Linkage relationship of genes curl and His1 is conserved in Pisum sativum and P.fulvum

The genus Pisum comprises only two true species: P. sativum L., including several subspecies, and P.fulvum Sibth. et Smith. The latter species is well adapted to the arid habitat of the Near East and should carry many genes useful for constructing new cultivars of pea. In spite of several chromosome rearrangements that took place during the divergent evolution of both species (1), their hybrids can give a few seeds. Therefore, the transfer of genes between the two Pisum species can be performed quite easily. The problem is how to trace the fate of the segments of the P. fulvum genome in the series of back-crosses to P. sativum. Recently we have undertaken a search for mutations marking the genome of P.fulvum.

500 seeds of P. fulvum (accession VIR6070, received from VIR, St Petersburg) were treated for 24 h with a 0.15% EMS solution. Several dozen mutations (mostly affecting chlorophyll pigmentation) were found in the M₂ generation. One morphological mutant we called curl because it was phenotypically very similar to the mutation curl of P. sativum (3). The interspecific F₁ hybrids of a cross between P. sativum SGE689, curl, (used as female) and the curl mutant of P.fulvum also exhibited a curl phenotype indicating homology of the genes affected.

The gene curl of P. sativum occupies a locus in linkage group V 4 cM from locus His1 encoding the major fraction of the histone H1 proteins (2). Among four P. fulvum accessions available from the VIR, two (namely, VIR2523 and VIR3397) possess the fast variant of the His1 histone fraction whereas two others (VIR6070 and VIR6071) have the slow variant. The alleles encoding these variants are referred to as His1^F and His1^S, respectively. The mutant (curl, His1^S) was crossed with a plant from accession VIR2523 (Curl, His1^F). F_l plants were heterozygous for His1 and had the Curl phenotype, F₂ segregation data (Table 1) confirm that curl is a recessive mutation and indicate fairly strong linkage between the curl and His1 loci (recombination fraction 10.3 ± 3.7%). This result shows that the linkage relationships of these two loci are conserved in the segments of the genomes of both Pisum species.

Table 1. Joint segregation of phenotypes curl and His1 in the F₂ of the cross between P. fulvum lines VIR6070 (curl His1^S) and VIR2523 (Curl His1^F).

Joint segregation c² = 39.72, P<0.0001, Recombination fraction 10.3 ± 3.7%. c² (3:1 for curl) = 0.45 (P>0.7); c² (1:2:1 for His1) = 0.49 (P>0.5).

1. Lamprecht, H. 1961. Agri Hort. Genet. 19:269-296.

2. Rozov, S.M., Temnykh, S.V., Gorel', F.L. and Berdnikov, V.A. 1993. Pisum Genetics
   25:46-51.

3. Sidorova, K.K. and Uzhintzeva, L.P. 1975. Pisum Newsl. 7:56.