Lesley M. M. and J. W. Lesley.
Segmental interchange has not been observed in tomato plants grown under natural conditions. It was observed in seven plants in a population of 49 plants of the variety Canary Export grown from seeds exposed to an initial dosage per seed of 10.8 u C of P32. Translocation, as indicated by a difference in size of the members of a pair of chromosomes at diakinesis, was also common. It may therefore be concluded that abnormalities of crossing-over are among the most frequent cytological results from this treatment.
One R1 plant from a treated seed, which as a seedling ha twin shoots and variegation, bore only 5 fruits from open pollination although it was healthy and resembled the control plants which were uniformly very fruitful. At meiosis a ring consisting of a larger and a smaller pair of chromosomes was found. Except for occasional lagging chromosomes meiosis was normal. From selfing 13 seeds were obtained. The six R2 plants that grew were all diploid. They consisted of:
1. A male-sterile plant with normal pairing.
2. A moderately fruitful plant, of normal appearance with one ring like that of the parent.
3. A brachytic plant with little good pollen and poor fertility with one ring like that of the parent.
4. A fully fruitful plant with normal appearance and normal pairing.
5. A moderately fruitful plant with small fruit and very few seeds.
6. A plant classified as a possible mutant with very little pollen or fruit. It had a ring like that of the parent and in addition one large ring.
R2 plant 1 was crossed wiyh control plant. One of the progeny selfed gave 13 plants. One ring of four of the R1 type was seen in six plants with reduced fertility, two rings of the types in R2 plant 6 in two of the male sterile plants. Only the pollen was examined in the four normally fruitful plants and in one with slightly reduced fertility . Plant 1 probably had only altered chromosomes since it had no rings. It seems possible that one at least of the members of the larger ring found in plant 6 and the progeny of plant 1 may contain a deficiency since it has not been found alone, and when it occurs in combination with the other ring, the plant is male-sterile or very nearly so. The occurrence of two rings in the progeny of the R1 plant in which only one ring was found is not fully understood. The fact that this plant had twin shoots and variegation suggests that different parts of the R1 plant may have differed cytologically.