Eva Křístková

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.

Wild Lactuca germplasm for lettuce breeding: current status, gaps and challenges

In this review, we present a critical analysis of the current status of wild Lactuca L. germplasm in relation to its utility for lettuce breeding. We discuss wild Lactuca germplasm in ex situ collections from the perspectives of taxonomy, biogeography, biology and ecology, gene pools, field exploration and acquisition, descriptor development, characterization and evaluation, and enhancement. Future research and other activities related to wild Lactuca germplasm and their continued exploitation in lettuce breeding are considered.

Variation in chromosome numbers and nuclear DNA contents in genetic resources of Lactuca L. species (Asteraceae)

Fifty accessions of 25 Lactuca species,L. serriola ×L. sativa and Mycelismuralis were analyzed for chromosome number and relative DNA amountvariation. In the majority of Lactuca species studiedchromosome counts, as earlier reported (n = 8, 9, 17), were verified; however,for L. dregeana andL. homblei (probablyL. schweinfurthii orL. longespicata) the chromosome number(n = 9) was determined for the first time. Relative nuclear DNA content,estimated by using flow cytometry (DAPI staining), showed that 2C DNA contentranged from 2.02 pg in L.capensis to 17.96 pg inL. canadensis. Statistical and clusteranalysis of data based on relative nuclear DNA contents correspond fairly wellwith recently accepted taxonomic classification of the genusLactuca. However, the position of certain species as wellas clarification of taxonomic determinations of someLactuca accessions needs further examination.

Species spectra, distribution and host range of cucurbit powdery mildews in the Czech Republic, and in some other European and Middle Eastern countries

The occurrence and geographic distribution of powdery mildew on cucurbits was studied in the Czech Republic, Austria, France, Germany, Great Britain, Italy, Slovakia, Slovenia, Spain, Switzerland, the Netherlands, as well as in Turkey and Israel, during the period 1995–2000. In total, 599 leaf samples with powdery mildew symptoms were collected from cucurbits from 166 locations within the Czech Republic; an additional 69 samples were collected from 42 locations elsewhere. Two powdery mildews (Golovinomyces cichoracearum and Podosphaera xanthii) were identified. The host range included the cultivated cucurbits (Cucumis melo, C. sativus, Cucurbita pepo, C. maxima, and Citrullus lanatus) and several other species. P. xanthii was the only powdery mildew pathogen found in Spain, Israel, and Turkey. P. xanthii and G. cichoracearum were detected in the other surveyed countries, occurring in both mixed infections and separately. In the more northerly latitudes and higher elevations, G. cichoracearum is more often the single species. G. cichoracearum was the dominant powdery mildew species in the Czech Republic (detected in 98.8% of the locations there); P. xanthii was found as the lone species in 1.2% of locations. At 28.4% of locations, G. cichoracearum was found with P. xanthii as mixed infections. The hyperparasitic fungus Ampelomyces quisqualis was found in 30% of the samples from the Czech Republic and was also recorded in Austria, Italy, Slovenia, Switzerland, and Great Britain.

AFLP analysis of Lactuca saligna germplasm collections from four European and three Middle Eastern countries

Lactuca saligna L. (least lettuce, willow-leaf lettuce) is widely distributed around the Mediterranean basin and extends to the Caucasus and temperate Europe; its extra-European distribution covers the Middle East. The aim of this study was to estimate the level of molecular variation and the extent of genetic differentiation of L. saligna in accessions collected in natural and semi-natural habitats in Europe and the Middle East. In sum, 67 accessions of L. saligna, originating in four European countries (Czech Republic, France, Italy, Portugal) and three Middle Eastern countries (Israel, Jordan, Turkey), were compared on the basis of AFLP polymorphism. AFLP analysis of the accessions revealed 415 (84.7%) polymorphic fragments out of 490 fragments amplified by means of seven primer pair combinations. The number of bands produced by individual primer pair combinations ranged from 44 to 101. The UPGMA dendrogram generated from Jaccards similarity matrix showed a similar genetic background of accessions from the Middle East (Turkey, Israel, Jordan), which were quite distinct from the group of accessions from the European part of the Mediterranean basin (Italy, France, Portugal). Surprisingly, two accessions, one from the Czech Republic (central Europe) and one from Israel, proved genetically wholly separate from all other accessions of L. saligna and are themselves wholly separate. Accessions originating in various eco-geographical conditions were found to differ significantly in their genetic polymorphism.

Parallel Evolution Under Domestication and Phenotypic Differentiation of the Cultivated Subspecies of Cucurbita pepo (Cucurbitaceae)

Parallel Evolution under Domestication and Phenotypic Differentiation of the Cultivated Subspecies ofCucurbita pepo(Cucurbitaceae). Cucurbita pepo (pumpkin, squash, gourd, Cucurbitaceae) is an ancient North American domesticate of considerable economic importance. Based on molecular genetic polymorphisms, two cultivated lineages of this species, each consisting of very many edible–fruited cultigens, have been recognized, C. pepo subsp. pepo and C. pepo subsp. texana. However, the phenotypic commonalities and differences between these two subspecies have not as yet been systematically collected and organized. Among the evolutionary developments common to the two subspecies are the increased size of the plant parts, less plant branching, and premature loss of chlorophyll in the exocarp of the fruits. In both subspecies, bush growth habit, conferred by allele Bu, is common to the cultigens grown for consumption of the immature fruits, as is the deviation from the 1:1 ratio of fruit length to fruit width. A major characteristic differentiating between the edible–fruited cultigens of the respective subspecies are the longitudinal protrusions, in subsp. pepo, versus depressions, in subsp. texana, of the fruit surface corresponding with the subsurface primary carpellary vein tracts. Subsp. pepo also has larger fruits and larger and longer seeds. In addition, some alleles affecting stem color, leaf mottling, multiple flower bud production, and fruit characteristics are frequently occurring to nearly fixed in one subspecies but are rare to less common in the other.

Wild Lactuca species, their genetic diversity, resistance to diseases and pests, and exploitation in lettuce breeding

Current knowledge of wild Lactuca L. species, their taxonomy, biogeography, gene-pools, germplasm collection quality and quantity, and accession availability is reviewed in this paper. Genetic diversity of Lactuca spp. is characterized at the level of phenotypic and phenological variation, variation in karyology and DNA content, biochemical traits, and protein and molecular polymorphism. The reported variation in reaction to pathogens and pests of wild Lactuca spp. is summarized, including the viral pathogens (Lettuce mosaic virus-LMV, Mirafiori lettuce virus/Lettuce big vein virus-LBV, Beet western yellows virus-BWYV, Tomato spotted wilt virus-TSWV, Cucumber mosaic virus-CMV, Lettuce necrotic stunt virus-LNSV), bacterial pathogens (corky root-Rhizomonas suberifaciens, bacterial leaf spot-Xanthomonas campestris pv. vitians), fungal pathogens (downy mildew-Bremia lactucae, powdery mildew-Golovinomyces cichoracearum, anthracnose-Microdochium panattoniana, stemphylium leaf spot-Stemphylium spp., sclerotinia drop-Sclerotinia spp., verticillium wilt-Verticillium dahliae, fusarium wilt-Fusarium spp., pythium wilt-Pythium tracheiphylum, P. uncinulatum), nematodes (potato cyst nematode-Globodera rostochiensis, root-knot nematode-Meloidogyne spp., incognita, hapla, javanica, enterolobii), insects and mites (the green lettuce aphid-Nasonovia ribisnigri, the green peach aphid-Myzus persicae, the potato aphid-Macrosiphum euphorbiae, leafminer-Liriomyza spp., L. langei). The approaches used to exploit wild Lactuca spp. in lettuce breeding (interspecific hybridization, cell and tissue culture, transformation) are dicussed, and known examples of lettuce cultivars with traits derived from wild Lactuca spp. are described.

Cucurbit powdery mildews: methodology for objective determination and denomination of races

Cucurbit powdery mildew (CPM), a disease on field and greenhouse cucurbit crops worldwide, is caused most frequently by two obligate erysiphaceous ectoparasites (Golovinomyces orontii s.l., Podosphaera xanthii) that are highly variable in their pathogenicity and virulence. Various independent systems of CPM race determination and denomination are used worldwide, having to date been differentiated on different cultivars or lines of melon (Cucumis melo L.). We briefly review historical perspectives and the current state of understanding of the virulence variation of the two CPM pathogens at the pathogenic race level, their differentiation and their designation. Furthermore, we propose for use by the international CPM research, breeding, seed and production community new tools to enhance research, communication and management of CPM. These tools consist of five components: 1) a set of 21 differential genotypes of Cucumis melo L. for the identification of CPM races; 2) a triple-part, septet code for meaningful, concise designation of CPM races; 3) protocols for maintaining CPM isolates and differential genotypes and for laboratory assays to examine the virulence of CPM isolates; 4) rules and principles of practical application of this system in breeding, seed production and cucurbit growing, including a proposal of a race denomination suitable for practical application; and 5) crucial activities leading to the implementation and running of new tools for CPM research and management. The five components of this package have equal importance, forming a compact system, and none of them can be omitted.

Virulence of Czech cucurbit powdery mildew isolates on Cucumis melo genotypes MR-1 and PI 124112

Abstract The responses of Cucumis melo genotypes MR-1 and PI 124112 to 20 isolates of powdery mildew pathogens (Erysiphe cichoracearum, Sphaerotheca fuliginea) that originated from Cucurbita spp. were evaluated on leaf discs as part of a pathotype and race determination programme in the Czech Republic. One isolate of S. fuliginea produced limited mycelia on MR-1. One isolate of E. cichoracearum was virulent on MR-1, while six other isolates infected MR-1, which reacted showing symptoms of incomplete resistance. In the set of 10 mixed ( E. cichoracearum+S. fuliginea ) isolates only one was virulent on MR-1 and another one on PI 124112. These genotypes expressed incomplete resistance after inoculation with eight mixed isolates. This is the first experimental evidence of differential responses, i.e., incomplete resistance or susceptibility, by C. melo genotypes MR-1 and PI 124112 to cucurbit powdery mildew isolates at the true leaf stage. Expression of resistance or incomplete resistance responses of C. melo Iran H to E. cichoracearum and two mixed isolates was recorded. Until now, Iran H has been considered a universal susceptible host. These reactions indicate that in this genotype could be located unknown race-specific resistance factor(s) to one or both species of powdery mildew.

Resistance in Cucurbita pepo and Cucurbita maxima germplasms to cucumber mosaic virus

SummaryA total of 384 Cucurbita pepo and Cucurbita maxima accessions were evaluated in growth chambers or glasshouse tests for resistance to cucumber mosaic virus (CMV). Seedlings were mechanically inoculated at the cotyledon stage, and scored for symptoms on cotyledons and true leaves 7 and 18 days after inoculation. Significant variation in resistance was found. A limited number of accessions were free of visual symptoms of infection. One C. pepo accession and thirteen C. maxima accessions showed a high level of resistance. Generally, C. maxima may be considered more resistant to CMV compared to C. pepo. There is no close relationship between origin, fruit morphotypes and CMV resistance in either species. Some accessions (e.g., C. pepo PI 438699; C. maxima PI 176530, PI 265555, PI 368564, PI 500483) could be useful for the future breeding programmes. The C. pepo cvs. ‘Cinderella’ and ‘Defender’ F1, previously described as resistant, showed maximum susceptibility to the yellow strain of CMV.