Inheritance of pear-shaped fruit in tomato.

Warnock, S. J.

Hederick and Booth (1907) reported that pear-shaped fruit was due to a single recessive gene. Jones (1917) showed this gene linked to vine type (d locus). McArthur (1925) reported segregation and linkage results for pear-shaped similar to Hederick and Booth and proposed that the recessive gene be designated pr. Lindstrom (1926, 1927) conclusively demonstrated that the pr locus was identical to the locus that conditioned ovate fruit shape and suggested since this gene conditioned the ellipsoidal features of shape that the recessive condition should be designated oval (o) rather than pr. McArthur (1931) accepted this interpretation. The pr symbol was subsequently used by Butler (1954) to designate propeller and is so used at the present time (Gene Stock List, Rept. Tomato Genet. Cooperative 37, 1987). The interpretation by Lindstrom (1927) has been carried down in the literature to the present day (Stevens and Rick, 1986). This interpretation, however, has left unresolved the genetics of pear-shaped fruit in tomato. Yeager (1937) showed that pear-shaped fruit was due to the constriction of oval fruits by the corolla.

In the present investigation the corolla was removed from the two pear varieties, Yellow Pear and Roma, prior to hybridization to confirm the findings of Yeager (1937). In each case the early removal of the corollas changed the form of the fruit to a more oval condition. The 2 pear-shaped varieties, further, were reciprocally crossed to demonstrate that there was no difference in their genetics (Table 1). One unexplained oval fruit occurred in the Yellow Pear x Roma cross. In crosses of oval by pear-shaped cultivars, segregation for pear shape occurred in a 3:1 ratio oval: pear. Segregating plants classed in progeny tests in the F3 generation also segregated 3:1 oval: pear (Table 2). It was concluded that pear-shaped fruit is produced by a single recessive gene. This is a new gene which apparently apportions greater tensile strength to the corolla. When present in the homozygous recessive condition in conjunction with homozygous o, fruits are constricted in very early stages of development producing pear-shaped fruit. Based on work by Yeager (1937) and on the present work it is proposed that this new gene be called constricting corolla (cc).

Evaluation of digenic segregation for flesh color (r locus) and corolla character suggested a weak linkage for these 2 characteristics. Three of 4 segregating populations studied appeared to sort independently (Table 3); a fourth, Roma x Yellow Plum F2 had a low probability of fit to 9:3:3:1 ratio with an excess of parental types. Pooling of the 4 sets also suggested an excess of parental types. The sets were tested and found homogeneous (X^2 = 4.00, P = .20 - .30). The pooled data were subsequently classed into non-parental and parental types and tested against a 10:6 ratio which resulted in a poor fit for independent assortment (X^2 = 8.08, P =.01). The recombination value for this data was .41 +/- .03.

Table 1. Monogenic segregation in the F2 for oval-pear

                           F2 Segregation  Ratio  X^2     P 
    Hybrid                  Oval*   Pear  tested        Value 
Yellow Plum x Roma           80     21     3:1   0.85  .30-.50
Roma x Yellow Plum          106     37     3:1   0.04  .80-.90
Yellow Plum x Yellow Pear   119     30     3:1   1.76  .10-.20
Yellow Pear x Yellow Plum   114     25     3:1   3.82  .05-.10
Yellow Pear x Roma            1     99      -      -      -
Roma x Yellow Pear            0     27      -      -      -
Table 2. Combined classification for oval-pear segregation in F3 families in progeny tests.

                No. Seg.   Plant      Ratio    X^2      P
   Hybrid       F3 Fam   Oval*  Pear  tested          Value    
Yel Pl x Roma     14     173     67     3:1   1.09   .20-.30
Roma x Yel Pl     24     273     99     3:1    .52   .30-.50
Yel Pl x Yel Pr   19     206     84     3:1   2.66   .10-.20
Yel Pr x Yel Pl   28     308    104     3:1    .01   .90-.95
Table 3. Digenic segregation for corolla character (cc) and flesh color (r) in the F2 and F3 generations for two oval by pear hybrids.

                    Red   Yel   Red   Yel   Ratio    X^2    P
Parents       Gen  oval*  oval  pear  pear  tested         Value 
Yel Pl x Roma  F2    52    28    16    5    9:3:3:1  5.34  .10-.20
Roma x Yel Pl  F2    73    30    37    3    9:3:3:1  8.63  .02-.05
Yel Pl x Roma  F3    69    34    27    8    9:3:3:1  3.44  .30-.50
Roma x Yel Pl  F3   125    47    44   13    9:3:3:1   .59  .80-.90
Total               319   139   124   29    9:3:3:1  9.51  .02-.05
*All parents are homozygous for the oval (o) gene. These homozygous o fruits are oval in the presence of the dominant allele and pear-shaped in the presence of the recessive allele of the new gene. Hence, fruit phenotype was used to class the alleles of the new gene.

Literature cited:

Butler, L. 1954 Propellar, pr. Rept. Tomato. Genet. Coop 4:9.

Hedrick, U.P. and N. O. Booth 1907 Mendelian characters in tomatoes. Proc. Amer. Soc. Hort. Sci 5:19-24.

Jones, D. F. 1917 Linkage in Lycopersicum. Am. Nat. 51:608-621.

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 shapes of tomato fruit. Jour. Agr. Res. 34:961-985.

MacArthur, J. W. 1925 Genetic linkage in the tomato. Anat. Rec. 31:350.

MacArthur, J. W. 1931 Linkage studies with the tomato III. Fifteen factors in six groups. Tran. Royal Canadian Inst. 18:1-19.

Stevens, M. A. and C. M. Rick 1986 Genetics and Breeding. pp 35-109. In: J.G. Atherton and J. Rudich (eds). The Tomato Crop. Chapman and Hall London.

Yeager, A. F. 1937 Studies on the inheritance and development of fruit size and shape in the tomato. Jour. Ag. Res. 55:141-152.