Ser appears to be the serrate leaflet locus
mapped on linkage group III
Weeden, N.F. Dept. of Plant Sci. and Plant Path.
Montana State Univ., Bozeman, MT USA
Ambrose, M.J. John Innes Centre, Norwich, UK
Lamprecht (3) identified three types of leaflet serration present in the Pisum germplasm: 1) scalaris forma, or ‘step-form’ 2) serratus, or saw-form and 3) incisus or deeply cut. These types are believed to be controlled by three distinct loci: Td, Ser and Inci, respectively (3, 9). The JIC pgene collection website (www.jjc.bbsrc.ac.uk/cgi-bin/germplas/geneID) lists the type lines for these genes as follows: Ser: JI 2781 (= WL 1414), Td: JI 2679 (= WL 6) and Inci: WL 1292 or Wt 16 155. According to Lamprecht (3), Td is normally found in European germplasm, whereas Ser is typical of P. sativum ssp. abyssinicum and a line from Afghanistan (WL 1414) and Inci is limited to lines from south Israel. Lamprecht (2) found that Td displayed linkage with Fa and assigned it to the N-Z-Fa group now forming the upper portion of LG IV (10). However, several other investigators have reported linkage between Td and markers on LG III (4, 5, 6), and Marx (5) questioned which linkage group actually contained Td. We believe that Ser is located on LG III, and that further studies are necessary to determine where Td is located.
The confusion appears to have developed when Marx reported linkage between the serrate leaflet phenotype, which he believed to be produced by Td, and the LG III marker b (5). Marx used line A 886-193 as his source of Td, a line for which the serrate leaflet phenotype could be traced back to a “Pisum abyssinicum” line obtained from Dr. K. Dobbs (5). Grajal-Martin and Muehlbauer (1) used a related Marx line (A778-26-6) to map Td to LG III near Lap1. Polans (5) further established the linkage between serrate leaflets and markers in the middle of LG III using two lines (Marx’ A 778-26-6 and Weeden’s 82-14n). The line 82-14n is actually a sample of PI 268480, a P. sativum ssp. sativum line from Afghanistan. Smirnova (6) reported linkage between weakly serrate leaflets (lines WIR 4907 and WIR 319) and Le, another LG III marker. Finally, Lorenzi et al. (3) found that the serrate leaflet gene in P. s. ssp. abyssinicum was tightly linked to Cipor, a DNA marker approximately midway between Lap1 and Le.
Except for Smirnova (6), all the ‘Td’ lines used in the above studies were either P. sativum ssp. abyssinicum (4), derived from this source (A 886-193 and A 778-26-6) or from a line from Afghanistan (6). According to Lamprecht (3), all these lines possess Ser rather than Td. In order to test this possibility, allelism was examined between the serrate leaflet phenotype in WL 1414 (type line for Ser) and a line carrying the serrate leaflet phenotype derived from P. sativum ssp. abyssinicum. All of the approximately 100 F2 plants examined exhibited the serrate phenotype (N.F. Weeden, unpublished), confirming that the two genes were allelic or controlled by very closely linked loci.
At present we are unable to distinguish between the “allelic” and “closely linked” alternatives because the third gene discussed by Lamprecht, Inci, appears to map very near Ser. Lorenzi et al. (4) indicated that their “Td” (now known to be Ser) mapped to LG III between Lap1 and Np. Święcicki (9) also found linkage between b and the serrate leaflet phenotype in line Wt 702, although he was uncertain of the gene involved, referring to it tentatively as “Inci” based on its phenotype. Subsequently, Smirnova (8) mapped Inci in WIR 2521 to LG III between B and Np. Although the linkage value between B and Np was smaller than expected, the position assigned for Inci was indistinguishable from the position Lorenzi et al. (4) assigned to Ser. An allelism test is clearly required between Inci and Ser, for these two may represent the same locus.
We suggest that the gene that has been mapped in most of the above studies is Ser, and that the consensus map be changed to reflect this conclusion. The position of Td is uncertain, although Lamprecht’s data placing it on LG IV remains the most relevant. The sample of WL 6 that we had available did not exhibit strongly serrate margins, and we were not able to confirm a LG IV location.
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