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.     

Germplasm Release: Three Tetraploid Potato Clones with Resistance to Common Scab

Common scab caused by the soil-borne bacterium Streptomyces scabies is a serious disease for the potato industry. We have identified a strong source of resistance in the diploid wild relative Solanum chacoense. This resistance has been introgressed into tetraploid cultivated potato via unilateral sexual polyploidization. This paper describes three hybrid clones (M8, M16, M17) for use by potato breeding programs to enhance resistance to common scab. They were created by crossing a diploid clone (50% S. tuberosum, 50% S. chacoense) to tetraploid cultivars, producing hybrids with 75% cultivated and 25% wild germplasm. The clones are male and female fertile, and are adapted to temperate zone production environments.     

Segregation of leptines and other glycoalkaloids inSolanum tuberosum (4x) ×S. chacoense (4x) crosses

A clone, 8380-1, selected fromSolanum chacoense (PI 458310) for its high foliage content of the leptine glycoalkaloids, a factor in resistance to Colorado potato beetle, was doubled in chromosome number from 2n=2x=24 to 2n=4x=48. Three 4x clones were crossed with sixS. tuberosum (4x) clones. Foliage glycoalkaloid contents were measured for 452 F1 hybrids from 15 crosses. The 4xchacoense parental clones were not different in respect to glycoalkaloid contents and were similar to the original 2x clone. All F1 hybrids synthesized foliage leptines ranging from 9 to 369 mg/100 g fresh weight (fw) with a mean content of 113 mg/100 g fw. The proportion of leptines in the total glycoalkaloid content ranged from 1% to 62% with a mean of 25%. The 4xchacoense parent mean leptine content was 1482 mg/ 100 g fw which was 90% of the total glycoalkaloid content. Tubers from 136 hybrids and the threechacoense parental clones were tested for glycoalkaloid contents. The tuber solanine + chaconine contents of the 136 hybrids ranged from 30 to 180 mg/100 g fw with a mean of 79. The mean tuber content of the threechacoense parental clones was 157 mg/100 g fw. Leptines were not found in any of the tubers.     

Response of six wild potato species to chloride and sulfate salinity

Eleven accessions belonging to six species ofSolanum (S. bulbocastanum,S. chacoense, S. gourlayi, S. microdontum, S. papita, and S.sparsipilum) were tested for resistance to salt. Resistance was measured by survival and growth (dry weight of tops) of plants treated with solutions of NaCl and Na₂SO₄. The six species could be grouped into four classes based on good to poor resistance to salt solutions (1.S. chacoense, 2.S. gourlayi, 3.S. microdontum, S. sparsipilum, S. bulbocastanum and 4.S. papita). There was a close relationship (r=0.94**) between the survival of plants and growth of surviving plants treated with salt solutions. There was no relationship between known heat or drought resistance of various accessions and salt resistance. Results indicate there is a large genetic base available to improve the salt resistance of the cultivated potato.     

Transmission of Scab Resistance to Tetraploid Potato Via Unilateral Sexual Polyploidization

Resistance to common scab continues to be a high priority trait for potato breeders. We have identified a source of resistance in the diploid wild potato relative Solanum chacoense and have introgressed it into cultivated potato by crossing it to a dihaploid. A clone generated by crossing two full-sib hybrids is highly resistant and produces both 2n pollen and 2n eggs. This clone, named 4–48, is homozygous for a major QTL for scab resistance derived from S. chacoense. Clone 4–48 was reciprocally crossed to three round white cultivars Megachip, Pike, and White Pearl. Common scab resistance was transferred to tetraploid offspring, with transmission through the male parent generally more effective than through the female parent. The majority of progeny (70%) exhibited stability for resistance to common scab across environments. This germplasm will be useful for breeding new resistant cultivars.     

Resistance to Columbia root-knot nematode inSolanum ssp. and in hybrids ofS. hougasii with tetraploid cultivated potato

Several tuber-bearingSolanum species were screened for resistance to races 1 and 2 of Columbia root-knot nematode,Meloidogyne chitwoodi. Reproductive factor (R_f = P_f/P_i) was assessed and used to infer host resistance. Several clonal selections in one Plant Introduction accession ofSolanum hougasii showed high levels of resistance to both races. Crosses ofS. hougasii with tetraploid breeding clones yielded 14 vigorous F₁ hybrids. Three of these interspecific hybrids expressed non-host (R_f<0.1) responses to race 1 and poor host (0.1f<1.0) responses to race 2. Six hybrids were nonhosts to race 1 but good hosts (R_f>1.0) to race 2. Three hybrids were good hosts to both races, and one was a poor host to race 1 and non-host to race 2. The occurrence of resistance to both races in the F₁ hybrids indicates success in the first step of introducing resistance to races 1 and 2 ofM. chitwoodi to the cultivated potato gene pool.     

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.     

Leptines and other glycoalkaloids in tetraploidSolanum tuberosum xSolanum chacoense F2 Hybrid and Backcross Families

The leptine glycoalkaloids fromSolanum chacoense Bitter are potential resistance factors to Colorado potato beetle,Leptinotarsa decemlineata Say. A selected sample of 17 F₁ hybrids (4x) from crosses of a 4xS. chacoense clone that synthesizes leptines (8380-1) with 4xS. tuberosum L. lines were selfed to generate F₂ hybrids (4x) and were also backcrossed toS. tuberosum. Glycoalkaloid (GA) content in foliage and tubers was measured for 786 sibling genotypes from the two generations in the field at Beltsville, Maryland. Leptines were found in the foliage of all F₂ hybrids and in 98% of the backcross genotypes. Leptines were not detected in tubers from either generation. Foliage concentrations of leptines for the F₂ hybrids averaged 156 mg/100g fresh weight (FW). The proportion of the total GA content consisting of leptines averaged 42%. By backcrossing the F₁ hybrids toS. tuberosum the average concentration of leptines was reduced to 44 mg/100g FW. The proportion of leptines averaged 16%. The tuber contents of solanine plus chaconine glycoalkaloids averaged 52 mg/100g FW for the F₂ hybrids and 27 mg/100g for the backcross genotypes.     

Segregation of leptine glycoalkaloids and resistance to Colorado potato beetle (Leptinotarsa decemlineata (Say)) in F2Solanum tuberosum (4x) ×S. chacoense (4x) potato progenies

Solanum chacoense Bitter is resistant to the Colorado potato beetle (CPB),Leptinotarsa decemlineata (Say). Resistance has been associated with the presence of a rare class of glycoalkaloids, the leptines. In this study, seven tetraploid, F2S. tuberosum xS. chacoense families were evaluated for foliar production of leptines I and II, leptinines I and II, and α-solanine and α-chaconine; and screened for resistance to CPB in the laboratory and field. Resistance was correlated with the concentrations of glycoalkaloids on a family and an individual basis. Leptine concentrations ranged from undetectable to a high of 18.0 mg/g dry weight. All of the progeny produced solanine and chaconine. Family 9623 had the highest mean leptine concentration and the lowest mean leaf disk feeding and CPB defoliation levels. Family 9616 had the lowest mean glycoalkaloid concentration and ranked as one of the most susceptible families. Regression analyses of solanine + chaconine, leptine I and II, and leptinine I and II foliar concentrations versus leaf disk consumption and field defoliation revealed that only increased foliar levels of leptines resulted in decreased CPB feeding. The regression models for leptines versus leaf disk consumption and field defoliation were highly significant, accounting for 17% and 26% of the variation in consumption and defoliation, respectively. To the best of our knowledge, this is the first work reporting the impact of leptine and leptinine concentrations on CPB feeding in tetraploid,S. tuberosum xS. chacoense potato hybrids. Results are discussed within the context of breeding for resistance to CPB.     

The incorporation of resistance toGlobodera Pallida intoSolanum Tuberosum germplasm adapted to North America 1

Potato seeds of 24 families consisting primarily ofSolanum tuberosum ssp.andigena with someS. vernei germplasm that were segregating for resistance to potato cyst nematodes (Globodera pallida races P₄A and P₅A andG. rostochiensis race R₁A) were obtained from the International Potato Center. These seeds produced 468 clones with sufficient tubers for evaluation for resistance toG. pallida races P₄A and P₅A in pot tests at the International Potato Center. Twenty-six of these clones, selected for a high degree of resistance toG. pallida races P₄A and P₅A, were crossed with neotuberosum ×Solanum tuberosurn hybrids that had been selected for resistance toG. rostochiensis race R₁A (golden nematode) and the viruses PVX and PVY. The resultant progenies possessed a high degree of resistance to all three races of the potato cyst nematode. From these progenies, 23 clones were selected for resistance to the three races (G. pallida P₄A and P₅A,G. rostochiensis R₁A) of potato cyst nematodes. The better adapted clones with resistance to the 3 races of potato cyst nematodes will be used in the next cycle of back-crossing.     

Potato germplasm with combined resistance to leafroll virus and viruses X and Y

Potato germplasm with high levels of combined resistance to potato viruses X, Y, and leafroll was identified and used to produce improved parental clones with similarly high levels of resistance. Resistance was determined from the amount of tuber infection following inoculation of plants in the field. Parental germplasm with the best multiple resistance came from two backgrounds, eitherSolanum tuberosum group Andigena derived from the Cornell University neo-tuberosum program, or from complex hybrids ofS. tuberosum and wild solanums that were produced by the Max Planck Institute and the Polish Institute for Potato Research. Two Aberdeen, ID selections, A85519-6 and A85530-10, with gp. Andigena ancestry, have had no tuber-borne infection of PVX, PVY, or PLRV during four years of intensive field testing. We have not been successful in combining virus S resistance with resistance to the other viruses.     

Glycoalkaloids and resistance to the Colorado potato beetle inSolanum chacoense Bitter

Resistance of 20 F₂ Solarium chacoense Bitter clones to the Colorado potato beetle,Leptinotarsa decemlineata (Say), was measured in a field test. Levels of total glycoalkaloids (TGA) and composición of the glycoalkaloid mixtures in foliage of the clones were also determined. Clones with either commersonine or dehydrocommersonine as the major foliar glycoalkaloid were significantly more resistant (lower damage ratings, fewer larvae and adult insects) than clones with solanine and chaconine. Damage ratings were negatively correlated (r = -0.67, p = 0.01) with foliar TGA levels. The results indicate that the types of glycoalkaloids present in the foliage ofS. chacoense may be as important as the level of TGA in limiting damage and numbers of insects.     

Screening for Chip-Processing Potato Line from Introgression of Wild Species’ Germplasms with Post-Harvest Storage and Chip Qualities

The processing of potatoes into chips is expanding in China. There is a need for new processing cultivars that are well-suited for the local ecological environment. Eleven potato varieties were bred from hybridization and backcrossing between the local cultivated potato varieties (Solanum tuberosum L.) and wild potato species. Lines from different wild species’ germplasms showed that the ability to accumulate reducing sugars was significantly different during low temperature storage (4 °C). A correlation analysis was conducted to determine the correlation coefficient among reducing sugars, acid invertase, free amino acids, chip colors and the content of acrylamide after storage at room and low temperatures. The lines 0706-116, 0737-6 and 0726-205 had low levels of reducing sugars, acrylamide content and acceptable chip colors for potato chip processing. The results indicated that the transfer of wild species’ processing traits into local cultivars by hybridization and continuous backcrossing is an effective potato breeding method and that the wild germplasm resources S. phureja and S. chacoense are suitable for improving the processing traits of local varieties.     

Leaf effects of wild species ofSolanum and interspecific hybrids on growth and behaviour of the potato tuber moth,Phthorimaea operculella Zeller

Summary Four introductions ofSolanum berthaultii wild species and sevenS. tuberosumxS. berthaultii hybrids were evaluated by antibiosis and antixenosis laboratory tests with potato tuber moth. Some morphological and chemical traits related to the trichomes were analysed. Two clones of the wild speciesS. sparsipilum and five ofS. pinnatisectum, characterised by high tuber resistance, were tested for leaf resistance, both by antibiosis and antixenosis assays. The genotypes with high density of trichomes A and with high exudate PPO activity, showed a moderate negative effect on pupal weight and fecundity in the antibiosis tests. Trichomes B exudate showed a strong repulsive effect on oviposition of adult in the antixenosis tests. TheS. pinnatisectum clones revealed a good leaf resistance level, whereas theS. sparsipilum clones showed lower levels of antibiosis and antixenosis.     

Selection and utilization of solanum phureja clones with high resistance to different strains of pseudomonas solanacearum

Over 250 accessions ofSolanum phureja from Colombia and 300S. phureja—S. tuberosum hybrids were screened in the greenhouse for resistance toPseudomonas solanacearum (isolate K-60). Each plant was inoculated by stem puncture at the pre-bud stage and then held at a constant 28 C for 15 days. Seventeen clones with different levels of resistance to K-60 were inoculated with nine additional isolates representing all three races of the bacterium. The reactions of individual clones varied from resistance to almost all isolates, resistance to only one isolate, or complete susceptibility. Crosses amongS. phureja clones and betweenS. phureja and 24-chromosomeS. tuberosum stocks gave progeny with various percentages of resistant plants. Clones with resistance equal to that inS. phureja were found in theS. phureja × S. tuberosum crosses. Tests conducted in growth chambers showed that resistance was expressed more frequently at high light intensity (2000 ft-c) than at low intensities (1300 ft-c) at 24 C and 28 C. Resistance appears to be relatively simply inherited and the prospects for transferring a high level of resistance into cultivated forms are promising.     

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.     

Interspecific crossability and cytogenetic analysis of sexual progenies of Mexican wild diploid 1EBN speciesSolanum pinnatisectum andS. cardiophyllum

Mexican wild diploid species,Solanum pinnatisectum (S. pnt) (2n=2x=24, 1EBN: endosperm balance number) is a useful germplasm source of late blight and Colorado potato beetle (CPB) resistance in potato improvement. However, it is very difficult to cross this species with other 1EBNSolanum species. Sexual hybrids among three accessions ofS. pnt and two accessions ofS. cardiophyllum (S. cph) (2n=2x=24, 1EBN) were studied. There were large differences in the cross-compatibility among the genotypes and accessions from these two 2x-1EBN species. Interspecific incompatibility existed in the crosses betweenS. pnt andS. cph, in whichS. cph functioned only as the male parent. The crosses with accessions PI 275236 ofS. pnt produced 35 hybrids following the conventional propagation procedures. Seven hybrids were obtained with theS. pnt accession PI 275233 with the aid of embryo rescue, while hybridization involving accession PI 253214 resulted in no fruit. The cytogenetic analysis indicated that all of the hybrids derived from crosses of accession PI 275233 ofS. pnt withS. cph had 2n = 24 chromosomes and were pollen fertile. Crosses involving accession PI 275236 ofS. pnt produced both 2x (2n=24) and 3x (2n=36) hybrids. Meiotic analysis at metaphase I of pollen mother cells (PMCs) showed a fairly high rate of chromosome pairing that averaged between 10.10 and 11.10 bivalents per cell in most of the 2x hybrids, indicatingS. pnt andS. cph have the similar genome. A high frequency of trivalents and quadrivalents were observed in 3x hybrids derived fromS. pnt 2 ×S. cph 1, indicating homology exists among these chromosomes. These results suggest that specific gene(s) and not either differences between genomes or EBN controlled interspecific crossability and embryo development. The disease and insect tests on the 2x and 3x hybrids revealed that all have high levels of resistance to both late blight and CPB. Thus it could appear that selection of genotypes is a key for successful interspecific hybridization when using Mexican wild diploid species as a source of economic important traits.     

QTL Analysis of Late Blight Resistance in a Diploid Potato Family of Solanum spegazzinii × S. chacoense

Several quantitative trait loci (QTL) for resistance to late blight have been reported in diploid potatoes. The diploid wild potato species Solanum chacoense possesses a high degree of horizontal resistance to late blight. In the present study, we report on QTL mapping for late blight resistance in a diploid mapping population of 126 F₁ of Solanum spegazzinii (susceptible) × S. chacoense (resistant). The area under the disease progress curve (AUDPC) values for late blight resistance using the “whole plant in vitro assay” and the “detached leaf assay” on the mapping population displayed quantitative variation. Out of 64 AFLP primer-pairs combinations and SSR markers, a total of 209 significant AFLP loci were placed onto the 12 linkage group of potato covering a total map length of 6548.1 cM. QTL analysis based on the AUDPC dataset of the “whole plant in vitro assay” using the interval-mapping option identified two QTL (LOD?>?2.5) located on linkage groups IX and X, which explained 14.70 and 3.40% variation, respectively. The present study revealed the presence of potential new genetic loci in the diploid potato family contributing to quantitative resistance against late blight.     

Resistance to soft rot (Erwinia carotovora subsp.atroseptica) in tetraploid potato families obtained from 4x-2x crosses

Diploid potato clones, interspecific hybrids ofSolanum species, having in their originS. tuberosum,S. chacoense, S. yungasense, S. phureja, S. gourlayi, andS. demissum, with resistance to soft rot, were crossed to tetraploid potato clones in 4x-2x crosses. The 24 tetraploid families obtained in a North Carolina II design were examined for tuber resistance to soft rot in a laboratory test and for basic agronomic traits in field trials conducted for two consecutive years. In addition, one family originating from a 4x-2x cross of two susceptible parents was tested. Statistical analysis of the data revealed significant general (GCA) and specific combining ability (SCA) effects, year, GCA (female) × year, GCA (male) × year, and SCA × year upon the inheritance of resistance to soft rot. About 35% of the progeny was selected as resistant to tuber soft rot, and of these 11% showed high resistance combined with good tuber yield, tuber weight, and tuber appearance. The relationships between resistance to soft rot and chosen agronomic traits were not noted or were weakly significant and sporadic. The resistance to tuber soft rot found in diploid potato hybrids can be transferred to the cultivated tetraploid pool through 4x-2x crosses, and a high frequency of offspring posses resistance.     

Performance of populations derived by selecting for resistance to potato leafhopper in A 4XSolanum Tuberosum X 2XSolanum Chacoense cross

Intercross and backcross populations derived from aSolanum tuberosum L. (2n = 2x = 48) ×Solanum chacoense Bitt. (2n = 2x = 48) cross by selecting for resistance to potato leafhopper (PLH) (Empoasca fabae Harris), were tested in the field. In F2 and F4 populations, the levels of nymphal infestation and leaf necrosis from PLH feeding were considerably lower and tuber yields were much lower compared with those measured on the susceptible cultivar Kennebec. No differences were found between the two populations. Backcrosses of the F2 and F4 populations toS. tuberosum decreased resistance to PLH. Resistance to infestation was still greater than that of Kennebec; severity of leaf necrosis equaled that of Kennebec. Tuber yields increased, but were less than Kennebec’s yield. Foliage types shifted closer to those ofS. tuberosum. Three generations of selection and intercrossing within the backcross populations did not change the level of resistance to PLH but did tend to lower tuber yields. Foliage types remained primarilyS. tuberosum in appearance although distinctive types segregated with increased frequency. A second backcross toS. tuberosum did not change the level of resistance to PLH or the level of tuber yield relative to those of the first backcross or Kennebec.