Chromosome banding patterns in Lettuce species (Lactuca sect.Lactuca,Compositae)

Chromosome banding patterns obtained with C- and N- banding, and AgNO₃ staining were studied in somatic metaphase complements of fourLactuca species.L. sativa andL. serriola have almost identical chromosome morphology, andL. saligna differs only slightly from them, butL. virosa is quite distinct from the other species. A gross comparison of the banded karyotypes suggests a closer relationship ofL. saligna toL. sativa/serriola than toL. virosa. Our data agree with the results of previous crossing experiments in these species but conflict partly with recent RFLP data which indicate a closer phenetic relationship ofL. saligna toL. virosa than toL. sativa/serriola. Such a discrepancy may be explained assuming that domestication ofL. sativa/serriola resulted in an increased selection pressure on unique DNA sequences as demonstrated by the RFLP data. Differential evolution of specific heterochromatin classes (and presumably of highly repetitive DNA classes), as revealed by chromosome banding techniques was not linked to domestication. Thus the disparity in conclusions about relationship (in terms of genetic similarity) as based on the different experimental approaches reflects a non-parallel evolution of highly repetitive vs. unique DNA classes.     

Numerical morphological analysis of Lettuce cultivars and species (Lactuca sect.Lactuca,Asteraceae)

L. sativa L. cultivars were compared morphologically with accessions ofL. saligna L.,L. serriola L., andL. virosa L. in order to define the infra- and interspecific variation. Multivariate analysis (principal component analysis) distinguished four groups corresponding with the four species. Infraspecific variation (e.g., colour, leaf shape) withinL. sativa is the largest, because breeding has caused a large variation in vegetative features; infraspecific variation withinL. serriola is also large. Three plants of one accession were placed betweenL. sativa andL. serriola because they showed morphological characteristics of both species. They are still classified asL. sativa. The morphological differences betweenL. sativa andL. serriola are too large to consider these two as one species. The descent of the cultivar groups and the four species is described.     

Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

Specificity of interactions between eight Lactuca species and 8 Bremia lactucae isolates was studied in seedlings and adult plants of 36 Lactuca accessions plus one L. serriola × L. sativa hybrid. Pathogenicity of the isolates and/or plant susceptibility was expressed by sporulation intensity. A highly compatible relationship was observed in all of L. serriola accession/isolate interactions tested. A differential reaction was found in numerous cases testifying to physiological specialization of the pathogen in a wild pathosystem. Nonspecific nondifferential compatibility (quantitative resistance) can be expected in L. serriola PI 281876. Age dependent resistance (seedlings versus adult plants, and vice versa) and heterogeneity of reactions were also recorded. The comparisonof B. lactucae isolates from L. sativa and L. serriola has shown a significant shift of pathogenicity in favour of L. serriola accessions. A high level of resistance was found in the L. serriola × L. sativa hybrid. The existence of basic incompatibility can be expected in L. saligna and L. virosa as well as in such taxonomically remote species as L. viminea, L. squarrosa and L. biennis. Other taxonomically remote species, i.e. L. dentata and L. alpina, exhibited a compatible reaction, although the reaction of the former was differential. A high level of sporulation was recorded in all accession/isolate interactions of L. alpina.     

Crossing and selfing experiments in theOrnithogalum umbellatum/augustifolium complex

The fertility relationships ofOrnithogalum umbellatum, O. angustifolium and 9 related taxa were studied.O. umbellatum andO. angustifolium, which are not interfertile, are both recognized as a comparium. Pollination of five species belonging to theO. umbellatum/angustifolium polyploid complex, i.e.O. umbellatum, O. angustifolium, O. baeticum, O. monticolum andO. algeriense, resulted in a moderate seed set. However, the seeds obtained after these interspecific crosses did not germinate. Six related species, i.e.O. exscapum, O. nivale, O. comosum, O. collinum, O. gussonei andO. woronowii showed a very low seed set after being crossed. One exception occurs:O. nivale ×O. exscapum. The seed set was also low after the complex species had been crossed with some related species, but there was one exception: both reciprocal crosses betweenO. monticolum andO. woronowii yielded some viable seeds. No other interspecific crosses gave rise to viable seeds. Bulbil-producing species have a lower seed set after self-pollination than species which do not produce bulbils.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex IV.—Previous contributions: (I–III):Raamsdonk (1982, 1985a, 1985b).     

Host specificity and virulence variation in populations of lettuce powdery mildew pathogen (Golovinomyces cichoracearum s. str.) from prickly lettuce (Lactuca serriola)

Fifty-four isolates of Golovinomyces cichoracearum (GC) sensu stricto were collected during the period 2008–2010 from natural populations of prickly lettuce (Lactuca serriola) growing in the Czech Republic. Population variation in virulence was assessed with a previously developed race differential set, comprising 13 accessions of four Lactuca species (L. serriola, L. sativa, L. saligna, L. virosa, and L. sativa ‘Hilde’ × L. serriola hybrid). GC isolates differed in their host specificity and virulence; most were able to infect most Lactuca spp. accessions (i.e., complete compatibility), but some showed only moderate virulence (i.e., incomplete compatibility). ‘Avirulent’ reactions were the least common, and these were most frequently observed on L. virosa (LVIR/50) and L. saligna (09-H58-1013). Furthermore, a temporal shift in virulence variability was recorded for the Czech GC populations. Generally, virulence of GC to the Lactuca spp. accessions increased during the study period. Across individual years, the most variable were reactions of GC to L. serriola accession (PI 273617), L. sativa cv. ‘Colorado’, L. saligna (09-H58-1013) and L. virosa (LVIR/50). A broad spectrum of virulence (v)-phenotypes was determined among the 54 isolates; however, differences in the reaction patterns of individual isolates were mostly small and related to differentiation between moderately and completely compatible interactions. However, most of the v-phenotypes characterized were unique to a given population in one year. Altogether, 16 v-phenotypes were identified among 16 isolates tested in 2008, 10 v-phenotypes were determined among 10 isolates tested in 2009, and 24 v-phenotypes among 28 isolates tested in 2010; i.e., different v-phenotypes were identified in different localities.     

Microsatellite fingerprinting in lettuce (Lactuca sativa L.) and wild relatives

Southern hybridisation with a single microsatellite probe, (TCT)₁₀, sufficed to discriminate between a representative set of cultivars/accessions of lettuce, Lactuca sativa L., and its wild relatives L. serriola, L. saligna and L. virosa. Variability within cultivars was tested in a relatively modern cultivar (Hector), where no variation was found, and in an older and morphologically more variable cultivar (Madrilene), where heterogeneity was observed in the TCT fingerprint. (TCT)₁₀ fingerprinting should be useful for variety identification and homogeneity testing in lettuce. Received: 25 July 1997 / Revision received: 5 August 1997 / Accepted: 30 August 1997     

Hybridization studies in the genusSilene sectt.Siphonomorpha andAuriculatae (Caryophyllaceae)

Ten species in the genusSilene sectt.Siphonomorpha andAuriculatae were crossed artificially involving 612 crosses to test inter- and infraspecific, intervarietal and intersectional crossability. In sect.Siphonomorpha all interspecific crosses (between diploids) failed due to cross- or seed-incompatibility; however, intervarietal crosses betweenS. gigantea var.gigantea andS. gigantea var.incana produced hybrids. In sect.Auriculatae hybrids were produced betweenS. vallesia andS. boryi, both tetraploids, but crosses between these and the diploid species were unsuccessful. The delimitation and status of the species in both sections was supported by the crossing results.     

Field water relations of a compass plant, Lactuca serriola L.

Abstract Field water relations of Lactuca serriola serriola and L. serriola integrifolia were examined. Leaf conductance to water vapour was high early in the morning and declined rapidly during the midday hours. Leaf water potentials decreased to their minima early in the morning and remained low all day. Afternoon recovery of leaf conductance occurred occasionally. Leaf conductance was shown to have a linear response to vapour concentration difference. No differences were seen between L. serriola serriola and L. serriola integrifolia. The pattern of diurnal gas-exchange activity appeared to be complemented by the pattern of intercepted solar irradiance which results from the compass plant leaf orientation observed in L. serriola.     

Characterization of New Highly Virulent German Isolates of Bremia lactucae and Efficiency of Resistance in Wild Lactuca spp. Germplasm

Four German isolates (FS1, SR2, SAW1 and DEG2) of Bremia lactucae originating from lettuce cultivars with R‐factors R18 and Dm6 + R36 were used for detailed characterization of virulence factors (v‐factors) and for the study of the resistance efficiency in wild Lactuca spp. germplasm. The highest complexity of v‐phenotype was recognized in isolate DEG2, which overcomes resistance in cv. Mariska (R18) and line CS‐RL (L. serriola × L. sativa, R18 + ?), until now known as resistant to all known races of B. lactucae in Europe. However, some sparse sporulation also occurred on cv. Titan (Dm6 + R36). The isolates SR2 and SAW1 overcome the resistance based on the gene R36, but are avirulent to R18. The v‐phenotype of SR2 is highly complex with the most important v‐factors being present except for v14 and v18. The isolate FS1 is the first in Germany originating from a cultivar with R18 (cv. Samourai). The search for efficient sources of resistance in 64 accessions of 11 wild Lactuca spp. and primitive forms of L. sativa showed broad variation in accession–isolate interactions. Expression of race‐specific resistance in wild Lactuca spp. (L. serriola, L. viminea, L. virosa) was recorded frequently. Lactuca indica and L. saligna could be considered as the most efficient sources of resistance against isolates FS1, SR2 and SAW1. The isolate DEG2 showed the highest level of virulence. On seedlings of L. saligna, which is considered as a most important source of resistance against B. lactucae, there was frequently recorded limited sporulation, however this response cannot be considered as a susceptible. Except for some L. saligna accessions (CGN 05310 and CGN 05315), the resistance to all studied isolates was only observed in one accession of L. serriola (PI 253467).     

Non-random leaf orientation in Lactuca serriola L.

Abstract Leaf shapes and leaf orientation of Lactuca serriola serriola and serriola integrifolia were studied. Leaf shapes in L. serriola serriola differed greatly from those of L.serriola integrifolia, but leaf surface areas were similar. In exposed habitats, leaf orientation of cauline leaves of both forms was non-random, with leaves almost vertical and tending to orient with their lamina normal to the east and west. In the shade, cauline leaves oriented randomly. An experiment demonstrated that the orientation of leaves did not change significantly once they were fully expanded. The leaf orientation in L. serriola affected the diurnal distribution of solar irradiance intercepted by a leaf. Peak solar radiation fluxes are incident on the rosette leaves at midday, but on the cauline leaves the peak solar radiation flux occurs early in the morning and again late in the afternoon. The significance of this unusual leaf orientation is discussed in relation to water loss and carbon gain.     

Experimental hybridization between catfishes of the families Clariidae and Pangasiidae in Thailand

Synopsis Hybrids between the clariid speciesClarias macrocephalus andC. batrachus and the pangasiid speciesPangasius sutchi were obtained by hormone injection of brood stock and artificial fertilization. Pure parental crosses as well as all possible hybrid combinations were obtained. Fertility, hatchability, and post-yolk absorption survival was high (66–99%) in all pure parental crosses and in all crosses between the two species ofClarias. In crosses betweenClarias andPangasius fertilization was also very high (68–97%) but hatchability varied from 11 to 23% and post-yolk absorption survival from 0% inPangasius sutchi ×Clarias batrachus to about 50% inPangasius sutchi ×Clarias macrocephalus . The longest-lived hybrids ofPangasius andClarias were those ofPangasius sutchi ×Clarias macrocephalus which survived until the experiment was prematurely terminated due to contaminated food after 4 1/2 months, at which point they had grown to total lengths of 8–14cm. The hybrids comprised four morphotypes, two relativelyPangasius-like and two relativelyClarias-like, but all markedly different from the parental species.     

Morphology and cytology of intergeneric hybrids involvingLeymus multicaulis (Poaceae)

The morphology and meiotic behaviour of pollen mother cells were studied in hybrids involvingLeymus multicaulis (2n = 28) ×Psathyrostachys huashanica (2n = 14),L. multicaulis ×P. juncea (2n = 14), andL. secalinus (2n = 28) ×L. multicaulis. Chromosome pairing was almost identical in theL. multicaulis ×P. huashanica, andL. multicaulis ×P. juncea hybrids, in which it averaged 7.30 univalents + 6.69 bivalents + 0.096 trivalents and 7.48 univalents + 6.75 bivalents, respectively. The meiotic pairing in the two hybrids indicated that oneL. multicaulis genome was closely homologous with theP. huashanica andP. juncea genomes. BothP. huashanica andP. juncea are possibly donors of oneL. multicaulis genome. Chromosome pairing in theL. secalinus ×L. multicaulis hybrid averaged 4.49 univalents + 11.71 bivalents + 0.02 trivalents, indicating that the genomes ofL. multicaulis andL. secalinus are to some degree homologous. However, they are sufficiently differentiated to insure species distinctness.     

Effects of seed-irradiation on meiosis in M1 plants of Lactuca and related plants

Meiosis was studied in control and seed-irradiated materials of Lactuca sativa, cultivars Tom, Cos and Webbs, L. serriola from the wild, and Cichorium intybus. In meiosis of the M₁ plants from irradiated seed, observations of univalent and multivalent formation, bridge formation at Anaphase I and II, micronucleus formation and persistence, and pollen fertility, were carried out, and compared with controls. Quantitative estimations of bridge formation were made in L. sativa Tom and Cos and in L. serriola, at anaphase I only. It was found that the frequency of anaphase I bridges and reduction of pollen fertility in the M₁ and also M₂ generation, were different for each variety or species; these could be sequenced radiation-resistant to sensitive in the order Tom, Cos and L. serriola.     

Fertility relationships ofGeranium (Geraniaceae): sectt.Ruberta,Anemonifolia, Lucida andUnguiculata

Cross-pollinations were carried out among 11 briefly described species ofGeranium. Eight species pairs produced hybrids, of which five had not been reported before. The close relationship ofG. purpureum, G. robertianum andG. rubescens (sect.Ruberta) was confirmed; they form a polyploid series (diploid, tetraploid and octoploid on base x = 16). ForG. canariense (sect.Anemonifolia), another octoploid on base x = 16, the results suggest greater affinity with the former section.G. maderense andG. palmatum of sect.Anemonifolia (2n = 68) are confirmed as closely related to each other.G. maderense produced hybrids withG. robertianum (2n = 64; sect.Ruberta) and withG. cataractarum (2n = 36; sect.Unguiculata). Meiosis in the latter hybrid suggests allopolyploidy between parents with 2n = 32 and 2n = 36. Whereas all these species clearly form a very close alliance,G. lucidum (sect.Lucida) andG. macrorrhizum andG. dalmaticum (both sect.Unguiculata), appear genetically more isolated from them. One plant ofG. macrorrhizum ×G. dalmaticum was raised. — In crosses where hybrids or non-germinating seeds resulted, the reciprocal cross in the majority of cases produced a greatly inferior result or none at all. This asymmetry of response could in some cases be explained by inability of pollentubes from short-styled parents to reach the ovary of a long-styled species and in others by a modification of Hogenboom's theory of incongruity, but neither explanation works for every case. In all our asymmetric results where the ploidy level differed the diploid was the successful female, not the tetraploid, as is usually the case. — Some variation in results from year to year could be attributed to weather conditions.Dedicated to Hofrat Univ.-Prof. DrK. H. Rechinger on the occasion of his 80th birthday.     

Molecular diversity at the major cluster of disease resistance genes in cultivated and wild Lactuca spp.

Diversity was analyzed in wild and cultivated Lactuca germplasm using molecular markers derived from resistance genes of the NBS-LRR type. Three molecular markers, one microsatellite marker and two SCAR markers that amplified LRR-encoding regions, were developed from sequences of resistance gene homologs at the main resistance gene cluster in lettuce. Variation for these markers were assessed in germplasm including accessions of cultivated lettuce, Lactuca sativa L. and three wild Lactuca spp., L. serriola L., L. saligna and L. virosa L. Diversity was also studied within and between natural populations of L. serriola from Israel and California; the former is close to the center of diversity for Lactuca spp. while the latter is an area of more recent colonization. Large numbers of haplotypes were detected indicating the presence of numerous resistance genes in wild species. The diversity in haplotypes provided evidence for gene duplication and unequal crossing-over during the evolution of this cluster of resistance genes. However, there was no evidence for duplications and deletions within the LRR-encoding regions studied. The three markers were highly correlated with resistance phenotypes in L. sativa. They were able to discriminate between accessions that had previously been shown to be resistant to all known isolates of Bremia lactucae. Therefore, these markers will be highly informative for the establishment of core collections and marker-aided selection. A hierarchical analysis of the population structure of L. serriola showed that countries, as well as locations, were significantly differentiated. These differences may reflect local founder effects and/or divergent selection. Received: 7 March 1999 / Accepted: 25 March 1999     

Experimental documentation of natural hybridization inCactaceae: Origin of Lloyd's Hedgehog Cactus,Echinocereus ×lloydii

The origin ofEchinocereus ×lloydii Britt. & Rose, pro sp. (Lloyd's Hedgehog Cactus) was investigated using comparative morphology, cytology, biochemistry, and particularly, artificial hybridization. Numerous artificial crosses between the putative parentsE. coccineus Engelm. (a species of claret-up cactus) andE. dasyacanthus Engelm. (Texas Rainbow Cactus) were successful, resulting in the production of hundreds of seeds with hybrid embryos. The F₁ hybrid progeny (i.e., syntheticE. ×lloydii) grew to sexual maturity in about four and one-half years, whereupon successful backcrosses and F₂ generation hybrids were also obtained. The known F₁ hybrids closely approximated naturalE. ×lloydii. The fertility of these syntheticE. ×lloydii was high, like their natural counterparts. The populations ofE. ×lloydii in Pecos County, Texas are inferred to have originated as the result of natural interspecific hybridization. It is assumed thatE. ×lloydii or similar plants may arise wherever the parental taxa grow sympatrically.     

Interspecific somatic hybridization between lettuce (Lactuca sativa) and wild species L. virosa

Somatic hybrids between cultivated lettuce (Lactuca sativa) and a wild species L. virosa were produced by protoplast electrofusion. Hybrid selection was based on inactivation of L. sativa with 20mM iodoacetamide for 15 min, and the inability of L. virosa protoplasts to divide in the culture conditions used. Protoplasts were cultured in agarose beads in a revised MS media. In all 71 calli were formed and 21 of them differentiated shoots on LS medium containing 0.1mg/l NAA and 0.2mg/l BA. Most regenerated plants exhibited intermediate morphology. These plants were confirmed as hybrids by isoenzyme analysis. The majority of somatic hybrids had 2n=4x=36 chromosomes, and had more vigorous growth than either parent. Hybrids had normal flower morphology, but all were sterile.     

Genetic diversity in the top onion,Allium ×proliferum (Alliaceae), analysed by isozymes

Polymorphisms for six enzyme systems (GPI, IDH, PDG, PGM, SKD, and TPI) were analysed in the top onion,Allium ×proliferum. Five multilocus isozyme genotypes were found. The banding patterns of top onions were compared with those ofA. ×wakegi, A. cepa, A. fistulosum, A. altaicum, and artificial hybrids between these three species. One top onion type and one artificial hybrid had identical banding patterns. Shallots andA. altaicum, the wild progenitor ofA. fistulosum, cannot be distinguished from the common onion andA. fistulosum, respectively; these species are also potential contributors to the top onion's gene pool.     

PCR-based fingerprinting using AFLPs as a tool for studying genetic relationships in Lactuca spp.

AFLP markers were evaluated for determining the phylogenetic relationships Lactuca spp. Genetic distances based on AFLP data were estimated for 44 morphologically diverse lines of cultivated L. sativa and 13 accessions of the wild species L. serriola, L. saligna, L. virosa, L. perennis, and L. indica. The same genotypes were analyzed as in a previous study that had utilized RFLP markers. The phenetic tree based on AFLP data was consistent with known taxonomic relationships and similar to a tree developed with RFLP data. The genetic distance matrices derived from AFLP and RFLP data were compared using least squares regression analysis and, for the cultivar data, by principal component analysis. There was also a positive linear relationship between distance estimates based on AFLP data and kinship coefficients calculated from pedigree data. AFLPs represent reliable PCR-based markers for studies of genetic relationships at a variety of taxonomic levels.     

A second spontaneous hybrid in the genusLeucaena (Leguminosae, Mimosoideae)

The detection of hybridity inLeucaena is discussed in relation to: (i) traditional criteria, (ii) molecular criteria and (iii) models to predict hybrid leaf morphology. Morphological, geographical and molecular evidence for the occurrence of interspecific hybrids betweenL. leucocephala andL. diversifolia in south-central Mexico, northern Guatemala, Jamaica, Dominican Republic, the Philippines and Papua New Guinea is presented. Predicted mean hybrid leaf trait values calculated from parent material are compared with data from putative hybrids and shown to be similar. The origin of these hybrids is discussed and shown to be the result of artificial sympatry resulting from indigenous, and recent exotic, domestication of the parent species. The hybrid is described asL. ×spontanea.