Inheritance of Three Groups of Indole Alkaloids in Reed Canarygrass

Certain tryptamine alkaloids and their derivatives appear to cause the severe diarrhea seen in sheep and sometimes in cattle that graze reed canarygrass, Phalaris arundinacea L. This malady is either absent or less prevalent in animals that graze trytamine-carboline-free, gramine-containing clones. Our objectives were to study the mode of inheritance and genetic relationships among indole alkaloid phenotypes in this species. We characterized three groups based on chemical structure and occurrence in breeding materials of seven of the nine known indole alkaloids. Group G consisted of gram. ine; group T included N-methyltryptamine (NMT), N,Ndimethyltryptamine (DMT), and 2-methyl-l,2,~,4~tetrahydro-β- carboline (MTHC); and group MeO included 5-methoxy-N-methyltryptamine (5-MeO-NMT), 5-methoxy- N,N-dimethyltryptamine (5-MeO-DMT) and 2-methyl- 6-methoxy-l,2,3,4-tetrahydro β-carboline (6-MeO.THC). A genetic model was proposed on the basis of data obtained from progeny analysis following self-pollination and hybridization within and between alkaloid groups. The model was tested by analyzing F₁ and F₂ families from separate crosses between groups G and T, within group G, and testcrosses to group G of selected F₁ plants. The results verified a two-gene model in which a single dominant allele T at one locus controls synthesis of alkaloids for phenotypes in group T and a single dominant allele M at a second locus controls synthesis of alkaloids for phenotypes in group MeO. Phenotypes in group G are produced only when both recessive alleles m and t are homozygous. The M allele is epistatic to T and the two loci appear to be closely linked. Unidentified modifying factors appear to affect this interpretation in certain genetic backgrounds, and require further studies to ascertain their mode of inheritance. Alleles M and T had frequencies of 0.21 and 0.01, respectively, in the diverse reed canarygrass source, NCRCI. The fact that gramine is synthesized only in the presence of the double recessive will enable plant breeders to select directly for this type without progeny testing to verify the genotype.