An assay to quantify vascular colonization of potato byVerticillium dahliae

A procedure was developed and tested to evaluate potato germ plasm for relative rates of vascular colonization byVerticillium dahliae. The number of colony forming units (CFU) per ml of plant sap, extracted from stems and plated on a medium, was used to assess vascular colonization from plants grown for 100 days in a field plot infested withV. dahliae. Sap extracted from main stem tissue at the ground line gave more CFU ofV. dahliae than tissue at the mid and apical region of the main stem. Aliquots of 0.05, 0.1 and 0.2 ml of plant sap were equally efficient in measuring vascular colonization. Thirty-three clones were evaluated for amount of vascular colonization in field and greenhouse tests with the former giving the best results. Cultivars and clones resistant to Verticillium wilt in Idaho, Maine, Minnesota, North Dakota and New York each had a low index of wilt and a low number of CFU/ml ofV. dahliae in plant sap in these tests. Clones intermediate in both wilt index and vascular colonization as well as selections with a high wilt index and extensive vascular colonization were found using the fresh sap assay method. Correlation values of, r = 0.92, r = 0.91 and r = 0.86 were observed between CFU/ml and percentage of foliar wilt for 11 clones/cultivars in 1986, 1987 and 1988, respectively. The correlation between CFU/ml and both moisture and temperature for the cultivars Kennebec and Russet Burbank, during a 6-yr period was r = 0.83.     

Efficacy of metam sodium for controllingVerticillium dahliae prior to potato production in sandy soils

The efficacy of metam sodium (MS) for controlling Verticillium wilt of potato was evaluated in two field experiments conducted in a sandy soil, heavily infested withVerticillium dahliae, and previously treated with MS. Compared to control plots where AUDPC value was 3141 (in 1999) and stem infection was 71.2% (in 2000), in plots treated with 600 L MS/ha AUDPC values were reduced by 57% to 80%, and stem infection was reduced by 49–54%. The incidence of infected dry stems, evaluated at the end of each season, was significantly reduced by all MS treatments, especially by 900 L/ha applied to a 60-cm depth (1999). Disease incidence in daughter tubers was also significantly reduced by all MS treatments. Yields obtained with 600 L/ha MS applied to a 30-cm depth were 32% and 21% higher than in the control in 1999 and 2000, respectively. In plots treated with 600 L/ha MS applied to a 60-cm depth yields were 17% and 28% higher than in the control in 1999 and 2000, respectively. With 900 L/ha MS applied to a 60-cm depth, yield was 21% higher than in the control in 1999. The yield of the low MS dose (300 L/ha), applied only in 2000, was not significantly different from the control. The differences in yield were due to the greater percentage of tubers larger than 45 mm. Yield reduction was highly correlated with disease severity expressed as AUDPC (in 1999 experiment). The net income in the 600 L MS/ha treatments was higher than in the control in both experiments. No indication of enhanced biodegradation was observed in the present study.     

Hatching of potato cyst nematodes in root diffusates collected from twenty-five potato cultivars

Root diffusates were collected from pot-grown plants of 25 potato cultivars by leaching the soil with distilled water. The activities of the leachates collected in this way were assayed by exposing cysts of the Ro1 population of Globodera rostochiensis (Wollenweber) Behrens and the Pa3 population of G. pallida (Stone) Behrens to a geometric series of dilutions of the leachates and counting the numbers of juveniles that hatched. ‘Log activity’ values for the diffusates were computed: whereas the diffusates from most cultivars hatched G. rostochiensis well, some hatched G. pallida well and some hatched it poorly. The implications of this difference for the distribution of the two species of nematodes and for the relative tolerance of potato cultivars in the field are discussed.     

Seasonal variation and effects of wheat rotation on populations ofVerticillium dahliae Kleb. in Ohio potato field soils

Soil population levels ofVerticillium dahliae in Ohio were monitored from May–October, 1982–1985, in 15 fields in potato-wheat rotation and two fields in potato monoculture. Population levels in fields in rotation ranged from 0 to 86 microsclerotia/10 g of air-dried soil with average values during each 6-month sampling period of 9.7, 12.9, 9.6 and 19.6 microsclerotia/10 g of soil for 1982, 1983, 1984 and 1985, respectively. In at least 2/3 of the fields sampled each year, soil populations ofV. dahliae peaked in either July or August, regardless of whether fields were under wheat rotation or potato monoculture. Of the 15 fields under potato-wheat rotation, 13 showed a general pattern of increased populations ofV. dahliae in one or both years following cropping to potato. Among those 13, significantly higher populations (P < 0.05) were observed in one wheat field in 1983 and in eight fields in 1985. In the two fields in potato monoculture, one consistently had population levels ofV. dahliae 3–4 times higher than any other field sampled in this study. Factors that may contribute to periodic changes inV. dahliae populations, implications of these changes in interpreting soil population data, and usefulness of a potato-wheat rotation in managingV. dahliae populations in Ohio are discussed.     

Diagnosis ofVerticillium dahliae in potato seed tubers with immunoassay techniques

Summary Three immunoassay techniques were compared with an isolation technique for detectingVerticillium dahliae in seed potato tubers. Immunofluorescent labelling was the most sensitive technique and the percentage infection levels determined for eight field-grown tuber samples were similar to those obtained by a traditional isolation method. Modified Mancini and Ouchterlony assays were less sensitive and gave the lowest values. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel; No 982-E, 1984 Series. This research was supported by The Netherlands-Israel Cooperative Potato Research Program.     

Fumigation of potato soils in Washington

Partial soil sterilization with Picfume, Vapam, Vorlex, Terraclor, Telone and combinations of Telone and Picfume have been included in studies for one or more years between 1960 and 1963. All the chemicals tested except Terraclor resulted in yield increases statistically and economically larger than the yields of potatoes produced on the untreated check plots. Partially sterilizing the soil in the fall resulted in large increases in yield of potatoes the following year. The effect of the partial sterilization of the soil lasted for at least two years. The causes for the increases in yield are not known. “Early dying” disease caused byVerticillium alboatrum was known to be present, but increases in yield also resulted from the use of Telone which is predominantly a nematocide. Pathogenic nema were few in number. A combination of Picfume and Telone, economically feasible in Washington, produced large yield increases over a two-year period and did not produce an off flavor in the potatoes when applied in the fall.     

Growth and yield of potato plants grown from microtubers in fields

Despite many reports of thein vitro production of microtubers, little is known about plant growth and yield from microtubers planted in the field. This study clarified differences in growth and yields between potato plants grown in the field from microtubers and from conventional seed tubers. The experiments were performed at Hokkaido University, Japan, over four years. Conventional seed tubers of about 50 g and microtubers of two sizes (0.5–1.0 g and 1.0–3.0 g) of the latematurity cultivar Norin 1 were planted, and plant growth and tuber yields were analyzed. The microtuber plants had a lower initial increase in root and leaf area index than conventional seed tuber plants, but had the same leaf area index after about 40 days from emergence. The first tuber formation in microtuber plants was about 7 days later than in conventional seed tuber plants, while tuber bulking occurred about 14 days later in microtuber plants. Consequently, the onset of tuber weight increase was later in microtuber plants, but the rate of increase thereafter was similar between conventional seed tuber and microtuber plants. At harvest the tuber fresh weight of microtuber plants was 82% that of conventional tuber plants, suggesting a potential for using microtubers for field planting.     

Hypersensitive and enzyme responses in potato tuber tissue treated withVerticillium dahliae and arachidonic acid

Wound-healing tuber tissues from two potato cultivars, one resistant (cv. Reddale) and one susceptible (cv. Kennebec) to Verticillium wilt caused by the fungusVerticillium dahliae were treated with elicitor preparations of either an autoclaved mycelial extract of the fungus or with the fungal component arachidonic acid (AA). Wound-healing tissues were analyzed for hypersensitive cell browning (HCB) and alterations in lipoxygenase (LOX), polyphenoloxidase (PPO), and peroxidase (PER) activities, because all three enzymes are thought to be involved in the hypersensitive response and plant defense. Healing Reddale tissues that were treated with the elicitors exhibited a much more rapid and intense HCB than did the healing Kennebec tissues. By 96 h, Reddale tissues treated with either elicitor preparation appeared dark brown and necrotic. Treated Kennebec tissues appeared only slightly darker than the controls after 96 h. LOX, PPO and PER activities in treated Reddale tissues were significantly less than that found in the control after 48 h, and by 96 h PPO and PER activities were nearly zero. In contrast, LOX activity in AA-treated Kennebec disks was higher than in the control at 96 h, while the activities of PPO and PER had decreased to about 60% of the control at the same time period. Our results show that HCB is strongly correlated withV. dahliae and AA elicitor treatments in the resistant vs. the susceptible cultivar, while the overall role of the three enzymes in cell browning and death remain unclear.     

Differential diagnosis ofVerticillium dahliae in potato with antisera to partially purified pathogen-produced extracellular antigens

Summary An extracellular protein-lipopolysaccaride antigen (PLP) was purified from culture fluids ofVerticillium dahliae. Antiserum produced in rabbits to the PLP detected the antigen in homogenates of tubers, stems and leaves ofV. dahliae-infected potato plants but not in extracts of healthy potato tissue or extracts of potato plants infected by other fungal pathogens. The antigen was not detectable in extracts of potato isolates ofV. tricorpus, V. nigrescens andV. nubilum or various other fungi. The antigen was shown to be different from cross-reactive antigens detected by antisera to mycelial antigens. When used as a tool for specific diagnosis ofV. dahliae infection in potato, antiserum to PLP was more reliable than that prepared against fungal body antigens. Publication of the Agricultural Research Organization No 245-E.     

Recent development in potato ridging on marine soils in the Netherlands

Summary Dutch farmers have developed various methods of making the elod-free ridges required for modern mechanical potato harvesting. Measurements showed however, that the ridges were smaller than the optimum 500–600 cm², although when the seed-bed was prepared 8–10 cm of loose soil was often present. Contrary to general belief ridging operations decreased rather than increased the amount of loose soil (6.5 cm). This was due to compaction before and during planting; after planting the amount compacted was equal to the amount loosened. Compaction can be reduced by limiting the number of passes over the ground through the use of powered implements for preparing the seed-bed, by combining implements, by making ridges in 1 or 2 operations soon after planting combined with chemical weed control, by using narrow tyres, by removing the loose soil in front of the wheels, and by increasing the distance between rows to 75 cm.

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Zusammenfassung Den holl?ndischen Landwirten ist es gelungen, die Kartoffeld?mme ohne Kluten herzustellen, was für die Ernte mit dem Sammelroder unerl?sslich ist (Abb. 2–6). Aus Messungen geht aber hervor, dass dies auf Kosten der Dammgr?sse geschehen ist, die in erster Linier durch die Anforderungen des Rodens bestimmt wird: m?glichst wenig leicht siebbarer Boden und konzentrierter Knollensitz hoch im Damm. Um das Grünwerden der Knollen und eine Infektion mit Braunf?ule zu verhindern, muss der Damm einen minimalen Umfang, der mit 500–600 cm² angenommen werden kann, aufweisen. Ein Versuch über den Einfluss der Gr?sse eines Dammes auf Wachstum und Lage der Knollen (Abb. 1) hat gezeigt, dass ein Damm von 350 cm² zu klein und ein solcher von 750 cm² nicht besser ist als ein Damm von 550 cm² Feldmessungen haben ergeben, dass trotz einer anf?nglich 8–10 cm dicken Schicht lockeren Bodens nach dem Pflanzen nur · 6,5 cm davon übrigblieb und dass diese Schichtdicke w?hrend des Wachstums ungef?hr konstant blieb. Wahrscheinlich wird also etwa die gleiche Bodenmenge, die von den H?ufelk?rpern gelockert wird also etwa die gleiche Bodenmenge, die von den H?ufelk?rpern gelockert wird, wieder zusammengepresst. Aber auch vor und w?hrend des Auspflanzens geht viel lockerer Boden verloren. Dieser Verlust steigt an, je m?chtiger die lockere Schicht (Abb. 8) und je breiter die Reifen sind (Abb. 7 und 10). Der Verlust lockeren Bodens kann eingeschr?nkt werden, indem beim Auspflanzen und der Saatbettvorbereitung Maschinen mit schmalen Reifen verwendet werden, die zudem den lockeren Boden vor den R?dern beiseite schieben (Abb. 9). Eine weitere Einschr?nkung wird durch das Herabsetzen der Zahl der Arbeitsg?nge errecht, zum Beispiel durch die Kombination von angetribenen oder nicht angetriebenen Ger?ten sowie durch die chemische Unkrautbek?mpfung. Auch die Arbeitsweise beim H?ufeln ist wichtig: wenn man immer durch die gleichen Spuren f?hrt, wird weniger lockerer Boden festgedrückt (Abb. 11). Schliesslich gestattet ein breiterer Reihenabstand, aus der gleichen Menge lockeren Bodens gr?ssere D?mme zu machen (Abb. 12). Dabei werden auch die Furchen breiter, so dass nur ein kleiner Teil der D?mme festgepresst wird. Ein Reihenabstand von 75 cm hat grosse Vorteile: der Weg/ha/Arbeitsgang ist kürzer, die aufzunehmende Bodenmenge/ha beim Roden kleiner, und der Abstand passt in die Normierung von 12,5 cm.

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Résumé Les agriculteurs hollandais ont réussi à réaliser les buttes sans motte indispensables pour la récolte à l’arracheuse-ramasseuse (Fig. 2–6). Mais il résulte de mensurations que ce résultat est obtenu au détriment de la grosseur de la butte, laquelle est déterminée en premier lieu par les exigences de l’arrachanges, le moins possible de terre légère passant au crible, par la formation concentrée et en hauteur des tubercules dans la butte. La prévention du verdissement des tubercules et de l’attaque du mildiou exige un contour minimum dont la surface peut être estiméc à 500–600 cm². Une recherche sur l’influence de la grosseur des buttes sur le développement et l’emplacement des tubercules (Fig. 1) a montré qu’une butte de 350 cm² est trop petite, mais non qu’une butte de 750 cm² est meilleure qu’une de 550 cm². Des mesures effectuées au champ montrent qu’une couverture originelle en sol meuble de 8–10 cm après la plantation s’abaisse à 6.5 cm seulement et que cette épaisseur reste à peu près constante pendant la végétation. Il est aussi vraisemblable que cette méme épaisseur de sol qui est ameublie par les buttages, est de nouveau comprimée. également avant et pendant la plantation, beaucoup de terre meuble se perd. Cette perte augmente avec l’accroissement de la couche meuble (Fig. 8) et de la largeur des bandages (Fig. 7 et 10). La perte de terre meuble peut être limitée en utilisant des bandages étroits pour la plantation et la préparation du lit des plants en même temps en poussant de c?té la terre meuble avant les roues (Fig. 9). Une plus grande économic sera obtenue par la réduction du nombre de pratiques culturales. par exemple en combinant les outlis. motorisés ou non, et par le désherbage chimique. De même la fa?on d’utiliser le buttoir est conséquente: on comprime moins le sol meuble quand on passe toujours par les mêmes sillons (Fig. 11). Finalement une distance accrue entre les lignes permet de réaliser de plus grosses buttes avec la même quantité de sol meuble (Fig. 12), et, en outre, les sillons seront plus larges de sorte qu’un mains grand nombre de buttes seront tassés. L’écartement de 75 cm est fort avantageux. Cet écartement diminue les parcours par hectare pour les fa?ons culturales et la quantité de sol ramassée par hectare lors de l’arrachage, en même temps cette distance se conforme au réglage de 12,5 cm.

     

Potato virus X isolates from potato collected in eastern Canada with different symptoms in tobacco differ in their coat proteins

Three Canadian isolates of potato virus X (PVX) that produced distinctly different symptoms in tobacco (Nicotiana tabacum cv. Samsun) were analyzed for differences in their coat proteins using SDS-PAGE, denaturing isoelectric focusing, peptide analysis and nucleotide sequencing. The amino acid sequence of the coat protein in a mild isolate differed from that of isolates that produced severe or intermediate symptoms at two locations. However, the amino acid sequences of the Canadian isolates that produced severe or intermediate symptoms were identical and were the same as the coat proteins of PVX isolates from Argentina, China, The Netherlands, and United Kingdom. These results suggest that regions of the PVX genome in addition to the coat protein gene may be involved in viral-host interactions.     

Quantification of Field Resistance to Verticillium dahliae in Eight Russet-Skinned Potato Cultivars Using Real-Time PCR

Changes in potato production over the past 10 to 20 years, have resulted in increased emphasis being placed on breeding for resistance to Verticillium wilt, caused by Verticillium dahliae Kleb. While many russet-skinned cultivars recently have been released with reported resistance to Verticillium wilt, information is lacking on the level of pathogen colonization, and therefore, the level of true genetic resistance is not known. Eight russet-skinned cultivars were grown in field trials with low and high levels of V. dahliae in the soil, and evaluated for wilt, stem colonization, yield, and tuber vascular discoloration. A recently developed QPCR assay was validated, with strong relationships to culture plating assays over three stem sampling dates. Additionally, stem colonization levels, as determined by QPCR, were related to wilt and tuber vascular discoloration. However, total yield did not exhibit a strong relationship to any other parameter evaluated in this study. Results from these studies indicate that varying levels of true resistance are present in the russet-skinned cultivars evaluated, and that the QPCR assay can be reliable in rapidly evaluating resistance to V. dahliae under field conditions. Based on pathogen quantification using stem colonization derived from traditional plating assays and QPCR, the resistance level of several cultivars is more clearly defined and discussed.     

Assessing fungicide resistance in populations of Alternaria in Idaho potato fields

Early blight, caused by the fungus Alternaria solani and brown leaf spot, caused by Alternaria alternata, are important diseases of potato crops in Idaho. In recent years growers have reported a reduction in efficacy of fungicides traditionally used in the past decade to control early blight. In 2009, a collection of A. solani 39 isolates were screened for resistance to azoxystrobin, pyraclostrobin, boscalid and famoxadone. Fungicide sensitivity testing was done using spiral plate dilution gradients. Results showed that of 39 isolates screened, all were resistant to azoxystrobin and three were resistant to boscalid. None were resistant to pyraclostrobin or famoxadone. In summer 2010, more isolates were collected (9 A. alternata and 26 A. solani) and the survey was expanded to include more fungicides with four different modes of action that targeted succinate dehydrogenase (SDH), methionine biosynthesis, mitochondrial respiration and multi-site contact activity. New isolates of A. solani and A. alternata were also collected from two additional sites. The results showed that 57% of the isolates were resistant to boscalid as well as an average of 63% of the isolates being resistant to the strobilurin fungicides. Seven and 15% of isolates were resistant to penthiopyrad (an SDH inhibitor), and pyrimethanil (a methionine biosynthesis inhibitor), respectively. However, none of the isolates were resistant to fluopyram (an SDH inhibitor) or a mixture of fluopyram and pyrimethanil. Although there appears to be cross resistance developing in Alternaria spp. to some of the new SDH inhibitors like penthiopyrad, others such as fluopyram are still showing limited to no resistance development in Alternaria spp. in Idaho.     

Pratylenchus spp. andVerticillium spp. in New Brunswick potato fields

A survey of New Brunswick potato fields with symptoms of early dying was conducted in September 1990 and 1991. Root lesion nematodes (Pratylenchus spp.) were detected in 43 of 46 fields in 1990 and in 37 of 43 fields in 1991. In 1990 and 1991 populations averaged 910 and 410 nematodes g-¹ dry root and 1030 and 720 nematodes kg¹ dry soil, respectively. Previous crops did not affect nematode populations, except in one comparison where the number of nematodes in potato roots in 1990 was higher when the previous crop was cereal than in 1991 when the previous crop was peas.Pratylenchus crenatus was more prevalent thanP. penetrans. Root-knot nematodes(Meloidogyne hapla) were detected at a few sites at low population levels only in 1991. In 1991,Verticillium albo-atrum was detected in all 37 potato fields where fungal analyses were conducted, and the average population was 350 propagules g¹ dry soil. Soil populations ofV. alboatrum did not differ in fields in which either Russet Burbank or Shepody were being grown, nor did previous crops have any effect.Verticillium dahliae was detected in 17 fields at very low populations, usually below 1 propagule g¹ dry soil. There were no significant correlations (P<0.05) between populations of P.crenatus orP. penetrans in soil or roots and populations ofV. albo-atrum orV. dahliae propagules in soil.