Varietal differences in the susceptibility to pointed fruit malformation in tomatoes: histological studies of the ovaries

Differences were found among three tomato cultivars (cvs.) in their susceptibility to pointed-fruit malformation. Pointed fruits are characterized by a conical, rather than a round shape. This type of fruit malformation is often found in winter-grown plants and is due to an uneven development of the locules. Transverse cross-sections of the fruit revealed that one or more of the locules had not developed, forming a flattened side, while the other side of the fruit was round (normal) in shape, because of the presence of developed placenta(s), with seeds and jelly filling their cavity(ies). Histological examination of the ovaries showed that under high night temperatures all the locules, of all the examined cvs., were normal and contained placentas with attached ovules. Ovaries that developed under lower night temperatures contained deformed locules: in the less severe cases the placenta was retarded, with fewer attached ovules than normal; in the most severe ones the locules were severely deformed and the placentas and ovules were absent. The number of deformed ovules per fruit and the degree of deformation were cultivar- and night temperature-dependent. Artificial pollination of the affected ovaries and exogenous auxin application did not improve the fruit shape. It is, therefore, concluded that the absence of placentas, seeds and jelly from one or more locules brings about the formation of a malformed, pointed (lop-sided) fruit.