THE FIRST GENETIC MAP AND POSITIONS OF MAJOR FRUIT TRAIT LOCI OF BITTER MELON (Momordica charantia)

Journal of Plant Science & Molecular Breeding

Penulis

Chittaranjan Kole, Bode A. Olukolu, Phullara Kole, Virendra K. Rao, Anju Bajpai, S. Backiyarani, Jogendra Singh, R. Elanchezhian, and Albert G. Abbott

Bitter Melon (Momordica charantia L.) (in Indonesia it is called as Pare/Paria) is a kind of plant which is traditionally cultivated both for food vegetable and medicine either in tropical or subtropical areas of all over the world.  Nonetheless, it still remains as an underutilized crop and no serious efforts have been made for elucidation of its genome or its genetic improvement. In fact, the genome size is more than twice the genome size of other cucurbits,
but in contrast to other popular cucurbits (melon, watermelon, and cucumber), there is no genetic linkage map for bitter melon and no information on map position of horticulturally desirable trait related to fruit quality and yield.

Two of M. charantia varieties (M. charantia var. charantia and M. charantia var. muricata  are highly contrasting in shape, size, and many other qualitative and quantitave traits. M. charantia var charantia produces white, glossy, and non spiny fruits that have higher values for average length, maximum diameter, and weight. It also produces yellow stigma and black seed. In contrast with it, M. charantia var. muricata produces green, dull, and spiny fruits. It produces vis-à-vis green stigma and creamy seed. However, It is important to map many quantitative and qualitative traits (especially for traits which are economically important) for their precise breeding using molecular markers.

In this study, the researcher used a set of 146 F₂ individuals derived from a cross between two parents belonging to the two botanical varieties mentioned above and a set of AFLP markers to construct the first genetic linkage map for bitter melon. Qualitative traits including fruit color (green/white), luster (dull/glossy), surface structure (spiny/non-spiny), stigma color (yellow/green) and seed color (black/creamy) were visually scored. Quantitative traits including length (cm), maximum diameters (cm), and weight (g) of each fruit was measured and averaged. The number of mature unripe and ripe fruits were pooled together to record the total fruit number per plant and these matured fruit was recorded as the fruit yield.

The genetic linkage map constructed includes 108 AFLP markers and 5 qualitative trait loci distributed over 11 linkage groups spanning a total of 3060.7 cM with an average marker interval of 22.75 cM. Seven of the linkage groups contained 9 to 28 markers dispersed over 234.7 to 889.8 cM. The other four linkage groups had 2 to 5 markers dispersed over 16.6 to 78.5 cM. Segregation distortion was for 31 of the 108 markers at P_0.001. The result showed that their F₁ bore green, dull, and spiny fruits; yellow stigma and black seeds. The F₂ plant exhibited monogenic (3:1) segregation for fruit color (X²=0.50). fruit luster (X²=0.76), fruit surface structure (X²=0.76) and stigma color (X²=0.63); but digenic mode of inheritance (9:7) for seed color (X²=0.46). The values for the mean, variance, standard deviation, coefficient of variation, and range for these traits recorded on the F₂ population are provided in Table 1. A very high correlation coefficient value was observed between fruit yield and number (0.86) and between fruit weight and diameter (0.89).

Tabel 1. Basic statistic for five quantitative

Traits	Mean	Variance	Standard Deviation	Skew-ness	Kurto-sis	Range
Length (cm)	5.6	1.9	1.37	0.35	0.04	2.3-10.2
Diameter (cm)	3.5	0.35	0.60	0.04	-0.07	1.9-5.0
Weight (g)	20.8	106.8	10.33	0.63**	-0.21	3.0-48.0
Fruit number	13.3	87.8	9.37	0.98**	0.26	1.0-43.0
Yield (g)	3105.5	99212	314.98	2.00**	5.57**	3.0-1988

** denotes significance at P_0.01 level

LG*	Number of loci	Map length (cM)	Average marker interval (cM)
1	28	889.8	31.78
2	20	563.6	28.18
3	13	376.1	28.93
4	10	282.4	28.24
5	10	275.5	27.55
6	9	253.9	28.21
7	10	234.7	23.47
8	5	78.5	15.70
9	3	51.1	17.03
10	3	38.5	12.83
11	2	16.6	8.30
Total	113	3060.7	22.75

*LG designates linkage group

The map positions of qualitative traits is provided in Table 2. LG1 contained three qualitative traits including fruit surface structure, luster (both of them being closely linked), and stigma color. Fruit color was mapped on LG7. Only one of the two genes (digenic mode of inheritance) controlling seed color was mapped on LG3. A total of 12 quantitative trait loci (QTLs) were detected for the five quantitative fruit traits based on additive and dominance models. Fruit length had two QTLs (LG7 and LG2). Fruit diameter and weight had one QTL each (LG1). Fruit number had four QTLs (2 in LG1, LG2, and LG5). Fruit yield had for QTLs ( 2 in LG1, LG2, LG3).