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

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<strong>of</strong> cells, becomes enclosed by periderm, then turns brown,<br />

shrinks, and collapses to produce a cavity: 2) necrotic starchfree<br />

cells differentiate, causing a brown spot approximately I<br />

mm in diameter, <strong>of</strong>ten in the center <strong>of</strong> very small tubers, and<br />

produce a cavity that enlarges with tuber growth and is<br />

surrounded by a partially suberized ca<strong>mb</strong>ium layer: 3) internal<br />

tissue tensions cause splitting, which results in a lens-shaped<br />

cavity not preceded by cell necrosis. Translocation <strong>of</strong> substances<br />

from the central portion <strong>of</strong> the tuber and resorption in other<br />

parts <strong>of</strong> the plant may also be involved.<br />

Epidemiology<br />

Epideology hbefore<br />

Hollow heart is most severe during growing seasons or under<br />

cultural practices favoring rapid tuber enlargement. Rapidly<br />

growing tubers have a relatively higher incidence <strong>of</strong> hollow<br />

heart than do those that grow more slowly. Moisture stress<br />

(deficiency) followed by conditions favoring rapid growth<br />

predispose the uber to hollow heart,<br />

HJollo%%heart is lre(luc tis severe in fields with poor stands<br />

where plants are irregularly spaced. Practices that inhibit rapid<br />

tuber growth or that stimulate large nu<strong>mb</strong>ers <strong>of</strong> small tubers,<br />

such as close spacing <strong>of</strong> plants, reduce incidence <strong>of</strong> hollow heart,<br />

Marginal potassium deficiency may be a factor in hollow heart<br />

predisposition, particularly in cultivars prone to the disorder,<br />

Increasing potassium fertility over that required for normal<br />

growth reduces hollow heart incidence.<br />

Identification for Marketing<br />

X-ray examination <strong>of</strong> whole tubers under water effectively<br />

identifies the condition without tuber destruction. Removal <strong>of</strong><br />

large tubers and those with low specific gravity is only partially<br />

effective in eliminating hollow heart potatoes before marketing.<br />

Control<br />

I) <strong>Potato</strong> cultivars differ ii severity <strong>of</strong> incidence and in the<br />

type <strong>of</strong> internal cavity produced.<br />

2) Close and regular spacing <strong>of</strong> plants increases competition<br />

and prevents excessively rapid tuber enlargement, which usually<br />

reduces incidence <strong>of</strong> hollow heart.<br />

3) Avoid missing hills in planting, and use sound cultural<br />

practices to assure good stands.<br />

4) Maintain uniform soil moisutre levels to stimulate uniform<br />

tuber growth rates.<br />

5) Additional potassium fertiliation reduces incidence <strong>of</strong><br />

hollow heart even though total yields may not be increased.<br />

Selected References<br />

CRUMBIL. I.I ). C. NELSON, and M. E. DUYSI-N. 1973.<br />

Relationships <strong>of</strong> hollow heart in Irish potatoes to carbohydrate<br />

reabsorption and growth rate <strong>of</strong> tubers. Am. <strong>Potato</strong> .1.50:266-274.<br />

FINNEY. E. R., Jr., and K. II. NORRIS. 1978. X-ray scans for<br />

detecting hollow heart in potatoes. Am. <strong>Potato</strong> . 55:95-105.<br />

NEI.SON, ). C. 1970. Effect <strong>of</strong> planting date. spacing, and potassium<br />

Fig. 15. Hollow heart, showing transverse and longitudinal<br />

splitting.<br />

14<br />

on hollow heart in Norgold Russet potatoes. Am. <strong>Potato</strong> J.<br />

47:130-135.<br />

VON WENZI,, H. 1965. Die histologische tnterscheidungdreier'lypen<br />

von Ilohlheriigkehbe Kairt<strong>of</strong>felk nollen. Z. Pflan7enk1r.<br />

Pflanienschut,72:411-417.<br />

(Prepared by W..i. Hooker)<br />

Surface Abrasions<br />

Immature tubers that are mechanically injured during harvest<br />

the periderm is mature exhibit feathering, i.e., shreds <strong>of</strong><br />

loose skin exposing underlying flesh (Fig. 16). The wound may<br />

heal under optimum conditions but frequently dehydrates,<br />

becomes somewhat sunken, and turns dark brown with a sticky<br />

surface due to bacterial growth. Such tuers do not store well.<br />

Mature tubers mav be skinned by rough handling during<br />

harvesting and grading operations, thus providing infection<br />

courts for wound pathogens. Sunken scald spot develops when<br />

fresh wounds are dehydrated, especially after tubers are allowed<br />

to stand for some time in direct sunlight or desiccating ind<br />

before storage. Surface discoloration <strong>of</strong> wounds, with<br />

associated rot problems, also follows low emperature storage<br />

before wound healing is complete. Such tubers may become<br />

flaccid from dehydration.<br />

Control<br />

I) Avoid mechanical damage at every stage <strong>of</strong> the digging,<br />

harvesting, and grading operatiots.<br />

2) Protect tubers from sunlight and heat;avoid excessive<br />

dehydration before storage.<br />

31 Provide optimum storage conditions until wounds are<br />

completely healed.<br />

Selected References<br />

SMITH. W. ... Ir. 1952. Effect <strong>of</strong> storage temperatures, injury, and<br />

exposure on weight loss and surface discoloration <strong>of</strong> new potatoes.<br />

Am. <strong>Potato</strong> .1.29:55-61.<br />

WHITEMAN, T. M., and .1.1M.L.UTZ. 1954. Sunken scald spot field<br />

injury evident in stored potatoes. Am. <strong>Potato</strong> .1 31:43-49.<br />

(Prepared by W. .1.Hooker)<br />

Tuber Cracks<br />

Tuber cracking is <strong>of</strong> four types: I) growth cracks from<br />

internal pressure, 2) growth cracks from virus infection, 3)<br />

mechanically produced cracks, and 4) harvest cracks.<br />

Growth cracking (bursting) usually follows the long axis <strong>of</strong><br />

the tuber and results from internal pressure exceeding the tensile<br />

strength <strong>of</strong> surface tissues during tuber enlargement. High<br />

internal turgor pressure develops from tissue expansion during<br />

rapid tuber growth. Fertilizer placed so that growth is<br />

excessively rapid increases growth cracking. Growth cracks in<br />

''<br />

Fig. 16. Immature tuber surfaces, skinned and abraded.

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