DETAILED DOCUMENTATION OF THE OBSCURATUM PHENOMENON IN PISUM

PNL Volume 17

1985

RESEARCH REPORTS

Loennig, W.-E.

Institute of Genetics, University of Bonn

Federal Republic of Germany

In a line of Pisum sativum (arvense) there appeared the phenomenon

long known as obscuratum (1, 3-7, 9), showing a certain percentage of

self-colored, violet-black seeds among a large majority of violet

spotted ones (F, Fs, or F Fs). The character requires the presence of

anthocyanin (A) for expression but it is not heritable. Although the

phenomenon has often been observed and described, few data are available

providing actual counts and percentages. Tables 1 and 2 give such data

gathered in the experimental fields of Bonn in 1983 and 1984. Table 1

shows the numbers of seeds and the percentages of violet-black seeds in

seven families derived from individual plants which themselves bore only

spotted seeds.

Table 1. Percentages of violet-black and partly colored seeds of

seven families of a line of Pisum arvense (1983).

The violet-black seeds from these populations were selected and the 184

plants grown from them were investigated in the field in 1984 (Table 2).

Table 2. Percentages of violet-black and partly colored seeds. All

the plants producing these seeds were grown from violet-black

seeds.

The 122 self-colored or partly colored seeds were distributed on 24

(13%) of the 184 plants; all 24 plants also bore spotted seeds. Three

categories could be distinguished for the colored seeds: five plants

bore only violet-black seeds, eight plants bore violet-black and partly

colored seeds, and eleven plants had only partly colored seeds, so that

the ratio of the first two categories to the last was nearly 1:1 (in

four groups of plants we found the following ratios: 6:6 in 71 plants;

2:2 in 48 plants; 3:2 in 44 plants; and 2:1 in 21 plants).

PNL Volume 17 1985

RESEARCH REPORTS 41

Table 3 gives an example of the distribution per plant for each

category (we usually counted from the first fertile node upwards).

Sixteen plants grown from partly colored seeds were also investi-

gated. They produced 1,448 seeds, 35 of which were violet-black and 6

partly colored (2.42% and 0.41%, respectively). The violet-black and

partly colored seeds were distributed on 3 (19%) of the 16 plants. All

three plants bore violet-black as well as partly colored seeds.

After having crossed the P. arvense line with long P. sativum lines

(latter being derived from hybrids between mutant 489C and DGV), the F₂

was investigated for violet-black and partly colored seeds. The pheno-

menon of somatic instability had also appeared in the F1, but was not

counted in larger numbers there. Table 4 gives the details for the

three F2 families investigated, but since only A plants produce colored

seeds, only their seeds are given in the table.

Table 4. Percentages of violet-black and partly colored seeds in three

F₂ families of the cross P. arvense x P. sativum ( 1983).

From family No. 3 of Table 4 40 Light brown^1/ seeds were selected

(details about segregations for seed coat colors of similar crosses, see

Marx [8]). In the 30 F3 plants evaluated in 1984, exactly 1500 seeds

were counted, none of which was violet-black or partly colored. The

light brown seeds were generally very slightly spotted, but some of them

did not show spotting. These F3 plants may have lost the gene (or ele-

ment) which makes possible the instability to the degree described

above. However, as already noted by Lamprecht (4), there may be a cer-

tain relationship between the percentage of violet-black seeds and the

amount of insolation. In contrast to the sunny summer of 1983 in

Central Europe, we had long periods of rain in 1984, which may explain

the general differences in the percentages of violet-black seeds produced.

^1/ A discussion of the nomenclature concerning flower and seed coat color

is beyone the scope of the present paper. The terms are only descriptively

and tentatively used in their normal usage of everyday language.

PNL Volume 17 1985

RESEARCH REPORTS

Freeling (2), commenting on the work of McClintock and the ques-

tion how insertion elements are recognized, writes (p. 281): "The most

common way to recognize an insertion element is when the element lowers

or obliterates the expression of a gene, but reverts frequently to the

nonmutated phenotype. This genetic instability is usually recognized as

variegated somatic tissue." He continues that in maize transposons

"are known to reside in each of the eight genes necessary for complete

anthocyanin (purple) pigmentation" and that transposons "were discovered

at these genes simply because somatic instability is easily recogni-

zable".

The question whether transposons are involved in the obscuratum

phenomenon may be answered by future experimental work in molecular

genetics.

1. Blixt, S. 1972. Agri Hort. Genet. 30:1-293.

2. Freeling, M. 1984. Ann. Rev. Plant Physiol. 35:277-298.

3. Fruwirth, C. 1909. Arch Rass. u. Ges. Biol. 6:433-469.

(Quoted by Blixt, 1972).

4. Kajanus, B. 1913. Fuhlings Landw. Ztg. 62:153-160.

(Quoted by Lamprecht, 1956.

5. Lamprecht, H. 1956. Agri Hort. Genet. 14:19-33.

6. Lamprecht, H. 1958. Agri Hort. Genet. 16:49-53.

7. Lamprecht, H. 1974. Monographie der Gattung Pisum.

8. Marx, G. A. 1984. PNL 16:43-45.

9. Rimpau, W. 1891. Landwirthschaftliche Jahrbucher 20:366-369.

(Quoted by S. Blixt, 1972).

Acknowledgement: I thank Prof. Marx for providing references to the

obscuratum.

Erratum

PNL 16, p. 41

1) There is a typographical error on line 2 of the last paragraph.

It should read: "As no Fa plants with..." (Fa instead of fa).

2) Concerning the editor's comment in brackets (line 4, same paragraph)

the author maintains he is sure that it was a non-fasciated plant.