APHIS-2006-0045

Regulatory Analysis and Development

PPD, APHIS

Subject: Docket No.APHIS-2006-0045. Evaluation of asymptomatic citrus
fruit (*Citrus* spp.) as a pathway for the introduction of citrus canker
disease (Xac).

To whom it may concern

Citrus production in **Argentina** is one of the most important agri
exporting activities, the quality and quantity of such production has
been increasing I the last three decades, in the domestic markets as
well as international markets such as European Union, Asia, Russia, etc.
The current lemon production comes from Tucuman province which is the
most important exporting area in the world.

Since late 1970, Argentinean Northeast Region has been a citrus canker
endemic area. Important scientific research has been carried out by
Argentine researchers together with experts from European Union and
other regions regarding epidemiology, biology and disease management.

The National Health and Agrifood Quality Service **(SENASA**),
responsible for phytosanitary **certification for argentine export**,
has gathered great experience and information regarding citrus exports
regulation and disease management since the beginning of the exports in
1960s.

During this period of export mainly for European Union, Argentina
through SENASA, has implemented a certification system for exports that
guaranties healthiness for 250,000 tn of fresh fruits per year to that
destination.

Having into account the strong volumes exported to the European Union,
no canker outbreak has been reported so far, which origin has been
associated with the shipped fruit.

It has been demonstrated that the presence of casual epiphytic bacteria
in fruit is a low frequent situation and of very low incidence in sites
of production without symptoms and there is no scientific evidence that
proves that an epidemic could be initiated as from asymptomatic
commercial fruit. Civerolo (1997)

In the framework of argentine certification system, in the last years
several laboratory analysis have been carried out on asymptomatic fruit
after the packing process, which have proved the absence of *Xanthomonas
axonopodis pv.* citri.

All this background is in accordance with the conclusion of Docket
No.APHIS-2006-0045 regarding the risk that asymptomatic fruit represent
in trade, and also strengthens the fact that fruit by itself either with
or without symptoms does no represent a pathway of introduction of such
pest in a free area.

In order to improve some specific items, quotations from the original
document are written in italic with the comments written below. These
comments were made by Regional Plant protection Organization (COSAVE)
integrated by Argentina, Bolivia, Brazil, Paraguay and Uruguay.

On page 6, *"Bacteria can proliferate on leaves\...\..."* , it should be
re-written as "[Bacteria do not proliferate as an epiphyte on
leaves.."]{.underline} . Because it is contradictory with what is stated
on page 9 and others *"Xac is considered a relatively labile
bacterium\....."* and there are many scientific documents supporting
this, such as Timmer et.al.;1996, Belasque JR.J; Rodríguez Neto,J.; 2000
and Verdier et.al.

On page 8 the title *" Phytosanitary evidence regarding asymptomatic
fruit a pathway "* should be changed to [" Phytosanitary evidence
regarding fruit a pathway"]{.underline} , because all the events
considered in the document, include asymptomatic and symptomatic fruit,
or infected and contaminated fruit , or diseased and healthy fruit,
which are different expressions used within the text.

*Event 1: Infected/contaminated fruit is harvested.*

On page 9, *"Researchers in Argentina..........(Risk assessment,
2005)"*, should be changed to "[Researchers in Brazil]{.underline}....."
because this quotation is referred to the following paper: BELASQUE
Jr.J.; RODRIGUEZ NETO, J. Sobrevivencia da bactéria causadora do cancro
cítrico (Xanthomonas axonopodis pv.citri) em frutos de laranja nao
infectados com a doença. Summa Phytopathologica, 26 (1): 128 (Resumo
153).

Empirical experience obtained from laboratory analysis carried out in
the framework of the certification system strongly supports these
statements.

On page 9, under "*Conclusions for the first event*" :

"*The presence of canker infected fruit in an infected orchard is
likely; however the **prevalence** of diseased fruit and of healthy
fruit with epiphytic Xac will be epidemiologically insignificant ".* It
is important to note that prevalence is not a correct term. It may be a
matter of incidence, as epidemiological term to quantify on fruit.

*"Xac is likely to be present in groves if active infections occur
within the **export grove** or in nearby groves from which the bacteria
may be introduced by wind driven rain".* This is applicable to groves,
independently of the final destination of the fruit. It is not necessary
to make reference to neighboring groves or to the dispersal pathway.

On page 10, "*Under the systems approach, the **prevalence** of citrus
canker diseased fruit will be low."* The same comment than on page 9,
prevalence is not a correct term, may be it is a matter of incidence, as
a possible epidemiological term to quantify pest in fruit.

Also on page 10, "*Infected fruit express detectable symptoms and are
likely to be culled or not harvested."* Under "Evidence", it is
necessary to consider the differences in species susceptibility and the
relationship between symptomatic and asymptomatic fruit.

In this item it is also necessary to change *"Researchers in Argentina
...."* mentioned above.

*Event 2: Inoculum on infected/contaminated fruit survives the
packing/treatment process*.

On page 11, *" ............substantially reduces Xac viability in
lesions."* Literature cited does not refer to Xac viability in lesions.

On page 11 under *"Conclusions for the second event":*

*"The likelihood of inoculum on **infected fruit** surviving the packing
and treatment process is very low."* It is necessary to make reference
to contaminated fruit.

*"Symptomatic fruit (**the main source of inoculum)** is highly unlikely
to pass through the packing process"*. Fruits are not the main source of
inoculum in the Xac life cycle and it is possible, but unlikely, that
symptomatic fruit passes through the packing process.

*"Standard packinghouse procedures and postharvest treatments prescribed
by the systems approach will remove, devitalize and/or immobilize the
pathogen"*. Immobilize the pathogen is not the right term for this
bacteria.

*Event 3: Inoculum on infected/contaminated fruit survives shipment*.

On page 12 under *"Conclusions for the third event"* :

*"If bacteria survive the packing process, they will have a high rate of
mortality during shipping."* Under "evidence" of this item reference to
Verdier et.al.'s paper, should be included.

*"Bacteria that survive on or in fruit after post harvest treatment will
not multiply or cause disease development in the treated fruit".* Fruit
cooling prior and during shipment, which is a standard process in trade
of fresh fruit, has not being considered in this event. It must be taken
into account that, if some bacteria are capable to survive postharvest
treatment they should be affected by low temperatures.

*On page 13: Event 4: Infected/contaminated fruit go to a suitable area
with conditions for infection.*

This event must not consider contaminated fruit, due to the fact that
packing and shipping processes make the survival of epiphytic bacteria
not possible.

On page 13 under *"Conclusions for the fourth event":*

*"Although shipment of imported infected fruit to a suitable habitat is
possible, the fraction that would be shipped to suitable habitat is
small."* This is not only applicable to imported fruit but also to
domestic market fruit.

***Event 5: Inoculum from infected/contaminated fruit encounters a
suitable host and is able to incite disease.***

This event must not consider contaminated fruit, due to the fact that
packing and shipping processes make the survival of the bacteria not
possible, and conclusions on page 14 read: *"It is unlikely that viable
bacteria from an infected fruit would encounter a suitable host under
the conditions required for disease development".*

## On page 15 under "Summary":

*["These points consistently argue that asymptomatic fruit is not
epidemiologically significant as a pathway for introducing citrus canker
if produced under the conditions of a systems approach consistent with
the assumptions of this analysis"]{.underline}.*

Reference to symptomatic fruit that was considered in the events
analyzed above, should be included.

## Uncertainty

On page 16, *"........The following identifies key research needs that
would strengthen regulatory decision making.*

*"[Issue]{.underline}: Can symptomatic fruit that has been treated (with
SOPP, chlorine, or other appropriate disinfectant) transmit the bacteria
that cause the disease, (i.e., can disease be incited on healthy trees
or seedlings from infected, symptomatic fruit that has been treated
post-harvest)?"*

*[Reason]{.underline}: Phytosanitary requirements are not justified if
treated fruit with lesions are not a pathway."*

According to the conclusions of this document, there is enough evidence
to adopt a regulatory decision. Further research could strengthen the
evidence but everywhere in the world, there is no historical evidence
that an outbreak can originate from citrus fruit (page 15). See related
comment in Risk Assessment 2005.

*["Issue]{.underline}: What are the differences in the efficacy of
various post-harvest treatments (e.g., SOPP, chlorine, etc) at rendering
symptomatic fruit epidemiologically insignificant?*

*[Reason]{.underline}: Chlorine is a common standard; it is also highly
unstable. Alternative products and their activity need to be better
understood."*

The fact that chlorine is unstable is not related to the efficacy of the
treatment on symptomatic or asymptomatic fruit. Other aspects
(corrosiveness on equipment, degree of activity, organic production,
restriction to the use of determined phytosanitary products) make
advisable to explore the possibility to use other non chlorine based
disinfectants. According to the conclusions of this document there is
enough evidence to adopt a regulatory decision. Further research could
strengthen the evidence but is not an obstacle to regulatory decision.

*["Issue]{.underline}: What is the relationship between the proportion
of symptomatic fruit in the field and the proportion of infected fruit
after post-harvest culling?*

*[Reason]{.underline}: Infected groves or partially infected groves may
be part of an exporting area. Evidence shows that in Argentina, up to
20% of the fruit for export is harvested with canker blemishes. It is
therefore useful to understand how effective post-harvest culling is in
producing asymptomatic fruit. If, for example, culling is highly
effective regardless of how "dirty" the incoming fruit is, then field
practices are less important in a systems approach."*

The evidence (20% of infected fruit) quoted from Argentina is not
correct.

Field experience and research performed in Argentina and other countries
show that is possible to obtain asymptomatic fruit normally below 5% and
in many cases it is possible to obtain free symptoms sites of production
(0% of infected fruit).

In Argentina the fruit to export never come in to the packing house with
level higher than 3% (for EU market is 0%) to obtain asymptomatic fruit
at the end of the process.

On the other hand, MERCOSUR has sent a certification proposal based on
1% of tolerance at the entry to the packing house to European
Commission, which has been scientifically supported and currently under
discussion.

Uruguay and Argentina have information about the relationship between
the proportion of symptomatic and asymptomatic fruit in the field, and
also the efficacy of packing process.

Experience carried out in Argentina demonstrates the culling capacity of
the packing process to obtain fruit free of canker.

But also according to the conclusions of this document, there is enough
evidence to adopt a regulatory decision. Further research could
strengthen the evidence but is not an obstacle to regulatory decision.

*[Issue]{.underline}: What is the efficacy of specific packinghouse
equipment and procedures in removing blemished fruit?*

*[Reason]{.underline}: Optical scanners in commercial use have been
reported to accurately detect less than 1 in 100,000 \*blemished\* fruit
(only a small proportion of the blemishes might be attributed to citrus
canker). This would appear to be a highly effective mitigation. However,
data have not been provided on the consistency, effectiveness, or other
characteristics of optical scanning systems, or their relative
effectiveness compared to manual systems.*

According to the conclusions of this document there is enough evidence
to adopt a regulatory decision. Further research could strengthen the
evidence but is not an obstacle to regulatory decision.

> **Ing. Agr. Carlos CASAMIQUELA**
>
> **VICEPRESIDENT**
>
> **SENASA**
>
> **REPÚBLICA ARGENTINA**