Genetic diversity of Panax vietnamensis var. langbianensis populations in Lam Vien plateau - Vietnam detected by inter simple sequence repeat (ISSR) markers

Panax vietnamensis var. langbianensis is a new variety from Lam Vien plateau of Vietnam. In this study, inter simple sequence repeat (ISSR) markers were employed to investigate the genetic diversity and variability of 115 individuals belonging to two naturally distributed populations of this variety, which classified by habitat. Genetic diversity at the taxon level was high (HeT = 0.284 and PPBT = 97.2 %). The result showed lightly higher genetic diversity in population in Lac Duong region (HeLD= 0.228 and PPBLD = 81.5 %) as compared to those located in Dam Rong region (HeDR= 0.213 and PPBDR = 79.4 %). The interpopulation gene differentiation was high (GST Total = 0.221) with the genetic distance among populations was DLD-DR = 0.191. Gene flow within populations was Nm = 0.8793. In Lac Duong population, the genetic diversity of older group (HeLD O = 0.233; PPBLD O = 77.1%) was higher than of younger group (HeLD Y = 0.214; PPBLD Y = 72.4 %) and the intergroup gene differentiation was GSTDL = 0.0205 with the genetic distance between these two group was DLD O-Y = 0.0061 showed the risk of reduction in genetic diversity. In Dam Rong population, the genetic diversity of older group (HeDR O = 0.204; PPBDR O = 75.2 %) was equal to younger group (HeDR Y = 0.209; PPBDR Y = 72.7 %) and the intergroup gene differentiation was GSTDR = 0.0304 with the genetic distance between them was DDR O-Y = 0.01393 showed the stability in genetic diversity. Data for genetic diversity and variation from this study can be used to further investigate and protect this variety for conservation and development purposes and for sustainable exploiting and use of these valuable natural resources.

Genetic Differentiation and Host Specificity Among Populations of Alternaria spp. Causing Brown Spot of Grapefruit and Tangerine × Grapefruit Hybrids in Florida

Alternaria spp. were sampled from brown spot lesions in several geographically separated citrus groves and different grapefruit and tangerine × grapefruit hybrid cultivars in Florida and screened for variation at 16 putative random amplified polymorphic DNA loci. Populations of the pathogen on two hybrids, Minneola and Orlando, in five locations throughout Florida were moderately differentiated (Nei's coefficient of gene differentiation [GST] = 0.12) among locations. The hypothesis that host-specialized forms of Alternaria spp. cause brown spot on different Citrus spp. and cultivars was tested by estimating genetic differentiation among isolates sampled from different hosts and by pathogenicity assays. Isolates sampled from grapefruit and the hybrid cv. Nova were genetically distinct from isolates sampled from other hybrid cultivars including Robinson, Sunburst, Minneola, Orlando, and Murcott. No differentiation could be detected among isolates sampled from this latter group of hybrids. Quantitative pathogenicity assays on leaves using spray inoculation revealed that ‘Nova’ isolates were not significantly more pathogenic on ‘Nova’ compared with isolates from ‘Minneola’ and ‘Orlando’. Similarly, grapefruit isolates were not significantly more pathogenic on grapefruit compared with isolates from ‘Minneola’. Isolates from all hosts had similar disease rankings on each inoculated cultivar, with ‘Minneola’ the most susceptible, followed in decreasing order of susceptibility by ‘Orlando’, ‘Sunburst’, ‘Nova’, and ‘Duncan’ grapefruit. Rough lemon was generally immune to all isolates tested; however, occasional brown spot lesions were observed on leaves of this host with isolates from grapefruit. No evidence was found to support the hypothesis that unique genotypes of the pathogen, which are more virulent on ‘Sunburst’ or grapefruit, have been introduced to Florida. Populations of Alternaria spp. causing brown spot of citrus on grapefruit and ‘Nova’ in Florida are genetically distinct from isolates on other cultivars, and we speculate that these populations are in the early stages of adaptation to and possible speciation on these hosts.

Gene Differentiation in Pacific Salmon (Oncorhynchus sp.): Facts and Models with Reference to Pink Salmon (O. gorbuscha)

Analyzing population genetic data usually involves examining relationships among populations followed by analysis of the distribution of genetic variability. Genetic relationships are often depicted with multidimensional scaling or trees constructed from genetic distances; genetic variation within and among populations is partitioned using gene diversity measures such as FST or GST. Genetic distances or gene diversity are often used to estimate influences of gene drift, migration, and/or selection on observed gene differentiation. We used allozyme data for pink salmon populations to examine the theoretical models available for estimating magnitudes of these factors in Pacific salmon populations. The models included (1) mutation and gene drift; (2) mutation and migration; (3) migration and gene drift; and (4) gene drift, migration, and selection. These models suggest that gene drift and migration are probably important at the lowest levels of population hierarchy, but even very small forces such as weak heterogeneous selection and low migration levels may be important at higher levels. The accuracy of some estimates should be questioned because for many situations appropriate models are either not yet available or are not sufficiently refined. Also, the dynamic genetic structure of salmon populations makes it unlikely that the steady state assumed for many theoretical models has obtained.

Specific status of Aquarius cinereus (Puton) and A. najas (De Geer) (Hemiptera: Gerridae) and the extent of hybridization in the Mediterranean region

Results of field observations, cross-breeding experiments, morphometry, and starch gel electrophoresis suggest that A. cinereus and A. najas are specifically distinct. Cross-breeding experiments between the two taxa in the laboratory were only successful when using males of A. cinereus and females of A. najas. Field observations on mixed populations in spring did not reveal any pre- or postcopulae involving partners of the two taxa (assigned by body length). Instead all pairs observed consisted of conspecific males and females. Morphometry of field caught adults of A. najas and A. cinereus yielded a clearly bimodal distribution of body length with only very few individuals of intermediate size. Therefore, body length alone allows reasonable separation of the two taxa in natural populations. Although F1-hybrids from laboratory rearings (photoperiod 18L:6D, temperature ∼ 23°C) differed only marginally in body length from A. najas reared under the same conditions, backcrosses and also F2-hybrids were of intermediate size. In the field individuals of both taxa are predominantly wingless, but both hybrids and backcrosses from the laboratory showed a net shift in morph ratio with many longwinged specimens. Vertical starch gel electrophoresis of three monomorphic (Apk, Got-2, Mdh-2), six polymorphic loci with low levels of polymorphism (Idh-1, Fum, Got-1, Mdh-1, Me, 6-Pgd) and three highly polymorphic loci (Es-4, Idh-2, Pgm) suggests that the two taxa do not share a common gene pool. Gene differentiation among all A. cinereus populations as measured by Nei's GST values is very low. Between Tyrrhenian and continental A. najas populations, however, gene differentiation is very high, and in the same order of magnitude as gene differentiation between the two taxa A. cinereus and A. najas in sympatric populations. Our field observations, together with morphometric data, laboratory rearings, and information on wing polymorphism, suggest that hybridization in natural populations is rare.