Linkage tests between pat-2 and marker genes bls and sf on chromosome 3

A recent paper by Vardy et al. (1989) mentions linkage relations between pat-2 (parthenocarpic-2) and bls (baby-lea syndrome, chr 3L, 74), and between pat-2 and sf (solanifolia, chr. 3L, 111). The pat-2 locus is thought to be located between bls and sf, closer to sf, than to bls. On the other hand, there is no linkage between pat-2 and sy (sunny, chr. 3S, 46). According to our own results, we concluded that pat-2 and bls are independent (Philouze, 1983). Our linkage studies with marker genes on chromosome 3 have been continued.

In a first step, we studies the cross between LA782 (a sy sf stock from the University of California, Davis) and the parthenocarpic cv Severianin. A strong impression arose from the F2 population, that there was no linkage between pat-2 and sy nor sf. However, the results cannot be published, owing to the difficulty to class a few F2 plants as [pat-2] or [pat-2+]. Fruit setting of AL782 was low, even in favorable environmental conditions; production consisted of only a few irregular, fasciated fruits. Fruit settings is made more difficult because of the sf gene itself which, in addition to a modification of leaf shape, is characterized by abnormal flowers.

This led us to continue this work with marker genes introduced in a well-known genotype: bls (GCR 29) and sf (GCR 392). The GCR stocks were received from Glasshouse Crops Research Institute, G.B. They are isogenic lines of the cv. Alisa Craig, in which the mutant genes were introduced by backcrosses. Two [pat-2] lines were used: Severianin (large fruits with may locules), and the parthenocarpic isogenic line of Monalbo, in which we introduced the pat-2 gene by backcrosses. The fruits of Monalbo are medium-sized, two-loculated, like in Ailsa Craig.

F2 plants from the 4 crosses realized between the 2 [pat-2] lines and the 2 GCR marker stocks were grown in a glasshouse (for growing conditions, see table 1). Most of the plants were grown in pots in a heated glasshouse. Some other plants were grown in a "cold" glasshouse. From each of the 4 crosses, a u/u pat-2/pat-2 recombinant (u = mutant bls or sf) was crossed with the F1 u/+ +/pat-2. Plants from the 4 testcrosses were grown in soil in a "cold" glasshouse (table 2).

Parthenocarpy was estimated as the ability to produce seedless open- pollinated fruits with the same appearance as seeded open-pollinated fruits, and/or, for F2 plants grown in pots in a heated glasshouse, as the ability to develop fruits from emasculated non-pollinated flowers. The results of the F2 studies are given in table 1, those of the testcross studies in table 2. The probabilities for Chi^2 (with Yates correction) calculated for hypothesis of independence between pat-2 and bls, and between pat-2 and sf, are higher than 0.05, with one exception. However, the significant deficit (P , 0.01) of [bls+ pat-2] plants in the cross (GCR 29 x Severianin) does not go in the direction of a linkage between pat-2 and bls. In conclusion, we did not find, in our experimental conditions, any evidence for linkage between pat-2 on the one hand, and on the other hand bls and sf.

Table 1. Studies of F2

_______________________________________________________________________
F2 from                 No. plants (a+b)  pat-2       X^2  hypothesis
                       ________________             ___________________
crosses     Phenotypes Total  +  pat-2   plants(%)   3:1    Probability
_______________________________________________________________________
GCR 29          +        21   17    4       19      0.15    0.7
x Severianin    bls      25   17    8       32      0.33    0.50 - 0.70

GCR 29          +        20   17    3       15      0.60    0.30 - 0.50
x Monalbo       bls      20   11    9       45      3.27    0.05 - 0.10

Severianin      +        24   21    3       13      1.39    0.20 - 0.30
x GCR 392       sf       26   20    6       23      0       1.00

GCR 392         +        25   20    5       20      0.12    0.70 - 0.80
x Monalbo       sf       26   24    2        8      3.28    0.05 - 0.10
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b) "Cold" glasshouse. Sowing on January 21, plantation in soil on March 9, t^o^ minimum: 10 deg.C to 12 deg.C, from the plantation till the end of April"

a & b) Inforescences limited to 8 - 10 flowers.

Table 2. Studies of Testcrosses

_________________________________________________________________________
Testcrosses                No. of  plants   pat-2        X^2 hypothesis
                         _________________            ___________________
from crosses  Phenotypes Total [+]  pat-2  Plants(%)  1:1     Probability
_________________________________________________________________________
GCR 29           +       50    37    13      26      10.58   < 0.01
x Severianin    bls      50    30    20      40       1.62   0.20 - 0.30

GCR 29           +       50    32    18      36       3.38   0.05 - 0.10
x Monalbo       bls      50    27    23      46       0.18   0.50 - 0.70

Severianin       +       50    24    26      52       0.02   0.9
x GCR 392       sf       50    27    23      46       0.18   0.50 - 0.70

GCR 392          +       50    29    21      42       0.98   0.30 - 0.50
x Monalbo       sf       50    19    31      62       2.42   0.10 - 0.20
_________________________________________________________________________

Literature cited:

Philouze J. 1983 Attempts to map pat-2. Tomato Genetics Cooperative Report 33, 9-11.

Vardy, E., D. Lapushner, A. Genizi and J. Hewitt 1989 Genetics of parthenocarpy in tomato under a low temperature regime. Euphytica 41, 9-15.