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.     

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.     

Resistance to potato leaf roll virus inSolanum brevidens

Summary Plants ofSolanum brevidens graft-inoculated with potato leaf roll virus (PLRV) grew vigorously and had a normal healthy appearance. Although presence of the virus was confirmed in all inoculated plants by graft tests to potato and/orDatura stramonium, recovery of PLRV fromS. brevidens PI 218228 usingPhysalis floridana and the aphidMyzus persicae was erratic and only few test seedlings became infected. Ease of recovery of the virus using aphids was not influenced by presence of a continuous graft union with infected potato. Testing ofS. brevidens PI 245763 withM. persicae was not possible due to poor aphid survival on plants of this accession.     

The protein,non-protein and total nitrogen inSolanum tuberosum,ssp.andigena potatoes

Total protein estimated from 80% ethanol insoluble nitrogen in residue ofS. tuberosum, ssp.andigena tubers agreed well with results obtained by Potty method and estimation of non-dialyzable nitrogen. The method is simple, rapid and applicable for screening large numbers of samples. Dry matter, total nitrogen, protein nitrogen and non-protein nitrogen were analyzed for 50 clone samples harvested in Huancayo, Peru, and correlations between the various constituents are statistically analyzed and discussed. An increase in total nitrogen with an increase of protein nitrogen was observed. Clones with higher dry matter normally showed lower % of non-protein nitrogen. The percentage of protein nitrogen to total nitrogen varied from 40 to 74% in the 50 clone samples and clonal differences in protein production were evident.     

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.     

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.     

Foliar solanidine glycoside levels inSolanum tuberosum populations selected for potato leafhopper resistance

Solanum tuberosum L. Gp. Tuberosum populations that had been recurrently selected for resistance to potato leafhopper,Empoascafabae (Harris), were tested for levels of foliar solanidine glycosides. Leafhopper infestation level was 57% lower than for the unselected population after seven generations of selection. The mean concentrations of foliar solanidine glycosides significantly (P<05) increased from 40 mg/100 g fresh weight (fw) in the unselected population to 65 mg/100 g fw in the population developed from seven generations of selection for leafhopper resistance. The linear relationship between the level of leafhopper infestation and the concentration of foliar solanidine glycosides among population means was significant (P<01) and negative (r=?0.85).     

Tuber yields and specific gravities inSolanum tuberosum populations recurrently selected for resistance to potato leafhopper

Solanum tuberosum genotypes from the 3rd, 5th, and 7th generations of recurrent selection for resistance to potato leafhopper were compared with genotypes from the base, unselected population for tuber yield and specific gravity over a five year period. Mean tuber yields of the genotypes in the 3rd and 5th generations were equal to the yield of those in the base population. The mean tuber yield in the 7th generation was significantly lower than the mean in the base population and the means in the other selection generations. However, the mean tuber specific gravities of the 5th and 7th generation genotypes were slightly higher than the mean in the base population. The variability of tuber yield among genotypes in the 7th selection generation was lower than the variability in the base population and in the 3rd and 5th selection generations. It was concluded that there was moderate genetic potential for selecting genotypes with resistance to potato leafhopper that had acceptable tuber yields in the 3rd and 5th selection generations, but by the 7th generation the potential was considerably lower. The genetic potential for selecting resistant genotypes with acceptable tuber specific gravities remained about the same in each of the selection generations.     

Relative Braunfäuleresistenz beiSolanum tuberosum ssp.andigena

Zusammenfassung Ergebnisse systematischer Prüfung auf relative Resistenz der Knollen von 1274 Herkünften der ssp.andigena (adg) genenüberPhytophthora infestans werden mitgeteilt. Die Methode des Kn?llchenstestes erm?glichte dabei das Eindringen des Pilzes direkt ins Knollenmark oder über die intakte Schale. Nur etwa 1% der Herkünfte enthielt einen Anteil von >25% Idiotypen mit gutem Resistenzniveau. Eine Analyse der Fundorte ergab keine Anhaltspunkte für die gezielte Suche von Resistenzquellen. Ergebnisse aus der züchterischen Nutzung von adg betreffen die ph?notypische Resistenz der Nachkommen und weitere Merkmale.

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Summary Results are reported of late blight resistance inS. tuberosum ssp.andigena (adg) and its use in breeding. Tests were carried out on material of the gene bank in Gross Lüsewitz (GLKS). Seedlings were cultivated under glass cover in a 6-years test period. To examine tuber resistance toPhytophthora infestans the following test was set up: 2–5 tubers per idiotype, up to 8 idiotypes per accession and year of test were taken and 1274 different accessions were examined with an average number of 23 idiotypes and 59 tubers from each. Inoculation was made by fresh deep cuts to the pith and by subsequent immersion in a solution of zoospores, 6–9×10⁴ ml⁻¹ with a mixture of the pathotypes (1.2.3.4.5.7.10.11, 1.2.3.4.7.8.10 and 1.2.3.4) at a temperature of 16–18°C and at an air humidity of >90%. Evaluation of the presence of aerial mycelium and browning after 7 days allowed the calculation of a resistance score (B_K): grade 9 (highly resistant) to grade 1 (highly susceptible). The mean values derived from the accessions (Fig. 1) revealed that a medium level of susceptibility is dominating and that they rarely exceed average levels of cultivars. Approximately 1% of the accessions contained ≥25% of idiotypes with B_K ≥6 and these may be interesting for breeding purposes. Table 1 shows the analysis of accessions with the most favourable mean values. Geographic evaluation did not yield indications for a more purposeful search for sources of resistance, since detailed reports on find-spots were missing (Table 2). Combination tests withPhytophthora-resistant genes of adg for crosses of adg withS. demissum (dms) andS. stoloniferum (sto) proved to be more useful as they partly showed good heritable resistance to haulm and tuber infection ofP. infestans (Table 3). The problem of the possible role of unknown r-genes is discussed. Only a few crosses with ssp.tuberosum (tbr) generated a progeny with sufficient resistance. Selection from such progeny over several years resulted after the second year in rejections, mainly because of susceptibility for viruses, too small tubers and lack of flowering (Table 4). Results of varietal research of the former German Democratic Republic proved that with the use of suitable parents in breeding for nematode resistance,Phytophthora susceptibility from adg could be balanced off (Table 5). The cultivar Auralia is a good example of the importance of adg in achieving a high level of resistance to late blight.

     

Research inSolanum spp. of sources of resistance to the potato tuber mothPhthorimaea operculella (Zeller)

Summary The potato tuber moth (PTM) represents a dangerous pest on potato crop in Italy, spreading out from southern areas to central and northern areas. Introductions ofSolanum berthaultii, S. commersonii, S. pinnatisectum, S. sparsipilum, S. spegazzini, S. sucurense, S. tarijense wild species andS. tuberosum × S. berthaultii hybrids were evaluated for resistance to a PTM population isolated from a field in central Italy, by means of an antibiosis test on tubers in the laboratory and of an antixenosis trial in the field. SeveralS. sparsipilum andS. pinnatisectum clones showed an antibiosis effect on larval survival and antixenosis of the aerial and the hypogeal parts of the plant. In the field, the genotypes with leaf glandular trichomes did not revcal the expected antixenosis effect of the acrial part of the plant.     

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.     

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.     

Starch to sugar interconversion inSolanum tuberosum L. I. Influence of inorganic ions

No relationship could be found between calcium, magnesium, potassium, total phosphorous contents, and reducing sugar accumulation in apical and basal portions of Russet Burbank tubers. However, a highly significant positive correlation was found between inorganic phosphorous content of tubers and reducing sugar accumulation. Inorganic phosphorous and sugar levels were highest in the basal portion of moisture stressed and low temperature stored tubers, suggesting a relationship between inorganic phosphorous and enzymatic activity in the interconversion of starch to sugars in potatoes. Tubers stored at 5.5 C and 15.5 C had higher contents of calcium and magnesium in the basal portion and significantly higher potassium content in the apical portion. Storage temperatures or moisture stress during growth appeared to have no significant influence on calcium, magnesium, potassium or total phosphorus contents of the tubers.     

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.     

Inheritance of extreme resistance to potato virus Y in potato

Summary Segregation for extreme resistance to PVY was evaluated in progenies derived from crossing two extremely resistant potato clones with parents differing in resistance. Resistance was evaluated after mechanical inoculation with PVY^O and PVY^N, and after graft inoculation with PVY^O. Biological and serological tests (ELISA) were used for virus detection. The extreme resistance is governed by a single dominant gene, but observed segregations deviated from the expected ratios. Considerable modifying effects were detectable, depending on the potato genotype and virus isolate, for a significant excess of susceptible genotypes was observed in some progenies. Moreover, genotypes with non-parental types of resistance to PVY were observed.     

Resistance to virus S in the potato

On the basis of data from 18 crosses, resistance to potato virus S of the type encountered in Saco potato, segregated as an homozygous recessive. Neither Saco nor seedlings found to be resistant in greenhouse tests became infected when grown in the field and brushed with PVS-infected haulms. Meanwhile, susceptible seedlings from a cross segregating resistant and susceptible became infected in both greenhouse and field as readily as did seedlings from a cross producing only susceptibles. Resistance to PVS segregated independently of resistance to PVX.