No abstract

Spatially restricted gene flow and resulting spatial genetic structure are generally considered as being the primary controlling factors in the dynamics of biparental inbreeding depression in a wide range of plant species. However, wind-pollinated angiosperm trees have not been studied adequately in this respect. The present study analyses the relationships among parental genetic similarity, outcrossing distances, progeny vigour and mortality in Polylepis australis (Rosaceae), a wind-pollinated treeline species endemic to Argentina. We investigated whether spatial genetic structuring occurs in anthropogenically fragmented P. australis woodlands of the Córdoba Mountains. We also performed a controlled crossing experiment using pollen collected from different distances. Genetic variability (using RAPD-PCR), vigour (N-metabolism capacity) and mortality of the resulting progeny were contrasted with progeny from unmanipulated flowers. We found a continuous decrease in parental genetic similarity with spatial distance among mates and an increase in N-metabolism capacity in the progeny produced from pollen at increasing distances, as well as a very high mortality of seedlings resulting from short-distance crosses. Additionally, our results suggest that there is still fragment connectivity in P. australis through long-distance pollen-mediated gene flow.

Aedes aegypti showed the ability to develop resistance to different insecticides, including temephos, the most widely used larvicide. The objectives of this work were to 1) determine the resistance value of 4 natural subpopulations of Ae. aegypti, identified by their different haplotypes, to the insecticide temephos "Abate 1G (1%)"; 2) determine the lethal concentration (LC)50 and LC90 values by using the Rockefeller strain as control; and 3) estimate the resistance ratios. Mosquito samples were collected in Catamarca, Córdoba, and Posadas (Argentina) and in Yacuiba (Bolivia). Six insecticide concentrations were tested. The Rockefeller strain and the Posadas sample showed susceptibility to the diagnostic concentration (0.012 mg/liter), whereas the mortality in Catamarca was 87%. In the Yacuiba and Córdoba collections, mortality was 74% and 75%, respectively, indicating resistance. These results were coincident with those of the Probit analysis from which the highest resistance ratios were estimated for the last 2 subpopulations (5.2 and 4.9, respectively). Before this study, no information was available about the existence of resistance in natural populations of Ae. aegypti in the studied area.

The effects of insect cadavers infected with three isolates of Heterorhabditis bacteriophora and one isolate of Steinernema diaprepesi on a population of Meloidogyne incognita in pepper (Capsicum annuum) and summer squash (Cucurbita maxima) were evaluated in greenhouse experiments carried out in Santa Fe (Argentina). Insect cadavers were obtained for the experiments from last instar larvae of Galleria mellonella and Tenebrio molitor that had been infected with entomopathogenic nematodes. Two six-day-old insect cadavers per pot were placed below the soil surface, and the soil was inoculated with 100 second-stage juveniles of M. incognita. Sixty days after inoculation, the following parameters were recorded for each plant: number of leaves; dry weight of aerial parts; numbers of galls, egg masses and eggs; and numbers of galls, egg masses and eggs g -1 of root fresh matter. In pepper, the only variable affected by the infected cadavers with respect to control was the number of eggs in the treatment involving T. molitor cadavers infected with the H. bacteriophora isolate Rama Caída. In summer squash, several treatments using infected cadavers resulted in a decrease in the numbers of galls and egg masses. Only the treatment involving G. mellonella cadavers infected with the H. bacteriophora isolate Rama Caída proved to be efficient in reducing the number of M. incognita eggs. Our results indicated that the application of insect cadavers infected with the entomopathogenic nematodes studied might reduce M. incognita damage in pepper and summer squash plants.

The plant‐parasitic nematode Nacobbus aberrans sensu lato is an agricultural pest of quarantine importance. Due to the morphometric, physiological and genetic variability observed within the species, there is no agreement on the taxonomy of this nematode. The objective of this study was to analyse the ITS rDNA region and the D2–D3 expansion segments of 28S rDNA in 10 Argentine populations and one from Ecuador and to establish their phylogenetic relationship with other known sequences from South and North America. Phylogenetic trees of the ITS gene showed seven statistically well‐supported clades; the high and significant Fst values obtained among these groups confirmed this partitioning. The Argentine populations here considered were separated into three clades: one comprising a population from the Andean region and two grouping nematodes from lower altitudes. Three other clades were distinguished for South American populations, which included known sequences of individuals from Peru, Bolivia and north of Argentina. The other clade included sequences from Mexico, Ecuador and two Argentine populations of unknown origin. The important degree of genetic divergence observed among Andean populations suggests that the Andes may have played a crucial role in speciation of Nacobbus, which would have originated in this region. Although D2–D3 segments exhibited lower variation, they were useful for establishing phylogenetic relationships among the Argentine populations considered in this work. As there are no other GenBank sequences available for these segments, it was not possible to make comparisons with other populations from South and North America. The considerable genetic differentiation observed in ITS rDNA region among Nacobbus populations showed evidence of cryptic species within the N. aberrans s.l. complex. Integration of morphological and morphometric studies and molecular analyses considering other genes may aid in the identification of species and their phylogenetic relationships within this genus.

No abstract

Meloidogyne hapla and Nacobbus aberrans are plant-parasitic nematodes that form galls in the roots of infected plants and cause important economic losses. Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis infect and kill insects via toxins produced by their symbiotic bacteria. EPNs have shown to have an antagonistic effect on different plant-parasitic nematode species in field and greenhouse trials. The aim of the present work was to evaluate, in tomato plants in greenhouse, the effect of the application of three Argentine EPN isolates, their symbiotic bacteria and cell-free supernatants, on a population of M. hapla and two populations of N. aberrans. Sixty days after inoculation, the number of galls and egg masses, the nematode reproduction factor (RF) and plant biomass were calculated. None of the plant-parasitic nematode populations or plant biomass was affected by infective juvenile inoculation of the different EPN isolates. Bacterial action differed among populations; M. hapla was the most susceptible one, with a significant reduction in the number of galls, egg masses and RF caused by the application of the three bacterial strains. The most significant effect was produced by the cell-free supernatants on nematode RF, with reductions of 62-90%, caused by bacterial metabolites. The different inoculation alternatives of the EPN-bacterial symbiont complex tested in the present work (infective juveniles, bacteria and cell-free supernatant) are compared for the first time for plant-parasitic nematode species.

Entomopathogenic nematodes of the families Heterorhabditidae Poinar, 1976 and Steinernematidae Chitwood & Chitwood, 1937 are used for biological control of insect pests. An isolate of Steinernema diaprepesi Nguyen & Duncan, 2002 was recovered from a carrot field in the locality of Santa Rosa de Calchines (Santa Fe Province, Argentina). These nematodes were characterised based on morphological, morphometric and molecular studies. Their symbiotic bacterium was identified as Xenorhabdus doucetiae Tailliez, Pagès, Ginibre & Boemare, 2006 by sequencing the 16S rRNA gene. The isolate of S. diaprepesi studied exhibits some morphometric differences with the original description, especially in the first generation adults. This is the first description of the species in Argentina.