Genetic polymorphism in Chondrilla (Asteraceae) in southern European Russia and the nature of Chondrilla juncea L

We studied genetic diversity in 54 populations of nine sexual and apomictic species of the genus Chondrilla (C. acantholepis, C. ambigua, C. brevirostris, C. canescens, C. graminea, C. juncea, C. laticoronata, C. latifolia and C. pauciflora) in SE European Russia and neighboring territories of NW Kazakhstan. We analysed the trnT–trnF region of plastid DNA and the internal transcribed spacer of ribosomal DNA (ITS1–5.8S–ITS2) using statistical parsimony, maximum likelihood and neighbor net methods. Two major evolutionary lineages, roughly corresponding to the two subgenera traditionally recognized in the region, were revealed. Within the first evolutionary lineage (subgenus Brachyrhynchus), the sexual diploid C. ambigua and its putatively hybrid apomictic derivatives C. brevirostris, C. laticoronata and C. pauciflora could be recognized. Their identity was also confirmed by analyses of ISSR markers. The second evolutionary lineage (subgenus Chondrilla) comprises C. juncea, C. acantholepis, C. canescens, C. graminea and C. latifolia in European Russia, but analyses of morphological variability and the genealogy of plastid and nuclear markers favor their treatment as the single facultatively apomictic species C. juncea. The results demonstrate that an apomictic mode of reproduction does not necessarily result in the formation of genetically separated microspecies.     

DOES COSMOPOLITANISM RESULT FROM OVERCONSERVATIVE SYSTEMATICS? A CASE STUDY USING THE MARINE SPONGE CHONDRILLA NUCULA

The sponge species Chondrilla nucula has a simple morphology and a very wide geographical distribution. To verify whether the latter might be an artifact of the former, samples of this species were collected across 10,000 km of its range, in the Mediterranean, the Caribbean, and the southwestern atlantic. The classical (spicule morphology) and molecular (allozymes) systematic approaches were compared, to try to define the geographic limits between populations and detect possible cryptic species. We found five distinct genetic forms within C. nucula that sometimes showed morphological homogeneity and other times plasticity. The difference in size of spicules could not be related to the clear-cut genetic differences, suggesting that the use of spicule sizes for sponge systematics should be reappraised. The population of one of the genetic forms along 3000 km of the Brazilian coast was highly structured (F_ST = 0.21; N_em = 0.96). Our results reject the null hypothesis of cosmopolitanism of C. nucula and indicate that the putative worldwide distribution of some marine sponges, and possibly many other benthic invertebrates, may be the result of overly conservative systematics. Cryptic species appear to be particularly prevalent when genera are well defined but species are characterized by only a few morphological characters.     

Frequency-dependent selection in a wild plant-pathogen system

This study investigated the occurrence of the rust fungus Puccinia chondrillina in clonal populations of its host plant, Chondrilla juncea. In 16 populations spread across eastern Turkey, 48 different multilocus isozyme phenotypes were identified in the host. Of these clones, 88% were restricted to single localities, while the remaining 12% were found in 2–11 populations. For 13 of the 16 plant populations the commonest host clone was always infected. Indeed, at ten sites this clone was the only one found to carry disease. In the remaining three populations the rusted plants were all of the second commonest isozyme type. The possibility of such a tight association of rust incidence with host clone frequency simultaneously across a wide geographic area is very low (P0.023), supporting the contention that the pathogen P. chondrillina may be imposing negative frequency-dependent selection on these C. juncea populations.     

Three new species of the genus Leveillula from Iran

 Based on molecular and morphological studies, Leveillula guilanensis sp. nov. on Chondrilla juncea, L. lactucae-serriolae sp. nov. on Lactuca serriola, and L. mindii sp. nov. on Mindium laevigatum are described from Iran. Received: May 7, 2002 / Accepted: September 5, 2002 Correspondence to:S. Takamatsu     

Unusual microtubular cytoskeleton of apomictic embryo sac of Chondrilla juncea L.

Summary. The mature apomictic embryo sac of Chondrilla juncea is highly vacuolated and demonstrates a polarization similar to that of the amphimictic gametophyte. The microtubule cytoskeleton of this embryo sac is uncharacteristic and relatively weak. The microtubules are positioned along cell walls and resemble cortical microtubules of somatic cells. They do not form the parallel, brushlike structures observed around the filiform apparatus of synergids in the amphimictic embryo sac. In the apomictic embryo sac, the microtubules of both the egg cell and the central cell develop a cortical-like structure, which is entirely different from the radial arrangement observed around the nuclei in the amphimictic embryo sac. Correspondence and reprints: Department of Plant Cytology and Embryology, Jagiellonian University, Grodzka 52, 31-044 Kraków, Poland.     

Evaluation of weed eradication programs: the delimitation of extent

Eradication is a management strategy that can provide substantial ecological and economic benefits by eliminating incursions of pest organisms. In contrast to eradication efforts that target other pests, weed eradication programs can be very protracted owing to the presence of persistent seed banks and difficulties in detecting the target. Hence there is a need to develop criteria to assist in the evaluation of progress towards eradication. Knowledge of the extent of a weed incursion (the ‘delimitation’ criterion) is considered fundamental for eradication success, as an incursion will progress from any infestations that remain undetected and thus uncontrolled. This criterion is examined with regard to eradication programs targeting Bassia scoparia L. A.J. Scott [= Kochia scoparia L. Schrader], Chondrilla juncea L. (both in Western Australia) and Orobanche ramosa L. in South Australia. The B. scoparia incursion, which has been eradicated, was largely delimited within 12 months of the inception of its eradication program. In contrast, the Western Australian C. juncea incursion has never been delimited, owing to insufficient investment in surveillance during an eradication program spanning 30 years. An exponential decrease in the detection ratio (infested area detected/area searched) over time suggests that delimitation has been approached within 6 years of the inception of the eradication program for O. ramosa. An effective surveillance program is essential for achieving delimitation of a weed incursion.