Chromosomic studies in Zephyranthes citrina baker (Amaryllidaceae), a polyploid ornamental / Estudios cromosómicos en Zephyranthes citrina baker (Amaryllidaceae), un poliploide ornamental

ABSTRACT Zephyranthes citrina is an ornamental American bulbous plant used as an ornamental garden crop for the aesthetic qualities of its yellow perigonium. The objective of this work was to characterize the species by classical chromosome staining and fluorochrome banding. A sporophytic chromosome number of 2n=8x=48 chromosomes was observed, being the karyotypic formula 20 m + 26 sm + 2 st. Satellites were detected in the short arm of metacentric chromosomes 8, 9, 11 and 12, which colocalized with constitutive heterochromatin CMA+/DAPI-/0 bands. The karyotype comprised chromosome pairs with terminal constitutive heterochromatin bands that included satellites and heteromorphic clusters indicating that it is an allooctoploid. These results will be used as a tool for monitoring genetic improvement, in interspecific crosses and its progenies and in biotechnological procedures by in vitro culture.

RESUMEN Zephyranhtes citrina es una planta bulbosa americana, ornamental, utilizada en jardines por las cualidades estéticas de su perigonio amarillo. El objetivo de este trabajo fue caracterizar citogenéticamente la especie con tinción clásica convencional y bandeo cromosómico. Se observó un número cromosómico esporofítico de 2n=8x=48, siendo la fórmula cariotípica 20 m + 26 sm + 2st. Se detectaron satélites en el brazo corto de los cromosomas metacéntricos 8, 9, 11 y 12, que co-localizaron con bandas de heterocromatina constitutiva CMA+/DAPI-. El cariotipo comprendió pares de cromosomas con bandas de heterocromatina constitutivas terminales que incluyeron satélites y grupos heteromórficos que indican que es un alooctoploide. Estos resultados serán usados como herramientas en el monitoreo del mejoramiento genético, en análisis de cruzamientos interespecíficos y progenies y en procedimientos biotecnológicos de cultivo in vitro.

An improved technique for obtaining well-spread metaphases from plants with numerous large chromosomes.

Preparations that contain well-spread metaphase chromosomes are critical for plant cytogenetic analyses including chromosome counts, banding procedures, in situ hybridization, karyotyping and construction of ideograms. Chromosome spreading is difficult for plants with large and numerous chromosomes. We report here a technique for obtaining cytoplasm-free, well-spread metaphases from two Amaryllidaceae species: Sprekelia formosissima (2n = 120) and Hymenocallis howardii (2n = 96). The technique has three main steps: 1) pretreatment to cause chromosome condensation, 2) dripping onto tilted slides coated with a thin layer of pure acetic acid and 3) application of steam and acetic acid to produce cytoplasmic hydrolysis, which spreads the chromosomes.

Three new teosintes (Zea spp., Poaceae) from México.

PREMISE OF THE STUDY: Teosinte species are the closest relatives of maize and represent an important but increasingly rare genetic resource for maize improvement and the study of evolution by domestication. Three morphologically and ecologically distinct teosinte populations were recently discovered in México. The taxonomic status of these rare and endangered populations was investigated by detailed comparisons to previously characterized wild Zea species. • METHODS: Three new teosinte populations were compared to known teosinte taxa on the basis of morphological, ecogeographic, cytological, and molecular characteristics. Phenetic and phylogenetic analyses were performed using morphological and molecular data, respectively. • KEY RESULTS: The newly discovered populations are distinct from each other and from other Zea species to represent three new entities based on their unique combinations of morphological, ecological, ploidy, and DNA markers. A perennial diploid population from Nayarit is distinguished by early maturing plants, and having male inflorescences with few tassel branches and long spikelets. A perennial tetraploid population from Michoacán is characterized by tall and late maturing plants, and having male inflorescences with many branches. An annual diploid population from Oaxaca is characterized by having male inflorescences with fewer branches and longer spikelets than those found in the sister taxa Z. luxurians and Z. nicaraguensis, plants with high thermal requirements, and very long seed dormancy. • CONCLUSIONS: Evidence from multiple independent sources suggests placement of the three new populations of teosinte as distinct entities within section Luxuriantes of the genus Zea. However, more extensive DNA marker or sequence data are required to resolve the taxonomy of this genus.

Intergenomic recombination in F1 lily hybrids (Lilium) and its significance for genetic variation in the BC1 progenies as revealed by GISH and FISH.

Intergenomic recombination was assessed in a BC1 population of Oriental (O)xAsiatic (A) lilies (Lilium) backcrossed to Asiatic parents. This population consisted of 38 plants generated from the 2n gametes from 2 genotypes (951502-1 and 952400-1) of the diploid F1, Orientalx Asiatic lilies (2n=2x=24) as parents. In the majority of BC1 plants, there was evidence that first division restitution, with and without crossovers, resulted in functional gametes. However, there were 5 BC1 plants in which 2n gametes originated from indeterminate meiotic restitution (IMR). Based on the number of recombinant chromosomes for a particular homoeologous pair, 3 types of plants were identified: (i) those with both the reciprocal product of a crossover (O/A, A/O, where O represents the centromere of the O genome and A the recombinant segment of Asiatic chromosome, and vice versa); (ii) those with 1 normal chromosome of the O genome and a recombinant chromosome (O, A/O); and (iii) those with 1 normal chromosome of the A genome and a recombinant chromosome (A, O/A). An important feature of A x OA backcross progeny is the occurrence of substitutions for the segment distal in the crossover wherever the recombinant chromosome O/A was present. In the case of IMR, the substitution occurred for both proximal and distal recombinant segments. The significance of these substitutions is that they offer the potential for the phenotypic expression of recessive genes in polyploids (i.e., nulliplex genotype).

Use of 2n gametes for the production of sexual polyploids from sterile Oriental x Asiatic hybrids of lilies (Lilium).

Sixteen Oriental and 12 Asiatic cultivars were crossed in 158 different combinations. A total of 708 F1 hybrids were obtained from 86 of the different combinations of 15 Oriental and 11 Asiatic cultivars. Because the Lilium cultivars (2n=2x=24) used for the production of these hybrids belong to two different taxonomic sections-Archelirion (0) and Sinomartagon (A), respectively-the F1 hybrids (OA) could be obtained only through embryo, embryo sac rescue, ovary slice or ovule culture. Most of the F, hybrids were highly sterile (did not produce viable n gametes) due to the failure of chromosome pairing. However, in a few cases F1 plants were found that produced viable 2n pollen at variable frequencies. These 2n pollen grains were successfully used for the production of backcross progenies. Using genomic in situ hybridization we found intergenomic recombinant chromosomes in the sexual polyploid progenies. These results indicate that there are effective prospects for combining important horticultural traits from the two main groups of cultivars of lilies through sexual polyploidization.