Effect of Temperature on Pollen‐Tube Growth in Trifolium repense after Cross‐ and Self‐Pollinations1

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Abstract
The effect of temperature on pollen‐tube growth in a self‐incompatible clone of white clover (Trifolium repens L.) was studied under controlled environment‐chamber conditions of 15, 25, and 35 C. After cross‐pollinations, the overall growth rate increased with each increase in temperature, but the effect on early stages of growth was more prominent. After self‐pollinations, the incompatible pollen tubes temporarily made steady growth comparable to the growth of the compatible pollen tubes, and then their growth was arrested. At 15 C, the arrest occurred in the upper and middle parts of the style; no pollen tubes penetrated into the ovary. At 25 C, the arrest occurred in the lower part of the style and the upper part of the ovary; no pollen tubes entered the ovule. At 35 C, cessation of tube growth was less common, and a large proportion of the ovules were fertilized. These observations indicate that at low and intermediate temperatures, self‐incompatibility in T. repens is caused by abnormal growth of the pollen tubes. High temperature enhances pollen‐tube growth and thus tends to break down or circumvent the incompatibility mechanism.

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