Heterogeneity of gene expression in stromal fibroblasts of breast carcinomas and normal breast

Abstract #105

Background: The cancer microenvironment plays a critical role in tumor development and progression. Cancer associated fibroblasts (CAF) constitute a significant component of the tumor stroma and participate in reciprocal communication with the tumor cells. Information on differential gene expression specifically in stromal fibroblasts is sparse and data describing the variability of gene expression in CAF and normal fibroblasts (NF) is currently lacking. The purpose of this study was to identify genes differentially expressed in CAF and matched NF and to analyze the heterogeneity of gene expression profiles in the two cell types.
 Materials and methods: Fibroblast cell cultures were established from 6 patients with primary invasive breast cancer. Gene expression profiles were generated using oligonucleotide microarrays (Affymetrix HG-U133 Plus 2.0). Differentially expressed genes were ranked using Empirical Bayes modeling. A cut-off value of 0.005 was chosen for the posterior probability of equivalent expression. Lists of overexpressed genes were generated after eliminating genes with less than two-fold overexpression.
 Results: 17 genes were overexpressed in CAF compared to NF with known functions in paracrine and intracellular signaling, transcription regulation and extracellular matrix production. Using the same posterior probability cut-off, we identified 7 genes which were expressed at least two-fold higher in NF than in CAF. These genes have purported roles in steroid hormone metabolism, transcription, migration and cell signaling. Using semiquantitative RT-PCR and immunohistochemistry, we confirmed the over- and underexpression of a subset of 10 differentially expressed genes. The heterogeneity of gene expression in CAF vs. NF was compared with F-tests to determine variances. The estimated probability of NF gene expression variance being higher than CAF gene expression variance was 0.547 with a 95% confidence interval of 0.543 to 0.551 (p<0.0001), indicating that gene expression is more variable in NF than in CAF. By ranking the q-values of individual genes we identified 3 known genes, which show a significant difference in variance between CAF and NF (p<0.05).
 Conclusion: Altered gene expression in fibroblasts likely contributes to tumor growth and progression by enhancing ECM production, promoting stromal-epithelial paracrine signaling and altering steroid hormone metabolism. The inter-individual heterogeneity of gene expression in NF may indicate that the mammary stroma varies between individuals, supporting the hypothesis that the ability of the stroma to act as a barrier to cancer development and tumor progression may also be variable. Conversely, the heterogeneous gene expression in NF may be a reflection of a relative synchronization and uniformity of gene expression in CAF.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 105.

The application of random regression models in the genetic analysis of monthly egg production in turkeys and a comparison with alternative longitudinal models

Random regression models (RR) have become a popular methodology for the genetic study of longitudinal data since the last decade. The first objective of the current study was to investigate the application of RR models for the genetic analysis of egg production in turkeys. Data collected from a heavy dam line were used to estimate genetic parameters with 2 RR models, one having second-order Legendre polynomials as regression over time (RR2) and another with third-order polynomials (RR3). The second objective was to benchmark the performance of RR models with more conventional methods, so genetic parameters were reestimated using a multitrait (MT) and a repeatability model. To assess the model efficiency of predicting missing values, a reduced data set was used, and for each model, the predicted values of the deleted records were compared with the true values. The RR models were further compared against each other by eliminating the last period and estimating the MS error of the predictions for both models. The repeatability model had the poorest performance in predicting missing values. Heritability estimates from RR2 and MT models were close, whereas the RR3 model estimates were different. Both RR models demonstrated better prediction ability than the MT model. However, when RR models were compared solely, the RR2 model resulted in the smallest MS error. The results indicated that the RR3 model overfitted the data, suggesting that the choice of the appropriate polynomial order requires careful consideration. The present study illustrated that the application of RR models for the genetic analysis of egg production in turkeys is not only feasible but also offers a high accuracy of prediction.

Selection for litter size at day five to improve litter size at weaning and piglet survival rate

Selection for total number of piglets born (TNB) since 1992 has led to a significant increase in this trait in Danish Landrace and Danish Yorkshire but has also been accompanied by an increase in piglet mortality. The objective of this study was to estimate the genetic and phenotypic parameters for litter size and survival to find alternative selection criteria to improve litter size at weaning. Data from Landrace (9,300 litters) and Yorkshire (6,861 litters) were analyzed using REML based on a linear model including genetic effects of sow and service-sire. The estimates of heritability (based on the sow component) for TNB, number born alive (NBA), and number alive at d 5 after birth (N5D) and at weaning (about 3 wk, N3W) ranged from 0.066 to 0.090 in Landrace and 0.050 to 0.070 in Yorkshire. Genetic correlations between TNB and N3W were 0.289 in Landrace and 0.561 in Yorkshire, but between N5D and N3W the estimated genetic correlation was 0.995 in both populations. The approximate estimates of heritability for survival rate per litter at birth (SVB = NBA/TNB), from birth to d 5 (SV5 = N5D/NBA), and from d 5 to weaning (SVW = N3W/N5D) were 0.130, 0.131, and 0.023, respectively, in Landrace, and 0.095, 0.043, and 0.009, respectively, in Yorkshire. Genetic correlations between TNB and survival rates at different stages were negative. On the other hand, genetic correlations between N5D and survival rates and between N3W and survival rates were strongly or moderately positive, except for the correlations with SVW in Yorkshire. The results suggest that selection for N5D could be an interesting alternative to improve litter size at weaning and piglet survival for Danish Landrace and Danish Yorkshire.

Bayesian analysis of the linear reaction norm model with unknown covariates

The reaction norm model is becoming a popular approach for the analysis of genotype x environment interactions. In a classical reaction norm model, the expression of a genotype in different environments is described as a linear function (a reaction norm) of an environmental gradient or value. An environmental value is typically defined as the mean performance of all genotypes in the environment, which is usually unknown. One approximation is to estimate the mean phenotypic performance in each environment and then treat these estimates as known covariates in the model. However, a more satisfactory alternative is to infer environmental values simultaneously with the other parameters of the model. This study describes a method and its Bayesian Markov Chain Monte Carlo implementation that makes this possible. Frequentist properties of the proposed method are tested in a simulation study. Estimates of parameters of interest agree well with the true values. Further, inferences about genetic parameters from the proposed method are similar to those derived from a reaction norm model using true environmental values. On the other hand, using phenotypic means as proxies for environmental values results in poor inferences.

Foot Pad Dermatitis and Hock Burn in Broiler Chickens and Degree of Inheritance

A total of 2,118 birds from 2 strains were allocated to 12 groups of 93 to 100 each in 2 time-separated replicates. The development of foot pad dermatitis (FPD) and hock burn (HB) were recorded weekly from d 8 to slaughter on a set sample of live animals (7 per group). In addition, feet and hocks of all birds were investigated at slaughter at either 4, 6 (fast-growing strain), 8, or 10 (slow-growing strain) wk of age. Lesions were scored for both the left and right foot and classified according to a scale from 1 (no lesion) to 9 (very severe lesions) for FPD and from 1 (no lesion) to 3 (very severe lesions) for HB. No FPD lesions and very few low-grade HB lesions were found in chickens from the slow-growing strain. In the fast-growing strain, the first signs of FPD and HB were seen in wk 2. The incidence of both types of lesions increased thereafter. Foot pad dermatitis was more frequent in females (49 vs. 36%, P < 0.05). Body weight did not affect FPD, but more HB were found at higher BW (P < 0.01). Egg weight influenced neither FPD nor HB. Variance and covariance components were analyzed using a multivariate animal model, in which scores for FPD and HB were transformed into logarithmic scale. The analyses were carried out using restricted maximum likelihood algorithm. Heritabilities were estimated to be 0.31 +/- 0.12 (SE) for FPD, 0.08 +/- 0.08 for HB, and 0.38 +/- 0.13 for BW. Genetic correlations among these traits were low and nonsignificant. Phenotypic correlation between BW and FPD was low and nonsignificant and between BW and HB was 0.17 +/- 0.05 (P < 0.01). The relative high heritability of FPD and the low genetic correlation to BW suggested that genetic selection against susceptibility to FPD should be possible without negative effects on BW gain.

Activation of the stress protein response prevents the development of pulmonary edema by inhibiting VEGF cell signaling in a model of lung ischemia-reperfusion injury in rats

Lung endothelial damage is a characteristic morphological feature of ischemia-reperfusion (I/R) injury, although the molecular steps involved in the loss of endothelial integrity are still poorly understood. We tested the hypothesis that the activation of vascular endothelial growth factor (VEGF) cell signaling would be responsible for the increase in lung vascular permeability seen early after the onset of I/R in rats. Furthermore, we hypothesized that the I/R-induced pulmonary edema would be significantly attenuated in rats by the activation of the stress protein response. Pretreatment with Ad Flk-1, an adenovirus encoding for the soluble VEGF receptor type II, prevented I/R-mediated increase in lung vascular permeability in rats. Furthermore, the I/R-induced lung injury was significantly decreased by prior activation of the stress protein response with geldanamycin or pyrrolidine dithiocarbamate. In vitro studies demonstrated that VEGF caused an increase in protein permeability across primary cultures of bovine macro- and microvascular lung endothelial cell monolayers that were associated with a phosphorylation of VE- and E-cadherin and the formation of actin stress fibers. Activation of the stress protein response prevented the VEGF-mediated changes in protein permeability across these cell monolayers and reduced the phosphorylation of VE-and E-cadherins, as well as the formation of actin stress fibers in these cells.

Divergent Selection on Feather Pecking Behavior in Laying Hens Has Caused Differences Between Lines in Egg Production, Egg Quality, and Feed Efficiency

The correlated changes in egg production, egg quality, and feed efficiency (FE) due to selection for feather pecking (FP) were investigated by analyzing the data from an experiment including 2 divergently selected lines and a control line. The experiment was conducted with hens from 42 to 46 wk (hatch 1) and 39 to 43 wk (hatch 2) of age in the fifth generation of selection. The number of FP bouts per hour in the low FP line (LFP) was lower than the high FP line (HFP; 0.38 vs. 2.01), and total plumage score in line LFP was better than in line HFP (16.9 vs. 11.6). During the 4 wk, egg number and egg mass in line LFP were higher than those in HFP (24.4 vs. 18.3 and 1,223 vs. 1,132 g, respectively). On the other hand, line HFP had greater egg weight (60.7 vs. 59.2 g), albumen height (73.0 vs. 64.9 in Haugh units), shell thickness (38.1 vs. 37.0 mm), and yolk percentage (30.6 vs. 29.5%) than the LFP line. The control line was intermediate for those traits. The residual feed consumption (RFC) was highest in line HFP, lowest in line LFP, and intermediate in line C. Partial regressions of feed consumption (FC) on BW gain and egg mass were not significantly different among the 3 lines, whereas a significant difference in regression on metabolic BW (32.6 g/d in line LFP, 38.0 g/d in control line, and 43.4 g/d in line HFP) was observed. In addition, there was a negative regression of FC per day on plumage score (-1.73 g). The adjustment for plumage score accounted for 60% of the difference between regressions on metabolic BW in lines LFP and HFP. These results indicated that selection for FP has led to a change in egg production, egg quality, and FE. The better FE in line LFP resulted from a lower requirement for maintenance energy. The later was partly accounted for by a better plumage cover.

Variance components and selection response for feather-pecking behavior in laying hens

Variance components and selection response for feather pecking behavior were studied by analyzing the data from a divergent selection experiment. An investigation indicated that a Box-Cox transformation with power lambda = -0.2 made the data approximately normally distributed and gave the best fit for the model. Variance components and selection response were estimated using Bayesian analysis with Gibbs sampling technique. The total variation was rather large for the investigated traits in both the low feather-pecking line (LP) and the high feather-pecking line (HP). Based on the mean of marginal posterior distribution, in the Box-Cox transformed scale, heritability for number of feather pecking bouts (FP bouts) was 0.174 in line LP and 0.139 in line HP. For number of feather-pecking pecks (FP pecks), heritability was 0.139 in line LP and 0.105 in line HP. No full-sib group effect and observation pen effect were found in the 2 traits. After 4 generations of selection, the total response for number of FP bouts in the transformed scale was 58 and 74% of the mean of the first generation in line LP and line HP, respectively. The total response for number of FP pecks was 47 and 46% of the mean of the first generation in line LP and line HP, respectively. The variance components and the realized selection response together suggest that genetic selection can be effective in minimizing FP behavior. This would be expected to reduce one of the major welfare problems in laying hens.

Influence of early or late start of first feeding on growth and immune phenotype of broilers

1. The changes in body weight (BW) gain, immune phenotype and viability of commercial broilers, either given feed and water immediately after hatch or food-deprived for 24 or 48 h, were analysed in order to study the effect of early or late start of first feeding. 2. Chickens fed immediately had a 6.1% higher BW at slaughter age than those food-deprived for 48 h, while those chickens food-deprived for 24 h only had a 1.4% higher weight than those deprived for 48 h. 3. Those fed immediately and those food-deprived for 24 h did not differ significantly in BW. 4. Humoral immune status was measured as specific IgG antibody production and concentration of IgM and IgG in serum. Cellular immunological variables were the proportion of circulating leukocyte subpopulations and the relative expression of leukocyte surface markers, including the relative expression of Major Histocompatibility Complex (MHC) antigens. 5. Differences were found between the three feeding treatments in the relative expression of MHC class II molecules, the relative expression of BU-1 molecules, and the ratio of CD4:CD8 single positive cells. 6. For the MHC class II molecules, a lower expression was found on the surface of mainly B-cells in chickens fed immediately compared with the two other feeding regimes. 7. These results suggest that food deprivation for 48 h may be unfavourable to the growth, viability, and the immune performance of broilers, whereas deprivation for 24 h appears to be acceptable for growth and normal immunological performance.

Historical and contemporary multilocus population structure of Ascochyta rabiei (teleomorph: Didymella rabiei) in the Pacific Northwest of the United States

The historical and contemporary population genetic structure of the chickpea Ascochyta blight pathogen, Ascochyta rabiei (teleomorph: Didymella rabiei), was determined in the US Pacific Northwest (PNW) using 17 putative AFLP loci, four genetically characterized, sequence-tagged microsatellite loci (STMS) and the mating type locus (MAT). A single multilocus genotype of A. rabiei (MAT1-1) was detected in 1983, which represented the first recorded appearance of Ascochyta blight of chickpea in the PNW. During the following year many additional alleles, including the other mating type allele (MAT1-2), were detected. By 1987, all alleles currently found in the PNW had been introduced. Highly significant genetic differentiation was detected among contemporary subpopulations from different hosts and geographical locations indicating restricted gene flow and/or genetic drift occurring within and among subpopulations and possible selection by host cultivar. Two distinct populations were inferred with high posterior probability which correlated to host of origin and date of sample using Bayesian model-based population structure analyses of multilocus genotypes. Allele frequencies, genotype distributions and population assignment probabilities were significantly different between the historical and contemporary samples of isolates and between isolates sampled from a resistance screening nursery and those sampled from commercial chickpea fields. A random mating model could not be rejected in any subpopulation, indicating the importance of the sexual stage of the fungus both as a source of primary inoculum for Ascochyta blight epidemics and potentially adaptive genotypic diversity.

Molecular systematics of citrus-associated Alternaria species

The causal agents of Alternaria brown spot of tangerines and tangerine hybrids, Alternaria leaf spot of rough lemon and Alternaria black rot of citrus historically have been referred to as Alternaria citri or A. alternata. Ten species of Alternaria recently were described among a set of isolates from leaf lesions on rough lemon (Citrus jambhiri) and tangelo (C. paradisi × C. reticulata), and none of these isolates was considered representative of A. alternata or A. citri. To test the hypothesis that these newly described morphological species are congruent with phylogenetic species, selected Alternaria brown spot and leaf spot isolates, citrus black rot isolates (post-harvest pathogens), isolates associated with healthy citrus tissue and reference species of Alternaria from noncitrus hosts were scored for sequence variation at five genomic regions and used to estimate phylogenies. These data included 432 bp from the 5' end of the mitochondrial ribosomal large subunit (mtLSU), 365 bp from the 5' end of the beta-tubulin gene, 464 bp of an endopolygalacturonase gene (endoPG) and 559 and 571 bp, respectively, of two anonymous genomic regions (OPA1-3 and OPA2-1). The mtLSU and beta-tubulin phylogenies clearly differentiated A. limicola, a large-spored species causing leaf spot of Mexican lime, from the small-spored isolates associated with citrus but were insufficiently variable to resolve evolutionary relationships among the small-spored isolates from citrus and other hosts. Sequence analysis of translation elongation factor alpha, calmodulin, actin, chitin synthase and 1, 3, 8-trihydroxynaphthalene reductase genes similarly failed to uncover significant variation among the small-spored isolates. Phylogenies estimated independently from endoPG, OPA1-3 and OPA2-1 data were congruent, and analysis of the combined data from these regions revealed nine clades, eight of which contained small-spored, citrus-associated isolates. Lineages inferred from analysis of the combined dataset were in general agreement with described morphospecies, however, three clades contained more than one morphological species and one morphospecies (A. citrimacularis) was polyphyletic. Citrus black rot isolates also were found to be members of more than a single lineage. The number of morphospecies associated with citrus exceeded that which could be supported under a phylogenetic species concept, and isolates in only five of nine phylogenetic lineages consistently were correlated with a specific host, disease or ecological niche on citrus. We advocate collapsing all small-spored, citrus-associated isolates of Alternaria into a single phylogenetic species, A. alternata.

Fabrication of ordered arrays of InP microstructures by wet chemical etching with Au masks

Ordered arrays of InP microstructures have been fabricated on InP(001) substrates by wet chemical etching in aqueous HCl with patterned Au masks. The masks were produced by Au deposition through copper grids or a monolayer of polystyrene microspheres. Square InP mesas (20 x 20 microns) and pillars (approximately 100 nm in both diameter and height) were both produced and characterized by scanning electron microscopy and atomic force microscopy.

Effects of alcohol on blood pressure and production of vascular aldosterone and corticosterone

AIMS

The aims of this study were to search for the role of alcohol in blood pressure regulation in rats and to investigate the effects of alcohol on the production of vascular aldosterone and corticosterone.

METHODS

Male Wistar rats received alcohol 0.7 g x kg(-1) x day(-1) (alcohol-treated group 1) or 1.4 g x kg(-1) x day(-1) (alcohol-treated group 2) or 2.1 g x kg(-1) x day(-1) (alcohol-treated group 3), orally, for 3 months, and blood pressure was monitored by a pressure transducer. Systolic blood pressure increased in Wistar rats treated with alcohol compared to control rats. Mesenteric artery perfusion ex vivo was performed and pressor responses to norepinephrine were determined. The pressor responses to norepinephrine in mesenteric arteries treated with alcohol were significantly increased. The perfusate from the mesenteric arteries was collected and applied to a Sep-Pak C 18 cartridge column for reverse-phase high-performance liquid chromatography and aldosterone and corticosterone levels were determined by radioimmunoassay, aldosterone was decreased but corticosterone was increased in the perfusate from arteries treated with alcohol.

RESULTS

Reverse transcriptase polymerase chain reaction showed that alcohol inhibited the expression of 11beta-HSD2 and CYP11B2 mRNA in mesenteric arteries.

CONCLUSIONS

These results reveal that alcohol is able to induce hypertension and provide evidence that alcohol inhibits the transcriptions of both 11beta-HSD2 and CYP11B2 in the vasculature, leading to lower aldosterone and higher corticosterone production in vessels, and increased vasoconstrictor responses to norepinephrine.

Stimulation of Na-K-2Cl cotransporter in neurons by activation of Non-NMDA ionotropic receptor and group-I mGluRs

In a previous study, we found that Na(+)-K(+)-2Cl(-) cotransporter in immature cortical neurons was stimulated by activation of the ionotropic N-methyl-D-aspartate (NMDA) glutamate receptor in a Ca(2+)-dependent manner. In this report, we investigated whether the Na(+)-K(+)-2Cl(-) cotransporter in immature cortical neurons is stimulated by non-NMDA glutamate receptor-mediated signaling pathways. Expression of the Na(+)-K(+)-2Cl(-) cotransporter and metabotropic glutamate receptors (mGluR1 and 5) was detected in cortical neurons via immunoblotting and immunofluorescence staining. Significant stimulation of cotransporter activity was observed in the presence of both trans-(+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD) (10 microM), a metabotropic glutamate receptor (mGluR) agonist, and (RS)-3,5-dihydroxyphenylglycine (DHPG) (20 microM), a selective group-I mGluR agonist. Both trans-ACPD and DHPG-mediated effects on the cotransporter were eradicated by bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-AM, a Ca(2+) chelator. In addition, DHPG-induced stimulation of the cotransporter activity was inhibited in the presence of mGluRs antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) (1 mM) and also with selective mGluR1 antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) (100 microM). A DHPG-induced rise in intracellular Ca(2+) in cortical neurons was detected with Fura-2. Moreover, DHPG-mediated stimulation of the cotransporter was abolished by inhibition of Ca(2+)/CaM kinase II. Interestingly, the cotransporter activity was increased by activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. These results suggest that the Na(+)-K(+)-2Cl(-) cotransporter in immature cortical neurons is stimulated by group-I mGluR- and AMPA-mediated signal transduction pathways. The effects are dependent on a rise of intracellular Ca(2+).

Off-diagonal long-range order in Bose liquids: irrotational flow and quantization of circulation

On the basis of gauge invariance, it is proven in an elementary and straightforward manner, but without invoking any ad hoc assumption, that the existence of off-diagonal long-range order in one-particle reduced density matrix in Bose liquids implies both the irrotational flow in a simply connected region and the quantization of circulation in a multiply connected region, the two fundamental properties of a Bose superfluid. The origin for both is the phase coherence of condensate wave functions. Some relevant issues are also addressed.

Divergent selection on feather pecking behaviour in laying hens (Gallus gallus domesticus)

A selection experiment was initiated in 1996 in which selection for (HP line) and against (LP line) feather pecking was performed. The foundation stock was a White Leghorn layer strain established in 1970 and maintained since then as a random bred control line at the Institute. Six hatches were produced over three generations. At the age of 68 weeks (generation 0, 1996), 35 weeks (generation 1, 1997), 30 weeks (generation 2, 1998), and 27 weeks (generation 3, 1999) female birds were transferred to observation pens and their feather pecking behaviour was recorded. In each generation, 30 females and 8 males were selected from approximately 200 females and 60 males. The selection criterion was breeding value estimated by animal model on the trait 'number of bouts of feather pecking per bird per hour'.Feather pecking behaviour in adult hens was significantly higher in HP than in LP. In generation 2 the following was recorded: 3.10 versus 1.37 bouts per bird per hour (P<0.01), 7.04 versus 3.58 pecks per bird per hour (P<0.05) and the proportion of hens recorded feather pecking in the 180min observation period was 67 versus 56% (P<0.05). In generation 3 the following was recorded: 4.56 versus 0.63 bouts per bird per hour (P<0.001), 13.9 versus 2.51 pecks per bird per hour (P<0.001) and the proportion of hens recorded feather pecking in the 180min observation period was 75 versus 49% (P<0.001).In generation 3, plumage condition was better in LP on neck, breast, back, wings and tail, as well as overall (P<0.001). Body weight did not differ between lines in generation 2, but in generation 3, HP hens were on average heavier than LP hens at the age of 27 weeks (1435g versus 1371g, P<0.001).

Relationships in broiler chickens between lameness, liveweight, growth rate and age

Thirteen genotypes of poultry were selected to represent a wide range of growth profiles and were fed either a non-limiting or Label Rouge diet. The birds' degree of lameness and liveweight were measured after 54 and 81 days. The birds reared on the Label Rouge diets were less lame than birds of the same genotype reared on the non-limiting diet. More traditional and slower growing genotypes tended to be less lame than the modern genotypes reared on the same feeding regimen. All the birds, irrespective of their genotype or diet, were less lame after 54 days than after 81 days. However, when liveweight was included in the analysis as a covariable, many of the differences disappeared. Only age at assessment significantly affected the walking ability of the birds, with the birds being approximately 0.6 units of gait score worse at 54 days of age than at 81 days. The regression coefficient between gait score and liveweight was 1.262 at 54 days and 1.128 at 84 days. The results indicated that liveweight was an important determinant of lameness in the diverse range of genotypes examined, that growth rate was also an important determinant of lameness and that younger birds may be more sensitive to differences in liveweight than older birds.

Host Specialization in the Charcoal Rot Fungus, Macrophomina phaseolina

ABSTRACT To investigate host specialization in Macrophomina phaseolina, the fungus was isolated from soybean, corn, sorghum, and cotton root tissue and soil from fields cropped continuously to these species for 15 years in St. Joseph, LA. Chlorate phenotype of each isolate was determined after growing on a minimal medium containing 120 mM potassium chlorate. Consistent differences in chlorate sensitivity were detected among isolates from different hosts and from soil versus root. To further explore genetic differentiation among fungal isolates from each host, these isolates were examined by restriction fragment length polymorphism and random amplified polymorphic DNA (RAPD) analysis. No variations were observed among isolates in restriction patterns of DNA fragments amplified by polymerase chain reaction covering the internal transcribed spacer region, 5.8S rRNA and part of 25S rRNA, suggesting that M. phaseolina constitutes a single species. Ten random primers were used to amplify the total DNA of 45 isolates, and banding patterns resulting from RAPD analysis were compared with the neighbor-joining method. Isolates from a given host were genetically similar to each other but distinctly different from those from other hosts. Chlorate-sensitive isolates were distinct from chlorate-resistant isolates within a given host. In greenhouse tests, soybean, sorghum, corn, and cotton were grown separately in soil infested with individual isolates of M. phaseolina that were chosen based on their host of origin and chlorate phenotype. Root colonization and plant weight were measured after harvesting. More colonization of corn roots occurred when corn was grown in soil containing corn isolates compared with isolates from other hosts. However, there was no host specialization in isolates from soybean, sorghum, or cotton. More root colonization in soybean occurred with chlorate-sensitive than with chlorate-resistant isolates.