Identification and characterization of a novel whitefly-transmitted member of the family potyviridae isolated from cucurbits in Florida

ABSTRACT A novel whitefly-transmitted member of the family Potyviridae was isolated from a squash plant (Cucurbita pepo) with vein yellowing symptoms in Florida. The virus, for which the name Squash vein yellowing virus (SqVYV) is proposed, has flexuous rod-shaped particles of approximately 840 nm in length. The experimental host range was limited to species in the family Cucurbitaceae, with the most dramatic symptoms observed in squash and watermelon, but excluded all tested species in the families Amaranthaceae, Apocynaceae, Asteraceae, Chenopodiaceae, Fabaceae, Malvaceae, and Solanaceae. The virus was transmitted by whiteflies (Bemisia tabaci) but was not transmitted by aphids (Myzus persicae). Infection by SqVYV induced inclusion bodies visible by electron and light microscopy that were characteristic of members of the family Potyviridae. Comparison of the SqVYV coat protein gene and protein sequences with those of recognized members of the family Potyviridae indicate that it is a novel member of the genus Ipomovirus. A limited survey revealed that SqVYV also was present in watermelon plants suffering from a vine decline and fruit rot recently observed in Florida and was sufficient to induce these symptoms in greenhouse-grown watermelon, suggesting that SqVYV is the likely cause of this disease.     

土霉素对柑橘黄龙病的防治效果及对柑橘产量和品质的影响

为有效防控柑橘黄龙病，于2017年在佛罗里达大学柑橘研究与教育中心的奥本代尔市柑橘试验场进行田间试验筛选黄龙病的防治药剂及其浓度，测定注射土霉素后叶片中柑橘黄龙病菌亚洲种Cadidatus Liberibacter asiaticus、土霉素、淀粉含量、柑橘产量、出汁率、可溶性固形物含量和酸度，显微镜下观察注射土霉素后淀粉粒的分布。结果表明，浓度为1.6g/株土霉素处理180 d后柑橘叶片中黄龙病菌亚洲种含量减少幅度最大，为91.78%；注射浓度为1.6g/株土霉素后7d，叶片中土霉素含量达142.2 μg/kg，注射后11 d叶片中土霉素含量达到最大，为239.8 μg/kg，注射后45 d叶片中土霉素含量低至99.6 μg/kg以下；注射后7~90d，叶片中黄龙病菌亚洲种含量呈波浪形变化，注射90 d后叶片中黄龙病菌亚洲种含量一直处于增长趋势，叶片中黄龙病菌亚洲种含量总体随着土霉素含量的升高而降低；注射浓度为1.6g/株土霉素后，叶片中淀粉含量大幅度下降，60d时达到最低值，为3.3 μg/mm²，90d时达到峰值，为14.5 μg/mm²；单株产量为16.7 kg，与注射浓度为0.8 g/株土霉素处理差异不显著，但均显著高于其它2个处理；柑橘出汁率、可溶性固形物和酸度均与清水对照差异不显著。表明土霉素可有效抑制黄龙病菌亚洲种，减少柑橘叶片内淀粉含量，增加柑橘产量，但对果实品质未产生显著影响。     

MINERALIZED ARTERIOSCLEROSIS IN A CAT

In radiographs of a domestic short haired cat of unknown age, mineralization was identified in the pulmonary parenchyma, peripheral pulmonary vessels, the aortic outflow tract, aortic valve, celiac artery, cranial mesenteric artery, and the internal and external iliac arteries. The diffuse arterial mineralization was characterized histopathologically as arteriosclerosis. This is the first report of mineralized arteriosclerosis in a cat with corresponding radiographic signs. The arteriosclerosis is thought to be due to systemic hypertension but a definitive cause for the profound mineralization was not found. Causes of soft tissue mineralization are reviewed.     

Integrating animal movement with habitat suitability for estimating dynamic migratory connectivity

Context

High-resolution animal movement data are becoming increasingly available, yet having a multitude of empirical trajectories alone does not allow us to easily predict animal movement. To answer ecological and evolutionary questions at a population level, quantitative estimates of a species’ potential to link patches or populations are of importance.

Objectives

We introduce an approach that combines movement-informed simulated trajectories with an environment-informed estimate of the trajectories’ plausibility to derive connectivity. Using the example of bar-headed geese we estimated migratory connectivity at a landscape level throughout the annual cycle in their native range.

Methods

We used tracking data of bar-headed geese to develop a multi-state movement model and to estimate temporally explicit habitat suitability within the species’ range. We simulated migratory movements between range fragments, and calculated a measure we called route viability. The results are compared to expectations derived from published literature.

Results

Simulated migrations matched empirical trajectories in key characteristics such as stopover duration. The viability of the simulated trajectories was similar to that of the empirical trajectories. We found that, overall, the migratory connectivity was higher within the breeding than in wintering areas, corroborating previous findings for this species.

Conclusions

We show how empirical tracking data and environmental information can be fused for meaningful predictions of animal movements throughout the year and even outside the spatial range of the available data. Beyond predicting migratory connectivity, our framework will prove useful for modelling ecological processes facilitated by animal movement, such as seed dispersal or disease ecology.

     

Anatomical distribution of abnormally high levels of starch in HLB-affected Valencia orange trees

The citrus disease Huanglongbing (HLB or citrus greening) is characterized, among other symptoms, by extraordinary levels of starch accumulation in leaves. This condition denotes imbalances in carbohydrate source sink relationship which in turn may have direct implications in the overall health of HLB-trees and in future strategies to manage the disease. Using light, scanning, and transmission electron microscopy we investigated the extent of carbohydrate partitioning imbalances throughout the tree. In all aerial tissues, starch accumulation in HLB-affected trees far exceeded that of HLB-negative control trees. Starch accumulated extensively in photosynthetic cells as well as phloem elements and vascular parenchyma in leaves and petioles. In stems, starch was commonly observed in xylem parenchyma and in the phelloderm of HLB-affected trees but absent from control samples. In contrast, roots from HLB-affected trees were depleted of starch whereas roots from control trees contain substantial starch deposits. The data supports the notion that the substantial changes in carbohydrate partitioning observed throughout the citrus tree may not only be a result of HLB infection, but in itself, a cause for the rapid decline and death of infected trees.     

Assessing the impact of Diplocardia ornata on physical and chemical properties of compacted forest soil in microcosms

 The influence of compaction on Diplocardia ornata (Smith) burrowing and casting activities, soil aggregation, and nutrient changes in a forest soil were investigated using pot microcosms. Treatments included two levels each of compaction, organic matter, and earthworms. Both burrowing and casting activities were more abundant in uncompacted soil than in compacted soil. Bulk density decreased in microcosms of compacted soil containing D. ornata from 1.76 g cm^–3 to 1.49 g cm^–3 over the study period. The overall percent of aggregates in the same size classes in compacted soil was less than the percent of aggregates in uncompacted soil. The mean percent of aggregates in earthworm casts for size classes 0.25–1.00 mm was higher for compacted soil than for uncompacted soil. The reverse was true for aggregates in class sizes 2.00–4.00 mm. Soil compaction also affected soil microbial biomass carbon and soil inorganic N concentrations. These results indicate that the burrowing and casting activities of earthworms in compacted forest soils, as in soils of agricultural and pastured lands, can help ameliorate disturbed soils by improving aggregation, reducing bulk density, and increasing nutrient availability. Received: 1 September 1999     

土霉素处理对Valencia夏橙中淀粉及相关基因表达的影响

黄龙病(Huanglongbing,HLB)会造成柑橘韧皮部坏死堵塞,导致光合同化物运输不畅,淀粉大量积累。在感染HLB的4年生Valencia夏橙病株上分别注入0.1和0.2 g·株~(-1)土霉素(Oxytetracycline,OTC),90 d后运用qPCR检测,病株中HLB病原菌(Candidatus Liberibacter asiaticus,Las)含量均明显降低,且0.2和0.1 g·株~(-1) OTC处理的效果相当。I2/KI显色及LM观测表明,0.2 g·株~(-1) OTC处理后植株的淀粉含量从注射前的18.58μg·mm~(-2)减少至90 d的5.24μg·mm~(-2),而0.1 g·株~(-1)的处理90 d仅降至11.88μg·mm~(-2)。高效液相色谱(HPLC)检测结果表明,注射后90 d内,试验用浓度0.2 g·株~(-1) OTC在植株体内可降解至200μg·kg~(-1)以下。基因表达结果表明,注射0.2 g·株~(-1) OTC后30和90 d,淀粉合成及分解相关基因表达量均下降,其中淀粉合成相关基因AGPase表达量下降最显著,这与OTC注射后30和90 d叶片内淀粉含量下降结果一致。     

The effect of suppression treatments on the uptake of 15N by intercropped corn from labeled alfalfa (Medicago sativa)

In greenhouse experiments, we examined the N transferred to intercropped corn from ¹⁵N-labeled alfalfa shoot residue and intact roots in an undisturbed soil system in response to two different suppression treatments and complete killing of alfalfa. The alfalfa treatments included complete killing (glyphosate only), glyphosate injury + cutting, and cutting only, with alfalfa shoot residue returned to the soil surface in all three treatments. Corn was planted in each pot following application of the treatments. When alfalfa was suppressed by glyphosate injury + cutting, corn had recovered 12% of the alfalfa N by 8 weeks of growth, but with cutting only, N recovery by corn was reduced to 4.0%. The completekill treatment resulted in 8% recovery by corn of alfalfa N. In all treatments, most of the alfalfa-N remained in the soil organic pool. A second experiment tested a cutting only treatment with ¹⁵N-labeled alfalfa residue returned to the soil surface. The ¹⁵N-labeled alfalfa residue contributed 4.1% of N to corn during the 8-week growth cycle. Twice as much ¹⁵N was found in the active microbial biomass pool in the two treatments with live intereropped plants compared to the monoculture treatments with complete killing (non-intercropped) and the control treatment of alfalfa regrowth only. An analysis of the change in the ¹⁵N content of the undisturbed alfalfa roots from just before the suppression until 8 weeks later suggested that approximately 80% of the root ¹⁵N was lost from the plant suppressed by cutting. This corresponds to 28% of the total N released from the alfalfa. The results suggest that the degree of legume suppression was a key factor in the availability of legume N to the second crop. When the two species were intercropped, more of the N available from legume residues went to plant uptake and microbial biomass and was not stabilized as quickly in the soil organic pool. Appropriate management schemes must be designed to increase N availability to the second crop without yield reduction. These studies suggest severe suppression is necessary; if successful, more of the N can be maintained in active pools.     

The Effect of Cyst Nematode Race 3 and Bradyrhizobium japonicum Interactions on Nodulation and Other Agronomic Characters of Three Soybean Genotypes

The effect of soybean cyst nematode (SCN) race 3 and strains of Bradyrhizobium japonkum interactions on nodulation and other agronomic characters of several soybean genotypes was investigated. Nodule weight was reduced in soybean cultivar Ogden treated with SCN plus Bradyrhizobia strains USDA 110 and 6 and on soybean cultivar Essex treated with SCN plus strain USDA 6. The result was reversed on soybean cultivar Essex treated with SCN plus strain USDA 110. The nodule number also decreased on soybean cultivars Ogden and Essex treated with SCN plus strains USDA 110 and 6. The fresh root weights of soybean cultivars Ogden and Essex treated with SCN plus strain USDA 110 were heavier than the fresh root weight of Essex treated with SCN plus strain USDA 6. Lower nitrogen content of stems and leaves was noted only in cultivar Essex treated with SCN plus strains USDA 110 and 6. Bradyrhizobia strain USDA 110 was more efficient in the initiation of nodules in cultivars Ogden and Essex than strain USDA 6. The nitrogen-fixing capacity of strain USDA 6 in Ogden was better than strain USDA 110. The differences in the agronomic performances of the various soybean genotypes were due to their degree of susceptibility to SCN and Bradyrhizobia strains and also to their genetic make-up.