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Backus E.A.,San Joaquin Valley Agricultural science Center | Morgan D.J.W.,Mt. Rubidoux Field Station
Phytopathology | Year: 2011

The pathogen that causes Pierce's disease of grapevine, Xylella fastidiosa, is the only known bacterial, arthropod-transmitted plant pathogen that does not circulate in the vector's hemolymph. Instead, bacteria are foregut-borne, persistent in adult vectors but semipersistent in immatures (i.e., bacteria colonize cuticular surfaces of the anterior foregut, are retained for hours to days, but are lost during molting). Yet, exactly how a sharpshooter vector inoculates bacteria from foregut acquisition sites is unknown. The present study used confocal laserscanning microscopy to identify locations in undissected, anterior foreguts of the glassy-winged sharpshooter colonized by green fluorescent protein-expressing X. fastidiosa. Spatial and temporal distributions of colonizing X. fastidiosa were examined daily over acquisition access periods of 1 to 6 days for both contaminated field-collected and clean laboratory-reared Homalodisca vitripennis. Results provide the first direct, empirical evidence that established populations of X. fastidiosa can disappear from vector foreguts over time. When combined with existing knowledge on behavior, physiology, and functional anatomy of sharpshooter feeding, present results support the idea that the disappearance is caused by outward fluid flow (egestion) not inward flow (ingestion) (i.e., swallowing). Thus, results support the hypothesis that egestion is a critical part of the X. fastidiosa inoculation mechanism. Furthermore, results suggest a cyclical, spatiotemporal pattern of microbial colonization, disappearance, and recolonization in the precibarium. Colonization patterns also support two types of egestion, termed rinsing and discharging egestion herein. Finally, comparison of acquisition results for field-collected versus laboratory-reared sharpshooters suggest that there may be competitive binding for optimum acquisition sites in the foregut. Therefore, successful inoculation of X. fastidiosa may depend, in large part, on vector load in the precibarium. © 2011 The American Phytopathological Society. Source

Sisterson M.S.,San Joaquin Valley Agricultural science Center
Journal of Economic Entomology | Year: 2014

A method to improve an assay relating adult feeding to egg maturation by the glassywinged sharpshooter (Hemiptera: Cicadellidae) was evaluated. The assay consisted on confining females to cowpea stems and quantifying feeding and egg maturation. Feeding was quantified by measuring excreta production. The number of eggs matured during the assay was estimated by taking the difference between female egg load (number of mature eggs carried by a female) at end of the assay (determined by dissection) and mean egg load of a subset of females dissected at start of the assay. Estimates of the number of mature eggs produced by females using the aforementioned approach improve as variability in egg loads of females entering the assay declines. As egg loads of females are variable, a pretreatment designed to reduce variance in egg loads of females entering the assay was evaluated. To accomplish this, females were divided into two groups. The control group was placed directly into the assay. The pretreatment group was given an oviposition period on sorghum before the assay. An oviposition period on sorghum was expected to reduce variance in egg load among females, as previous research found that sorghum was suitable for oviposition but provided poor nutrition for egg maturation. Dissection of a subset of females from each group before the assay determined that the mean and variance in egg load of females receiving the pretreatment was significantly reduced compared with females in the control group. Analysis of results from the feeding assay found that there was a significant relationship between feeding and egg maturation for females receiving the pretreatment, but not for females in the control group. Thus, reducing the mean and variance in egg load of females entering feeding assays resulted in detection of a significant positive relationship between feeding and egg maturation that otherwise would not have been observed. © 2014 Entomological Society of America. Source

Yokoyama V.Y.,San Joaquin Valley Agricultural science Center
Environmental Entomology | Year: 2012

The mobility of olive fruit fly, Bactrocera oleae (Rossi), late third instars before pupation, teneral adults before flight, and mature adults restricted from flight were studied under mulches in greenhouse cage tests, in horizontal pipes, vertical bottles and pipes filled with sand, and by observation on smooth laboratory surfaces. Percentage adults emerging from pupae and percentage adult females that escaped soil, fabric, and paper mulches over a soil or sand substrate ranged from 63 to 83, and 4053%, respectively. Percentage adults emerging from pupae and percentage adult females that walked through the open interior of 1.526.10-m horizontal pipes of 1.52.0-cm inner diameter ranged from 57 to 81, and 2761%, respectively. Percentage adults emerging from pupae that escaped through sand depths of 2.510.2, and 12.720.3 cm, ranged from 68 to 87, and 1288%; and percentage adult females that escaped ranged from 46 to 58, and 3870%, respectively. In 15.4-cm-inner-diameter pipes filled with different heights of sand, the highest percentage of the total number of adults that emerged in the control were found from 0 to 20.3 cm, and ranged from 37 to 71%. Ten to 47% of adults were found from 20.3 cm to below the surface, and 621% escaped to the top of 20.350.8 cm high sand columns. In column heights of 55.9 and 61 cm, pressures at the bottom caused by the weight of the sand above were 91.4 and 99.7 g/cm2, respectively, and a mean of <1 adult escaped to the top. Before pupation, the late third instars were found to travel continuously for 6.9 h over 23.9 m at a speed of 6.0 cm per min, when placed on a smooth surface, at 22.2°C. Teneral females and males that could not fly, made ≈7 stops totaling 1113 min, walked at a speed of 5762 cm per min, and began a rest period of 8384 min duration, at 8589 min before flight. Males walked a distance of 13.1 m in 22 min, which was greater than females that walked for 9.6 m in 17 min, at 2022°C and 35% RH. The mobility of the third instars and the teneral adults is discussed in relation to potential control techniques in olive orchards. © 2012 Entomological Society of America. Source

Shouse P.J.,Us Salinity Laboratory | Ayars J.E.,San Joaquin Valley Agricultural science Center | SimUnek J.,University of California at Riverside
Agricultural Water Management | Year: 2011

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal to deal with this problem is sequential biological concentration (SBC), which is the process of recycling drainage water on increasingly more salt tolerant crops until the volume of drainage water has been reduced sufficiently to enable its final disposal by evaporation in a small area. For maximum effectiveness this concept will require crop water reuse from shallow groundwater. To evaluate the concept of sequential biological concentration, a column lysimeter study was used to determine the potential crop water use from shallow groundwater by alfalfa as a function of ground water quality and depth to ground water. However, lysimeter studies are not practical for characterizing all the possible scenarios for crop water use related to ground water quality and depth. Models are suited to do this type of characterization if they can be validated. To this end, we used the HYDRUS-1D water flow and solute transport simulation model to simulate our experimental results. Considering the precision of the experimental boundary and initial conditions, numerical simulations matched the experimental results very well. The modeling results indicate that it is possible to reduce the dependence on experimental research by extrapolating experimental results obtained in this study to other specific sites where shallow saline groundwater is of concern. © 2011. Source

Nwugo C.C.,San Joaquin Valley Agricultural science Center | Duan Y.,U.S. Department of Agriculture | Lin H.,San Joaquin Valley Agricultural science Center
PLoS ONE | Year: 2013

Citrus huanglongbing (HLB) is a highly destructive disease of citrus presumably caused by 'Candidatus Liberibacter asiaticus' (Las), a gram-negative, insect-transmitted, phloem-limited α-proteobacterium. Although almost all citrus plants are susceptible to HLB, reports have shown reduced susceptibility to Las infection in lemon (Citrus limon) plants. The aim of this study is to identify intra-species specific molecular mechanisms associated with Las-induced responses in lemon plants. To achieve this, comparative 2-DE and mass spectrometry, in addition to Inductively Coupled Plasma Spectroscopy (ICPS) analyses, were applied to investigate differences in protein accumulation and the concentrations of cationic elements in leaves of healthy and Las-infected lemon plants. Results showed a differential accumulation of 27 proteins, including an increase in accumulation of starch synthase but decrease in the production of photosynthesis-related proteins in Las-infected lemon plants compared to healthy plants. Furthermore, there was a 6% increase (P > 0.05) in K concentration in leaves of lemon plants upon Las infection, which support results from previous studies and might represent a common response pattern of citrus plants to Las infection. Interestingly, contrary to reports from prior studies, this study showed a general reduction in the production of defense-related pathogen-response proteins but a 128% increase in Zn concentration in lemon plants in response to Las infection. Taken together, this study sheds light on general and intra-species specific responses associated with the response of citrus plants to Las. © 2013 Nwugo et al. Source

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