Several investigators have pointed out the variability of fruit shape on the same plant without elucidating the cause (Butler, 1952; Lindstrom, 1926, 1927; Yeager, 1937). During our recent investigation on genetics of pear-shape (Warnock 1990) observations on the variable expression of pear shape were made and suggested causes have been presented here.
Two single plant selections were made in a 'Yellow Pear' planting, one a type in which fruits were more constricted than those of the parent (Selection A), and the second a type in which fruits were less constricted than those of the parent (Selection B). These two selections were progeny tested at Davis and the distinctions on which selection was made held. It was noted that the two selections varied in fruit size from the parental material on progeny testing. Based on a random sample of 100 fruit, Selection A had the smallest fruit (4.1 gr/fruit), followed by the parental line (6.9 gr/fruit), with Selection B having the largest fruit, (17.2 gr/fruit). Pearing was more pronounced in the selection with reduced fruit size and less pronounced in the large fruited selection than in the check. Some fruits of the small-fruited selection were unable to shed the corolla and corollas were retained to maturity. This information suggested that smaller oval fruits are more strongly constricted by cc than are larger oval fruits.
Additionally, in several instances over several years it has been noted that elongated or oval fruits of machine harvest varieties during high temperatures and depleted field moisture conditions tended to be pear-shaped. It was apparent that this pear shaping was due to the corolla constricting the fruit even though cc was not present. It is hypothesized that the corolla becomes more fibrous under these conditions and is shed with greater difficulty. If true, fruit size and moisture-temperature relationships work in conjunction to account for much of the variability of pear-shaped fruits on the same plant. For example, first set fruits are frequently larger and are usually set under cooler, moister conditions. They would have less constriction because of larger size and lower tensile strength of the corolla while fruit set later during usually warmer, drier conditions would tend to be more strongly constricted both because fruit is smaller and tensile strength of corolla is greater. Hence, there could be a range of intensity in pear-shaped fruit on the same plant for these reasons.
Literature Cited:
Butler, L. 1952. The linkage map of the tomato. Jour. Hered. 43:25-35.
Lindstrom, E. W. 1926. Linked inheritance in tomatoes. Iowa State Col. Jour. Sci. 1:3-13.
Lindstrom, E. W. 1927. The inheritance of ovate and related shaped of tomato fruit. Jour. Agr. Res. 34:961-985.
Warnock, S. J. 1990. The nature and inheritance of pear-shaped fruit in tomato. Report of the Tom. Genet. Coop. 40:38-40.
Yeager, A. E. 1937. Studies on the inheritance and development of fruit size and shape in the tomato. Jour. Ag. Res. 55:141-152.