Expressivity and inheritance of the nipple-tip trait in tomato.

Tikool S.K. and N. Anand

The fruit trait referred to as nipple-tip and given the symbol n is reported to be polymeric, quantitatively variable and unsatisfactory, MacArthur (1934a) as quoted by Rick (1956). Reported here are our results on the expressivity of this gene and its inheritance using a high yielding line (Sel-4) as a source of n. The degree of expression of the n gene was calculated on the basis of presence or absence of this trait in 10 fruiting clusters per plant. Averages were computed from 20 randomly selected plants in a population of Sel-4 compared with one of its derivatives, Sel-4-1, selected for poorer expression of the n gene. The expression of n in the former was 92 percent as compared to only 58 percent in the latter (Table 1). A 't' test established the 2 populations to be genetically different from each other.

Table 1.  Expressivity of the nipple-tip trait.
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             Total no.  No. of fruits
Populations  of fruits  with nipple-   Expressivity
  studied    scored     tip                for n (%)
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  Sel-4      223           205             92.1

  Sel-4-1    181           119             58.6
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  't' value   -             -              3.31**
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While raising the F2 progenies of crosses, Sel-4 with 2 flat fruited lines, viz., IHR 663-12-3 (a bacterial wilt resistant line) and IHR 249-2 (a high solids line), scoring for the presence of nipple-tip trait was carried out on a visual basis on each plant. The segregation ratios obtained are presented in Table 2.

These ratios fit well into a 15:1 F2 ratio (Table 2) indicating the nipple-tip trait to be under the control of 2 recessive genes. Possible genotype of Sel-4 would thus be n\1\n\2\/n\1\n\2\.

Table 2.  Genetic ratios observed in F2 and BC populations.
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                               Observed ratio
                Blossom end  ___________________
     Line         of fruit   Flat  Nipple tipped  X^2   Prob
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663-12-3          Flat         41         0       -    0.5-

Sel-4             Nipple tip    0        38       -

663-12-3 x Sel-4  Flat         35         0       -

663/Sel-4 F2      -            93         8    0.68  0.5 to 0.3

249-2             Flat         50         0       -

249-2 x Sel-4 F2  -           168        16    1.43  0.3 to 0.2
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Literature cited:

Rick, C.M. 1956. Cytogenetics of tomato. Adv. in Genet.