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Temperature Effects on Megagametophytic Development in Meadowfoam

Dep. of Crop Sci., Oregon State Univ., Corvallis, OR 97331

^* Corresponding author.

Seed yield of meadowfoam (Limnanthes alba Benth.), an open-pollinated winter annual, is partially determined by the number of seeds per flower. Each flower has the potential for five seeds, but typically an average of two seeds per flower has been measured in the cultivar Mermaid. The causes of less-than-maximum seeds per flower are not known. Therefore, an investigation of the effects of temperature on the growth rates of the unfertilized ovule and embryo sac and on megagametophytic structure was conducted. Treatment effects at 0, 48, 96, and 144 h postanthesis (HPA) under the regimes of 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 rate (ESOWGR), embryo sac length, ovule length, and embryo sac/ovule length growth rate (ESOLGR) was significantly (P < 0.01) lower at 15/15 °C than at higher temperatures. Growth rate for embryo sac width, ESOWGR, and ESOLGR was significantly (P < 0.05) higher at 24/15 than at 33/15 °C. At anthesis, the number of flowers with four or five normal appearing megagametophytes was approximately the same in all temperature regimes. However, over time, with each warmer temperature regime there were 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. This temperature effect may explain some of the yearly variation in seed yield and suggest the need for timely pollinator management, especially during periods of rapid bloom when temperatures are typically above 24 °C.

Received for publication February 25, 1988.