Natural Genes and Mechanisms for Resistance to Viruses in Cultivated and Wild Potato Species (Solanum spp.)

The types of resistance to viruses in potato are immunity, extreme resistance coded for by the R genes and hypersensitivity coded for by the N genes. Immunity prevents the establishment of virus infection, whereas extreme resistance is expressed as an extremely low virus titre resulting from restricted virus multiplication or localization of virus infection in the plant without obvious necrotic reactions. Expression of the N genes can also lead to localization of the virus infection followed by necrosis at the infection site. Tolerance to virus infection and resistance to inoculation and virus vectors are useful components of field resistance. Virus or virus strain specific resistance genes have been identified in cultivated and wild potato species and transferred to cultivated potato. However, combining resistance to the three globally most important viruses PLRV, PVY and PVX has proved difficult, and new sources of broad spectrum resistance to viruses are required for potato breeding. New molecular techniques will enhance the isolation of the natural resistance genes and studies of gene regulation.     

Elucidation of virus-host interactions to enhance resistance breeding for control of virus diseases in potato

Potato virus Y (PVY) and Potato mop-top virus (PMTV) are viruses whose geographical distribution is expanding and economic losses are increasing, in contrast to most of other viruses infecting potato crops. Most potato cultivars lack broad-spectrum resistance to the new, genetically complex strains of PVY, and no efficient resistance to PMTV is known in potato. Control of the vectors of these viruses is not an efficient or possible strategy to prevent infections. Studies on molecular virus-host interactions can discover plant genes that are important to viral infection or antiviral defence. Both types of genes may be utilized in resistance breeding, which is discussed in this paper. The advanced gene technologies provide means to fortify potato cultivars with effective virus resistance genes or mutated, non-functional host factors that interfere with virus infection.     

Strategies for engineering virus resistance in transgenic plants

Summary Transgenic virus-resistant plants were first produced in 1986 by genetically engineering tobacco plants to express the coat protein of tobacco mosaic virus. The introduction of coat protein transgenes has since proved to be an extremely effective and generally applicable approach to engineering virus resistance in crop plants. Extensive field trials with transgenic, virus-resistant tobacco, tomato, potato and cucumber lines have confirmed not only the durability of the resistance under natural conditions but the ease with which virus-resistant lines retaining the original cultivar traits can be recovered.A number of alternative anti-viral strategies based on transgenes from a surprisingly wide variety of sources have also been developed. These include the use of viral genes coding for proteins involved in the replication cycle and in systemic transport of viruses within the plant, the use of interfering viral RNA sequences, and the use of transgenes derived from plant and animal sources. In the latter category, the use of mammalian antibodies to confer disease resistance in plants is a particularly exciting new development. Considerable progress has also been made towards the molecular cloning of natural anti-viral resistance genes in plants.     

Correlation between late blight resistance and foliage maturity type in potato

The genetics of race-non-specific foliage resistance against Phytophthora infestans, of foliage maturity type, and of their association in potato (Solanum tuberosum) were studied. Six progenies were derived from a half-diallel set of crosses between diploid potato clones that represented a broad pool within the genus Solanum and were free of any of the 11 known R genes for late blight resistance. The progenies were evaluated for resistance to late blight and for foliage maturity type, and five of them showed a significant correlation between the two traits. The correlation did not account for all variation that was present for both traits, as reflected in the analysis in which the relative AUDPC values were adjusted for foliage maturity type. The present study adds to previous results: resistance against P. infestans always coincides with late foliage maturity. However, the results also indicate that some selection for late blight resistance without affecting the foliage maturity type should be possible.     

Heritility of field resistance to potato leafroU virus in cultivated potato

Potato progenies in a line x tester mating design and the clonal parents were screened for field resistance to potato leafroll virus (PLRV) to determine the heritability of this trait. Twelve advanced potato clones or varieties were crossed as pistillate parents to two pollen testers. The seedling progenies and clonal parents were exposed to aphid-transmitted potato leafroll virus for two growing seasons. Cumulative infection by potato leafroll virus was determined by post-season sero-logical indexing of foliage grown from sprouted tubers after 2 years of exposure. Narrow-sense heritability was estimated from regression of mid-parent on progeny as h = 0.72. This estimate indicates a high level of useabie genetic variance for PLRV resistance in advanced breeding materials. Although variation in resistance to PLRV appears to be a quantitative trait in susceptible and moderately resistant clones, per-formance of the most resistant parents suggests that genes with major effects may be present. These results are similar to the conclusions of other researchers who found one or two genes controlling the pheno-types of extreme resistance, resistance to infection, or suppression of virus titre.     

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.     

马铃薯抗病毒遗传及与产量性状的关系

本文研究了马铃薯对卷叶和花叶病毒抗性的遗传及与产量性状的关系.结果表明,抗病性与群体产量没有显著的遗传相关性,抗病性主要通过保证马铃薯植株的正常生长发育而间接保持群体的高产稳产性能.马铃薯对卷叶病毒抗性、株高、茎粗、有效株率和主要产量性状的遗传主要由亲本的累加基因效应决定,且同一亲本在不同性状上的一般配合力效应差异较大.因此,抗病高产育种中各目标性状的协调选择是十分重要的.群体有效株率和茎粗的选择可使抗病性和丰产性同步提高.马铃薯对花叶病毒的抗性、加性和非加性作用同时存在.群体抗病性、有效株率和产量的遗传进度高,选择潜力大.     

马铃薯重要性状QTL定位及3个抗病性状分子标记辅助选育

马铃薯是我国主要粮食作物之一,马铃薯分子育种研究具有重要意义。在二倍体马铃薯中,重要性状控制基因的QTL定位及克隆已经有大量报道。近年,随着同源四倍体分析软件的开发,四倍体马铃薯的遗传图谱构建和QTL定位也取得了突破性进展。分子标记是马铃薯育种的重要辅助手段,可快速准确筛选出多个优良性状。对马铃薯重要农艺性状的QTL定位和克隆,以及3个抗病性状分子标记辅助选育的研究进展进行概述,为加快马铃薯分子育种研究提供参考和实践依据。     

Molecular characterization of the progeny of <Emphasis Type="Italic">Solanum etuberosum</Emphasis> identifies a genomic region associated with resistance to potato leafroll virus

Potato leafroll virus (PLRV; Genus Polerovirus; Family Luteoviridae) is one of the most important virus pathogens of potato worldwide and breeders are looking for new sources of resistance. Solanum etuberosum Lindl., a wild potato species native to Chile, was identified as having resistances to PLRV, potato virus Y, potato virus X, and green peach aphid. Barriers to sexual hybridization between S. etuberosum and cultivated potato were overcome through somatic hybridization. Resistance to PLRV has been identified in the BC₁, BC₂ and BC₃ progeny of the somatic hybrids of S. etuberosum (+) S. tuberosum haploid × S. berthaultii Hawkes. In this study, RFLP markers previously mapped in potato, tomato or populations derived from S. palustre (syn S. brevidens) × S. etuberosum and simple sequence repeat (SSR) markers developed from tomato and potato EST sequences were used to characterize S. etuberosum genomic regions associated with resistance to PLRV. The RFLP marker TG443 from tomato linkage group 4 was found to segregate with PLRV resistance. This chromosome region has not previously been associated with PLRV resistance and therefore suggests a unique source of resistance. Synteny groups of molecular markers were constructed using information from published genetic linkage maps of potato, tomato and S. palustre (syn. S. brevidens) × S. etuberosum. Analysis of synteny group transmission over generations confirmed the sequential loss of S. etuberosum chromosomes with each backcross to potato. Marker analyses provided evidence of recombination between the potato and S. etuberosum genomes and/or fragmentation of the S. etuberosum chromosomes.     

Early selection for extreme resistance to potato virus Y and tobacco etch virus in potato using a β-glucuronidase-tagged virus

The Ry_sto gene from Solanum stoloniferum introduced into potato cultivars (Solanum tuberosum L. ssp. tuberosum) confers resistance to potato virus A, potato virus V and potato virus Y (PVY). In addition to PVY, tobacco etch virus (TEV) and a TEV construct that encodes β‐glucuronidase (TEV‐GUS) were inoculated to determine the inheritance of resistance to these viruses in progenies obtained from potato cultivars containing the Ry_sto gene. While cultivars ‘Karlena’ and ‘Delikat’ were susceptible, ‘Bettina’ and clone 927eY were resistant to PVY, TEV and TEV‐GUS, as determined by enzyme linked immunosorbent assay, biotest and GUS assay, respectively. The segregation ratios obtained from the progenies of ‘Bettina’בDelikat’ and 816eY בKarlena’ indicate that resistances to PVY and TEV are governed by one dominant gene or two genes tightly linked in coupling phase. Evidently, Ry_sto confers broad spectrum resistance to potyviruses. TEV resistance could be reliably detected 4 days after inoculation with the TEV‐GUS construct by GUS assay. Therefore, the GUS‐tagged TEV construct can be used for early selection for resistances based on the gene Ry_sto or closely linked genes.     

马铃薯帚顶病毒研究进展

综述了近年来国内外马铃薯帚顶病毒(PMTV)所取得的研究进展;简述了PMTV的分布与传播、分子特征、病理特征、致病机理及其检测方法,认为PMTV主要出现在气温冷凉的高纬度、高海拔地区的马铃薯上,能通过种薯和粉痂菌传播,诱导马铃薯块茎发生环状坏死;分析了该病毒的特殊性及防治的难点;认为今后要深入研究粉痂菌、马铃薯、PMTV三者之间的相互作用,挖掘PMTV抗性基因,开展马铃薯抗PMTV育种,建立快速准确的PMTV检测方法,探讨同时防治粉痂病和PMTV的途径。     

Components of resistance to ryegrass mosaic virus in a clone of Lolium perenne and their strain-specificity

Summary The extreme resistance to ryegrass mosaic virus (RMV) of a clone of Lolium perenne L. was due to a combination of two distinct types of resistance: resistance to infection and resistance to multiplication and movement of virus within the plant. Resistance to infection was quantitatively inherited and highly effective against three strains of RMV, while resistance to multiplication and movement was controlled by two complementary recessive genes and was effective against only two of the three RMV strains.     

Transfer of resistance to Verticillium dahliae Kleb. from Solanum torvum S.W. into potato (Solanum tuberosum L.) by protoplast electrofusion

Summary Interspecific somatic hybrid plants were regenerated after electrofusion of mesophyll protoplasts with the objective of transferring resistance to Verticillium dahliae from Solanum torvum into potato. Early selection of the putative hybrids was based on differences in cultural behaviour of the parental and hybrid calli (particularly the ability of the latter to regenerate early) in combination with morphological markers. Four putative hybrids were recovered from hundreds of calli, probably resulting from complementation of the two parental genomes. The regenerates were tetraploids (2n=4×=48 chromosomes) and exhibited intermediate traits including leaf form, plant morphology and the presence of anthocyanin. The hybrid nature of the four selected plants was confirmed by examining isoenzyme patterns for isocitrate dehydrogenase (Idh), malate dehydrogenase (Mdh), phosphoglucoisomerase (Pgi) and 6-phosphogluconate dehydrogenase (6-Pgd). While the hybrid plants rooted readily and grew vigorously under in vitro conditions, in the greenhouse their development and growth were retarded by difficulties in rooting. When grafted on potato or S. torvum rootstocks, the hybrid plants recovered normal development and growth. Again, they exhibited intermediate morphological traits. Tests for resistance realized in vitro with medium containing 50% Verticillium wilt filtrate showed that all the somatic hybrids were resistant to the fungus filtrate.     

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.     

Intraspecific somatic and sexual hybridisation between dihaploid lines of Solanum tuberosum L.: evaluation of morphological traits and resistance to late blight Phytophthora infestans (Mont.) de Bary in the foliage

Intraspecific tetraploid somatic and sexual hybrid plants have been resynthesised following protoplast fusion and by sexual crosses between two dihaploid potato (Solanum tuberosum) lines each possessing complementary agronomic traits. The dihaploid PDH 40 possesses good tuber shape and yield but has foliage susceptibility to late blight (Phytophthora infestans). On the other hand, the dihaploid PDH 727 possesses resistance to blight in the foliage but has a low yield of small and irregular shaped tubers. Since it was only possible to use a partial selection strategy based on culture media to facilitate recovery of somatic hybrid plants-further morphological and esterase isozyme based characterisations were performed to identify somatic hybrid plants from amongst the non-hybrid plant material. When the blight resistance of both the intraspecific somatic and sexual hybrid plants was assessed there was no significant difference in the mean resistance value and it was intermediate between those of their parents. However, the range of resistance was much wider among the sexual hybrids than among the plants derived from somatic fusion. An assessment of tuber yield between tetraploid sexual and somatic hybrids showed no significant difference and it was higher than that of either parent value. The implication of these results in the context of potato genetics and breeding is discussed.     

Inheritance and stability of the virus-resistant gene in the progeny of transgenic sweet potato

Viral diseases of sweet potato are very prevalent and often seriously damaging to the plants. In particular, the severe strain of the sweet potato feathery mottle virus (SPFMV‐S) causes ‘obizyo‐sohi’ disease in Japan. In order to confer viral resistance against SPFMV using current biotechnology, a transgenic sweet potato has been produced, introducing hygromycin‐resistant (hpt) and SPFMV‐S coat protein (CP) genes, which have shown a significant resistance to SPFMV‐S. In the breeding programme, it is important to confirm that the viral resistance conferred in T₀ plants can be inherited by their progeny. In the present study, progeny were obtained from crosses between the transgenic T₀ and a non‐transgenic variety of sweet potato. The results showed that the CP gene was inherited by the next generation and that the stability of viral resistance was also confirmed. Thus, this production system for the virus‐resistant transgenic sweet potato is useful in practical breeding.     

马铃薯重要农艺性状的相关性、主成分与聚类分析

为明确国内外马铃薯种质资源在云南大春季的表现,本研究对68份马铃薯品种(系)的出苗率、长势、主茎数、茎粗、株高、开花性、病情发展曲线下面积(area under disease progress curve, AUDPC)、成熟期、商品率、单株块茎数、单株块茎重、平均块茎重、匍匐茎数量、匍匐茎长度共14个农艺性状进行相关性、主成分与聚类分析。结果表明:单株块茎数、AUDPC、单株块茎重、开花性的变异程度较明显,变异系数分别为50.42%、43.91%、39.81%和39.67%;单株块茎重与长势、茎粗、株高、开花性、商品率、平均块茎重、匍匐茎数量极显著正相关,与单株块茎数显著正相关,与成熟期极显著负相关。AUDPC与成熟期极显著正相关且相关系数达到0.802。在主成分分析中,前6个主成分方差累积贡献率为83.290%,可用来代替14个农艺性状指标。聚类分析将68份马铃薯品种(系)分为3个类群,Ⅰ类群表现为晚熟、高抗晚疫病病,Ⅱ类群表现为中熟、中抗晚疫病,第Ⅲ类群表现为早熟感晚疫病。本研究结果为云南大春马铃薯种质资源的合理利用提供了科学依据。     

引进马铃薯种质资源在干旱半干旱区的表型性状遗传多样性分析及综合评价

马铃薯种质资源缺乏,适宜干旱半干旱条件下生长的品种更为紧缺,引进马铃薯种质是丰富种质资源的有效途径。本文采用Shannon-Wiener’s多样性指数及综合得分(F值)对119份从秘鲁国际马铃薯中心引进的马铃薯材料的表型性状(出苗率、株高、茎粗、叶面积、生育期、单株结薯数、单株产量、商品率、干物质含量和块茎长宽比)进行遗传多样性分析及综合评价。结果表明,参试材料的10个表型性状中生育期遗传多样性最为丰富;茎粗、叶面积、生育期、单株结薯数、单株产量、商品率、干物质含量、块茎长宽比对马铃薯种质资源表型性状综合值具有显著影响,这些指标可用于旱作条件下对马铃薯种质资源的综合评价;综合得分F值与所测经济性状(单株产量、商品率、干物质)具显著相关性,可作为马铃薯种质资源的主要评价指标;引进材料中CIP393228.67和CIP 385561.124在干旱区,CIP304350.95、CIP392797.22、CIP388615.22在半干旱区分别表现出较好的丰产稳产特性。这些材料综合评价较好,可有效补充中国马铃薯种质资源。     

A comparison between single plant plots and five plant plots for the initial selection stage of a potato breeding programme

Summary The efficiency of single plant selection in the initial selection stage of a potato breeding programme was examined. A random sample of potato clones was grown in single plant plots and also in tworeplicates of five plant plots. After harvest, each plot was visually assessed by three potato breeders; total tuber weight and number of tubers per plant were also recorded, from which mean tuber weight was calculated. The error variances of the single plant plots were found to be significantly greater than from the five plant plots for total tuber weight, mean tuber weight and number of tubers per plant, but not significantly different for breeders' preference. Coefficients of correlation between single and five plants plots were significantly greater than zero for all traits examined, but they were lower than the corresponding correlations between the two replicates of five plant plots. Although a random sample of clones was examined, each clone had been assessed for breeders' preference the previous year. When the clones were grouped according to the previous years preference scores, it was found that the correlation coefficients between single and five plant plots for breeders' preference were inversely related, in magnitude, to the mean preference score of each group. It was concluded that single plant selection was generally ineffective, particularly when only the better clones, from the previous years assessment, are examined.