Morphological and pathogenic characterization of Corynespora cassiicola isolates reveals specific genotypic interactions in soybean

Soybean target spot, caused by the fungus Corynespora cassiicola, is an important disease in northwestern Argentina (NWA). A cultural, morphological, and virulence characterization of 24 C. cassiicola isolates from different geographic localities in NWA was performed. The isolates were classified into five different cultural phenotypes, one of which has not been previously described. The ribosomal DNA internal transcribed spacer region sequence from five representative isolates (587 bp) exhibited 100% identity with C. cassiicola. A high variability of conidial morphology was observed among isolates, but no correlation with cultural phenotype was observed. When the soybean cultivar A 8000 RG was challenged with the 24 isolates, different degrees of virulence were observed, ranging from highly virulent to nonvirulent. No association of virulence with cultural or morphological characters was observed, but a relationship with geographical origin was demonstrated. Histopathological studies were performed on a nonvirulent and a highly virulent isolate. Microscopic observations of infected tissues of the former showed low mycelium development restricted to the upper epidermis, a thickening of the cuticle and primary wall of subepidermal cells, and accumulation of callose in phloematic vessels. In tissue infected with the latter, there was abundant mycelium development accompanied by cellular disorganization in mesophyll cells. Pathological challenges of isolates on nine different cultivars indicated that the degree of virulence of isolates depends on the plant genotype, demonstrating that the C. cassiicola–soybean interaction is highly specific. Understanding the genetic basis of this interaction will provide new information for better disease management and breeding strategies.     

Genotypic and phenotypic characterization of Streptomyces species associated with potato crops in the central part of Colombia

In Colombia, Streptomyces scabiei (syn. S. scabies) is commonly believed to be the causal organism of scab disease in local potato crops. However, very little is known about this organism and about the diversity and pathogenicity of the Streptomyces species associated with potato crops in Colombia. This study, therefore, aimed to elucidate aspects regarding the diversity of these bacteria associated with potato crops in a particular region of Colombia and evaluate their pathogenicity. We obtained 33 isolates of Streptomyces from netted, superficial and deep-pitted potato scab lesions from two main potato-producing regions in Colombia. Of these, 17 were pathogenic based on in vitro and in planta assays. None of these isolates carried the txtA, txtB, or nec1 genes, commonly associated with pathogenicity in Streptomyces, and characteristic of the pathogenicity island (PAI). We also characterized all isolates based on phenotypic characteristics and analysed their phylogenetic relationships using the 16S rRNA, atpD, recA, rpoB, and trpB genes. The isolates were highly diverse, placed in nine clades with 15 different phenotypes. The 17 pathogenic isolates were placed into three clades, namely S. pratensis, S. xiamenensis, and unknown species. This study is a preliminary investigation towards understanding scab disease in Colombia through the study of both pathogenic and nonpathogenic species present in scab disease lesions in potatoes. Also, this is the first report of Streptomyces species associated with potato tubers in Colombia.     

Response of Earthworm (Dichogaster saliens) To Different Feeding Substrates

Dichogaster saliens is an epigeic earthworm normally found in tropical agro-ecosystems. Due to its ecological feature, it was hypothesized that this earthworm can tolerate substrates enriched with fresh organic matter. The aim of this study was to test the effect of different substrates on the weight and reproduction of Dichogaster saliens in microcosms, with controlled temperatures of 27°C and a humidity of 33%. After 90 days of the experiment, substrates with 1.5% Mucuna pruriens var. utilis had the highest individual fresh weight of 360 ± 127 mg, and the highest growth rate of 3.54 ± 5.03 mg day^?1. These substrates had cocoons with most biomasses, and casts with the highest content of organic matter (4.81%), N (0.24%), available P (29.3 mg kg^?1) and k (2 cmol kg^?1). Substrates with 1.5% cow manure had a lower individual fresh weight of 55 ± 49.4 mg. The control treatment (soil without amendment) presented the lowest individual fresh weight. Although it was concluded that D. saliens responded positively to substrates with fresh organic matter, more experiments must be conducted to test the effect of substrates with higher percentages of organic matter.     

Tropical macrophyte degradation dynamics in freshwater sediments: relationship to greenhouse gas production

Purpose

We investigate the potential of increasing temperature on CH₄ and CO₂ (C gas) production in order to predict the C gas production in tropical freshwater ecosystems. We explored seasonal variation of C gas production by simulations of the anaerobic decomposition of Utricularia breviscapa within the sediment of a tropical aquatic system, using a bioassay response, within the context of carbon cycling.

Materials and methods

We incubated U. breviscapa detritus in lake water from Óleo Lagoon, Brazil, and measured rates of CO₂ and CH₄ production over 138 days at four distinct temperatures simulating seasonal conditions of the lagoon from which the plant was collected. Periodically, subsamples of gases contained in the headspace of the decomposition chambers were collected, and the concentrations of CO₂ and CH₄ were quantified by gas chromatography.

Results and discussion

Methane production was limited at temperatures below 20 °C. Higher temperatures favored formation of CO₂, while CH₄ was a secondary product. The CO₂ from the anaerobic metabolism of the sediment was the dominant final product.

Conclusions

Based on the responses from the bioassays simulating the anaerobic decomposition of the prevalent U. breviscapa, we conclude that in the cooler (<20 °C) season (June and July), CH₄ production is limited, and that year-round dominant mineralization product is CO₂. Our warmer incubations (i.e., >20 °C temperatures) indicate that CO₂ and CH₄ productions are both favored during warmer seasons, but CH₄ appears with a delayed response. Within the range of temperatures of this tropical environment, biogenic C gas emissions from anaerobic degradation processes in sediments contribute strongly to the accumulation of C gas through carbon dynamics.     

Structural Modifications of Gluten Proteins in Strong and Weak Wheat Dough During Mixing

The network‐forming attributes of gluten have been investigated for decades, but no study has comprehensively addressed the differences in gluten network evolution between strong and weak wheat types (hard and soft wheat). This study monitored changes in SDS protein extractability, SDS‐accessible thiols, protein surface hydrophobicity, molecular weight distribution, and secondary structural features of proteins during mixing to bring out the molecular determinants of protein network formation in hard and soft wheat dough. Soft wheat flour and dough exhibited greater protein extractability and more accessible thiols than hard wheat flour and dough. The addition of the thiol‐blocking agent N‐ethylmaleimide (NEM) resulted in similar results for protein extractability and accessible thiols in hard and soft wheat samples. Soft wheat dough had greater protein surface hydrophobicity than hard wheat and exhibited a larger decrease in surface hydrophobicity in the presence of NEM. Formation of high‐molecular‐weight (HMW) protein in soft wheat dough was primarily because of formation of disulfides among low‐molecular‐weight (LMW) proteins, as indicated by the absence of changes in protein distribution when NEM was present, whereas in hard wheat dough the LMW fraction formed disulfide interaction with the HMW fraction. Fourier transform infrared spectroscopy indicated formation of β‐sheets in dough from either wheat type at peak mixing torque. Formation of β‐sheets in soft wheat dough appears to be driven by hydrophobic interactions, whereas disulfide linkages stabilize secondary structure elements in hard wheat dough.     

Endometrial angiogenesis induced by uterine insufflation with an oxygen–ozone gas mixture in mares

Ozone (O₃) therapy has been used to improve peripheral tissue oxygenation in humans and domestic animals. The goal of the present study was to characterize histological changes in the endometria of healthy equines following tissue exposure to gas mixtures enriched with different concentrations of O₃. Cycling mares without endometrial degeneration were divided into three groups according to treatment (n = 9 mares/group). The uteri from the O₃, ½O₃ and control groups were insufflated for 3 min with gas containing 42, 21 and 0 μg O₃ ml^-1, respectively. Treatments were performed every three days from D0 to D6. Endometrial samples were collected immediately before the first treatment and 24 hr after the last treatment. The following nine histological parameters were evaluated: (i) the number of endometrial blood vessels, (ii) endometrial vascular degree (EVD), (iii) increase rate of blood vessels, (iv) increase rate of EVD, (v) glandular total area, (vi) glandular lumen area, (vii) intraglandular secretion area, (viii) glandular epithelial height and (ix) luminal epithelial height. In the O₃ group, a positive effect from treatment (p < .01) was detected for all vascular parameters (i, ii, iii and iv), glandular total area, intraglandular secretion area and glandular epithelial height. Compared to the control group, the ½O₃ group had greater (p < .01) EVD (84.1 ± 12%) and a higher increase rate of blood vessels (151.9 ± 47.1%). Uterine insufflation with low or intermediate concentrations of the O₂–O₃ gas mixture induced endometrial angiogenesis. Morphometry, but not morphology, of the endometrial glands was affected by local O₃ therapy. These findings would be of great significance for the development of new therapies for infertility in mares.     

PCR diagnosis of Fasciola hepatica in field-collected Lymnaea columella and Lymnaea viatrix snails

Fasciolosis, caused by the trematode Fasciola hepatica, is a zoonosis of economic importance in livestock that is emerging as a chronic disease in humans. The intermediate hosts are lymnaeid snails, in which diagnosis of infection is traditionally based on cercarial shedding, tissue sectioning and crushing. We developed a PCR assay for the sensitive and specific detection of F. hepatica in field-collected Lymnaea sp. snails. A primer pair was designed to amplify a 405 bp fragment of the cytochrome c oxidase subunit 1 gene of F. hepatica. The PCR assay showed a limit of detection of 10 pg of genomic F. hepatica DNA. No cross-reactions were observed with samples from other related trematode species or from the snail hosts Lymnaea columella and Lymnaea viatrix. DNA sequencing of the amplicon showed 100% homology with F. hepatica, and 75-89% homology with other trematodes on regions that did not include the entire set of primers. Two samples from Argentina were analysed. For snails in sample 1 (n = 240), identified as L. columella, the infection rate was 17.5 and 51.3% by direct examination and PCR, respectively. For snails in sample 2 (n = 34), identified as L. viatrix, the infection rate was 2.9 and 61.8% by direct examination and PCR, respectively. Differences in infection rates between these diagnosis methods were significant for both samples. Our PCR technique showed to be effective for detecting specific F. hepatica infections of low intensity in the intermediate host, and hence it could be used to study the epidemiological situation in a given area, as well as to assess host suitability for the parasite.     

Characterization of genetic diversity of puroindoline genes in Mexican wheat landraces

Grain hardness is a major factor determining milling performance of common wheat. It determines the amount of damaged starch generated during milling, and therefore the end use of a given variety. One hundred and two lines from 15 Mexican wheat landraces were analyzed for grain hardness and for its genetic control. Sixteen lines were hard and 86 were soft-textured. All hard lines could be explained by a mutation in either the Pina-D1 or Pinb-D1 genes. In six hard lines there was no amplification of Pina-D1, suggesting that this gene was deleted (Pina-D1b allele). The remaining ten hard lines showed the presence of both Pina-D1 and Pinb-D1. Sequencing the Pinb-D1 genes of the hard lines revealed the presence of two different alleles (Pinb-D1b and Pinb-D1e). The results substantiate the importance of very old Mexican landraces as potential sources of genetic diversity for key quality traits in the development of modern wheat cultivars with different grain textures.