PENETRANCE AND SEED PRODUCTION IN PISUM

PNL Volume 16 1984

RESEARCH REPORTS

Gottschalk, W.

and A. Abou-Salha

Institute of Genetics, University of Bonn

Federal Republic of Germany

Two polymeric genes of Pisum, bif-1 and bif-2, are responsible for

altering the monopodial shoot into a dichotomous shoot. The agronomic

value of these genotypes is reduced by the unstable penetrance of the

genes involved. In spite of this disadvantage, mutant 1201A, homozygous

for bif-1, showed higher productivity than its mother variety in most of

the 22 generations tested so far (Fig. 1, lefthand part). Mutant 157A,

homozygous for bif-2, was found to be not as productive as 1201A con-

sidering the mean values of 12 generations. Recombinant R 837 is

homozygous for gene bif-1, gene efr for earliness and a gene for

waxlessness. The seed production of this genotype was relatively low.

Fig. 1. Relationship between seed production of bifurcated Pisum

genotypes and the penetrance of the bif-gene. Left: The yield

of mutants 157A, 1201A and of recombinant R 837 in different

generations. Each dot is the mean value for one generation.

Right: The yield of the same genotypes in the last 4 gener-

ations in relation to the penetrance of the bif-genes. Solid

circles: Bifurcated plants. Open circles: Entire strains with

bifurcated and non-bifurcated plants.

20 PNL Volume 16 1984

RESEARCH REPORTS

The penetrance of the two bif-

genes varies from year to year

depending on the climatic

conditions. In the three

genotypes mentioned, a certain

correlation between penetrance and

seed production was observed, the

productivity of the strains

decreasing with decreasing

penetrance (Fig. 1, righthand

part). This, however, did not

hold true for mutant 37B contain-

ing a multiple allele of bif-1.

This allele shows full penetrance,

but the seed production of the

mutant was lower than that of

mutant 1201A (bif-1/bif-l, reduced

penetrance) over 5 generations

(Fig. 2). Mutant 37B evidently

has another mutant gene which

Influences yield negatively but

which has no morphologically

discernible effect.

We have used some bifurcated

genotypes for crosses with other

lines of our collection In order

to combine bif-1 with other mutant

genes. Surprisingly, quite a

number of different genes were

found to influence the penetrance

of bif-1 positively or negatively.

Some examples are given in Fig. 2.

Recombinant R 177 is homozygous

for bif-1 and sg (small seeds,

deriving from the fasciated mutant

489C), the latter gene having a

stabilizing effect on bif-1. As a

consequence, the number of seeds

per plant is higher than In 1201A,

but the seed size is reduced.

Therefore, R 177 was crossed with

mutant 1000 (having larger seeds)

giving rise to recombinant RM 1010

homozygous for bif-1 and a gene

for almost normal seed size. All

the plants of this genotype were

bifurcated. Thus, not only gene

8g of mutant 489C but also a gene

of mutant 1000 had a stabilizing

effect on the penetrance of bif-1

which, however, did not result in

the increased seed production

expected.

Fig. 2.

Seed production of the bifurcated

mutant 37B and the bifurcated re-

combinants R 20D, R 20E, R 177,

RM 1010 with stablized penetrance

of gene bif-1. Right: Recombinant

R 836 with extremely low penetrance

of bif-1. Each dot represents the

mean value for the trait "number

of seeds per plant" for one genera-

tion as related to the control

value of the mother variety

DVG = 100%.

PNL Volume 16 1984

RESEARCH REPORTS

Recombinant R 20D is homozygous for bif-1, efr and a gene for long

internodes. The plants are tall and repeatedly bifurcated. They begin

flowering very early due to the presence of efr but seed ripening is

considerably delayed. The high yield of this genotype is mainly due to

the completely stabilized penetrance of bif-1 in this combination.

Plants of recombinant R 20E likewise were early and repeatedly bifur-

cated, with full penetrance of bif-1, but their internodes were strongly

shortened. This may be the main reason for their relatively low seed

production.

The opposite effect was noted in recombinant R 836, homozygous for

bif-1 and a gene for waxlessness. In this combination, the penetrance

of gene bif-1 was very low, demonstrating thereby a negative influence

of the gene for waxlessness on the penetrance of bif-1.

Correspondingly, the seed yield of this genotype was lower than that of

mutant 1201A and of the initial line. Some mutant genes, which suppress

the action of bif-1 completely or reduce its penetrance markedly, are

under study.



	20 PNL Volume 16 1984	RESEARCH REPORTS

		The penetrance of the two bif- genes varies from year to year depending on the climatic conditions. In the three genotypes mentioned, a certain correlation between penetrance and seed production was observed, the productivity of the strains decreasing with decreasing penetrance (Fig. 1, righthand part). This, however, did not hold true for mutant 37B contain- ing a multiple allele of bif-1. This allele shows full penetrance, but the seed production of the mutant was lower than that of mutant 1201A (bif-1/bif-l, reduced penetrance) over 5 generations (Fig. 2). Mutant 37B evidently has another mutant gene which Influences yield negatively but which has no morphologically discernible effect. We have used some bifurcated genotypes for crosses with other lines of our collection In order to combine bif-1 with other mutant genes. Surprisingly, quite a number of different genes were found to influence the penetrance of bif-1 positively or negatively. Some examples are given in Fig. 2. Recombinant R 177 is homozygous for bif-1 and sg (small seeds, deriving from the fasciated mutant 489C), the latter gene having a stabilizing effect on bif-1. As a consequence, the number of seeds per plant is higher than In 1201A, but the seed size is reduced. Therefore, R 177 was crossed with mutant 1000 (having larger seeds) giving rise to recombinant RM 1010 homozygous for bif-1 and a gene for almost normal seed size. All the plants of this genotype were bifurcated. Thus, not only gene 8g of mutant 489C but also a gene of mutant 1000 had a stabilizing effect on the penetrance of bif-1 which, however, did not result in the increased seed production expected.
	Fig. 2. Seed production of the bifurcated mutant 37B and the bifurcated re- combinants R 20D, R 20E, R 177, RM 1010 with stablized penetrance of gene bif-1. Right: Recombinant R 836 with extremely low penetrance of bif-1. Each dot represents the mean value for the trait "number of seeds per plant" for one genera- tion as related to the control value of the mother variety DVG = 100%.