Compendium of Potato Diseases - (PDF, 101 mb) - USAID

the Potato Association of America).
In 1914, Dr. Orton, accompanied by Dr. Appel of Germany,
Dr. H. T. Gussow of Canada, Dr. Johanna Westerdijk of
Holland, and potato specialists from the USDA. visited the
principal potato-growing areas of 13 states extending from
Maine to California to study disease and other problems related
to seed production. This study stimulated interest and added
impetus to the movement for organized inspection programs.
These efforts culminated i. the first official Potato Seed
Certification Conference, which was held in Philadelphia, PA,
on December 28, 1914. Representatives from Canada.
Germany, Ireland, the USDA, and 12 states participatud. At
this conference, the basic framework of the present seed potato
certification programs was formulated,
Dr. Orton recommended that "a system of official inspection
and certification" be established in each of the seed-growing
states, with emphasis being placed on "freedom from disease,
varietal purity and vigor." The suggestion was also made that
programs be administered by a "state agency such as an
Experiment Station and protected by suitable legislation
penalizing misu.,- of certificates." The proposal, which
suggested that programs be operated on a voluntary basis and
that growers stand the cost of inspection, also outlined
procedures for making field inspections, established disease
tolerances, suggested the use of certificates and official tags for
inspected seed, and proposed size and quality of tubers. Even
though virus infections were not suspected at the time, the
proposal recognized that "degeneration" or "running-out" of
seedstocks was tuber-transmitted and suggested that "seed"
tubers be selected from healthy-appearing stocks.
Seed potato certification programs in North America became
a reality during 1913-1915, when Canada (New Brunswick and
Prince Edward Island), Idaho, Maine, Maryland, Vermont. and
Wisconsin established official programs. Ten more states
started programs between 1916 and 1919, followed by three
additional Canadian provinces and eight states during
1920-1922.
In the early days of certification in North America, inspectors
were confronted with the problems of varietal mixtures, varietal
synonyms, and degeneration ur "running-out" of seed stocks.
The confused picture of the degeneration complex started to
clear when Quanjer et al in 1916 first established the infectious
nature of potato leafroll by graft transmission; shortly
thereafter, Oortwijn Botjes (1920) and Schultz and Folsom
(1921) reported independently that the aphid Myzus persicae
transmitted the causal entity of leafroll from plant to plant.
Subsequent investigations exposed the involvement of
numerous tuberborne virus diseases, such as mild and severe
mosaic and spindle tuber (the causal agent of which is now
known to be a viroid), with seed degeneration. Recognition of
these diseases by certification personnel provided the ba,: far
their subsequent control. A tremendous improvement in yield
and quality ofseed stocks occurred after certificatior personnel
had mastered the diagnosis of virus diseases,
Present Day Seed Potato Certification
eent DaypSdPotato Certification ayand
Seed potato certification today represents a voluntary
agreement between the seed grower and the certif.ing agency. In
the United States, programs are handled by individual states
TABLE V. Field Tolerances (%)for Certified Potatoes, as Required
by Wisconsin Certified Seed Potato Agency, Madison
Disease or Varietal Inspection
Mixture First Second or Subsequent
Leafroll 1.5 1.0
Mosaics 2.0 1.0
Spindle tuber 1.0 1.0
Total 3.0 3.0
Bacterial ring rot 0.0 0.0
Varietal mixture 1.0 0.1
104
and administered by state departments of agriculture, land
grant universities, grower associations, or various combinations
of these agencies. In Canada, seed potato certification is a
federal program carried out hythe Plant Quarantine Division of
the Department of Agriculture. Since all agencies have been
given official status by their respective state or national
governments, protection against the fraudulent use of the term
"certified seed potatoes" has been assured. Disclaimer clauses
limiting liability to the value of the seed are commonly used by
all agencies to protect both the grower and the agency.
Each agency publishes certification standards outlining
eligibility requirements for inspection, grower fee schedule.
disease tolerances, grade requirements, winter tests, and rules
governing sale of certified seed. Application inspection forms
are sent to individual growers before the planting seaso n
requesting alisting of cultivars, classification and source of seed
lots, acreage, field numbers and location, previous crop history
of fields, and date of planting. This information is used by the
agency to determine eligibility for inspection.
Fields are planted with pretested and approvea seedstocks.
Practicesareadopted that minimizethespread ofvirusesand of
pathogens borne by soil and debris. Procedures for inspections
vary among states but, in general, are quite similar. A minimum
of two field inspection- is made during the growing season at a
time most opportune for detecting diseases and varietal
mixtures by visual examination. Field tolerances fordisease and
varietal mixtures vary among agencies but, in general, are quite
similar. Those currently used in Wisconsin for the Certified class
are fairly typical (Table V).
Failure to meet the tolerances is cause for rejection and, in
addition, certification may also be denied for the prevalence of
other diseases such as blackleg, haywire, or wilts. Lack of
isolation, unsuitable cultural conditions, high aphid
populations, nematodes, unsatisfactory performance of test
samples, orotherfactorsthat mayimpairseed valuemayalso be
cause for rejection. Of the acreage rejected from 1968-1972 in
North American agencies certifying over 1,000 acres per year,
bacterial ring rot, leafroll, varietal mixture, mosaic, and
blackleg accounted for 5.6, 0.8, 0.7, 0.5, and 0.4(,', respectively.
Harvest inspections are required by some agencies, whereas
others require both a harvest and a bin inspection, which
identifies the stored seed and includes estimates of volume,
grade, and tag eligibility. Certification is not complete until the
seed has been graded for quality and size in conformity with seed
grades and identified with official tags and seals and has passed
inspection by the State-Federal Inspection Service. Inspection
reportsare issued to the grower by the inspectoraftereach field,
harvest, and bin inspection.
Most agencies in North America certify two basic classes of
seed potatoes-"Foundation" and "Certified." Requirements
for the production of Foundation class seed are much more
rigid, e.g., Foundation class seed growers mus, enter their entire
acreage for inspection, field tolerances for disease are
approximately one fourth of those allowed for Certified classes;
and requirements for seed source, land, isolation, sanitation,
the handling and storage of the crop are much more
stringent. This class of seed isused to plant certified seed potato
fields, Many certifying agencies require a winter test as part of
their Foundation class requirement. A few agencies have made
it compulsory for all seed lots, irrespective of class. These tests,
which are conducted in Alabama, California, or Florida, where
wing conditin f a , Caiforia, o dieasere
growing conditions favor symptom expression of diseases,
consist of field planting 300-800 tubers per lot and reading the
resulting plants for disease content, primarily 'irus, and other
factors pertinent to seed productivity. To receive Foundation
designation, most agencies require that a seed lot shall not show
a total in excess of 0.5% of the diseases mosaic, leafroll, and
spindle tuber in the winter field test.
Because of the short interval between harvest and planting of
the winter test in Florida, dormancy ofcertain cultivars must be
broken. Rindite, a 7:3:1 mixture of ethylene chlorohydrin (2chloroethanol),
ethylene dichloride (I ,2-dichloroethane), and