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New Mexico State University (2017)

Classical and molecular investigations in breeding for fertility restoration and disease resistance in Capsicum annum

Barchenger, Derek W.,

Titre : Classical and molecular investigations in breeding for fertility restoration and disease resistance in Capsicum annum

Auteur : Barchenger, Derek W.,

Université de soutenance : New Mexico State University

Grade : Doctor of Philosophy (PhD) Plant and Environmental Sciences, 2017

Capsicum sp. (chile pepper) is an increasingly important crop because of its use as a vegetable, spice, colorant, and medicinal value. Some of the most significant problems facing chile pepper producers and researchers include pure seed production, disease resistance, and hybrid cultivar development. We conducted three experiments to address these concerns and provide a basis for future work in these areas. Although a caging system is widely adopted for breeder seed production, it requires laborious and time consuming hand-removal of open flowers and fruit prior to caging to ensure genetically pure seed. The use of 2000 ppm ethephon was found to reduce the number of flower buds, open flowers, and fruits on diverse chile pepper germplasm, while not influencing end of season growth index, mature fruit number, or seed number. The effect of ethephon was genotype specific and was strongly influenced by the environment. One of the most devastating pathogens to chile pepper production worldwide is Phytophthora capsici (Leon.). In order to develop an anticipatory breeding program, 18 New Mexico Recombinant Inbred Lines were used as a host differential to characterize the races in Taiwan, where 24 new races were identified, and virulence was observed to be geographically specific, with more virulent races on the west coast and less virulent races on the east coast. Through targeted sequencing of 63 unique SNP sites, the isolates in Taiwan were found to reproduce primarily asexually, have varying ploidy level, and have a relatively narrow genetic base. Virulence of P. capsici might be associated with genetic recombination, and the pathogen might become triploid when sexual reproduction is not possible as a means to increase virulence factors. This universal host differential allows scientists to collaborate on a global scale as well as on a local scale for gene deployment. For affordable and efficient hybrid cultivar development, cytoplasmic male sterility (CMS) and nucleus-controlled restorer-of-fertility (Rf) genes are required. Accurate molecular markers associated with CMS are widely used in chile pepper ; however, molecular markers associated with Rf are not widely applicable and the genetic mechanisms involved in Rf are still largely unknown. In other species, Rf genes have been found to encode pentatricopeptide repeats (PPR). Based on reported PPR domains in model organisms, 552 PPR domains were identified and mapped throughout the genome. Nearly 30% of these PPRs had high structural similarity to previously reported PPRs. Additionally, of these 13 candidate genes had high similarity to previously reported Rf genes. These candidate genes were diverse with no consistent gene sequence associated with a particular phenotype when characterized in 16 A-, B-, and C-lines. This genetic diversity could be a reason why no widely applicable markers have been found for Rf in chile pepper. The candidate genes identified here provide targets for plant breeders to develop program specific molecular markers for Rf. Overall, this work provides insights into some important questions in chile pepper breeding and genetics, but also offers a basis for future work not only in chile pepper, but also other crops.

Présentation (NMSU Library)

Page publiée le 14 octobre 2018