Diploid potato germplasm derived from wild and land race genetic resources

Diploid cultivated species, haploids derived from tetraploid cultivars, and their wildSolanum relatives were used to generate various diploid potato genetic stocks. These stocks have significant value in potato breeding because: 1) genetic diversity in the potato population can be kept variable with the diploid germplasm which confers genetic variation from wild and cultivated species; 2) crossability of this diploid germplasm is facilitated by the function of 2n gametes; and 3) high levels of pest resistances originating from the process of introgression of the wild and cultivated genetic resources can be used to improve the tetraploid cultivated potato genepool.     

Identification of parents suitable for molecular mapping of immunity and resistance genes in solanum species

A survey of DNA polymorphisms and bacterial ring rot reactions inSolanum species was conducted to identify parents that when crossed would produce an F₁ mapping population useful for identifying DNA markers tightly linked to genes for immunity or resistance to bacterial ring rot.Solanum tuberosum, S. acaule, diploidSolanum species, doubled monoploid lines ofS. phureja, and somatic fusion hybrids betweenS. tuberosum andS. brevidens were established in tissue culture from single true potato seeds or tubers and evaluated for bacterial ring rot reactions in greenhouse studies with root-inoculated tissue cultured plantlets. Establishment of tissue culture stocks insured the availability of homogeneous genetic material for use in bacterial ring rot assays and genetic analyses. Presence ofClavibacter michiganense subsp.sepedonicum was assessed in stems by an immunofluorescence antibody assay (IFAS). Two accessions were found to be immune to bacterial ring rot. DNA polymorphisms were detected within and among 24 accessions evaluated with 24 RFLP markers and 10 arbitrary oligonucleotide primers (RAPDs). These results identify parents suitable for future mapping of gene (s) for immunity or resistance to bacterial ring rot.     

Consecutive elisa screening with monoclonal antibodies to detect potato virus YN

In a 1992 survey of potato fields in Canada for the tobacco veinal necrosis strain of potato virus Y (PVY^N), initial enzyme-linked immunosorbent assay (ELISA) screening with one monoclonal antibody (MAb 295.5) followed by a second ELISA screening with a panel of several MAbs (4E7, Bioreba, 1F5 and 295.5) was assessed as a means of rapidly identifying positive samples prior to confirmation by bioassay. MAbs 4E7 and Bioreba were used in double antibody sandwich (DAS) ELISA, while MAbs 1F5 and 295.5 were used in triple antibody sandwich (TAS) ELISA. In the second ELISA, MAbs 4E7, 1F5 and Bioreba all enhanced test specificity relative to the retest with MAb 295.5. All the MAbs were found to react, to some degree, with isolates of the common strain of PVY (PVY^O), but MAb 4E7 was the most specific widi no cross-reaction being observed at, or above, the signal to noise (S:N) threshold of 4:1. However, this MAb was also the least sensitive. At the S:N threshold of 4:1, its sensitivity was 68%, compared to a sensitivity of close to 100% for the other MAbs     

Solanum berthaultii Hawkes affects the digestive system,fat body and ovaries of the Colorado potato beetle

Ovarian development and fecundity of Colorado potato beetles reared on the resistant potato species,Solanum berthaultii were reduced compared to females reared on the susceptible potato,S. tuberosum. Striking changes in the appearance of the digestive tract and large quantities of undigested plant material in the midgut of females reared onS. berthaultii suggest that ovarian development might be impaired by poor nutritional quality ofS. berthaultii foliage. Alternatively, enlargement of the midgut by undigested plant material might physically limit ovarian development and subsequent fecundity. These results suggest that a major impact ofS. berthaultii on CPB performance occurs in the physiology of digestion and reproduction.     

Water deficit effects on potato leaf growth and transpiration: Utilizing fraction extractable soil water for comparison with other crops

Numerous studies have demonstrated that physiological responses of many crops to the fraction of extractable soil water conforms to a generalizable pattern. This suggests that differences among crops in their drought tolerance are largely due to differences in the total amount of transpirable water the crop can extract. Potato is frequently assumed to be more drought sensitive than other agronomic crops due, at least in part, to a shallow root system. In the research reported here, potato leaf growth and transpiration response to water deficits were determined as a function of fraction transpirable soil water (FTSW). Transpiration was unaffected by water stress until a critical FTSW was achieved when 64% to 80% of the extractable soil water was depleted depending on the cultivar. This was similar to the response reported for 8 other agronomic crops. In terms of transpiration, potato hypersensitivity to drought stress appears to be due to less effective soil water extraction. Leaf growth, however, showed a unique response to soil water deficits. Leaf growth began to decline when 40% of the extractable soil water was depleted. The associated critical FTSW was higher than any previously reported for all other crops. These data indicate that in addition to extracting less soil water, an additional physiological process related to leaf expansion must be contributing to the potato’s hypersensitivity to drought.     

Comparison of some diagnostic assays for bacterial ring rot of potato: A case study

The results of testing 48 stems and tuber samples, representing 15 seed lots from several different growers, for the presence of the causal organism of bacterial ring rot,Clavibacter michiganensis subsp.sepedonicus with the gram stain, latex agglutination (LAT), enzyme-linked immunosorbent assay (ELISA), and a DNA hybridization assay (DHA) were compared. The frequency with which positive tests were obtained varied significantly among assays and was associated with symptom expression in samples. Detection was highest with the serological assays and lowest for DHA. Use of the gram stain, in conjunction with either LAT, ELISA, or DHA reduced the number of positive diagnoses, but increased the agreement between results for different assay combinations. Based on a comparison of results for both individual samples and seed lots, the performance of LAT and ELISA for diagnostic purposes were equivalent. DHA was found to be less useful due to limitations in test sensitivity forC. m. sepedonicus, but it does give unequivocal diagnoses of samples where bacterial populations are sufficient to allow detection.     

An approach to field screening potato genotypes for potato leaf roll virus resistance

Eight potato cultivars and two advanced breeder selections were assessed for field resistance to the potato leaf roll virus (PLRV) following field exposures in which PLRV-infected Russet Burbank plants were used as inoculum sources within treatments. This screening protocol provided consistent PLRV resistance ratings despite year-to-year variation in PLRV pressure. Secondary disease incidence based on enzyme-linked immunosorbent assay (ELISA) of foliage from tuber progeny ranged from 0–87% in 1990 and 0–67% in 1991, and was consistent with reported PLRV resistance ratings for eight of ten genotypes. Agreement between visual assessment and ELISA on plants from harvested tubers was 94% in 1990 and 83% in 1991, for all genotypes. However, agreement data were inconsistent from year-to-year, with the exception of three genotypes. In both years, current season infection, based on ELISA of foliage, was detected in less than two percent of the plants and, was inadequate as a measure of secondary PLRV incidence. Green peach aphid (GPA) populations did not differ among genotypes at sampling times during the season, but the PLRV concentration in GPA colonizing Russet Burbank plots was significantly higher than in GPA colonizing any other genotype.     

Use of seedling tubers from TPS in southern Italy

The TPS seedling tuber technique can be successfully adopted in developing as well as in developed countries as a standard agronomic system for potato production. Experimental work has been started in order to select the best parental lines and to evaluate the appropriate breeding schemes for the use of this technique in southern Italy. During 1989 48 true potato seed (TPS) families with different genetic backgrounds were tested for seedling tuber production and they produced a good yield. The seedling tuber families were tested for tuber production during 1990 by subdividing them in two size classes: 25mm-35mm and 35mm-45mm. The highest yield was attained by 4X x 2X families and the analysis of variance indicated significant differences with regard to tuber size and TPS families for both total and marketable tuber yield. This technique has significant potential for providing tubers for both the fall and winter crop in Italy.     

Identification of genetic factors influencing chip color in diploid potato (Solanum spp.)

A genetic map was constructed with a combination of isozymes, restriction fragment length polymorphisms (RFLPs) and randomly amplified polymorphic DNA (RAPDs) to apply quantitative trait loci (QTL) analysis to identify genetic factors that contribute to chip color in potato. The diploid population used was a cross between aSolanum tuberosum haploid andS. chacoense hybrid used as female parent and aS. phureja clone used as male. Chip color was determined visually on samples fried from tubers stored at 10C. On a scale of 1 (light color) to 10 (dark color), the population ranged from 2 to 8 while the parents average chip color was 3.5. Based upon one-way ANOVAs (P < 0.05), 13 genetic markers showed significant associations which represent a total of six QTLs. A multiple locus model based upon the markers that have the largest effect per QTL explained 43.5% of the phenotypic variation for chip color in the population and increased to 50.5% when one significant epistatic interaction was included in the model. All the significant marker associations were identifed in theS. tuberosum-S. chacoense hybrid. Through preliminary data, the results of this study suggest that additive effects contribute a significant portion of the genetic variation for chip color. The identification of these QTLs for chip color variation provides the means to apply marker-assisted selection to introgress these genes into the cultivated potato germplasm.     

Response ofColletotrichum coccodes to fungicidesin vitro

Black dot is an important disease of potato that affects all plant parts. The causal agent,Colletotrichum coccodes, is commonly found on potato tubers used for seed. Our objective was to determine thein vitro sensitivity ofC. coccodes to the fungicides maneb, thiabendazole, imazalil and CGA 173506, a phenylpyrrole. These fungicides are currently used, or are being tested for use, as potato seed treatments in the United States. All four fungicides reduced radial growth, sclerotial germination and spore germination ofC. coccodes at 10 μg/ml and higher. The fungicide concentrations that inhibited radial growth by 50% were 2 μg/ml, 5 μg/ml, 35 μg/ml, and 40 μg/ml for imazalil, CGA 173506, maneb and thiabendazole, respectively. TBZ was less inhibitory than the other three fungicides and stimulated sclerotial productionin vitro. Isolates ofC. coccodes differed in their sensitivity to maneb, thiabendazole and imazalil in radial growth, but not spore and sclerotial germination, assays. On CGA 173506, radial growth of fourC. coccodes isolates was inhibited, but these isolates produced sectors which grew normally. Germination of most sclerotia from these isolates was inhibited, but some germinated and produced normal colonies in the presence of CGA 173506. OneC. coccodes isolate was resistant to this fungicide in all assays.     

RBM134: A mutant of Russet Burbank susceptible to blackspot bruise

A radiation induced mutant of Russet Burbank was recovered that is more susceptible to blackspot bruise than the original cultivar. The mutant was evaluated and characterized for several agronomic and biochemical traits. Compared to Russet Burbank the mutant had slightly lower tuber yield, smaller average tuber weight, a higher number of tubers per plant, higher percent tuber dry matter, similar total tuber dry matter yield, lower tuber protein and higher free tyrosine content. Vine growth and appearance was indistinguishable from Russet Burbank. This mutant should provide an excellent tool for better understanding the tuber characteristics contributing to blackspot bruising in potatoes.     

Extreme resistance to infection by potato virus Y and potato virus X in an advanced hybridSolanum phureja — S. Stenotomum diploid potato population

Samples of 4285 individuals from a hybridSolanum phureja Juz. et Buk. —S. stenotomum Juz. (Phu-Stn) and 105 individuals ofSolanum phureja (Phu) diploid potato populations were twice inoculated with potato virus Y strain “o” (PVY°) using the air brush technique. After discarding seedlings with PVY visual symptoms both in the greenhouse and in the field, 1508 seedlings were judged to be resistant to PVY° (35.2%). Only 5.7% of the Phu seedlings were PVY° resistant compared to 35.2% of the Phu-Stn seedlings. At harvest, a mild selection pressure for yield and tuber appearance was applied and 602 Phu-Stn clones were chosen for further evaluation. Selected clones were re-evaluated for PVY° resistance in the greenhouse. Clones were mechanically inoculated twice with PVY°. Clones susceptible to PVY° were determined by visual observations, ELISA (Enzyme-linked immunosorbent assay) tests, grafting of tobacco PVY° infected shoots on potato clones, and infectivity tests usingNicotiana tabacum as a PVY° plant indicator. In the process, 224 clones were found to be extreme resistant to infection by PVY°, with an overall frequency for PVY° extreme resistance of 5.2%. In another experiment, the first year Phu-Stn PVY° resistant clones (554 clones) were mechanically inoculated twice with “common” strain of potato virus X (PVX). Similarly, we discarded clones susceptible to PVX by combining visual evaluation and ELISA with PVX re-inoculation of negative clones and an infectivity test, usingGomphrena globosa as a PVX plant indicator. After this process, seven extreme resistant and eight resistant clones to infection by PVX were found; the overall frequency of PVX extreme resistance was 1.3%. Five clones were extreme resistant to both PVY° and PVX.     

Nitrogen and potassium fertilization of potatoes: Sugars and starch

Considerable evidence exists that both N and K influence potato (Solanum tuberosum L.) yields and quality. The impact of nutrients on tuber quality parameters under field conditions should be identified so optimum management practices can be utilized. We evaluated the N and K fertilization by K-sources effects on concentrations of nutrients, reducing sugars, sucrose and starch in the stem and apical tuber ends from two irrigated field experiments with the Russet Burbank cultivar. Nitrogen rates of 0,112, 224 or 336 kg ha^?1 were combined with selected K rates of 0, 112, 224 or 448 kg ha^?1 as either KCl or K₂SO₄ arranged as an incomplete factorial. A multiple linear regression model was fit to the data and used to predict the response surface for a complete factorial for each K-source. Nitrogen applications increased or decreased reducing sugars in the apical and stem ends, respectively. Potassium decreased reducing sugars in both tuber ends. Sucrose was higher in the apical end than in the stem end but was not appreciably affected by fertilizer treatment. Nitrogen and potassium applications reduced dry matter and starch concentrations in both tuber ends. Potassium had a smaller effect on the apical end when starch was expressed on a dry weight basis, indicating that increased water content was a factor in the K effect. Both N and K concentrations in the tuber ends were negatively related to starch concentrations, but the relationship was different for the apical and stem ends. Tuber Cl concentration indirectly affected starch concentrations in the stem end when KCL was applied. The K fertilization effect on specific gravity depended upon the K concentration in the harvested tuber and was independent of K fertilizer source. These data illustrate the effects of preplant N and K fertilization rates on final tuber quality parameters. Additional studies are needed to further define the effects of nutrient concentrations at different plant growth stages.     

Genetic relationships of Japanese potato cultivars assessed by RAPD analysis

Seventy-three breeding lines and cultivars, which included all Japanese cultivars, were assessed by random amplified polymorphic DNA (RAPD) analysis. Thirty-one of 40 decamer primers revealed 84 scorable RAPDs. Using these RAPDs, 67 of 73 cultivars were distinguished from each other. One of the cultivars released as a protoclonal variant was able to distinguish from the parent by increasing the number of primers surveyed. Based on the number of different RAPDs between each pair of accessions, cluster analysis was performed to exploit genetic diversity in Japanese cultivars. Closely related cultivars deduced from their pedigrees were clustered closely, indicating that similarities based on the presence vs. absence of RAPDs were reflections of genetic similarities. Old Japanese cultivars, as suggested by their similarity of chloroplast DNA toS. tuberosum ssp.andigena, were indeed clustered with ssp.andigena accessions, supporting these were relic cultivars of early European potatoes. The present study suggests that Japanese potatoes are an interesting mass of genetic diversity including North American, European, and Andean germplasms and relic potatoes.     

Yield development in potatoes as influenced by cultivar and the timing and level of nitrogen fertilization

Path-coefficient analysis based on an ontogenetic model was used to study the relationships between tuber yield and yield components as influenced by cultivar and nitrogen fertilization. Four experiments were carried out from 1987 to 1989 in Granada, southern Spain. Two of these experiments used six potato cultivars with a single N rate, while the other two experiments used one cultivar and nine levels of N, split between planting and top-dressing. Variation in tuber yield between cultivars resulted mainly from differences in stem number per m² followed by tubers per stem and, to a lesser extent, average tuber weight. In N experiments, however, average tuber weight was the only yield component that showed a significant direct effect on yield, while the number of stems per m² and tubers per stem had negligible direct effects. In addition, the ontogenetic model used indicated compensatory mechanisms during the formation of the three yield components in the potato, which resulted stronger in the N experiments.     

Nutrient concentration relationships between the fourth petiole and upper-stem of potato plants

Successfully evaluating the nutritional status of a crop during growth and development is dependent upon sampling an identifiable plant part. Consistently sampling a petiole of the same maturity in potatoes (Solanum tuberosum L.) is difficult. We evaluated the nutrient relationships between the upper-stem and the fourth petiole from Russet Burbank plants in field studies having N, P, K, Zn or Mn variables. The upper-stem was obtained by excising the stem below the sixth leaf and removing all leaves and the terminal meristem. Petole NO₃-N, P, K, Zn and Mn concentrations were from deficient to sufficient. The NO₃-N, P and K concentrations were similar in the fourth petiole and upper-stem, while the Zn concentration was 40% higher in the upper-stem. Calcium, Mg and Mn concentrations were lower in the upper-stem than in the fourth petiole. Copper and S relationships were not adequately defined. The fourth petiole’s NO₃-N, P and K diagnostic concentrations now used to monitor plant nutrient status can also be used for upper-stem samples. Zinc diagnostic concentrations should be increased, while Ca, Mg and Mn concentrations should be adjusted downward in the upper-tem. Additional data are needed to refine the Ca and Mg relationships, and to establish relationships for Cu, S and other essential nutrients. A significant advantage of using the upper-stem is the elimination of the petiole selection problem when sampling.     

Nitrogen and potassium fertilization of potatoes: Evaluating nutrient element interactions in petioles with response surfaces

We studied the effects of fertilizer N and K rates on the nutrient concentrations in petioles of Russet Burbank potato grown on a low-K, low-Cl, highly calcareous Millville silt loam soil. Phosphate and CaSO₄ were applied uniformly so that P and S did not limit plant growth. An incomplete factorial experimental design, utilizing 14 combinations of fertilizer N and K, including two forms of K, was used to develop a multi-dimensional regression model. This model was then used to produce response surfaces as an aid to analysis of the results and to illustrate the fertilizer treatment effects and their interactions on petiole chemistries. Nitrogen, K and Cl fertilizers had complex effects on petiole concentrations of NO₃-N, SO₄-S, Cl, K, Ca and Mg. Nitrate-N and Cl were mutually antagonistic. Soil N had a large positive effect on petiole K and Mg levels and, to a lesser extent, petiole Ca levels. There was competition between K and Mg in petiole concentration. The sum of K, Ca and Mg was essentially constant across fertilizer treatments and sampling times. The sum of NO₃-N, SO₄-S and Cl was highly variable. The ratio of cations to anions ranged between three and five across fertilizer treatments and sampling times. The data indicate that calibration of the major nutrient element concentrations in potato petioles, as a guide to fertilization, requires knowledge of background soil fertility conditions with respect to N, K, Cl, Ca and Mg, and an understanding of the antagonisms and synergisms among these elements.     

Inheritance of potato chip color at the 24-chromosome level

Potato chip color is an important trait in determining quality and acceptability of cultivars for processing. Therefore, the genetics of potato chip color is important in varietal breeding. The use of 2xS. tuberosum Group Tuberosum haploid × 2x wild species hybrids provides disomic inheritance for genetic analysis of chip color. Two hundred forty haploid-species hybrids representing crosses between 15 haploids and 10 species were evaluated for potato chip color after 21 days reconditioning (18 to 20C) following 6 months at 4C. Phenotypic variation for chip color was found among the haploid-species hybrids. Crosses between good, medium, and poor performing clones were made in all combinations and 136 families were obtained. Progeny were evaluated for reversion resistance (chipping direct from 10C storage) and reconditioning (chipping from 4C after tuber warming) chip color. Variation for chip color was found among the progeny for each trait. Significant correlations between reversion resistance and reconditioning were found. Yet, the use of at least two chip tests (one for reversion resistance and one for reconditioning) is more informative than the use of one test and subsequent predictions made, regarding the other trait. A three locus hypothesis for both reversion resistance and reconditioning is proposed for the inheritance of each trait. One dominant allele at each of the three loci is necessary for good chipping. One or two loci may be common to both characteristics. Good chipping 2x hybrids that produce 2n pollen can be used to transfer this trait to the 4x level through use of 4x × 2x crosses.     

Resistance to thiabendazole and thiophanate-methyl in canadian isolates ofFusarium sambucinum andHelminthosporium solani

Resistance to both thiabendazole (TBZ) and thiophanate-methyl (TPM) was observed in Canadian isolates ofFusarium sambucinum andHelminthosporium solani recovered from diseased potato tubers. Resistance was not found in isolates ofFusarium avenaceum, Fusarium culmorum, Fusarium equiseti andFusarium solani. A high level of resistance to both TBZ (EC₅₀ 180 to ?500 mg/l) and TPM (EC₅₀ ?500 mg/l) was observed forH. solani isolates, whereasF. sambucinum exhibited a relatively low level of resistance to TBZ (EC₅₀ 34 to 71 mg/l) and a high level of resistance to TPM (growth uninhibited by 2,500 mg/l). The incidence ofF. sambucinum resistant to the benzimidazoles was lower (60%) than that observed forH. solani (95%)     

Nitrogen and potassium fertilization of potatoes: Yield and specific gravity

Potassium and N fertilization is often required for maximum potato (Solanum tuberosum L.) production. Nitrogen, K, and K-sources (KCl, K₂SO₄ are known to affect yield and quality of potatoes but N and K interactions as affected by K-source have not been defined. This study evaluated the N*K and K-source interactions on Russet Burbank tuber yields and specific gravity (SG) in two irrigated field experiments. Nitrogen rates of 0, 112, 224 or 336 kg ha^-1 were combined with selected K rates of 0,112, 224 or 448 kg ha^-1 as either KC1 or K₂SO₄ in an incomplete factorial. A multiple linear regression model was fit to the data and used to predict yield and SG for a complete factorial for each K-source. Both N and K applications increased yields independent of K-source. Nitrogen decreased yields at the 336 kg ha^-1 rate. Potassium increased yields up to 448 kg K ha^-1. Both K-sources decreased SG a similar amount with N application; without N, KC1 decreased SG but K₂SO₄ did not. Nitrogen also decreased SG. Petiole NO₃-N and K concentrations were positively related to yields and negatively to specific gravities. The petiole K concentration 100 days after planting should be above 4.5 for highest tuber yields. The N*K*K-source interaction was important for yields at low available N and for SG at adequate N availabilities. This study showed that N or K fertilizers can be applied according to their respective soil test concentration and the crop’s requirement, generally without consideration of K-source.