F.S. Howlett
The fruit setting aspect of tomato production is a subject of perennial importance and increasingly concerns both research specialists and the moreinformed producers. Over the last three decades, reports of experimental work have presented much valuable information upon which our present concepts are based. In analyzing the nature of the more recent publications one might conclude that the results present nothing spectacularly new but rather supplement and extend the basic concepts. No one questions the underlying requirement of functional gametes and their union to form a developing embryo and endosperm. However, at this time the effect of various environmental complexes and treatments upon flower development seems to be of major significance.

Only a few illustrations need be cited to indicate the nature of recent research. The pronounced effects of added carbon dioxide upon fruit set in the earliest developed clusters on tomato plants growing under relatively low light conditions has stimulated some interesting questions. The reported effect of increasing fruit weight under such conditions must also be considered in relation to the fruit setting process. Recent work designed to ascertain the most effective day air temperature range correlated with prevailing light intensity also must be considered in this connection. In addition, the fact that an adequate supply of reserve carbohydrates is necessary for the enlargement of floral initials to the point of anthesis must be kept in mind in considering the chemical basis for maximum fruit setting. Research designed to measure the effect on fruit set of artificial illumination as a supplement to daylight is also pertinent to the problem. Recent studies designed to measure the effectiveness of electric pollination equipment such as so-called buzzers indicate the extent to which maximum pollen transference seems to be of outstanding concern.

Finally the current improvement in disease resistant varieties emphasizes the necessity of considering the facility of pollen transference in these newly constituted strains and hybrids. Prior to a brief discussion of several environmental factors upon tomato fruit setting the writer wishes to indicate the significance of the various stages in the fruit setting process in a species such as the tomato in which so-called bud drop may occur prior to anthesis. In certain species the flowers will reach anthesis regardless of unfavourable environmental conditions. But in the tomato, while floral initials even though minute are formed under practically all conditions, the size they attain prior to cessation of growth is more or less negatively correlated with the magnitude of the influence of certain environmental factors. Actually the number of flowers within a given cluster or truss, which attain even half size, may vary greatly. A similar situation occurs with respect to attainment of the anthesis stage. Obviously the attainment of anthesis is not necessarily associated with pollen viability or functionalibility of the gametes. Flower structure at anthesis may not be conducive to rapid and massive pollen transference to the stigma and by no means can pollen tube growth be assumed to be satisfactory or fertilization take place with even a reasonable proportion of female gametes. But at this point, it seems pertinent to point out that while perceptible enlargement of the ovary signifies that "a fruit has set", the nature and extent of immediate development thereafter is actually "part and parcel" of the fruit setting process. The proportion of female gametes fertilized, their precise location in the developing fruit has a profound effect upon fruit size and the contents of the locules. With few gametes fertilized and consequently few seeds starting to develop the fruits may be small and lacking in gelatinous pulp in one or several locules.

DOI: 10.17660/ActaHortic.1966.4.10

Acta Horticulturae