Hederick and Booth (1907) reported that pear-shaped fruit was due to asingle recessive gene. Jones (1917) showed this gene linked to vine type (dlocus). McArthur (1925) reported segregation and linkage results forpear-shaped similar to Hederick and Booth and proposed that the recessive genebe designated pr. Lindstrom (1926, 1927) conclusively demonstrated that thepr locus was identical to the locus that conditioned ovate fruit shape andsuggested since this gene conditioned the ellipsoidal features of shape thatthe recessive condition should be designated oval (o) rather than pr.McArthur (1931) accepted this interpretation. The pr symbol was subsequentlyused by Butler (1954) to designate propeller and is so used at the presenttime (Gene Stock List, Rept. Tomato Genet. Cooperative 37, 1987). Theinterpretation by Lindstrom (1927) has been carried down in the literature tothe present day (Stevens and Rick, 1986). This interpretation, however, hasleft unresolved the genetics of pear-shaped fruit in tomato. Yeager (1937)showed that pear-shaped fruit was due to the constriction of oval fruits bythe corolla.
In the present investigation the corolla was removed from the two pearvarieties, Yellow Pear and Roma, prior to hybridization to confirm thefindings of Yeager (1937). In each case the early removal of the corollaschanged the form of the fruit to a more oval condition. The 2 pear-shapedvarieties, further, were reciprocally crossed to demonstrate that there was nodifference in their genetics (Table 1). One unexplained oval fruit occurredin 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. Segregatingplants 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 asingle recessive gene. This is a new gene which apparently apportions greatertensile strength to the corolla. When present in the hom*ozygous recessivecondition in conjunction with hom*ozygous o, fruits are constricted in veryearly stages of development producing pear-shaped fruit. Based on work byYeager (1937) and on the present work it is proposed that this new gene becalled constricting corolla (cc).
Evaluation of digenic segregation for flesh color (r locus) andcorolla character suggested a weak linkage for these 2 characteristics. Threeof 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 ratiowith an excess of parental types. Pooling of the 4 sets also suggested anexcess of parental types. The sets were tested and found hom*ogeneous (X^2 =4.00, P = .20 - .30). The pooled data were subsequently classed intonon-parental and parental types and tested against a 10:6 ratio which resultedin a poor fit for independent assortment (X^2 = 8.08, P =.01). Therecombination 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-.50Roma x Yellow Plum 106 37 3:1 0.04 .80-.90Yellow Plum x Yellow Pear 119 30 3:1 1.76 .10-.20Yellow Pear x Yellow Plum 114 25 3:1 3.82 .05-.10Yellow 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-.30Roma x Yel Pl 24 273 99 3:1 .52 .30-.50Yel Pl x Yel Pr 19 206 84 3:1 2.66 .10-.20Yel 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 PParents Gen oval* oval pear pear tested Value __________________________________________________________________Yel Pl x Roma F2 52 28 16 5 9:3:3:1 5.34 .10-.20Roma x Yel Pl F2 73 30 37 3 9:3:3:1 8.63 .02-.05Yel Pl x Roma F3 69 34 27 8 9:3:3:1 3.44 .30-.50Roma x Yel Pl F3 125 47 44 13 9:3:3:1 .59 .80-.90Total 319 139 124 29 9:3:3:1 9.51 .02-.05__________________________________________________________________*All parents are hom*ozygous for the oval (o) gene. These hom*ozygous o fruitsare oval in the presence of the dominant allele and pear-shaped in thepresence of the recessive allele of the new gene. Hence, fruit phenotype wasused 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.
