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. ______________________________________________________ Total no. No. of fruits Populations of fruits with nipple- Expressivity studied scored tip for n (%) ______________________________________________________ Sel-4 223 205 92.1 Sel-4-1 181 119 58.6 ______________________________________________________ 't' value - - 3.31** ______________________________________________________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. _______________________________________________________________ Observed ratio Blossom end ___________________ Line of fruit Flat Nipple tipped X^2 Prob _______________________________________________________________ 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 _______________________________________________________________Literature cited:
Rick, C.M. 1956. Cytogenetics of tomato. Adv. in Genet.