Genetical control and linkage relationships of Isozyme markers in sugar beet (B. vulgaris L.). 2. NADP- and NAD-specific malate dehydrogenases, 6-P-gluconate dehydrogenase, shikimate dehydrogenase, diaphorase and aconitase.

The NADP-specific malate dehydrogenase isozymes were controlled by multiple gene systems. Three genes coding for dimeric enzymes segregated in a dependent fashion (NADP-Mdh 1, NADP-Mdh 2, NADP-Mdh 3). A fourth gene (NADP-Mdh 4), also coded for dimers, but was not polymorphic in B. vulgaris. A fifth gene (NADP-Me 1) coded for enzymes active as monomers. Two genes were found to control the main zone of NAD-specific malate dehydrogenase: one coded for dimers (Mdh 1), while a second (Mdh 2) was not polymorphic in the assessions studied. 6-P-Gluconate dehydrogenase was not polymorphic in B. vulgaris; the two types detected on SGE1 electrophoresis were due to developmental expression of the different systems. No genetical segregations could be detected in progeny of crosses of the distinct phenotypes. A shikimate dehydrogenase gene (Skdh 1) that coded for monomers was identified. The diaphorase system was rather complex, but one gene (Dia 1) coding for monomeric enzymes could be identified. Aconitase was found to be controlled by two independent genes (Aco 1, Aco 2), both polymorphic and coding for proteins active as monomers. Tight linkage was found between the genes NADP-Mdh 1, NADP-Mdh 2 and NADP-Mdh 3. Linkage was also found between a pollen fertility restorer (Z) and the Mdh 1 gene. The identification of linkage with Aco 1 needs further investigation. R segregated independently from Mdh 1, Aco 1 and Dia 1. Independent segregations were scored for isozyme genes Pgm 2, Icd 1, Ak 1, Gpi 1, Aco 1 and Dia 1.