Black spot resistance in field peas advanced
GroundCover™ Issue: 116 | Author: Nicole Baxter
Bonnie Hargreaves was awarded a GRDC undergraduate honours scholarship to investigate black spot in field peas to better understand how to breed for resistance
The need to combine minor genes with cumulative disease-resistance effects has become clear through new research into black spot, which has confirmed the apparent absence of any major resistance genes despite extensive international screening of chickpea germplasm.
Researcher Bonnie Hargreaves set out to evaluate the link between black spot resistance and flowering time using field peas sourced from a diverse breeding population at the University of Western Australia (UWA).
Diverse genetic material was sourced from a 12-year UWA research project led by Professor Wallace Cowling at the UWA Institute of Agriculture, based on interbreeding Australian commercial varieties with elite European lines, Chinese landraces, Greek landraces and wild peas with black spot resistance.
Despite extensive screening, no major resistance genes for black spot were found and complete resistance to the major pathogen Didymella pinodes has yet to be identified.
Ms Hargreaves says the goal of her Bachelor of Science in Agriculture honours thesis project was to show that resistance could, nonetheless, be improved by bringing together minor genes with additive effects. She also sought to show that resistance was heritable on a single plant basis. With this knowledge, breeders could still improve black spot resistance in new varieties.
In summer 2012-13, under the supervision of Professor Cowling, 100 plants were crossed. In April they were planted in glasshouse trays, segregating progeny (first generation of plants as a result of the crossing in 2012-13) and self-pollinated progeny from each parent plant. Also included were Australian commercial varieties susceptible to black spot, for use as control plants.
Before planting, Ms Hargreaves sowed the susceptible commercial field pea variety Helena around the border of the trial at UWA’s Shenton Park Field Station to promote the spread of black spot disease.
In May, 1400 seedlings were transplanted to the trial site. Ms Hargreaves added field pea straw infected with black spot fungus, to encourage the establishment and spread of black spot.
Ms Hargreaves found significant spatial trends for disease and flowering time across the trial. Resistance to black spot was shown within the F1 progeny and she confirmed black spot resistance was heritable on a single plant basis, with a moderate heritability.
Heritability for flowering time was slightly higher. Individual plants were found with resistance to black spot and early flowering times suitable for southern Australia: “However, the correlation between the two traits indicated that later flowering times meant better resistance to black spot,” she says.
Ms Hargreaves’s research also showed the value of a new trial design, with the inclusion of self-pollinated seed of parent plants as well as cross-pollinated F1 progeny seed.
“In future, pedigrees and genomic information could be used to improve accuracy of selection for black spot resistance,” she says.
Pedigrees that take into account information from all relatives across all generations can be associated with individual plants to give a more accurate idea of their breeding values – which means that more accurate selections can be made in the next round of breeding to improve black spot resistance.
Professor Kadambot Siddique, director of the UWA Institute of Agriculture, says that while moderate resistance to black spot has been found in existing field pea germplasm, this new breeding method coupled with new genomic technology could speed up genetic improvements for black spot resistance and other desirable traits.
Professor Cowling says Ms Hargreaves’s work has the potential to lead to the development of an Australian commercial variety with polygenic resistance to black spot. (Polygenes are genes with an individual effect on a phenotype that is too small to be observed, but that can act together with others to produce observable variation.)
“More importantly, her work could lead to a new rapid method of breeding self-pollinating plants, based on genomic selection, which we have been developing at UWA over the past 12 years,” he says.
More information:Bonnie Hargreaves
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