Browsing by Author "Flay, Casey Damian"
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- ItemMolecular breeding for resistance to biotic threats in kiwifruit (Actinidia chinensis) : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, Manawatu, New Zealand(Massey University, 2023-12-08) Flay, Casey DamianThis thesis takes a genomic approach to assist kiwifruit breeding programs by identifying genomic loci that contribute to resistance to biotic threats. Three different biotic threats were investigated that represent some of the most destructive to the kiwifruit industry. These were made up of two pests including latania scale (Hemiberlesia lataniae) and Brown headed leafroller (Ctenopseustis obliquana) and the pathogen Psa (Pseudomonas syringae pv. actinidiae). Together these pests and pathogen represent the predominant feeding mechanisms of, sucking from H. lataniae, chewing from C. obliquana, and infection from the necrotrophic pathogen Psa. The inclusion of these pests and pathogen was thought to provide a well-rounded knowledge of the molecular mechanisms that influence both monogenic and polygenic resistance traits in kiwifruit. Moreover, because these experiments were conducted on multiple kiwifruit families at different sites over time with multiple interactions occurring between organisms, an appreciation was gained for the sources of error that affect experiments, and the effects of those errors on the interpretation of the resulting genomic data. The projects that make up this thesis first analyse kiwifruit (Actinidia chinensis var. chinensis) families of different sizes to identify the molecular architecture for resistance to H. lataniae. Once the monogenic region for resistance to H. lataniae was identified, existing datasets were interrogated for individuals with the loci associated with resistance. Furthermore, due to an absence of H. lataniae resistance in the elite tetraploid gold fleshed A. chinensis var. chinensis breeding program, a diploid individual resistant to H. lataniae that produced unreduced gametes was crossed with tetraploid males and screened for tetraploid individuals that contained markers for H. lataniae resistance. Unfortunately, the experiments investigating the molecular architecture for resistance of A. chinensis var. chinensis to C. obliquana using genotyping by sequencing (GBS) data was unsuccessful due to multiple factors discussed in chapter 4. The last project broke away from the traditional association mapping approach to identify quantitative trait loci (QTL) for Psa resistance from several A. chinensis families that had lost individuals due to Psa. This fast, inexpensive, and powerful approach used a modified bulked segregant analysis (BSA) with bulking methods similar to that of selection mapping. The methodology was validated using pools created with a variable number of males and the sensitivity of detection determined by identifying QTL at the known sex locus. The full experiment then analysed whole genome sequence (WGS) data from eight pools containing multiple families to identify QTL associated with survival to Psa. Together these experiments will advance the kiwifruit breeding program by providing the molecular architecture for two of the most prevalent biotic threats affecting kiwifruit production. Utilising the markers for resistance to H. lataniae and developing markers to target the QTL for resistance to Psa will enable breeding programs to use these markers as selection criteria in commercial breeding programs, increasing the rate at which cultivars resistant to these biotic threats can be developed.
- ItemMultiple mating and mate choice in Sitophilus oryzae (L.) (Coleoptera : Curculionidae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Protection (Entomology) at Massey University, Palmerston North, New Zealand(Massey University, 2010) Flay, Casey DamianThe rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) is a major pest of stored grains throughout the world. A recent study found a reduction in fecundity and fertility in females that are exposed to multiple males. However, the mechanism behind this is unknown. In the first experiment we examined female S. oryzae fitness decline and behaviour in response to male density (i.e. 1, 5 and 10 males) maintained with a single female. Results show that female fecundity and longevity significantly decreased with increased male density (P < 0.01). However there was no significant effect of male density on fertility. Mating time significantly increased with male density (P < 0.01) but feeding and foraging time decreased from male density 1 to male density 5 and 10 (P < 0.03). The decrease in fecundity under high male density is proposed to be caused by increased damage by male reproductive organs. The second experiment examined precopulatory sexual selection in S. oryzae. Results show that both sexes select for large genitals. In addition males select for the number of mature eggs in females. These traits may directly affect the reproductive fitness of these insects. In the final experiment we examined how multiple mating affected female reproductive fitness in the laboratory. Results indicate that over sixty days females permanently paired with males, mated twice with different males and four times with the same males did not suffer from significant fertility decline while females mated once, twice with the same males and four times with different males had significant fertility declines. It is suggested that mating once or twice with the same males is not enough for females to maximise their reproductive fitness. The significant fertility decline in females that mated with four different males may be caused by reproductive organ damage or other factors which decreases their fertility due to excessive polyandry.