ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00210.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Phylogenetic systematics is based on genealogy, rather than overall similarity, and a cladogram constitutes a potentially falsifiable hypothesis that can bring a new perspective to our understanding of the distribution and biogeography of a group of organisms. Sufficient data now exist for phylogenetic analysis of the Heteroderidae. New data at new levels of analysis comprise potential falsifiers for existing schemes.

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00211.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The co‐evolutionary process is believed to have resulted, through interaction of wild populations of potato cyst nematodes and their hosts in geological time, in the resistant hosts now utilized in plant breeding programmes and in nematode populations with genes for resistance‐breaking or virulence. It is argued that all such interactions between highly adapted, truly parasitic plant nematodes and their hosts are likely to be governed by gene‐for‐gene interrelationships. Practical implications of this hypothesis are that only pathotypes (resistance‐breaking races) defined against identified resistance genes are scientifically sound and of practical value; that, in the case of potato cyst nematodes, other pathotypes (Ro2, Ro3, Ro5 and Pa2 and Pa3) should be abandoned; and that oligogenically based resistance to potato cyst nematodes, especially important in providing resistance toGlobodera pallida, is non‐durable. Working definitions of the terms ‘pathotype’, ‘host‐race’ and ‘

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00212.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

By reference mainly to cyst nematodes, certain aspects concerning the species category and intraspecific categories are considered. Special attention is paid to the existence of cryptic or sibling species, the possibility of interspecific hybridization, the phenomenon of reduced reproductive compatibility of certain populations within a species and the loss of subspecies and race identity in mixtures. Both terms ‘biological or physiological race’ and ‘pathotype’ can be used to express differences in host specificity in nematology, entomology and plant pathology. A distinction is made between the two categories and differences among them are outlined in detail. Whereas ‘race’ is considered as a population concept, pathotypes are defined as virulence phenotypes. Races are genetically variable groups of related populations, while pathotypes area priori‘artificial’ entities, established for practical reasons and characterized by constancy of their rele

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00213.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A race is defined as a population of which all individuals carry the same combination of virulence genes. For an easy and ready identification of races, it is necessary that both races and host differentials breed true to type. Clonal reproduction (races, differentials) and self‐fertilization (differentials) provide for this. The tests should be carried out under specified conditions. The differentials should carry resistance genes with large effects. Two informative systems of race classification have been described and discusse

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00214.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Cet article est une revue bibliographique des résultats obtenus dans l'étude des protéines et enzymes des genresHeteroderaetGlobodera.Ces travaux ont permis de mettre en évidence une variabilité inter et intraspécifique. L'utilisation de ces caractères, comme outil taxonomique, ne sera optimisée qu'à condition de pousser aussi loin que possible l'analyse génétique de ces phénotypes. De plus, si l'on veut caractériser des entités subspécifiques (pathotypes), par les protéines ou enzymes, il est nécessaire de travailler sur des protéines liées à la fo

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00215.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

After making simplifying assumptions, the ability of female potato cyst nematodes to develop and reproduce is modelled by expressions of the typeix·xandix·(1 ‐x), wherexis the frequency within a population of females able to circumvent the effects of a real resistance gene. Such females are potentially able to develop to maturity and reproduce to maximum capacity. For this class of femalesix= 1, i.e. they are unaffected by the resistance gene. The frequency of other classes of females is given by (1 ‐x) and for themixranges in value from just less than 1 to 0 according to the effectiveness of the gene. Whenixapproaches 0, females in these classes are eliminated and the gene responsible is said to be a ‘major’ resistance gene. For values ofixgreater than 0, the genes responsible are called ‘minor’ genes. If full reproductive power is 1, then the total reproductive power in the presence of the resistance gene is [x+ix(1 ‐x)] or when several genes are present by [x+ix(1 ‐ x)]·[y+iy(1 ‐y)]·[z+iz(1 ‐z)] etc. That is, the effects of these genes depend on the frequencies of females able to reproduce in their presence and on the effectiveness of the different genes as measured byi.Furthermore, ‘major’ and ‘minor’ genes are part of a continuum described byi.The model is used to illustrate the effects of combining ‘major’ and ‘minor’ genes and the effects of some arbitrary combinations are calculated. Data with which to test the model are sparse but what little there is tends to support it. Interactions between resistance genes, the fitness of females, the selection of males and the effects of resistant cultivars on populations are discussed. Selection by resistant potato hybrids in pots is surprisingly rapid and sometimes becomes evident after only five generations. Ways in which resistant cultivars might be used to prolong the useful life of re

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00216.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Breeding for resistance toGlobodera pallida, at the International Potato Center (CIP), is directed at pathotypes P4A and P5A. The polygenic nature of resistance and the variability of pathotypes complicate breeding and testing for resistance. Recurrent selection for resistance genes and for agronomic characteristics is used to increase resistant gene frequency in potato populations. Mass seedling screening, as an early indicator of segregation ratios in a progeny, and a petri‐plate technique for accurate assessment of resistance in potato clones have proven to be useful aids in selecting for resistance. Clones with partial resistance could be grown by farmers under certain conditions; partial resistance may also be useful in breeding programmes. New differential or tester clones which are better adapted and resistant to P5A populations should be utilized in the Andean region. AlthoughSolanum tuberosumssp.andigenahas been the main source of resistance, especially to pathotype P5A, the CIP breeding programme should now turn to wild species in order to broaden the base of resistanc

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00217.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Results of field trials of cultivars resistant or partially resistant toGlobodera pallidaare reported. The effects of the varying resistance levels on the nematode populations were examined. The initial population levels had an important effect on the Pf/Pi ratio. The ranking of the cultivars using the field Pf/Pi values consistently agreed with the resistance ranking obtained using the closed canister method of assessment. Many of the partially resistant cultivars effectively limited the level of increase of the final cyst‐nematode population, if not decreasing the levels from their initial values. It is argued that such partial resistance can contribute positively to the control of potato cyst nematodes within the context of a crop rotatio

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00218.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Experiments assessing the quantitative resistance of potato clones to potato cyst nematodes tend to produce variable results because of genotype‐environment interactions. Despite these interactions clones are ranked in the same way even when a major environmental factor such as initial nematode population density is changed. It is also argued that as the reproductive rate is so environmentally sensitive the use of fixed levels of nematode multiplication rate as criteria for classifying clones is inappropriate. It is proposed that standard resistant and partially resistant clones be included in all assessment tests. They would act as delineators of resistance classes and would allow easy comparisons to be made between tests whether conducted in glasshouse or fiel

ISSN:0250-8052    

DOI:10.1111/j.1365-2338.1985.tb00219.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY