THE LIKELY FLOWERING GENOTYPE FOR SEVERAL CULTIVARS AND MUTANTS

4 0 RESEARCH REPORTS

PNL Volume 13

1981

Murfet, I. C.

Botany Department, University of Tasmania, Hobart, Australia

Table 1 shows the likely flowering genotype, in terms of the four loci

lf, e, sn, and hr (5), for seven commercial cultivars which have recently

been used in this laboratory for various purposes. Some estimates are based

purely on phenotypic behavior and others also make use of the results of

crosses.

Useful estimates of the flowering genotype can often be made from quite

a small quantity of information. For example, 'Austrian Winter' flowered

at node 24 in an 18h photoperiod and in excess of node 70 in an 8h photoperiod

(temperature: night 17°C/day 23-27°C). The high flowering node in long days

indicates the presence of Lf^d and the very large response to photoperiod

indicates combination Sn Hr. 'Early Dun' also flowered at node 24 in an 18h

photoperiod and Lf^d is again indicated. However, the photoperiod response

of 18 nodes does not clearly indicate either Sn hr or Sn Hr and further

analysis would be required to resolve the genotype. [Berry and Aitken (1)

have estimated a genotype of Lf^d Sp_ Hr for the related cultivar 'Dun'.] 'Rondo

showed a 10 node response to photoperiod clearly indicating a genotype of

Sn hr. However, the flowering node of 16 in a 24h photoperiod is consistent

with either Lf or lf and further tests would be necessary to differentiate

the alternatives. 'Puke' and 'Frosty' also showed a limited, quantitative

response to photoperiod consistent with genotype Sp hr and in these varieties

tests using continuous light from the start of germination give a minimum

flowering node of 10 (lowest scale leaf counted as node 1) indicating genotype

lf (4,5). Puke and Frosty both gave a bimodal distribution of flowering node

under short days¹, segregating into two phenotypes EI and L (2). This behavior

is not necessarily indicative of heterogeneity since it can occur in genotype

If e Sn hr as a result of variable penetrance of gene Sn in terms of flowering

node [see Hobart line 61a (3,4)]. However, the unlikely possibility that

Puke and Frosty are heterogeneous for the E/e pair of alleles should not be

discounted.

PNL Volume 13 1981

RESEARCH REPORTS

A 1

'Progress no. 9' and 'Laxton's Superb', unlike the other varieties, showed

no response to photoperiod. They therefore carry sn. The cross Progress no. 9

x Hobart line 53 (If e Sn hr) gave an with a phenotype like Hobart line

60 (lf E Sn hr). The genotype of Progress no. 9 is therefore lf E sn hr.

The F1's of Laxtons Superb x Puke and Laxtons Superb x Frosty were late like

line 53. Laxtons Superb therefore appears to be lf e sn hr.

The reports by Sidorova et al (6,7) of certain induced flowering mutants

are of interest for at least two reasons. Firstly, one of the mutants appears

to be at the sn locus and all mutants so far tested (5) against the four locus

system have proved to be at the lf locus. Secondly, the reports provide data

on many characters including response to photoperiod, time to maturity, seed

yield, etc., and this allows an estimate to be made of the genotypes. Un-

fortunately, there is some uncertainty over the scoring system used and for

the purpose of this estimation I have assumed that nodes were counted from

the second scale leaf as one and that "flowering node" means node of first

open flower in this case (i.e. abortive flower initials were not counted as

flowers). Using these assumptions the mutation giving rise to 218 is almost

certainly of the type, or equivalent to, Sn to sn. This step is consistent

with the lower flowering node, earlier onset of flowering, reduced time from

the beginning to the end of flowering and from sowing to maturity, reduced

yield, and loss of sensitivity to photoperiod (2). Mutants 2 and 319 are

consistent with mutations from Lf_ to lf^a and Lf to lf respectively. Note

these mutations promoted the onset of flowering but time to maturity was

brought forward only marginally in mutant 2 and actually delayed in mutant

319, the yield was not reduced, and there was no loss of photoperiod response.

As a tentative hypothesis we may estimate the genotype of the initial variety

•Torsdag' as Lf E Sn hr, mutant 2 as lf^a E Sn hr, mutant 319 as lf E Sn hr,

and mutant 218 as Lf E sn hr. These estimates are also consistent with

the findings of Sidorova et al., that all three mutants are recessive, that

mutant 218 is not allelic with 2 and 319, and that 2 and 319 are allelic but

not identical.

Persons who would like us to estimate flowering genotypes for particular

varieties are invited to send samples to me (about 20 seeds per variety) care

of Chief Quarantine Officer (Plants), Dept. of Agriculture, P.O. Box 192B,

Hobart, Tasmania, 7001, Australia.

We would also like to receive seed of any flowering mutants (and their

initial lines) if and when they become available for release.

1. Berry, G. J. and Y. Aitken. 1979. Aust. J. Plant Physiol. 6:573-87.

2. Murfet, I. C. 1971. Heredity 26:243-57.

3. Murfet, I. C. 1973. Aust. J. Biol. Sci. 26:669-73.

4. Murfet, I. C. 1977. pp. 385-430 in The Physiology of the Garden Pea.

(Eds. J. F. Sutcliffe and J. S. Pate. Academic Press, London).

5. Murfet, I. C. 1978. PNL 10:48-52.

6. Sidorova, K. K., V. V. Khvostova, and L. P. Uzhintzeva. 1974. PNL (>:47.

7. Sidorova, K. K:, and L. P. Uzhintzeva. 1977. PNL 9:51.