The identification of three new blossom-end morphology genes: n-2, n-3, and n-4.

Barten, J.H.M., Scott, J.W. and Gardner, R.G.

Univ. of Florida, IFAS, 5007 60th Street East, Bradenton, FL, 34203

A successful approach to obtain smooth, pinpoint blossom-end scars in large-fruited, fresh-market tomatoes has been to select genotypes with a pointed blossom-end morphology (Gardner, 1990). In many breeding lines, however, pointedness is associated with adaxial leaf curl (Gardner, 1990, 1991), which may aggravate foliar disease problems (Nash and Gardner, 1988). We report on three new breeding lines (NC140, Fla890559-24, and Fla894413-1) with pointed blossom-ends, but without leaf curl. The relationship among the blossom-end morphology genes in these three new sources and previously described blossom-end morphology genes (persistent style (pst) in LA2-5, beaky (bk) in LA986, beaky-2 (bk-2) in LA1787 (Barten et al.,1992a), and nipple tip (n) in LA2353) was investigated.

The percentage pointed fruit per plant was calculated from observations on 10 young (1-4 cm diameter) and 10 mature fruit, and for parental and F1 generations the data were averaged over 10 plants. For each mutant, pointedness was inherited recessively, with various levels of incomplete dominance in heterozygous condition (Table 1). F2 segregation did not deviate significantly from 3 normal to 1 mutant, except for pst in LA2-5, where mutants were underrepresented, probably due to association with deleterious genes (Barten et al., 1992a). F1 and F2 allelism tests indicated that bk in LA986 was allelic with pst in LA2-5 (Table 2). The blossom-end morphology in both accessions was very similar to bk described by Young and MacArthur (1947). Other F1 allelism tests were sometimes unclear (Table 2), due to incomplete dominance. In the F2's, however, transgression of percentage pointed fruit below that of the least pointed parent plant occurred in all crosses (Table 2), indicating complementation between different blossom-end morphology genes. Proposed gene symbols for the blossom-end morphology genes in NC140, Fla890559-24, and Fla894413-1 are n-2, n-3, and n-4, respectively, since their phenotype is similar to n, described by MacArthur (1934). None of the mutant parents in this experiment had adaxial leaf curl, and further research is needed to establish the relationship between leaf curl associated pointedness and the blossom-end morphology genes described here.

Table 1. Pooled data for wildtype crosses involving various blossom-end morphology genes.

                  Pointed fruits (%)        F2 segregation* 
Cross (P1 x P2)     P1   P2      F1     wt:m  X^2^(3:1) P val
wt x LA2-5 (pst)     6  100(p)** 18(u)  52: 7   5.43    0.020
wt x LA986 (bk)      8   99(p)   73(u)  48:10   1.86    0.173 
wt x LA1787(bk-2)    8   64      21     84:32   0.41    0.522 
wt x LA2353 (n)      7   86      13     61:24   0.47    0.493 
wt x NC140           3   22      11     24: 6   0.40    0.527 
wt x Fla890559-24    6   49      18     40:19   1.63    0.202 
wt x Fla894413-1    10   55      16     23: 7   0.04    0.842
* F2 plants with a lower percentage pointed fruit than the minimum in the mutant parent were counted as wildtype (wt).

** The type of blossom-end morphology is indicated when parents differ: p = prominent, columnar blossom-end characteristic for LA2-5 and LA986, u = rounded, less prominent, u-shaped blossom-end as in LA2353.

Table 2. F1 and F2 allelism tests for various blossom-end morphology genes.

                                 Pointed fruits (%)  F2 segregation*
Cross (P1 x P2)                  P1     P2      F1  <=Low Mid >=High
LA986(bk) x LA2-5 (pst)        100(p)**100(p) 100(p)   -    -     -
LA1787(bk-2) x LA2-5/LA986(bk)***67(u) 100(p)  60(u)  39   39     6
LA2353 (n) x LA2-5/LA986 (bk)   83(u)  100(p)  81(u)  29   87    27
LA2353 (n) x LA1787 (bk-2)      83      67     46     19   29     9
NC140 x LA2-5/LA986 (bk)        20(u)  100(p)  36(u)  17   30     3
Fla890559-24 x LA2-5/LA986 (bk) 49(u)  100(p)  70(u)   6   16     5 
Fla894413-1 x LA2-5/LA986 (bk)  49(u)  100(p)  87(u)  22   29    13
NC140 x LA1787 (bk-2)           20      70     41      1   29     0
Fla890559-24 x LA1787 (bk-2)    50      67     57     22   23    12
Fla894413-1 x LA1787 (bk-2)     60      70     46     17    5     8
NC140 x LA2353 (n)              20      77     12     11   17     0
Fla890559-24 x LA2353 (n)       50      83     33     20   30     8
Fla894413-1 x LA2353 (n)        60      77     46     17   11     2
NC140 x Fla890559-24            17      58     14      8   15     7
NC140 x Fla894413-1             20      60     27     19    8     1
Fla890559-24 x Fla894413-1      47      60     53     14   11     5
* <=Low = Number of F2 plants with equal or lower percentage pointed fruit than the minimum in least pointed parent, >=High = Number of F2 plants with equal or greater percentage pointed fruit than the maximum in most pointed parent, Mid = Number of F2 plants in between.

** See Table 1.

*** Data were pooled for crosses involving LA2-5 and LA986, since both had the same blossom-end morphology gene.

This work establishes the presence of four different nipple tip genes, and probably other blossom-end morphology genes are yet unidentified. Breeders may backcross these blossom-end morphology genes into otherwise desirable breeding lines and ultimately intercross complementing parents to obtain hybrids with pinpoint blossom-end scars, but without pointed mature fruits and without leaf curl. Barten et al. (1992a) indicated that n, n-2, and n-3 seemed most promising for such an approach. Alternatively, a pointed breeding line may be crossed with a non-pointed, but reasonably smooth, breeding line (Gardner, 1990), since Barten et al. (1992b) have shown that the inheritance of blossom-end scar size is predominantly additive.

Literature Cited:
Barten, J.H.M., J.W. Scott and R.G. Gardner 1992a. J. Amer. Soc. Hort. Sci. (In press).

Barten, J.H.M., Y. Elkind, J.W. Scott, S. Vidavski and N. Kedar 1992b. Euphytica (In press).

Gardner, R.G. 1990. Hortsci 25:989-990.

Gardner, R.G. 1991. TGC Report 41:81, 85, and 86.

MacArthur, J.W. 1934. J. Genetics 29:123-133.

Nash, A.F. and R.G. Gardner 1988. J. Amer. Soc. Hort. Sci. 113:264-268.

Young, P.A. and J.W. MacArthur 1947. Texas Agr. Exp. Sta. Bul. 698.