Genetic analyses and mapping of resistance to fusarium basal rot in onion

Authors: STRALEY, ELIZABETH - University Of Wisconsin; MARZU, JEN - University Of Wisconsin; Havey, Michael

Submitted to: Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2021
Publication Date: 12/2/2021
Citation: Straley, E., Marzu, J., Havey, M.J. 2021. Genetic analyses and mapping of resistance to fusarium basal rot in onion. Journal of the American Society for Horticultural Science. 7,538. https://doi.org/10.3390/horticulturae7120538.
DOI: https://doi.org/10.3390/horticulturae7120538

Interpretive Summary: Fusarium basal rot (FBR) is a major soil-borne disease of onion for which genetic resistance is the most effective method of control. The objectives of this study were to identify sources of FBR resistance, assess the efficacy of selection to increase levels of FBR resistance, and develop segregating families for genetic mapping of FBR resistance. Onion accessions were evaluated for FBR resistance and percent survival ranged from 0 to 78%. Survivors from accessions showing FBR resistance were intercrossed, progenies were evaluated for FBR resistance, and one cycle of selection increased seedling survival by 18 to 52%. Selections were crossed to male-sterile lines and hybrids showed different levels of FBR resistance, an indication of specific combining ability. Segregating families were produced from the cross of FBR-resistant W440 with susceptible B5351, and survival evaluated using the seedling screen. Initial mapping of single nucleotide polymorphisms (SNPs) using a small segregating family revealed putative quantitative trait loci (QTL) on chromosomes 2 and 4 significantly associated with FBR resistance. The QTL on chromosome 2 showed codominance for FBR resistance, and the QTL on chromosome 4 showed dominance for FBR resistance. A second QTL on chromosome 4 from W440 decreased FBR resistance. Plants from families with different genotypes across the 1.5 logarithm of odds (LOD) regions on chromosomes 2 and 4 were self-pollinated and progenies evaluated for survival using the seedling screen. The genomic region on chromosome 2 was validated and segregated as a codominant resistance. The region on chromosome 4 initially associated with Fusarium resistance was significant at P < 0.10 and showed dominance for resistance. The region on chromosome 4 associated with decreased resistance was validated with these additional families and the heterozygous genotype significantly reduced resistance to FBR. These results are in agreement with previous studies reporting relatively high heritabilities and specific combining ability for FBR resistance, and will be of interest to onion breeders for the development of FBR-resistant onion cultivars.

Technical Abstract: Fusarium basal rot (FBR) is a major soil-borne disease of onion (Allium cepa) for which genetic resistance is the most effective method of control. The objectives of this study were to identify sources of FBR resistance, assess the efficacy of selection to increase levels of FBR resistance, and develop segregating families to map FBR resistance. Onion accessions were evaluated for FBR resistance using a seedling screen in a controlled environment, and percent survival ranged from 0 to 78%. Survivors from accessions showing FBR resistance were intercrossed, progenies were evaluated for FBR resistance, and one cycle of selection increased seedling survival by 18 to 52%. Selections were crossed to male-sterile lines and hybrids showed different levels of FBR resistance, an indication of specific combining ability. Segregating families were produced from the cross of FBR-resistant W440 with susceptible B5351, and survival evaluated using the seedling screen. Initial mapping of single nucleotide polymorphisms (SNPs) using a small segregating family revealed putative quantitative trait loci (QTL) on chromosomes 2 and 4 significantly associated with FBR resistance. The QTL on chromosome 2 showed codominance for FBR resistance, and the QTL on chromosome 4 showed dominance for FBR resistance. A second QTL on chromosome 4 from W440 decreased FBR resistance. Plants from families with different genotypes across the 1.5 logarithm of odds (LOD) regions on chromosomes 2 and 4 were self-pollinated and progenies evaluated for survival using the seedling screen. The genomic region on chromosome 2 was validated and segregated as a codominant resistance. The region on chromosome 4 initially associated with Fusarium resistance was significant at P < 0.10 and showed dominance for resistance. The region on chromosome 4 associated with decreased resistance was validated with these additional families and the heterozygous genotype significantly reduced resistance to FBR. These results are in agreement with previous studies reporting relatively high heritabilities and specific combining ability for FBR resistance, and should be useful for development of FBR-resistant onions.