Variation in resistance level of potato genotypes and virulence level of potato cyst nematode populations

Summary In two experiments, using different testing methods, the number of newly formed cysts was determined on nine potato genotypes with resistance from various sources. Ten potato cyst nematode (PCN) populations were used in these experiments. Rank correlation between numbers of cysts over potato genotype-PCN population combinations for both experiments was high (r_s = 0.90). Dendrograms for PCN populations and potato genotypes were constructed, based on a simultaneous hierarchical clustering procedure for potato genotype-PCN population interaction terms. Several virulence groups could be identified within Globodera rostochiensis as well as within G. pallida. Host genotypes, derived from the same sources of resistance, were clustered in different resistance groups.     

Breeding for quantitative resistance to potato cyst nematode (Globodera pallida) in tetraploid potatoes using dihaploids and unreduced gametes

Summary Dihaploids were produced from tetraploids resistant to potato cyst nematode (Globodera pallida (Stone)). High levels of resistance were found in the dihaploids and three were used to produce tetraploid progenies by crossing them with susceptible tetraploid cultivars. One dihaploid, PDH505, produced more highly resistant offspring than the other two, PDHs 417 and 418. The latter gave progenies whose levels of resistance were similar to those obtained from susceptible dihaploids crossed with resistant tetraploids.The differences between the progenies of the resistant dihaploids were probably due to different modes of unreduced gamete formation (PDH505 producing gametes by first division restitution (FDR) and PDHs 417 and 418 by second division restitution (SDR)) although cytological studies would be necessary to confirm this. The methods by which dihaploids could be utilised in a tetraploid potato breeding programme are discussed in relation to the mode of unreduced gamete formation.     

Pathotype-specificity in potato cyst nematodes,a reconsideration

Summary Within the two potato cyst nematode (PCN) species, Globodera rostochiensis and G. pallida, eight pathotypes are presently discerned by seven differential Solanum clones, whereby resistance is defined as a Pf/Pi ratio <1.0, and susceptibility as a ratio above 1.0. This pathotyping is felt to be unsatisfactory. Reconsidering the original data and data published by others resulted in the conclusion that there are only three reliably recognizable Ro-pathotypes Ro1/Ro4, Ro2/Ro3 and Ro5. The differential clones 60.21.19 and 65.346.19 differentiate only between the two species. Within G. pallida it does not seem possible to identify pathotypes reliably. The resistance-virulence pattern is of a quantitative nature fitting a polygenic system. There appear to be pathotype-specific effects, which are not large enough to identify and classify pathotypes reliably. It is therefore suggested to rename the Ro-pathotypes into Ro1 (old Ro1 and Ro4), Ro3 (old Ro2 and Ro3) and Ro5 (old Ro5) and to speak of more and less virulent Pa-populations.The rigorous requirements for resistance in various countries present great problems to the breeders and result in the removal of much valuable partial resistance. Especially with G. pallida these rigorous requirements are probably an obstacle rather than an encouragement to solve the pallida problem.     

The importance of wild potato species resistant to the potato cyst nematode,Globodera pallida,pathotypes P4A and P5A,in potato breeding. II. The crossability of resistant species

Summary Over 2400 pollinations were made to investigate the crossability relationships between cultivated potatoes, and wild diploid species from Series Tuberosa and Circaeifolia, as well as wild polyploid species in Series Tuberosa and Longipedicellata resistant to potato cyst nematode, Globodera pallida pathotypes P₄A and P₅A. Wild diploids in Series Tuberosa crossed easily with cultivated diploid species, except with Solanum lignicaule where most pollinations failed, and seed set was extremely low (0.2 seeds per pollination or less). It is suggested that this species is 1EBN. S. capsicibaccatum is clearly isolated from Series Tuberosa, but can form hybrids with S. lignicaule, which can act as a bridging species to S. tuberosum haploids. S. gourlayi and S. oplocense can be crossed with both subspecies of S. tuberosum, but S. papita, Series Longipedicellata is reproductively isolated from the tetraploid cultigens. The crossability data are discussed in the light of germplasm utilisation for breeding potato varieties resistant to potato cyst nematode.     

The importance of wild potato species resistant to the potato cyst nematode,Globodera pallida,pathotypes P4A and P5A,in potato breeding. I. Resistance studies

Summary Seven wild diploid potato species, Series Tuberosa, representing 1023 clones were screened for resistance to the potato cyst nematode, Globodera pallida. Over 25% of the clones were resistant to pathotype P₄A and almost 30% were resistant to pathotype P₅A. The resistance in hybrid progenies of these and other resistant species with cultivated potatoes was evaluated, and over 2200 seedlings were screened. High frequencies of resistance (>50%) to P₄A were found in progenies with Solanum leptophyes, S. vernei, S. gourlayi and S. capsicibaccatum, whereas resistance to P₅A was found in these species as well as S. sparsipilum. The importance of nematode resistant wild species for potato breeding is discussed.     

New sources of resistance to the potato cyst nematodes Globodera pallida and G. rostochiensis in the Commonwealth Potato Collection

The Commonwealth Potato Collection contains 77 species following the incorporation of the personal collection of Professor JG Hawkes. The material originates from several expeditions to the Americas and represents a potentially valuable source of resistance to pests and pathogens, including potato cyst nematodes (PCN). The germplasm from the Hawkes collection screened in this study included taxa mainly from Mexico, Bolivia, Argentina and Peru. Seedlings of 198 accessions, from 63 different species were screened for reaction to the PCN species G. pallida and G. rostochiensis. Of the 198 accessions tested, 56% contained G. pallida-resistant clones and 53% contained clones resistant to G. rostochiensis. Twelve species in this survey are believed to contain novel, previously unreported sources of resistance. The geographical distribution of resistance indicated a contrast between the two PCN species. Although, as in previous studies, resistance to G. rostochiensis was centred on Bolivia and Argentina, G. pallida resistance was found across the geographical range of tuber-bearing Solanum. The possibility of cross-resistance arising from selective pressure from the more northern species G. mexicana is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Durability of resistance against potato cyst nematodes

A requirement for evaluating the effectiveness of major resistance genes (R-genes) is detailed knowledge of the genetic variability of the nematode populations in an area. Obtaining insight in the genetic variation in an area is a tour de force, because qualitative data are not sufficient allele frequency data at well studied loci are required. Another important step in predicting the durability of major R-genes is to study the parasite at the molecular level. Also for nematodes it seems that R-genes are part of a molecular surveillance system recognising foreign molecules. For potato cyst nematodes it is becoming clear that numerous proteins are secreted to manipulate the host plant and it may be assumed that some of these secretory proteins are also recognised by the host. Knowledge of the molecular nature and function of these avirulence gene products may reveal clues to predict the durability of an R-gene. R-genes that recognise avirulence gene products that have a crucial function in the nematode maybe very durable. When the current molecular models for gene-for-gene interactions are correct, the durability of an R-gene may be predicted by studying the dispensability factor and functional constraints of the avirulence gene products. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chilean potato germplasm with resistance to potato viruses Y and S

Summary Four clones of the Chilota Potato Collection from the germplasm bank of the Universidad Austral de Chile, with potential combined resistance to PVX, PVY and PVS, were mechanically inoculated with these viruses in order to demonstrate wether they were truly resistant or not. Virus coat protein in the inoculated clones was determined by means of NCM-ELISA, DAS-ELISA, Western Blot and NASH.Two of the four inoculated clones were resistant to both PVY and PVS. This information will allow the utilization of these two clones in plant breeding programs.Abbreviations NCM-ELISA Nitrocellulose membrane enzyme-linked immunosorbent assay - DAS-ELISA double antibody sandwich enzyme-linked immunosorbent assay - NASH nucleic acid spot hybridization     

New sources of resistance to potato cyst-nematodes in the Commonwealth Potato Collection

Summary Accessions obtained from the Commenwealth Potato Collection were evaluated for resistance to European populations of potato cyst-nematodes (PCN). With over 36% of the current collection assessed, resistance to pathotypes of both Globodera rostochiensis and G. pallida were identified in 16 species from Argentina, Bolivia or Peru. Resistance to all PCN pathotypes was particularly prevalent in species from the Andean regions of Bolivia and North Argentina, supporting the hypothesis of co-evolution of the potato and PCN in these regions.     

The use of systems analysis and modelling of growth and development in potato ideotyping under conditions affecting yields

Annual crops are usually only grown during part of the year when environmental conditions are favourable. The factors that limit the length of the available growing season for a crop are discussed from the points of view of meteorology, crop physiology and crop management. Crop yields that may be expected depend on the length of the growing season, how well the available season is used by a growing crop and on environmental factors that define (e.g. temperature, daylength and solar radiation), limit (e.g. the availability of water and nitrogen) or reduce (e.g. pests and diseases) yields. Designing genotypes for such environments requires quantitative knowledge of the influence of environmental factors on the length of the season and on dry matter accumulation and partitioning. This approach is discussed and as example the potato crop is used grown under various climatic conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding for resistance to cereal cyst nematode in wheat

Summary The progress of a backcross breeding programme to introduce resistance against the cereal cyst nematode into wheat is described. Methods of resistance screening and criteria for selection are detailed and the results discussed with reference to alternative procedures for the introduction of new resistance genes into major breeding programmes.     

The effect of varying the number of drills per plot and the amount of replication on the efficiency of potato yield trials

Summary The effect on yield trials of altering plot size was examined by investigating plots with varying numbers of drills (each with six tubers) planted. No evidence was found of the ware yield per drill being affected by different plot sizes nor any effect attributable to neighbouring drills, whether these were planted with another clone or left unplanted. Increasing the number of drills per plot did increase the precision of the estimated clone means as did, of course, increasing the number of replicates. It appeared, however, that increasing the number of replicates was a more efficient way to increase precision. Thus it was concluded that the most efficient utilization of limited planting space was to grow single drill plots with maximum replication.     

Genetics of self-compatibility in dihaploids of Solanum tuberosum L. 5. The S-genotype of tetraploid potato cultivar gineke

Summary Investigations of the genetics of self-compatibility and self-incompatibility in dihaploids and diploid derivatives from cv. Gineke revealed the presence of S ₁, S₂ and S ₃ at the S-locus of Gineke and in addition an S ₁-allele on a translocation. By means of a complete tester set involving the S-alleles S ₁, S₂ and S ₃ (all from Gineke) and S ₄ (from Black 4495) it was demonstrated that some Gineke dihaploids were compatible with all six testers. This indicated a fourth S-allele in Gineke, which differs from those in the tester series and was therefore assigned S ₅. Additional evidence was obtained from an analysis of F₁'s from crosses of two S ₅-bearing dihaploids and one of the testers. So the S-genotype of cv. Gineke was identified as S ₁S₂S₃S₅/S₁, the second S ₁ being the S-allele on a translocated fragment.     

The use of dihaploids in increasing the homozygosity of tetraploid potatoes

Summary Electrophoresis banding patterns of the tuber proteins of 12 dihaploids of the cultivar Pentland Crown showed that four had types of patatin unlike that of the parent. The patatin types of somatically chromosome-doubled clones derived from three of the dihaploids were identical to those of the dihaploid progenitors. Fourteen dihaploids produced from the chromosome-doubled derivative (PDH40X2) of one dihaploid, which had a variant patatin, had the patatin type of the parent dihaploid.The experiment showed that dihaploids and somatic chromosome doubling could be used to fix variation found in heterozygous tetraploid potatoes. Used together, haploidisation and chromosome doubling can generate highly homozygous tetraploids for use by plant breeders.     

The effect of seed tuber weight on characters in the first and the second clonal generation of potato populations

Summary Fifty-five populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones adapted to the northern temperate zone have been studied in the seedling and the first and second clonal generation. This paper only deals with the effect of seed tuber weight on various important agronomic characters which are selected for in early clonal generations, independently of the type of crosses.The results showed that a distinction has to be made between the effects of differences in seed tuber weight within and between seedlings, i.e. genotypes. The effects on the first clonal generation of differences in weight of the tubers within seedlings and those of the first heaviest tubers between seedlings were similar and comparable to seed tuber weight effects within cultivars. In contrast to the within seedlings effects the between seedlings effects proved to be heritable. This is concluded from the fact that, on average, independent of seed tuber weight seedlings with larger first heaviest tubers performed better in the second clonal generation than those with smaller ones. Notably plant height, general impression, date of maturity and particularly tuber yield and mean tuber weight in the second clonal generation were related to the weight of the first heaviest tubers of the seedlings. The potentialities of these findings for an early generation selection are discussed.     

Correlations within and between characters between and within generations as a measure for the early generation selection in potato breeding

Summary The main objective was to determine the reliability of selection in early generations of a potato breeding programme. To that end data were recorded in the seedling generation, an early and a late harvested experiment of the first clonal generation and the late harvested second clonal generation on up to 30 genotypes of 55 populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones, adapted to the northern temperate zone. Phenotypic correlations were computed per population in almost all possible combinations within and between characters between and within generations. The mean across 55 comparable correlation coefficients was considered to be the best estimate of the relationship concerned.In all four experiments data were collected on number of tubers, tuber yield and mean tuber weight; in the three experiments of the two clonal generations in addition on date of emergence, number of stems, plant height, haulm type, and general impression of the underground plant parts and in the two late harvested clonal generations on date of maturity and under water weight.The results confirmed that general impression which is largely decisive for the selection in early generations, is a little reliable measure. However, from the magnitude of the mean correlations between experiments within characters it must be concluded that selection for most of these separate characters is hardly more reliable. An exception was date of maturity for which a mean correlation was determined of r=0.78 between the two clonal generations. The second strongest mean correlations, perhaps surprisingly, were for tuber yield, viz. r=0.52 between the seedling generation and the late harvested first as well as the second clonal generation and r=0.63 between the late harvested clonal generations. From the correlations between characters it appeared that for a high tuber yield, besides its components, in particular an early emergence, a large plant height, an attractive haulm type and a late maturity are of importance.The main conclusion is that, as long as not enough seed tubers are available for the layout of statistically sound experiments, a negative instead of a positive selection should be applied to avoid the rejection of most of the valuable genotypes in an early stage. On the basis of the results directives for the application of such a negative selection are given.     

DNA marker-assisted evaluation of potato genotypes for potential resistance to potato cyst nematode pathotypes not yet invading into Japan

One of major objectives of crop breeding is conferring resistance to diseases and pests. However, large-scale phenotypic evaluation for many diseases and pests is difficult because strict controls are required to prevent their spread. Detection of disease resistance genes by using DNA markers may be an alternative approach to select potentially resistant accessions. Potato (Solanum tuberosum L.) breeders in Japan extensively use resistance gene H1, which confers nearly absolute resistance to potato cyst nematode (Globodera rostochiensis) pathotype Ro1, the only pathotype found in Japan. However, considering the possibility of accidental introduction of the other pathotypes, breeding of resistant varieties is an important strategy to prevent infestation by non-invading pathotypes in Japan. In this study, to evaluate the prevalence of resistance genes in Japanese genetic resources, we developed a multiplex PCR method that simultaneously detects 3 resistance genes, H1, Gpa2 and Gro1-4. We revealed that many Japanese varieties possess not only H1 but Gpa2, which are potentially resistant to other pathotypes of potato cyst nematode. On the other hand, no genotype was found to have the Gro1-4, indicating importance of introduction of varieties having Gro1-4. Our results demonstrate the applicability of DNA-marker assisted evaluation of resistant potato genotypes without phenotypic evaluation.     

Introgression of resistance to Columbia and Northern root-knot nematodes fromSolanum bulbocastanum into cultivated potato

Summary Resistance toMeliodogyne chitwoodi races 1 (MC1) and 2 (MC2) andM. hapla (MH) derived fromSolanum bulbocastanum was introduced into the cultivated potato gene pool through somatic fusion. The initial F₁ hybrids showed resistance to the three nematodes. Resistance to reproduction on roots by MC1 was accompanied by resistance to tuber damage in F₁ clones. Tuber damage sometimes occurred, however, in hybrids of BC₁ progeny resistant to reproduction on roots when MC2 and MH were the challenging nematodes. Resistance to reproduction was transferred into BC₁ individuals, but a greater proportion of BC₁ progeny was resistant to MC1 than to MC2 or MH. Resistance to MC1 appears to be dominant and discretely inherited. F₁ and BC₁ progeny were pollen sterile, but seed were produced from crosses using cultivated tetraploid pollen sources. Approximately 11 and 33 per cent of pollinations produced berries on F₁ and BC₁ pistillate parents, respectively. Seed yield increased fourfold overall in crosses with F₁ compared to BC₁ individuals.Abbreviations MC1 Meloidogyne chitwoodi race 1 - MC2 Meloidogyne chitwoodi race 2 - MH Meloidogyne hapla - Rf Reproductive factor     

Evaluation of seedling selection for salinity tolerance in potato (Solanum tuberosum L.)

Summary Salt-tolerance in potato (Solanum tuberosum L.) was selected on the basis of germination and survival of seed sown in trays of perlite suspended in either 75 or 150 mM NaCl. Salinity reduced the germination of seed. Genetic differences in salt-tolerance were apparent with salt reducing germination more in seed collected from cv. Cara than in that collected from cv. Maris Piper. Progeny from the seedling selection were then grown to maturity to produce tubers.The relative tolerance of the parental cultivars and of unselected and selected progeny to long-term exposure to salinity was examined in a pot experiment in which plants were irrigated with either fresh water or 50 mM NaCl solution from one week after plant emergence. In this experiment, salinity significantly reduced leaf conductance, total dry matter production and partitioning of assimilate to tubers. Salinity reduced dry matter production and assimilate partitioning to tubers to a greater extent in Cara than in M. Piper. Progeny selected for short-term salt-tolerance did not exhibit greater long-term salt-tolerance than unselected progeny, and both were more sensitive than M. Piper.These results demonstrate genetic variation in salt-tolerance in potato. However, although there was a correlation between the performance of the parent to long-term salinity and survival of progeny in the seedling selection, there was no correlation between short- and long-term salt-tolerance. This suggests that characters underlying short-term tolerance may contribute to long-term tolerance but do not of themselves confer long-term tolerance. Future progress in selecting for improved salt-tolerance depends on understanding the effects of salinity on the physiological processes underlying growth and carbon partitioning.     

Coagulable protein in potato: Screening method and prospects for breeding

Summary From tubers of 34 varieties of Solanum tuberosum, extracts were prepared and analysed for crude protein and coagulable protein by the Kjeldahl method. Content of coagulable protein was 0.37–1.24%. From the same material, juice was prepared with a juice centrifuge and analysed for coagulable protein by the Kjeldahl and microbiuret method. The average amount of coagulable protein in the juice was 81.8% of the total coagulable protein. The correlation coefficient between coagulable protein in the juice and total coagulable protein was 0.956. The correlation coefficient between Kjeldahl and microbiuret data for coagulable protein in the juice was 0.956. Analysis of tuber juice by the microbiuret method is recommended as a rapid screening technique for coagulable protein.Relationships between protein data of the 34 varieties and earliness, yield and content of dry matter were analysed statistically. Content of coagulable protein in fresh material correlated with content of dry matter (rs=–0.756), yield of fresh potatoes (r=–0.615) and earliness (r=–0.361) but not significantly with yield of dry matter (rs=–0.309). Coagulable protein in dry matter correlated with fresh yield (r=–0.525), but not significantly with content of dry matter (r=–0.260), yield of dry matter (r=–0.131) and earliness (r=–0.054). Path coefficient analysis showed that 67% of the variation in coagulable protein in fresh material was statistically determined by earliness, content of dry matter, fresh yield and content of uncoagulable protein in fresh material, whereas only 34% of the variation in content of coagulable protein in dry matter was determined by these components. A high content of coagulable protein in fresh or dry matter can be combined with early maturity and with high yield of dry matter. Coagulable protein in dry matter seems to be a more suitable criterion of selection than coagulable protein in fresh material.