Evaluation of potato clones for resistance to tuber and stem rot induced byErwinia chrysanthemi

Tubers of 149 clones ofSolarium tuberosum subsp.andigena (andigena) from four self-pollinated (S₁) families (Jak 072, 702440, 700718 and Och 5331) obtained from true seed were rated for resistance toErwinia chrysanthemi. The clones were classified into four arbitrary categories based on disease reaction: resistant, intermediate, susceptible, and very susceptible. In family Jak 072, 23% of the clones were resistant and 61% intermediate. In family Och 5331, 22% of the clones were susceptible and 67% very susceptible; and in families 702440 and 700718, 38% and 29% of the clones were intermediate and 45% and 40% were susceptible, respectively. Tubers of 11 clones chosen to represent each one of the four categories were inoculated withE. chrysanthemi (Ech), E. carotovora subsp.carotovora (Ecc) andE. carotovora subsp.atroseptica (Eca). Clones responded similarly toEch andEca. However,Ecc induced significantly more rot thanEch orEca, presumably favored by the temperature of incubation (25°C). Clones Jak 072-17 and Jak 072-18 were resistant to the three bacterial pathogens. Above ground stems of 6 of the 11 selected clones inoculated withEch were susceptible to stem rot. No correlation was found between the response of tubers and above ground stems to tuber and stem rot induced byEch.     

Resistance toErwinia carotovora subsp.atroseptica in second backcross populations of somatic hybrids betweenSolanum tuberosum andS. brevidens

Summary Eleven clones obtained from a cross between cv. Katahdin and fusion products betweenSolanum tuberosum and the non tuber-bearing speciesS. brevidens, were backcrossed again withS. tuberosum (clone AR80-127-5). Small tubers harvested from 583 seedlings of these second backcross (BC2) populations were screened for tuber tissue resistance toErwinia carotovora subsp.atroseptica under aerobic conditions. After multiplication in the field. BC2 clones again were screened for soft rot resistance under aerobic as well as anaerobic conditions. In general, the resistance of the BC2 populations was reduced in comparison with the BC1. Variation for resistance was found within the BC2 populations, but there was no correlation between the results of the three tests performed. Four BC2 populations were also screenned for resistance to blackleg in the field. Significant differences were found between populations for mean percentage of diseased plants, but these differences could not be explained by the resistance of the parental clones.     

Storage of seed potatoes in pallet boxes. 1. The role of tuber surface moisture on the population of Erwinia bacteria

Summary Three stocks of seed potatoes contaminated with soft rot Erwinias were stored for 172 days in a commercial pallet box store. Three treatments were applied: naturally ventilated boxes, forced air ventilated boxes and single tubers on trays. Skin resistance values were 2.3, 9.4 and 19.3 megohm respectively. Rewetting events numbered 4, 7 and 15.Erwinia carotovora pv.carotovora (Ecc) andErwinia carotovora pv.atroseptica (Eca) declined in all stocks and treatments. Ecc declined significantly faster in the forced air ventilated treatment. The more frequent rewettings in the trays reverse the benefit of their drier skins. In the earliest sprouting stock, the naturally ventilated, but not the forced ventilated boxes, showed a decrease in skin resistance and corresponding increase in Ecc as spring approached. Forced ventilation in the first 14 days after harvest halved the level of silver scurf compared to the naturally ventilated treatment.     

Erwinia carotovora subsp.atroseptica infection promotes verticillium wilt development in potato in Israel

Summary The interaction betweenErwinia carotovora subsp.atroseptica (Eca) andVerticillium dahliae and its effect on symptom development in potato cultivars showing different degrees of resistance to them was examined over two seasons in irrigated fields in a hot, dry climate. Four cultivars were used: Cara, highly resistant to blackleg and tolerant to Verticillium wilt; Pentland Crown also resistant to blackleg but susceptible to Verticillium wilt; Désirée, moderately susceptible to blackleg but tolerant to Verticillium wilt; and Maris Bard, susceptible to both diseases. Seed tubers were inoculated with Eca immediately after harvest in Scotland, to simulate natural infection, and then planted in Israel in soil naturally infested byV. dahliae. In Verticillium tolerant cultivars, Eca infection increased the rate of colonization byV. dahliae and significantly enhanced symptom development, as assessed by suppression of plant height and wilt symptoms. This report is a portion of the Ph.D. thesis of the senior author in Ben-Gurion University of the Negev.     

The effect of green crop lifting on the contamination of seed potato tubers by pathogenicErwinia spp.

Summary In the Netherlands seed potato crops are harvested when still green, the haulm being destroyed before harvest. We compared the effect on the contamination of seed potatoes byErwinia carotovora subsp.atroseptica (Eca) andE. chrysanthemi (Ech) of the common method of haulm destruction by flailing and chemically destroying remaining stems, with the recently developed green crop lifting method. After chenical haulm destruction the levels of contamination with both Eca and Ech surviving cold storage were found not to differ significantly from those after green crop lifting. Losses due to watery wound rot (Pythium ultimum) were considerable in the warm and humid conditions during 1991, especially after green crop lifting.     

Soft rot and blackleg reactions in diploid potato hybrids inoculated withErwinia spp.

From 1993 to 1996 three groups of potato genotypes were evaluated for resistance toErwinia spp.: (1) 31 interspecific diploid hybrids (28 resistant and three susceptible), (2) five hexaploid or pentaploid somatic hybrids ofSolanum tuberosum (tbr) ×S. brevidens (brd), and (3) eight cultivars. Two evaluation methods were applied: tuber point inoculation with eitherErwinia carotovora ssp.atroseptica (Eca) orE. chrysanthemi (Ech) to test tuber soft rot resistance and stem base inoculation with Eca to test blackleg resistance. Some resistant diploid hybrids and somatic hybrids oftbr × brd were superior to cultivars for both tuber and stem resistance. Tuber and stem resistance toErwinia spp. in the most resistant diploid hybrids were equal to the highly resistant somatic hybrids oftbr xbrd. Tuber resistance to Eca was highly correlated to tuber resistance to Ech (r=0.815***). In two years of evaluation for stem resistance, three diploid hybrids and a derivative of one of the somatic hybrids (USA M 264) failed to develop symptoms of blackleg following inoculation with Eca, Analyses of variance for tuber and stem resistance indicated significant effects of genotype, year and genotype × year interaction. A positive relationship between tuber and stem resistance toErwinia spp. has been found, however the genetic control of resistance in tuber and stem is partially independent. In the case of Eca the correlation coefficient was r = 0.725***. Therefore it should be possible to obtain resistant genotypes to both blackleg and tuber soft rot. Several resistant diploid hybrids were selected from among those tested, which also have several other characters desirable for potato breeders.     

Resistance to blackleg and tuber soft rot in sexual and somatic interspecific hybrids with different genetic background

Diploid interspecific hybrids from crosses betweenSolanum tuberosum haploids andS. canasense, S. multidissectum, andS. tarijense, along with tetraploid and hexaploid somatic hybrids S.tuberosum (+)S. commersonii, were screened for resistance to blackleg and tuber soft rot byErwinia carotovora subsp.atroseptica andE. carotovora subsp.carotovora. Among the diploid hybrids, those involving clone mlt la of S.multidissectum and tar 2b ofS. tarijense yielded the highest number of genotypes resistant to both blackleg and tuber soft rot. By contrast, all the hybrids involving clone tar 1lb ofS. tarijense were susceptible to both bacterial diseases. As far as resistance of somatic hybrids is concerned, the most interesting genotype was the tetraploid one which showed resistance to both blackleg and tuber soft rot Significant correlations were found betweenE. carotovora subsp.atroseptica andE. carotovora subsp.carotovora both in resistance to blackleg and in resistance to tuber soft rot, suggesting that resistance to the two subspecies is controlled by the same gene/s or that the relevant genes are linked. On the other hand, correlations between blackleg and tuber soft rot were never significant, indicating that different mechanisms may control resistance in tuber and stems. Alternatively, the resistance could be controlled by the same gene/s under a different spatial/temporal expression pattern. Twelve diploid sexual hybrids and one tetraploid somatic hybrid were selected for resistance to blackleg and/or tuber soft rot and for tuber characteristics.     

Identification of stem soft rot (Erwinia carotovora subspeciesatroseptica) resistance in potato

Development of potato cultivars resistant to Erwinia species (Erwinia carotovora subspeciesatroseptica, E. carotovora subspeciescarotovora, andErwinia chrysanthemi) causing soft rot of stems and tubers involves identification and transfer of the resistance to breeding lines possessing desirable agronomic traits. In total, 363 accessions of six wildSolanum species, three somatic hybrids and nine sexual progeny of somatic hybrids were screened for stem soft rot resistance. Thirty-one, 50, and 67 percent of accessions ofSolanum boliviense, Solanum chacoense, and Solanumsanctarosae, respectively, were resistant or highly resistant, whereas, 100, 97, and 95 percent of accessions ofSolanum canasense, Solanum tarijense, andSolanum spegazzinii were susceptible or highly susceptible, respectively. Two tuber soft-rot resistant somatic hybrids, A937 and T355-11 produced earlier by the fusion ofSolanum brevidens (PI 218228) andSolanum tuberosum (PI203900) orS. tuberosum cv. Russet Burbank, respectively, and the sexual progeny of A937 andS. tuberosum cv. Katahdin were also highly resistant. Transfer of resistance fromS. brevidens to somatic hybrid (A937) and subsequently to the progeny suggests that the resistance is simply inherited. In addition to the identification of 65 resistant or highly resistant clones of wildSolanum species, this study has identified three tuber soft rot-resistant clones that are also resistant to stem soft rot. Potato cultivars showed a range of responses to the pathogen.     

Preliminary selection of antagonists ofErwinia carotovora subsp.atroseptica (Van Hall) Dye for application during green crop lifting of seed potato tubers

Summary Green crop lifting (GCL) for haulm killing was developed in The Netherlands and offers ideal conditions for controlling the blackleg pathogenErwinia carotovora subsp.atroseptica (Eca) by antagonists. Based on the use of mini-tubers or young tubers from field crops, two bioassays for wound protection were developed. GCL was simulated by artificially skinning or wounding tubers, inoculating the damaged skin with Eca, treating with antagonists and incubating in either potting compost or outside in field soil. Mainly fluorescent pseudomonads, pre-screened for in vitro antagonistic activity on agar and high soft rot reducing ability on tuber slices, were tested in the mini-tuber bioassay. Strains giving the highest degree of wound protection were further tested individually and in combination under field conditions in the young tuber bioassay. One individual strain and two combinations, resulting in reduction of contamination levels on skinned surfaces of 85% and between 60% and 70%, respectively, show good potential for biological control of blackleg.     

Comparison of the interactions ofErwinia carotovora ssp.atroseptica withPhytophthora infestans, Phoma foveata andFusarium coeruleum in rotting potato tubers

Summary An interaction betweenP. infestans andE. carotovora subsp.atroseptica (Eca) in rotting tubers was confirmed and the biochemical basis for its occurrence investigated. The pH of tissue infected withP. foveata became alkaline whereas tissue infected withP. infestans orF. coeruleum did not rise above neutrality, which could promote pathogenicity of Eca by maintaining pH closer to the optimum for polygalacturonase activity. Polygalacturonase, pectate lyase and galactanase were detected in cultures of all three fungi grown on media containing cell wall material or pectin from tubers. AsP. infestans produced more polygalacturonase than the other two fungal tuber rot pathogens the possibility was investigated that oligogalacturonide products of enzymatic degradation of pectin byP. infestans stimulates pathogenicity of Eca. However, while tubers soft-rotted after infiltration with supernatant from fungal cultures grown on tuber cell wall material, controls showed that rotting resulted from infiltration rather than the products contained in the infiltrated water.     

Effect of applying nitrogen fertilizer to a potato seed crop on the susceptibility of the daughter plants toErwinia carotovora subsp.atroseptica

Summary Seed potatoes of cvs Record and Bintje were grown with 30, 80 or 130 kg N/ha. In the subsequent growing season the seed tubers, which were inoculated or not with two concentrations ofErwinia carotovora subsp.atroseptica (Eca), were subjected to the same fertilization treatment. The incidence of blackleg and the level of seed tuber decay increased from the uninoculated treatment to the higher inoculum level, but the degree varied considerably from one year to another. Cv. Bintje was more susceptible to blackleg and yield loss caused by Eca than cv. Record. In 1990, when disease incidence was high, the proportion of blackleg stems increased with increasing doses of nitrogen fertilizer which had been applied to the seed crop, but was not significantly affected in 1988 and 1992. Seed tuber decay was retarded by the lowest nitrogen dose. The yield of the subsequent crop was not affected by the nitrogen dose applied to the seed crop.     

Resistance toErwinia spp. in diploid potato with a high starch content

Summary Tubers of diploid interspecific hybrids, hexaploid somatic hybrids ofSolanum tuberosum andSolanum brevidens, a fusion parental line (S. tuberosum) and several Polish and American commercial cultivars were screened for resistance toErwinia carotovora subsp.atroseptica andErwinia chrysanthemi, in laboratory tests. Both groups of hybrids showed a high level of resistance to soft rot and gave a similar type of resistant reaction, which distinguished them from the cultivars and fusion parent. Tubers of the diploid interspecific hybrids had a high starch content. Our results indicate the possibility of obtaining breeding material with a high starch content and resistance to bacterial soft rot.     

Effects of contamination byErwinia carotovora subsp.carotovora andE. carotovora subsp.atroseptica of potato seed tubers and of cultivar resistance on blanking or nonemergence and blackleg development in Valencia,Spain

Summary High grade potato seed tubers of three cultivars were inoculated in Scotland by vacuum infiltration in suspensions ofErwinia carotovora subsp.carotovora and subsp.atroseptica in different combinations, and transported to Valencia, Spain. They were cut into two to three pieces and planted in January 1984, 1985 and 1986 in fields furrow irrigated before and after emergence. High incidences of blanking and blackleg were associated with seed inoculated with high numbers ofE.c. atroseptica alone or together withE.c. carotovora and not with high or low numbers ofE.c. carotovora alone.E.c. atroseptica predominated at emergence in March in rotting seed pieces which failed to produce a plant, regardless of the seed treatment, and in diseased stems in April but it was replaced byE.c. carotovora in May. The levels of blanking and blackleg after inoculating 16 cultivars with both erwinias were not correlated between years nor were they significantly different within years among most of the cultivars.     

The resistance of potato plants toErwinia carotovora subsp.atroseptica in relation to their calcium and magnesium content

Summary The effect of adding gypsum (CaSO₄) to growing media on the resistance toErwinia carotovora subsp.atroseptica (van Hall) Dye of potato (Solanum tuberosum L.) stems and mother and daughter tubers was examined in field and glasshouse experiments. The decayin situ of inoculated mother tubers from field plots treated before planting with gypsum was significantly delayed compared with tubers sampled from non-amended plots. Blackleg development was also significantly delayed in the gypsum-amended plots; however, for both mother tubers and stems the increased resistance associated with the application of gypsum later disappeared. Stem resistance tended to be related to tissue calcium and magnesium concentrations which were higher in plots treated with gypsum than in untreated plots. Daughter tubers produced in plots amended with gypsum generally contained a higher concentration of calcium in their cortex and were more resistant to decay byE. carotovora subsp.atroseptica but the effect was not consistent.     

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.     

Soft-rot resistance combined with other tuber characters in long day-adaptedSolanum phureja

Summary Offspring were produced from a cross between two long-day-adaptedSolanum phureja clones which carried resistance to tuber soft rot (Erwinia carotovora subsp.atroseptica). In tests carried out on the produce of field-grown plants raised from tubers, over fifty per cent of the 173 offspring were found to be highly resistant. Assessments were also carried out of tuber yield, mean tuber weight, tuber number, shape, regularity, flesh colour, texture of the steamed flesh, fry colour, after-cooking blackening, sprout length after storage and overall dormancy. There were statistically significant differences between clones for all characters (P<0.001). Twelve of the clones were selected on the basis of high resistance, yield, tuber weight, regularity of shape and absence of after-cooking blackening. The value of resistant long-day-adapted diploid material for commercial breeding is discussed.     

Evaluation for chipping and tuber soft rot (Erwinia carotovora) resistance in potato clones from unilateral sexual polyploidization (2x × 4x)

The aim of this work is the evaluation of tetraploid potato clones with germplasm fromS. chacoense andS. phureja for chipping and resistance to tuber soft rot (Erwinia carotovora subsp.carotovora). Tetraploid potato clones were obtained via 2n eggs through 2x–4x crosses. Cytological mechanisms were investigated in the diploid hybrid 2n-egg producer used as parent in the unilateral sexual polyploidization scheme; the omission of the second meiotic division and cytokinesis failure at the end of meiosis were identified with a genetic consequence equivalent to second division restitution (SDR). Tuber marketable yield, specific gravity and chip-processing ability evaluated at harvest and after cold storage with and without reconditioning were higher in some clones as compared to theS. tuberosum tetraploid parent. Tuber soft rot resistance, contributed byS. chacoense, was successfully transferred to the4x level. After inoculation withErwinia carotovora subsp.carotovora and estimation of the rotted area, one tetraploid clone proved to be resistant and three partially resistant. The genetic value of exotic germplasm and sexual polyploidization strategy are discussed in relation to potato improvement.     

Effect ofErwinia carotovora subsp.atroseptica on yield of potatoes from cut and uncut seed tubers in Valencia

Summary The effect on the development of blackleg symptoms and on yield of inoculating seed tubers of 15 cultivars withErwinia carotovora subsp.atroseptica (Eca) was investigated. Tubers were planted either whole or as pieces. Eca inoculation reduced the mean yield per plant by 8% for whole tubers and by 12% for cut tubers. There was no correlation between blackleg symptoms and yield loss.     

Die Effizienz der Nassfäuleabwehr bei der Wundheilung von Kartoffelknollen. 2. Der Einfluss auf die Resistenzbewertung von Genotypen

Zusammenfassung Die wundheilbedingte Infektionsabwehr beeinflusst das Resistenzverhalten der Knollen. Sie ist bei f?uleanf?lligen Genotypen effizienter als bei widerstandsf?higen. Die Resistenzbewertung von Genotypen nach der H?he der befallsausl?senden Erregerdichte wird von den Vegetationsbedingungen beeinflusst. Sie korreliert mit einer Bewertung nach dem Ausmass der F?ulesymptome, nicht aber mit dem Ausmass einer enzymatischen Mazeration.

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Summary A cultivar collection was assessed for tuber resistance to the soft rot organism,Erwinia carotovora subsp.atroseptica (=Eca), and for the strength of the defence reaction associated with wound healing, by measuring the inoculum density needed to initiate infection (effective dose). Wound healing was more efficient in susceptible genotypes than in resistant ones (Fig. 1b), and resulted in changes of the ranking of cultivars, and a narrowing of the variation for soft rot resistance (Fig. 1a). No relationship was found between enzymic maceration of tissue and effective dose (Fig. 2a). The resistance ratings of cultivars were in general agreement with the effective dose and with symptom expression (Fig. 2b). Resistance behaviour was modified by growing conditions (harvest year) (Table 1), and cultivars need therefore to be assessed over several years.

     

Transgenic potatoes expressing anErwinia pectate lyase gene — results of a 4-year field experiment

Summary Four potato lines of cv. Désirée that express the pectate lyase (PL) isoenzyme 3 ofErwinia carotovora subsp.atroseptica were examined in a 4-year field experiment with respect to plant development, tuber yield and resistance of tuber tissue toErwinia soft rot. The PL3 degrades plant cell wall pectin into unsaturated oligogalacturonates eliciting plant defence responses. In one line, enzyme expression was controlled by the CaMV 35S promoter (C) and in three lines it was driven by the potato patatin B33 promoter (D). Plant development of the D-lines in field plots was not distinguishable from that of the non-transgenic counterpart. Also tuber yield was not too different. By contrast, plants of the C-line were smaller than those of the nontransformed counterpart and also showed reduced tuber yield. There were no significant differences in dry mass, starch and protein content of tuber tissue between PL transgenic and non-transgenic potatoes. But compared with the latter, field-grown tubers expressing the PL displayed an enhanced resistance toErwinia soft rot. Thus, average rotting caused byEc-bacteria was diminished in tubers of PL-transgenic lines by 34.1%. The resistance of tubers toEc soft rot was significantly correlated with the PPO activity in tuber tissue.