PNL Volume 18

1986

RESEARCH REPORTS

BRANCHING IN PISUM: EFFECT OF THE FLOWERING AND LENGTH GENES

Floyd, R. S. and I. C. Murfet

University of Tasmania

Hobart, Tasmania, Australia

Several flowering genes are reported to influence branching in peas,

Photoperiodic lines have a much greater tendency to produce basal laterals

than day neutral lines (1) and this holds whether they initiate flowers at

a high or low node. The ability to respond to photoperiod is conferred by

genotype Sn Dne (2) and the effect of this gene combination on both flower-

ing and branching is further increased by gene jir (3,10). Compared with

Sn Dne stocks, day neutral Pisum stocks of genotype sn Dne or Sn dne reduce

outgrowth of basal laterals from photoperiodic Lathyrus odoratus scions

(11). The Sn Dne combination also delays the appearance of aerial laterals

from the upper nodes in veg plants (8). It is suggested the Sn Dne system

may achieve these effects by producing in short days a graf t-transmissible

substance whose primary role is to direct assimilate flow (4,8,11).

contrast, flowering genes Lf-d and veg have a less basic effect. Both

result in increased production of aerial laterals (6,8). By delaying (Lf-d)

or preventing (veg) flower initiation they increase the number of potential

sites for lateral outgrowth and the underlying changes which take place

during this delay result in lateral outgrowth. In lf sn segregates seed

yield was found to be derived wholly from pods borne on the main shoot

while in the latest Lf-d sn segregates yield was derived partially or wholly

from pods on lateral branches (6).

PNL Volume 18 198b RESEARCH REPORTS

The genes Le/le, La/la, Cry/cry-c /cry-s and Na/na determine several

internode length classes ranging in size from the extremely short nana type

through dwarf, cryptodwarf , tall and slender (reviewed 9). The present study

was designed primarily to examine the effect of these length genes on

branching by the use of segregating progenies and near iso-lines. However,

some additional data on the effect of flowering genes is also presented.

Several other length loci have been established including lk and ls (7).

Gene lk results in the erectoides phenotype characterized by short Inter-

nodes, thick brittle stems, and other features including increased apical

dominance while gene ls results in a nana phenotype (7). A nana line

carrying ls (line K202) was included in this study but it should be noted

that K202 also differs from its initial line 'Torsdag' in respect of a

second unnamed length mutation (7).

All plants were grown in the phytotron, one plant per 14 cm pot, in a

1:1 mixture of vermiculite and dolerite chips. Nutrient solution

(Hoaglands) was applied once a week. Temperatures were approximately 20-

26C day and 17C night. The short day (SD) photoperiod consisted of 8h of

natural light. A long day (LD) photoperiod of 24h was obtained by use of

the natural day extended by light from a mixed fluorescent/incandescent

source giving approximately 10 Wm at pot top.

Effect of flowering genes. All photoperiodic (Sn Dne) lines studied

produced more basal laterals in SD than LD. In many such lines a 24h

photoperiod completely suppressed outgrowth of basal laterals, e.g. in

Torsdag (Table 1) or WL1770 (Table 2). Other photoperiodic lines with a

very strong tendency to form basal laterals in SD also produced some basal-

laterals in a 24h photoperiod, e.g. WL 1766 (Table 2). SD also caused a

marked upward shift in the zone of aerial laterals in Torsdag (Table 1).

We attribute this upward shift and increased basal lateral production in SD

to activity of the Sn Dne system. In continuous light, activity of this

system is suppressed (5). Again in K218 (Sn dne) a day neutral isoline to

Torsdag (see 2), activity of the system is largely blocked by dne (2) and

basal lateral production did not occur in 8h or 24h conditions. K218 also

was devoid of significant aerial laterals.

Segregation for the flowering gene pair E/e in cross (8xI₃) F2 in SD

gave 15 tall early photoperiodic (E) and 6 tall late photoperiodic (e)

segregates with mean flowering nodes of 13.9 and 23.8, respectively. The

late plants produced over ten times as many aerial laterals as the early

plants (Table 2). Thus the greater potential for aerial lateral production

in plants with a high flowering node can be realized, at least partially,

and gene e, in these specific circumstances, achieves an end effect on

aerial branching similar to Lf (6) or veg (8). The underlying mechanism

is of course quite different.

Effect of the length genes. From a comparison of the pairs

slender/dwarf, tall/dwarf, cryptodwarf/dwarf, tall/nana, and dwarf/nana

(Table 2) it is clear that the shorter internode type generally displays

the stronger tendency to produce basal laterals. The tendency was so

strong in the na nana types that they often bore basal laterals on basal

laterals while the first order laterals on average exceeded the main shoot

in total length. The one marked exception to the general pattern concerns

the nana line K202 which displays a much lower tendency to produce basal

laterals than its tall initial line Torsdag, although their lengths dif-

fered by a factor of 9. The lack of branching in K202 cannot be attributed

PNL Volume 18 1986 RESEARCH REPORTS

to poor growth since vigor in K202 was comparable with that of na nana

lines or to gene ls alone since a second length mutation is also present in

K202 (see 7). Moreover, the _ls type line, M26 (nana habit), shows profuse

basal branching (J. B. Reid, personal communication) in accord with the

pattern established for the na_ nana plants (Table 2).

No general trend was apparent for the effect of the length differences

on aerial laterals except for the paucity of such laterals in nana types

(Table 2).

We suggest that the length genes may influence branching in Pisum by

altering the level of available nutrients. One thing is certain, the

flowering and length genes have major effects on branching and the back-

ground for these genes and environmental factors such as photoperiod should

be taken into account in any study of branching per se although some genes

with specific effects on branching may be expressed regardless of these

factors.

1. Doroshenko, A. V. and V. [. Rasumov. 1929. Tr. Prikl. Bot. Oenet.

Sel. 22 :2 19-2 76.

2. King, W. M. and I. C. Murfet. 1985. Ann. Bot. 56:815-846.

3. Murfet, I. 1973. Heredity 31:157-164.

4. Murfet, I. 1985. Pp. 97-126 in Handbook of Flowering, Vol. IV. Ed.

A. H. Halevy, CRC Press.

5. Murfet, T. C. and J. B. Reid. 1974. Z. Pflanzenohysio1. 71:323-331.

6. Murfet, I. C. and J. B. Reid. 1985. pp. 67-80 in The Pea Crop: A

Basis for Improvement. Eds. P. D. Hebblethwaite, M. C. Heath, and T.

C. K. Dawki n s, Butter wo r t h s.

7. Reid, J. B. 1986. Ann. Bot. (in press).

8. Reid, J. B. and I. C. Murfet. 1984. Ann. Bot. 53:369-382.

9. Reid, J. B., 1. C. Murfet, and W. C. Potts. 1983. J. Exp. Bot.

34:349-364.

10. Ross, J. J. 1983. PhD Thesis, Univ. of Tasmania.

11. Ross, J. J, and 1. C. Murfet. 1985. Ann. Bot. 56:847-856.