UBC Theses and Dissertations
Some factors affecting pollen viability in a tomato breeding program. Charles, Winston Benson
In the tomato-growing areas in southern Canada, it is desirable to have commercial varieties having the character of being able to set fruit at relatively cool temperatures. Puck a non-commercial variety sets fruit at temperatures between 55° and 65°F. Experiments attempting to identify the mechanism of the desirable character of Puck in terms of pollen viability were done. The tomato varieties, Puck, Bonny Best, Earliana 498, and their reciprocal crosses, were grown both in the field and in greenhouses. Various factors affecting variability in pollen samples and pollen viability determinations, were studied. Experimental results indicated that a sample of pollen taken at anthesis consists of mature, immature, and empty grains. The relative proportions of the three classes of grains depended upon the method of collection used, the time of collection and the location of the pollen source on the plant. The greater the variability in the sample, the larger is the representative sample size required for microscopic examination at a chosen degree of tolerance. The staining technique gave the highest percentages of viable pollen. Low viability percentages were obtained in vitro, and these are attributed to bursting of some of the normal mature grains during pollen tube initiation. A quantitative in vivo procedure of counting pollen tubes by callose fluorescence under ultra violet light, was developed. Variations in the in vivo results can be ascribed to variation in the concentration of pollen growth factor (PGF) which appeared to vary with the number and density of grains used in pollinations. Results showed increased germination percentages when the number of grains used was increased. The most suitable number and density for maximum group effect has not been investigated. The variety Puck gave higher viability percentages than Bonny Best in most cases. Further investigations of the problem would require more precise control of environmental factors during pollen development, and exposure of pollen following anthesis.
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