Watermelon chlorotic stunt virus from the Sudan and Iran: Sequence Comparisons and Identification of a Whitefly-Transmission Determinant

ABSTRACT The genomes of two Watermelon chlorotic stunt virus (WmCSV) isolates, one from the Sudan and one from Iran, were cloned and sequenced. Sequence relationship with other geminiviruses characterizes WmCSV as a typical Eastern Hemisphere geminivirus with a bipartite genome. The two geographically distant WmCSV isolates from Africa and the Middle East share a very high overall sequence similarity: 98% between their DNA-A and 96% between their DNA-B components, and their respective capsid proteins are identical. A single amino acid change in the capsid protein (N131D) renders WmCSV whitefly nontransmissible. This region of the capsid is also implicated in transmission by Bemisia tabaci of Tomato yellow leaf curl virus.     

Characterization of infectious bursal disease viruses isolated in 2007 from Delmarva commercial broiler chickens

A study was performed in 2007 to isolate and characterize infectious bursal disease viruses (IBDVs) in commercial broilers grown in the Delmarva (DMV) Peninsula region of the United States. Bursae of Fabricius were collected weekly from 1 to 4 wk of age from broilers on 10 farms with a history of poor performance. Microscopic pathology was used to determine the infectious bursal disease (IBD) status of the broilers. Bursae from 1- and 2-wk-old broilers did not show IBD microscopic lesions. Moreover, broilers on 1 of the 10 farms were IBD lesion free at 3 and 4 wk of age. However, 3 of 9 and 9 of 9 farms yielded broilers with IBD-affected bursae from 3- and 4-wk-old commercial broilers, respectively. Ten IBDV isolates were recovered from 3 of 3 lesion-positive bursal pools at 3 wk of age and 7 of 9 lesion-positive bursal pools at 4 wk of age. Analysis of the viral protein (VP) 2 genes identified all isolates as serotype 1 Delaware (Del) variant viruses. Five field isolates, each representing different molecular clades of the Delaware variant viruses, were selected for further study. Experimental infection of specific-pathogen-free white leghorn chickens with isolates DMV/4813/07, DMV/4947/07, DMV/4955/07, DMV/5038/07, and DMV/5041/07 produced gross and microscopic pathology of the bursa consistent with Delaware variant infection. Monoclonal antibody testing showed DMV/4813/07, DMV/4947/07, DMV/ 4955/07, and DMV/5041/07 to be similar to previous recognized variant viruses. However, DMV/5038/07 was found to be unreactive with the monoclonal antibodies that typically recognize reference strains STC, Del E, GLS, RS593, and AL2. In a challenge of immunity study, 10-day-old progeny from breeders immunized with a commercially available inactivated IBDV vaccine containing the Del E and classic strains were protected to a lesser degree against isolate DMV/5038/07 compared to Del E challenge based on microscopic lesion scores (P < 0.01) of the bursa. This result suggests the virus is antigenically different from the Del E strain contained in the vaccine. Collectively, the monoclonal antibody and progeny challenge of immunity findings suggest DMV/5038/07 is antigenically different from the Del E strain contained in the vaccine.     

Prognostic factors for successful outcome following urethral rupture in dogs and cats

Twenty dogs and 29 cats were identified with urethral rupture. Males predominated in both groups. The most common cause of urethral rupture in dogs was vehicular trauma, and in cats it was trauma associated with urethral obstruction and catheterization. Clinicopathological findings, type of surgical correction, time to surgery, type of urinary diversion, and duration of urinary diversion were not statistically associated with the outcome. In this study, the presence of multiple traumatic injuries was associated with a poor outcome.     

Malvastrum leaf curl Guangdong virus is a distinct monopartite begomovirus

Virus isolates GD6, GD7, GD8, GD9 and GD10 were obtained from Malvastrum coromandelianum showing leaf curl symptoms in Guangdong Province of China. A specific 500 bp product was consistently detected in total DNA extracts, amplified with universal primers specific for members of the genus Begomovirus. Analysis of their partial DNA sequences revealed that they are isolates of the same begomovirus species, sharing 92·8%–97·1% nucleotide sequence identity. The complete DNA sequences of both GD6 and GD9 were found to be 2767 nucleotides, with all the characteristic features of begomovirus genome organization. The two isolates have less than 85·2% nucleotide sequence identity with other reported begomoviruses. Consequently, GD6 and GD9 are considered to be isolates of a novel begomovirus species, for which the name Malvastrum leaf curl Guangdong virus (MLCuGdV) is proposed. Sequence analyses suggest that MLCuGdV may have arisen by recombination between viruses related to Papaya leaf curl China virus , Tomato leaf curl Philippines virus and other undiscovered virus ancestors. Neither the DNA-B component nor the DNAβ molecule associated with these begomovirus isolates was found. An infectious clone of GD6 was constructed. GD6 efficiently infected Nicotiana benthamiana , N. glutinosa and Petunia hybrida by agro-inoculation, and Malvastrum coromandelianum by whitefly transmission, inducing leaf curling, vein swelling and stunting symptoms. GD6 was also infectious in N. tabacum , but did not induce observable disease symptoms.     

Silicon,biological seed treatment and cutting reduce the intensity of leaf spot diseases affecting Lolium multiflorum

Italian ryegrass is a major pasture crop cultivated mainly for feeding cattle in southern Brazil. The choice of crop is based on nutritional quality and the shortage of pastures that occur during the winter in the southernmost part of Brazil. In this region, the production of biomass and seeds are threatened by diseases, in particular fungal diseases that affect the foliage. In this study we identified and monitored the natural occurrence of a complex of leaf spotting diseases and evaluated the effects of combined management practices to reduce the intensity of foliar diseases: seed treatment with Trichoderma atroviride, soil amendment with silicon and cutting frequency (none, one or two cuts). Three diseases were present in a two-season experiment: grey leaf spot (Pyricularia oryzae), brown leaf spot (Bipolaris sorokiniana) and parrot's eye leaf spot (Cercospora sp.). Grey leaf spot had the highest severity, regardless of treatment, during the first season, and was the only disease present in the following season. Grey leaf spot dominated, and plants receiving only one cut were more prone to P. oryzae infection. The treatments with silicon or T. atroviride reduced the relative disease by 40% to 80%, in relation to untreated and uncut regimes. This study showed the main leaf spot diseases associated with L. multiflorum. Moreover, it demonstrates for the first time in the region the effectiveness of reducing leaf spot via the application of silicon in the soil, inoculation of seeds with T. atroviride and managing the cutting regime.     

PCR‐based identification of cacao black pod causal agents and identification of biological factors possibly contributing to Phytophthora megakarya's field dominance in West Africa

Among the Phytophthora species that cause black pod of cacao, P. megakarya is the most virulent, posing a serious threat to cacao production in Africa. Correct identification of the species causing the black pod and understanding the virulence factors involved are important for developing sustainable disease management strategies. A simple PCR‐based species identification method was developed using the species‐specific sequences in the ITS regions of the rRNA gene. A phylogenetic tree generated for 119 Phytophthora isolates, based on the 60S ribosomal protein L10 gene and rDNA sequence, verified the PCR‐based identification assay and showed high interspecific variation among the species causing black pod. Phytophthora megakarya isolates were uniformly virulent in an assay using susceptible cacao pod husks inoculated with zoospores, while the P. palmivora isolates showed greater divergence in virulence. The virulence of P. megakarya was associated with earlier production of sporangia and an accelerated induction of necrosis. While zoospore germ tubes of both species penetrated pods through stomata, only P. megakarya produced significant numbers of appressoria. A hypersensitive‐like response was observed when attached SCA‐6 pods were inoculated with P. palmivora. SCA‐6 pods became vulnerable to P. palmivora when wounded prior to zoospore inoculation. Phytophthora megakarya was more aggressive than P. palmivora on attached SCA‐6 pods, causing expanding necrotic lesions with or without wounding. Phytophthora megakarya is predominant in the Volta region of Ghana and it remains to be seen whether it can displace P. palmivora from cacao plantations of Ghana as it has in Nigeria and Cameroon.     

Water and nitrate budgets in a rendzina cropped with oilseed rape receiving varying amounts of fertilizer

Pollution of the environment by nitrogen (N) has emerged as a serious concern in agriculture, especially in the case of crops such as oilseed rape. To assess the effect of N fertilization on N dynamics, the movements of water and nitrate were determined in a rendzina near Châlons-en-Champagne (eastern France) cropped with oilseed rape with three levels of fertilizer N and in a bare control. From in situ micrometeorological measurements, actual evapotranspiration rates were computed with an energy budget and used to calibrate an evapotranspiration model based on meteorological data and crop leaf area index. Water flow below 120 cm was then deduced from periodic measurements of soil moisture contents and precipitation, and the associated nitrate leaching fluxes were calculated from the NO₃ concentration measured at the same depth. Denitrification rates and ammonia volatilization were monitored in the field after fertilizer applications, and crop assimilation of nitrogen was determined frequently during the growth cycle. A nitrate budget gave an approximation of the in situ net mineralization fluxes. The water balance was influenced by the crop and its fertilization: the crop's canopy and roots enhanced the water loss by evapotranspiration and contributed to diminish the soil water storage, whereas drainage volumes were about the same for all cropped treatments, and significantly greater in the bare soil. The rainy winter was particularly favourable to leaching, and losses were much greater (+ 41%) under the over-fertilized crop than under the non-fertilized one, but remained less (– 42%) than those under the bare control soil. Bilans hydriques et azotés d'une culture de colza sur rendzine avec différentes doses d'engrais Les pollutions de l'environnement par l'azote sont devenues une préoccupation majeure en agriculture, particulièrement dans le cas des cultures comme le colza. Pour évaluer les effets de la fertilisation azotée sur la dynamique de l'azote, les transferts d'eau et de nitrate d'une rendzine ont été mesurés près de Châlons-en-Champagne (Est de la France) sur des parcelles expérimentales de colza avec trois niveaux de fertilisation azotée et sur une parcelle témoin en sol nu. A partir de mesures micrométéorologiques in situ, l'évapotranspiration réelle a été calculée par bilan énergétique de la surface du sol, et un modèle d'évapotranspiration ayant pour entrées des données météorologiques classiques et l'indice foliaire de la culture a été calibré. Le flux net d'eau sous 120 cm a été alors déduit de mesures périodiques de teneur en eau du sol et de précipitations, et les flux de nitrate associés ont été calculés à partir des concentration mesurées à la même profondeur. Les flux de dénitrification et la volatilisation d'ammoniac ont été mesurés au champ après les apports d'engrais; l'absorption d'azote par la culture a été déterminée fréquemment pendant le cycle de croissance. Enfin, un bilan azoté a donné l'ordre de grandeur de la minéralisation nette. Le bilan hydrique a été influencé par la culture et sa fertilisation: le couvert végétal et les racines ont accentué les pertes d'eau par évapotranspiration et par conséquent le stock d'eau, tandis que la lame d'eau drainée était à peu près la même pour tous les traitements cultivés, et significativement plus élevée pour le sol nu. L'hiver particulièrement pluvieux a été très favorable au lessivage, et les pertes ont été beaucoup plus fortes (+ 41%) sous la culture sur-fertilisée que sur la culture non-fertilisée, mais elles sont restées inférieures (– 42%) à celles sous sol nu. Nomenclature     

The effect of nitrogen fertilization and shading on the incidence of “colour spots” in sweet pepper (Capsicum annuum) fruit

SUMMARY

“Colour spots” (CS) in pepper fruit is a physiological disorder characteristic of some sweet pepper cultivars. The symptoms are yellowish spots on the outer surface of affected fruits. We investigated the effects of shading and nitrogen supply on the susceptibility of three sweet pepper cvs (Maor, Lady Bell and 899) to CS. The most susceptible was ‘Maor’. The incidence of CS was promoted by high N and shading. The fruits of all cultivars had lower nitrogen concentrations than the leaves but there were no significant differences in fruit N content between Maor and the CS-insensitive cultivars. The CS-affected areas of the pericarp tissue had higher calcium concentrations than unaffected tissue. Differences in magnesium or potassium concentrations in these spots were less pronounced. Scanning electron microscopy revealed that the affected pericarp cells contained crystals, presumably of calcium oxalate. Only in ‘Maor’ fruits was the oxalate concentration elevated by approximately nine-fold when the nitrogen supply to shaded plants was increased. We suggest that in the fruits of the sensitive cultivar, oxalic acid production is enhanced under high-nitrogen + shading conditions and causes the CS damage, possibly be chelating intracellular calcium.