A rapid screening technique for drought resistance in potato (Solanum tuberosum L.)

Summary The reduction in growth in the dark of leaf dises floated over polyethylene glycol 6000 solution of water potential −0.4 MPa, relative to the growth of similar leaf dises floated over water for the same period, varied in the range 10–87% in 28 genotypes. The growth reductions in the genotypes tested were in general agreement with what is known about their drought resistance. Publication No. 906, Central Potato Research Institute, Simla.     

Diploid genotype DW.84-1457, highly resistant to potato leafroll virus (PLRV)

Summary The diploid clone DW.84-1457 which has outstanding resistance to potato leafroll virus (PLRV), has been selected at the Mlochów Centre of the Institute for Potato Research. It has in its pedigree PLRV-resistant clones from the Max Planck Institute nos. MPI 44.1016/10, MPI 44.335/130 and MPI 49.540/2. Its behaviour in the field and response to aphid inoculation indicate high resistance to infection, and the low concentration of the virus in graft-inoculated plants indicates high resistance to multiplication. This combination within one genotype of two aspects of resistance is not connected with hypersensitivity, and is heritable. Clone DW.84-1457 has other desirable characters such as extreme resistance to potato virus X (PVX), high resistance to potato virus M (PVM) and good table and processing quality. It is being utilized in the development of parental lines, both at the diploid and tetraploid level.     

Hydrolysis of glycoalkaloids fromSolanum tuberosum L. haulm by enzymes present in plant material and by enzyme preparation

Summary This paper deals with the kinetics of enzymatic hydrolysis of glycoalkaloids from potato (Solanum tuberosum L.) haulm. The hydrolysis was carried out by the action of the enzymes present in fresh haulm, juice of fresh haulm and in haulm dried at various temperatures. The highest degree of enzymatic hydrolysis of 90% was obtained during fermentation of haulm dried at 40 °C after 30 h incubation time. The enzyme preparation was obtained from the juice of fresh potato haulm by using capillary dialysator HM 16 (AQM 1681, 1.6 m² Hemofan 8 υ). The best degree of enzymatic hydrolysis by enzyme preparation, 68%, was achieved after 20 h time of incubation. The enzyme preparation from juice of fresh haulm was characterized by K_m of 0.70 mM at pH 5.5 and 35 °C.     

Screening for resistance to early blight (Alternaria solani) in potato (Solanum tuberosum L.) using toxic metabolites produced by the fungus

Summary The phytotoxic components of the culture filtrate of the fungusAlternaria solani Sor, which causes early blight in potato, were used in this study to differentiate between resistant and susceptible genotypes selected to represent a range of reactions when screened in the field. Detached leaflet assays, using spores and toxic metabolites from the culture filtrate, were compared with field ratings and a whole-plant glasshouse test. Rank correlations between several detached leaflet tests were highly significant (P<0.01) but the correlations between these tests and the glasshouse and field tests were poor. The disease ratings obtained in the various tests were clustered into four groups and assigned to resistance classes. For many of the genotypes there was a good correspondence between resistance classes for all test methods. Divergent results between tests were associated with foliage maturity characteristics of the genotypes. Contribution no. 3879050 of the Lethbridge Research Station.     

Assessing the resistance to gangrene of progenies of potato (Solanum tuberosum L.) from parents differing in susceptibility

Summary The resistance to gangrene (caused byPhoma exigua var.foveata) of progenies from two hybridisation schedules involving cultivars resistant, susceptible, or of intermediate reaction to gangrene was assessed. Two methods of sampling tubers from field-grown single-plant plots of 18 clones representing each progeny were used: one tuber was taken from each plant, and a bulk sample of 18 tubers was selected at random from the whole progeny. Gangrene resistance was assessed after incubating tubers which had been rolled in cornmeal-sand inoculum ofP. exigua var.foveata, and was expressed as a percentage of tubers infected. Results from the two methods of sampling correlated closely, and agreed well with tests in a subsequent year on 10-tuber samples of each individual clone. It is concluded that an 18-clone sample adequately represented each progeny, and that the mid-parent gangrene score satisfactorily predicted the resistance of the resulting progeny. There are indications that susceptibility tended to be dominant. The implication of these findings to breeding for resistance to gangrene is discussed.     

High temperature storage of potato (Solanum tuberosum L.) for processing — a feasibility study

Tubers of three potato cultivars were stored at room temperature (20–39°C, 30–75% RH), under an insulated storage run on passive evaporative cooling (16–30°C, 70–90% RH) and a refrigerated storage (2–4°C, 90–95% RH) for 14 weeks and studied periodically for storage losses, reducing sugar content and dry matter percent of tubers, in order to explore the possibility of storing potatoes for processing at higher temperatures. Physiological losses in tubers remained less than 10% until 12 weeks of storage under evaporatively cooled storage. Reducing sugar contents increased by only 52.4–242.1% in tubers stored in evaporatively cooled storage as compared to 90.5–484.2% increase in tubers stored in refrigerated storage until 14 weeks. Potatoes stored in evaporatively cooled store were more suitable for processing into chips and french fries due to lower physiological losses and lower reducing sugar content of tubers.     

Varietal and environmental effect on the glycoalkaloid content of potato (Solanum tuberosum L.)

The tubers of 14 potato varieties were analysed for glycoalkaloids. The level of glycoalkaloids in tubers of all the varieties analysed are within the safe limits for human consumption. The peels of tuber contained about 60–70% of the total glycoalkaloids present in the whole tuber. The levels of glycoalkaloids in leaves and tubers were correlated (r=0.865). There was a significant increase in the content of glycoalkaloids in peels of tubers exposed to sunlight. Glycoalkaloid contents increased at the rate of 1.9mg/100g fresh weight per day in peels of Kufri Jyoti tubers exposed to diffused sunlight.     

Cryotherapy of Potato Shoot Tips for Efficient Elimination of Potato Leafroll Virus (PLRV) and Potato Virus Y (PVY)

Viral diseases constitute a major constraint to high yield and high quality production of potato. Potato leafroll virus (PLRV) and Potato virus Y (PVY) are among the most damaging potato viruses and are prevalent in most potato growing areas. In the present study, attempts were made to eliminate PLRV and PVY by three cryogenic protocols, i.e., encapsulation-dehydration, encapsulation-vitrification and droplet. Results showed that both PLRV and PVY could be efficiently eliminated by cryogenic treatments with 83–86% and 91–95% of frequencies of virus-free plantlets obtained for the former and latter, respectively. Frequencies of virus-free plantlets produced by cryogenic treatments were higher than those by meristem culture (56% for PLRV and 62% for PVY) and thermotherapy (50% for PLRV and 65% for PVY), and similar to those by thermotherapy followed by meristem culture (90% for PLRV and 93% for PVY). Survival (75–85%) and regrowth (83–89%) from cryo-treated shoot tips were higher than those from meristem culture (50–55%) and thermotherapy followed by meristem culture (40–50%), but similar to those from thermotherapy (80–87%). The morphology of the plantlets regenerated from cryo-treated shoot tips was similar to that of non-treated plantlets. Thus, cryotherapy would provide an alternative method for efficient elimination of potato viruses, and can be simultaneously used for long-term storage of potato germplasm and for production of virus-free plants.     

Comparison of resistance evaluation in potato variety assessment

Summary Results of varietal assessment in France, Germany, Great Britain. The Netherlands and Poland have been compared for two characters: resistance to potato virus Y (PVY) and tuber resistance toPhytophthora infestans. In total 75 varieties were evaluated in more than one country. All evaluations were expressed or could be transformed into a 9-grade resistance scale. Evaluations did differ considerably due to two main reasons: countries differed in severity of evaluation (mean resistance level ascribed to varieties) and the relative resistance level ascribed to individual varieties depended on the country. Differences between countries in severity of the evaluation could exceed two grades in resistance to PVY and three grades in tuber resistance toP. infestans. In the relative resistance ascribed to individual varieties the differences between countries were larger, reaching up to 6 grades in evaluation of resistance to PVY and up to 8 grades in evaluation of tuber resistance toP. infestans. To achieve consistent variety assessment results from different countries, it will be necessary to use agreed standard varieties and more consistent evaluation methods. Professor Dr. K.M. Świeżyński passed away on 27th July 2000     

Effect of functional female and male fertilities on crossability in diploid potato breeding

Summary Functional female fertility (FFF) and functional male fertility (FMF) were studied in diploid potato clones, includingS. tuberosum haploids, F₁ hybrids between haploids and otherSolanum species, and in progenies from subsequent hybridisations. The results of 402 crosses between 91 diploid potato clones revealed that 60% of all genotypes had low levels of FFF as well as low levels of FMF regardless of their origin and degree of hybridity. Failed crosses (without any fruits at all) and those with a low level of success (with less than 3 seeds per pollinated flower) constituted 69% of all studied crosses. Most of these had resulted from parents with low levels of FFF and FMF, and these two characteristics were expressed independently. Functional female fertility affected crossability behaviour no less than FMF, therefore both FFF and FMF should be controlled in diploid potato clones involved in breeding. Reliable FFF and FMF estimates can be based only on crossing results. The coefficient of multiple correlation between seeds per pollinated flower in crosses and FFF and FMF estimates of the parental clones was 0.80 (P<0.01). Hence the compilation and analysis of the results of diploid potato crosses allow a reliable assessment of FFF and FMF and consequently the prediction of crossability with a degree of sufficient accuracy.     

Male fertility and freezing tolerance of hybrids involvingSolanum tuberosum haploids and diploidSolanum species

Summary Male sterility of (haploid x species) hybrids often hampers the exploitation of wildSolanum species in breeding for cold tolerance. In a study aimed at finding ways round these problems, we found that one accession of the cold tolerant wild speciesS. sanctae-rosae gave progenies segregating for male fertility in crosses withtuberosum haploids. Moreover, a source of male fertility restorer gene(s) was hypothesized in the (haploid x species) hybrid UP88-C80 (tbr x chc). A relatively high freezing tolerance was found in the progenies coming fromtuberosum haploid xsanctae-rosae crosses and some hybrids showed a freezing killing temperature as low as −5.4°C. Although the most tolerant clones did not shed pollen, at least one clone (Sr6,tbr x sct) combined male fertility, 2n pollen production and good freezing tolerance (−3.9°C) and might be directly used in crosses with tetraploidS. tuberosum in order to introgress resistance to low temperature intuberosum form. Contribution no. 137 from the Research Centre for Vegetable Breeding-CNR. Research supported by National Research Council of Italy, special project RAISA, subproject no. 2, paper no. 2776.     

Evidence that resistance to potato leafroll virus accumulation in tetraploidsolarium tuberosum L. is controlled by one or few major genes that are not complementary

Summary Previous investigations into the inheritance of resistance to accumulation of potato leafroll virus indicated a dominant major-gene effect, but the segregation ratios in progenies of crosses were a closer fit to a model involving two complementary genes (both required for resistance and one present in the susceptible parent cultivar, Maris Piper) than to a single gene model. In this study, we tested the complementary gene hypothesis by backcrossing susceptible segregants from one of these progenies to their susceptible parent, Maris Piper. No resistant segregants were found in the five backcross progenies examined, so the complementary gene hypothesis was not supported. There was significant variation between susceptible progeny-members in these backcrosses. The progeny of another, highly resistant parent clone, G. 8107(1), selfed, was also examined: all members were resistant. Whilst there is evidently a dominant major-gene effect involved, this is not the whole picture and there are other unidentified genetic effects.     

Unsaponifiable lipids from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary Fractions containing Δ⁵- and Δ⁷-sterols, 4-methyl-sterols, triterpenic alcohols, tocopherols and hydrocarbons were isolated by TLC from petroleum ether extracts of the haulm and tuber sprouts of cv Désirée. Sterol and triterpenic alcohol fractions of unsaponifiable lipids of the haulm and tuber sprouts were found to contain twelve sterols and four triterpenic alcohols, respectively. 24R-4-stigmasten-3-on, Δ⁷, Δ⁷, lanosterol, cycloeucalenol and obtisufoliol have not been identified previously in unsaponifiable lipids from haulm and sprouts. In the hydrocarbon fractions of the haulm extract, C₂₃-to C₃₃-n-parafins, C₁₉-and C₃₁-cyclohexyl hydrocarbons, C₂₂-to C₃₈-olefins and squalene were identified, and in the hydrocarbon fractions of the tuber sprouts C₁₂-to C₂₆-olefins and squalene were identified.     

Comparison of the micro-precipitin test andChenopodium quinoa for the detection of potato virus S

Summary The micro-precipitin test and a bioassay using the local-lesion hostChenopodium quinoa were compared for their efficiency in detecting potato virus S in some potato cultivars grown in the open. TheC. quinoa bioassay was more sensitive than the serological test but used more space and was time-consuming. Guest worker from April–October 1976 as a fellow of the International Agricultural Centre, Wageningen, the Netherlands     

Effect of crop rotation,cultivar and nematicide on growth and yield of potato (Solanum tuberosum L.) in short rotations on a marine clay soil

Summary The effects of cropping frequency on the yield of potato and on the development of soil-borne diseases was studied from 1979 to 1985 in a crop rotation experiment on a marine clay soil. Tuber yield decreased markedly with increasing cropping frequency. The yield of cv. Hertha was reduced by 27% in continuous cropping and by 15% in a wheat/potato or sugar beet/potato rotation, when compared with the rotation wheat/sugar beet/oats/potato. However, a pot experiment showed that yield depression in continuous cropping depended on the cultivar used. Crop growth declined in the second part of the growing season, and senescence accelerated as the cropping frequency increased.Verticillium dahliae was the most important yield-reducing factor. Root infection by this fungus was stimulated by the root-lesion nematodePratylenchus neglectus.     

Effects of heat tolerance on expression of resistance toPresudomonas solanacearum E. F. Smith in potato

Summary Twelve potato clones with different genetic background for resistance to bacterial wilt and adaptation were tested for resistance to a race 1 and a race 3 isolate of the pathogen at three locations in the Philippines representing different ranges of ambient temperature. The results showed that the genes for heat tolerance are crucial for resistance. Stability analysis indicated that clones with both resistance and heat tolerance genes displayed higher and more stable resistance to the race 1 isolate than those clones having only resistance genes. The latter group tended to have higher values of both regression of disease index on environmental index and deviation from the regression in the stability analysis. Host — pathogen interaction effects were found to be statistically significant but small compared to main effects of isolates and clones. The involvement of genes with different effects on wilt resistance is discussed. Introduction     

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.     

Response of two potato clones (S. tuberosum L.) to contrasting temperature regimes in the field

Two potato clones (S. tuberosum L.) were grown in the field under contrasting temperature regimes during the crop cycle. Differential growth and yield was observed in the clones studied. Differences in yield were due to the decreased proportion of tubers larger than 3.5 cm in length as well as to the differences in dry weight and percent of dry matter in tubers. Yield reductions per plant were 52 and 94% for Alfa and Herta, respectively, in the warmer regime compared with the cooler regime. Apparent photosynthesis rates measured in Herta were maximum (45 umol.m^?2.s^?1) during tuber filling. Stomatal resistance and apparent photosynthesis rate were reduced by high temperature, indicating mesophyllic inhibition of photosynthesis. Dark respiration was promoted by moderately high temperature and differed significantly between clones, with Herta showing the higher rates.     

Influence of seed tuber infestation,chemical seed treatment,and pre-harvest climate on incidence of gangrene and dry rot of potato (Solanum tuberosum L.)

Summary In each of the five years 1978 to 1982, seed lots of cv. Bintje, variously infested byPhoma foveata Foister andFusarium solani var.coeruleum (Sacc.) Booth, as found by wound and cut tests, respectively, were planted in a series of field experiments at six sites in Sweden. A statistically significant relationship between seed and progeny infestation was found forP. foveata each year, and in three years forF. solani. Benomyl and thiabendazole mist treatments of seed tubers at grading in spring controlled the development of gangrene and dry rot in treated seed tubers, but did not consistently reduce the levels ofP. foveata andF. solani infestation in progeny from treated seed tubers. The site of cultivation markedly influenced mean levels ofP. foveata infestation, which were found to be related to temperature and rainfall during a 40 day pre-harvest period at the trail sites; however, mean levels ofF. solani infestation were not so related.     

Effect of haulm treatment and harvest time on incidence of tuber rots of potato (Solanum tuberosum L.) after standard wounding and on frequency of stem lesions caused byPhoma foveata Foister

Summary Various haulm treatments and harvest times differentially influenced the incidence of storage rots in potato tubers (Solanum tuberosum L.) in field experiments in Sweden performed over 4 years. The incidence of gangrene caused byPhoma foveata Foister (Phoma exigua var.foveata (Foister) Boerema) increased in cv. Bellona after spraying haulms with diquat as did the amount of infection caused byFusarium avenaceum (Corda ex. Fr.) Sacc. in all three cultivars (Bintje, Bellona, and Magnum Bonum). The lowestP. foveata infection levels occurred after pulling haulms. Late harvesting increased the frequency ofP. foveata in cvs Bintje and Bellona both at 2 and 4 wks interval between haulm treatment and harvest. Tuber and visible stem infection caused byP. foveata were correlated for cvs Bintje and Bellona, but not for cv. Magnum Bonum. The possible relation between tuber and stem infection is discussed.