Date of Award
Master of Science (MS)
Plant and Environmental Science
Dr. Jeffrey W. Adelberg
Dr. William C. Bridges, Jr.
Dr. Ksenija Gasic
Dr. Christopher A. Saski
Prunus is a genus widely cultivated to produce edible fruit including almond (P. amygdalus), peach (P. persica (L.) Batsch), cherries (P. avium and P. cerasus), among others. The cultivation of Prunus is economically important for several regions of the United States and relies on appropriate cultivars and rootstocks that are adapted to a growing region. Encroaching plant pathogens are forcing breeders to use sexually compatible germplasm from related species for introgression of novel alleles that confer tolerance or resistance. This is especially true in the rootstock breeding where interspecific hybridization is often used to address abiotic and biotic stresses in soil. Interspecific hybrids are often sexually sterile and require vegetative propagation. The use of aseptic micropropagation enables rapid, large-scale multiplication of novel germplasm. However, Prunus micropropagation methods are highly genotype specific and require inquiry into each variety. Therefore, this thesis presents the development of new techniques of in vitro rooting for the purpose of propagation as well as in vitro pathogen screenings clonal propagation. Four IBA treatments, a 4-day 15 µM IBA then a transfer to IBA-free medium, a 30 sec 1 mM IBA quick-dip with growth in an IBA-free medium, a 15 µM IBA continuous application, and an IBA-free treatment, in combination with four nutrient salt formulations, Murashige and Skoog (MS), half strength MS, Driver and Kuniyuki (DKW), and new Prunus medium (NPM), eight Prunus genotypes were screened for in vitro responses as well as post-acclimatization responses to determine treatment combinations to maximize quality. The development of propagation techniques first utilized the conventional semi-solid agar, and secondly utilized an aerated phenolic foam matrix. Agar is broadly used in micropropagation and was used to develop methods of rooting suited for commercial propagation. However, aberrant root structure has been observed when roots developed in agar which may create problems with acclimatization. Alternatively, root anatomy in plants grown in the foam matrix have been observed to resemble field-grown plants making this medium a better choice for live co-coculture challenges with plant pathogens in order to closely mimic field conditions. With rooting on agar medium, the application of IBA promoted rooting and enabled 100% survival post-acclimatization in seven of eight genotypes when plants were treated with the best nutrient-IBA treatment combination. Prolonged exposures to IBA had deleterious effects on plant quality and subsequent plant growth. A 4-day 15 µM IBA induction followed by subculturing to IBA-free medium has been documented to work well but is costly due to two media and the additional transfer required. As an alternative, a 30 sec quick-dip that was conducted at the time of transfer and identified as an alternative rooting method in some genotypes screened. Plants that had larger root systems in agar produced larger plants in the greenhouse and callus accumulation did not impact subsequent growth. Rooting in Oasis® was largely genotype specific and success was driven with the application of IBA improving rooting in all genotypes with the exception of peach-plum hybrid ‘MP-29’. All ‘Guardian®’ peach seedling clones performed poorly in Oasis® despite an attempt to find a superior seedling. However, ‘GF-305’, the other peach genotype screened in these works, did exceptionally well rooting in Oasis®. In both matrices, in vitro plant quality positively correlated with plant quality after acclimatization. The combination of these two studies serves as foundational information propagation of novel interspecific Prunus genotypes.
Lawson, John, "In Vitro Rooting Techniques In Prunus Spp. for Propagation And Disease Screening for Armillaria Root Rot (ARR) Resistance" (2022). All Theses. 3932.