Daubeny, Hugh A.
A previous report by Hornby and Daubeny (TGC 6) indicated genetic differences between the varieties Puck and Bonny Best in production of viable pollen, germination of pollen, and fertilization at relatively low temperatures. Studies carried out by the junior author gave further information on the production of viable pollen, pollen germination, and, in addition, stylar elongation of flowers on varieties grown at relatively low temperatures in the field and in the greenhouse at Cornell University, Ithaca, New York. The purpose of obtaining this information was to attempt, to elucidate the morphological mechanisms which might be involved in differential fruit set of tomato varieties at sub-optimum temperatures for the process.
Under greenhouse conditions of 50 deg. F. at night and 60 deg. F. during the day and low light intensities, Puck flowers produced approximately 20% viable pollen which was greater than the percentage produced by flowers of Bonny Best, Valiant, Red Cloud, Fireball, Valnorth, or Rutgers. The data suggest that, under the greenhouse conditions described, lack of viable pollen might be an important factor limiting fruit set. These varieties growing under field conditions, when night temperatures were lower than 55 deg. F. and light intensities were high, all produced consistently high amounts of viable pollen, between 68% and 88% per flower. The same was true of the F1 progenies of various varieties crossed with Puck. It was concluded that viable pollen was not a factor limiting fruit set when night temperatures were relatively low in the field.
Fruit and seed set and pollen germination studies were done under the cool temperature greenhouse conditions. Because of the low amount of viable pollen produced sander these conditions it was necessary to use pollen produced at a warmer temperature. It was confirmed that Puck pollen germinated better at the low temperature than pollen of Bonny Best. Puck pollen tended to increase seed set. Puck, and to a lesser extent, Earliana, used as female parents were not as sensitive to the lower temperatures as John Baer and the Cornell breeding line 54-179 used as female parents.
In 1957 and 1958 data on stylar elongation of flowers on field grown plants were obtained. In both years, the varieties John Baer and Earliana and the F1 progenies involving these varieties crossed with Puck produced considerably more early flowers with elongated styles than the other varieties studied. The percentage of flowers setting fruit for John Baer and Earliana was very low and this was partly correlated with elongation of the styles. Due to the fact that many flowers of these two varieties and of the other varieties studied did not show elongation and still failed to set fruit was concluded that this was not the only factor involved in the failure to set fruit at low temperatures.
In conclusion, the data pertaining to failure of varieties and progenies to set fruit under low temperature conditions suggested that more than one morphological phenomenon is involved.