Section Arachis is the largest of nine sections in the genus Arachis and includes domesticated peanut, A. hypogaea L. Most species are diploids (x = 10) with two tetraploids and a few aneuploids. Three genome types have been recognized in this section (A, B and D), but the genomes are not well characterized and relationships of several newly described species are uncertain. To clarify genomic relationships in section Arachis, cytogenetic information and molecular data from amplified fragment length polymorphism (AFLP) and the trnT-F plastid region were used to provide an additional insight into genome composition and species relationships. Cytogenetic information supports earlier observations on genome types of A. cruziana, A. herzogii, A. kempff-mercadoi and A. kuhlmannii but was inconclusive about the genome composition of A. benensis, A. hoehnei, A. ipaensis, A. palustris, A. praecox and A. williamsii. An AFLP dendrogram resolved species into four major clusters and showed A. hypogaea grouping closely with A. ipaensis and A. williamsii. Sequence data of the trnT-F region provided genome-specific information and showed for the first time that the B and D genomes are more closely related to each other than to the A genome. Integration of information from cytogenetics and biparentally and maternally inherited genomic regions show promise in understanding genome types and relationships in Arachis.

Cultivated peanut, Arachis hypogaea L., is a tetraploid (2n = 4x = 40) species thought to be of allopolyploid origin. Its closest relatives are the diploid (2n = 2x = 20) annual and perennial species included with it in Arachis sect. Arachis. Species in section Arachis represent an important source of novel alleles for improvement of cultivated peanut. A better understanding of the level of speciation and taxonomic relationships between taxa within section Arachis is a prerequisite to the effective use of this secondary gene pool in peanut breeding programs. The AFLP technique was used to determine intra- and interspecific relationships among and within 108 accessions of 26 species of this section. A total of 1328 fragments were generated with 8 primer combinations. From those, 239 bands ranging in size from 65 to 760 bp were scored as binary data. Genetic distances among accessions ranged from 0 to 0.50. Average distances among diploid species (0.30) were much higher than that detected between tetraploid species (0.05). Cluster analysis using different methods and principal component analysis were performed. The resulting grouping of accessions and species supports previous taxonomic classifications and genome designations. Based on genetic distances and cluster analysis, A-genome accessions KG 30029 (Arachis helodes) and KSSc 36009 (Arachis simpsonii) and B-genome accession KGBSPSc 30076 (A. ipaensis) were the most closely related to both Arachis hypogaea and Arachis monticola. This finding suggests their involvement in the evolution of the tetraploid peanut species.

on the derivation and existence of this material is fragmentary (Ternovsky, 1941(Ternovsky, , 1945Goodspeed, 1942; Kos-Tobacco mosaic virus (TMV)-resistant flue-cured tobacco (Nicotitoff and Georgieva, 1944; Kostoff, 1948; Valleau, 1952; ana tabacum L.) cultivars have been developed using the N gene Oka, 1961). derived from N. glutinosa L. Their adoption has been low, however, because of unfavorable linkage drag effects. Strategies to overcome It was later demonstrated that recombination could this problem might include pursuit of alternative introgression events occur between chromosome H and the N-carrying chroand/or use of molecular markers for selection against deleterious alien mosome in Holmes Samsoun (Gerstel and Burk, 1960), chromatin. Previous workers demonstrated the presence of a TMVand this line is believed to have been the ultimate source resistance mechanism on more than one chromosome of the tobacco of TMV resistance used in all tobacco breeding in the genome. The objectives of this research were to determine the relative USA (Valleau, 1952; Wernsman, 1992). High yielding genomic positions of TMV resistance loci in a set of 12 TMV-resistant cultivars of burley tobacco with N-mediated resistance tobacco accessions and to use amplified fragment length polymorhave been developed and accepted by growers. TMVphism (AFLP) markers for characterization of this material with reresistant flue-cured cultivars have also been developed. spect to linked alien chromatin. Five accessions were found to carry These have not been widely grown, however, because a TMV resistance gene on chromosome H. Seven accessions were found to carry a resistance factor on an alternative chromosome. of decreased yield and quality associated with the resis-Polymerase chain reaction results indicated that the N gene from N.tance. Available data suggest that these negative associglutinosa is responsible for resistance in all 12 accessions. A set of ations are due to linkage drag effects rather than pleiot-168 AFLP markers specific to the N. glutinosa donor chromosome

mentally sustainable method for controlling blue mold. Naturally occurring resistance within N. tabacum is gen-Blue mold, caused by the fungal pathogen Peronospora tabacina erally very low, however (Rufty, 1989). Resistance can D.B. Adam, is one of the most important foliar diseases of tobacco (Nicotiana tabacum L.). Identification of molecular markers linked be found within several Nicotiana species of Australian to genetic factors controlling resistance would facilitate development origin where blue mold is endemic and has reportedly of resistant cultivars. Bulked segregant analysis was used to screen been introgressed into cultivated tobacco from N. deb-1216 random amplified polymorphic DNA (RAPD) primers for theirneyi Lea, 1963), N. ability to reveal polymorphism between DNA bulks from susceptible goodspeedii Wheeler (Wark, 1963(Wark, , 1970, and N. veludoubled haploid (DH) lines and resistant DH lines possessing resistina Wheeler (Wark, 1963(Wark, , 1970. Resistance induced tance derived from cultivar Ovens 62. Fifteen RAPD markers were by treatment of flue-cured cultivar Virginia Gold with tentatively identified as being linked to a major gene conditioning the mutagen triethylene iminotrazine has also been reresistance to blue mold. These 15 markers (12 in coupling phase ported (Marani et al., 1972). Few resistant cultivars are linkage with resistance and three in repulsion phase) were found to available to growers worldwide, however (Shoemaker,

Germplasm from closely related diploid relatives of tobacco (Nicotiana tabacum L.) could be of value for continued genetic modification of this species and for mapping quantitative trait loci (QTLs). We examined near isogenic tobacco lines and hybrids differing for an introgressed genomic region from N. tomentosa Ruiz and Pavon designated as Many Leaves that exhibits a large influence on leaf number and correlated traits. Within a 'Red Russian' genetic background, the region acted in an additive to partially dominant fashion to delay flowering time, and increase leaf number, plant height, and green leaf yield. Evidence of epistasis was observed as the region affected these traits to varying degrees in diverse near isogenic hybrids. Fifteen amplified fragment length polymorphism (AFLP) markers of N. tomentosa origin were mapped within a single linkage group of 34.5 cM using a population of 207 BC(1)F(1) individuals segregating for Many Leaves. Composite interval mapping produced 2-LOD confidence intervals for likely QTL positions influencing leaf number (3.1 cM region), plant height (2.9 cM region), and days to flowering (3.3 cM region). These intervals were overlapping. Results demonstrate that genomic regions with large genetic effects can be transferred to tobacco from closely related diploid relatives, and that sufficient recombination within these regions may permit mapping of genes controlling quantitative traits. Materials and results described here may be useful in future research to gain insight on the genetic control of the transition from vegetative to reproductive development in Nicotiana.