Such a plant possessing a maximum of earliness and fruit ripening concentration should be mechanically
harvested by cutting the stems far enough above ground to avoid separation of stones, soil, and green fruits.
Seeking a genetic basis for such a plant, 7 tomato stocks were crossed with the mutants eramosa, minuta,
parva, rigida, rigida2 , torosa, torosa2, unicaulis (all of the foregoing = Stubbe'smutants), non-branching (Alexander),
and lateral suppressor {Darby). The F2 generations were screened in field plantings. "Monostem" phenotypes, very
close to the above-outlined ideotype, were found in the progenies involving torosa as a parent. Some of these
monostem plants were crossed with 13 common tomato varieties and the subsequent progenies selected for the
traits peculiar to the ideotype.
To check the breeding potential of to2, 21 of the monostem lines thus selected (14 S6, 1 S5, 1 S4, 1 S3, 2
BC1S5,
2 BC1S3) were compared with the cvs. UC-105 and Chico III. The earliest monostem lines ripen on the
average of 20 days before Chico III; a maximum of ripening concentration was shown by the I truss - 1 flower - I fruit
phenotypes; the highest yield performance was shown by monostem plants bearing 2-3 trusses with 2-3 fruits each,
obviously less concentrated in fruit ripening and not upright. In contrast, the dwarf monostem phenotypes were
upright, but their fruits were severely affected by radial cracking. A high frequency of "double flowers" and "double
fruits" (see figure) appeared related with the "monostem" feature.
On the basis of such genetic material we believe it is possible to select "monostem" lines promising for
breeding very early tomato varieties endowed with optimum fruit ripening concentration and suitable to high density
population for mechanical harvesting also in non-favorable soils and climates.
Farrell, M. and C. M. Rick
Recurring mutants at established loci.
In screening progenies of 1782 M1 plants derived from EMS-treated seeds (cv. VFNT Cherry, synthesized
by Dr. Paul Smith at U.C., Davis), we found three mutants which complementation tests have demonstrated to be
allelic to alb, c, and d. Crosses to homozygous standard marker stocks exhibited hairy stems, an incompletely
dominant trait conferred by the multiply-marked tester on the maternal hairless cv. VFNT Cherry mutants in all F1's,
which also expressed the mutant phenotypes. The dwarf (d) and albescent (alb) F1's were carried through to the F2
generation which segregated for the other test markers. The dwarf phenotypes in the F 's segregated inter se, with
81 of 274 being of scorable size one month earlier than the remaining 194 --- results not significantly different from a
1:3 ratio (x2 = 2.7). Thus, these two alleles sharing a common locus are of different genetic constitution (mutons of a
single recon). The new dwarf mutant, a more extreme phenotype with thicker, more rugose and recurved leaves,
shorter internodes and a slower growth rate, is dominant to the original d allele, which occurred as a spontaneous
mutation.
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