AN ASSOCIATION BETWEEN THE PRESENCE OR ABSENCE OF BASAL STEM ANTHOCYANIN AND ALLELES AT THE D LOCUS IN PISUM

RESEARCH REPORTS PNL Volume 11 1979

AN ASSOCIATION BETWEEN THE PRESENCE OR ABSENCE OF BASAL STEM ANTHOCYANIN

AND ALLELES AT THE D LOCUS IN PISUM

Marx, G. A. New York State Agricultural Experiment Station, Geneva, NY U.S.A

and C. Nozzolillo University of Ottawa, Canada

The preceding article provides background information about PI 356980

in relation to its use in studies of basal stem anthocyanin. Although this

accession was found to contain plants with, and plants without, basal stem

anthocyanin (PNL 9:42-45, 1977; PNL 10:63, 1978; PNL 10:64-65, 1978), any

conclusions drawn from studies of this accession are bound to be ambiguous

until the genetic situation is clarified. Accordingly, reciprocal crosses

were made at Geneva using plants of four sublines of PI 356980 provided by

C. Nozzolillo and designated by her as 2-4, 2-8, 5-18, and 10-5. Sublines

2-4 and 2-8 were lines with, whereas 5-18 and 10-5 were lines without, basal

stem anthocyanin. The field-grown F1 plants from these crosses produced

some 3500 seeds, approximately 1400 of which were retained in Geneva and

2200 of which were forwarded to Ottawa (where not all have been analyzed).

When remnant selfed seeds from plants of these four second-generation

(G2) lines were planted, line 2-4 was found to produce plants with and plants

without basal anthocyanin whereas 2-8 produced plants exclusively with and

5-18 and 10-5 produced plants exclusively without basal anthocyanin. Since

the seeds in each instance derived from individual selfed plants, line 2-1

was clearly heterozygous for a gene(s) controlling the presence or absence

of basal stem anthocyanin. Significantly, moreover, the plants of this line

which showed red stems also expressed the "w" allele at D locus whereas the

plants without basal anthocyanin (green stems) manifested the "co" allele

at the same locus. Although the field-grown Fi plants from the crosses

involving 2-4 (D^w) and the other sublines (all D^co) were not scored for basal

anthocyanin, they were scored for D^w and D^co. Eighteen were classified as

D^w and 11 as D^co, clearly showing that at least some of 2-4 plants used as

parents were heterozygous D^w/D^co (D^w is known to be dominant to D^co).

In the F2 of crosses involving 2-4 plants as one parent, progenies

from the 11 F1 plants which were D^co were exclusively green-stemmed (Table 1)

In contrast, the 18 F1 plants scored as D^w produced progenies segregating

both for D^w - D^co and for the red and green stem. In these populations

all 722 (151 at Geneva and 371 at Ottawa) of the F₂ plants with D^w exhibited

basal stem anthocyanin whereas all 243 (117 at Geneva, 126 at Ottawa) of

the F2 plants with D^co were without stem anthocyanin. Scoring was easy

and clear except for two plants which showed so little pigment as to be

questionable. Progeny tests of these two plants showed them to be heterozy-

gous for D^w/D^co, the D^w segregants being unmistakably red stemmed, and the

D^co segregants being green stemmed. Thus, without exception, the D^w allele

in this line was found to be associated with red stems whereas the D^co

allele was associated with green stems. The combined total of 965 plants

(468 observed at Geneva and 497 at Ottawa) is large enough to suggest pleio-

tropy rather than tight linkage but even more plants would be desired.

Bearing on the question of linkage vs pleiotropy are observations of

subline 2-8 and progeny from crosses with it. This subline, like 2-4,

shows basal stem anthocyanin but, unlike 2-4, it is D^co rather than D^w.

F2's of crosses between 2-8 and either 5-18 or 10-5 (both green stemmed)

PNL Volume 1 1979

RESEARCH REPORTS

showed a clear 3:1 ratio of red vs green stems but without segregation for

alleles at the D locus since all are D^co. Obviously, therefore, red stems

can occur in association with D^co, suggesting that the association found

in subline 2-4 may be an expression of linkage rather than pleiotropy.

But this cannot yet be accepted as fact since it is also possible that the

basal anthocyanin in sublines 2-4 and 2-8 is determined by entirely different

genes.

The cross 2-8 and 2-4 is especially noteworthy in light of the fact that

both lines have red stems but 2-8 is D^co and 2-4 is D^w. Since, however, the

F1 was D^co and the F₂ showed a 3 red : 1 green ratio without segregation for

"w" or "co" at the D locus, we can only conclude that the 2-4 parental plant

was heterozygous and that in the only F1 seed obtained, we were unlucky enough

to draw the gamete containing D^co (and also green stem). Thus, this cross

bears repeating.

These results confirm and expand the findings presented in the previous

article by showing that at least one type of stem pigmentation is under

monogenic control and by showing a close association between basal stem

pigmentation and the "w" allele of the D locus. It would appear, therefore,

that a concrete beginning has been made with respect to the genetic control

of stem pigmentation in peas. The type of expression reported here is clear

in the seedling stems immediately upon emergence from the growing medium;

later the pigmentation tends to fade. It is recognized that this may be

only a small part of a larger story since different types and expressions

of stem pigmentation have been encountered by us and by others.