1:00 pm - 2:00 pm
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Longfei Wu. This seminar is open to the general public to attend.
Thesis Topic: Mapping QTL associated with partial resistance to Aphanomyces and Fusarium root rot in field pea and evaluation of Aphanomyces euteiches resistance by bulked segregant RNA-seq
PhD with Drs. Stephen Strelkov and Sheau-Fang Hwang.
Seminar Abstract: Root rot, caused by Aphanomyces euteiches and Fusarium spp., is an important disease of field pea (Pisum sativum) that can be managed with polygenic resistance. An F8 recombinant inbred line (RIL) population derived from the cross ‘Reward’ × ‘00-2067’ was evaluated for reaction to A. euteiches under field and greenhouse conditions. Genotyping was conducted with a 13.2K single-nucleotide polymorphism (SNP) array and 222 simple sequence repeat markers. Significant genotypic effects and G×E interactions were detected in all experiments. Mapping of quantitative trait loci (QTL) identified 8 major-effect (R2 >20%), 13 moderate-effect (10%<R2<20%) and 6 minor-effect (R2<10%) QTL. A genomic region on chromosome 4 was most consistently responsible for partial resistance to A. euteiches.
To evaluate resistance to Fusarium spp., the cultivars ‘Reward’ and ‘00-02067’ were screened with Fusarium solani, F. avenaceum, F. acuminatum, F. proliferatum and F. graminearum under greenhouse conditions. Significant differences in root rot severity were found between the cultivars in response to F. avenaceum and F. graminearum, and these species were tested against the F8 RIL population. While no significant QTL were detected following inoculation with F. avenaceum, 5 QTL for root rot severity and 3 QTL each for vigor and plant height were identified for F. graminearum. The two most stable QTL for partial resistance to F. graminearum were located chromosome 4, coinciding with the region associated with partial resistance to A. euteiches. This region may be important for root rot resistance breeding and marker development.
Resistance to A. euteiches was evaluated further with another RIL population derived from the cross ‘Carman’ × ‘00-2067’. Strongly resistant (R) and susceptible (S) individuals were used to construct R and S bulks, respectively, for bulked segregant RNA-seq (BSR-seq) analysis. Approximately 4.3-5.1 GB read pairs were aligned to the pea reference genome and 44,757 genes were examined for expression level. Twenty-one differentially expressed candidate genes were identified, with 52.3 K SNPs detected between the R and S bulks. Eighty-five of the variants were located in 12 candidate genes. The identification of novel genes associated with partial resistance to A. euteiches may facilitate efforts to improve management of this pathogen.