Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F1 tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.

An F2 population (Allium fistulosum x A. cepa) of 20plants, 10 BC1,[(A. fistulosum x A. cepa) x A. cepa], and 50 BC2 plants, [(A. fistulosum x A. cepa) x A. cepa] x A. cepa were studied cytogenetically and characterized for four isozyme alleles plus various morphological characteristics. All of the progenies were in A. fistulosum (the bunching onion) cytoplasm. In the F2 population we observed non-random chromosomal and allelic segregation, suppression of bulb onion allelic expression, and abnormalities in mitosis and meiosis. Most BC2 plants resembled A. cepa (the bulbing onion) morphologically, but anthers, filaments, pistils, and petals were abnormal. Only 3 plants, and these were most nearly like the F1 hybrid morphologically, produced any seeds.The data and observations support the hypothesis of nuclear-cytoplasmic incompatibility interactions between the bunching and bulb onion species.

Some interspecific hybrids between geographically separated diploid taxa of Grindelia have meiotic configurations which indicate interchange heterozygosity, while others do not. Hybrids between G. procera Greene, G. hallii Steyermark, and G. camporum var. davyi (Jepson) Steyer‐mark (all from California) have 6II***, as do those between G. oxylepis var. eligulata Steyermark (Mexico) and G. squarrosa (Pursh) Dunal (Utah and New Mexico). When G. procera, G. camporum var. davyi, and G. hallii are crossed to G. oxylepis var. eligulata the hybrids have 4II and 1IV as do hybrids between G. oxylepis var. eligulata and G. havardii Steyermark (New Mexico). The G. procera × G. havardii and G. camporum var. davyi × G. havardii hybrids had a maximum configuration of 2II and 2IV, which indicates the interchanges in the genomes of the California diploids and G. havardii do not involve the same chromosomes. Hypothetical chromosome end arrangements and names for the respective genomes, based on G. oxylepis as a standard, are presented. These data corroborate a previously published phylogenetic scheme of the genus based on morphological, ecological, and distributional studies.

Previous studies of chromosome relationships of Grindelia species recognized three basic genomes designated Oxylepis, Hallii, and Havardii. Differences are based on different end arrangements of the chromosomes resulting from reciprocal translocations. This report will review and give additional information about the genomes and interrelationships of 17 species. All of the species are diploids (2n = 12) and show six bivalents at meiosis. Species in this study that have the Oxylepis genome are G. oxylepis var. eligulata, G. fastigiata, G. inornata, G. revoluta, and G. squarrosa. Species that have the Havardii genome included G. havardii, G. grandiflora, G. lanceolata, G. littoralis, and G. texana. The Hallii genome is present in G. camporum var. davyi and G. procera. Hybrids of species with the same genome have six bivalents at meiosis. Hybrids between species with the Oxylepis genome and those having the Havardii genome have four bivalents and one quadrivalent at meiosis. Likewise for Oxylepis x Hallii hybrids. A new genome is presented for G. subalpina which would explain the configurations of two bivalents and two quadrivalents observed in G. subalpina x G. havardii and G. subalpina x G. fastigiata hybrids. This is designated the Subalpina genome. Species tested but with genomes as yet undetermined are G. acutifolia, G. arizonica, G. nana, and G. scabra.

Mitotic and meiotic studies were performed on Allium fistulosum, A. cepa, their F1 hybrid, and ten selected backcross (BC)1 plants [(A. fistulosum x A. cepa) x (A. cepa)]. Each BC1 plant had at least one A. cepa isozyme allele (Pgi, Idh, or Adh). Chromosome morphology and behavior differed among plants. Meiocytes were observed with one, two, or three bridges and/ or fragments, indicating at least three paracentric inversions between A. fistulosum and A. cepa. Unusual crossing over and multivalent associations suggest that the 5F subtelocentric chromosome of A. fistulosum is involved in at least one translocation. The number of bridges and fragments and multivalent associations varied between the F1 hybrid and BC1 progenies. The F1 hybrid and all BC1 progenies were either sterile or had very little seed set. Fertility was not restored in any of the selected BC1 plants.