Confirmation on location of Dsc on linkage group VI


Hagh Nazari, A., and Sharma, B.                                         Div. of Genetics, Indian Agric. Res. Inst.

                                                                                                                           New Delhi, India


            Dull seed coat (gene Dsc) was reported as a Mendelian trait in pea by Marx (1). The character was reported to be linked to Pl (where genotypes with Pl also had darker seed coat than pl lines) but segregates independently as a dominant factor. The character was scored in a (anthocyanin inhibitor) backgrounds by Marx (1988) to ensure that the blackish pigment in the seed coat was not related to anthocyanin synthesis. Variable expression in glasshouse and field screening, as well as other problems such as interaction with the r (wrinkled seed) phenotype has been reported (M. Ambrose, personal communication). Dsc was mapped by Marx (1) near Pl in linkage group VI (2). The gene symbol Dsc was however dropped from the 1993 genetic map of pea (3) because of insufficient confirmation of its existence and chromosomal location. It remains to be confirmed whether this trait is really controlled by a separate specific gene or appears only as pleiotropic effect of other gene(s). In the former case, the location of gene needs to be confirmed.

Подпись: Table 1. Joint segregation analysis of dull seed coat (Dsc) with black hilum (Pl) in pea

Cross	Gene pair	F2 segregation		Chi-square	RF %	SE %
		DD	DR	RD	RR		Locus 1 (3:1)	Locus 2 (3:1)	Joint		
P 1597 x P 1563	Pl–Dsc	163	5	3	46		0.94	0.43	178***	3.8	1.3
P 1563 x P 1597	Pl–Dsc 	111	2	3	32		0.14	0.32	121***	3.5	1.5
Pooled over two crosses	Pl–Dsc	274	7	6	78		0.77	0.57	296***	3.7	1.0
Heterogen-ecity									3.57		1.0

Both crosses had dominant alleles in the coupling phase.
***Significant at 0.0001 level
            To investigate the inheritance and determine the map position of the gene causing dull seed coat the line P 1597 (Pl, dull seed coat) was crossed with P 1563 (pl, bright seed coat) in both (direct and reciprocal) directions. To nullify the effect of environmental fluctuations, the F1 seeds were grown in the phytotron. Table 1 presents data obtained from joint segregation analysis of F2 populations of the two crosses (direct and reciprocal). In both crosses monogenic segregation for dull seed coat was in good fit to the ratio of 3 dull : 1 bright seed coat, confirming the dominant nature of dull seed coat trait. Joint segregation analysis for Dsc and Pl in the F2 of the cross in both directions showed a significant linkage between these two genes. Based on the

pooled analysis of data of the cross the gene Dsc maps 3.7 + 1 crossover units away from the gene Pl on linkage group VI. The precise location of the gene Dsc in relation to the other markers on linkage group VI is under investigation.



1.   Marx, G.A. 1988. PNL 20: 25-26.

2.   Weeden. N.F., Ambrose, M., and Święcicki, W.K. 1991. Pisum Genetics 23: cover.

3.   Weeden, N.F., Święcicki, W.K., Ambrose, M. and Timmerman, G.M. 1993. Pisum Genetics 25: 4 and cover.