Date of Award

Winter 2020

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Thomas M. Davis

Second Advisor

Lise L. Mahoney

Third Advisor

Marta R. M. Lima

Abstract

THE DEVELOPMENT OF KNOWLEDGE AND RESOURCES RELEVANT TO THE GENETIC MANIPULATION OF DAY NEUTRAL FLOWERING HABIT IN STRAWBERRYBY

SAMIKSHYA RIJAL

University of New Hampshire, December 2020

Cultivated strawberry, Fragaria ×ananassa (Duch.) is an economically valued small fruit, well known for its nutritional benefits. For agricultural production, two types of strawberry cultivars are bred: Short Day (SD) varieties, which require specific day length to initiate flowering, and Day Neutral (DN) varieties, which are photoperiod insensitive. The DN trait confers continuous flowering and extended harvesting. Understanding the genetic determinants of this important trait in the octoploid/cultivated strawberry (2n = 8x = 56) is of interest to many researchers. Genetic manipulation by molecular breeding and bioinformatics, and genetic engineering are ways to study the molecular basis of this trait. The goal of the present study was to use these approaches, the former to reveal genetic regions and genes responsible for the DN trait in an octoploid strawberry, and the latter to manipulate the DN related genes in a strawberry genetic model system consisting of an ancestral diploid species, Fragaria iinumae, and an ancestral octoploid species, F. virginiana. A linkage map of F. virginiana was constructed based on the phenotypic segregation for the DN trait, and the genotypic segregation of array-based Single Nucleotide Polymorphism (SNP) markers. The backcross F1 (BCF1) progenies of two F. virginiana accessions were used for linkage mapping and marker-trait association study. SNP markers were genotyped on the Axiom IStraw90K Array, and then used for linkage mapping by JoinMap. As a prerequisite for the study of gene editing for the DN trait, in vitro systems including tissue regeneration were developed for F. virginiana progenies used in the study, and for diploid ancestor F. iinumae. In my study population of F. virginiana, four genetic loci were associated with the DN trait. One strong locus mapped in the linkage group (LG) 14 belongs to the same homoeology group, HGIV, as a previously identified QTL FaPFRU in cultivated strawberry. None of the identified QTL matched with the location of the flowering related gene discovered in F. vesca, SEASONAL FLOWERING LOCUS (SFL), which belongs to HGVI. The four mapped QTLs, homeo-QTLs (in LG2, LG3)/HGI, LG10/HGIII, and LG14/HGIV, and the predicted genes within can be used to reveal candidate genes. The in vitro system was established for successful aseptic seed germination, in vitro germplasm management, and tissue regeneration. Upon the analysis of candidate genes for the DN trait, gene editing can be implemented to confirm the functional relationship between the gene and the DN response. Also, editing the SFL gene in F. iinumae can be implemented to confer DN flowering in F. iinumae, to establish it as a second diploid model species for the genus Fragaria.

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