T-type chloroplast DNA inSolarium tuberosum L. ssp.tuberosum was conferred from some populations ofS. tarijense Hawkes

The highly heterozygous and tetraploid nature of potato (Solanum tuberosum L. ssp.tuberosum) has hampered discovery of its wild ancestral species. Chloroplast DNA is a very reliable indicator to trace maternal ancestry of crops. Most of the common potato (grown worldwide) has unique, T-type chloroplast DNA derived from Chilean cultivated potato (both areS. tuberosum ssp.tuberosum). Analyzing seven different chloroplast DNA markers, I found all the T-type accessions of cultivated potatoes shared the same chloroplast DNA haplotype only with some accessions ofS. tarijense Hawkes and its derived hybrids. Thus, I conclude that some populations ofS. tarijense acted as the maternal ancestor of potato.     

Distribution of the 241 bp deletion of chloroplast DNA in wild potato species

The common potato (Solanum tuberosum L. ssp.tuberosum) has T-type chloroplast DNA characterized by a 241 bp deletion. To explore the maternal ancestry of the common potato, a total of 566 accessions of 35 wild species, collected mostly from central Bolivia to northern Argentina, were determined for presence or absence of the deletion by a simple PCR assay using primers flanking the deleted region of chloroplast DNA. Sixteen out of 80 accessions ofS. tarijense, S. berthaultii, andS. neorossii showed a shorter PCR amplified fragment. Sequencing of these fragments revealed that the same 241 bp was deleted at the same position in these accessions. This strongly suggests that the deletion event had occurred in wild species.     

An analysis of the hybrid nature ofsolanum xedinense Berth, using molecular, cytological and crossability studies

Summary Solanum xedinense Berth., a pentaploid (2n=5x=60) interspecific hybrid between the cultivated potato and the wild speciesSolanum demissum Lindl., represents evidence of genetic exchange between wild and cultivated species. It has been found in Central Mexico at altitudes between 2000 and 3500 meters, growing in and along the edges of cultivated fields, roadside thickets, forest margins and along irrigation ditches. This study examined the hybrid nature of S.xedinense using molecular, cytological and crossability data. RAPD and AFLP markers were used to supportS. xedinense as a hybrid between the cultivated potato andS. demissum. Meiotic analysis and crossability studies were used to examine the potential ofS. xedinense to form offspring. Several accessions ofS. tuberosum L. subsp.tuberosum and subsp.andigena Hawkes,S. demissum and an accession ofS. xedinense were used in the study. Artificial hybrids betweenS. tuberosum subsp.tuberosum andS. demissum were included for comparison. Molecular analysis positioned the natural and artificial hybrids as an intermediate group between the parental populations, supporting their relationship with the parental populations. Meiosis was abnormal in both natural and artificial hybrids, and reduced crossability was noted forS. xedinense. Although gene flow appears to happen between wild and cultivated potato, the potential for the natural hybrids to become established may depend mostly on their ability to clonally propagate themselves.     

Glandular pubescence,glycoalkaloid composition,and resistance to the green peach aphid,potato leafhopper,and potato fleabeetle inSolanum berthaultii

Fifteen accessions ofSolarium berthaultii Hawkes andS. berthaultii xS. tarijense Hawkes were assessed for resistance to field infestations of the green peach aphid,Myzus persicae (Sulzer), potato leafhopper,Empoasca fabae (Harris), and potato fleabeetle,Epitrix cucumeris (Harris). Accessions bearing both Type A and Type B glandular trichomes were much more resistant to the green peach aphid and potato leafhopper than accessions bearing Type A hairs alone. All accessions had significantly smaller populations of these 3 pests than S.tuberosum cultivars. Total glycoalkaloid (TGA) content of foliage and tubers was not correlated with insect populations. Foliar TGA levels of field-grown plants varied among accessions, ranging from < 2–240 mg/100 g fresh wt. Solasonine and solamargine were the major foliar glycoalkaloids while solamarines predominated in tubers.     

Seed protein variation within accessions of wild and cultivated potato species and inbredSolanum chacoense

Summary Soluble proteins in seed potato were analyzed by electrophoresis (PAGE). The Index of Variation (IV) was calculated in order to estimate variation within each accession of wild and cultivated potato species andS. chacoense selfed lines. Seeds of 34 accessions representing 14 species from six taxonomic series were analyzed. The IV ofS. chacoense selfed lines decreased from 47.7 in the S₂ to 12.9 in the S₇ generation. The average IV for the self-incompatible diploid species was 41.2, whereas that of the selfcompatible diploid species,S. polyadenium, was 21.3. TetraploidS. tuberosum ssp.andigena andS. sucrense had an average IV of 62.2, which is much higher than that observed in any other diploid species. The naturally selfing speciesS. acaule (4x), and its colchicine-doubled derivative (8x), showed very low variation (IV=7.5). The IV appears to reflect heterozygosity and is affected by the breeding mode and the genetic constitution of diploid parents for derived polyploids.     

Reaction ofSolanum tuberosum andSolanum species toMeloidogyne hapla

The reactions of 218 clones ofSolanum tuberosum and 238 accessions of 55 tuber-bearingSolanum species toMeloidogyne hapla were determined by planting them in soil naturally infested withM. hapla and the microsclerotial form ofVerticillium alboatrum. Degree of root galling was rated from none (0) to severe (5). Incidence of root galling on clones was slight as evidenced by ratings of 0, 0.5 and 1.0 for 38, 32 and 18 percent of them, respectively. As incidence of root galling increased there was a tendency for percentage of galled tubers and internal tuber infection byM. hapla to increase. Of many family progenies ofS. tuberosum tested, those from family B7147 (Penobscot x W39-1) were the most resistant toM. hapla. Incidence ofM. hapla root galls andVerticillium alboatrum wilt symptoms onS. tuberosum clones indicated there was no apparent interaction between these two pathogens. Eighty-one percent of the 238 accessions remained free from root galls.Solanum species free from root galls and represented by three or more accessions werebrachycarpum, bulbocastanum, cardiophyllum, hjertingii, hougasii, infundibuliforme, kurtzianum, martinasense, multidissectum, multiinterruptum, papita, sparsipilum, spegazzinii, stoloniferum, tarijense, andvernei. S. microdentum (PI320312) andS. tuberosum ssp.andigena (PI245926) had the most extensive root systems free ofM. hapla galls.     

Cytoplasmic substitution inSolanum. II. Tuber characteristics of reciprocal backcross progeny

Summary Recurrent backcrosses (BC) were used to introduce nuclear factors ofS. tuberosum L. ssp.tuberosum into the cytoplasm of Andean potatoesS. tuberosum ssp.andigena (Juz. and Buk.) Hawkes andS. phureja Juz. and Buk. Each generation BC was produced in reciprocal directions to test the effect of cytoplasmic substitution on yield. This report analyses tuber number, tuber weight, and tuber length of BC₂ and BC₃ substitution into ssp.andigena cytoplasm and BC₂ and BC₂ substitutions intoS. phureja cytoplasm. Direction of cross had no consistent significant effect on yield components of ssp.andigena substitution lines. InS. phureja reciprocal progenies direction of cross was responsible for significant differences of some reciprocal sets. When there were significant differences the higher yield usually occurred when ssp.tuberosum was the pistillate parent, but in some progenies when ssp.tuberosum was the pistillate parent the yield was significantly lower than in the reciprocals. It is suggested that differences between reciprocals resulted from chromosomally encoded gene action, resulting from maternal and/or paternal effects, rather than cytoplasmic factors. Authorized for publication as paper No. 7494 in the Journal Series of The Pennsylvania Agriculture Experiment Station.     

Cytoplasmic evaluations during substitution backcrossing inSolanum

Summary Sterility-resistant cytoplasmic factors ofSolanum tuberosum spp.andigena (Juz. & Buk.) Hawkes and ofSolanum phureja (Juz. & Buk.) were combined with chromosomal genes ofS. tuberosum ssp.tuberosum. Eleven morphological characters of reciprocal F₁ and BC₁ progenies were monitored to evaluate rate of progression towards characteristics occurring in the recurrent ssp.tuberosum parent. Female and male fertilities of F₁ and BC₁ populations were also evaluated. Cytoplasmic factors did not influence morphological parameters consistently, except those relating directly to fertility. Differences between reciprocal progeny depended more upon the genes of individual parents used in crosses than on cytoplasm source. No consistent reciprocal differences occurred in tuber characters and those differences which arose seem to reflect a maternal rather than a cytoplasmic influence. F₁ and BC₁ progenies containing the sterility-resistant cytoplasmic factors of ssp.andigena or ofS. phureja had higher fertility than their respective reciprocal progenies with cytoplasm of ssp.tuberosum. Pennsylvania Agricultural Experiment Station Journal Series No 6212.     

Use of RAPD markers in potato genetics: Segregations in diploid and tetraploid families

The objective of the present study was to evaluate random amplified polymorphic DNA (RAPD) as a source of markers for use in investigations in potato genetics. Segregation of 18 loci in diploidSolanum goniocalyx xS. phureja and 12 loci in tetraploidS. tuberosum ssp.tuberosum ×S. tuberosum ssp.andigena families fitted Mendelian and tetrasomic ratios, respectively. Eight loci in the diploid progeny were arranged in three linkage groups. Segregations of these markers fitting expected ratios indicate that they can be effectively used in potato genetics, breeding and evolution.     

Cytoplasmic substitution inSolanum. I. Seed production,germination, and sterilities of reciprocal backcross generations

Summary Genes ofSolanum tuberosum L. ssp.tuberosum were introduced into cytoplasm ofS. tuberosum ssp.andigena (Juz. & Buk.) Hawkes andS. phureja Juz. & Buk. to reduce cytoplasmic sterilities. Alleles that influenced berry set and seed content produced differences between reciprocal progenies. Their expressions were interpreted in terms of genes of the maternal and/or paternal parents. When the ssp.andigena genotype was introduced from the maternal parent if favoured high berry set and low seed number. Maternal ssp.tuberosum favoured lower berry set and higher seed number. The source ofS. phureja cytoplasm, aS. phureja×S. chacoense F₁, used as maternal parent favoured lower berry and seed set. During successive backcrosses progeny expressions approached those of the recurrent ssp.tuberosum pollen parents. A low level of pollen sterility occurred in BC₂ plants, unrelated to direction of cross or cytoplasmic factors. By BC₄, seed set and fertility were as good as ssp.tuberosum, and recurrent backcrossing could be terminated without loss of seed production or fertility. Pennsylvania Agricultural Experiment Station Journal Series No. 7493.     

Potato germplasm collecting expedition to Chile, 1989, and utility of the Chilean species

A joint Chilean, United States potato (Solanum sect.Petota) germplasm collecting expedition was conducted in Chile between January 21–March 30, 1989. The trip resulted in collections ofSolanum brevidens (50 accessions),S. etuberosum (28 accessions),S. maglia (3 accessions) and indigenous primitive landraces ofS. tuberosum (24 accessions). Comments are presented on the habitats, distribution, and potential and realized breeding value of these species.     

Reaction of some wild and cultivated potato varieties to charcoal rot

With a view to select potato varieties possessing resistance to charcoal rot, laboratory tests were carried out at the Central Potato Research Institute, Simla (India). Five hundred and twenty six clones comprising tuber-bearing species ofSolanum and varieties and hybrids of potato were screened for their reaction toMacrophomina phaseoli (Maubl.) Ashby. A high degree of resistance was observed in six clones ofSolanum chacoense and four hybrids withS. chacoense germ plasm, while moderate susceptibility was observed in another six clones ofS. chacoense, three clones ofSolanum tuberosum ssp.andigena and nineteen hybrids produced at the Institute.     

Selfing rates in two wild polyploid solanums

The rate of selfing in the wild, tuber-bearing speciesS. gourlayi Hawkes (2n = 4x = 48) andS. oplocense Hawkes (2n = 6x = 72) was estimated from progeny of plants nulliplex for the “parallel spindles (ps) allele. The estimated values for plants grown in experimental plots were 22% forS. gourlayi and 1% forS. oplocense. The quantitative method used appears to be a simple and efficient way to calculate selfing rates in polyploids. Knowledge of selfing rates is useful for basic population genetic studies and for plant breeding and seed production of economic crops. There is a need for genetic markers inSolanum species if selfing rates are to be taken into consideration for the selection of an appropriate breeding method for the production of true potato seed.     

Pollen-pistil incompatibility in a diploid hybrid potato population with cultivated and wild germplasm

The basis of low seed set was investigated in a diploid hybrid population with germplasm from the cultivated speciesSolanum tuberosum spp.tuberosum andS. tuberosum ssp.phureja and the wild speciesS. chacoense. Controlled crosses were performed following an incomplete diallel mating design which included the hybrid population and the parental species. Pollen grain germination and pollen tube growth were observed with fluorescence microscopy in 174 intrapopulation and interspecific combinations of genotypes. Fifty percent of the combinations of genotypes within the hybrid population and 46% of those between this population and the parental species were incompatible; overall, 71% of the interspecific combinations of genotypes were compatible when plants of the hybrid population were used as females, vs. 5% when used as males. Although the site of reaction could vary in a given intrapopulation or interspecific cross with the combinations of genotypes, pollen tube inhibition occurred in the first third of the style in 42% of them. Since the gene pool of the hybrid population had been widened with germplasm from other geographic areas and the genotypes ofS. tuberosum ssp.tuberosum, S. chacoense andS. tuberosum ssp.phureja used in this study were not the ones involved in the original crosses, it is concluded that the S-locus is not controlling the incompatibility reaction but rather that a cross-incompatibility system, possibly governed by more than one locus, is acting.     

Exploitation of Exotic, Cultivated Solanum Germplasm for Breeding and Commercial Purposes

Native potato species (NPS) are cultivated potatoes which do not belong to S. tuberosum ssp. tuberosum. They are maintained by the farmers of the Andes for subsistence under harsh environmental conditions where other potatoes cannot compete. Within the huge phenotypic variability between and within these species certain accessions possess resistances to different pests and diseases, remarkable culinary and processing quality and favourable nutritional properties. We present first evaluation results of a set of NPS for these characters and discuss prospects for exploiting this valuable germplasm for breeding and for developing novel products for niche markets.     

Species relationships between a wild tetraploid potato species,Solanum acaule bitter, and its related species as revealed by rflps of chloroplast and nuclear DNA

Solanum acaule Bitter is a wild, disomic tetraploid potato species widely distributed in the South America. In this study, species relationships between eight accessions ofS. acaule and 108 accessions of 27 morphologically closely related species were investigated using chloroplast and nuclear DNA RFLPs. Chloroplast DNA types were determined for most of the accessions based on restriction digestion patterns of entire chloroplast DNA. C type chloroplast DNA was common inS. acaule andS. albicans (a hexaploid derivative fromS. acaule), which was also found inS. megistacrolobum, S. sanctae-rosae,S. raphanifolium, and several other Peruvian species in seriesTuberosa. Nuclear DNA was analyzed by Southern hybridization with 31 single-copy RFLP probes. One hundred and thirty-four bands were scored, from which a UPGMA dendrogram was constructed to show overall similarities among accessions.Solanum acaule andS. albicans (andS. demissum) formed a cluster with a high similarity, and then, this group was clustered withS. megistacrolobum andS. sanctae-rosae. The resulting cluster was well separated from other clusters. Thus, we suggest that an initial tetrasomic tetraploid arose from eitherS. megistacrolobum orS. sanctae-rosae. Interestingly, a Mexican hexaploid speciesS. demissum showed the closest similarity toS. acaule andS. albicans, suggesting that they shared a common ancestry.     

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.     

Progress report: Resistance to the Colorado potato beetle and potato leafhopper inSolanum tuberosum subsp.andigena

An extensive collection of 1527 clones ofS. tuberosum subsp.andigena was screened in 1973 in unreplicated plots to test for resistance to the Colorado potato beetle and potato leafhopper. All clones were susceptible to the beetle. Of 17 clones selected in the 1973 tests for resistance to the potato leafhopper, 7 selections were significantly more resistant than the control (Katahdin) in a replicated experiment in 1974.     

Some studies on the distribution and incidence of potato mop-top virus in Peru

Symptoms of PMTV are distributed widely in potatoes in the highlands (Andes) of Peru, but have not been found in coastal plantings; they were observed in 9 out of 22 Peruvian Departments. Incidences of over 10% of affected plants in one or more crops were found in 14 different localities. Thirteen cultivars with symptoms were observed, 9 wereSolanum tuberosum subsp.andigena Juz. & Buk., 3 were hybrids ofS. tuberosum subsp.andigena xS. tuberosum subsp.tuberosum L orS. Curtilobum Juz. & Buk. and 1 wasS. juzepczukii Buk. Symptoms were also seen in 29 clones of the potato germplasm collection of the International Potato Center. Distribution and prevalence of PMTV in Peru appear to be related to those rainfall and temperature conditions that favour its fungus vectorSpongospora subterranea (Wallr.) Lagerh.