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Cucurbit Genetics Cooperative Report 20:27-29 (article 13) 1997

A Genetic Model of Bitter Taste in Young Fruits of Melon*

Ma Dewei, Sun Lan, Liu Yun Hui, Zhang Yanping and Liu Haihe

Center of Biological Technology In The Agricultural University of Hebei, Bao Ding 071001, P.R. China

*The project supported by National Natural Science Foundation of China.

Abstract. The bitter taste of young fruits obtained from F1 and F2 individuals from crosses among various varieties of melon (Cucumis melo) from different regions were analyzed. The results showed that bitter taste in young fruits was determined by two pairs of the genes which were independently inherited and dominantly complementary. Progeny between varieties from the same center of origin did not express dominant complementation, whereas progeny from different centers of origin did.

Introduction. The bitter taste in the young fruits of melon is a significant quality character that is easy to determine. When melon germplasm from all over the world was studied, it was found that ripe fruits did not show the bitter taste, but young fruits were divided into two types: (1) bitter, and (2) non-bitter. The young fruits of wild melon showed a strong bitter taste, whereas the young fruits of local cultivars from all over the world were mostly non-bitter. In the cultivars that were selected by crossing and genetic recombination, some of hem had the bitter taste and others did not. To date, the inheritance of bitter taste in immature fruits has scarcely been studied.

It was documented that bitter taste in young melon fruits is a dominant character (5), which is seen in other cucurbits (2,3,4). The bitter taste in young fruits of melon is from cucurbitacin (1). The production of cucurbitacin is mainly determined by genetic factors; however, environmental conditions can also affect production. Japanese researchers suggested that the inheritance of bitter taste may have epistatic interactions, but there has been no report on how these genes interact.

Materials and Methods. The C. melo genotypes used this study were genetically stable after a number of selfing generations. The name, origin and botanical variety (e.g., inodorus, conomon) of these materials are presented in Table 1.

The research was performed in an experimental plot of the Agricultural University of Hebei. The materials were strictly selfed for three generations again after previous selfing, then bitter and other genetic traits were recorded. In order to observe the inheritance of characters in progeny of crosses of bitter x bitter (BxB), bitter x non-bitter (BxNB) and non-bitter x non-bitter (NBxNB), the crosses were made with different genotypes. The bitter taste in young fruits was checked 12 days after fruit set.

During crossing, the stamens of the flowers of female-parents were strictly removed the day before flowering, and bags were put on the emasculated flowers. Flowers of the male-parent were bagged on the day of flowering, the flowers were pollinated, bagged, labeled and marked. For selfing, female and male flowers from the same plant were bagged on the day before flowering. At 7:00-8:00 a.m. the next day, flowers were pollinated, bagged and marked. Six hybrid combinations (Africa Wild X S-3, Africa Wild x Sichuan Wild, Sichuan Wild X B-10, B-10 X Honey Dew, S-3 X W-B, and Honey Dew x Nunong) were selected according to the F1phenotypes, and 200 F2 individuals were planted for each.

Results. Bitter x bitter crosses. The F1 hybrid of the cross between the two bitter parents (Africa Wild x Sichuan Wild) showed bitter taste (Table 1). Of the 200 F2 plants grown from this cross, all of them also had the bitter phenotype (Table 2).

Bitter x non-bitter crosses. In all BxNB crosses, the F1s were bitter. When two of these crosses (Africa Wild x S-3, and Sichuan Wild x B-10) were selfed, the F2s had B:NB ratios of 73:27 and 74:26, respectively. In the significance test of standard deviation (P=0.4122 and P=0.6241), this segregation followed a 3:1 ratio (P 0.06) and showed Mendelian inheritance (Table 2).

Non-bitter x non-bitter crosses. When both parents were non-bitter, only four of the 10 F1hybrids were non-bitter (Honey Dew x Nunong, Honey Dew x W-B, Nunong x W-B, S-3 x B-10). For these crosses, all of the young fruits in the F2 populations showed the non-bitter character (e.g., Honey Dew x Nunong). Surprisingly, six F1s from NBxNB combinations (S-3 crossed with Honey Dew, Nunong, and W-B; B-10 crosses with Honey Dew, Nunong, and W-B) showed bitter taste.

Complementary expression. In two NBxNB combinations which gave rise to bitter F1s(Honey Dew X B-10, S-3 X W-B), F2segregation (B:NB) was 114 to 86 and 116 to 84, respectively, and obviously did not correspond to the ratio (3:1) determined by a single dominant gene. In the test of standard deviation (p=0.8377, p=0.7263), the result corresponded to a ration 9:7 for the F2segregation (P 0.05), suggesting complementary gene action of two independent genes. When there was a homozygous recessive condition at either locus, the dominant expression at the other locus is prohibited. That is, non-bitter (AAbb) x non-bitter (aaBB) -- F1bitter (AaBb) -- bitter F1(AaBB[or AABb]) -- F2, 3 A_BB (bitter): 1 aaBB (non-bitter) [or 3 AAB_(bitter): 1 AABB (non-bitter)].

Dominant complementation and ecophenotypes of melon. When materials which originated from continental climate regions in Middle Asia and West Asia were crossed, the progeny did not suggest dominant complementation (e.g., C. melo var. cantalupensis [W-B]). This indicated that there was recessive homogeneity in the two pairs of genes controlling the bitter taste. Similarly, when the material originating from East Asia (C. melo var. makuwa [S-3], C. melo var. conomon [B-10]) were hybridized with each other, the F1and F2 populations did not have the bitter taste, which suggested that these materials were also homozygous recessive at both loci.

Discussion. The inheritance of the bitter taste in the young fruit of melon is controlled by two independent genes which have a complementary relationship. The bitter taste in young fruits is a primitive character. In the long-period of naturalization and selection, bitter types have been gradually eliminated, but the recessive variance with the non-biter (The bitter A_B_--the non-bitter aaBB or AAbb) has remained. The cultivars with the recessive variable homozygotes from the same secondary center of origin did not express dominant complementation, neither in selfing or in crossing. However, when the different recessive variable cultivars from the different original centers were crossed each other, they did express the dominant complementation. The results from this research may provide important information for the study of the origin, evolution and taxonomy of melon.

Table 1. Species of melon and their F1performance of bitter taste in young fruits.

Genotype
Honey Dew
Nunong
W-B
S-3
B-10
Africa Wild
Sichuan Wild
Origin
Variety
Honey Dew
X
X
X
0
0
0
0
America
C. melo var. inodorus
Nunong
X
X
0
0
0
0
Japan
C. melo var. reticulatus
W-B
X
0
0
0
0
Italy
C. melo var. cantalupensis
S-3
X
X
0
0
Hebea
C. melo var. makuwa
B-10
X
0
0
Guangdong
C. melo var. conomon
Africa Wild
0
0
Africa
C. melo var. agrestis
Sichuan Wild
0
Sichan
C. melo var.agrestis

Note: 0 = bitter; X = not bitter.

Table 2. F2 segregation from crosses between various varieties of melon.

Number of F2 Plants
Expected F2 segregation (3:1)
Cross
Type
F1
B
NB
B
NB
Africa Wild x Sichuan Wild
BxB
B
200
0
100
0
Africa Wild x S-3
BxNB
B
145
55
72.5
27.5
Sichuan Wild x B-10
BxNB
B
147
53
73.5
26.5
Honey Dew x Nunong
NBxNB
NB
0
200
0
100
B-10 x Honey Dew
NBxNB
B
114
86
57
43

Literature Cited

  1. Rehm, S., P.R. Enslin, A.D.T. Meeuse and J.H. Wessels. 1957. Bitter principles of the Cucurbitaceae, VII. The distribution of bitter principles in the family. J. Sci. Agric. 8:679-686.
  2. Govind, C.S. and C.V. Hall. 1973. Identifying cucurbitacin in cotyledons of Cucurbita pepo L. cv. Black Zucchini. HortSceince 8:136-137.
  3. Sharma, G.C. and C.V. Hall.1971. Cucurbitacin B and total sugar inheritance in Cucurbita pepo L. related to spotted cucumber beetle feeding. J. Amer. Soc. Hort. Sci. 96:750-754.
  4. Andeweg, J.M. and J.W. De Bruyn. 1959. Breeding of non-bitter cucumbers. Euphytica 8:13-20.
  5. Barham, W.S. 1953. The inheritance of a bitter principle in cucumbers. Proc. Amer. Soc. Hort. Sci. 62:441-442.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 23 October, 2009