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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Subtropical Plant Pathology Research

2012 Annual Report

1a.Objectives (from AD-416):
To examine if fruit are a viable pathway for dissemination to, and establishment of, G. citricarpa in areas currently free of Black Spot in other states and overseas.

1b.Approach (from AD-416):
To accomplish this, we plan to conduct a non-regulatory motivated probabilistic risk assessment of the life history of G. citricarpa and examine the survival and persistence of G. citricarpa lesions on developing and mature fruit. This will be done via a stochastic model and Monte Carlo simulation with sensitivity analyses to assess the true risk of G. citricarpa moving through all steps in the pathway and becoming established in the termination point of the pathway, i.e., new previously uninfected areas.

3.Progress Report:

This research is related to inhouse project objective 3. Develop or improve comprehensive integrated disease management strategies.

The model continues to be refined by identifying and adding data for individual steps in the marketing and distribution pathway. We have identified, clarified and initiated gap filling research on: Testing inoculum viability of packinghouse treated and untreated fruit through time. Examination of the mitigating factors that control field spread of black spot and its rate of increase. Determining the proportion of fruit culled in packinghouses in South Africa and Brazil. Studies to determine the infectious period of conidia from fruit collected from groves. We are also continuing to review the literature to exhume for the bits of data on fruit susceptibility, culling practices, storage and shipping losses, marketing and repack losses, consumer discards, dispersal patterns in wind and rain, disease susceptibility of various cultivars, import and export information including flowering dates, harvest, fruit distribution and transport patterns, and per capita consumption in various countries.

In addition we have determined/modified locations as points of origin and end points of fruit distribution and obtained weather data for 8 new locations as well to better reflect the range of possible environmental niches across the international distribution network.

During the succeeding portion of the project, progress was made predominantly on: Data gleaned from literature on black spot now has been incorporated into the model and the model continues to be refined. Additional data continues to be gleaned and refined from black spot literature. This data from the literature is incorporated by defining new mathematical distributions relative to each data parameter and incorporating these distributions into the various steps of the model pathway. We have determined/modified locations as points of origin and end points of fruit distribution and obtained, and these have now been incorporated into the model framework. The weather data for these 8 new locations that better reflects the range of possible environmental niches across the international distribution network, have been defined and their associated weather data has now been incorporated into the model. In the previous quarter of the grant cycle, we had identified, clarified and initiated gap filling research as described above. Research on these topics is now ongoing in South Africa and Brazil.

We are currently in the final phases of developing the agenda for the January 24-26, 2012 meeting of the January 24-26, 2012. At that meeting we will continue to garner the intellectual capacity of the international team to continue refining the design of the citrus black spot (CBS) risk model, report on the progress being made on the gap filling research that is currently ongoing, identify any additional gap filling research that is needed, assign any potential new gap filling research needs to appropriate collaborators.

During January 24-26, 2012 a third meeting of the citrus black spot modeling team was convened in Fort Pierce, Florida. We spent three days going through all steps of the model verifying each step in the pathway and discussing it in detail. We identified additional gap filling research that was needed to either complete the model or strengthen the model at various points in the pathway. Assignments of gap filling research were accepted by Brazilian, South Africa, and U.S. members of the team.

The Brazilian team members are conducting gap-filling research on port of entry rejection and the number of fruit disposed of and/or diverted at that point in pathway. The Brazilians will also be looking at the incidence of disease fruit pre-and post-packinghouse to determine the culling rate for CBS for that step pathway. They will also be exploring harvesting of entire trees and the number of infected fruit that occur at the center of the tree versus at the periphery and the whole tree.

The South African team members are following up with a series of experiments to determine the percentage of calls due to CBS postharvest, number of CBS symptomatic fruit that are packed, i.e. lesion fruit that are missed during packinghouse, lesion development during cold storage and shelf life, and picnidiospore production and viability in packinghouse treated versus nontreated fruit. South Africans will also be exploring estimates of the incidence increase due to latent infections. Members of the U.S. team will be looking at fruit disposal from prior studies conducted by USDA APHIS to determine how and at what proportion consumers discard fruit. We will also be exploring the susceptibility of infection of various endpoints of pathways, i.e. regions within various countries, from the CBS data from NAPFAST.

Associated with that meeting we also visited 2 local citrus packinghouses and the group also had protracted discussions with their CEOs to better understand not only the packinghouse but various steps within the pathway including shipment from the field to the packinghouse, storage into greening rooms, shipping to international ports, redistribution and transshipment to end points, distribution to endpoint losses, market losses, consumer losses, and consumer discard of declining fruit as well as peels from consumed fruit. We also discussed how to obtain better data for post-packinghouse distribution, shipment and transshipment, marketplace and consumer losses. The CEO supplied us with considerable information from his own business and put us in contact with others within the industry and in Europe who could supply us with additional information.

The U.S. team also engaged the Florida citrus packers to glean data relative to shipment, transshipment, market, and consumer fruit losses due to culling and discard.

Much of the information gleaned from the above have now been entered into the model. The model is fully functional and is producing reasonable output at this point for the test pathway - from Southeast Florida to Northeast Spain. Once a model is fully developed and validated for this pathway, other pathways will begin to be explored with varying initiation and endpoint locations. This is necessary to ensure that we include pathways for which CBS is likely to be transmitted as well as pathways for which transmission is unlikely. This gives the model overall validity.

A no-cost extension was requested for the first year of the study to enable researchers to adequately utilize funding and resources.

Last Modified: 4/23/2014
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