Hafen, L. and E. C. Stevenson.
The mutant sl has yellow petals, is cross fertile, and when grown in Indiana under summer and winter conditions, has never produced anthers with viable pollen. The mutant sl\2 differs from sl in that it has a vestigial development of the anthers and occasionally flowers are found with anthers that contain viable pollen. Male-sterile sl\3 is similar to sl\2, but anther development and the production of viable pollen appear to be greater. Under winter conditions in the greenhouse, practically all of the flowers of sl\4 have normal appearing anthers with abundant pollen, particularly when the plants are old; otherwise it is similar to sl\3. The mutant Sl\5 is similar to sl in that anther production is practiclly nil, but differs in that it has sepal-like petals, and is highly sterile.
Each of the mutants, when crossed with normal fertile Pritchard, produced F1 plants with normal flowers. Segregations in F2 and backcross progenies indicated that each mutation was conditioned by a single recessive gene.
The next step was to see if the mutations were controlled by the same or different genes. Some of the results of the testcrosses between these five mutants are presented in Table 1.
Table 1. Summary of segrega4.1ions obtained from crosses made
to test identity of tomato mutants.
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Mutant (sl\5 x Pritchard) sl\4 sl\3 sl\2
*
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sl 38F, 36S 181F 26IF 64IF
sl\2 16F, 14IF 59IF 40IF
sl\3 20F, 16IF 46IF
sl\4 37F, 28IF
sl\5
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* F denotes a fertile plant; IF, an incompletely-fertile
one; S, a sterile plant with no anthers.
The sterile plants in the testcross sl x (sl\5 x Pritchard) contained no
anthers and the petal color was yellowish green, intermediate between the
yellow petal color of sl and the green color of sl\5. Our first impression of
the results of the crosses of sl\2, sl\3, and sl\4 by (sl\5 x Pritchard) was
to classify the incompletely-fertile plants as sterile even though anther
development was greater than in the original mutants. However, upon selfing
these incompletely-fertile plants from the three testcrosses,
incompletely-fertile and sterile plants in a 2:1:1 ratio were obtained.
Selfing of plants classified as normal gave segregations in a ratio of 3
fertile:1 sterile. The incompletely-fertile plants, therefore, were
heterzygous for the two male-sterility factors.The results of the six testcrosses between sl, sl\2, sl\3, and sl\4 (crosses can be made without the use of the F1 because sl\2, sl\3, and sl\4 occasionally produce flovers that contain one or more anthers with viable pollen) gave F1 plants that were incompletely fertile; anther development definitely was greater than in each mutant. Seed of these F1 plants has been saved and will be planted in the field in 1958.
We have rejected the hypothesis that different genes determine male sterility in each case and any two of them in heterozygous condition interact to interfere with normal anther production, because true breeding normal fertile lines were not obtained in the F3 generation. The hypothesis being tested at the present time to explain the interrelationship of the mutants is that the genes are members of an allelic series, and when any two of them are present in heterozygous condition, they somehow complement each other to produce anthers. Our preliminary studies support this hypothesis.