28                        PNL Volume 20                     1988 RESEARCH REPORTS
Murfet, I. C.                                                  Botany Dept., University of Tasmania
Hobart, Tasmania 7001, Australia
While examining the effect of extended daylength on internode length in Pisum lines considerable variation in response was noted among dwarf lines. In particular, the dwarf lines 53 (le La crys) and 85 (le La cryc) , which had much the same internode length in 8 h short days (daylight), differed markedly in their response to an extended daylength regime consisting of 8 h daylight plus 16 h of incandescent light (3 mkmol m-2 s-1 at pot top). Line 85 was highly responsive with some in-ternodes increasing in length five-fold. The internodes of line 53 were also substantially longer in the 24 h regime but in contrast the maximum response was only a little more than half that shown by line 85. The res­ponse of the (53 x 85) F1 was intermediate between that of the two pa­rents but much closer to the line 53 habit. The F2 segregated cleanly in 24 h conditions into 3 line 53-type (short internodes, low response): 1 line 85-type (long internodes, high response). The minority class bred true in F3. Six pure breeding short selections and 15 long selections, each derived from a different F2 plant, were crossed to line 8 (le la cryc) and one 48 seed F2 progeny raised from each cross. The short selections always contributed an le La cry3 gamete and the long selections an Le La cryc gamete. These results indicate the short internode, low response/long internode, high response difference is asso­ciated with the crys/cryc genetic difference. A night break failed to trigger an increase in internode length in either line 53 or line 85 so the effect is not a true photoperiod response.
In summary, on an le La background plants with genotype crys showed a lower response to a daylength extension with incandescent light than cryc plants, allele crys was dominant to allele cryc, and crys segregates were clearly shorter than crys/cryc segregates in 24 h conditions (i.e. segregation was discrete). In 8 h conditions segregation for the crys/cryc pair was obscured but progenv tests indicated that crys segregates were, on average, marginally shorter than cryc segregates. These results contrast with the situation on a le la background where allele cryc is dominant to crys and le-la crys plants (slender) are longer than le la cryc plants (cryptodwarf) (1,2,4). The effect of the crys/cryc difference on an le la background was also examined using a segregating progeny. The crys segregates were again less responsive to extended daylength than cryc segregates in both relative and absolute terms. Thus the cryptodwarf-/slender difference was clearest in the 8 h conditions although segrega­tion was discrete in either 8 h or 24 h conditions. Based on data for lines representing several other internode length genotypes the microcryp-todwarf/cryptodwarf and tall/dwarf differences were also more clearly evi­dent in 8 h than 24 h conditions. In contrast, the very short internode nana types, e.g. na (6) or ls (5), were more readily distinguised from short dwarf (le) lines in 24 h conditions since the nana lines were less responsive to extended daylength. Detailed results of this study will be presented elsewhere (3).
PNL Volume 20                     1988 RESEARCH REPORTS                    29
1.   De Hann, H. 1927. Genetica 9:481-497.
2.   Lamm, R. 1937. Hereditas 23:38-48.
3.   Murfet, I. C. 1988. Ann. Bot. (in press).
4.   Rasmusson, J. 1927. Hereditas 10:1-150.
5.   Reid, J. B. 1986. Ann. Bot. 57:577-592.
6.   Wellensiek, S. J. 1971. PNL 3:46.