Part of the tomato breeding program at Davis is concerned with the problem of shattering and subsequent loss of fruit. It has been suggested that the j gene, which eliminates the pedicel joint and easy abscission of the fruit might be incorporated to advantage. In checking available varieties and stocks, however, it was found that all those that carry j also carry lf, which causes extreme preliferation of shoots and is otherwise undesireable. A search for j Lf individuals was then conducted in BC and F2 generations segregating for these genes with the following results:
Generation J Lf J lf j Lf j lf Total
Backcross 145 0 0 137 282
F2 716 11 0 222 939
(All in coupling phase)
The first point of interest is the very short linkage distance between j and
lf. According to BC there is no crossingover, according to F2, about 1%, the
difference between the two probibly not being significant. But the ammount of
c.o. is much less than the value indicated by Young and MacArthur(Texas A.E.S.
Bul. 698, 1947), which according to linear map distance is about 10%.The second point deals with the absence of j Lf crossovers, the phenotype especially saught here. Since a special effort was made to find this recombination, it is very doubtful whether any such individuals would have been overlooked. If they are equally as viable as J lf -- and there is no apparent reason why they should not be -- one would expect about 6 per 1,000 in the F2. The probability that none would be found in a population of 939 is 0.994 = 0.0035. This discrepancy might be explained in several ways involving lethals although each requires several rather unlikely assumptions.
In recent correspondence, Dr. L. Butler has kindly transmitted his figures for j and lf. They also indicate a low crossover figure, but include some j Lf individuals. At the same time, J lf is about three times as frequent as j Lf, a difference that is probably significant because large numbers are involved. Although j Lf thus seems to be viable, its reduced frequency is nevertheless unusual.
The writer should be very grateful to have seed of any stocks that are known or suspected to be j Lf.