Evaluation of yeasts for biological control of Fusarium dry rot of potatoes

Thiabendazole-resistant strainsof Fusarium sambucinum andF. solani var.coeruleum threaten to negate chemical control options for post harvest treatment of Fusarium dry rot. Biological control of dry rot of storage tubers is feasible using bacterial antagonists (25). The impact of yeasts on dry rot has not been investigated. Initial biological control tests employed strains of twenty species of yeasts from the ARS Culture Collection (NRRL). Strain selection was based on strain isolation from plant matter or from environments that would indicate a high likelihood of strain survival in soil. The control potential of these and 29 additional strains isolated from soil adhering to recently harvested tubers was evaluated using a whole Russet Burbank tuber bioassay. At 2xl0⁶ cells/ml, only two unidentified strains andCryptococcus laurentii strain NRRL Y-2536 reduced disease (P=0.05, P=0.10, respectively) while bacterial strainPseudomonas fluorescens 2-79 (NRRL B-15132) was more effective (P=0.01). Conversely,Debaryomyces robertsiae increased disease (P=0.05). No yeast strains significantly controlled disease in a subsequent trial. One of six additional strains ofC. laurentii (P=0.10), none of five strains ofPichia farinosa and neither unidentified strain controlled disease at 5 x 10⁷ cells/ml whereasP. fluorescens again reduced disease (P=0.01). After 6 h, four yeast strains decreased and three increased conidial germination ofF. sambucinum R-6380 though there were no differences after 18 h. Five yeast strains, including two strains ofC. laurentii (NRRL Y-2536, NRRL Y-7139) were marginally effective in controlling disease incited byF. solani var.coeruleum S-1257. Though additional testing may identify yeast strains with considerable promise as biological control agents active against Fusarium dry rot, evidence to date indicates bacterial agents have a greater potential for commercial development.     

Population structure ofGibberella pulicaris (AnamorphFusarium sambucinum) from potato tuber dry rot in North America and Europe

Gibberella pulicaris is the sexual stage ofFusarium sambucinum, the major cause of potato tuber dry rot in North America and Europe. In a previous study 42 strains from dry-rotted tubers in North America were analyzed for genetic diversity by mating type and vegetative compatibility group (VCG) tests. In the present study, an additional 96 strains from North America, 21 strains from Europe, and six strains from other geographic areas were analyzed. Both mating types, MAT1-1 and MAT1-2, occur widely outside North America. In contrast, all but two, Canadian, strains of the 138 North American strains analyzed to date are MAT1-1. VCG analysis provides additional evidence that genetic diversity ofG. pulicaris from potato tubers is high in Europe but low in the United States. These results suggest that the potential for pathogen change due to sexual recombination is low in the United States, but may be higher in Europe. Limited genetic diversity ofG. pulicaris in the United States indicates that there are likely to be few barriers to heterokaryon formation and asexual recombination in the field. Thus, the potential exists for rapid spread and persistence of advantageous mutations throughout theG. pulicaris population, which may have contributed to the recent proliferation of strains resistant to the fungicide thiabendazole which has been widely used to control tuber dry rot.     

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.     

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.     

Postharvest suppression of potato dry rot (Fusarium sambucinum) in prenuclear minitubers by arbuscular mycorrhizal fungal inoculum

Arbuscular mycorrhizae (AM) have been shown to increase plant resistance to root-rotting pathogens. This study was conducted to determine whether a commercial peat-based medium containing the AM fungusGlomus intraradix (Schenck & Smith) could influence postharvest progression of tuber dry rot in prenuclear minitubers of potato (Solanum tuberosum). Minitubers grown in this medium had significantly less tuber dry rot (20–90% reduction) when later inoculated with the dry rot fungusFusarium sambucinum relative to minitubers grown in an identical peat-based medium without the AM fungus. This disease suppression was also demonstrated in a high-input commercial greenhouse, and occurred despite only trace levels of AM colonization of the parent plants, and with no evidence of enhanced plant phosphorus nutrition or differences in minituber mineral content. These results suggest that the AM fungal inoculum has potential for use in suppression of tuber dry rot of potato.     

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.     

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.     

Contamination of soil and transmission of seedborne potato dry rot fungi (Fusarium spp.) to progeny tubers

A survey of selected potato soils in Maine was made to determine the species and populations ofFusarium spp. present.Fusarium solani ‘Coeruleum’ was most often isolated butFusarium roseum ‘Sambucinum’ was not recovered from any soil. Crops or cropping sequences in general showed no direct relationship to observed Fusaria populations or tuber dry rot. Field studies were conducted to determine the effect ofFusarium contaminated seed on soil and daughter tuber contamination. Whole and cut seed were inoculated withFusarium roseum ‘Sambucinum’ and half of each lot treated with thiabendazole (1500 ppm) to controlFusarium seed decay. Soil populations ofF. roseum ‘Sambucinum’ were higher near plants produced from non-treated, cut seed tubers. No increase inFusarium populations was found between plants or near plants produced from whole or thiabendazole treated seed. Daughter tuber contamination was greatest from plants produced from non-treated contaminated cut seed, and lowest from whole or treated seed. Whole non-treated seed produced daughter tubers with contamination equal to treated whole seed. This indicates that the use of whole seed could be a method to reduce daughter tuber contamination and reduce reliance on chemical treatments. Cut seed contaminated withFusarium spp. is an important source of daughter tuber contamination which can result in a high amount of tuber dry rot in storage.     

Summit Russet: A new russet potato variety with good fresh market and frozen processing qualities

Summit Russet (A84118-3), the result of the cross A77236-6 x TND329-1Russ, was released in 2003 by the USDA/ARS and the Agricultural Experiment Stations of Idaho, Oregon, and Washington. The vines of Summit Russet are erect, with very thick stems, large yellowish-green leaves and abundant white flowers. The tubers are tan, with medium russet skin, long-flattened shape, a slightly prominent eyebrow, white flesh, and moderately prominent pith. Tuber dormancy is very long. Summit Russet was compared with Russet Burbank in trials across the Pacific Northwest for yield, quality, and disease response. In general, Summit Russet produced similar or lower total yields than did Russet Burbank, but higher U.S. No. 1 yields. In Idaho variety trials, Summit Russet exhibited resistance to second growth, growth cracks, blackspot bruise, and stem-end discoloration, and moderate susceptibility to hollow heart and shatter bruise. In comprehensive product quality evaluations, Summit Russet was rated superior to Russet Burbank for french fry quality and similar for baked potato quality. French fry quality was retained after long-term storage. In replicated disease trials, Summit Russet was found to have good resistance to common scab, early blight tuber rot, and Verticillium wilt, and moderate resistance to Fusarium dry rot and tuber net necrosis caused by PLRV. It demonstrated susceptibility to late blight, foliar PLRV, PVX, PVY^o, and bacterial soft rot. Biochemical analysis of Summit Russet tubers showed them to be higher in total solids and sucrose, and lower in dextrose than those of Russet Burbank. Tuber glycoalkaloid concentration as measured from tubers produced in 1994–1996 trials was 6.7 mg 100 g¹.     

Alturas: A multi-purpose, Russet potato cultivar with high yield and tuber specific gravity

‘Alturas’, a late-maturing, high-yielding, russet potato cultivar with high tuber specific gravity, was released in 2002 by the USDA-ARS and the Agricultural Experiment Stations of Idaho, Oregon, and Washington. Originally selected for dehydration processing, its cold-sweetening resistance also makes it suitable for processing out of storage into french fries and other frozen potato products. Culinary quality is high, with larger tubers suitable for fresh market if heavily russeted skin is not essential. Alturas consistently produced greater total and U.S. No. 1 yields than ‘Russet Burbank’ and ‘Ranger Russet’ in southern Idaho trials. Across other western trial sites, total yields of Alturas have on average been 29% and 14% greater than Russet Burbank and Ranger Russet, respectively. Alturas is resistant to Verticillium wilt (Verticillium dahliae) and early blight (Alternaria solani). Compared with Russet Burbank and Ranger Russet, Alturas is less susceptible to corky ringspot and foliar and tuber infection by late blight (Phytophthora infestans). It also is less susceptible to tuber net necrosis and Fusarium dry rot than Russet Burbank, and is more resistant to common scab (Streptomyces scabies) than Ranger Russet. However, Alturas is more susceptible to infection by PVY and PVX than Ranger Russet. Total nitrogen application recommendations for Alturas are approximately 40% less than those for Russet Burbank. Alturas requires 15% to 20% more water during the growing season than does Russet Bur-bank.     

Defender: A high-yielding, processing potato cultivar with foliar and tuber resistance to late blight

The potato cultivar Defender is high-yielding, white-skinned, and notable for having foliar and tuber resistance to late blight infection caused byPhytophthora infestans (Mont.) de Bary. It was released in 2004 by the USDA-ARS and the agricultural experiment stations of Idaho, Oregon, and Washington. Defender is suitable for processing into french fries and other frozen potato products directly from the field or from storage. Defender also may be used for fresh markets in regions such as California, where cultivars with long tubers and white skin are traditionally grown. Resistances to late blight and other potato diseases make Defender an ideal candidate for organic potato production. Defender consistently produced greater total and U.S. No. 1 yields than ‘Russet Burbank’ in Idaho trials. In early harvest trials conducted in the western U.S., average total yields of Defender were 17% and 23% greater than yields for ‘Ranger Russet’ and ‘Shepody’, respectively. In full-season trials conducted in the western U.S., Defender averaged 10% and 15% higher yields than Ranger Russet and Russet Burbank, respectively. Specific gravity of Defender is consistently high, with values comparable to those of Ranger Russet; tuber ascorbic acid (Vitamin C) levels are also high. In addition to late blight, Defender also is resistant to tuber early blight (Alternaria solani, (Ellis & G. Martin), L.R. Jones & Grout), potato virus X, and net necrosis; it has moderate levels of resistance to Verticillium wilt (Verticillium dahliae, Kleb), pink rot, foliar early blight, corky ringspot, and Erwinia soft rot. Defender is susceptible to scab (common and powdery) and potato leafroll virus; it has moderate susceptibility to dry rot (Fusarium spp.) and potato virus Y. Susceptibilities to internal necrosis, tuber greening, and blackspot bruise also have been noted, but may be minimized through cultural and harvest practices.     

Evaluation of bio-control agents for management of dry root rot of chickpea caused by Macrophomina phaseolina

Dry root rot of chickpea caused by Macrophomina phaseolina is an important disease affecting chickpea production areas in India, the largest producer of this crop in the world. The disease is primarily controlled through the use of fungicidal seed treatments. In this study, several isolates of two bio-control agents, Trichoderma viride and Pseudomonas fluorescens, were assessed for their ability to reduce the growth of M. phaseolina under laboratory conditions and subsequently used for field studies. The most effective isolate of each bio-control agent and the commonly used chemical seed-treatments, carbendazim and hexaconazole were evaluated. In addition to the use of the fungicides and bio-control agents individually as seed treatments, the study also included a trial combining soil application through bio-agent enriched farm-yard manure, along with seed treated with the bio-control agent. It was found that this combination showed maximum germination, least root rot incidence and highest yields as compared to the other biological or chemical seed treatments included in this study. This paper reports the identification of native isolates of T. viride and P. fluorescens that can be used under field conditions to control dry root rot of chickpea in tropical regions and demonstrates the use of a method of application that could significantly improve the efficacy of disease control while using bio-control agents.     

Comparative susceptibility of some potato cultivars to dry rot caused byFusarium sulphureum andF. solani var.coeruleum

Summary The susceptibility of 15 potato cultivars to dry rot caused byFusarium sulphureum andf. solani var.coeruleum was examined over 8 years. Tubers were wounded, inoculated, incubated at 10°C for 7–8 weeks and the size of the rot assessed.F. sulphureum was the more aggressive species. There was little correlation between the rank order of susceptibility of the cultivars to the two pathogens, but a higly significant correlation between years. Two years' tests are deemed sufficient to assess susceptibility to both species.     

Sensitivity of Pectobacterium carotovorum to hydroxytyrosol-rich extracts and their effect on the development of soft rot in potato tubers during storage

A hydroxytyrosol-rich olive mill wastewater (HROMW) (29.3% weight:dry weight) and a hydroxytyrosol-rich extract (HRE) (52.7% weight:dry weight) were prepared from the fresh olive mill wastewater (OMW) using hydrolysis and post-hydrolysis purification processes. The minimal bactericidal concentrations of HROMW and HRE against Pectobacterium carotovorum subsp. carotovorum were 72 and 40 g L⁻¹, respectively. According to the European standard method (EN 1276: 1997), HROMW and HRE showed powerful disinfectant properties and reduced the viability of P. carotovorum by more than 5 log units after a contact time of 5 min at 2% dry weight:volume. Curative and preventive controls of potato soft rot were obtained by treatment of tubers with HROMW or HRE 3 days before or 3 days after their infection with P. carotovorum, respectively. The soft rot development during potato tuber storage was significantly reduced by treatment with HRE. This extract could be used in eco-friendly strategies of post-harvest disease control and could substitute for chemical pesticides.     

Management of fusarium basal rot (Fusarium oxysporum f. sp. cepae) on shallot through fungicidal bulb treatment

Fusarium basal rot caused by Fusarium oxysporum f.sp. cepae is an economic disease of shallot. Field experiments were conducted at Debre Zeit during 2006 and 2007 cropping seasons to determine effective fungicides and their method of application for the management of fusarium basal rot of shallot. The field was naturally infested with F. oxysporum f. sp. cepae and treatments were arranged in randomized complete block design in four replications. Five fungicides, Mirage 50 WP, Folicur 25 EC, Seed plus 30 WS, Penncozeb 80 WP and Ridomil Gold 68 WG were evaluated as seed bulb dressing and bulb dip treatments against basal rot in the field and storage. Bulb dressing with Mirage, and dip treatment in Seed plus reduced the disease incidence by 40% and 43%, respectively over control. These fungicides also resulted in a significant reduction in severity, basal rot affected cull bulbs on shallot. Bulb rot during three months of storage on concrete ground floor and on wire mesh shelves was also reduced by seed bulb treatment over control. The highest increase in yield was obtained from bulb dressing with Mirage (42%) and Seed plus (45%) and from bulb dip treatment in Seed plus (44%) over control. Fusarium basal rot caused 45% loss in yield and 12-30% of bulb loss in the storage. The study showed that basal rot of shallot can be managed effectively by seed bulb dressing or dip treatment in Mirage or Seed plus.     

Biocontrol of bacterial wilt of potato with an avirulent strain ofpseudomonas solanacearum: interactions with root-knot nematodes

Field tests for biological control of bacterial wilt of potatoes, caused byPseudomonas solanacearum, were conducted in Florida in 1984 and 1985. Potato seedpieces of tolerant (Ontario) and susceptible (Pungo and/or Atlantic) cultivars were immersed in a suspension of the avirulent, non-bacteriocinogenic strain ofP. solanacearum, B82, prior to planting in naturally-infested soil. Relatively low populations ofP solanacearum (2 to 4 log cfu/g soil) and root-knot nematodes (0 to 33 larvae ofMeloidogyne incognita/100 cm³ soil) were present in the soil before planting. In 1984, there was approximately a 50% reduction in incidence of bacterial wilt and brown rot in B82-treated plants of cultivar Atlantic, as compared with controls. With cultivar Ontario, on the other hand, disease incidence was very low and differences between treatments were not significant. In 1985, the incidence of bacterial wilt was low in all plots. Treatment with strain B82 reduced incidence of tuber brown rot in all cultivars, but differences between treatments were not significant at P = 0.05. There was a significant correlation, however, between incidence of wilt and root-knot nematode populations in the soil. Therefore, the possibility that control of bacterial wilt in 1984 was indirect,i e, via an effect of B82 treatment on root infection byM incognita, was examined. Greenhouse tests were conducted to determine the potential effect of seedpiece treatment with strain B82 on nematode infection of cultivars Atlantic and Ontario. In two out of three trials, the B82 treatment significantly reduced incidence of root knot. These results suggest that interactions of the biocontrol agent with root-knot nematodes may determine the effectiveness of a treatment designed for bacterial wilt control in the field.     

St. Johns: A round white potato variety for fresh market

The St. Johns potato variety is high-yielding and late-maturing with attractive, round to oblong, white-skinned, white-fleshed tubers with mediumshallow eyes. Its major use is expected to be as a maincrop tablestock variety. Taste panels rated St. Johns better than or equal to Katahdin in texture, color, mealiness, and flavor. St. Johns tubers do not show the net necrosis caused by potato leafroll virus, and are resistant to golden nematode, corky ringspot, hollow heart, and blackspot bruising. St. Johns is also moderately resistant to greening, shatter bruise, verticillium wilt, early blight, common scab, the common race of late blight, leafroll,Fusarium sambucinum (dry rot) andErwinia carotovora (soft rot), although some breakdown has been reported in commercial storages. Symptoms of leafroll virus infection are somewhat difficult to detect.     

Resistance to gangrene (Phoma exigua var.foveata) and dry rot (Fusarium solani var.coeruleum) in potato tubers. 2. Evaluation of genotypic differences in pectin-bound magnesium and calcium for screening purposes

Summary The levels of incorporation of Mg and Ca into tuber cell walls and middle lamellae were compared with the intensity of attack byPhoma exigua var.foveata (P.e.f.) (gangrene) andFusarium solani var.coeruleum (F.s.c.) (dry rot) in six genotypes varying in their levels of resistance. The Mg:Ca ratio was higher in those genotypes more resistant toP.e.f., while the cation effect on attack byF.s.c was variable. Although genotype resistance may be improved by extra Mg bridges in the pectin structure the genotypic differences in susceptibilty to gangrene could not be explained by differences in Mg content assessed from alcohol-insoluble solids. Analyses of breeders' selections showed no general relationship between Mg or Ca contents and disease incidence. Therefore, genotypic differences in incorporation of these cations could not be used for screening for improved resistance.     

A simple and efficient method to assess susceptibility of potato to stem rot byErwinia carotovora subspecies

Limited development of blackleg resistant potato cultivars has been ascribed to the lack of an effective and reliable test for large scale blackleg resistance screening. A method using leaf petioles was developed for assessing susceptibility of potato stems to blackleg pathogens (Erwinia carotovora subspeciesatroseptica andE. c. subspeciescarotovora). Fifty grams of sterile autoclaved silica sand in Magenta jars (GA-7 vessel, Magenta Corp., Chicago, Illinois) was drenched with bacterial suspension, (17 ml, 2.6 × 10 to 2.6 × 10⁷ cfu/ml) and freshly cut petioles from 5 to 6 week-old plants were inserted to about 5 mm into the sand. The Magenta jars with lids closed were kept on a laboratory bench (20 ±2 C, 16 hours light). The arrangement provided near ideal post-inoculation incubation environment of high humidity for pathogen multiplication and rot development in the petioles. Length of rot was recorded 72 hours after inoculation. Linear regression of rot development on inoculum concentration had R² ≥ 0.80. The petioles inoculated and incubated by this method produced measurable rot lesions with a bacterial concentration as low as 2.6 × 10⁴ cfu/ml and differentiated between the resistant cultivar Russet Burbank and the susceptible cultivar Sangre at all the inoculum concentrations used. Furthermore, susceptibility ranking of five cultivars obtained by this method agreed in general with their reported field reactions. The method is simple and sensitive, and could be used for large scale screening for stem rot resistance in wildSolanum species and early generation breeding populations.     

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.