Leslev, Margaret M. and J. W. Lesley.
A single varigeated mutant was found in R2 from a nonvarigated, normal looking Rl plant from a seed of the varietv Canary Export which had been soaked for 5 days in a solution of the isotope P32 with an initial dose of 10.8 microcuries. The leaves of the mutant were green irregularly splashed with small white areas. A few leaflets were distorted and nearly white, especially at the edges, some fruits were striped with two shades of green. Occasional well defined non-pubescent areas appear. These vary from spots to a few leaves or even a weak sterile shoot and are non-variegated. The original mutant 54 27 G1 was dwarfed and had a few buds which contained a few pollen mother cells. This unpromising variegated (V) mutant was selfed and gave one non-variegated (NV) plant very much like the parent in appearance and fertility. The F1, of 54 27 G1 x normal looked normal. F2 from two F1 plants contained 30 NV and 2 V. An NV F2 plant selfed gave 3 V, two NV mutants and one almost normal fruitful plant. An NV F3 selfed gave 7 NV. An NV F2 backcrossed to 54 27 G1 (V) gave 7 V and 4 NV mutants and one normal NV. The most normal looking plant was fruitful. Two other NV plants had a good many fruits which were small and often seedless. Both in F2 and backcross V plants were less fruitful than NV but some V plants had decidedly more buds and more P.M.C. than 54 27 G1. The non-pubescent tissue was found in V plants of F3 and in the backcross. In several cases NV progeny resulted from open pollination of variegated plants but the evidence from controlled pollination indicates that variegation is recessive.
The sibs of 54 27 G1 were pale and varied in fertility. Two were pollen sterile and had green anthers in mature flowers. All of them had 12 pairs of chromosomes. In one pollen sterile sib, one pair of chromosomes was often dissociated and non-conjunction of all or many pairs occurred frequently.
The original V plant 54 27 G1 contained 12 pairs of chromosomes plus a tiny fragment, or more often the same number but with two trivalents of chromosomes of normal size and a third consisting of the fragment and one of the smaller pairs. Once a ring of six was seen. Unpaired chromosomes occur at M1 and lag at A1 and A2. Both simple and complex bridges were found. The single V plant from selfing 54 27 G1 had 12 pairs plus a tiny fragment. All three F3 V plants had the tiny fragment, one of them was trisomic and bridges were found in two. The NV plants studied included ons with 12 pairs and normal meiosis and one trisomic.
All the V plants from the NV F2 backcrossed to 54 27 G1 had the tiny fragment but, as in F3, both V and NV plants may be trisomic or have 12 pairs and normal meiosis or 12 pairs including a tetravalent. The tetravalent consists of a chain; only very rarely an apparent ring was found. One of the NV plants had a tiny fragment; the rest lacked it. The most normal looking plant had 10 pairs and a tetravalent.
Longitudinal sections of root tips of 54 27 G1 show infrequent bridge formation and an occasional lagging chromosome. The laggard is usually small but may be of normal size.
The original V plant occurred in R2 from a normally green R1 plant and F1 plants also look normal. It therefore seems unlikely that the tiny fragment is the cause of the variegated or splashed appearance. What looked like a spindle fiber has been seen on the fragment, and it is often found on the metaphase plate in meiosis. It is possible that the fragment and the chromosome from which it came both have a partial attachment construction and thus sometimes fail to divide normally in mitosis. The nature of the somatic instability is being studied further.