Temperature effects on postanthesis floral phenology and megagametophytic development in meadowfoam Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cz30px07k

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  • Meadowfoam (Limnanthes alba Benth.), an open-pollinated herbaceous winter annual, is adapted to Mediterranean climates and produces a seed oil with industrial uses. Seed yield in meadowfoam is partially determined by the number of seeds produced per flower. The flower is protandrous with the stigmata becoming receptive 1-3 days after anther dehiscence, depending on temperature. Each flower has the potential of producing 5 seeds, but an average of 2 seeds per flower is typical on a field basis. The causes of less-than-maximum seed set are not known. Preliminary growth chamber work showed that temperature had an effect on the average number of seeds per flower produced at different postanthesis pollination times. Review of the literature showed that temperature affected embryo sac viability and subsequent seed set. Therefore, an investigation of the effects of temperature on postanthesis floral phenology and development of the unfertilized ovule and embryo sac and on megagametophytic structure was conducted. Treatment effects at 0, 48, 96, and 144 hours postanthesis (HPA) under three growth chamber temperature regimes (15/15, 24/15, and 33/15°C alternating day/night) were measured. Growth rate for embryo 'sac width, ovule width, embryo sac/ovule width growth ratio (ESOWGR), embryo sac length, ovule length, embryo sac/ovule growth ratio (ESOLGR) was significantly lower at 15/15°C than at higher temperatures. Growth rate for embryo sac width, ESOWGR, and ESOLGR was significantly higher at 24/15 than at 33/15°C. At anthesis the percent of viable appearing megagametophytes was not significantly different between the temperature regimes, but a significant decrease was seen at 48 HPA in the 33/15°C temperature regime and at 96 HPA in the 24/15°C regime, while the decline in viable appearing megagametophytes was gradual over time in the 15/15°C regime. At anthesis, the number of flowers with four and five normal appearing megagametophytes was approximately the same in all temperature regimes. However, in the warmer temperature regimes over time, increasing numbers of abnormal embryo sacs, wherein the egg apparatus pulled away from the micropyle resulting in the megagametophyte appearing to float within the embryo sac were seen. At anthesis no visible temperature effect was observed in the floral phenological development. At 2 days postanthesis, in both the 24/15 and 33/15°C regimes there was a rapid progression of anther and stigmatal development with a subsequent increase in embryo sac growth, whereas in the 15/15°C regime there was little change. The large amount of plant-to-plant variability in frequencies of viable appearing megagametophytes indicates the possibility of selection for lines with inherently higher degree of viability than those currently available. This temperature effect may explain some of the yearly variation in seed yield and suggests the need for timely pollinator management, especially during periods of intense bloom when temperatures are typically above 24°C and the duration of megagametophyte viability is decreased.
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