Starch-sugar interconversion inSolanum tuberosum L. II. Influence of membrane permeability and fluidity

A strong relationship was found between membrane permeability and starch to sugar conversion in stored potatoes. Tissue from tubers stored at low temperature had higher sugar content and more permeable membranes than from that of tubers stored at high temperature. Tubers, moisture stressed during growth and stored at 5.5 C, accumulated more reducing sugars and had more permeable membranes than tubers from normally irrigated plants when stored at the same temperature. The basal portion of Russet Burbank tubers accumulated more sugars and was also found to have significantly more permeable membranes than the apical portion. Examination of membrane order with spin-labeled lipid probes showed that the order parameter of amyloplast membranes was less at low temperatures than when measured at higher temperatures. Membranes examined with spin-labeled lipid probes from tubers stored at 5.5 C and 15.5 C showed similar order parameters at all temperatures measured between 0 and 25 C with a linear decrease in S values at higher temperatures. These results strongly indicate a physical change of membranes with changing temperature, thus influencing sugar accumulation, which is also reversible, as indicated by loss of sugars during the reconditioning process.     

Tolerance to potato leafhopper inSolanum tuberosum L. gp. Tuberosum clones

We identified clones inSolanum tuberosum L. gp. Tuberosum breeding populations that, although susceptible to infestation by potato leafhopper,Empoasca fabae (Harris), exhibited a tolerance which was manifested by the ability to produce higher than expected tuber yields when heavily infested with leafhoppers. Such tolerance was noted in a number of clones in varying degrees, but one, B6930-1, was exceptional. It sustained only a 19% loss in tuber yield compared to ‘Katahdin,’ a susceptible cultivar, that averaged 33% lower tuber yields under similar infestation levels. We studied the seasonal growth patterns of this clone and compared them to those of Katahdin, and B6705-10, a breeding clone with known resistance to leafhopper infestation. We found that much of B6930-l’s tolerance results from its early, vigorous vine growth and its early and rapid rate of tuber bulking, enabling this clone to escape some of the effects of leafhopper feeding, whereas Katahdin was usually just beginning to tuberize at the height of leafhopper infestation.     

Shoot inhibition inSolanum tuberosum. I. Response to ammonium and nitrate nitrogen sources

Solanum tuberosum Group Tuberosum plants grown in a non-nutritive media exhibit a shoot inhibition which follows the normal tuber bud dormancy. The shoot inhibition is characterized by very slow growth of the aerial portion of the plant with little leaf development. An external source of nitrogen, either nitrate-N or ammonium-N, applied to the roots of Iopride plants overcame the inhibition while only a nitrate-N source was effective in overcoming the inhibition of Kennebec plants. Group Phureja and Stenotomum and otherSolanum species evaluated did not show the shoot inhibition phenomenon.     

An evaluation of bromoethane for breaking tuber dormancy inSolanum tuberosum L.

Bromoethane was evaluated for its suitability to induce dormant tubers to sprout. Bromoethane immediately broke dormancy and caused multiple sprouting when applied to whole tubers as a vapor at 0.1 or 0.2 ml/L for 24 h at room temperature. Superficial and localized necrosis developed on the tubers if proper skin set had not occurred either in the field or after a curing period. In fall greenhouse trials, bromoethane treatment of whole tubers of the cultivars Red Pontiac, Russet Burbank, Bintje, Kennebec and Caribe induced them to sprout 40 to 70% earlier than untreated controls. Application of bromoethane significantly increased the mean rate of shoot elongation by 2.8 mm/day although there was no significant difference in its effect among the cultivars.     

Influence of moisture stress during growth on14CO2 fixation and translocation inSolanum tuberosum L.

Moisture stressing of potato plants resulted in reduced¹⁴CO₂ fixation and translocation of labelled photosynthates from leaves to tubers. A majority of the label was recovered in the sugar fraction of both leaves and tubers. The amount of labelled¹⁴C recovered in the organic acid fraction of tubers of normally irrigated plants was significantly higher than in tubers which had been moisture stressed. In the other fractions, the differences were not significantly different. Injection of uniformly labelled sucrose into the basal portion of attached tubers of stressed and non-stressed plants showed greater translocation of labelled carbon by tubers of stressed plants from basal to the apical portion and also into the stems as compared to non-stressed plants.     

Resistance to potato virus Y inSolanum tuberosum spp.andigena

Tests were made on lines ofSolanum tuberosum spp.andigena to determine 1) whether resistance to potato virus Y exists in the Andigena germplasm, 2) the nature of its inheritance, and 3) the type of resistance. Results of the isolation and identification studies indicated that the pathogen involved was a common strain of potato virus Y. Under field conditions susceptible plants frequently escaped infection. However, field exposures over two seasons resulted in the same ratios as tests in which the same progenies were mechanically inoculated. Mechanical inoculation at the seedling stage proved to be a reliable means of transmission and resulted in accurate screening for resistance. Of 641 tub × tub clones tested, all were susceptible to the virus. Of 366 tub × adg clones tested, 170 were resistant and 196 were susceptible. This fits a 13:15 ratio, assuming random chromatid segregation and a single dominant gene conferring resistance. Plants that were resistant following mechanical transmission were also resistant when inoculated by aphids, indicating the reliability of mechanical transmission as a means of screening for resistance. To determine the type of resistance, top-graft and approach-graft tests were made. Failure to recover the virus from resistant plants inoculated by either grafting method suggests that immunity is the type of resistance involved.     

Screening for gibberellin deficiency mutants inSolanum tuberosum ssp.andigena

A GA deficiency mutant was previously described in a single population ofSolanum tuberosum ssp.andigena (adg). A representative sample of 120 adg populations in the US Potato Genebank was screened for the dwarfing mutant. Up to 500 seedlings of each adg population were evaluated. Dwarfs were detected in 14 populations from a minimum of 0.2% to a maximum of 27.7%, indicating that the allele is not particularly rare or at risk of loss from the Genebank.     

Decapitation and genetic markers as related to haploidy inSolanum tuberosum

Summary Numerous haploids ofS. tuberosum are required if their value for breeding and genetic studies is to be adequately explored. Genetic markers, particularly pigmentation of the pre-transplant seedling, allows for early elimination of hybrids and consequently the ready detection of potential haploids among the F₁ from interspecific matings. Decapitation is an effective means of markedly increasing the number of seeds per pollination following such interspecificSolanum matings. The combined use of suitable genetic markers and decapitation substantially increases the efficiency of detecting haploids. Crops Research Division, Agricultural Research Service, USDA Cooperation of the Inter-Regional Potato Introduction Project (IR-1) in providingSolanum materials is hereby acknowledged.     

Changes in endogenous abscisic acid,soluble sugars and proline levels during tuber dormancy inSolanum tuberosum L.

Abscisic acid (ABA), sucrose, reducing sugars and proline contents were monitored over an eleven-month period in tubers of three potato cultivars that varied in tuber dormancy. ABA and proline levels increased after top pulling the haulms and were not affected by harvest date. Proline did not change in either a storage temperature or cultivar-specific manner. The highest concentrations of ABA were found in tubers stored at 2°C while the lowest concentrations occurred in tubers stored at 20°C. At 10°C, the end of tuber dormancy in the cultivars Kennebec and Nooksack (but not Sebago) coincided with the decline in ABA content. There was no evidence of a threshold concentration of ABA below which sprouting would occur. Tuber samples of 10 different cultivars were removed from 10°C and placed in 20°C storage (in darkness). Initial ABA concentrations (i.e., at the time of removal from 10°C storage) were positively correlated with duration of dormancy and negatively correlated with subsequent rates of sprout elongation at 20°C. Sucrose content was negatively correlated with duration of dormancy. Reducing sugars responded primarily to storage temperature and did not appear to be related to dormancy or sprouting.     

Effect of cold storage on proteinase and chorismate mutase activities inSolanum tuberosum L. Genotypes differing in blackspot susceptibility

Potato tubers (Solanum tuberosum) from genotypes differing in chemical susceptibility to the physiological disorder blackspot bruise (TXA 763-5, Atlantic, Ranger Russet, Russet Burbank, and Lemhi Russet) were stored for eight months at 3 C. Protein extracts from each cultivar were assayed for proteinase and chorismate mutase (CM) activities. During cold storage, three of five genotypes tested increased in their ability to develop melanintype pigments responsible for blackspot. Concurrent with this were increases in either endopeptidase, aminopeptidase, or CM activities or combinations of enzyme activities specific to genotypes. These increases in enzyme activity may be responsible for the increase in levels of the melanin precursor tyrosine, associated with cold storage of potato tubers.     

Salt tolerance inSolanum kurzianum andS. tuberosum cvs Alpha and Russet Burbank

Summary The cultivated potatoSolanum tuberosum cvs Alpha and Russet Burbank and the wild speciesS. kurzianum were compared with respect to salt tolerance. Plants of the wild species were found to be more salt tolerant than those of the cultivated species since their growth was less impaired by the salinity, although they accumulated more sodium and less potassium ions in the shoot. Unlike the whole plant, callus derived from the wild plants was not more tolerant than that from the cultivated species. Differences in the responses to salinity between cultivated and wild plants, and between the whole plants and calli derived from them are discussed. Based on these differences and the similarity of the physiological responses to salt stress betweenS. kurzianum and the wild salt-tolerant relatives of tomato, the former is suggested as a potential source of genes for increasing the salt tolerance of potato.     

Association between trichome characters and agronomic traits inSolanum tuberosum (L.)XS. berthaultii (hawkes) hybrids

In 1977, a program to develop potato cultivars with insect resistance based on the glandular trichomes found onSolanum berthaultii was initiated at Cornell University. Associations between agronomic and trichome characters were suspected due to difficulties in selecting hybrid plants with both insect resistance and acceptable agronomic characteristics. Plants from backcrosses and intercrosses were studied. A strong association between the presence of B trichome droplets and undesirable agronomic characteristics was established in backcrossed generations. The backcross plants bearing droplets produced significantly lower yields, fewer tubers, later maturing plants, and poorer foliage and tuber appearance than their sibs without the droplets. In intercrosses, no associations were found. Good MEBA scores were seldom found in backcrossed plants without B droplets. The associations observed are speculated to be due to linkage or structural genomic differentiation between the genomes of the species involved in these populations.     

Progeny mean, heterosis and heterobeltiosis inSolanum tuberosum x tuberosum andS. tuberosum x andigena families under a short day sub-tropic environment

Summary Solanum tuberosum x tuberosum (TxT) families were compared withS. tuberosum x andigena (TxA) families as progeny mean, heterosis and heterobeltiosis for ten important agronomic characters by evaluating 72 cross combinations (36 of TxT and 36 of TxA, from 18 common female parents), for three successive seedling and clonal generations under short day sub-tropic conditions. TxA families had more vigorous progenies, higher tuber yield, higher number of tubers, larger tubers and better general impression than TxT families. The TxA families were inferior to the TxT families for characters such as tuber colour and uniformity of tuber colour, but their progeny means were within the acceptable range. High progeny means of TxA families were associated with high heterosis and high heterobeltiosis in these families, although there were a few exceptions. High mean performance for tuber yield and tuber number were associated with high variance of these traits in TxA families. It is concluded that, unlike under long day environments, andigena adapted to short days can be used advantageously for exploiting heterosis in the potato breeding programmes of short day subtropic environments.     

Green peach aphid resistance by glandular trichomes inSolanum tuberosum xS. berthaultii hybrids

Three interspecific F₃ hybrid clones ofSolarium tuberosum L. x 5.berthaultii Hawkes bearing both Type A and Type B glandular trichomes were assessed for resistance to the green peach aphid,Myzus persicae (Sulzer). In glasshouse trials, aphid mortality and population development on hybrid clones were similar to those on the aphid-resistant parent,S. berthaultii. Trichome exudate of the hybrid, B227-63, was as effective in aphid immobilization as that ofS. berthaultii. Field populations of the green peach aphid on hybrids were intermediate between those onS. berthaultii and susceptibleS. tuberosum cultivars.     

Disease resistance inSolanum phureja and diploid and tetraploidS. tuberosum × S. phureja hybrids

Summary DiploidSolanum phureja, diploid and tetraploidS. tuberosum × S. phureja hybrid, and tetraploidS. tuberosum backcross clones were assessed for resistance to commercially important diseases. There was a reduction in the expression ofS. phureja characteristics with increasing dosage ofS. tuberosum genetic material. The generally high resistance of theS. phureja group to common scab, potato leafroll virus and potato virus Y decreased, while resistance to gangrene, foliage and tuber blight tended to increase. Resistance genes were probably well dispersed throughout theS. phureja genotype so that many were lost on hybridisation, butS. phureja could be a useful source of scab and virus resistance in the production ofS. tuberosum cultivars.     

Reciprocal differences in the photoperiod reaction of hybrid populations inSolanum tuberosum

Large reciprocal differences were observed inSolanum tuberosum, when a mixed population of Group Phureja and Gp. Stenotomum was reciprocally crossed with a population of Gp. Tuberosum haploids. In the progeny reciprocal differences were observed for tuber initiation, tuber set, vine senescence, tuber yield, flowering, and male fertility. These differences were large in the F₁ generation, but were less dramatic when the populations were inter-mated to form F₂ generations. It is proposed that most of the reciprocal differences were due to a difference in photoperiod response in the reciprocal populations. Cytoplasmic inheritance or dauermodification are considered the most likely explanations for this difference in photoperiod reaction.     

Restriction fragment length polymorphism inSolanum spp for the construction of a genetic map ofSolanum tuberosum L.: a preliminary study

Summary When using two restriction enzymes and DNA probes from different sources, high levels of restriction fragment length polymorphism (RFLP) were observed in Southern blot hybridisation experiments, among 6 di(ha)ploid genotypes ofSolanum tuberosum and some closely related species. In 3 F1 sample populations of 14 individuals each, both heterozygosity and segregation of hybridisation patterns were observed. The non-radioactive biotin-dUTP/SA-AP method for DNA detection on Southern blots proved to be satisfactory and reliable.