Browsing by Author "Ham, Hannel"

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    Investigating pollination success between Pinus radiata and selected pine species
    (Stellenbosch : Stellenbosch University, 2018-03) Ham, Hannel; Du Toit, Ben; Kanzler, Arnulf; Botha-Oberholster, Anna-Maria; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Pinus radiata is not only an important commercial plantation species in the Southern Hemisphere, but it is highly susceptible to Fusarium circinatum. Interspecific hybridisation attempts between P. radiata and some pine species is an ongoing process to improve F. circinatum tolerance. To date, limited pollination success between P. radiata and some pine species (P. tecunumanii, P. oocarpa, P. pringlei and P. patula) might be a result of biological or reproductive barriers that limit gene flow between species. Seven Pinus species (P. tecunumanii, P. oocarpa, P. pringlei, P. maximinoi, P. elliottii, P. taeda and P. patula) and one interspecific hybrid (P. patula×tecunumanii) with F. circinatum tolerance were selected as possible hybridisation partners for P. radiata. Previous studies indicated that the eight pure pine species are grouped in three distinctly different subsections with no difference in the karyotype. A generic Pinus cross-pollination protocol was developed and tested. Pollination success was evaluated with pathology diagnostic tests and DNA fingerprinting. Not only did the pathology tests indicate that all the screened seedlings were indeed infected and susceptible to F. circinatum (as would be expected from P. radiata pure species seedlings), but DNA fingerprinting assigned seedlings to the P. radiata population. Low pollen germination and pollen contamination from external sources might have contributed to the limited pollination success. However, Computed Tomography (CT) scans were successfully conducted to determine seed set of intact cones at 104 weeks after pollination. The generic protocol was adapted (green woven cloth bags to be replaced regularly, seal openings created by bulb applicators daily, sterilise breeding equipment, needles and female strobili before bagging and pollination events) and tested to determine whether pollination success could be improved. Studies on the climatic conditions inside (micro) and outside (macro) the pollination bags indicated that placement of the bags in the top northern side of P. radiata trees at the Karatara seed orchard, might increase temperatures closer to Sabie temperatures where the eight pine taxa (eight pure species and one hybrid) yield viable seed. Temperature fluctuations between day and night time are more severe at Karatara than Sabie and might be a constraint to pollination success. Three circadian models were developed to simulate climatic conditions at Karatara (micro and macro) and Sabie (average between Tweefontein, Witklip and Spitskop seed orchards). Biplots (discriminant analysis and principal component analysis), resembling the natural provenance climate data, grouped P. elliottii, P. taeda and P. radiata with Karatara, indicating good site species matching. When altitude was ignored as a vector, P. patula was grouped with the trio as well. In vivo pollination success between P. radiata, P. tecunumanii, P. oocarpa and P. maximinoi were determined by counting the number of visible ovules, pollen grains inside the ovules, pollen grains outside the ovules and pollen tubes. Data was collected with a standard fixation-dehydration-embedding histology sequence over the seven-week period, indicating that P. radiata×oocarpa, P. radiata×tecunumanii and P. radiata×maximinoi, differed significantly from P. radiata×radiata for all four factors investigated. The paraffin wax method was not suitable to study conelets older than eight weeks. MicroCT scans were used to confirm if fertilisation occurred between 15 to 16 months after pollination. Seed were visible from week 68 after pollination and viability of seed could be determined with quantitative porosity and defect analyses. Pearson correlation with biplots between natural provenance data (altitude, precipitation and temperature), PTGR (length and width) and hydrated pollen grain size (length and width) at micro- and macrotemperature regimes for the eight pure species, identified three distinct climatic response groups. These are (1) P. oocarpa and P. tecunumanii; (2) P. maximinoi and P. patula; and (3) P. elliottii and P. taeda. Although P. pringlei and P. radiata were not included in the three distinct climatic response groups, P. pringlei grouped with P. patula because of altitude, while P. radiata grouped with P. elliottii and P. taeda due to precipitation and minimum temperature. Data collected at Karatara during this study, correlated with previous studies indicating that P. radiata is better adapted to drier summers and wetter winters than the more tropical species. Therefore, pollination success at Karatara is not likely to be constrained by site factors, but if the pollen partner is not comparable with the temperature regimes at Karatara, it might result in limited pollination success. Therefore, data collected indicated that P. elliottii and P. taeda might be potential hybridisation partners for P. radiata. During this study valuable information was collected in terms of pollen grain size, PTGR, climatic data, three circadian models, in vivo pollination success and microCT scans. As this study focused on climate and pollen aspects, future studies need to concentrate on the female strobili, such as the hormonal and/or chemical interaction and whether ovule abortions are affecting pollination success.