PI-009: Seed Potato Tuber Inspection
Appendix 8: Malformed and Damage

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8a: Malformed

Malformed

Malformed tubers may take different forms. The tuber may have been exposed to adverse environmental conditions, or have a physiological defect, resulting in a knobby (36), pointed (37), curved (38), creased (39), or dumbbell shaped (40) tuber. In general, irregularities in soil moisture and nutrients are the common environmental factors responsible for malformed tubers. Growth cracks (41, 42) in the tuber may be caused by very rapid growth, usually when a rainy period follows a long dry spell. Growth cracks most often occur towards the bud end of the tuber and usually extend lengthwise. The cracks vary in size but usually heal over with no rot following the injury. Herbicide damage (43, 44) may result in malformed tubers, depending on the developmental stage of the plants at the time of exposure. Herbicides residues may be remaining in the soil, or drift from adjacent fields.

Scoring:

Tubers are to be scored as malformed when they are significantly different in shape from a typical tuber representative of the variety. Growth cracks are scoreable when they materially affect the bud end of the tuber (affect eyes and are not shallow) or extend more than 2/3 the length of the tuber in the aggregate.

36 | Knobby Tuber
Picture 36 - Knobby Tuber. Description follows.
Description for 36

This image of a potato demonstrates a potato that is malformed. The potato has yellow skin, with its centre being a spherical shape and, there are smaller knob-like bumps protruding from the centre. There are six knobs visible on the potato.

37 | Pointed Tuber
Picture 37 - Pointed Tuber. Description follows.
Description for 37

This image of a potato demonstrates a potato that is malformed. The right side of the potato in the image is a large round portion that becomes a curved, pointed end towards its left side.

38 | Curved Tuber
Picture 38 - Curved Tuber. Description follows.
Description for 38

This image of a potato demonstrates a potato that is malformed. The potato has dark-brown russeted skin, with a crease on the underside causing both of its ends to curve downwards.

39 | Creased Tubers
Picture 39 - Creased Tubers. Description follows.
Description for 39

This image of potatoes demonstrates potatoes that are malformed. This image consists of three potatoes, each with a creamy-yellow skin. Each potato has two lobes attached together vertically, causing them to look similar to lungs. Between the two lumps there are creases.

40 | Dumbbell Tubers
Picture 40 - Dumbbell Tubers. Description follows.
Description for 40

This image of potatoes demonstrates potatoes that are malformed. This image consists of two potatoes with light-yellow skin, and are dumbbell-shaped – they have large ends and a thinner middle.

41 |Growth Cracked Tubers
Picture 41 - Growth Cracked Tubers. Description follows.
Description for 41

This image of a potato demonstrates a potato that is malformed. This potato has a light brown skin, and has a very large growth crack on its visible left side, which penetrates about one-half through the potato, with one side leaning backwards and the other forwards.

42 | Growth Cracked Tuber
Picture 42 - Growth Cracked Tuber. Description follows.
Description for 42

This image of a potato demonstrates a potato that is malformed. This potato has a light brown skin, and has a very large growth crack on its visible left side, which penetrates about one-half through the potato, with one side leaning backwards and the other forwards.

43 | Herbicide Damaged Tubers
Picture 43 - Herbicide Damaged Tubers. Description follows.
Description for 43

This image of a potato demonstrates a potato that is malformed. This potato has a light brown skin, and has a very large growth crack on its visible left side, which penetrates about one-half through the potato, with one side leaning backwards and the other forwards.

44 | Herbicide Damaged Tuber
Picture 44 - Herbicide Damaged Tuber. Description follows.
Description for 44

This image of a potato demonstrates a potato that has experienced malformation. This potato is an orange-brown colour, and demonstrates herbicide damage as the potato has many growth cracks giving it a blocky, shattered appearance.

8b: Insect Damage

Insect Damage:

Some of the more common insects which may feed on, or cause scoreable damage to tubers are listed below.

Wireworm (click beetle) larvae (45, 46, 47), Agriotes obscurus, A. lineatus and A. sputator have overlapping life cycles, so that tuber damage can occur at any stage during tuber development. Early season injury occurs when the tubers are small and the larva causes deep, funnel-shaped cavities which form as the tubers mature. Mid-season injury results in the formation of pits 6 to 12 mm deep and 1.5 to 3 mm in diameter, sometimes lined with discolored scar tissue. Late season injury consists of clean cut round holes and scar tissue is not prominent.

Flea beetle, Epitrix tuberis, may cause surface injury, internal injury or both. Surface injury consists of pimple-like eruptions or rough, winding galleries (trails) approximately 3 mm wide and of varying length. Internal injury consists of single, or groups of narrow, brown slivers or feeding tunnels that extend into the tuber between 5 to 20 mm. Cracks may occur where these tunnels come together.

Grub damage (48, 49) is caused by the larvae of June beetles or cutworms (Polyphylla spp.). The earlier that feeding damage occurs during tuber development, the larger the affected area will be as the tuber develops. Damage consists of small to large feeding cavities between 5 to 20 mm or more in diameter. The irregular-shaped cavities usually are wider than they are deep, with characteristically rough ridges inside them. Half or more of the tuber can sometimes be consumed.

Insect feeding damage is scored under the Malformed and Damage tolerance when either:

  1. feeding damage exceeds an aggregate area of more than 10% of the surface; or
  2. Two or more eyes of the tuber are affected

Live insects and visible feeding damage should be noted in the comments section of the inspection report.

45, 46 | Late season wireworm damage - tunnels up to 3 cm deep
Picture 45 , 46 - Late season wireworm damage - tunnels up to 3 centimetres deep. Description follows.
Description for 45 and 46

Photo 45: This image of a potato demonstrates a potato with insect damage. This is a light-yellow and brown skin potato with several holes and dark brown spots taking up 20% of the visible surface area. The holes are caused by late season wireworm damage, and the tunnels in the holes can be up to three centimeters deep.

Photo 46: This image of a potato demonstrates a potato with insect damage. This is an up-close image of a potato demonstrating the holes caused by late season wire-worm damage. In this image the potato has rough texture, with five holes being shown. Each hole is an irregular shape with a light-brown edge and inside.

47 | Internal wireworm
Picture 47 - Internal wireworm. Description follows.
Description for 47

This image of two potatoes demonstrates potatoes with insect damage. Both of the potatoes in the image have light-brown skin, with the one on the left being somewhat larger than the one on the right. The potato on the left in the picture has had 75% of the skin on its visible surface area peeled away, exposing dark brown spots demonstrating internal wireworm damage. The potato on the right has had 50% of the skin on its visible surface area peeled away, also demonstrating the spots underneath which have occurred due to internal wireworm damage.

48 | White grub damage
Picture 48 - White grub damage. Description follows.
Description for 48

This image of a potato demonstrates a potato with insect damage. This potato has a light-brown skin, with a hole the size of a nickel on its visible side due to white grub damage. The interior of the hole is an orange-brown colour.

49 | Severe cutworm feeding damage
Picture 49 - Severe cutworm feeding damage. Description follows.
Description for 49

This image of seven potatoes demonstrates potatoes with insect damage. Each potato in the image has a light-brown and light-yellow skin, with a hole in the centre of its visible side. Each potato has one visible irregularly-shaped hole with the interior of the holes being a dark-brown or orange colour, and the exterior of the hole being a dark-brown or purple colour from bruising.

8c: Mechanical and Physiological Damage

Mechanical damage:

50 | Digger cuts on tubers are a result of mechanical injuries, cuts may be deep into the tuber, may be lengthwise or crosswise slab cuts exposing large areas.

50 | Digger cuts
Picture 50 - Digger cuts. Description follows.
Decription for 50

This image of a potato demonstrates a potato with mechanical and physiological damage; this potato is specifically an example of mechanical damage. This potato has a light brown and yellow skin with a few small brown spots. It demonstrates an example of a shattering bruise – there are several cracks in the top of the visible portion of the potato the cracks radiate from the bruise on the potato.

51 | Shattering bruises is a term used to describe recent injury to a potato from rough handling. Bruises or shattering are characterized by slight to severe breaks in the potato skin, and nearly always result in damage to the underlying tissue. Punctures, scratches or breaks may take place in many forms. In some lots, almost invisible bruising or shattering is followed by extensive rot

51 | Shattering bruises
Picture 51 - Shattering bruises. Description follows.
Decription for 51

This image of a potato demonstrates a potato with mechanical and physiological damage; this potato is specifically an example of mechanical damage. This potato has a light brown and yellow skin with a few small brown spots. It demonstrates an example of a shattering bruise – there are several cracks in the top of the visible portion of the potato, the cracks radiate from the bruise on the potato.

Mechanical damage is scored under the Malformed and Damage tolerance when;

  • the damage is not well healed and exceeds an aggregate area of more than 10% of the surface; or
  • the damage affects two or more eyes of the tuber

Physiological Damage:

52 | Air cracks may occur during harvest or packing, and after packing if the packages are too tight or handled roughly. They appear as fresh, longitudinal cracks and are scored if they materially or seriously affect the germination quality of the potato.

Air cracks are scored under the Malformed and Damage tolerance when:

  • they exceed an aggregate area of more than 10% of the surface; or
  • the surface cracks affect two or more eyes of the tuber
52 | Air cracks
Picture 52 - Air cracks
Description for 52

This image of a potato demonstrates a potato with physiological damage. The potato in this image has a light-yellow skin with a long curved line across it. The line is an air crack; it is very thin, its interior is an orange colour, and it extends three-quarters the length of the potato.

53 - Sunburn is caused when tubers are exposed to the sun during the growing season and the skin of the tuber turns green with chlorophyll, similar to the above ground parts of the plant. Typically, the bud end is affected and may involve only one area of the tuber; this condition may be accompanied by yellow or cream-colored discolouration of the inner flesh. Sunburn is caused by exposure to sunlight, as opposed to greening, which is caused by exposure to artificial light in storage.

Sunburn is scored under the Malformed and Damage tolerance when the green colouration causes damage to two or more eyes of the tuber are damaged and tuber vigour may be affected.

53 | Sunburn
Picture 53 - Sunburn. Description follows.
Description for 53

This image of a potato demonstrates a potato with physiological damage. The potato in this image is a light-yellow colour with dark-green patches which are caused by exposure to the sun.

54 | Ingrown sprouts are a problem when potatoes are stored for long periods at high temperatures (near 16°C), or have been exposed to a sprout inhibitor. The sprouts grow inward causing bulges and cracks in the tubers. Sometimes small new tubers develop inside the mother tuber.

Ingrown sprouts are scored under the Malformed and Damage tolerance when two or more eyes of the tuber are affected

54 | Ingrown Sprout
Picture 54 - ingrown sprout. Description follows.
Description for 54

This image of a potato demonstrates a potato with an ingrown sprout. This potato has a light-brown skin with a split in the skin near the centre of the potato - it takes up less than 5% of the visible surface area. The split has occurred due to ingrown sprouts growing inwards – through the hole in the skin you can see the sprout growing into the potato.

55 | Grass Root Injury is caused by quack grass (Elymus repens) or other similar grass species. The sharp growing points of the rhizomes penetrate into or completely through the tubers. There may be evidence of the rhizome attached to the potato.

Grass root injury is scored under the malformed and damage tolerance when two or more eyes of the tuber are affected regardless of the depth.

55 | Grass Root Injury
Picture 55 - grass root injury. Description follows.
Description for 55

This image of a potato demonstrates a potato with a grass root injury. This potato is a light-yellow colour. On the top of the potato on the left side there is a dark-brown and white grass root penetrating the potato; it is a grass root injury caused by the grass growing and its sharp points penetrating the potato.

56, 57, 58 | Skin spot caused by Polyscytalum pustulans, is characterized by purplish-black, slightly raised spots up to 2 mm in diameter, singly or in groups over the surface of the tuber. They may appear either at random over the surface or aggregated around the eyes. Sometimes it may result in larger necrotic areas forming over the tuber surface. These necrotic areas can be picked out, leaving circular pits of healthy flesh.

Skin spot is scored under the Malformed and Damage tolerance when:

  • Purplish-black, slightly raised areas which do not penetrate the flesh, affect more than 10% of the surface area in the aggregate; however, if skin spot penetrates the flesh it may be scored as dry rot as appropriate.
56 | Skin Spot
Picture 56 - Skin Spot. Description follows.
Description 56

This image of a potato demonstrates a potato with skin spot caused by Polyscytalum pustulans. The potato is a light-yellow colour with many dark red-brown spots of various sizes.

57 | Skin Spot
Picture 57 - Skin Spot. Description follows.
Description for 57

This image of a potato demonstrates a potato with skin spot caused by Polyscytalum pustulans. The potato is a golden-yellow colour with a large amount of tiny white-yellow bumps, taking up a large portion of the visible side's surface area.

58 | Skin Spot
Picture 58 - Skin Spot. Description follows.
Description for 58

This image of a potato demonstrates a potato with skin spot caused by Polyscytalum pustulans. The image is of an up-close picture of a potato; its skin is a yellow-brown colour with light brown-grey rough spots.

8d: Internal Necrosis (Viral)

Internal Necrosis (Viral) - Causal agents:

Tuber necrosis may be attributed to viral infections by Potato Mop Top Virus (PMTV), Tobacco Rattle Virus (TRV), or Potato Virus Y (PVY)N/NTN. Tuber necrosis may also be referred to as spraing depending on the viral agent (TRV, PMTV). Certain potato viruses which cause tuber necrosis are of particular significance to the Canadian seed potato industry.

Internal Necrosis (Viral) - Symptoms:

Generally, affected tubers show rings, semi-circles or spots on the surface, with brown necrotic lines, arcs and rings in the flesh. Tuber symptoms are, on occasion, limited to internal symptoms only. The tuber skin over some of the brown, sunken rings will often crack. The affected tissues are moderately firm and corky. Some mild infections may exhibit symptoms similar to Internal Brown Spot.

Tobacco Rattle Virus (TRV) (59, 60, 61, 62, 63) is the type-member of the genus Tobravirus, and is the causal agent of the disease commonly referred to as corky ring-spot.

59 | Tabacco Rattle Virus - internal necrosis
Picture 59 - Tabacco Rattle Virus - internal necrosis. Description follows.
Description for 59

This image of a potato demonstrates a potato with internal necrosis, caused by Tobacco Rattle Virus (TRV). The potato in this image has been sliced, revealing its cream-coloured centre. In the centre of the potato there are a few golden-brown spots and curved lines of necrotic tissue.

60 | Tabacco Rattle Virus – external symptom
Picture 60 - Tabacco Rattle Virus – external symptom. Description follows.
Description for 60

This image of a potato demonstrates a potato with internal necrosis, caused by Tobacco Rattle Virus (TRV). This image is of a red skin potato with several rough dark-brown spots. The spots are defined through embedded ring-spots.

61 | Tabacco Rattle Virus – external symptom
Picture 61 - Tabacco Rattle Virus – external symptom. Description follows.
Description for 61

This image of a potato demonstrates a potato with internal necrosis, caused by Tobacco Rattle Virus (TRV). The potato in this image has a light-yellow skin; on it there are several rough golden-coloured spots, most of them being rings or partial rings. At the top left of the potato there is a golden ring which takes up 5% of the viewed surface area – overall the rings and spots take up 30% of the visible portion of the potato.

62 | Tabacco Rattle Virus - internal
Picture 62 - Tabacco Rattle Virus - internal. Description follows.
Description for 62

This image of two potatoes demonstrates potatoes with internal necrosis, caused by Tobacco Rattle Virus (TRV). The potatoes in this image each have had 95% of its skin peeled off, exposing the cream-coloured centre beneath. Both potatoes have several groupings of dark-brown ring-spots.

63 | Tabacco Rattle Virus - internal necrosis
Picture 63 - Tabacco Rattle Virus - internal necrosis. Description follows.
Description for 63

This image of two potatoes demonstrates potatoes with internal necrosis, caused by Tobacco Rattle Virus (TRV). Each potato has had 75% of their skin peeled off, exposing the cream-coloured centre beneath. Both potatoes have several groupings of dark-brown ring spots.

Potato Mop Top Virus (PMTV) (64, 65, 66) is a member of the genus Furovirus and vectored by the powdery scab fungus. PMTV may be transmitted to new sites by planting of virus infected seed with powdery scab lesions

64 | Potato Mop Top Virus - internal necrosis
Picture 64 - Potato Mop Top Virus - internal necrosis. Description follows.
Description for 64

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Mop Top Virus. This is an up-close image of a potato; it is light-yellow with a cluster of several dark brown-grey spots and lines of necrotic tissue. The cluster takes up 40% of the visible surface area.

65 | Potato Mop Top Virus - internal necrosis
Picture 65 - Potato Mop Top Virus - internal necrosis. Description follows.
Description for 65

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Mop Top Virus. This is an up-close image of a potato; it has an almost white centre with orange-brown vertical lines of necrotic tissue on its right side.

66 | Potato Mop Top Virus - external symptom
Picture 66 - Potato Mop Top Virus - external symptom. Description follows.
Description for 66

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Mop Top Virus. The potato in this image has yellow skin with some orange spots. There is a large spot which is irregularly shaped and a lighter colour than the rest of the skin – it takes up 80% of the visible surface area.

8d: Internal Necrosis (necrotic strains of PVY)

Potato virus Y (PVY) is the type-species of the Potyvirus genus, often occurring as a complex of virus strains. Recognized strains include, but are not limited to: PVYO, PVYN, PVYNTN (may include several distinct isolates/groups) and PVYN:O. Visible tuber symptoms are typically caused by PVYNTN (67, 68, 69, 70, 71).

67 | Potato Virus Y - external symptom
Picture 67 - Potato Virus Y - external symptom. Description follows.
Description for 67

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Virus Y. The potato has a dark-yellow skin with an orange-red ring of necrotic tissue on the top of it.

68 | Potato Virus Y - external symptom
Picture 68 - Potato Virus Y - external symptom. Description follows.
Description for 68

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Virus Y. The potato in this image has a light-yellow skin with an irregular shape made up of multiple rings and partial rings on the top of it. The shape takes up 80% of the visible surface area and is outlined with an orange-brown colour.

69 | Potato Virus Y - external symptom
Picture 69 - Potato Virus Y - external symptom. Description follows.
Description for 69

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Virus Y. The potato in this image has a light-yellow skin with an irregular shape made up of multiple rings and partial rings on the top of it. The shape takes up 80% of the visible surface area and is outlined with an orange-brown colour.

70 | Potato Virus Y - internal necrosis
Picture 70 - Potato Virus Y - internal necrosis. Description follows.
Description for 70

This image of a potato demonstrates a potato with internal necrosis, caused by Potato Virus Y. The potato in this image has a dark-brown skin and has been cut to reveal its interior; the edge of the interior portion is a combination of orange and dark-brown necrotic tissue, leaving a small portion of its centre its normal cream colour.

71 | Potato Virus Y - external symptom
Picture 71 - Potato Virus Y - external symptom. Description follows.
Description for 71

This image of two potatoes demonstrates potato with internal necrosis, caused by Potato Virus Y. Both potatoes have a yellow skin with spots that are outlined in an orange-coloured necrotic tissue. The spots on the potato in the left take up 50% of the visible surface area, whereas the spot on the potato on the right takes up 60% of its visible surface area.

Scoring:

In order to assess tuber samples for internal necrosis, sub-samples must be cut and examined internally. Section 4.3 Sampling and Cutting Procedure for Internal Defects provides detailed information on this procedure.

  • Internal necrosis caused by TRV, PMTV, and necrotic strains of PVY are scored separately under Internal Necrosis, and must be added to other malformed and damage counts for a combined total under the Malformed and Damage tolerance.

8e: Internal Discoloration

Internal discolouration caused by physiological factors including frost, heat or drought:

Scoring:

Internal discolouration caused by physiological factors such as drought or temperature extremes is scored under Damage when the tuber vigour, storage or seed germination may be affected. If the discolouration penetrates greater than 13 mm into the flesh of the tuber or on a tuber cut to expose the largest surface area, if more than 10% of the exposed flesh area is affected by internal discolouration, it is scoreable. If the discolouration penetrates less than 13 mm at the stem end then the discoloration may be scoreable as stem end discoloration. There can be secondary factors present, such as wet or dry rot, and the tubers should not be scored under internal discoloration, but rather it should be scored under the disease, defect or condition affecting the tubers. Mild symptoms of blackheart are scored under the Malformed and Damage tolerance, however if associated with decay, score under soft rot or dry rot as appropriate.

72 | Necrotic spots in vascular tissue caused by heat Necrosis
Picture 72 | Necrotic spots in vascular tissue caused by heat Necrosis. Description follows.
Description for 72

is the result of high temperatures, especially when vines die early in light sandy soil. Affected tubers show slate-grey to brown patches in tissue near and perhaps associated with the vascular system. There are no external symptoms and diagnosis is dependent on cutting the tubers.

73 | Grey to black discolouration caused by Chilling
Picture 73 | Grey to black discolouration caused by Chilling. Description follows.
Description for 73

In some frost affected tubers, dark grey blotches or areas resembling black heart develop in the internal tissue. Chilling injury will reduce the vigour of the tuber and/or may contribute to no-top disease where the mother tuber will directly produce progeny tubers without producing a plant.

74 | Chilling injury of the vascular tissue
Picture 74 | Chilling injury of the vascular tissue. Description follows.
Description for photo 74

In some frost affected tubers, dark grey blotches or areas resembling black heart develop in the internal tissue. Chilling injury will reduce the vigour of the tuber and/or may contribute to no-top disease where the mother tuber will directly produce progeny tubers without producing a plant.

75 | Internal brown spot
Picture 75 | Internal brown spot. Description follows.
Description for 75

Internal Brown Spot (75) may be due to a lack of adequate soil moisture during the latter part of the growing season or during the harvesting process. No external symptoms are evident. Groups of dead cells which are free from fungi and bacteria appear as irregularly distributed and shaped, dry, brown or rust-coloured spots in the flesh of the tuber.

76 | Blackheart
Picture 76 | Blackheart. Description follows.
Description for 76

is mainly a storage problem caused by high temperatures, accompanied by poor aeration. The centre of the tuber usually turns slate grey, then dark and finally black. The tuber may dry and split towards the centre portion of the tuber. In extreme cases, the potatoes break down.

77 | Mahogany Browning
Picture 77 | Mahogany Browning. Description follows.
Description for 77

appears as reddish-brown areas or blotches in the flesh. They occur in irregular patches anywhere in the flesh. The margins are not defined; no sharp lines exist between discoloured and normal tissue. The colour of the affected tissue varies in intensity from light to reddish brown, and tissues are of normal texture. Varieties vary in susceptibility, but under sufficient exposure to chilling temperatures (0°C - 1°C); most will develop some degree of mahogany browning.

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