The effect of potato virus X on susceptibility of potato tubers toFusarium roseum ‘Avenaceum’

Potato virus X (PVX)-free and mild PVX-infected tuber lines originating from the same Katahdin clone were compared for susceptibility to tuber rot incited byFusarium roseum (Lk.) Synd. and Hans. ‘Avenaceum’. The effect of interval between top-kill and harvest on development ofFusarium tuber rot was also determined. A series of tubers from both PVX-free and PVX-infected tuber lines was either (i) mechanically bruised and inoculated by immersion in a spore suspension ofF. roseum ‘Avenaceum’, (ii) mechanically bruised but not inoculated, (iii) inoculated only or (iv) neither bruised nor inoculated. Tubers from all treatments were then stored at temperatures of 18–21 C (65–70 F) for a 3-week period prior to being placed at 4 C (39 F) for the remainder of the storage period. The amount of rot was determined after a 5–6 month storage period at the latter temperature. In a 4-year study PVX-free tubers were significantly (1% level) more susceptible to infection byF. roseum ‘Avenaceum’ than tubers infected with mild PVX. PVX-free tubers left in the ground for 2 or 3 weeks after top-kill were significantly (1% level) more susceptible toFusarium dry rot than those infected with the virus; however, there was no significant difference in disease incidence between PVX-free and PVX-infected tubers when harvested 4–5 weeks after top-kill. Tubers, both PVX-free and PVX-infected, remaining in the ground for a 2 week period following top-kill were significantly (1% level) more susceptible toFusarium tuber rot than those harvested 3 weeks after top-kill; similarly, both PVX-free and PVX-infected tubers harvested 3 weeks after top-kill were significantly (1% level) more susceptible than those left in the ground for a 4–5 week interval.     

Investigations into the mode of resistance of potato tubers toFusarium roseum ‘Sambucinum’

In a histological study comparing tuber resistance of potato clone B7200-33 and susceptible variety “Russet Burbank” toFusarium roseum ‘Sambucinum’, the formation of suberin and wound periderm was found to be an important resistance mechanism. In B7200-33 tubers a continuous suberin layer was formed whereas in ‘Russet Burbank’ tubers the suberin was formed in clumps so that the pathogen easily could invade the tissue between the clumps but not through a continuous layer. Wound periderm also was formed at a more rapid rate in B7200-33 than in ‘Russet Burbank’ tubers thereby “walling off” the pathogen and reducing decay.     

Seed potato contamination with fusarial propagules and their removal by washing

Seed potatoes from Maine, New Brunswick (Canada), Wisconsin, Minnesota and North Dakota were examined during 4 years for contaminating fusarial propagules on tuber surfaces. The degree of contamination was estimated by counting the number of infections that developed on cut surfaces of 100 pieces cut from 50 tubers removed from the tops of 6 cwt bags. Lesion counts were made after 2-weeks incubation at 13 to 16 C. Of seventy-seven seed stocks examined, 29 developed lesions on 91–100% of the seed pieces. Twenty-four of these heavily contaminated stocks came from Maine and New Brunswick. For the different years,Fusarium solani was obtained from 70 to 90%, andF. roseum from 5 to 28% of the lesions cultured each year. BothFusaria were on potatoes from the different production areas. The infectious propagules were in soil washed or brushed from tuber surfaces, and surface-borne inoculum from the tubers. A preliminary report on identifying contamibefore cutting. Plant emergence and productivity were correlated with tuber contamination.     

Comparative effects of cut and treated seed tubers vs untreated whole seed tubers on seed decay, Rhizoctonia stem canker, growth, and yield of Russet Burbank Potatoes

Whole seed tubers have been reported to have performance advantages over seed tubers that have been cut, even if the cut tuber pieces are treated with a fungicide dust. For this study, whole seed tubers were compared to cut seedpieces and to cut seedpieces treated with four different commercial fungicide dusts for five consecutive seasons. A new field generation 3 Russet Burbank seed lot was used for each of the five years of this study. Both whole tubers and cut seedpieces were inoculated withFusarium spp., and the seedpieces were then treated with a fungicide dust. Inoculated and uninoculated untreated controls were also included. Emergence,Fusarium seed decay,Rhizoctonia stem canker, stem numbers, and vigor, as well as yield and grade data were obtained.Rhizoctonia stem canker in stems grown from whole seed tubers was significantly higher than in stems from seedpieces receiving fungicide treatment in several of the study years. Predicting whole seed tuber performance is difficult because performance varies more from year to year than performance of cut and treated seedpieces. Yield performance of whole seed tubers was not significantly better than cut and fungicide-treated seedpieces in any experimental year, and yield of large (over 280 g) tubers was significantly less than that recorded for two of the treatments when data from all five years were combined. This study demonstrated that untreated whole seed did not outperform cut and treated seedpieces for vigor, stem numbers, disease ratings, or yield in small plot comparisons for five consecutive seasons.     

Effect of dormancy releasing chemicals on subsequent tuber response tofusarium sambucinum

The effects of the dormancy releasing chemicals, Rindite and bromoethane, on subsequent tuber response to dry rot were evaluated. Seed tubers of the cultivars Sebago and Acadia Russet were treated with Rindite or bromoethane, and subsequently inoculated with sterile distilled water or spore suspensions ofFusarium sambucinum Fuckel f. 6 Wollenw. After storage for 1 or 11/2 months, tubers were rated for dry rot and dormancy release. Development of seed tuber breakdown byFusarium was not significantly affected by pretreatment with Rindite or bromoethane regardless of any effect on tuber dormancy.     

Impact of Seed Cutting and Seed-Borne Inoculum on Daughter Tuber Common Scab and Plant Growth

Common scab (CS), caused primarily by the filamentous, soilborne bacterium Streptomyces scabies, creates significant challenges in the production of quality potato tubers in global growing regions. Over the past several decades, numerous studies been conducted to improve our understanding of the impact of cultural and pesticide treatments for managing the health of progeny daughter tubers. None of the previous studies, however, have addressed differences between the impacts of CS from whole seed vs. cut seed pieces on resulting disease on daughter tubers. A greenhouse trial was conducted during 2013–2014 to assess the impact of seed type and CS severity on plant health and CS on daughter tubers. Cut and suberized ‘Snowden’ seed pieces (~2 oz.) exhibiting 0, 5, and ≥50% CS severity were sown in 3-gal pots containing a 50:50 mix of sterilized sand and field soil. Whole ‘Snowden’ seed tubers (~2 oz.) with the same three levels of CS severity were sown under the same conditions. At harvest, approximately 20% of daughter tubers from asymptomatic seed pieces (both cut and whole) exhibited symptoms of CS. Disease incidence and severity significantly increased for pieces that had 5 and ≥50% CS across both experiments. Plants grown from whole seed had significantly higher yield, on average, when compared to cut seed. Daughter tubers produced from whole seed resulted in higher CS incidence than those from cut seed in one of our two experimental trials. Our results indicated a clear advantage to plant common scab-free seed potatoes with the aim of producing healthier daughter tubers.     

Fungicide treatment of seed tubers infected with thiabendazole-resistantHelminthosporium solani andPolyscytalum pustulans for controlling silver scurf and skin spot on stored progeny tubers

Summary Seed tubers, cv. Désirée, derived from stocks treated annually with thiabendazole were infected with thiabendazole-resistant strains ofHelminthosporium solani andPolyscytalum pustulans. Samples of seed tubers were either untreated or immersed for 5 min in fungicide suspensions of thiabendazole, imazalil or thiabendazole plus imazalil and planted on four farms in 1988 and 1989. After harvest, tuber samples from each treatment were treated with thiabendazole and stored for 6 months. Applying imazalil or thiabendazole plus imazalil to seed tubers decreased the severity of silver scurf and skin spot on stored progeny tubers. Thiabendazole applied to seed tubers or to progeny tubers after harvest did not affect the severity of either disease, but post-harvest treatment decreased the incidence of black scurf after storage.     

Effect of production temperature of seed potatoes on subsequent yielding potential

A two year experiment was conducted to test if the temperature environment under which seed potatoes are produced significantly affects the tuber development and yield of the resultant potato plants. Six temperature regimes were established in the controlled facility of the Biotron. Two generations ofSolanum tuberosum ‘Kennebec’ tubers were grown in these environments and the yielding ability of plants produced from these tubers was tested in greenhouse facilities. Plant growth and tuber yields were similar to those which might be expected under field conditions, and marked differences in the development and productivity as a result of the production environment of the seed tubers were apparent. However, no evidence was found to support the contention that seed potatoes originating from cooler environments had any increased potential to produce higher yielding plants than comparable seed from warm environments. Even within a generation, the highest yields were found in the warmest environments, somewhat modifying the concept that the potato is strictly a cool-season crop. Other possible non-pathogenic explanations for previously observed differences in seed quality as a result of the production environment are discussed.     

The control of silver scurf and development of thiabendazole resistance inHelminthosporium solani as affected by the rate of fungicide applied to potato seed tubers

Summary Seed tubers were immersed in suspensions of thiabendazole (Storite) or thiabendazole plus imazalil (Extratect) at different concentrations and planted in a field experiment. During the following 2 years samples of the produce were planted after treatment with the same fungicide formulation used on the seed. Silver scurf on daughter tubers decreased as concentrations of fungicide increased and Extratect gave better disease control than Storite applied at the same thiabendazole concentration. Isolates ofH. solani resistant to thiabendazole were found on seed tubers 6 weeks after treatment with Storite, and also on daughter tubers after the first application of the higher rates of Storite; their incidence increased with further annual treatments. In 3 years no thiabendazole-resistant isolates were found after treatment with Extratect. Chlamydospores ofH. solani developed when sensitive isolates were subcultured onto agar containing thiabendazole. Isolates sensitive to thiabendazole were slightly more sensitive to imazalil than resistant ones.     

Serogroups ofErwinia carotovora involved in systemic infection of potato plants and infestation of progeny tubers

Enrichment techniques and serological strain typing methods were used to determine the source of stem and progeny tuber populations ofErwinia carotovora (Ec) in 1980 and 1981. Plots were established in a field that had been planted with potatoes since 1972. Seed tubers of cultivars Russet Burbank and Norgold Russet were assayed forErwinia carotovora pv.carotovora (Ecc) andErwinia carotovora pv.atroseptica (Eca) by tuber peeling and direct plating and plating following enrichment in a pectate-based broth. Levels of seed tuber infestation ranged from undetectable to 2.4 × 10⁴ colony-forming units per g peel tissue. Prior to planting Ecc was detected in soil samples from field plots by enrichment in a pectate-based broth. Ec was isolated from symptomless plants with increasing frequencies from 8 weeks following planting regardless of the level of Ec populations in seed tubers. At harvest progeny tuber recontamination was low and not related to levels of seed tuber Ec populations. In 1980, serological typing of representative Ecc isolates indicated serogroups III, XXIX, and unknown strains isolated from the soil but not the seed tubers prior to planting were isolated from stems and progeny tubers. Serogroup XXIX was isolated from soil, seed, stems and progeny tubers in 1981. Throughout both years, Ecc was isolated more frequently than Eca from seed, soil, stems, and progeny tubers. These data emphasize the potential for reinfestation of seed stocks and infection of plants by populations of Ecc that overwinter in soil under Wisconsin conditions.     

Inventaire,distribution et agressivité des espèces ou variétés deFusarium rencontrées sur la pomme de terre ou dans son environnement dans différentes zones agroécologiques du Pérou

Résumé L'inventaire et la distribution de la flore fusarienne dans les 3 zones agroécologiques du Pérou (C?te, Sierra, Haute-Selva) sont étudiés.F. oxysporum est l'espèce la plus fréquemment isolée puis, en ordre décroissant,F. solani etF. roseum (et ce, aussi bien à partir de plantes présentant des sympt?mes qu'à partir du sol). Cette flore s'est révélée très stable d'une région à l'autre. L'inoculation sur tubercules, des souches des différentes espèces ou variétés deFusarium isolées à partir des plantes et du sol entra?ne très fréquemment des pourritures importantes.

---

Summary A survey was carried out ofFusarium species in three agroecological zones in Peru (Coast, Sierra and High Selva) (Table 1). Information was obtained on the characteristics of PeruvianFusarium flora, the distribution of isolates and their aggressivity (Tables 2 and 3). TheFusarium flora is characterised by its stability and the absence of diversity. Thus, it is stable in all three agrochemical zones of Peru (Fig. 1):F. oxysporium is by far the most common species followed byF. solani andF. roseum isolated from both diseased plants and the soil. Qualitative or quantitative differences inFusarium populations were not found between regions in spite of widely different climatic conditions, crop rotation systems and land preparation practices. It is notable that a close relationship was found between the plant and soil populations: the proportions ofFusarium species or varieties present in the soil and in the plant were similar. Furthermore, aggressivity on tubers of the differentFusarium species or varieties whether isolated from plants or the soil indicated that the risks of crop contamination and the subsequent development of rots were closely related to the health status of the soil and possibly of the plant (Table 4). Finally, this study shows that the biology ofFusarium is a complex problem which involves the soil, the plant and the tuber. It should be examined by studying factors affecting fungal wilt symptom expression and populations ofFusarium isolates during tuber storage.

     

The role of stem inoculum in the transmission ofFusarium sulphureum to potato tubers

Summary Over 2 years, seed tubers or stems were inoculated withFusarium sulphureum Schlecht. (F. sambucinum Fuckel f. 6 Wollenw.) and the incidence of dry rot on daughter tubers assessed by standardised wound tests. The amount of stem and soil inoculum was also measured in one year. Inoculating stem bases resulted in greater concentrations of spores on the stem bases, greater soil populations at harvest and more dry rot on tubers than inoculating the seed tuber. Overall, the incidence of dry rot and the amount of stem and soil inoculum was similar for the three methods of haulm destruction: cutting and removing the stems, applying sulphuric acid or applying diquat dibromide to the growing plants.     

Quality of stored potatoes improved by chemical treatment

A combination spray of CIPC, thiabendazole, and chlorine applied to potatoes at time of storage negated the detrimental effect of CIPC when applied to freshly harvested tubers. It also prevented sprouting and reduced the incidence of pressure bruise. The application of thiabendazole and chlorine reduced Fusarium tuber rot and the degree of tissue degradation around wounds, thereby increasing tuber quality.     

Influence of seed tuber infestation,chemical seed treatment,and pre-harvest climate on incidence of gangrene and dry rot of potato (Solanum tuberosum L.)

Summary In each of the five years 1978 to 1982, seed lots of cv. Bintje, variously infested byPhoma foveata Foister andFusarium solani var.coeruleum (Sacc.) Booth, as found by wound and cut tests, respectively, were planted in a series of field experiments at six sites in Sweden. A statistically significant relationship between seed and progeny infestation was found forP. foveata each year, and in three years forF. solani. Benomyl and thiabendazole mist treatments of seed tubers at grading in spring controlled the development of gangrene and dry rot in treated seed tubers, but did not consistently reduce the levels ofP. foveata andF. solani infestation in progeny from treated seed tubers. The site of cultivation markedly influenced mean levels ofP. foveata infestation, which were found to be related to temperature and rainfall during a 40 day pre-harvest period at the trail sites; however, mean levels ofF. solani infestation were not so related.     

Effect of whole seed tuber size and pre-plant storage conditions on yield and tuber size distribution of Russet Burbank

Field experiments were conducted in 1995, 1996, and 1997 at Agriculture and Agri-Food Canada’s Harrington Research Farm to assess the effect of whole seed tuber size and pre-plant seed storage conditions on processing yield (> 51 mm dia.) of potato (Solanum tuberosum L. cv Russet Burbank). Following commercial storage, seed tubers were stored at 4.4 C then subjected to one of three pre-plant treatments: (1) planted directly from storage, (2) held at 10 C for 3 wk before planting, or (3) green-sprouted for 3 wk before planting. Five sizes of whole seed were used (28, 42, 56, 70, and 84 g) with a variable size cut seed treatment added for comparison. Plots were harvested 138,134, and 131 days after planting in 1995, 1996, and 1997, respectively. Cut seed produced a higher yield of tubers > 51 mm diameter in comparison to all whole tuber seed sizes, with the exception of the 28 and 56 g sizes. In terms of total yield, the 28and 42-g whole seed tubers yielded significantly less than all other seed sizes examined. Warming or greensprouting seed tubers prior to planting did not increase tuber yield. The larger whole seed tuber sizes tended to result in greater numbers of stems and tubers per plant. To maximize marketable yield of Russet Burbank planted from whole seed tubers, it is recommended that the seed be between 28 and 42 g in size. Accepted for publication 25 May 2004.     

Role of seed tubers in the spread of plant pathogenicStreptomyces and initiating potato common scab disease

The influence of tuber-borne pathogenicStreptomyces on potato common scab incidence in daughter tubers was examined under micro-plot conditions. Visually healthy tubers, surface-disinfested healthy tubers, and tubers with 25% scab coverage were planted in pasteurized soil. At 30, 57, and 93 days after planting, soil and belowground plant parts were sampled from various zones around the mother tuber. The total population of actinomyctes was determined by plating on a semiselective medium, and colonies of pathogenicStreptomyces were identified using polymerase chain reaction (PCR) targeting thetxtA gene. At day 30, pathogenicStreptomyces populations were below detectable levels, whereas by day 93, measurable levels were present on the belowground plant parts and in soil adjacent to scabby mother tubers at 10⁴ to 10⁵ CFU g^?1 soil. Incidence of scab in the progeny tubers was 89% at harvest. Progeny tubers produced by visually healthy seed tubers had an incidence of 60% scab and substantial populations of pathogenicStreptomyces were present in the zone near the mother tuber (10⁴ CFU g^?1 soil). Plots planted with surface disinfested seed tubers had a very lowStreptomyces population in the tuber zone and yielded 100% marketable tubers. A perfect correlation (r = 1.00) was found between the population densities of pathogenicStreptomyces in the root zone and daughter tuber disease incidence indicating that measurement of such populations in the field can serve as an excellent predictor of scab disease. After harvest, populations of pathogenicStreptomyces (10⁶ to 10⁷ CFU g^?1 lesion tissue) remained high on the mother tubers.     

Elimination of fusarial contamination on seed potatoes

Pieces cut from seed potatoes naturally contaminated with fusarial propagules may produce poor stands if they are planted untreated in cold soils that retard sprouting. In 1972 and 1973, contaminated tubers were given various physical and fungicidal treatments in Maine to eliminate infectious propagules, and planted in North Carolina and Maine. Freshly cut and precut pieces from each of the treatments were evaluated for control of seedpiece decay. Washing tubers improved stands slightly and tended to reduce the number of small plants but did not increase yields. Precut pieces yielded significantly less than fresh cut in Maine and significantly more in North Carolina. All fungicides increased yields at both locations. Thiabendazole and benomyl practically eliminated the inoculum. In a pilot test, pieces cut from tubers sprayed with thiabendazole and benomyl in Maine produced plants and yields in North Carolina that confirmed experimental results and showed that fungicides reduce fusarial inoculum on seed potatoes.     

Interaction ofErwinia spp. andFusarium roseum ‘Sambucinum’ on the Russet Burbank potato

Laboratory and field studies with the Russet Burbank (RB) potato provide evidence for synergism betweenErwinia carotovora var. atroseptica (Ea) andFusarium roseunt ‘Sambucinum’ (Fs). When these pathogens were inoculated together, the severity of tuber rot was significantly greater than when either pathogen was inoculated separately. Similarly, these pathogens interacted to reduce yield. When both organisms were uniformly applied to puncture wounds on potato seed (inoculum suspension consisted of 10⁸ cells/ml Ea and 10⁵ cells/ml Fs), the total yield was reduced by 46% and U.S. #1 yield by 53%. These reductions occurred even though blackleg symptoms (caused by Ea) were negligible (< 1%). In contrast, inoculations withErwinia carotovora var.carotovora (Ec) and Fs did not interact to reduce potato yield. Potato yields were also not influenced when these pathogens (Ea, Ec, Fs) were separately inoculated.Verticillium wilt (Verticillium dahliae) was significantly less when tubers were inoculated with either Ea, Ec, Fs, Ea + Fs, or Ec + Fs than with uninoculated tubers.     

Cultivar response to Fusarium storage rot as affected by two methods of seed origin propagation; Clonal selection andin vitro culture

Progeny tubers from seed potatoes originating from either a traditional clonal selection method or the more modernin vitro tissue culture method of propagation were tested for storage rot response following inoculation of three tuber sites with twoFusarium species. Significant differences were found among disease responses for the twoFusarium species and for the four cultivars tested. Disease symptoms were less severe forF. solani var.coeruleum than forF. sambucinum. Fusarium sambucinum caused less disease in Superior than Kennebec, Russet Burbank and Sebago. Seed propagation method did not significantly affect disease response except for one case;in vitro culture of Kennebec had less disease due toF. sambucinum at the tuber side inoculation site than clonal selection. Kennebec and Superior inoculatedF. sambucinum had significant differences with respect to the number of years of field propagation for the tuber side inoculation site and for the tuber mean rot index. Significant differences in number of years of field propagation were also found for eye-ends of Superior tubers and stem ends of Russet Burbank tubers inoculated withF. solani var.coeruleum.     

Seasonal differences in the field performance of micropropagated potato under a short growing season in Quebec

Field performance comparisons between ex vitro plantlet-derived (EVPD) plants and seed tuber-derived (STD) plants ofRusset Burbank were conducted for two consecutive years under a short growing season in Quebec. The EVPD plants produced more potential seed tubers than STD plants although total tuber biomass of EVPD plants was less than that of STD plants. The frequency and weight distributions of tubers formed by the two types of propagates were different. The EVPD plants produced significantly more small sized tubers and fewer large sized tubers than the STD plants. Average tuber weight was less for EVPD than STD plants for each of five size categories. No significant differences were found in the fresh and dry weight of plants, leaves and stems at harvest time. However, plant height and growth habit differed between the two types of propagates. The EVPD plants had a unique appearance. They produced a single stem with extensive axillary bud development. The EVPD plants were apparently more susceptible to early water stress in the field than STD plants, probably due to an earlier production of stolons. No differences were found between ex vitro plantlet- or microtuber-derived plants, in plant growth or yield characteristics.