Resistance of tubers from different potato cultivars to soft rot caused byErwinia carotovora subsp.atroseptica

Mechanically harvested tubers of 14 potato cultivars grown on both loamy sand and silt loam soils were evaluated for resistance to bacterial soft rot caused byErwinia carotovora subsp.atroseptica. Cultivars were also assayed for calcium and dry matter content to determine possible correlations with soft rot resistance. Resistance of potato tubers to bacterial soft rot was assayed after harvest by inoculating tubers and determining percent surface area decayed after four days in a mist chamber. Tubers of the cultivars differed widely in resistance to bacterial soft rot. The ranking of the resistance of tubers from different cultivars to bacterial soft rot was similar for both soils, although disease severity in tubers from a particular soil type varied with the season. Of the cultivars tested, tubers of Butte, Russet Burbank, and Nor-gold Russet were ranked as the most resistant, whereas tubers of Redsen, Norchip, Norland and Belchip were rated as the most susceptible. Tubers of Rhinered, Red La Soda, Superior, Pontiac, Atlantic, and Nooksack were intermediate in resistance. Neither calcium concentration in medullar tissues nor dry matter of potato tubers alone could be correlated with ranking of the cultivars with respect to severity of bacterial soft rot. However, a multiple linear regression model incorporating both variables indicated that tubers with a high content of both calcium and dry matter were likely to be less susceptible to bacterial soft rot than were tubers with lower percentages of these variables.     

Comparison of the effectiveness of different methods of screening for bacterial soft rot resistance of potato tubers

Tubers from eight potato cultivars (cvs) grown at two different locations in Wisconsin were tested for bacterial soft rot resistance using different inoculation techniques. The procedures included 1) point inoculations of tubers with different inoculum levels followed by incubation in ambient or low oxygen condtions, 2) inoculation of mechanically bruised tubers followed by incubation in a mist chamber, and 3) a standard slice inoculation method. The point titration test followed by incubation in dew chamber and the mist chamber-bruise test showed similar patterns of resistance for cultivars that were used in these experiments. These two methods are considered to be effective for screening potato tubers for bacterial soft rot resistance. Point titration methods are very useful if only limited numbers of tubers are available. The mist chamber-bruise test is simpler than the other procedures; however, to obtain reproducible results large numbers of tubers are required. Because of the great variability of the results obtained in inoculation of slices, the reliability of this approach can be questioned as a standardized method for evaluation of resistance. Tubers of somatic hybrids ofS. brevidens andS. tuberosum and their sexual progeny were significantly more resistant to bacterial soft rot than tubers of moderately resistant cultivars when evaluated by each of the assay procedures.     

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.     

Post-harvest decay of second growth-induced glassy tubers of potato (Solanum tuberosum L.) cv. Bintje in relation to their specific gravity

Summary After the induction of second growth, tubers may develop physiological rot following complete starch depletion. Tubers from two crops were graded into specific gravity classes after harvest and the development of decay was monitored during storage for 9 weeks. Most decay took place within the first 5 weeks. Tubers with a specific gravity<1.010 usually decayed completely. About 80% of tubers with a specific gravity>1.020 remained intact. In the specific gravity class 1.010–1.020 more than 50% of the tubers were affected, but they did not all decay completely.     

Inoculation of potato tubers withErwinia carotovora during simulated commercial washing and fluming practices

The potential for bacterial soft rot in potato tubers was affected by laboratory simulation of some components of fluming and washing practices at commercial packinghouses. The potential was expressed as disease severity (average percentage surface decayed) after a standard 4-day incubation at 20°C in a mist chamber. Increased disease resulted when there was an increase in the following factors: a) duration of immersion of tubers in water; b) population of bacteria suspended in water; c) hydrostatic pressure on submerged tubers, and d) concentration of a surfactant (Triton X-100) in the suspensions. A sample of tubers from each tuber lot was uniformly moistened with tap water and then incubated to determine a base-level disease severity. Disease severity in Russet Burbank tubers from commercial storage increased from the base-level of 0.8% to 76% when tubers were immersed in 5 × 10⁶ colony-forming units (cfu)/ml ofErwinia carotovora pv.carotovora (Ecc) for 64 min prior to incubation. Disease severity was 64% when tubers were immersed in a similar suspension for only 0.1 min, but with a hydrostatic pressure of 230 cm of water. Severity values fourto fivefold above control levels (from immersion in water) resulted from an immersion for 5 min in 5 × 10³ cfu/ml with hydrostatic pressures of 5, 180, or 370 cm of water. A 20-fold increase in severity occurred when Red LaSoda tubers were immersed briefly (less than 5 s) in 5 × 10⁶ cfu/ml. Rinsing these tubers with tap water after inoculation, but prior to incubation, did not affect the subsequent development of decay. Thus, the high potential for bacterial soft rot in tubers that have been flumed or washed by water concentrated with soft rotErwinia cannot be reduced by washes or rinses with clean water.     

Calcium and potassium fertilization of potatoes grown in North Florida. II. Effect on the bacterial soft rot potential in the tubers

In studies on a sandy soil in Florida over a 3-yr period (1984–86), applications of Ca (CaSO₄) inconsistently affected the bacterial soft rot potential of potato tubers (Solanum tuberosum). The potential was estimated from the severity of the disease (percent surface area decayed) in tubers that had been immersed in an aqueous cell suspension ofErwinia carotovora subsp.carotovora and then incubated 4 days in a mist chamber at 24 C. With freshly harvested tubers (tested within 5 days after harvest), disease severity averaged 49, 11, and 4% over all treatments in 1984, 1985, and 1986, respectively, which was roughly proportional to rainfall on the crop,e.g., 37, 18, and 15 cm, respectively. Disease severity decreased, did not change, and increased with increased Ca rate (0, 450, and 900 kg.ha^-1) in 1984, 1985, and 1986, respectively. In each season, severity was affected by interactions involving the Ca treatments. Most interactions involved cultivar. The efficacy of Ca applications to potatoes grown in low Ca soils for enhancement of tuber resistance to bacterial soft rot may be limited by factors associated with environment or cultivar that are not completely understood.     

Bacterial soft rot potential in washed potato tubers in relation to temperatures of tubers and water during simulated commercial handling practices

The bacterial soft rot potential in potato tubers was affected by differences in temperature between tubers and suspensions ofErwinia carotovora at the time of inoculation by immersion. In general, disease severity after incubation was higher when tuber temperatures were higher as opposed to equal to or lower than that of water containing cells of the bacterium. Disease severity was also greater when tubers were stored at 20° to 23°C in contrast to 4° or 26° to 30°C for 16–18 h prior to immersion. Tubers with a pulp temperature of 8°C were more prone to bruise injury as compared with those at 18°C when struck with a pendulum type bruising instrument. When the injured tubers were inoculated and incubated, most bruises became infected with soft rot bacteria.     

The incidence of decay and factors affecting bacterial soft rot of potatoes

The incidence of tuber decay in rail car shipments of potatoes from the State of Washington was determined from 1965 to 1969 inclusive. Reinspection certificates revealed that 7.9% of the rail cars of potatoes shipped during this period were rejected due to tuber defects; tuber decay accounted for 63% of these rejected cars. Percentage of rejections due to tuber decay was greater for Russet Burbank than for Norgold Russet potatoes. Temperature, moisture, and oxygen levels influenced development of bacterial soft rot in freshly harvested potatoes and in potatoes stored for 3 months at 35 F (2 C) previous to treatment. When tuber surfaces were kept dry, no soft rot developed in 11 days over ranges of 50–70 F (10–21 C) and 2–20.5% oxygen levels. Freshly harvested tubers partially immersed in water did not rot when cooled to 40 F (4.4 C) in < 24 hours and held for 8 days under either 20.5 or 4% oxygen levels; however, tubers, rotted when stored similarly but at 50 F or higher temperatures. Partially immersed tubers incubated for 1 day or longer at 70 F developed soft rot in a low oxygen (4%) when later stored for, 8 days at 40 F. When rot occurred, the amount was always greater under lower oxygen levels irrespective of storage temperature. Of various cooling methods tested in rail cars loaded with 100 lb (45.4 kg) sacks of potatoes, prechilling of tubers and icing of cars prior to loading lowered floor temperatures most rapidly. Icing cars after loading lowered floor temperatures the slowest. In a carton shipment, the temperature remained above 68 F (20 C) in cartons after 8 days in transit, even though the wall and floor temperatures had cooled to near 55 F (12.8 C) by the second day. Oxygen level surrounding, tubers in the center of car loads of 100 lb sacks of potatoes was approximately 20.5% after 8 days transit.     

Application of a PCR-based test for detection of potato late blight and pink rot in tubers

A polymerase chain reaction (PCR)-based test for potato late blight (Phytophthora infestans) and pink rot (P.erythroseptica, P. nicotianae) diseases has been developed for use with potato tuber tissue. Primers based on sequence analysis of the ITS2 region of ribosomal DNA of late blight and pink rot pathogens were utilized in PCR assays of inoculated tubers and tubers harvested from plots known to have late blight and/or pink rot. Assays of artificially inoculated Kennebec and Russet Burbank tubers revealed thatP. infestans was detected by PCR as early as 72 h after inoculation and in the absence of visible symptoms. Much higher detection frequencies were obtained by PCR compared with plating on selective medium or placement of tissue in moist chambers. Tubers from plots known to have late blight and/or pink rot were tested using the PCR assay. Assay of late blight lesions showed ca. 80% recovery for late blight-infected tubers from the field. Results indicate that the PCR assay provides a rapid and accurate test for diagnosis of late blight and pink rot in potato tubers.     

Suppression of bacterial soft rot in potato tubers by application of kasugamycin

An immersion in aqueous solutions of Kasumin®, containing kasugamycin at 10 to 320 mg/L (ppm) for 1 to 320 sec delayed or prevented the development of soft rot on inoculated (Erwinia carotovora subsp.carotovora) tuber disks incubated over wet filter paper at 24C for 24 to 72 hr. Treatment efficacy decreased as inoculum level and incubation period increased. Short immersion periods were not as effective as longer ones. When stored tubers were inoculated withE. c. carotovora and incubated up to 5 days in fog chamber at 20 C, immersion treatments in 20 to 400 ppm kasugamycin either had no effect or increased soft rot development. By contrast, when the stored tubers were cut into sections before inoculation and treatment, immersion in 300 ppm reduced soft rot development on the cut surfaces from 83% (inoculated controls) to 3.2%. With non-inoculated sections, treatment with 25 ppm reduced the SAD from 13.3 to 0.6%. Wash or rinse treatment of freshly harvested tubers in 40 to 160 ppm produced a significant reduction in the severity of bacterial soft rot among tubers incubated for 72 to 96-hr. The 160-ppm treatment delayed disease onset by at least 24 hr. Pre-washing freshly harvested tubers with clean or chlorinated water prior to antibiotic treatment did not consistently improve the efficacy of the kasugamycin treatment.     

Evaluation of potato varieties and selections for resistance to bacterial soft rot

Potato varieties and selections were evaluated for resistance to bacterial soft rot caused byErwinia carotovora subsp. carotovora and Erwinia carotovora subsp. atroseptica in mist chamber. A randomized complete block design with a single treatment and 3 replications was used in this study. Potato lines were inoculated with bacterial suspension (10 tubers / line) using the puncture inoculation method and incubated for 4 days in a mist chamber at 21 C and 100 % relative humidity in the dark. Although there were differences in incidence of soft rot and in amount of weight reduction, most of the potato lines were susceptible to tuber soft rot. Mean incidence (%) of soft rot ranged from 10 to 100%. Mean reduction of tuber weight (%) ranged from 0.13 to 16.43 %. Among the varieties and selections tested, AF 522-5 was the most resistant to tuber weight loss, while AF 1424-7 was most susceptible. There were also significant differences between years, and a variety by year interaction. Testing over a period of years is recommended. A significant correlation coefficient of soft rot incidence (%) and reduction of tuber weight (%) was obtained (r=0.65; P=0.05), indicating that incidence was a fair measure of soft rot potential. However, the greater variability in results for incidence make weight loss a better measure of soft rot reaction. There was a significant difference among varieties in the reduction of tuber weight when potato lines were inoculated either 1 month or 2 months after harvest, but the interaction of time by year prohibits a conclusion as to which time gives a better test reaction. Late maturing varieties had slightly less weight loss than earlier maturing varieties.     

Reducing the potential for bacterial soft rot in potato tubers by chemical treatments and drying

The potential for bacterial soft rot caused byErwinia carotovora in freshly inoculated potato tubers was reduced up to 99% by immersion for 5 min in solutions of sodium hypochlorite (chlorine bleach) containing up to 10,000 ppm chlorine. Reductions up to 93% were achieved using a combination treatment of immersion in 1% citric acid for 5 min followed by airdrying. Immersion treatment alone in 1% aqueous solutions of citric, acetic, ascorbic, or malonic acid also significantly reduced the soft rot potential. In contrast, no reductions accompanied treatment with solutions of potassium or calcium acetate. All treatments including the combination immersion/airdrying treatment were much less effective if tubers had been infiltrated initially with soft rotErwinia or had numerous mechanical injuries. If tubers had not been infiltrated with the causal organism, immersing them in 1% citric acid reduced the potential nearly as much as a similar treatment with 1000 ppm chlorine. A 30-sec immersion in the latter was less effective than a similar treatment with 500 ppm a.i. CGA 78039, an experimental bactericide. However, air-drying, coupled with provisions for keeping tuber surfaces free from moisture, remains the most effective means of reducing losses to bacterial soft rot.     

Evaluation of immunofluorescence with monoclonal antibodies for detecting latent bacterial ring rot infections

Corynebacterium sepedonicum was detected in symptomless potato stems and tubers with immunofluorescence using monoclonal antibodies specific for the bacterial ring rot pathogen. The concentration of bacterial cells in potato tissue preparations ranged from >500 cells/microscope field to 1 cell per preparation. Symptomless tubers containing ring rot bacteria planted in field plots yielded plants with ring rot symptoms, plants with latent ring rot infections, or plants with no detectable levels of ring rot bacteria. Tubers with the greatest number of bacteria were most likely to develop plants expressing ring rot symptoms, but even some seed tubers with a low number of bacteria developed into plants with symptoms. Some seed tubers with high levels of ring rot bacteria produced plants with only low numbers ofC. sepedonicum.     

Influence of temperature and length of storage on resistance of potato to tuber rot induced byErwinia chrysanthemi

Tubers of 11 clones ofSolanum tuberosum subsp.andigena (andigena) and 12 cultivars ofS. tuberosum subsp.tuberosum (tuberosum) were inoculated with water suspensions (5.5 × 10⁴ 5.5 × 10⁵, 5.5 × 10⁶ CFU/ml) ofErwinia chrysanthemi. Tubers were inoculated immediately after harvest and after 6 and 16 wk of storage at 4 and 23°C. Tuber rot incidence in andigena and tuberosum increased as inoculum concentration increased. Based on tuber rot severity, clones of andigena were classified as resistant, intermediate, or susceptible and cultivars of tuberosum were classified as intermediate or susceptible. Rot severity increased in all tubers stored at 4°C and in tubers of tuberosum stored at 23°C; rot did not increase in tubers of andigena stored at 23°C. Electrolyte leakage (EL), total sugars (TS), reducing sugars (RS), non-reducing sugars (NRS) and dry matter (DM) were determined in non-inoculated tubers. There was a significant positive correlation between the rate of EL, concentration of RS and tuber rot in andigena and tuberosum. Tuber rot and DM were negatively correlated in tubers of andigena; but they were not correlated in tuberosum. Clones of andigena with low EL, TS, RS, and high DM were resistant to tuber rot, and the incidence of tuber rot in these clones was much less influenced by temperature and length of storage. The influence of temperature and length of storage on susceptibility toE. chrysanthemi may be explained by increased cell membrane permeability; increased leakage of accumulated sugars in potatoes stored at 4°C could favor bacterial proliferation resulting in more disease.     

Potato clone variation in blackspot and soft rot susceptibility,redox potential,ascorbic acid,dry matter and potassium

Tubers of 11 potato clones were compared for susceptibility to blackspot and soft rot, redox potential, ascorbic acid, dry matter, and potassium content. Evaluations were made before and after 6 mo storage at 3.9C. Clonal behavior was generally consistent over 2 yr. Significant differences occurred among clones for each factor except redox potential. Blackspot and soft rot were positively correlated in 5 of 8 comparisons. Neither blackspot nor soft rot was correlated with ascorbic acid or redox potential. Blackspot was positively correlated with dry matter in the fall but not after storage and was negatively correlated with potassium. Soft rot evaluated in air or air plus 8% CO₂ was positively correlated with dry matter in only 2 of 8 comparisons. Soft rot susceptibility did not increase with storage when inoculated discs were incubated in air but did increase when the discs were incubated in air plus 8% CO₂. Ascorbic acid was negatively correlated with redox potential only before storage and decreased to varying degrees in all clones during storage.     

Relationship of potato tuber periderm resistance to plant water status

Potato (Solanum tuberosum L. cv. Russet Burbank) tuber periderm resistance to water loss was monitored during the harvest season. Periderm resistance of tubers from water-stressed plants was compared with tubers from unstressed plants throughout a six-week harvest period, in order to determine the effect of plant condition on tuber resistance to water loss. Tubers stored for ten days at 4°C immediately following harvest were also monitored to determine if storage enhanced periderm resistance and if any difference occurred between tubers from stressed vines compared with those from unstressed vines. During the harvest season, tuber resistance to water loss was positively correlated with plant water stress, as measured by leaf water potential and leaf diffusive resistance. Storage of tubers after harvest also caused an increase in periderm resistance. The commercial practice of vine killing, therefore, may have a positive effect on reducing weight loss in storage by enhancing the resistance of tuber periderm to water loss.     

Resistencia de tuberculos a las fusaria que afectan papa en el Peru

Fungi of the genusFusarium Link isolated in Perú from potatoes (Solanum tuberosum L. subsp.andigena Juz. & Buk.) affected by: i) wilt, ii) dry rot of stored tubers, iii) secondary rot in tubers affected by “cork” disease (potato mop-top virus?), caused dry rot when inoculated to tubers of Renaacimiento variety. The identification of some of theseFusaria suggests thatFusarium solani Snyder & Hansen is associated with wilt and dry rot, andFusarium oxysporum Snyder & Hansen with rot secondary to cork disease. Tubers of eight potato varieties inoculated with fourFusaria representative of those isolated showed a great range in levels of susceptibility to colonization by theseFusaria, Sapa being the most susceptible variety, and Mantaro appearing to be the most resistant. These results suggest that useful levels of resistance toFusarium tuber rot are available in the Peruvian germ-plasm.     

Reaction of potato tuber slices toPhytophthora infestans in relation to physiological age

Tuber resistance toPhytophthora infestans was studied in relation to physiological age in tubers of the cultivars Atzimba, Katahdin, Kennebec, and Sebago. Resistance to race1,2,3,4 was evaluated in freshly harvested tubers, and tubers stored at 5 C for up to 215 days. Atzimba tubers were highly resistant when freshly harvested but became increasingly susceptible as they aged physiologically. Tubers of the other three cultivars were susceptible when freshly harvested and also when aged. Further, 57 tuber selections from among 11 crosses initially gave resistant reactions. However, after storage for six months at 5 C, 26.3% of the selections remained resistant, 22.8% were moderately resistant, 31.6% moderately susceptible, and 19.3% fully susceptible.     

Variation in pathogenicity on potato tubers and sensitivity to thiabendazole of the dry rot fungusFusarium avenaceum

Summary The majority of isolates ofFusarium avenaceum caused dry rot on potato tubers; many were as pathogenic asF. coeruleum. Pathogenicity ofF. avenaceum was not related to the plant species from which the isolates originated. Tubers of potato cv. Cara were more susceptible than those of cvs Romano or Maris Piper. Temperature (5–15° C) had no effect on lesion depth but lesions tended to be slightly wider at the lowest temperature. Two isolates (of 61) from wheat and white lupin had a moderate level of resistance to thiabendazole. The results are discussed in relation to the control of dry rot in stored potato tubers.     

Introgression and stabilization oferwinia tuber soft rot resistance into potato after somatic hybridization ofsolanum tuberosum ands. brevidens

Resistance to potato tuber soft rot caused byErwinia carotovora was transferred fromSolanum brevidens to the cultivated potato over the course of four backcross generations originating from a somatic hybrid. Soft rot reactions were determined via a tuber plug inoculation method developed during the course of these experiments. Soft rot resistance was highest in the somatic hybrid (only ca. 20% of tubers and plugs showed evidence of severe rotting) and lowest among progeny of control potato x potato crosses (ca. 80% of tuber plugs showed severe rot). Backcross generations involving somatic hybrids were intermediate in their reaction, and resistance stabilized to about 60% of tuber plugs showing severe rot in the BC₂ through the BC₄. Reciprocal crosses showed no difference in the inheritance of soft rot resistance, indicating that neitherS. brevidens norS. tuberosum donor cytoplasm had a significant effect on the expression of resistance. Crosses between BC₃ siblings where noS. brevidens genetic markers were detected but resistance was segregating demonstrated a dosage effect for soft rot resistance. We conclude that introgression of soft rot resistance has occurred and that at least one locus responsible for resistance inS. brevidens now resides in theS. tuberosum genome.