Kiran Shetty
Extension Potato Specialist
University of Idaho

Introduction

Fresh-pack or table stock potatoes hold a major market share of the United States potato industry revenue, and in Idaho alone roughly about 37 million cwt of fresh-pack potatoes are marketed every year.  The success of the fresh market industry is largely due to the efficient transporation and distribution systems currently in place. The primary modes of transportation of fresh pack potatoes to terminal markets and distribution centers across the United States are through refrigerated rail-cars and trucking systems.  Refrigerated rail cars are in use for long hauls (2000 miles or more) and generally a preferred mode of transportation for large single commodity loads with relative low freight charges.  An annual average of 12,000 car loads of potatoes are shipped via refigerated rail cars, with an estimated 1.4 billion pounds of fresh potatoes.  Rail car shipment procedures have steadily improved from bulk loading and top-ice cooling systems to palletized loads and ventilated mechanical refrigeration systems.  However, there have occasionally been problems in the methods of handling, loading, transportation and delivery of the product.  The information  herein outlines the physical, physiological and pathological reasons of some of the important problems that are encountered in transportation and marketing of fresh pack potatoes in refrigerated rail cars.

What is a potato?

This simple question is not intended to challenge the obvious knowledge of a well-known food crop.  However, in the context of knowing how this product is handled, transported and marketed in the fresh or table-stock market, it may be worthwhile to examine what this product is made of and how it reacts to different procedures and conditions during the entire chain of fresh marketing.

 A potato is botanically a ‘tuber’ and therefore an underground plant structure.  Although underground, the potato is anatomically a stem with rudimentary roots which may not be visible at all times.  The potato plant first produces a slender horizontal ‘root like’ structure called stolon, about 6 to 8 weeks from the time the plant starts to grow.  This stolon forms a hook at the end of it and starts swelling by the division of the parenchyma cells in the pith, followed by division in the cortex and vascular regions.  Starch begins to accumulate in the cortex and in the deeper tissue of the pith.  The epidermis or the outer skin layer is replaced by a much thicker suberized skin called periderm.  Lenticels or breathing holes are formed in the periderm by production of a loose mass of cells under the stomata of the original epidermis.  Tissues of the potato tuber have the ability to form periderm even after the potato is detached from the plant, provided satisfactory temperature and humidity conditions are maintained.  This is called  “wound-healing” which is very important in the defense mechanisms against invading disease organisms.  The tuber possesses buds or ‘eyes’ which house the apparatus for sprout growth.  Each individual bud is capable of producing a full potato plant after the period of dormancy or rest is completed.  The length of dormancy or rest varies among different varieties, and within a variety is determined by the cultural and environmental factors prior to harvest and the storage conditions thereafter.

The above information emphasizes that the potato is a living entity that is capable of respiring, transpiring (release water) and reproducing.  Respiration is a key metabolic process that tubers undergo and this process allows the release of energy through the breakdown of stored carbon compounds, which in this case is starch. During this process the tuber generates heat, which becomes an important consideration for storage and transportation of potatoes.  The need for refrigeration or cool temperatures during the post harvest life of the potato is to slow down the process of respiration and thereby maintain tuber quality.  The potato tuber is also roughly made up of 80 % water and 20 % starch, and therefore is capable of losing the internal water if subjected to low external vapor pressure or relative humidity.  When potatoes lose excessive moisture they shrink and may become unmarketable. Sprouting will significantly increases water loss in stored and transported potatoes.  Sprouting will also diminish the nutritive quality of the potato.  Therefore, sprout inhibitors are required after potatoes pass their dormant phase.

Physical and environmental conditions that affect fresh pack quality

One of the key physical parameters that determines quality of fresh pack potatoes is bruising (see segment on bruising). The inherent ability of potatoes to withstand bruising or wounding varies slightly between the time they are harvested until the time they are actually removed from storage.  Generally, freshly harvested potatoes will be highly hydrated and therefore susceptible to shatter bruises (see segment on bruising).  Tubers removed from storage will have undergone 4 to 10 percent shrinkage depending on the length of storage time as well as the storage conditions (temperature and relative humidity).  With this amount of shrinkage the potatoes ability to withstand shatter bruising will be slightly better than at the time they were harvested.  However, it is still imperative that potatoes be handled carefully so that new bruises are not inflicted during removal from storage.

In addition to level of hydration, the key environmental condition that determines the bruising potential of tubers is temperature.  Generally the best handling temperatures for potatoes is 45-65 F.  This is a mandatory temperature requirement for potatoes that are freshly harvested because during harvest potatoes are mixed with clods and rocks, increasing the risk of bruising.  Potatoes harvested cold (< 45 F) will be highly susceptible to bruising. Tuber pulp temperatures out of storage will depend on the storage set temperature and the conditions after removal.  If tuber pulp temperature is below 45 F the potatoes are extremely susceptible to bruising.  In general, potatoes must be handled and transported out of storage with care, by reducing drop heights and avoiding rough handling.

Bruising and its implications to the quality of fresh pack potatoes.

The type, amount and severity of bruises inflicted to potatoes from harvest, handing, storage, packaging, transportation and delivery operations can significantly impact quality. It is impossible to eliminate all bruising to potatoes but there are certainly procedures to minimize bruising, and the potential problems it causes.

Blackspot bruising

Black spot bruising or BSB is an internal bruise and evidence of it externally may not be very clear.  BSB is probably the most important bruising problem that potatoes are evaluated for at the receiving market. BSB occurs when potatoes strike against handling equipment, against themselves or are dropped on to the floor or any other hard surfaces.  The name ‘black spot’ describes the grayish or black coloration of tissue that occurs within 24-48 hours after the impact.  The intensity and severity of the coloration depends primarily on the impact itself as well as certain tuber and environmental characteristics.  The black pigment is due to the formation of melanin produced by the biochemical reaction of phenol substrates like tyrosine with the enzyme called polyphenol oxidase in the cells of the tuber.  This internal bruise does not require an opening in the skin of the tuber.  The reaction merely takes place because of the impact, thereby mixing the substrates and the enzymes. Black spot generally occurs beneath the vascular ring in the perimedullary tissue of the potato.  Tuber factors that determine the severity of BSB are temperature, hydration level of the cells, size and shape of the whole tuber, variety, cultural practices and maturity of the potatoes.  The handling factors that determine the severity of BSB are the drop heights, impact surfaces, impact angle and the amount of cushioning.

Shatter bruises

Impacts that tear and open the skin and underlying tissue of the potato are known as shatter bruises.  These injuries may be difficult to see at first, but become visible after the injury dries out.  Potatoes are extremely susceptible to shatter bruises when temperature drops below 45 F.  Generally potatoes with high water content (crisp) are more susceptible to shatter bruises than limp tubers.  Shatter bruises serve as entry points for many disease that may initiate during packing and subsequently develop during transportation.  Shatter bruises take a long time to wound heal compared to scuffing injuries (see below). In a recent survey it was observed that about 40% of the potatoes run through packing lines at 45 F or below are inflicted with at least 1 shatter bruise.  Sometimes 3 to 5 new shatter bruises are noticed in poorly managed packing lines.  Packing operations that have reduced drop heights and added additional cushioning materials in drop areas have significantly reduced shatter bruises on tubers during handling.

Scuffing

Scuffing is a peeling or abrasion of the skin, that does not penetrate into the internal tissue.  Potatoes generally have a better ability to heal scuffing injuries than shatter bruises, and therefore, scuffed tubers are less likely to decay.  However, under low humidity conditions, excessive scuffing injuries will aggravate water loss from the potatoes.  In packing operations the most scuffing injuries take place at the point where potatoes are unloaded.  In a well calibrated conveying system of a packing operation only about 10 % of the potatoes are scuffed.  Potatoes run directly out of the field need to be mature with proper skin-set to avoid scuffing injuries.

Pressure bruises

Pressure bruise takes place in storage, usually to tubers at the bottom of the potato.  This problem is primarily due to overloading the storage in combination with a low humidity in the storage environment.  These bruises are flattened or sunken areas on the surface of tubers.  The affected tissue will lose moisture and these areas become highly susceptible to black spot bruising.  The affected areas are also prone to infection by dry rot and soft rot.

Wound healing of potatoes and its importance in preventing diseases

Before the process of wound healing is reviewed it is necessary to study the structure of the skin or periderm of a potato tuber.  As explained earlier, the epidermis of the stem tissue is replaced by the periderm when the tuber is formed.  Periderm can also be formed in response to wounding or bruises that expose the internal potato tissue to pathogen entry.  The periderm is comprised of  three types of tissue: 1) the phellogen or cork cambium from which other cells of the periderm are produced; 2) the phellem or cork which is the protective outer surface of the periderm; and 3) the phelloderm which is the interior tissue to the cambium. The phellem contains dead, suberized cells when the potato tuber is mature. Suberin is a lipid-derived polymeric material.

When the potato tuber is shatter bruised or scuffed, the exposed tissue become vulnerable to infection by certain bacteria and fungi.  When injured, the tuber initiates a wound healing response which is regulated by the amount of oxygen available, the temperature (ideally 55 F) and relative humidity.  Although wound healing is rapid at temperatures above 55 F the risk of infection by bacteria and fungi also correspondingly increases.  The first response in wound healing is the process of lignification and suberization.  This response prevents moisture loss and limits the opportunity for bacteria and fungi to enter the wounded area.  This process is usually completed within 1 to 3 days if conditions are favorable.  Once suberization is complete, a series of new cells are constructed below the affected area, resulting in formation of wound periderm. The wound periderm is essentially a new set of skin to close the wound.  This may take 1 to 2 weeks, again the rate of wound periderm formation is controlled by the environmental conditions under which the potatoes are stored.  When potatoes are washed and packed wet, the presence of free moisture may interfere with the process of wound healing, thus providing the opportunity for pathogens to enter through shatter bruises.

In a recent study, a significant difference between shatter bruises and scuffing injuries was found in their ability to resist bacterial infection. Where shatter bruised and scuffed potatoes were infected by high concentration of soft rot causing bacteria (Erwinia carotovora c.) it was noticed that the shatter bruised potatoes developed substantial decay in the bruised area within 2 to 3 days at temperatures above 50 F, whereas the scuffed potatoes were not infected at all.  This may be explained by the fact that scuffed injuries tend to dry out faster than shatter bruises. In addition, adequate oxygen is available at the surface for faster wound healing to take place.  In a shatter bruise the wound remains wetter for a longer period of time, virtually restricting oxygen availability to the injured cells.  Therefore, the cell-division process to produce the wound barrier is considerably slowed down.  This could provide ample time for soft rot infection.  It is important that packing operations having a high risk of shatter bruising should first help minimize this problem or include a mandatory drying step before the potatoes a packed. (See section on --Guidelines to minimize soft rot decay in fresh pack potatoes).

Unloading and holding requirements at the packing center

Data collected from packing operations indicates that  most potato scuffing occurs at delivery points.  In some operations drop heights from the self unloading trucks to the receiving conveyors appear to be more than the bruising threshold of 6 inches.  Scuffing appears to be the primary injury at these points. This may be a result of ware and tare on the handling equipment,  exposing rough edges which scuff potatoes. These problems can be minimized by proper maintenance and frequent reinforcement of padding material at the receiving points.

Potatoes subjected to extreme temperature fluctuations become stressed and will be physiologically affected.  These temperature changes will break tuber dormancy and start sprouting, as well as impair wound healing.  Therefore, during trucking to packing operations potatoes should be tarped and not subjected to extreme cold or warm temperatures. To avoid this exposure delivery time should be minimized.

Some packing operations are equipped with holding bins to receive large loads from harvest or storage.  The turnover rate of potatoes from these bins may vary and will depend on the run-times of the packing operations.  It was observed that pulp temperatures of potatoes tends to increase 2 to 4 °F if the potatoes are retained for more than 24 hours.  This increase in temperature takes place because the potatoes release heat during respiration. In addition, the holding bins are not equipped with air flow systems and therefore it is not possible to vent the heat away.
This increase in temperature may not take place if the turnover rate is increased.  In situations were potatoes are delivered at pulp temperatures at or above 50 °F and then held for more than 24 hours in the holding bins, the potato temperatures can increase to 55 °F or more, which will also increase the risk of disease development.

Fresh pack defects and management strategies to minimize the problems

Potatoes are high value product and therefore market and consumer acceptance of this product depends significantly on how well the quality of the crop is preserved through delivary and utilization.  Potatoes inherently vary in their ability to change or deteriorate in quality, influenced by varietal characteristics and procedures during production, storage, handling and transport.   The two major classes of tuber defects are: 1) Quality defects and b) Conditional defects.

Condition defects change from point of origin to the distribution centers. In contrast, quality defects do not change during transportation and marketing procedures. Most potato post harvest diseases and shrinkage are classified as quality defects. These defects include sunburn or greening, growth cracks, and several internal disorders. Blackspot bruising and shatter bruises are defects that can fall under either of the above two categories depending on when the injury occurred.

The major condition defects are caused by a group of pathogenic bacteria and fungi.

Bacteria:  Bacteria is a diverse group of single-celled microorganisms.  The majority of bacteria range in size from 0.5 to 5 *m and come in different shapes.  Bacteria can reproduce rapidly when provided the right host and environment, and can occur in large numbers in a very short time.  Warm and wet conditions generally favor the growth and reproduction of bacteria.  Bacteria can spread easily through soil, water, equipment and tuber contact. They can enter the potato tuber through wounds or through natural openings like lenticels on the surface of the tuber.  The symptoms of bacterial infection on potato tubers are characterized by the slimy, soft areas of rots, often accompanied by a foul smell.  Two of the common bacterial storage diseases in potatoes are soft rot and ring rot.

Fungi: Fungi can exist as a single cell, but in most cases they are made up of more than one cell or simply termed multicellular.  A typical multicellular structure that is usually seen in a fungal infection on potato tubers is called mycelium.  Mycelium consists of filaments known as hyphae, which arise from a germinating spore.  In most cases a fungal life cycle can be described as follows:  from a spore to a hyphae, several hyphae make a complex of mycelia, from a mycelia specialized reproductive structures are produced that bear the spores, and these spores can start a new cycle.  Potato tubers can be affected by one or more stages of a fungus. Symptoms associated with a fungal infection on tubers are specific to the kind and stage of the fungus.  The hyphae can enter a potato tuber through a wound, a natural opening or sometimes through the skin of the potato.  Fungi, unlike plants, lack chlorophyll (the green molecule that the plants use to make food), and are therefore parasites (require a living host for their nourishment), or are saprophytes (can live on dead, decaying organic matter).  Different fungi are classified based on the nature of spores (reproductive structures) they produce, or on the presence or absence of cross-walls within the hyphae.  Fungi prefer wet and warm conditions for their growth, development and reproduction. Therefore, these conditions become important considerations in potato storage disease management.

Major bacterial disease of fresh pack potatoes

The major bacterial disease of fresh pack potatoes is soft rot.  It is caused by the bacterium Erwinia carotovara var. carotovara.  This pathogen can invade lenticels and wounds directly, or cause sencondary infection on areas of the potato tuber that was previously infected by other diseases.  Infected areas of the potato may externally appear tan to dark brown with water soaked texture to the skin, while internal tissue is wet, mushy or creamy. The affected areas show a definite border separating it from the healthy tissue.

Infection of potatoes can begin in the field in areas where other diseases exist, or in water soaked areas of the field.  In storage, bacterial soft rot may infect areas of the potato pile where other disease exist, supported by inadequate air movement or excessive condensation of free moisture.  Soft rot infection can be carried into packing operations and can provide a source of infection to other healthy potatoes through the wash water.  This problem can be aggravated if potatoes are shatter bruised, packed wet and subjected to warm holding and transit condition without adequate  ventilating air.  If favorable conditions continue, these infections can spread internally within a potato or from one potato to another in close proximity.

Important factors causing soft rot of fresh pack potatoes

1. Substantial inoculum in wash water can cause infection of healthy potatoes. Inoculum is  constantly supplemented by washing potatoes that carry the disease from storage.

2. Shatter bruises inflicted during sorting and packing can open infection sites on the skin of the potatoes. One shatter bruise about 0.5 inches in length can be sufficient to allow infection of soft rot bacteria.

3. Packing potatoes with pulp temperatures above 50 F and subsequently holding them for two days or more at temperatures above 50 F is favorable for soft rot decay.

4. The highest amount of soft rot developed in potatoes that were shatter bruised and packed wet.  This was particularly evident in potatoes that were packed in polybags and subsequently repacked in bailers. Pallet pressure also increased the chances of soft rot infection in these potatoes.

Guidelines to minimize soft rot problem in fresh pack potatoes

1. Eliminate and discard soft rot and other disease carrying potatoes before the washing procedure at the packing house.

2. Add clean water periodically in the wash area, and if the water is recycled incorporate a labeled disinfectant prior to start of a new cycle (see appendix for water sanitization).

3. Avoid shatter bruising potatoes along the packing line.  Provide extra cushioning pads in high impact areas.

4. Keep pulp temperatures between 45 and 50 F and dry potatoes before packing. Maintain  palletized loads at temperatures between 40 and 45 F in a well ventilated area.  If potatoes are brought into packing houses at pulp temperatures above 50 F, include a cooling step immediately after the packing, or place them immediately in transport cars that are precooled to 40 F with adequate air flow.  This procedure is especially critical if potatoes are treated with sprout inhibitors (CIPC) during packaging because it prevents wound healing of fresh shatter bruises.  Therefore, the only line of defense to inhibit soft rot development is by cooling potatoes immediately to 40 F.  A cooling platform or tunnel with forced refrigerated air system is being considered for cooling potatoes that are packed.

5. Treating potatoes with labeled chlorine based disinfectants that are insensitive to pH changes after the potatoes are washed could be beneficial in preventing new soft rot infection (see appendix).

6. Loading and distribution of palletized count cartons or bailers should be performed to ensure adequate air movement through the stack of packages inside the refrigerated rail car.  Improper loading pattern of the count boxes and bailers results in cooling air flow around the outside of the packages rather than through the packages. This causes the thermostat to prematurely reduce output from the refrigeration system.  While loading cars, do not run refrigeration for long periods with the doors open.  Loading and closing of doors should be conducted as fast as possible because water released from potatoes will be cooled and freeze on the cooling coil.  This will affect the initial refrigeration capacity during the ensuing transport.

7. Slip sheets and supporting material within and between pallets of packed potatoes should not interfere with air movement from the ceiling of the rail car through and out of the bottom of the stack of potatoes.  Research indicates that pallets stacked without slip sheets allow significantly better cooling of potatoes than in pallets with slip sheets.

8. Refrigerated rail-cars should ensure equal distribution of air along the ceiling plenum.  Increasing the air capacity, and/or maintaining continuous air flow inside the refrigerated  improves the cooling within the pallets.

9. Refrigerated rail cars should include a cleaning and sanitation procedure prior to shipping new loads of potatoes.

10. Temperature probes that are capable of recording internal product condition at either end of the car should aid in determining transit conditions.  Tuber pulp temperatures are good indicators of changes in post harvest life of transported potatoes.  Therefore sample of potatoes meant for recording product temperatures should be set aside for each load that is transported.  Recent micro-chip temperature recording devices with external probes can be placed in pre-determined areas of the rail car where the sample is located.

Major fungal disease of fresh pack potatoes

Dry rot

Dry rot in potatoes is caused by the fungus Fusarium sambucianum.  Generally this disease can be detected under a bruised area in a tuber.  Infected tuber tissue is black and white with a crumbly decay. Spread inside the tuber is irregular but there is distinct walled-off areas between the healthy tissue and the affected area of the tuber.  The external surface of the affected areas can be sunken and wrinkled.  When conditions are favorable (moist and warm) inside the packs this disease can invite bacterial soft rot as a secondary infection.

In most occasions this fungus infect potatoes during harvest and handling operations, therefore the inception of the disease has taken place before the potatoes are washed, sorted and packed. However, a new infection can originate during sorting and packing if the potatoes are bruised.  The initial infection and spread of the fungus may be slow at packing and shipping temperatures (45-50 F).  Subsequently, when the potatoes are received and distributed in the marketing centers this disease can seriously affect potatoes inside packages and progress significantly in the supermarkets, and after the consumer buys and stores the potatoes.

Guidelines to minimize dry rot decay of fresh pack potatoes

1. Because this disease begins before or during storage it is necessary to remove dirt and debris while the potatoes are prepared for storage.  A curing period of 2 to 3 weeks is necessary at temperature of 55 F and 95 % relative humidity, before the potatoes are cooled to 45 F for long term storage.

2. When potatoes are removed from storage they should not be subjected to new bruises.  Discard potatoes that show excessive dry rot decay before they are run through a packing line.

3. Avoid bruising during the packing operation.

4. A 500 ppm chlorine treatment followed by a drying procedure before the potatoes are packed will inhibit new infection.

5. The recommended temperature for storing and shipping packed potatoes is 42-45 F.

Silver scurf of fresh pack potatoes

Silver scurf is a fungal disease of potatoes caused by the fungus Helminthosporium solani.  The disease symptom is characterized by the presence of silvery lesions on the skin of the potato with substantial thickening of the skin in the affected areas.  Red potatoes usually lose the red pigment in the affected areas.  The fungus does not affect the internal areas of the potato.

This disease usually results from poor production and storage management practices.  In some cases this disease is noticeable at harvest, but in practice this disease usually increases and subsequently affects marketability of potatoes, 4 to 5 months after harvest.  Fresh pack potatoes can further lose their market value if infection increases in the count cartons and bailers.  High humidity, wet conditions and temperatures above 55 F will increase the infection inside the packages.  The fungal spores can contaminate handling and packing equipment.  In this case healthy potatoes can be infected during packing operations.  However, a new infection takes several weeks to express symptoms on the surface of the potatoes.
 Guidelines to minimize silver scurf disease of fresh pack potatoes.

1. All cultural practices, such as use of certified seed and appropriate seed treatment is the first step towards controlling silver scurf disease.

2. Potato storage must be cleaned and sanitized prior to storing new potatoes (see appendix).

3. Post harvest treatment of chlorine disinfectants at 500 ppm directly on the potatoes with adequate air movement through the pile can reduce new infection in storage.

4. Fresh pack potatoes should be cured around 50 F for 2 to 3 weeks and subsequently cooled to 40 -42 F for long term storage.  Free moisture from condensation must be avoided in storage.

5. Avoid bruising of potatoes while placing the potatoes into storage and also at the time of removal and handling.

6. An application of labeled disinfectants at 500 ppm chlorine before the potatoes are packed followed by a drying process will substantially reduce spread of old infection, as well as prevent new infection during marketing of the potatoes.

7. Packing lines must be periodically cleaned and decontaminated (see appendix).

8. Potatoes must be packed dry and placed in an environment where the pulp temperatures remain at or below 45 F.
 

Table 1.  U.S. Table Stock Grade Tolerances

 1. U.S. Extra No. 1

 Total Defects 5%

 Including:  For Bacterial Wilt,
  Ring Rot, Late Blight, Soft Rot,
  Wet Breakdown, or Freezing 2%

 Included in the 2%:  For Soft Rot,
  Wet Breakdown, or Frozen 1/2%

2. U.S. No. 1

 Total Defects 8%

 Including not more than:
  External Defects 5%
  Internal Defects 5%

 Or for Bacterial Wilt, Ring Rot,
  Late Blight, Soft Rot, Wet
  Breakdown, or Freezing 3%

 Included in the 3%:  For Soft Rot,
  Wet Breakdown, or Frozen 1%

3. U.S. Commercial

 “U.S. Commercial” consists of potatoes which meet the requirements of U.S. No. 1 grade except for the following:

 (a) Free from serious damage caused by:
  (1) Dirt or other foreign matter
  (2) Russet scab; and,
  (3) Rhizoctonia
 (b) Increased tolerances for defects.

 Total Defects 20%

 Including not more than:

 (1) 10% which fail to grade U.S. No. 2, including therein 6% external defects and 6% internal defects, of which not over 3% may be affected by freezing, southern bacterial wilt, ring rot, late blight, soft rot or wet breakdown, including therein not over 1% frozen or affected by soft rot or wet breakdown.

 4. U.S. No. 2

 Total Defects 10%

 Including not more than:
  External Defects 6%
  Internal Defects 6%

  Bacterial Wilt, Ring Rot, Late
  Blight, and Soft Rot, Wet
   Breakdown, or Frozen 3%

 Included in the 3%:  For Soft Rot, Wet Breakdown, or Frozen 1%
 Table 2  Standards of weight range for designated count cartons

 Range

 Count Average Count* Weight

Larger then 50 size 10 percent over 5 percent over 15 oz.
 or under or under or larger

 50 “ 45-55 48-53 12-19
 60 “ 54-66 57-63 10-16
 70 “ 63-77 67-74 9-15
 80 “ 72-88 76-84 8-13
 90 “ 81-99 86-95 7-12
 100 “ 90-110 95-105 6-10
 110 “ 99-121 105-116 5-9
 120 “ 108-132 114-126 4-8
 130 “ 117-143 124-137 4-8
 140 “ 126-154 133-147 4-8
Smaller than 140 “ 10 percent over 5 percent over 4-8
 or under or under

*Applicable to lots.

 The following tolerances by weigh, are provided for potatoes in any lot which fail to meet the weight range for the designated count:

  (a) not to exceed 5 percent for undersize; and
  (b) not to exceed 10 percent for oversize.

 (2) Potatoes packed in cartons (except when used as a master container) shall be U.S. No. 1 or better grade and conspicuously marked as to size.  However, potatoes of U.S. Extra No. 1 Grade shall be no smaller than 110 size nor larger than 60 size.

 (d) Inspection.  Except when relieved of such requirement pursuant to paragraphs (e) and (f), or (g) of this section,

  (1) No handler shall handle potatoes unless such potatoes are inspected by either the Idaho Federal-State Inspection Service or Oregon Federal-State Inspection Service and are  covered and accompanied by a valid inspection certificate, numbered notesheet, or Shipping Clearance Report:  Provided.  That a valid inspection certificate, numbered notesheet, or shipping clearance report is not required to accompany positive lot identified potatoes.