ammonium (NH4 +)-N, and amino acid of xylem sap after seed treatment with uniconazole powder (0, 2, 4, and 8 mg kg−1 seed) were investigated. Main root length, total lateral root lengths, first lateral root numbers, root nodule numbers, root vigor together with bleeding sap, bleeding sap–top ratio, root dry weight, and root/shoot ratio were increased, indicating uniconazole improved soybean root system in relay strip intercropping. Uniconazole powder treatment could increase NO3 −-N, NH4 +-N, and total amino acid of xylem sap, to increase the potential of leaf and root N reduction and assimilation, and increase of leaf and root N contents. Thus, results suggested that uniconazole treatment can improve root growth and N transfer mechanism of soybean to support its further growth.

Effect of sheep and horse grazing on species and functional composition of sub‐Mediterranean grasslands

AbstractQuestionsHow does horse or sheep grazing affect species richness, diversity and functional composition of plant communities in sub‐Mediterranean grasslands? What are the implications of grazing management for species conservation?LocationPastures dominated by Bromus erectus grazed by either sheep or horses in the Umbria‐Marches Apennines (central Italy).MethodsWe examined grasslands at altitudes ranging from 1000 to 1200 m a.s.l. on north‐facing slopes and with a slope angle of 20–40 °. In 20 plots of 1 m2 for each management type, canopy height and above‐ground phytomass were recorded. In 120 plots (60 for each management type) of 1 m2 the cover value of each species was recorded. Floristic diversity and community similarity of the sheep‐ and horse‐grazed conditions were compared. Functional plant traits and strategies or ecological requirements were also evaluated.ResultsThe sward was shorter and supported less above‐ground phytomass in the horse‐grazed area. The sheep‐ and horse‐grazed areas had similar floristic diversity. Accidental species were the species most affected. Plants with low‐nutrient requirement spread in horse‐grazed pasture. Functional traits of species were filtered by the system, resulting in diverse cover values of species. Horse grazing promoted plants with a robust defence strategy (avoidance and tolerance) that ensured leaves were replaced when horses were not grazing, as well as species with clonal growth. In the sheep‐grazed area, a higher level of selective defoliation and a delayed start to the grazing period promoted species with low palatability, a late‐flowering strategy and those intolerant to trampling by large herbivores (chamaephytes). The value of forage feed was slightly higher in horse‐grazed pasture. Grazing of horses was more effective than that of sheep for controlling dominant unpalatable tall grasses.ConclusionIn terms of biodiversity conservation, horse grazing may be considered as useful as sheep grazing, but only if managed at optimal stocking rates, because the increase in short grasses and annuals (growth forms with poor root systems) does not ensure maintenance of soil on steep slopes.

Rice leaf growth and water potential are resilient to evaporative demand and soil water deficit once the effects of root system are neutralized

Rice is known to be sensitive to soil water deficit and evaporative demand, with a greatest sensitivity of lowland-adapted genotypes. We have analysed the responses of plant water relations and of leaf elongation rate (LER) to soil water status and evaporative demand in seven rice genotypes belonging to different species, subspecies, either upland- or lowland-adapted. In the considered range of soil water potential (0 to -0.6 MPa), stomatal conductance was controlled in such a way that the daytime leaf water potential was similar in well-watered, droughted or flooded conditions (isohydric behaviour). A low sensitivity of LER to evaporative demand was observed in the same three conditions, with small differences between genotypes and lower sensitivity than in maize. The sensitivity of LER to soil water deficit was similar to that of maize. A tendency towards lower sensitivities was observed in upland than lowland genotypes but with smaller differences than expected. We conclude that leaf water status and leaf elongation of rice are not particularly sensitive to water deficit. The main origin of drought sensitivity in rice may be its poor root system, whose effect was alleviated in the study presented here by growing plants in pots whose soil was entirely colonized by roots of all genotypes.

Cyclic secondary somatic embryogenesis and efficient plant regeneration in camphor tree (Cinnamomum camphora L.)

An efficient protocol for secondary somatic embryogenesis in camphor tree is reported. Secondary somatic embryos (SSEs), initially obtained from the primary embryos of a nascent embryogenic culture in 2002, were proliferated and maintained for more than 4 yr via cyclic secondary somatic embryogenesis. Throughout this period, the embryo populations retained a high level of competence for plant regeneration. SSEs were produced on the surfaces of the cotyledons and radicular ends of maternal somatic embryos (MSEs). Histological observations of the various stages of secondary embryo development revealed four typical stages, namely, globular, heart-shaped, torpedo, and cotyledonary. The process of secondary embryogenesis continued in a cyclic way, with each newly formed embryo producing a subsequent generation of secondary embryos. In order to progress developmentally beyond proliferation cycles, cotyledonary embryos from one of embryogenic lines (L14) were cultured on Murashige and Skoog (MS) medium with 0.1–3.0 mg l−1 abscisic acid (ABA) or 0.05–1.0 mg l−1 thidiazuron (TDZ) in darkness for 2 mo to achieve maturation. Matured embryos were then transferred to MS-based germination medium containing either 0.1 mg l−1 TDZ, 0.2 mg l−1 indole-3-butyric acid (IBA), and 0.5 mg l−1 6-benzylaminopurine (BA) or 0.1 mg l−1 TDZ and 0.2 mg l−1 IBA and were cultured in light for germination. Over 50% of embryos matured in the presence of 0.5 mg l−1 ABA were able to germinate with shoots and poor root system. Frequencies of embryos germinating normal shoots among different genotypes did not change significantly. A total of 93% of the shoots from the germinated embryos converted to plantlets on half strength MS medium with 0.5 mg l−1 IBA by 3 wk. Plantlets acclimatized successfully to ex vitro conditions and developed as field-grown plants with normal appearance.

Growth and viability of mycorrhizal extraradical mycelia associated with three temperate orchid species

Growth and enzymatic activities of extraradical mycelia (ERM) of native mycorrhizal symbionts associated with three orchid species, Dactylorhiza fuchsii, D. majalis and Platanthera bifolia, were studied. ERM extracted from the mycorrhizosphere of these species showed features typical for fungi that form orchid mycorrhiza. In the first pot experiment, three different treatments were applied on tubers of D. fuchsii transplanted from a natural site: control (no specific treatment), reinoculated (surface-sterilized tubers reinoculated with mycorrhizal fungi-colonised roots), and benomyl (nonsterilized tubers treated with fungicide). However, no significant differences in ERM growth and intensity of root mycorrhizal colonisation at harvest were observed among these treatments. ERM associated with reinoculated D. fuchsii plants showed significantly higher alkaline phosphatase (ALP) enzymatic activity at week 36 than at week 24, but no differences were observed for NADH diaphorase activity. Benomyl application significantly reduced ALP activity in comparison with reinoculated plants at week 36. In the second experiment, plants of all three species were either untreated (control), or repeatedly treated with benomyl. Similarly to the results of the first experiment, benomyl application did not reduce the ERM growth of mycorrhizal symbionts associated with D. majalis and D. fuchsii. The low ERM growth associated with benomyl-treated P. bifolia was probably caused by poor root system development in this treatment. Significantly higher mycorrhizal colonisation was found for D. fuchsii compared to P. bifolia in control treatments at the end of cultivation. The ERM of native symbionts of the three orchid species studied seemed to have a different growth pattern over time and responded differently to fungicide application.

Growth and Yield of Six Rice Cultivars under Three Water-saving Cultivations

We evaluated the genotypic differences in growth, grain yield, and water productivity of six rice (Oryza sativa L.) cultivars from different agricultural ecotypes under four cultivation conditions: continuously flooded paddy (CF), alternate wetting and drying system (AWD) in paddy field, and aerobic rice systems in which irrigation water was applied when soil moisture tension at 15 cm depth reached −15 kPa (A15) and −30 kPa (A30). In three of the sixcultivars, we also measured bleeding rate and predawn leaf water potential (LWP) to determine root activity and plant water status. Soil water potential (SWP) in the root zone averaged −1.3 kPa at 15 cm in AWD, -5.5 and -6.6 kPa at 15 and 35 cm, respectively, in A15, and −9.1 and −7.6 kPa at 15 and 35 cm, respectively, in A30. The improved lowland cultivar, Nipponbare gave the highest yield in CF and AWD. The improved upland cultivar, UPLRi-7, and the traditional upland cultivar, Sensho gave the highest yield in A15 and A30, respectively. The yields of traditional upland cultivars,Sensho and Beodien in A30 were not lower than the yields in CF. However, the yields of the improved lowland cultivars, Koshihikari and Nipponbare, were markedly lower in A15 and A30. Total water input was 2145 mm in CF, 1706 mm in AWD, 804 mm in A15, and 627 mm in A30. The water productivity of upland rice cultivars in aerobic plots was 2.2 to 3.6 times higher than that in CF, while those of lowland cultivars in aerobic plots were lower than those in CF. The bleeding rate of Koshihikari was lower in A15 and A30 than in CF and AWD, and its LWP was significantly lower in A15 and A30 than in CF and AWD, but Sensho and Beodien showed no differences among the four cultivation conditions. We conclude that aerobic rice systems are promising technologies for farmers who lack access to enough water to grow flooded lowland rice. However, lowland cultivars showed severe growth and yield reductions under aerobic soil conditions. This might result from poor root systems and poor root function, which limits water absorption and thus decreases LWP. More research on the morphological and physiological traits under aerobic rice systems is needed.

Mechanical Stimuli Regulate the Allocation of Biomass in Trees: Demonstration with Young Prunus avium Trees

Plastic tree-shelters are increasingly used to protect tree seedlings against browsing animals and herbicide drifts. The biomass allocation in young seedlings of deciduous trees is highly disturbed by common plastic tree-shelters, resulting in poor root systems and reduced diameter growth of the trunk. The shelters have been improved by creating chimney-effect ventilation with holes drilled at the bottom, resulting in stimulated trunk diameter growth, but the root deficit has remained unchanged. An experiment was set up to elucidate the mechanisms behind the poor root growth of sheltered Prunus avium trees. Tree seedlings were grown either in natural windy conditions or in tree-shelters. Mechanical wind stimuli were suppressed in ten unsheltered trees by staking. Mechanical stimuli (bending) of the stem were applied in ten sheltered trees using an original mechanical device. Sheltered trees suffered from poor root growth, but sheltered bent trees largely recovered, showing that mechano-sensing is an important mechanism governing C allocation and the shoot-root balance. The use of a few artificial mechanical stimuli increased the biomass allocation towards the roots, as did natural wind sway. It was demonstrated that there was an acclimation of plants to the imposed strain. This study suggests that if mechanical stimuli are used to control plant growth, they should be applied at low frequency in order to be most effective. The impact on the functional equilibrium hypothesis that is used in many tree growth models is discussed. The consequence of the lack of mechanical stimuli should be incorporated in tree growth models when applied to environments protected from the wind (e.g. greenhouses, dense forests).

First Report of a γ 3-Proteobacterium Associated with Diseased Strawberries in Italy.

During the fall seasons of 2005 and 2006, diseased strawberry plants (Fragaria × ananassa Duch.) were observed in nurseries and production fields in Ferrara, Forli-Cesena, and Ravenna provinces (Emilia-Romagna region, northern Italy). Symptoms consisted of a conspicuous plant stunting with a poor root system. Older leaves rolled upward and displayed a marked premature purplish discoloration, while young leaves were cupped, chlorotic, generally reduced in size, and had shortened petioles. This strawberry disorder was similar to "marginal chlorosis", an infectious disease occurring in France that can be induced by two different phloem-limited uncultured bacteria: the γ 3-proteobacterium 'Candidatus Phlomobacter fragariae' and the stolbur phytoplasma (16SrXII-A). In strawberry production fields, 'Ca. P. fragariae' is reported as being the prevalent agent of this disease (1). Sixty-seven diseased plants were collected from production fields and nurseries for testing for 'Ca. P. fragariae'. Leaf samples were analyzed by 4',6-diamidine-2-phenylindole staining and PCR. Forty samples showed fluorescent DNA in the phloem, whereas no fluorescence was observed in symptomless strawberries. When tested by PCR with primers Fra4/Fra5, which amplify a 550-bp fragment of the 16S rDNA region of 'Ca. P. fragariae' (1), 13 of 36 strawberries from production fields and 1 of 31 nursery plants gave a positive reaction. On the other hand, 21 samples from nurseries and 5 from production fields tested positive for stolbur phytoplasma (3). No amplification was obtained with DNA from symptomless or healthy strawberry plants. Sequencing Fra4/Fra5 amplicons from three samples (GenBank Accession Nos. DQ362916-DQ362918) showed a 98.1 to 98.6% and a 98.3 to 98.8% identity with the published sequences of the French isolate "LG2001" (GenBank Accession No. AM110766) and the Japanese isolate J-B (GenBank Accession No. AB246669) of 'Ca. P. fragariae', respectively. Higher homology (99.2 to 99.8%) was found with another bacterium-like organism (BLO) of the γ 3-proteobacteria subgroup (GenBank Accession No. AY057392) associated with the syndrome "basses richesses" of sugar beet (SBR). Furthermore, PCR assays performed with primers Pfr1/Pfr4, specific for spoT gene of 'Ca. P. fragariae', did not show any amplification with DNA from the 14 diseased strawberry plants tested. This is in agreement with the SBR BLO identification (2). To better characterize the Italian isolates, the full-length 16S rDNA gene was analyzed with primers fd1/Fra4 and Fra5/rp1, which amplify the 5' and 3' region of 16S rDNA gene of the proteobacteria, respectively (2). PCR products from eight isolates were sequenced, and the 16S rDNA sequences obtained (GenBank Accession Nos. DQ538372-DQ538379) showed a 96.4 to 97.3% identity with the known 'Ca. P. fragariae' isolates, while a higher homology (99.4 to 99.9%) was again found with the SBR BLO. To our knowledge, this is the first report of a γ 3-proteobacterium affecting strawberry in Italy. In the genome region analyzed, our isolates are more similar to the SBR BLO than to 'Ca. P. fragariae'. Further work is in progress to investigate incidence, geographical distribution, epidemiology, and host range of this pathogen in Italy.