Extra-nuclear factors have been reported in peanut (Arachts hypogaea L.) for many traits including growth habit, stipule shape, pod constriction, resistance to leafspot disease, and calcium concentration. However, the role of extra-nuclear factors with the inheritance of many other peanut traits remains to be ascertained. The objective of this study was to determine the inheritance of stem color and non-nodulation, and whether their inheritance is influenced by extra-nuclear factors. The study was conducted on the F₁ and F₂ progenies obtained from a modified diallel design with two A. hypogaea genotypes, Argentine and T2442, and one A. monticola Krap. et Rig. genotype, as parents. Two plant parts (main and lateral stems) were visually classified for stem color (purple, mixed, or green). Plants graded as green-green, mixed-green, or mixed-mixed were grouped as green and all others as purple for genetic analyses. Plants were classified as non-nodulatingif symptoms of N deficiency were observed. Distribution of data for stem color was bimodal, supporting the grouping of data into two phenotypic classes (green and purple). The F₂ generation fit ratios of 1 green: 3 purple, 6 green: 10 purple, 9 green: 7 purple, 11 green: 5 purple, or 15 green: 1 purple depending on the parents. These results indicate that a) stem color may be determined by two sets of genes of which the first one may be responsible for purple pigmentation and the second one for green pigmentation, b) these two gene sets, comprising, respectively, one and two loci for purple and green pigmentations, may have epistatic relationships, c) extra-nuclear factors may function as alleles to nuclear genes responsible for stem color, and d) extra-nuclear factors may induce or modify relationships between traits when they interfere with nuclear genes determining these traits. In the F₂ of crosses with T2442 as one parent and either A. monticola or Argentine as the other, ratios of 57 nodulating: 7 non-nodulatmg plants and 54 nodulating: 10 non-nodulating plants were observed. These results indicate that a) non-nodulation trait may be determined by three independent non-duplicate genes and b) at least two homozygous recessive loci are required in a genotype for non-nodulation. The following genotypes are proposed for the three parents:

A. monticola: Ps1sPs 1gs1gs1 gs2gs2; N3N3 N4N4 N5N5

Argentine: gs1gs1 Gs1Gs1 gs2gs2; N3N3 N4N4 N5N5

T2442: ps1ps1 gs1gs1 Gs2Gs2; n3n3 n4n4 n5n5