Acquisition of potato leafroll virus byMyzus persicae from secondarily-infected potato plants of different genotypes

Summary The acquisition of potato leafroll virus (PLRV) byMyzus persicae nymphs from the top leaves of potato plants was studied throughout a growing season in relation to the antigen titre in those leaves and the feeding behaviour of the aphid. Secondarily-infected plants of eight potato genotypes with different levels of field resistance served as virus sources. Early in the growing season, plants were efficient sources for virus acquisition. The amount of viral antigen detected inM. persicae nymphs fed on the top leaves was strongly correlated with the titres of viral antigen in these leaves. Virus acquisition from the top leaves of older potato plants was markedly impaired and could not be correlated with their virus titre. With increasing age of the potato plants and the development of virus symptoms, the virus titre in the leaves declined and the initial weak correlation between the virus titre and field resistance ratings disappeared. Thus, screening secondarily-infected potato plants for field resistance to PLRV based on the concentration of viral antigen in leaves or in aphids fed on them should be avoided later in the growing season. The feeding rate ofM. persicae, measured by the number of honeydew droplets excreted, did not account for the reduced uptake of virus from older plants since it was not influenced by the age of the plant. Throughout the growing season, the feeding rate ofM. persicae nymphs on PLRV-infected plants was higher on genotypes with low levels of field resistance to PLRV than on genotypes with high ones.     

Field assessment of the relative importance of different aphid species in the transmission of potato virus Y

Summary Flying aphids were trapped throughout the summer on a vertical net downwind of a plot of PVY-infected potato plants. Of 6769 individuals caught, 165 transmitted PVY to tobacco test seedlings. Of 119 species or species groups caught, 20 were found to be vectors of which nine had not been recorded previously.Brachycaudus helichrysi, Myzus persicae, Phorodon humuli andAphis species accounted for 90% of transmissions andB. helichrysi alone for 52% of transmissions. The prospects of using this information to assess the amount of virus spread in a potato crop and of forecasting the timing and abundance of the main vectors are discussed.

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Zusammenfassung Im Abwind einer Parzelle mit PVY-infizierten Kartoffelpflanzen (7% PVY^O, 4% PVY^N, 89% beide) wurden fliegende Blattl?use in zwei vertikalen Netzen (4,4 m × 1,4 m mit hexagonalen L?chern mit 1,5 mm Durchmesser) gefangen und anschliessend auf Tabaks?mlinge überführt, um zu prüfen, ob sie PVY übertragen. Die Blattl?use wurden vom 8. Juni bis zum 8. August 1984 normalerweise an einem Tag pro Woche von 10 bis 17 Uhr gefangen. Im Laufe von 12 Fangtagen wurden 6769 sachte 52% der übertragungen bei nur 15% der totalen Fangzahl (Tab. 3).B. helichrysi mitMyzus persicae, Phorodon humuli und Species des GenusAphis ergaben sich als 90% der übertragenden Individuen bei nur 32% der gefangenen Proben. Acht Prozent der gefangenenB. helichrysi waren übertr?ger, dagegen nur 4,7% vonM. persicae. B. helichrysi k?nnte als Vektor besonders wichtig sein, weil sie in der Vegetationszeit Blattl?use von 119 Species oder Speciesgruppen gefangen, von denen 165 (2,44%) Tabak mit PVY inokulierten (Tab. 1). 133 Blattl?use übertrugen PVY^O und 32 übertrugen PVY^N (und m?glicherweise auch PVY^O). 20 Species oder Speciesgruppen waren Vektoren, von denen 9 (Cryptomyzus ballotae, Hyperomyzus lactucae, Metopolophium festucae, Myzus ligustri, M. myosotidis, Myzaphis rosarum, Sitobion avenae, S. fragariae undUroleucon spp.) erstmalig beschriebene Vektoren sind.Brachycaudus helichrysi verurfrüh auftritt (Tab. 2), wenn die Pflanzen am anf?lligsten sind und die Virus-Translokation zu den Knollen am schnellsten stattfindet. Die Aussichten zum Gebrauch dieser Information zur Absch?tzung des Aufbaues von Virusbefall im Bestand und die Aussichten für eine Vorhersage der Menge der wichtigsten Vektoren werden diskutiert. Es ist dringend erforderlich, die Biologie vonB. helichrysi zu untersuchen.

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Résumé Deux filets verticaux (4,40 m × 1,40 m à mailles héxagonales de 1,5 mm de diamètre) sont placés face au vent pour la capture des pucerons dans une parcelle de plants de pommes de terre contaminés par PVY (7% PVY^O, 4% PVY^N, 89% par les deux) puis les pucerons sont transferrés sur des plantules de tabac en milieu clos pour tester la transmission de PVY. Les captures de pucerons ont eu lieu du 8 juin au 8 ao?t 1984, en général à raison d'un journée par semaine, de 10 heures à 17 heures. Pendant les 12 premiers jours, 6769 pucerons de 119 espèces ou groupes d'espèces ont été capturés, les plantules de tabac ayant été inoculées par PVY avec 165 pucerons (2,44%) (tabl. 1). 133 pucerons étaient vecteurs de PVY^O et 32 de PVY^N (et probablement PVY^O). 20 espèces ou groupes d'espèces étaient des vecteurs dont 9 récemment enregistrés (Cryptomyzus ballotae, Hyperomyzus lactucae, Metopolophium festucae, Myzus ligustri, M. myosotidis, Myzaphis rosarum, Sitobion avenae, S. fragariae etUroleucon spp.).Brachycaudus helichrysi représentait 52% des transmissions mais seulement 15% du total capturé (tabl. 3).B. helichrysi, Myzus persicae, Phorodon humuli et les espèces du gèneAphis représentaient 90% des transmissions et 32% des captures seulement. 8,0% deB. helichrysi capturé a transmis le virus contre, 4,7% pourM. persicae. B. helichrysi peut être particulièrement important comme vecteur dans la mesure ou il appara?t t?t en saison (tabl. 2) lorsque les plantes sont très sensibles et la translocation di virus aux tubercules la plus rapide. Les perspectives à partir de cette connaissance sont discutées en vue d'analyser l'évolution du virus dans une culture et les prévisions de l'abondance des plus importants vecteurs. Une plus grande connaissance de la biologie deB. helichrysi devient urgente.

     

Environmental factors influencing aphid transmission of potato virus Y and potato leafroll virus

Summary The effect of temperature, relative humidity (RH) and light on aphid transmission of potato virus Y (PVY) and potato leafroll virus (PLRV) was studied using as vectorsMyzus persicae Sulz. andAphis gossypii Glov. Host susceptibility was enhanced by 48 h pre-inoculation exposure at 25°C and by 48 h post-inoculation exposure to 30°C. High RH (80%) in both pre- or postinoculation phases enhanced host susceptibility. Continuous fluorescent light (4000 lux) did not alter the rate of transmission of either virus. High RH (80–90%) and high temperature (25–30°C), when combined, increased virus transmission by 30–35%. Transmission rates were reduced by nearly 50% if RH was maintained at 50% in either of the two phases even if the temperature was 25 or 30°C. Both viruses were acquired by aphids earlier (13–20 days after inoculation) when the source plants were incubated at 25 or 30°C. Most virus was transmitted from plants inoculated with PVY 13 to 16 days and with PLRV 15 to 20 days previously. Transmission rates of PVY were enumerated from symptom expression on test plants and by Enzyme Linked Immunosorbent Assay (ELISA) whereas those of PLRV were enumerated from symptom expression alone.     

Influence of the duration of acquisition and inoculation feeding on the effectiveness of potato leafroll virus transmission byMyzus persicae Sulz

Summary In laboratory experiments PLRV transmission byMyzus persicae Sulz was shown to be possible even during a very brief feeding period onPhysalis floridana Rydb, in both acquisition and inoculation feeding. When the acquisition feeding time (AFT) was varied between 30 sec and 48 h the inoculation feeding time (IFT) was constant (48h) and vice versa: when the AFT was constant (48 h), the IFT was variable. The rate of infection was 2.2% following 30 sec AFT and 1.1% after 30 sec IFT. After 1 min feeding these infection rates increased to 7.9% and 1.8% respectively. The capacity for virus transmission was closely correlated with the increase in feeding time for both acquisition and inoculation feeding.     

The infection pressure of potato leafroll virus and potato virus Y in relation to aphid populations in Cyprus

Summary The infection pressure of two viruses, potato leafroll (PLRV) and potato virus Y (PVY), both common in seed potatoes grown in Cyprus, was determined in three experiments in 1982–83. Virus-free bait plants, of potato and four other species, were exposed weekly to field infection during the growing season (March–June), and then returned to an aphid-free glasshouse for symptom expression. Only tobacco plants produced clear symptoms enabling reliable assessment of PVY infection pressure. When assessed with ELISA or by tuber indexing, the potato plants were efficient baits for both viruses whose infection period commenced at emergence (mid March to early April) and ended within 6–7 weeks. The seasonal trend of aphid populations, determined with Moericke traps or 100-leaf counts, correspond to that of virus spread. Correlation and regression analysis of aphid and virus data implicated the alate form ofMyzus persicae as the principal vector of both viruses.     

Production of seed potatoes in Cyprus: the effects of roguing and planting date on the spread of potato leaf roll virus,tuber yield,and infestation by potato tuber moth

Summary Field experiments during 1984–6 tested the effects of planting date on the development of aphid infestations and the spread of potato leaf roll virus (PLRV) in rogued or unrogued plots of potatoes, cv. Spunta. Plantings were made each month from December to April, the customary time for planting being February. Aphid infestation in early-planted plots was severe throughout the growing season; plots planted in February were also severely infested early in the growing season but the populations later gradually declined to undetectable levels. Nevertheless, the incidence of PLRV in the latter plots was as high as in those planted in December-January. Late-planted crops escaped aphid infestation and PLRV infection, either in part (March planting) or completely (April planting). Such crops, however, were uneconomical due to poor yields and heavy losses from potato tuber moth infestation. Roguing significantly reduced the spread of PLRV in all years but its interaction with planting date was insignificant.     

Characterization of Solanum chomatophilum resistance to 2 aphid potato pests, Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer)

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) are responsible for yield reduction in potato (Solanum tuberosum) production by direct phloem feeding and by spreading viruses. Breeding resistant traits from Solanum chomatophilum into the potato germplasm provides alternative means to control aphid infestations. Integrated pest management strategy, using plant resistance, benefits from the characterization of the resistance and of its impact on aphid biology. Our objective was to characterize the resistance of S. chomatophilum by assessing the effects of accessions, plant parts on aphid performance, and by assessing the impact of the resistance factors on different aphid developmental stages and on alate morph production. Detailed aphid performance was obtained by measuring fecundity, survival, percentage of nymphs that reached adult moult, and population growth using whole plant and clip cage experimental designs. Accession and plant physiological age, but not aphid developmental stage, influenced all life-history parameters, except for alate morph production which was not induced on the resistant accessions. Plant part influence was independent of plant species and accession. Both experimental designs resulted in congruent resistance levels at the accession level for each of the two aphid species, supporting the use of any of them in S. chomatophilum resistance screening. PI243340 was resistant to both aphid species, while PI365324 and PI310990 were also resistant to M. euphorbiae and M. persicae, respectively.     

Effects of glandular foliar hairs on the spread of potato virus Y

Summary Sticky glandular hairs on the foliage of the wild potatoSolanum berthaultii hindered the departure of wingedMyzus persicae andBrachycaudus helichrysi. The presence of sticky hairs also decreased multiplication ofM. persicae, lessened probing and lessened acquisition of potato virus Y during 5 min access periods. It is suggested that if the glandular hairs were bred into potato cultivars, these features would help restrict the spread of aphidborne viruses in crops.

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Zusammenfassung Wie bereits früher gezeigt wurde, schützen klebrige Drüsenhaare auf den Bl?ttern der WildkartoffelSolanum berthaultii gegen verschiedene Kartoffelsch?dlinge einschliesslich der L?use; solche Haare gibt es in britischen Kartoffelsorten nicht. Ein Haartyp produziert ein klebriges Sekret an seiner Spitze, dieses Sekret kann mit ?thanol abgewaschen werden und eine st?ndige Berieselung mit Wasser verhindert eine Phytotoxizit?t. Ein zweiter Haartyp mit einer zellul?ren viergliedrigen Spitze wird durch das Waschen nicht beeinflusst. Drei Tage nach dem Aufsetzen von geflügeltenMyzus persicae oder geflügeltenBrachycaudus helichrysi (einem Vektor des Y-Virus der Kartoffel (PVY), der aber Kartoffeln nicht bef?llt) auf Planzen vonS. berthaultii oder von King Edward, blieben mehr als 85% auf mit Wasser berieseltenS. berthaultii, 45% auf mit ?thanol und Wasser gewaschenemS. berthaultii und nur 15–20% auf King Edward, unabh?ngig von der Behandlung (Abb. 1). Viele L?use, die aufS. berthaultii blieben, wurden gefangen und einige hatten durch das klebrige Sekret der Drüsenhaare verschmierte Mundpartien (Abb. 2).M. persicae nahm PVY h?ufiger von mit Wasser und ?thanol gewaschenen infizierten Bl?ttern vonS. berthaultii auf als von allein mit Wasser gewaschenen. Damit verbunden waren auch seltenere Probeeinstiche der L?use in mit Wasser gewaschene Bl?tter, aber h?ufige in Bl?tter deren Haare von dem klebrigen Sekret durch Alkoholwaschungen befreit waren. Diese im Gew?chshaus gewonnenen Ergebnisse zeigen, dass die Züchtung von Kartoffelsorten mit Drüsenhaaren, die vonS. berthaultii abstammen, helfen k?nnte, die Verbreitung der durch L?use übertragbaren Viren in Kartoffelbest?nden einzuschr?nken.

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Résumé Des poils foliaires glandulaires de la pomme de terre sauvageSolanum berthaultii ont déjà été observés comme protégeant de nombreaux ennemis de la pomme de terre, y compris les aphides. De tels poils ne sont pas connus sur les variétés britanniques. Un type de poil produit un exudat gluant à son extrémité. Ces exudats peuvent être lessivés par l'éthanol, dont on prévient la phytotoxicité par un rin?age immédiat à l'eau. Un second type de poil à extrémité cellulaire tétralobée n'est pas affecté par un tel lessivage. Trois jours après l'installation d'ailés deMyzus persicae on d'ailés deBrachycaudus helichrysi (un vecteur du virus Y de la pomme de terre (PVY) mais qui ne colonise pas la pomme de terre) sur les plants deS. berthaultii ou King Edward, 85% environ demeurent surS. berthaultii rincée avec de l'eau, 45% restent surS. berthaultii la vée à l'éthanol et à l'eau, et seulement 15–20% se maintiennent sur King Edward, quel que soit le traitement (fig. 1). La plupart des aphides restant surS. berthaultii sont piégés, et certains ont leurs pièces buccales engluées par l'exudat des poils glandulaires (fig. 2).M. persicae se multiplie plus lentement surS. berthaultii lavé à l'eau que surS. berthaultii lavé à l'éthanol.M. persicae acquiert le PVY plus fréquemment à partir des feuilles infectées deS. berthaultii lavées à l'éthanol et à l'eau que sur des feuilles seulement lavées à l'eau. Conjointement, les aphides explorent rarement les feuilles lavées à l'eau, mais visitent volontiers les feuilles dont les poils sont dépourvus de l'exudat gluant par lavage à l'éthanol. Ces résultats en serre suggèrent que les variétés de pomme de terre avec des poils glandulaires provenant de croisements deS. berthaultii pourraient aider à réduire l'extension de virus transmis par les pucerons dans les cultures de pomme de terre.

     

The influence of 2,4-D and kinetin on leaf callus formation in different potato species

Summary Leaf segments ofSolanum tuberosum andS. acaule can proliferate callus. However, callus formation and growth for a specific species depends on different concentrations of 2,4-D and kinetin (6-furfurylamino purine) used in a medium. Large amounts of creamy white friable callus could be proliferated fromS. tuberosum when explants were cultured in media containing 3 mg of 2,4-D and 0.3 mg of kinetin per liter. WhenS. acaule explants were cultured in the similar medium, the segment tended to become yellow; however, when it was subcultured onto a similar fresh medium, friable and creamy white callus was then formed. In a medium containing 0.3 mg of 2,4-D and 1 mg of kinetin per liter, the compact callus could be directly proliferated fromS. acaule leaf segments. Segments incubated under light formed less callus than those incubated in darkness. Scientific Journal Series No 10559 of the Minnesota Agricultural Experiment Station. This research was supported in part by a research contract from the International Potato Center, Lima. Peru.     

Influence of ambient forced-air ventilation rate on potato storage wastage

Summary Potatoes were stored in three insulated bins having ventilation rates of 0.0190, 0.0306 and 0.0417 m³/s·t. The results showed that in the climate of northern Italy potatoes can be stored successfully at ventilation rates of not less than 0.0306 m³/s·t resulting in product weight loss of less than 2.0% after 100 days' storage. The incidence of diseases and of sprouting was very low at rates of 0.0306 and 0.0417 m³/s·t, but greater at 0.019 m³/s·t because of the higher tuber temperature. Laboratory tests simulating ambient conditions confirmed the validity of a thermodynamic model simulating air-potato heat exchange.     

Effect of haulm treatments on the formation of microsclerotia ofVerticillium dahliae Kleb. on potato

Summary In four pot experiments, potato plants of cv. Element were artificially infected withV. dahliae. At an early and a late harvest haulms were killed chemically, by burning or by various other treatments, including cutting them into pieces of different lengths and keeping the debris on the soil surface or covering with soil. After 4 weeks the plant material was air-dried and the number of microsclerotia per mg was determined. At the early harvest, in two experiments, the chemical treatment yielded more microsclerotia than the cutting treatments. Covering colonised haulm tissue with non-sterilised soil was effective in inhibiting microsclerotia formation. Shorter haulm pieces led to fewer microsclerotia at the later harvest if the material was kept on the soil surface. The variation in microsclerotial yield and in treatment effects among the different experiments was large.     

New isolates of the necrotic strain of potato virus Y (PVYN) found recently in Poland

Summary In comparison to the previously known isolates of potato virus Y^N (PVY^N), some isolates found in Poland since 1984 are more infectious to potato plants, reach faster a higher concentration and induce milder disease symptoms. Potato cultivars resistant to the standard type of PVY_N may be susceptible to the new isolates whereas those that are extremely resistant to PVY remain extremely resistant to the new isolates. The potato cultivar Elipsa is suitable for the differentiation of PVY^N isolates.     

Extreme resistance to infection by potato virus X in genotypes of wild tuber-bearingSolanum species

Summary Clones derived from thirty-one different accessions (nineteen of Argentine origin) belonging to eightSolanum species were screened for resistance to infection by potato virus X strain cp (PVX cp) by mechanical inoculation of plantlets that had been micropropagated in vitro. Estimates of PVX multiplication obtained by enzyme linked immunosorbent assay and slot blot nucleic acid hybridization allowed the identification of resistant clones derived from five accessions belonging toS. commersonii S. oplocense, S. sparsipilum andS. tuberosum andigena. Resistant genotypes supported PVX concentrations 5 to 15 times smaller than did the susceptible control cultivar Spunta. Graft inoculation test confirmed the presence of extreme resistance similar to that conferred by the ‘immunity’ gene X¹ (also called RX_act).     

A simple assay system incorporating monoclonal antibodies for the detection of potato virus T

Summary Two monoclonal antibodies (McAbs) which react specifically with potato virus T (PVT) were produced and tested for cross reactivity with potato viruses (A, S, X, Y^o, Y^N, leaf roll), apple stem grooving virus (ASGV) and against healthy sap. They were found to be highly specific for PVT. These two McAbs form the basis of an enzyme-linked immunosorbent assay (ELISA) for the detection of PVT in infected plant material which is of key significance for potato quarantine.     

Assessing progenies of potato for resistance to early blight

Summary Progenies from crosses between cultivars varying widely in resistance to early blight (Alternaria solani Sor.), were assessed for resistance as true seedlings in a glasshouse in Scotland. The resistance of a representative sample of surviving genotypes from each progeny was compared with samples of the same progenies not previously exposed to the fungus, both in the glasshouse in Scotland and in the field in Israel. The exposed population was more resistant. Resistance was identified more effectively in adult plants from tubers in the glasshouse than in true seedlings and agreement between glasshouse and field assessment was better when progenies were compared rather than individual genotypes. The mid parent and progeny mean scores of the unexposed population were correlated at both sites, thus confirming that the resistance is heritable. Selecting resistant individuals at the seedling stage is suggested as a useful tool for resistance breeding, having first chosen the best parents for crossing.     

Diploid genotype DW.84-1457, highly resistant to potato leafroll virus (PLRV)

Summary The diploid clone DW.84-1457 which has outstanding resistance to potato leafroll virus (PLRV), has been selected at the Mlochów Centre of the Institute for Potato Research. It has in its pedigree PLRV-resistant clones from the Max Planck Institute nos. MPI 44.1016/10, MPI 44.335/130 and MPI 49.540/2. Its behaviour in the field and response to aphid inoculation indicate high resistance to infection, and the low concentration of the virus in graft-inoculated plants indicates high resistance to multiplication. This combination within one genotype of two aspects of resistance is not connected with hypersensitivity, and is heritable. Clone DW.84-1457 has other desirable characters such as extreme resistance to potato virus X (PVX), high resistance to potato virus M (PVM) and good table and processing quality. It is being utilized in the development of parental lines, both at the diploid and tetraploid level.     

Detection of strains of potato virus S by nucleic acid spot hybridization (NASH)

Summary Two complementary DNA (cDNA) clones (0.9 kb and 1.6 kb) reacting to the ordinary strain of potato virus S (PVS) were compared with single-stranded randomly primed cDNA (prepared to total genomic RNA) as probes for various strains of PVS, using the technique of nucleic acid spot hybridization (NASH). The cDNA clones detected 11 PVS isolates well, including both Andean and ordinary strains, while one of each strain was detected weakly. As little as 5 femtograms of PVS RNA could be detected. A low cross hybridization was observed with cDNA probes to PVS with potato virus M and carnation latent virus both members of the carlavirus group. No cross homology was detected with seven other potato viruses. NASH was as sensitive and specific as enzyme-linked immunosorbent assay (ELISA), with no pretreatments of crude sap being required before spotting on nitrocellulose filters. Cloned cDNA probes would be suitable for mass screening of PVS.     

Relationships between ground cover,intercepted solar radiation,leaf area index and infrared reflectance of potato crops

Summary In field trials with potato several methods determining the proportion of intercepted solar radiation by the crop were compared. Non-destructive measurement of the proportion of ground cover with the aid of a grid correlated well with the proportion of intercepted photosynthetically active radiation as measured with a tube solarimeter and with the leaf area index. Measurement of the infrared reflectance of the crop proved to be an efficient and objective method to show differences between treatments. Moreover, it showed a good correlation with ground cover and radiation interception until full closure of the canopy. Percentage ground cover is useful for assessing intercepted solar radiation and leads to fewer errors in calculation of efficiency of conversion into dry matter than the other methods.     

Reaction toPhytophthora infestans of potato genotypes with race-specific resistance

Summary Phytophthora infestans isolates collected in Poland in 1987–1995 were evaluated on detached leaflets of a differential series consisting of potato genotypes possessing resistance genes R1–R11. On the same differentials was evaluated over three years a highly virulentP. infestans isolate MP 245. Isolate MP 245 and those from natural populations ofP. infestans were seldom or inconsistently pathogenic to R5, R8 and R9. When leaflets of the differentials were infected with MP 245 the lesions were often small and sporulation weak. A statistically significant interaction was found between years and pathogenicity of MP 245 to individual differentials. Attempts to train the isolate MP 245 for pathogenicity to R9 were unsuccessful. The variation in specific resistance of potato genotypes may complicate the evaluation of their resistance toP. infestans, as well as the evaluation of the virulence spectrum of natural fungus populations. This variation may be due to changes in specific pathogenicity of the fungus or in specific resistance of the potato. Some differentials have a possibly useful resistance toP. infestans.     

Field performance of potato minitubers with different fresh weights and conventional seed tubers: Multiplication factors and progeny yield variation

Summary Multiplication factors and progeny yield variation in crops from minitubers of five weight classes (ranging from 0.13–0.25 g to 2.00–3.99 g) and conventional seed tubers were studied in field experiments in three years. Multiplication factors were calculated as the number and weight of progeny tubers produced per planted tuber or per unit planted tuber weight. They were lower for the lighter minitubers when calculated per tuber and higher when calculated per weight. Yield variation was described by coefficients of variation for the number and weight of progeny tubers produced. Variation over individual plants of a crop was higher in stands from the lighter minitubers. Variation over plots within a field was sometimes higher for the lighter minitubers, but variation over years was similar for all minituber classes. Variation over plots in progeny tuber weight was higher for minitubers than for conventional tubers.