Ellen B. Peffley

Chromosomal location of rDNA in Allium: in situ hybridization using biotin- and fluorescein-labelled probe

SummaryA biotin- and fluorescein-labelled probe of Helianthus argophyllus has been used to map specific repeated rDNA sequences by in situ hybridization on mitotic chromosomes of Alliwn cepa, Allium fistulosum, a diploid interspecific (Allium fistulosum x Allium cepa) F1 hybrid, and a triploid interspecific (2 x = A. cepa, 1 x = A. fistulosum) shallot. Hybridization sites were restricted to satellited and smallest pairs of chromosomes in both A. cepa and A. fistulosum. The number, size, and position of the hybridization sites distinguish homologous chromosomes and identify the individual chromosomes carrying the nucleolus organizing region (NOR) at the secondary constriction, as well as the individual chromosomes carrying an additional NOR. This in situ hybridization technique is the first reported in a plant species and offers new cytogenetic markers in Allium.

Somatic embryogenesis and plant regeneration in diploid Allium fistulosum × A. cepa F1 hybrid onions

Procedures were developed for disinfestation of non-dormant basal plate tissue excised from field grown basal plate tissue of diploid Allium fistulosum × A. cepa F1 hybrid onions. Contamination levels varied with the season and vegetative development of plant material. Callus initiated from basal plate tissue and immature inflorescences of the F1 hybrids was maintained on a BDS-based medium containing 0.75 mg/l picloram and 2.0 mg/l BA. When this medium was supplemented with vitamins and glycine, and with proline at 2.5 gm/1, somatic embryos began to form. Their development continued on a BDS-based shoot promotion medium containing 0.03 mg/l picloram and 0.32 mg/l 2iP supplemented with vitamins, glycine and proline. Genotypes differed significantly in the numbers of structures regenerated. Plantlets from somatic embryos were rooted into BDS or half-strength BDS medium without growth substances and were successfully transferred to sterilized potting mix in plastic commercial corsage boxes.

Plant regeneration from suspension cultures of Allium fistulosum and an A. fistulosum × A. cepa interspecific hybrid☆

Abstract Suspension cultures were initiated from friable nodule-forming calluses of five onion genotypes, two of Allium fistulosum L. and three of A. cepa L., and an interspecific A. fistulosum × A. cepa F 1 diploid hybrid. Eight liquid BDS (basal Dunstan and Short [2]) media supplemented with factorial combinations of plant growth regulators 2,4-dichlorophenoxyacetic acid (2,4-D), abscisic acid (ABA), or 6-benzylaminopurine (6-BAP) were used for initiating suspension cultures. More suspension cultures were initiated from A. fistulosum cultivars (30.0%) and the interspecific A. fistulosum × A. cepa diploid F 1 hybrid (25.0%) than from A. cepa cultivars (21.6%). Cell clumps cultured in liquid BDS medium with 0.5 mg/l ABA and 1.0 or 2.0 mg/l 2,4-D without 6-BAP were more finely dispersed than clumps cultured with 6-BAP in all genotypes. It was difficult to recover shoots from suspension cultures of A. cepa , but clumps from suspension cultures of the hybrid and A. fistulosum regenerated shoots which subsequently developed into plants.

Recombinant chromosomes of advanced backcross plants between Allium cepa L. and A. fistulosum L. revealed by in situ hybridization.

Abstract Cytological analysis of (Allium cepa L.×Allium fistulosum L.)×A. cepa L. F1BC3 plants revealed most plants were diploid with 16 chromosomes. Karyotypes of these plants showed recombinant chromosomes. Fluorescence and genomic in situ hybridization patterns of interspecific F1 hybrid and F1BC3 plants revealed A. fistulosum chromosomes or chromosomal segments. A highly repetitive 376-bp DNA sequence and genomic DNA of A. fistulosum revealed similar telomeric hybridization sites when hybridized onto A. fistulosum chromosomes. Cytogenetic evidence showed that A. fistulosum DNA has recombined into the A. cepa genome.

Bulb-type onion introgressants posessing Allium fistulosum L. genes recovered from interspecific hybrid backcrosses between A. cepa L. and A. fistulosum L.

Abstract Allium fistulosum possesses a number of traits which would be desirable in A. cepa. Thus far, no commercial A. cepa cultivars have been released which harbor Allium fistulosum traits. F1BC3 populations were generated for this study by backcrossing A. cepa to A. cepa×A. fistulosum hybrids. The F1BC3 plants were evaluated for plant morphology, floral characters, male- sterile cytoplasm, soluble solids and pungency, and isozymes. Overall growth habit and floral characters of the F1BC3 plants were much like A. cepa. We report here the recovery of recombinant, bulbing, and fertile A. cepa-type onions that exhibit A. fistulosum isozyme alleles and morphological markers. Recombination between A. cepa and A. fistulosum genomes was achieved using the introgression strategy of backcrossing A. fistulosum into A. cepa, thereby ameliorating the nuclear cytoplasmic barriers that occurred in previous less successful introgression attempts when plants were not in A. cepa cytoplasm. We believe this report to be the first demonstration of onion introgressants that are like A. cepa in appearance, are male- and female-fertile, and possess A. fistulosum genes.

Chromosome doubling of Allium fistulosum × A. cepa interspecific F1 hybrids through colchicine treatment of regenerating callus

Regenerating calluses of Allium fistulosum × A. cepa interspecific F1 hybrids were treated in vitro with colchicine. A factorial experiment was designed to test the effects of colchicine concentration and time on the recovery of tetraploid plants from in vitro-colchicine-treated calluses. Shoot production of regenerating calluses following in vitro colchicine treatment decreased with increasing colchicine concentration and treatment time. Cytological analyses of root tip cells from regenerated plantlets showed that chromosomes of control plantlets (not treated with colchicine) were not doubled. Chromosome number of some plantlets regenerated from in vitro-colchicine-treated calluses were doubled, resulting in tetraploids. Calluses treated with 0.1 or 0.2% colchicine in BDS liquid medium for 48 or 72 hours yielded the highest numbers of tetraploid plantlets. Chromosome bridges at anaphase or early telophase were observed in diploid and tetraploid plants; their potential use is discussed. These results demonstrate that in vitro-colchicine treatment of regenerating calluses of interspecific F1 hybrids is effective in recovering tetraploid plants.

The inheritance of a basal branching type in guar

Conflicting theories of inheritance of branching in guar [Cyamopsis tetragonoloba (L.) Taub.] have been reported. In this study, two lines differing in leaf surface and growth habit were used to make reciprocal crosses and form progeny populations in order to study how basal branching is inherited. Parents in the reciprocal crosses were PI 217923, which is an erect type with pubescent leaves that exhibits predominantly zero, but as many as four basal branches; and ‘Lewis’, which is a branching type with glabrous leaves that exhibits from two to ten branches at the base. Parental and progeny populations were evaluated for branching under field-grown conditions. Effect of plant spacing (seeding rate at 1 seed/cm vs. 1 seed/30 cm) on basal branching of PI 217923 and Lewis was studied. Hybrids were identified by erect branching and pubescent leaf surface. F1 plants had erect branching type and pubescent leaves, indicating that erect branching is dominant to basal branching and there is no maternal effect. Chi-square goodness-of-fit analysis revealed that F2 populations segregated in the expected 3:1 ratio (P<0.10–0.70), indicating that basal branching was controlled by one gene. We propose gene symbol Brh-1 for the gene that controls lack of branching as in segregating populations, Brh-1 is dominant to brh-1. Thus, the genotype of PI 217923 would be Brh-1/Brh-1 or Brh-1/brh-1 as it exhibits erect growth habit with little branching, while that of Lewis would be brh-1/brh-1. When grown at wider plant spacing (1 seed/30 cm), all branching increased, but 3 or 4 basal branches appeared in PI 217923, while the average number of basal branches in Lewis increased from 4.0 to 8.4.

The Inheritance and Variation of Gum Content in Guar [Cyamopsis tetragonoloba (L.) Taub.]

Abstract Guar [Cyamopsis tetragonoloba (L.) Taub.] is one of the most important industrial crops due to its richness in gum. Understanding the inheritance of gum content is a key to its successful genetic improvement. Gum content expression is reported to be controlled by additive, dominant, and epistatic effects, and modified by the environment. fg%, a relative gum content calculated by comparing with the gum content of Kinman was used as gum content (%) in this experiment. Reciprocal crosses of two lines of guar, PI 217923 and Lewis, were made to study the heritability of gum content (fg%). fg% of four plant introductions and four commercial varieties were studied in Lubbock in 1999–2002. Estimates of broad-sense heritability (h2 b.s.) of fg% in Lewis × PI 217923 and PI 217923 × Lewis were 75.53 and 52.74%, respectively. Estimates of narrow-sense heritability (h2 n.s.) of fg% were 40.00 and 29.00% for Lewis × PI 217923 and PI 217923× Lewis, respectively. At least one pair of genes were estimated to control the fg% expression in these two crosses. Significant differences of fg% were found among these eight entries. PI 217923 was found to have the highest fg% among the eight entries.

Elevated Carbon Dioxide Alters Hydrocarbon Emissions and Flavor in Onion

Bulb onion (Allium cepa), non-bulbing Japanese bunching onion (A. fistulosum), common chives (A. schoenoprasum) and garlic chives (A. tuberosum) have markedly different harvest indices. With the onset of bulbing, leaf production ceases, photosynthates are reallocated to the bulb, lowering production of new shoots and crop canopy. Successive harvests from the same planting allow for a cumulative harvest index. In testing the influence of growing plants under different CO2 conditions, a set of volatile methyl-ketones have been identified from onion that are emitted at higher levels when plants are grown at elevated CO2 compared to controls grown at ambient CO2 levels. Sensory panel taste testing has indicated differences in flavor for some cultivars when comparisons were made between plants grown at ambient and elevated CO2 conditions. In future studies we will examine if thiosulfinates generated from the enzymatic conversion of alk(en)yl cysteine sulphoxides contribute to flavor differences detected between ambient and elevated CO2 grown plants.

Esterase isozymes are useful to track introgression between Allium fistulosum L. and A. cepa L.

Polyacrylamide gel electrophoresis (PAGE) was used to study the polymorphism of esterases in Allium cepa L. and A. fistulosum L. Two varieties of each species, an A. fistulosum × A. cepa interspecific F1 hybrid, and (A. fistulosum × A. cepa) hybrid derivatives were analyzed for determination of banding patterns upon staining with α- and β-napthyl acetate substrates of esterase. Complex band patterns were observed. In total, 10 bands were detected between A. cepa and A. fistulosum — five inA. cepa, six in A. fistulosum with only one band common to both species. With the exception of one band unique to A. fistulosum which appeared only when stained with α-substrate, extracts of both A. cepa and A. fistulosum leaf tissue exhibited the same bands when stained with both α- and β-substrates. Bands stained with the different systems are distinguished by color: α-substrate always appeared black, while bands stained to β-substrate are always red. Esterase bands were assigned into 5 presumptive loci of four zones of activity with according to the migration distance of the bands from the front, color of each band upon staining with α- and β-substrates, and segregation observed in crosses and hybrid derivatives. Esterase enzymes detected in this study appear to be monomeric. Polymorphisms were identified between A. cepa and A. fistulosum by esterase banding patterns. Esterase enzymes provide an additional marker in monitoring introgression of foreign germplasm in interspecific onion breeding.