Variety trial of potatoes resistant to Verticillium wilt

Twenty varieties and advanced seedlings, reported tolerant toVerticillium wilt, were compared in field trials during spring and autumn on plots infested withV. dahliae and on comparable non-infested plots. Yield criteria were used to analyze the level of field resistance. Ona-2249 was the only variety tested which gave similar yields in both growing seasons and under both infested and non-infested soil conditions, as compared to those of Up-to-Date, the standard variety.     

Studies onFusarium wilt of potatoes. 1. Plant wilt and tuber infection in naturally infected fields

Summary Field surveys of 2600 plants during growth of the autumn crop and of 1700 plants of the spring crop showed that 6.5% and 4.0% respectively were attacked byFusarium wilt; on average, 40% of the tubers from wilted plants were infected. Similar results were obtained in an artificially infested field. Examination of 6105 planting positions in the field during growth of the autumn crop showed that 28.7% of seed tuber rots were caused byFusarium oxysporum f.sp.tuberosi, while in spring crop this percentage was much lower. The yield in an artificially inoculated field was reduced from 10 to 53% compared to controls, depending on the cultivar.

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Zusammenfassung In Felduntersuchungen wurden mitFusarium infizierte Pflanzen und Knollen nach dem Zufallsprinzip erfasst, und zwar an verschiedenen Orten in mehreren Feldern an jeweils mindestens 100 Pflanzstellen. Von den 2600 Pflanzen aus dem Herbstanbau und 1700 aus dem Frühjahrsanbau, waren 6,5% bzw. 4,0% von derFusarium-welke befallen (Tab. 5). Von 30 Pflanzen mit Welkesymptomen starben 6 vor dem Knollenansatz ab, die übrigen 24 hatten 119 Knollen, von denen 48 mitFusarium infiziert waren. Nach 3 Monaten waren von denselben Knollen noch 34% mitFusarium befallen (Tab. 6). Die Untersuchung des Knollenauflaufs an 6105 Pflanzstellen ergab im Herbst eine Auflaufrate von nur 81,7%. Von den restlichen 18,3% der nicht gekeimten Knollen wurden 29,7% nicht wiedergefunden, 23,3% hatten Nassf?ule und in nur 2,3% fauler Knollen wurdenRhizoctonia undSklerotium gefunden. 44,7% der F?ulen waren vonFusarium-Trockenf?ulen verursacht worden. Isolierungen von 106 dieser Knollen ergaben in 68 F?llen Befall mitFusarium oxysporum, das entspricht 5,2% von der gesamten Probe (Tab. 4). Die Ergebnisse aus dem Frühjahrsanbau waren ?hnlich, die Verluste jedoch viel geringer. In der experimentellen Arbeit wurden Knollen verschiedener Sorten aus Pflanzkartoffelgebieten verwendet sowie einF. oxysporum f.sp.tuberosi-Isolat von einer griechischen Kartoffelpflanze mit Welkesymptomen. Der Krankheitsindex erstreckte sich von 0,20 bis 1,07, so dass der mittlere Ertrag nicht reduziert war. Die neuen Knollen zeigten im Lager eine Gesamtinfektion mitFusarium von 5–42% (Tab. 7), was gut mit den Felduntersuchungen übereinstimmt. Die lineare Regression des Ertrages in Bezug auf den Krankheitsindex ergab eine Ertragsreduktion von 10 bis 53%.

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Résumé Au cours d'observations au champ réalisées dans différents endroits,Fusarium contamine les plantes et les tubercules dans pas moins de 100 cas par endroit. Un flétrissement provoqué parFusarium a été observé sur 2600 plantes en culture d'automne et sur 1700 plantes en culture de printemps, avec respectivement un taux de 6,5% et 4,0% (tabl. 5). Sur 30 plantes flétries, 6 sont détruites avant formation des tubercules. Les 24 plantes restantes produisent 119 tubercules dont 48 sont infectés parFusarium. Les mêmes tubercules, trois mois après, présentent 34% deFusarium (tabl. 6). L'examen de tubercules formés pendant l'automne dans 6105 endroits montre que 81,7% de tubercules ont germé et sur le reste non germé, 29,7% ont disparu, 23,3% sont pourris alors queRhizoctonia etSclerotium sont responsables de seulement 2,3% de tubercules pourris. Les 44,7% des tubercules restants sont atteints de pourritures sèches provoquées parFusarium. Les isolements réalisés à partir de 106 de ces tubercules metent en évidence la présence deF. oxysporum dans 68 cas ce qui représente 5,2% de l'ensemble des échantillons (tabl. 4). Les résultats concernant les cultures de printemps sont similaires mais les pertes sont plus faibles. Dans un travail expérimental sont utilisés des tubercules provenant de régions de production de différentes variétés de semences et un isolat deF. oxysporum f.sp.tuberosi provenant de plantes de pomme de terre flétries de Grèce. L'indice de maladie étant entre 0,20 et 1,07 ce qui ne réduit pas le rendement moyen. Les nouveaux tubercules stockés ont présenté un degré d'infection totale parFusarium de 5 à 42% (tabl. 7) ce qui est en complet accord avec les observations au champ. Une régression linéaire entre rendement et indice de la maladie montre des réductions de rendement de 10 à 53%.

     

The relationship betweenVerticillium wilt and the pinkeye disease on potatoes

In both greenhouse and field experiments, a relationship was evident between the organismVerticillium albo- atrum and the pinkeye disease of potatoes. The fungicide, benomyl, was used to controlVerticillium after 2 and 4 weeks of contact with young potato seedlings. The mature tubers formed on these seedlings had varying amounts of pinkeye, depending on the potato line or variety tested. Seedlings that were first seed treated with benomyl and then inoculated withVerticillium did not develop pinkeye.Rhizoctonia also induced or stimulated pinkeye development.     

Efficacy of soil fumigants for control of Verticillium wilt of potatoes

Soil fumigation with materials containing methyl isothiocyanate, 1, 3-dichloropropene, or trichloronitromethane, alone or in combination, delayed “early maturity disease” symptoms caused byVerticillium dahliae Kleb, in potatoes and increased yields. Soil fumigation increased the crop value as much as $818 per acre, depending on the material and rate, used when potatoes were grown for two consecutive years following fumigation. With the exception of trichloronitromethane, fall fumigation was as effective or more effective than spring fumigation.     

Prevalence of Verticillium wilt in potatoes in the Red River Valley area of Minnesota

Verticilium spp. were present in over 60% of potato fields in Clay, Marshall, Norman, and Polk Counties in the Red River Valley in Minnesota. ThreeVerticillium spp. were isolated from 27% of the potato stems collected in commercial fields during 1968–1972.Verticillium alboatrum andV. dahliae were recovered from infected stems in approximately equal amounts (51% to 47%), butV. nigrescens was recovered from less than 2% of all host-infected plants. Of 12 cultivars sampled, Superior, Kennebec, Red Pontiac, Sebago, Irish Cobbler, and Norland were most frequently infected.     

Measurement of field resistance of potatoes to Verticillium wilt (Verticillium dahliae)

Summary Twenty seven clones were trialled in the Negev, Israel, in both the Spring and Autumn planting seasons of 1984 and 1985 and of these clones 18 were also grown in the Spring of 1986. All clones were grown in fumigated soil (designated, Control) which was subsequently kept as disease-free as possible and in soil previously infested withVerticillium dahliae, the causal agent of Verticillium wilt and a component of the potato early-dying syndrome. The clones differed in maturity and showed a range of symptoms in the field. A true assessment of resistance or susceptibility could not be obtained unless allowance was made for the effects of maturity. Only a few clones showed significant resistance. The importance of the results, in relation to screening breeders' clones for resistance, is discussed.     

Comparison of inoculation methods for field studies on varietal response to verticillium wilt of potatoes

Verticillium albo-atrum, cultured on potato dextrose agar plates or on sterilized wheat kernels, was used to incite disease in field studies. Immediately prior to planting, seed potatoes were dipped in a spore/mycelium suspension that was prepared from agar plate cultures. A second inoculation treatment involved placing infested wheat kernels under the potato seed at planting time. Both inoculation methods resulted in verticillium wilt development. However, the inoculum suspension dip method resulted in slightly greater incidences of verticillium wilt than did the infested wheat method. Inoculation by means of a suspension dip immediately after cutting the seed resulted in more wilted plants than when seed was inoculated 24 hours or 7 days after cutting. The spore/mycelium suspension dip method is now routinely used for field studies on disease susceptibility or resistance in potato cultivars.