Graduate Thesis Or Dissertation

 

Natural outcrossing in spaced planted F₂ populations and solid seeded advanced generations of wheat (Triticum aestivum L. em Thell) Public Deposited

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  • This study was conducted to investigate the possible contamination of foreign pollen at different stages of a wheat breeding program. These included spaced planted F₂ segregating populations, replicated yield trials and seed multiplication. The experimental wheat materials consisted of four different F₂ populations, four cultivars and two experimental lines. Two genetic marker lines, Blue Hyslop and Blue Norco were used to determine the amount of possible outcrossing. The pollen of these marker lines carry genetic factors for blue aleurone color, thus the extent of outcrossing (wherever outcrossing had occurred in the experimental populations) could be immediately observed and determined during the same crop season. The mean percent outcrossing recorded was less than 1% in spaced planted F₂ populations, different replicated yield trials and seed multiplication conditions. The highest percentage of outcrossing of 5.6% was observed for a single plant in a spaced planted F₂ population. Under yield trial conditions, the highest percentage of outcrossing of 0.6% was recorded for the cultivar Hill 81 whereas the lowest value of 0.1% was recorded for experimental line SPN/AU/YMH. Under seed multiplication conditions, a sample taken at 0.5 m away from blue aleurone pollen source in low density planting had a mean outcrossing value of 0.5% for the cultivar Jackmar. Pollen load of marker lines relative to that of all entries in low seeding rate was high, consequently, the low seeding rate had higher levels of outcrossing than the high seeding rate. No significant effect on outcrossing was observed for Seeding rate x Entry interaction. However, effects of entry and sampling distance on outcrossing were significant. As sampling distance increased from the blue aleurone pollen source, the level of outcrossing decreased. Low positive correlation of 0.12 and 0.14 existed between outcrossing and plant height and tillers per linear meter respectively. Correlation of 0.70 was found between natural outcrossing and wind velocity. Results of this study suggest that outcrossing can occur in all stages of a breeding program. The results also indicate that an isolation distance of 2 m established for multiplication of registered and certified seed in the certification program of Oregon State University might not be adequate especially for such cuitivars as Jackmar and Hill 81. Furthermore, the level of outcrossing detected was high enough to distort and perhaps alter the genetic identity and integrity of the breeding material. A similar problem will exist if care is not exercised when growing valuable wheat germplasm in various collection centers.
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