A Cytogenetic Analysis of Certain Polyploids in Grindelia (Compositae)

Abstract

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.

Pollination biology of Grindelia covasii (Asteraceae), a potential crop for arid lands

“…There are 15 species in Argentina, eight of which are endemic (Cabrera, 1931;Ariza Espinar, 1976;Bartoli & Tortosa, 1994). Within the genus Grindelia, diploid (2n"12), tetraploid (2n"24) and hexaploid (2n"36) species, or populations within the same species, have been found (Schnack & Covas, 1947;Dunford, 1964;Hunziker et al, 1989;Bartoli et al, 1990Bartoli et al, , 1993.…”

Genetic and Ecotypic Differentiation in a Californian Plant Polyploid Complex (Grindelia, Asteraceae)

“…In addition, the two ecotypes are reproductively isolated under natural conditions, due to little overlap in flowering time and to selection against immigrants from the other ecotype [18]. As in Grindelia [33], intrinsic postzygotic isolation between ecotypes was not found [18].…”

“…They vary in stature (from 30 to 200 cm tall), woodiness (from not at all woody to having woody branches more than 1 m long), head shape and size, leaf and phyllary morphology, degree of succulence, amount of resin, and flowering time (from early summer to fall). These differences appear to be genetic, as they persist when the plants are grown in a common garden [33], [34]. Although there is clearly much morphological variation within Pacific Grindelia , and plants from two different habitats often have striking morphological differences, it is generally very difficult to draw clear boundaries between putative taxa when they are examined across their entire ranges.…”

Triploid and Tetraploid Hybrids From Diploid X Tetraploid Crosses in Grindelia (Compositae)

“…indicate another way in which genetic material may be exchanged between diploids and tetraploids, the formation of unreduced gametes in diploids being the first noted (Dunford, 1964). indicate another way in which genetic material may be exchanged between diploids and tetraploids, the formation of unreduced gametes in diploids being the first noted (Dunford, 1964).…”

“…which have been analyzed cytologically the common meiotic chromosome configuration is 12 bivalents, or 10 bivalents and 1 quadrivalent, or 8 bivalents and 2 quadrivalents, whereas Grindelia diploids (2n = 12) normally form 6 bivalents (Whitaker and Steyermark, 1935;Raven et al, 1960;Dunford, 1964). On the basis of bivalent and quadrivalent formation in hybrids obtained by crossing diploid and tetraploid taxa of Grindelia from California, as well as diploids X diploids, and tetraploids X tetraploids, it was concluded that Grindelia tetraploids were autopolyploids that had undergone some diploidization (Dunford, 1964).…”