Weller, J.L.                                                    Department of Plant Science, University of Tasmania
                                                                        GPO Box 252-55, Hobart, Tasmania 7001, Australia

The phytochromes are a family of photoreceptor proteins which mediate plant responses to light, primarily in the red and far-red regions of the spectrum. Recently identified recessive mutants at the fun1 locus in pea are deficient in the apoprotein of phytochrome A, the predominant phytochrome species found in etiolated tissue (10). fun1 mutants show a pleiotropic phenotype which includes a loss of sensitivity to far-red light for de-etiolation and a reduction in the promotion of flowering by long photoperiods (10). This is in contrast to phytochrome B-deficient lv mutants, which show reduced sensitivity to red but not far-red light, and flower early under short photoperiods (4, 9, 11). The lv locus has been mapped to group VI near wlo (8). It is likely that fun1 and lv mutants carry lesions in the structural genes for PHYA and PHYB, respectively, but this has yet to be proven.

To determine the linkage relationships of the fun1 locus, joint segregation of fun1 with various morphological marker loci was examined in the cross AF140 (fun1-1) ґ HL111 (multi-marker line A875-55-0 from the Marx collection). Mutant line AF140 was derived following EMS mutagenesis of cv. Torsdag (10). Table 1 shows that all individual segregations were in accordance with expectation (P > 0.2). Significant linkage was detected between fun1 and a in linkage group IA and between fun1 and k in linkage group II (Table 1). This evidence is relatively strong (P < 0.0001 for each joint segregation) and thus supports the recent connection of these two linkage groups (7). The present results indicate the following sequence: a...34...fun1...27...k...12...wb. These data imply a distance of about 60 cM between k and a, which suggests that group IA and group II as shown in the 1993 map (6) not only join but may also overlap. Several loci have recently been mapped below a on group IA, including His7 (1), blb (2), waxy1 (3) and Enod2 (5). The most distant of these loci, blb, is approximately 34 cM below a (2, I.C. Murfet, pers. comm.), and the present results thus predict blb and fun to be linked within about 5 cM. Further examination of linkage relationships will also be required to determine the positions of group II loci Fum and Dia3 relative to fun1, blb, Enod2 and group IA loci His7, lf and a.

Table 1. F₂ segregation data for fun1 and linkage group IA/II markers obtained from cross AF140 (fun1-1 a Wb K) ґ HL111 (Fun1 A wb k).

¹ D, dominant; R, recessive. The first-named locus is listed first.

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