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.     

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.     

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.     

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.     

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.     

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.     

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.     

A re-examination of apparent selection in Globodera pallida on Solanum vernei hybrids

Summary This paper re-examines the data in support of recent findings by Turner et al. (1984), that selection for virulence in Globodera pallida takes place on Solanum vernei hybrids. It is concluded that there are a number of factors that must be taken into account and that these data must be interpreted with caution.     

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.     

Development of an STS marker and SSRs suitable for marker-assisted selection for the BaMMV resistance gene rym9 in barley

Based on the RAPD marker OP‐C04H910 which is closely linked to the barley mild mosaic virus (BaMMV) resistance gene rym9 derived from the variety ‘Bulgarian 347’ the marker STS‐C04H910 cosegregating with OP‐C04H910 and generating a single additional band on plants carrying the recessive resistance encoding allele has been developed. Furthermore, the simple sequence repeats (SSRs) WMS6 and HVM67 have been integrated into the genetic map of the rym9 region on chromosome 4HL. Because of their close linkage to rym9 and distinct banding pattern STS‐C04H910 and HVM67 are well‐suited for marker‐ assisted selection, enhanced backcrossing procedures and pyramiding of resistance genes.     

分子标记技术及其在作物育种中的应用

论文综述了分子标记的基本类型及其在作物遗传育种中的应用,分析了应用过程中存在的问题,提出了解决的方法,并讨论了其应用前景。     

Exotic barley germplasms in breeding for resistance to soil-borne viruses

Summary Soil-borne mosaic inducing viruses, i.e., barley mild mosaic virus (BaMMV), barley yellow mosaic virus (BaYMV), and BaYMV-2, cause one of the most important diseases of winter barley in Western Europe. Since resistance of all commercial European barley cultivars is due to a single recessive gene (ym4) which is not effective against BaYMV-2, exotic barley germplasms (Hordeum vulgare L., H. spontaneum Koch) were screened for resistance to the different viruses and analyzed for genetic diversity concerning BaMMV resistance. In these studies it turned out that resistance to BaMMV is entirely inherited recessively and that a high degree of genetic diversity concerning resistance is present within the barley gene pool at least to BaMMV. Therefore, exotic barley germplasms are a very useful source for the incorporation of different resistance genes into barley breeding lines, thereby enabling the breeder to create cultivars adapted to cultivation in the growing area of fields infested by soil-borne viruses. Furthermore, in order to obtain more information on these germplasms they were evaluated for agronomic traits and isozyme, RFLP and RAPD analyses were carried out on these varieties to detect markers linked to the respective resistance genes and to obtain information on the genetic similarity between yellow mosaic resistant barley accessions derived from different parts of the world. Actual results of these studies are briefly reviewed.     

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.     

Selection for verticillium wilt resistance in potato breeding populations derived from four cross types

Verticillium wilt (VW) is one of the important yield-limiting diseases for potato production. To develop resistant clones, the potential for early generation selection was studied using three basic selection methods, individual, family, and within family selection, for two clonal generations. A total of 152 clones were derived from four cross types (2x × 2x, 2x × 4x, 4x × 2x and 4x × 4x). Clones were evaluated for maturity, symptom expression, yield and stem colonization in replicated trials. Heritability and selection response for the traits were estimated for each selection method. Direct selection in the second clonal generation and individual selection showed more gain than that from other methods. Both 2x × 2x and 4x × 2x families were higher yielding and had lower stem colonization scores than 2x × 4x and 4x × 4x crosses. Therefore, 2x × 2x or 4x × 2x crosses between carefully chosen parents with high yield and VW resistance may produce offspring with superior performance.     

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.     

Two RAPD markers linked to a major fertility restorer gene in pepper

Both major and minor genes control the restoring of fertility in the cytoplasmic male-sterility system in pepper (Capsicum annuum L.). Bulked segregant analysis (BSA) was applied to identify molecular markers linked to a major restorer gene (Rf) using the F₂ population of NiujiaojiaoNo.21 (rfrf)/Xiangtanwan (RfRf). Two random amplified polymorphic DNA (RAPD) markers linked to this allele were detected with 520 decamer primers with arbitrary sequences. OP13₁₄₀₀ is a tightly linked marker with a genetic distance of0.37 cm. OW19₈₀₀ is on the opposite side with a distance of 8.12 cm. Both markers were repeatable and easy to score. A panel of genotypes, including 13elite inbred lines with different fertility restoring ability, were assayed for the presence ofOP13₁₄₀₀ and OW19₈₀₀. The markers are absent in all sweet pepper lines, indicating that they will be most helpful for transferring Rf into sweet pepper lines. With the aid of these markers, the size of the backcross population for testcrosses can be minimized. Furthermore, these markers will be useful in genetic analysis of the minor genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding cowpea for resistance to Striga gesnerioides in the Nigerian dry savannas using marker‐assisted selection

Historically, conventional breeding has been the primary strategy used to develop a number of Striga‐resistant varieties currently grown in the Sahel of Western Africa. In this study, we have successfully developed and applied a marker‐assisted selection strategy that employs a single backcross programme to introgress Striga resistance into farmer preferred varieties of cowpea for the Nigeria savannas. In this strategy, we have introduced the Striga resistance gene from the donor parent IT97K‐499‐35 into an elite farmer preferred cowpea cultivar ‘Borno Brown’. The selected 47 BC₁F₂ populations confirmed the recombinants with desirable progeny having Striga resistance gene(s). The 28 lines selected in the BC₁F_2:4 generation with large seed size, brown seed coat colour and carrying marker alleles were evaluated in the field for resistance to Striga resistance. This led to the selection of a number of desirable improved lines that were immune to Striga having local genetic background with higher yield than those of their parents and standard varieties.     

Identification of RAPD markers linked to the Ns locus in potato

Using the RAPD method and bulked segregant analysis we identified four RAPD markers linked to a dominant gene Ns, responsible for a hypersensitive reaction of potato (Solanum tuberosum L.) to potato virus S (PVS) infection. The markers OPE15⁵⁵⁰, OPJ13⁵⁰⁰, OPG17⁴⁵⁰ and OPH19⁹⁰⁰ were found to be closely linked to the Ns gene in diploid potato clones. They are situated at 2.6, 3.3, 4.6 and 6.6 cM from Ns, respectively. As a source of the gene, clone G-LKS 678147/60, which is known to carry Ns transferred from S. tuberosum ssp. andigena was used. These RAPD markers were not amplified in resistant tetraploid clones containing Ns derived from the clone MPl65 118/3, also having an andigenum origin. This suggests that there may be two separate loci of Ns in the sources identified, or different alleles with the same specificity at a single locus, or that the genetic background of tetraploids tested results in different RAPD amphlification patterns.