b'TATERTALESBeware of Soil-borne Yield RobbersThere are several seed-borne diseases to check your seed for this growing season.SEVERAL SEED-BORNE potato diseases have the potentialaffected tubers. Sclerotia germinate producing a fungal growth to reduce plant stand early in the season and cause seriousinfecting sprouts and causing dark brown cankers which pinch off economic losses. It is extremely important to examine all seed lotssprouts. New sprouts will emerge, but they will be less vigorous carefully immediately after receiving the seed.than the first flush of sprouts resulting in weaker plants. Infec-To do this, take random samples of tubers and wash them. Thistions which kill sprouts before emergence result in poor stands. will allow you to see silver scurf, black dot and superficial commonRhizoctonia development is favoured by cool, wet weather. There scabwhich are not easy to see if the tubers are unwashed. Ifare seed treatments to provide protection against this disease.you find diseases or defects, check the receiving tolerances set by Blackleg ComplexIn Ontario, some species of soft rot the Canadian Food and Inspection Agency (CFIA). bacteria cause both tuber soft rot and blackleg. The disease EUGENIA BANKS,Common seed-borne diseases which cause seed decay andsymptoms are indistinguishable with tuber rot being wet and POTATOreduce yield are:granular. With time, the rotting tissue darkens from cream to SPECIALIST WITH Fusarium dry rot (Fusarium spp)External dry rot lesionsbrown to black. There is a sharp, dark line between healthy and THE ONTARIO POTATO BOARD are sunken and shriveled with concentric wrinkles. The internaldiseased tissue. PCR tests are required for correct identification. rotted tissue ranges from brown or grey to black and is dry andThese are both poor soil survivors who thrive under wet condi-crumbly. There is no noticeable smell. Fusarium often rots thetions. The bacteria overwinter in infected seed tubers in storage. centre of the tuber forming a cavity, and the walls of the cavitySecondary bacteria which invade infected tubers will give off a are lined with rotting tissue which may be white or yellow or pink.fishy smell.Fusarium spores can contaminate healthy seed during the cutting Pectobacterium atrosepticum aka old blacklegTuber de-operation. There are seed-piece treatments to prevent the spreadcay starts at the stolon attachment where tissue becomes black-of fusarium during seed cutting, but no seed treatment can turnened and soft. As the disease progresses, the entire tuber may bad seed good.rot. It is more common on wet, cool (below 25 C) environments. Infected plants may emerge, but they die early in the season. Pectobacterium parmentieriIts more aggressive than the old blackleg, designated as a better tuber rotter and can cause severe crop losses. It favours warmer temperatures than the old blackleg.Fusarium dry rot causes seed piece decay.PHOTOS: EUGENIA BANKS Late blight (Phytophthora infestans)Look for slightlyP. parmentieri is an aggresive tuber rotter. sunken, purplish areas on the tubers. A granular, reddish-brown, dry rot developing under the lesions and extending into the tuber Dickeya dianthicolaIts favoured by temperatures above flesh. Cutting seed will spread the disease to healthy tubers. CFIA25 C which explains why infected tubers will remain dormant in allows seed lots with up to one per cent of late blight. Not all in- storage. fected seed will rot in the ground and you could end up with about Another common soft rot bacterium, Pectobacterium caroto-150 infected seed pieces per acre. There are seed treatments tovorum subsp. carotovorum causes tuber soft rot and aerial stem control late blight but expect problems if its a cool, wet growingrot, but rarely causes blackleg. It may cause lenticel rot in high season. humidity storage conditions. Rhizoctonia black scurf (R. solani)Rhizoctonia does notThere are no seed treatments to control soft rots. Infected tu-cause seed decay but infects sprouts. Black, irregularly shapedbers need to be graded out carefully and seed cutters disinfested survival structures called sclerotia develop on the surface ofoften to reduce the spread of the bacteria. 40 SPUDSMART.COM SPRING 2021'