Segregation for pear-shaped fruit in a round by oval cross.

Warnock, S. J.

The recessive gene, constricting corolla (cc) mediates in the presence of o to produce pear-shaped fruit in tomato (Warnock 1990). Heterozygosity at either locus, when the alternate locus is homozygous recessive, results in a 3:1 segregation producing in the one case 3 round to 1 pear-shaped fruit, and in the other 3 oval to 1 pear-shaped fruit. Segregation in the former case is at the o locus and in the later case for alleles at the cc locus. The segregates with pear-shaped fruit in either instance have the same genetic constitution for pearing. Early workers (Hedrick and Booth, 1907; MacArthur, 1926; Lindstrom, 1926, 1927) failed to distinguish between these two segregating sets which resulted in considerable confusion concerning genetics of pear-shaped fruit. Because two loci are concerned, theoretically transgressive segregation for fruit shape should occur if appropriate parents entered the cross. A round type fruit with constricting corolla (cc/+) crossed with an oval type (+/o) should segregate 12 round, 3 oval and 1 pear type. Such segregation has not been reported in the literature. Evaluation of segregation following such a cross was therefore of interest. The cross CX8011 true breeding round x 'Yellow Plum' was made for this study in the greenhouse in the spring of 1989. The CX8011 round line is a mutant type that arose in CX8011 pear line and differed phenotypically from CX8011 pear in the fruit length characteristic only. This line was assumed to have the cc characteristic. This was subsequently substantiated by this investigation. F1 seed was increased in the field in the winter of 1989/90 in Mexico. and the resultant F2 seed was planted in Davis in the summer of 1990. A total of 244 F2 plants were examined and of these, 162 were round, 64 were oval and 18 were pear-shaped. Actual values were tested for goodness of fit against a 12:3:1 ratio for round-oval-pear (X^2 = 10.05, P= <0.01). Because of an excess of oval types there was a poor fit to the 12:3:1 ratio. However, pear types did occur as hypothesized and the frequency of non-pears to pears fit expectations (15:1). The X^2 for the 15:1 ratio was 0.64, P = 0.70-0.80.


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Lindstrom, E. W. 1926. Linked inheritance in tomatoes. Iowa State Coll. 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.

MacArthur, J. W. 1926. Linkage studies with the tomato. Genetics 11:387-405.

Warnock, S. J. 1990. Inheritance of pear-shaped fruit in tomato. Report of the Tom. Genet. Coop. 40:38-40.