The Importance of the Bolivian Wild Potato Species in Breeding for Globodera pallida Resistance

Screening for resistance to the potato cyst nematode, Globodera pallida, in potatoes from. Bolivia, was carried out in 1983 and 1984, using a mixture of four nematode populations representing pathotypes Pa₁, Pa₂ and Pa₃ From the 66 accessions of 17 species and subspecies evaluated, highly resistant genotypes were identified in 21 accessions from seven species. All had Pf/Pi values of 2 or less, whereas the susceptible control, Solanum tuberosum cv. ‘Disiree’ had Pf/Pi values of more than 2G in both tests. Two diploid wild species, S. brevicaule and S. leptophyes, showed the best resistant. The geographical distributional of resistant populations and the evolution of resistance in wild potato populations are discussed.     

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.     

The relations of broad nematode resistance to quality characteristics as a consequence of marker-assisted selection in potato breeding programs

Cultivating resistant varieties of potato is the most effective and environmentally sound method of protecting potato crops against pests and diseases. Potato cyst nematodes (PCN) are major nematode pests causing severe constraints in potato production worldwide. There are five pathotypes of Globodrea rostochiensis (Ro1–Ro5) and three of G. pallida Pa1–Pa3. Cultivation of potato varieties with broad nematode resistance may influence the growth of the wide spectrum of PCN pathotypes, but there is limited availability of such varieties on the market. The use of molecular markers allows for the effective selection of resistant genotypes at early stages of breeding. However, the impact of early selection for nematode resistance on the agronomic value of the final selected clones is a cause of concern for potato breeders. This study investigates the relationships between the presence of the combined resistance genes H1, Gro1-4 and GpaV_vrn, which confer resistance to the nematodes, and certain agricultural traits. Clones with broad nematode resistance conferred by the genes H1, Gro1-4 and GpaV_vrn presented yields and tuber morphology traits similar to those of the clones without identified resistance genes.     

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.     

Validation of molecular markers for pathogen resistance in potato

DNA markers have a large potential to improve efficiency and precision of conventional plant breeding programmes based on marker‐assisted selection (MAS). In our study, we have evaluated the predictive abilities of the SCAR marker RYSC3 and the CAPS marker GP122₅₆₄ with regard to the PVY resistance genes Ry_adg and Ry_sto, respectively, and of marker TG689 linked to H1 conferring resistance to Globodera rostochiensis and marker HC associated with high levels of G. pallida resistance. The evaluations were made in 28 cultivars and accessions and in 219 progeny genotypes descending from ten different crosses. We observed in all evaluated cultivars and accessions the expected marker patterns according to their phenotypic classification into resistant and susceptible genotypes. However, in part considerable discrepancies were observed when analysing progeny of controlled crosses involving these resistance sources, particularly with respect to H1. Based on these results, practical aspects for the efficient implementation of marker‐assisted selection are discussed, which consider the genetic origin of the material, costs aspects and methodology applied.     

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.     

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.     

Multiple resistance to diseases and pests in potatoes

Summary The potato has more characters of economic importance that need to be considered by the breeder than any other temperate crop. In Europe these include resistance to at least twelve major diseases and pests. Highest priority has been given to resistance to late blight (Phytophthora infestans), virus diseases (particularly those caused by potato leafroll virus and potato virus Y) and potato cyst nematode (Globodera rostochiensis andG. pallida). Useful sources of resistance are available and early generation screening techniques have been developed to allow positive selection for multiple resistance and the breeding value of clones used as parents to be determined. Progress in restriction fragment length polymorphism technology should result in more efficient selection in the future.     

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.     

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.     

Resistance to the Barley Yellow Mosaic Virus Complex — Differential Genotypic Reactions and Genetics of BaMMV-Resistance of Barley (Hordeum vulgare L.)

Barley yellow mosaic disease is caused by several viruses, i.e. barley yellow mosaic virus (BaYMV), barley mild mosaic virus (BaMMV) and BaYMV-2. The reaction of different barley germplasms to the barley mosaic viruses was studied in field and greenhouse experiments. The results show a complex situation; some varieties are resistant to all the viruses, while others are resistant to one or two of them only. Crosses between different barley germplasms were earned out in order to test whether genetic diversity of resistance against mosaic viruses does exist, particularly, BaMMV. A total of 45 foreign barley varieties were crossed to German cultivars carrying the resistance gene ym4. In F₂ of 27 crosses, no segregation could be detected, leading to the conclusion that the resistance genes of the foreign parents are allelic with ym4 e.g. Ym1 (‘Mokusekko 3’) and Ym2 (‘Mihori Hadaka 3’). A total of 18 crosses segregated in F₂ indicating that foreign parents, like ‘Chikurin Ibaraki 1’, ‘Iwate Omugi 1’, and “Anson Barley”, carry resistance genes different from the gene of German cultivars, e.g. ‘Asorbia’ or ‘Franka’. By means of statistical evaluation (Chi²-test), the observed segregation ratios were analyzed in order to obtain significant information on the heredity of resistance. All the resistance genes described here as being different from the gene ym4, act recessively. Most of the exotic varieties seem to carry only one resistance gene. In a few cases, more than one gene may be present.     

Molecular markers for late blight resistance breeding of potato: an update

Late blight is the most devastating disease of the potato crop that can be effectively managed by growing resistant cultivars. Introgression of resistance (R) genes/quantitative trait loci (QTLs) from the Solanum germplasm into common potato is one of the plausible approaches to breed resistant cultivars. Although the conventional method of breeding will continue to play a primary role in potato improvement, molecular marker technology is becoming one of its integral components. To achieve rapid success, from the past to recent years, several R genes/QTLs that originated from wild/cultivated Solanum species were mapped on the potato genome and a few genes were cloned using molecular approaches. As a result, molecular markers closely linked to resistance genes or QTLs offer a quicker potato breeding option through marker‐assisted selection (MAS). However, limited progress has been achieved so far through MAS in potato breeding. In near future, new resistance genes/QTLs are expected to be discovered from wild Solanum gene pools and linked molecular markers would be available for MAS. This article presents an update on the development of molecular markers linked to late blight resistance genes or QTLs by utilization of Solanum species for MAS in potato.     

Genotype × environment interaction for resistance to the white potato cyst nematode (Globodera pallida,pathotype E) in Solanum vernei x S. Tuberosum hybrids

Summary The standard root-ball test for assessing quantitative resistance of Globodera pallida in host material derived from Solanum vernei has produced variable results. This study of two sets of clones shows that genotype x environment interactions are responsible and that linear regressions (b) of phenotypic means on environments may enable good predictions to be made of the effects of the interactions. A relationship between the regression value (b) and phenotypic mean is shown for this material. The implication of this for a screening procedure in a potato breeding programme aimed at increasing potato cyst nematode resistance in adapted cultivars of S. tuberosum is discussed.     

马铃薯种质资源室内接种晚疫病的抗性鉴定

为了获得具有抗马铃薯晚疫病的品种,本研究以100份马铃薯种质资源为试材,采用室内离体叶片接种法和室内成株接种法进行晚疫病抗性评价,用高感品种Favorita接种后的症状为对照。室内离体接种鉴定结果为:‘CIP09-2’、‘CIP09-13’、‘DR-6’、‘DR-9’、‘花云’、‘R1R3’、‘云薯501’、‘R2’、‘BE13-3’等9份材料表现为高抗,占供试材料的9%;其它的15份表现中抗、44份表现抗病、23份表现感病和9份表现高感。欧氏距离类平均法聚类分析表明,聚为抗性品种的种质最多,其来源与马铃薯晚疫病的抗性没有太大关系。本研究对其中4份材料进行室内成株接种,结果表明:‘青薯10号’的抗病性高于离体叶片接种的抗性,为高抗品种;‘青薯9号’、‘2017ch-6’和‘费乌瑞它’抗性表现与离体叶片接种抗性鉴定结果一致。本研究发现所有供试马铃薯种质资源的抗性材料较丰富,可为抗病育种提供优质的亲本材料。     

Characterization of resistance to Globodera rostochiensis pathotype Ro1 in cultivated and wild potato species accessions from the Vavilov Institute of Plant Industry

Potato cyst nematodes (PCN) collected in six localities in the Leningrad region of North West Russia were identified as Globodera rostochiensis pathotype Ro1 and were used for subsequent resistance tests. Seventy‐nine accessions of cultivated and closely related wild potato species from the VIR collection in Russia were screened on resistance to G. rostochiensis pathotype Ro1 and on the presence of molecular markers for H1 and Gro1‐4 resistance genes. No associations were detected between the resistance level of diploid and tetraploid Andean and tetraploid Chilean potato landraces (indigenous cultivars) and their related wild species and their geographical distribution or presence of PCR‐based markers that are associated with the H1 and Gro1‐4 genes. At the same time, all susceptible genotypes lacked such markers. New sources of resistance were found and could be used in breeding.     

DNA marker for resistance to Puccinia horiana in chrysanthemum (Chrysanthemum morifolium Ramat.) “Southern Pegasus”

White rust caused by Puccinia horiana Henn. adversely affects chrysanthemum (Chrysanthemum morifolium Ramat.) production. The breeding of resistant varieties is effective in controlling the disease. Here we aimed to develop DNA markers for the strong resistance to P. horiana. We conducted a linkage analysis based on the genome-wide association study (GWAS) method. We employed a biparental population for the GWAS, wherein the single nucleotide polymorphism (SNP) allele frequency could be predicted. The population was derived from crosses between a strong resistant “Southern Pegasus” and a susceptible line. The GWAS used simplex and double-simplex SNP markers selected out of SNP candidates mined from ddRAD-Seq data of an F₁ biparental population. These F₁ individuals segregated in a 1:1 ratio of resistant to susceptible. Twenty-one simplex SNPs were significantly associated with P. horiana resistance in “Southern Pegasus” and generated one linkage group. These results show the presence of a single resistance gene in “Southern Pegasus”. We identified the nearest SNP marker located 2.2 cM from P. horiana resistance locus and demonstrated this SNP marker-resistance link using an independent population. This is the first report of an effective DNA marker linked to a gene for P. horiana resistance in chrysanthemum.     

Tagging and mapping of genes and QTLs of Nilaparvata lugens resistance in rice

The brown plant hopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae) is an important pest of rice, Oryza sativa L. (Poales: Poaceae). The need for N. lugens-resistant rice varieties able to cope with stressful conditions obviously requires that breeders better comprehend the physiology and genetic control of N. lugens resistance. In spite of several good reviews recently published, an integrated vision of current information on rice resistance to N. lugens stress has been lacking. Here the most recent data on the N. lugens resistance rice varieties is presented. An inventory is included of N. lugens resistance donors available for breeding programs and a comprehensive survey of current work on gene maps, chromosomal locations, quantitative trait locus (QTL) detection and cloning as well as marker-assisted selection to introgress favorable alleles into chosen rice lines. A schematic view of the rice chromosomes on which N. lugens resistance QTLs and genes are positioned is included. The graphical gene locus of major resistance genes and QTL positions that have been detected on different chromosomes involved in N. lugens response is also presented. We highlight missing information that could help to design better N. lugens resistant varieties, and evaluate the significance of the data presented for the future of rice breeding.     

Improving the yield, processing quality and disease and pest resistance of potatoes by genotypic recurrent selection

A potato (Solanum tuberosum Gp Tuberosum) breeding programme is described and analysed in which resistances to late blight [Phytophthora infestans (Mont.) de Bary] and the white potato cyst nematode (Globodera pallida) have been combined with a modest increase in yield and acceptable fry colour for processing. It began in 1991 and has involved cycles of crossing, selection between from 120 to 145 progenies (full-sib families), and clonal selection within the selected progenies. We have shown that the breeding scheme can operate on a 3-year cycle with limited within progeny selection, and on a 5- or 6-year cycle with more extensive within progeny selection. Six years are required when resistance to late blight is assessed in the tubers as well as the foliage. The more extensive within progeny selection is recommended once genes have been combined from sufficient parents to achieve one’s objectives. The yield increase after three cycles of indirect selection through breeders’ visual preference was only modest because it was operating against a decrease which would occur in the absence of selection. A practical improvement in the scheme would be to increase the number of progenies assessed to over 200, given the moderate to high heritabilities of the progeny and clonal tests. But this would require a considerable effort because the success rate achieved with the potato pollinations was typical at just over 30%. In the fourth cycle we showed how new breeding objectives and germplasm could be accommodated whilst continuing to maintain progress, something that is important in any long term breeding strategy.