Natural infection of banana by a satellite-containing strain of cucumber mosaic virus: nucleotide sequence of the coat protein gene and the satellite RNA

Banana plants expressing mosaic symptoms, from the Jordan Valley in Israel, were shown to be infected by a satellite-RNA-containing strain of cucumber mosaic virus (CMV). Double-stranded RNA isolated from field-infected banana, without passage through another host, was used as a template for synthesis of cDNA. The cDNAs corresponding to the coat protein (CP) gene and to the satellite RNA were cloned after polymerase chain reaction amplification. The nucleotide sequences of the CP and the satellite cDNAs were determined. The CP gene and its 3′ flanking sequence had 98% similarity to the CMV Fny nucleotide sequence and the two strains differed in only one amino acid of the CP. The associated satellite had a sequence similarity ranging from 95% to 85.6% with other CMV satellites. Analysis of banana suckers differing in symptoms’ severity indicated a correlation between the presence of satellite and attenuation of symptoms.     

Dynamic relationships between soil properties and foliar disease as affected by annual additions of organic amendment to a sandy-soil vegetable production system

Additions of organic amendments to agricultural soils can lead to improved soil quality and reduced severity of crop diseases. However, the relationship between disease severity and soil properties as affected by repeated additions of these amendments is poorly understood. The primary objectives of this study were to (i) resolve multivariate relationships between soil properties and foliar disease severity and (ii) identify soil properties that contribute to disease severity in an intensive irrigated vegetable production system receiving annual additions of fresh and composted paper mill residuals (PMR). Foliar diseases caused by Pseudomonas syringae pv. syringae on snap bean (bacterial brown spot) and P. s. pv. lachrymans on cucumber (angular leaf spot) are the focus of this report. The experiment consisted of a 3-year crop rotation of potato (1998 and 2001), snap bean (1999 and 2002), and cucumber (2000). Treatments included a non-amended fertilizer control and two rates of fresh PMR, PMR composted alone (PMRC), and PMR composted with bark (PMRB). Soil measures included total soil carbon (TC) and nitrogen (TN), particulate organic matter carbon (POMC) and nitrogen (POMN), volumetric soil moisture (VM) and in situ NO₃-N. Multiple regression (MR) and principal component analyses (PCA) were conducted to identify key soil properties that influenced the amount of disease. On average, the amount of TC in plots amended with PMR composts increased 77-178% from 1999 to 2002 compared to the non-amended soils. In 1999, a year in which compost additions reduced the amount of bacterial brown spot of bean, TC explained 42% of the total variation in disease severity in the best MR model. Midseason TN alone was inversely related to angular leaf spot incidence in 2000, while POMN explained 51% of the variation in the best MR model for that year. In 2002, a year in which PMRC-amended soils exacerbated brown spot symptoms, midseason quantities of TN explained 80% of the variation in disease severity. Unique to 2002, NO₃-N alone positively correlated with disease severity. Overall, the influence of soil carbon on disease severity was displaced by the increasing importance of TN and NO₃-N, indicating a transition from a C-dependent to an N-dependent system.     

Farm Management Effects on Rhizosphere Colonization by Native Populations of 2,4-Diacetylphloroglucinol-Producing Pseudomonas spp. and Their Contributions to Crop Health

ABSTRACT Analyses of multiple field experiments indicated that the incidence and relative abundance of root-colonizing phlD+ Pseudomonas spp. were influenced by crop rotation, tillage, organic amendments, and chemical seed treatments in subtle but reproducible ways. In no-till corn plots, 2-year rotations with soybean resulted in plants with approximately twofold fewer phlD+ pseudomonads per gram of root, but 3-year rotations with oat and hay led to population increases of the same magnitude. Interestingly, tillage inverted these observed effects of cropping sequence in two consecutive growing seasons, indicating a complex but reproducible interaction between rotation and tillage on the rhizosphere abundance of 2,4-diacetlyphloroglucinol (DAPG) producers. Amending conventionally managed sweet corn plots with dairy manure compost improved plant health and also increased the incidence of root colonization when compared with nonamended plots. Soil pH was negatively correlated to rhizosphere abundance of phlD+ pseudomonads in no-till and nonamended soils, with the exception of the continuous corn treatments. Chemical seed treatments intended to control fungal pathogens and insect pests on corn also led to more abundant populations of phlD in different tilled soils. However, increased root disease severity generally was associated with elevated levels of root colonization by phlD+ pseudomonads in no-till plots. Interestingly, within a cropping sequence treatment, correlations between the relative abundance of phlD and crop stand or yield were generally positive on corn, and the strength of those correlations was greater in plots experiencing more root disease pressure. In contrast, such correlations were generally negative in soybean, a difference that may be partially explained by difference in application of N fertilizers and soil pH. Our findings indicate that farming practices can alter the relative abundance and incidence of phlD+ pseudomonads in the rhizosphere and that practices that reduce root disease severity (i.e., rotation, tillage, and chemical seed treatment) are not universally linked to increased root colonization by DAPG-producers.     

Multiple statistical approaches of community fingerprint data reveal bacterial populations associated with general disease suppression arising from the application of different organic field management strategies

Multiple statistical analyses of terminal restriction fragment length polymorphism (T-RFLP) data were used to screen and identify bacterial populations involved in general disease suppression in an organically managed soil. Prior to sampling three different management strategies (i.e. mixed hay (H), tilled fallowing and open-field vegetables production) were used during the transition from conventional to organic farming, with and without compost amendment. The H transition strategy consistently led to the lowest damping-off disease incidence on two different crops in separate greenhouse and field experiments. Bacterial population structure in bulk soil and the rhizosphere of both crops was characterized using T-RFLP analyses of amplified 16S rDNA sequences. First, principal component analysis (PCA) revealed changes in the relative abundance of bacterial terminal restriction fragments (TRF) in response to transition strategy and/or compost amendment in eight different experimental contexts. In each context, a different subset of TRF substantially contributed to the variation along the first two principal components. However, terminal restriction fragment M148 contributed significantly to the observed variation in 6 out of the 8 experiments, and moderately in the remaining 2 experiments. As a second approach, nonparametric analyses of variance revealed that the relative abundance of TRF differed among treatments. While the responsive subsets identified varied somewhat by experimental context, M137, M139 and M141 were more abundant in samples from the H transition strategy in multiple experimental contexts. Subsequent correlation analyses revealed that TRF associated with disease suppressive treatments (i.e. H with and without compost) were frequently negatively correlated with damping-off disease incidence. As a group, these TRF were disproportionately associated with lower disease levels further indicating their role in disease suppression. Interestingly, in silico analysis of the bacterial 16S rDNA sequence database revealed that the TRF identified in this study (e.g. M137, M139, M141, and M148) might correspond to well-characterized genera of bacterial biological control agents.     

Monitoring the behavior of hypoxia-stressed Carassius auratus using computer vision

Behavioral variations of a school of fish (Carrasius auratus) in a tank were monitored using computerized vision while the fish were subjected to hypoxia stress conditions. Two video cameras viewed the tank, one from the side through a transparent wall and one from above. The images were processed by a PC-based image processing algorithm which provided three coordinates of the school's center of gravity, with the standard deviations of each coordinate, and the projected spatial distribution of the fish. Stressed fish differed from controls with the following behavioral responses: (i) the center of gravity moved upwards and horizontally away from the transparent wall; (ii) swimming speed was apparently reduced; (iii) there were strong fluctuations in all three directions associated with spreading and contracting of the school; (iv) the periodic amplitude of the motion in the vertical direction increased. This study might evolve into an automatic stress warning technique for fish farms, based on alterations in the behavior of fish when stressed.     

The mode of infection ofColletotrichum musae (Cke. and massee) causing tip rot of banana fruits in the plantation

The mode of infection ofColletotrichum musae, the main causal agent of tip rot of banana fruits in the Jordan Valley, was investigated. Immature, apparently healthy banana fruits cv. Dwarf Cavendish were inoculated by spraying spore suspensions on the distal end of the fruit. A correlation was found among type of flowers, age of fruits at inoculation time, concentration of spores in the inoculum, and the development of tip rot in the fruits. An infection rate of 100% was obtained with suspensions at a concentration of at least 5x10⁴ spores/ml on fruit with persistent flower parts, not older than 3 weeks after the curling of the hand bract. On fruits with deciduous flower parts, only inoculations of very young fruits still under bracts was successful. Penetration of the fungus through the perianths was assessed. Virulent inoculum was found to be present in the plantation; 100% infection was obtained by using a suspension prepared from dry leaves and debris collected around banana plants.     

Isolation of Corynebacterium pilosum and Actinomyces pyogenes from cystitis and vulvovaginitis infection in a 2-month-old female calf

Cystitis and vulvovaginitits, due to Corynebacterium pilosum and Actinomyces pyogenes infection in a 2-month-old female calf, is described. The prominent clinical signs were urinary incontinence, adherence of triple phosphate crystals to the vulvar hair and ulceration on the vulva, the ventral side of the tail skin and the perineum. Only a mild inflammation of the bladder mucosa and submucosa was seen on histological examination.     

Isolation of Corynebacterium pilosum and Actinomyces pyogenes from Cystitis and Vulvovaginitis Infection in a 2-month-old Female C

Cystitis and vulvovaginitits, due to Corynebacterium pilosum and Actinomyces pyogenes infection in a 2-month-old female calf, is described. The prominent clinical signs were urinary incontinence, adherence of triple phosphate crystals to the vulvar hair and ulceration on the vulva, the ventral side of the tail skin and the perineum. Only a mild inflammation of the bladder mucosa and submucosa was seen on histological examination.