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Breeding for resistance to narcissus basal rot. - HH1024SBU

Description
The primary objective of this strategic research is to bring basal rot resistant narcissus varieties to the marketplace more quickly.

None of the commercial varieties produced to the date have the high level of resistance associated with some Narcissus species but a few triploid hybrid lines arising from crosses between the species N. jonquilla and two varieties do appear to have this level of resistance (see final report on HH1008SBU). If tetraploid plants of resistant species can be produced and crossed with some commercial varieties then the species-type resistance may be expressed as the phenotype of the F1 generations. Even if this is not the case, the progeny should be fertile and further crossing can take place giving rise to new genotypes that may have the desired phenotype. The genetic basis of species resistance would be better studied by an analysis of the offspring derived from a cross between two species of opposite resistance phenotype. The distribution of resistance phenotypes in existing progenies from variety crosses should also be analysed to quantify the potential value of variety resistance in future breeding programmes.

If the current whole-plant assay for screening novel genotypes for resistance could be replaced with a faster and more precise method then commercially desirable high-resistance varieties would be identified more easily. Work undertaken in HH1008SBU has indicated one promising technique, viz. puncture inoculation of individual bulb scales, and this should be developed further.

Pathogen virulence may vary considerably between isolates, which in turn may affect the efficacy of resistance in some or all varieties of narcissus. This project also aims to determine variation within pathogen populations.

The proposed project meets the stated Policy Objective of AU HH10 by “improving the quality of genetic material” and thereby “enabling UK growers to retain and extend their share of the market.” It also conforms to the Scientific Objectives of “breeding plants with improved disease resistance” and “understanding the inheritance of specific components.”
Objective
1. To determine the basal rot resistance phenotypes of progenies where one or both parents are Narcissus species:

Reassess the basal rot resistance of 14 variety x species hybrid lines from HH1008SBU using larger sets of each bulb line to improve confidence in the result. This will determine the validity of the apparent complete resistance exhibited by a few progeny lines (Years 1 and 4). Examine the postulated recessive nature of high level resistance to basal rot in N. jonquilla by making new crosses between the susceptible N. pseudonarcissus and the resistant N. jonquilla (Year 2), and determining the resistance phenotype of the F1 generation (Year 4). Determine whether susceptibility in N. pseudonarcissus is homozygous or heterozygous by raising self-pollinated N. pseudonarcissus progeny (Year 2) and testing the resistance (Year 4.

2. To determine the basal rot resistance phenotypes of progenies from Golden Harvest x St Kevern:

Determine basal rot resistance in the F1 generations (maximum of 75 clonal lines) derived from crosses between the susceptible variety Golden Harvest and the moderately resistant St. Keverne (Years 2 and 3). Many such progenies were produced between 1985 and 1992, some have been screened once for resistance as single seeding bulbs but the surviving genotypes have never been re-tested nor have their relative resistances been determined. By comparing the resistance of clonal material from these lines to that of St. Keverne itself, the value of variety hybridisation in resistance breeding can be assessed.

3. To quantify the potential contribution of tetraploid Narcissus species resistance in hybrid offspring:

Attempt to double the chromosome complement of the diploid resistant N. jonquilla, N. canaliculatus, N. bulbocodium and N. broussonetii (Years 1 and 2). Test the basal rot resistance of any tetraploid bulbs produced (Year 4). These tetraploid bulbs can be used as parents that can be crossed with existing tetraploid varieties to generate fertile hybrids for further crossing or which may have more immediate commercial application if any of the F1 generation exhibit a high level of basal rot resistance. The F1 generations recently produced within HH1008SBU are triploid, and probably sterile. These proposed hybridisations will have to be carried out in a later project.

4. To quantify bulb responses to infection by F. oxysporum and to provide a rapid biological assay of resistance for use in breeding:

A positive correlation between response to fugal inoculation of detached scales and basal rot resistance of several varieties and species has been found in studies undertaken within HH1008SBU. This method will be evaluated using other varieties of known basal rot resistance status (Year 1). If this assay can discriminate between the resistance and susceptible lines identified in HH1008SBU then it will be used in place of more lengthy whole plant screening protocols in Objectives 1-3.

5. To measure the population diversity within 135 UK field isolates of F. oxysporum f. sp. narcissi:

Collect fungal isolates from the bulb stocks of a number of growers within the UK, including the east and south-west bulb-growing regions (Years 1 and 3). Quantify the virulence and fungicide sensitivity of the isolates (Years 1 and 4). Apply molecular methods (being developed in HH1748TBU) to examine variation in pathogen populations and to determine the relatedness of these and other Fusarium oxysporum collected from neck rots within HH1748TBU (Years 2 and 4).
Project Documents
• Final Report : Breeding for resistance to narcissus basal rot   (294k)
Time-Scale and Cost
From: 1999

To: 2003

Cost: £201,315
Contractor / Funded Organisations
Horticulture Research International
Keywords
Breeding              
Disease Control              
Farming              
Horticulture              
Narcissus              
Ornamentals              
Fields of Study
Horticulture
Horticulture