Does the gametophytic factor affect the hp ratio?

Mochizuki, T. and S. Kamimura

Kerr (1960) suggested that the deficiency of segregants was the result of slower emergence and subsequent growth and higher mortality of hp seedlings of normal seedlings. We have observed lower hp ratios even when germination was almost 100% when the hp phenotype was checked by anthocyan pigmentation in radicle. These results suggest that ratio of hp individuals within the seed population was originally lower than expected and that emergence growth rate and seed mortality are not the sole factors affecting the hp ratio. The frequently observed lower hp ratios were studied by the 'Yellow film method' (TGC Report No. 35, pp. 12-23) to check the hp ratio in segregating populations.

The high chlorophyll sources can be divided into two groups in F2 populations of hp x normal. The former produced the expected 3:1 ratio of hp plants, while the latter produced lower numbers of hp plants (Table 1). In the latter varieties, there may be some genetic factor which affects the hp ratio in segregating populations. The presence of sterility genes which affect the hp ratio are unlikely because of complete fertility of F1 and F2 plants. The presence of an unlinked repressor gene of hp is also unlikely since lines showing higher hp ratios than expected among F3 or backcross generation populations derived from heterozygous F2 plants (hp/+) would be expected if the repressor gene affected the action of hp (Table 2). It is possible to explain the distorted segregation of hp assuming a gametophytic gene located on the same chromosome as hp. From results of reciprocal crosses of hp x F1 (normal x hp), it is estimated that both male and female gametes are equally affected by the gametophytic gene (Table 3). Two gametophytic genes have been reported in tomato. They are Ge (on the 4th chromosome, Rick, 1966) and Gp (on the 9th chromosome, Pelham, 1968). Further studies are necessary to establish the presence and nature of this gametophytic gene affecting hp ratios.

Table 1.  Segregation ratio of high-pigment phenotype

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Lines                    hp     hp+       Goodness
                                          of fit^1^
______________________________________________________
(Parents)
   Morioka  9   (hp)     28      0
   Morioka  15   (hp)    40      0
   Morioka  16   (hp)    29      0
   Y-13-1524-10-64 (hp)  23      0
   Morioka  17   (hp)    53      0
   LA  1664  (hp)        26      0
   Manapal   (dg)        21      0
   305-33-13-2-1  (+)     0     23
   LA 348 (+)             0     25
   LA 806 (+)             0     46
   PU  74-43  (+)         0     34
   GT   70-050-01         0     45

______________________________________________________
(F2 populations)

M 9  X  305-31          288    903           0
M 9  X  GT              101    326           0
M  15  X  LA  348        77    190           0
M  15  X  LA 806        104    278           0
M  15  X  GT            178    565           0
M  16  X  PU74-43       226    682           0
Y-13      X  GT         208    539           0
M  17     X  GT         244    978           X
LA  1664  X  GT         131    591           X
Manapal   X  LA  348     50    285           X
Manapal   X  LA  806     60    280           X
Manapal   X  GT          94    508           X
_______________________________________________________
    ^ 1^0  =  Normal;  X  =deficient for hp
Table 2. Segregation in F3 and B1F1 populations from F2 (hp X normal) normal selected plants

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                           hp    hp+    Fitness
                                        test^1^
___________________________________________________________
No.  of  lines             32     15     (1:3)
___________________________________________________________
No.  of  plants in
segregated lines
   self  (F3)             514   1800  X  (1:3)
   X hp(B1F1)             363   1547  X  (1:1)
___________________________________________________________
     hp:Morioka 17, normal:GT 70-050-01
___________________________________________________________
    ^1^0 = normal; X = deficient for hp
Table 3. Segregation in  reciprocal  crosses  of  hp  X  normal

___________________________________________________________
Lines                   hp    Normal    Fitness
                                        test^1^
___________________________________________________________
   Morioka 17 (hp)      56       0
   GT 70-050-01 (+)      0      43
   F^1^2 (GT X M 17)     0      21
   F (GT X M 17)        48     244      X  (1:3)
   B1F1  (M 17 X F1)    50      90      X  (1:1)
   B1F1  (F1 x M17)     53     124      X  (1:1)
___________________________________________________________
   ^1^0 = normal; X  =  deficient  for hp