Factors affecting infection of potato tubers byAlternaria solani in Colorado

Potato tubers became infected byAlternaria solani at the time of harvest. Infection occurred only on wounded tubers irrespective of their depth in the soil. The presence of free moisture on unwounded tubers did not increase the incidence of infection, and immature unwounded tubers were not susceptible. Tuber infections may be reduced by allowing tubers to fully mature before harvest or possibly, by applying chemicals to the soil surface.     

The effect of temperature and relative humidity on wound healing and infection of potato tubers byAlternaria solani

Under environmental conditions favorable for wound healing, potato tubers became significantly (P = 0.05) more resistant toA. solani infection during a two-day interval between wounding and inoculation. This period coincided with the time required for wounded tubers to completely seal wounded surfaces by suberization at 15.6°C/98% RH. Suberization of the wounded surfaces provided tubers significant (P = 0.05) protection againstA. solani invasion but wound periderm development was also essential for total exclusion of the pathogen. Wound healing takes place faster at high temperatures and relative humidities. The effect of temperature is more critical in the wound healing process.     

Pre-harvest burning for control of tuber infection byAlternaria solani

Pre-harvest propane burning of vines and soil surface significantly reduced populations ofAlternaria solani spores on the soil surface in field studies. Infection of potato tubers harvested from burned fields was reduced in most cases. Laboratory studies indicated a minimum temperature of 200°C for 1–2 seconds was required to significantly (P = 0.05) reduce germination ofA. solani spores. This temperature was achieved at the soil surface in the field when plots were burned at tractor speeds of 2, 3, 4 and 5 mph. In practice burning at only 2, 3 and 4 mph significantly reduced spore populations and tuber infection in the field. Recontamination of plots after burning occurred relatively rapidly. The data show that propane burning at tractor speeds of 2–4 mph can effectively reduceA. solani infection of potato tubers by lowering fungus populations on the soil surface.     

Post-harvest chemical treatments for control of tuber infection byAlternaria solani

Post-harvest application of several chemicals, including captan, sodium hypochlorite, chlorine dioxide, triphenyl tin hydroxide, captafol, and iprodione signficantly (P=0.05) reduced infection of potato tubers (cv Norchip) byAlternaria solani. Application rates of 5.4 or 8.3 1 of chemical mixture/metric ton were effective although limited evidence indicated that the higher rate may provide additional control. Post-harvest treatments appeared to be effective when disease pressure, as measured by the numbers of lesions per tuber, was low to moderate and seemed to lose effectiveness when disease pressure was high. It is suggested that routine post-harvest applications of effective chemicals coupled with proper storage management in disease prone locations might be an economically feasible way to control early blight losses in storage.     

Pre-harvest chemical applications for control of tuber infection byAlternaria solani

Pre-harvest chemical applications significantly reduced populations of viableAlternaria solani spores on the soil surface in the laboratory and field and the infection of potato tubers in the field. Only formaldehyde consistently reduced spore germination and tuber infection in the laboratory and the field but Difolatan 4F, Difolatan 4F + DMSO (dimethyl-sulfoxide), Manzate D, Manzate D + DMSO and sodium hypochlorite often reduced fungus populations significantly. More work is necessary before pre-harvest chemical applications can be recommended for control of early blight tuber decay due to the variable performance of many chemicals and the relatively high cost and corrosiveness of formaldehyde, the most effective chemical in the study.     

The effect of stage of maturity and storage on the respiratory quotient of potato tubers

Summary A respiratory quotient for the tuber, during development, of about 1,0 is succeeded by a variable quotient during the senescence and death of the foliage, harvesting, and the early weeks of storage. Later a quotient of about 1,0 is again observed, but later still there is a considerable increase above this value, suggesting a greater participation of an anaerobic cycle or cycles.

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Zusammenfassung Der Atmungsquotient der Knolle liegt w?hrend der Entwicklung ungef?hr bei 1,0. Diesem folgt w?hrend des Alterns und Absterbens des Krautes, zur Zeit der Ernte und in den ersten Wochen der Lagerung ein ver?nderlicher Quotient. Sp?ter kann wieder ein Quotient von 1,0 beobachtet werden. Noch sp?ter steigt dieser Wert erheblich an, was auf eine st?rkere Beteiligung eines oder mehrerer anaerobischer Atmungszyklen schliessen l?sst.

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Résumé A un quotient respiratoire du tubercule, pendant le développement, d'environ 1, succède un quotient variable durant la sénescence et la mort du feuillage, la récolte et les premières semaines de la conservation. Plus tard on observe de nouveau un quotient respiratoire de 1 environ, mais, plus tard encore, il y a un accroissement considérable au-dessus de cette valeur, faisant supposer une participation plus grande d'un ou de plusieurs cycles anaérobies.

     

Post-harvest development ofRhizoctonia solani Kühn on potato tubers

Summary The number of tubers infected byRhizoctonia solani Kühn, but not the extent of infection, significantly increased when tubers were kept in a commercial bulk store for six months after harvest. Tubers were placed in a small cold store for eight weeks and kept under dry or wet conditions. The numbers infected significantly increased under dry conditions when tubers were harvested immediately after haulm destruction in August or September, but under wet conditions only when tubers were harvested in September. Wounds infected byR. solani could develop into extensive rots during storage particularly in wet conditions. Sclerotia are usually thought to be limited to the tuber surface, but some were found to penetrate the periderm to the cortex; moreover, the depth and extent of penetration could increase during storage.

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Zusammenfassung Knollen der Sorte Majestic wurden Mitte Oktober. vier Wochen nach der Krautvernichtung durch Spritzung von S?ure, geerntet. Nach sechsmonatiger Aufbewahrung in einem Handelslagerhaus zeigten die Muster, die in Nylonnetzen 300 mm unter der Spitze des Haufens lagerten, signifikante Zunahmen in der Anzahl der mitR. solani infizierten Knollen, aber nicht in der St?rke der Infektion. In einer zweiten Saison wurde das Kraut an einem von drei Daten (Tabelle 1) mit S?ure gespritzt und der Bestand sofort, nach zwei und nach vier Wochen geerntet. Die Knollen wurden w?hrend acht Wochen unter trockenen (Papiers?cke) oder feuchten (Papier mit Polythens?cken) Bedingungen bei 4 C gelagert. Die Anzahl infizierter Knollen nahm unter trockenen Bedingungen signifikant zu, wenn die Knollen sofort nach der Krautvernichtung im August oder September geerntet wurden; unter nassen Bedingungen jedoch nur, wenn die Knollen im September geerntet wurden (Tabelle 1). Auch der Schweregrad der Infektion stieg signifikant an; unter trockenen Bedingungen bei der ersten und letzten Ernte, unter nassen Bedingungen aber nur bei der letzten. Je l?nger die Knollen nach dem Absterben des Krautes im Boden blieben, um so gr?sser war die Anzahl mit innerer Infektion (Tabelle 2). Nach acht Wochen Lagerung wiesen die meisten, aber nicht alle Muster eine Zunahme an innerer Infektion auf. Die Tiefe des Eindringens des Pilzes nahm mit dem Abstand zwischen der Krautvernichtung und der Ernte zu, aber selten wurde der Erreger unter dem Periderm gefunden. Das Eindringen in die Schale geschah meistens w?hrend der Lagerung und vor allem in jene Knollen, die nach der Krautvernichtung vier Wochen im Boden gelassen wurden. Bis zu 50% eines Musters mit inokulierten Knollen konnten am Lager Innenf?ule entwickeln; die F?ulnis entwickelte sich unter nassen Bedingungen besser als unter trockenen. Die L?sionen befanden sich meist getrennt rund um das ursprüngliche Inoculum, aber einige vereinigten sich, eher unter nassen als unter trockenen Bedingungen.

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Résumé Des tubercules de la variété Majestic ont été récoltés à la mi-octobre, quatre semaines après défanage aux colorants nitrés. Six mois après stockage en vrac, dans un magasin, des échantillons, mis en filets de nylon 300 mm en dessous du sommet du tas, ont montré des augmentations significatives du nombre de tubercules infectés parR. solani, mais pas du degré de sévérité de l'infection. Une seconde année, le défanage aux colorants a eu lieu pour l'une des trois dates (tableau 1) et la parcelle a été récoltée immédiatement et aussi 2 et 4 semaines plus tard. Les tubercules ont été stockés à 4 C pendant 8 semaines en conditions sèches (sacs papier) ou humides (sacs papier avec plastique). En conditions sèches, on a une augmentation significative du nombre de tubercules infectés lorsqu'ils sont récoltés immédiatement après défanage en ao?t et septembre. En conditions humides, on a eu cette augmentation uniquement lorsque les tubercules ont été récoltés en septembre (tableau 1). La sévérité de l'infection augmente également de manière significative en conditions sèches pour la première et la dernière récolte, tandis qu'en conditions humides cette augmentation ne s'observe que pour la derniére récolte. Plus on maintient les tubercules dans le sol après la destruction des fanes, plus ceux-ci présentent une infection interne (tableau 2). Huit semaines après conservation, la plupart, mais pas la totalité, des échantillons ont montré une augmentation de l'infection interne. La profondeur de pénétration du champignon a augmenté parallélement à l'allongement de l'intervalle entre le défanage et la récolte, mais on a rarement trouvé l'agent pathogéne en dessous du périderme. La pénétration au niveau du cortex s'est produite le plus souvent pendant le stockage, et plus particulièrement pour les tubercules qui ont été arrachés 4 semaines après défanage. Les auteurs ont eu jusqu'à 50% de l'échantillon composé de tubercules inoculés avec des sympt?mes de pourritures internes pendant la conservation. Ces pourritures se sont mieux développées en conditions humides qu'en conditions sèches. Les lésions ont été le plus souvent discrètes autour de l'inoculum primaire, mais certaines ont fusionné, plus généralement en conditions humides qu'en conditions sèches de conservation.

     

The effect of storage conditions on subsequent field performance of potato seed tubers in Tunisia

Summary Seed tubers of four cultivars were grown under similar conditions and harvested simulataneously. They were stored in traditional dark storage, diffused-light storage, or cold storage, and with combinations of these three methods for 150 or 230 days beginning in the hot, dry summer period. The effect of storage conditions on emergence, stem and tuber number, tuber size distribution and yield is discussed. Results suggest an optimal combination of storage method, cultivar choice, and sprout management practices may be achieved to obviate the need for cold storage in warm climates. Emergence and yield were consistently good for the 150-day storage period when traditional storage was followed by diffused-light storage. The sam technology gave promising results for the 230-day period with cultivars Claustar or Désirée when seed was desprouted prior to planting.     

The effect of cultivar maturity on the resistance of potatoes to early blight caused byAlternaria solani

A series of clonal variants of common potato varieties which had been selected for different maturities were screened in the field for their resistance to early blight caused by the fungusAlternaría solani. Maturity of these cultivars was also rated in the field. A strong correlation was found between cultivar maturity and resistance to early blight. Earlier-maturing cultivars were more susceptible, and later-maturing cultivars were more resistant. Starch gel electrophoresis of the tuber enzymes of these cultivars indicated that the maturity variants did not differ with respect to the isozymes tested. This is consistent with the hypothesis that variants of the same cultivar, differing only in maturity, had been selected. These results therefore suggest that it may be difficult to select cultivars which are both early-maturing, and resistant to early blight.     

The effect of CCC on the initiation of potato tubers

Summary CCC, when applied to the roots of potato plants sufficiently early, brought forward the time of tuber initiation and growth. An increase in net assimilation rate at the time of rapid tuber growth was found for both CCC treated and control plants.     

The effect of glyphosate on the viability of seed potato tubers

Summary Glyphosate applied to a growing crop of potatoes adversely affected the growth of the harvested tubers in the following season. Some effects were produced at 0.018 kg/ha^*, equivalent to ca 1 % of a commercial application rate. Symptoms were more severe at higher rates.     

Effect of infection byRhizoctonia solani on the quality of tubers for processing

The effect ofRhizoctonia solani infection on the yield and quality of tubers destined for processing was evaluated in a 10 × 2 factorial experiment. Inoculation of 10 cultivars withR. solani significantly decreased total and marketable yields and significantly increased the number of malformed and fissured tubers as well as the number of tubers with black scurf. Specific gravity was significantly decreased in 3 of the 4 years. Chip color at harvest was adversely affected in 2 of the 4 years and over the 4 years combined; whereas chip color three months after harvest was adversely affected in all 4 years.     

Amylolytic activity in stored potato tubers. 2. The effect of low-temperature storage on the activities of α-and β-amylase and α-glucosidase in potato tubers

Summary Tubers of the potato cultivars Record, Wilja, Pentland Dell and Brodick (formerly clone 137371) were sampled before and after storage at either 4°C or 10°C. Reducing sugar content stayed constant during storage at 10°C in all four cultivars but rose greatly during the first 6–12 weeks of storage at 4°C in Record, Wilja and Pentland Dell but not in Brodick. Amylolytic activity was determined after 5 weeks storage using blockedp-nitrophenyl maltoheptaoside as substrate for α-amylase,p-nitrophenyl maltopentaoside as substrate for β-amylase, andp-nitrophenylglucopyranoside as substrate for α-glucosidase. The values obtained from tubers stored at 4°C were higher than those from tubers stored at 10°C, the differences being much less in Brodick than in the other three cultivars.     

The effect of condensation on sporulation ofHelminthosporium solani on potato tubers infected with silver scurf and held in simulated store conditions

Summary Chambers were designed to simulate environmental conditions present in commercial potato stores and were used to introduce condensation to tubers infected with silver scurf (Helminthosporium solani). The electrical resistance measured across the skin of tubers from the top of the chambers was consistently lower than that from the bottom of the chamber, and this was reflected in an increased number ofH. solani spores produced by the top tubers. An increase in the length of the condensation period resulted in the skin resistance remaining lower for a longer period and also resulted in higher number of spores. Tubers held at relatively high ambient temperatures (15 °C) required a shorter period of condensation to cause an increase in spore count. This investigation highlighted the need for close monitoring of store environments so that condensation events can be quickly identified and the tubers dried.     

The influence of storage factors on endogenous ethylene production by potato tubers

Throughout a 7-month storage period, Russet Burbank tubers continuously ventilated at 32 F (0 C) and 45 F (7.2 C) with atmospheres of 2% O₂, air, 4% CO₂, and intermittently ventilated with air, evolved ethylene at a rate no greater than 0.008 μ 1 Kg^?1 hr^?1. Tubers stored in 80% O₂ and 12% CO₂ produced ethylene at much higher rates. In all cases where sprouting occurred, the rate of ethylene production increased. Inoculation withFusarium roseum greatly stimulated ethylene production but inoculation withAlternaria solani did not.     

Sucrose accumulation during high-temperature storage of potato tubers

Summary Potato tubers stored in a farm store from April to October (monthly average temperature between 24.7 and 36.2°C) accumulated considerable quantities of total sugars. Sucrose was the main component though in the variety Kufri Chandramukhi reducing sugars accumulated in amounts equal to sucrose.     

Control ofRhizoctonia solani on potato by disinfection of seed tubers with organo-mercury compounds

Summary Although sclerotia ofRhizoctonia solani are commonly found on potato tubers in Scotland, the organism rarely causes a disease of any importance under the prevailing environmental conditions. However, it does cause a serious wilt disease in the southern and central areas of Africa which receive imported seed potatoes, and in these circumstances the value of disinfected seed is obvious. Of a number of possible organo-mercury disinfectants, solutions of soluble substances such as methoxyethylmercury chloride or ethoxyethylmercury chloride containing 100 ppm. mercury have been found to be the most generally suitable, although even these substances do not preven all sclerotia from germinating. The addition of a suitable wetting agent to the mercurial solution enhances its effectiveness in inhibiting germination or killing of the sclerotia. The potential effectiveness of any wetting agent at any given dilution under a variety of conditions can be predicted by assessing the sinking time by theDraves andClarkson (1931) method. Increasing the temperature of the dipping solution increases its effectiveness. None of the treatments described here (except treatment with methylmercuridicyandiamide) appeared significantly phytotoxic to the tubers. However, as the tubers employed in the experiments were lifted two to three months before treatment thereby allowing the skins to harden, and also because the number used was relatively small, definite conclusions on this point cannot yet be reached.

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Zusammenfassung Obwohl Sklerotien vonRhizoctonia solani allgemein auf Kartoffelknollen in Schottland vorkommen, verursacht dieser Organismus unter den vorherrschenden Umweltbedingungen hier nur selten schwerere Krankheiten. Dagegen ruft er eine ernstliche Welkekrankheit in den südlichen und Zentralgebieten Afrikas, wo Saatkartoffeln eingeführt werden hervor, und unter diesen Umst?nden ist der Wert desinfizierten Saatguts offensichtlich. Von einer Anzahl in Frage kommender organischer Quecksilber-Desinfektionsmittel erwiesen sich L?sungen l?slicher Substanzen, wie Methoxy?thylquecksilberchlorid oder ?thoxy?thylquecksilberchlorid, enthaltend 100 Millionstel Teile Quecksilber, im allgemeinen am geeignetsten, obwohl auch diese Stoffe nicht alle Sklerotien am Keimen hindern. Der Zusatz eines geeigneten Netzmittels zu der Quecksilberl?sung erh?ht die keimverhütende oder t?tende Wirkung auf die Sklerotien. Die potentielle Wirksamkeit eines Netzmittels bei einer bestimmten Verdünnung unter verschiedenen Bedingungen l?sst sich vorhersagen durch Ermittlung der Absinkzeit nach dem Verfahren vonDraves undClarkson (1931). Die Wirkung der Tauchl?sungen wird durch Erh?hung von deren Temperatur gesteigert. Keine der hier beschriebenen Behandlungen (ausser der Behandlung mit Methylmercuridi-cyandiamid) crwies sich den Knollen gegenüber als merklich phytotoxisch. Da jedoch die für die Versuche verwendeten Knollen zwei oder drei Monate vor der Behandlung gerodet worden waren, so dass eine H?rtung der Schale eintreten konnte, und ferner die Versuche nur mit einer relativ geringen Anzahl durchgeführt wurden, lassen sich diesbezüglich noch keine endgültigen Schlussfolgerungen ziehen.

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Résumé Bien que la présence de sclérotes deRhizoctonia solani sur les tubercules de pomme de terre soit générale en Ecosse, cet organisme provoque rarement une maladie de quelque importance dans les circonstances existantes. Cependant, il est cause d'un flétrissement grave dans les régions du sud et du centre de l'Afrique qui re?oivent des plants de pomme de terre importés, ce qui rend évidente la valeur de plants désinfectés. Parmi un certain nombre de désinfectants organo-mercuriques possibles, les solutions de substances solubles telles que le chlorure de méthoxyéthylmercure ou d'éthoxyéthylmercure contenant 0,01% de mercure se sont trouvées les plus généralement appropriées, bien que même ces produits ne puissent empêcher tous les sclérotes de germer. L'addition d'un mouillant approprié à la solution mercurique augmente son efficacité en ce qui concerne l'inhibition de la germination ou la destruction des sclérotes. L'efficacité possible de tout agent mouillant à n'importe quelle dilution et sous des conditions diverses, peut étre déterminée d'avance en observant la durée d'enfoncement selon la méthode deDraves etClarkson (1931). L'augmentation de la température de la solution où l'on plonge les tubercules renforce son activité. Aucun des traitements décrits ici (excepté celui au dicyandiamide de mercure) ne présenta de phytotoxicité sensible aux tubercules. Pourtant, les tubercules utilisés dans les essais ayant été récoltés deux ou trois mois avant le traitement, ce qui avait permis à la peau de se durcir, et vu le nombre assez réduit de tubercules observés, on ne peut encore tirer de conclusions définitives à ce sujet.