Foskett, R. L.
A genetic study of twin seedlings was begun in 1957. They have since been found in various lots of F1, F2, and standard variety seed. Seed was counted into lots of 100 and placed on green blotting paper for ease in observing emerging roots. Each lot of 100 seeds was placed in a separate germinating box, with a surface area approximating 4 x 5 inches. Germination took place in a controlled temperature chamber at 25 deg. C.
Examinations of the seed were made daily. Any seedling showing two roots was immedialuely removed to a covered petri dish and placed in light for complete emergence of tha two seedlings from the seed coat. Each seedling was then planted in a separate pot.
Two pairs of twin seedlings were found in F1 seed. One pair was from a cross between German Dwarf Bush and Yellow Plum. Each seedling produced red fruit, indicating genes from the maternal parent, and normal plant type, obtained from the pollen parent. Seedlings of the progenies from both plants segregated for the duarf characteristic. Another pair of twin seedlings was found in F1 seed of a cross between Red Jacket, containing the recessive potato leaf character, and Yellow Plum, containing the recessive yellow fruit. Each member of the pair produced the cut leaf character of the pollen parent and the red fruit of the seed parent. Seedlings of the progenies from both members of the pair segregated for leaf type.
Ten pairs of twin seedlings have been observed from F2 seed. One or more marker genes was present in each seed lot to give some indication of genetic similarity between members of each pair. Of the ten observed pairs, eight were identical for the marker genes. One plant from one pair was abnormal and died. Another pair differed in fruit color and fruit shape. Progenies of the twins observed from F2 seed are now being grown for further information concerning genetic similarity, but it appears that most twin seedlings in tomato are identical twins, having come from a single zygote. All plants reaching flowering age were highly fruitful.
Incidence of twin seedlings in the F2 seed tested was found to be approximately one in 975 seeds, or one in 800 actually germinated.
Rate of development often appears to be different in the early stages of growth between members of a pair, and this phase is being investigated with standard varieties.