Bohn, G. N.
Several U.S.D.A. tomato breeding lines usually set fruits 3 to 4 weeks earlier than commercial varieties during cool, humid, spring weather near La Jolla, California. An experiment was designed to determine whether an early line differs from a late variety in its ability to shed pollen or in the ability of its pollen tubes to grow during cool, moist weather.
On May 9, 1954 six flowers of early #1159 (Powers 34-7) and late #1164 (Pearson) were self-pollinated with a penknife, six were tagged but otherwise not disturbed, and six were cross-pollinated with pollen from the other line. Flowers on other plants were not disturbed at all.
Flowers of #1159 selfed, tagged, or left undisturbed set seeded fruits readily during the period from May 9 to May 16. The 6 emasculated flowers of #1164 that were treated with pollen from #1159 also set seeded fruits that grew at a normal rate. These data establish the ability of #1159 flowers to shed pollen and the ability of #1159 gametophytes to grow during this period. They establish, further, the ability of #1164 flowers to set seeded fruits if provided with pollen with the ability to grow under those conditions.
Flowers of #1164 that were selfed, tagged, or left undisturbed failed to set fruits during the period from May 9 to May 16. Emasculated flowers of #1159 treated with pollen from #1164 also failed to set fruits. The data, plus the observation that the flowers were shedding pollen during this period, establish the inability of the #1164 gametophytes to grow during that period. Similar, but less decisive results were obtained from pollinations made on May 30 and June 6 when temperatures were slightly higher, and after the plants had been attacked by psyllids.
The daily maximum temperature ranged from 63.5 deg. F to 66.5 deg. F in an instrument shelter 4 feet above ground some distance from the experimental field during the period from May 9 to May 16. The daily minimum ranged from 54 deg. F to 59 deg. F. Those records suggest that the critical temperature differentiating pollen germination, tube growth, and/or fertilization in the two tomato lines occurs between 55 deg. F and 65 deg. F.