Enhanced white rot control in garlic bulbil using organic-inorganic hybrid materials as coating membranes.

Organic-inorganic hybrid materials have a range of applications due to their unique properties. Their application in agriculture brings alternatives for the controlled release of nutrients in the soil, the seed coating, the transport of herbicides, and the treatment of plant diseases. The present study aimed to investigate the use of fungicides incorporated into hybrid membranes formed by synthetic hectorite (LAPONITE®) and polymers in the pre-treatment of garlic bulbils exposed to the pathogen Stromatinia cepivora, which causes white rot. The coatings were selected by a germination test, based on the bulbil sprouting index, and by a mycelial growth inhibition test, based on the percentage of mycelial growth inhibition. The chosen membranes were used to coat the bulbils for bioassays conducted in a biochemical oxygen demand incubator at 17 °C. The coated bulbils were planted in soil samples containing three different densities of Stromatinia cepivora: 0.1 g, 1.0 g, and 10 g of sclerotium per L of soil. Membranes containing 2% carboxymethyl cellulose and 2% LAPONITE® incorporated with (i) the fungicide tebuconazole (36 mg L-1) and (ii) the combination of the actives tebuconazole (36 mg L-1) and triadimenol (62 mg L-1) showed the total rate of sprouting and null indices of incidence of symptoms and mortality in its repetitions. The hybrid membranes were characterized employing several techniques, including X-ray diffraction, infrared and Raman spectroscopy, thermogravimetric analysis and differential scanning calorimetry coupled to mass spectrometry, and optical microscopy. Characterization data confirmed the presence of fungicides incorporated into the membranes. Some concentrations of fungicides were low enough not to be detected in all analyses performed, although they guaranteed a protective character to the bulbils about the fungus S. cepivora present in the soil, with a possibility of antifungal pre-treatment with a potential reduction in the concentration used.

Evidence of Pyricularia oryzae adaptability to tricyclazole.

Pyricularia oryzae is the etiological agent of rice blast, the most destructive disease in rice crops and chemical control based on fungicide is the main method used in its management. The aim of this study was characterize pathogenicity and identify P. oryzae isolates adapted to tricyclazole. P. oryzae monosporic isolates were collected in the state of Tocantins and inoculated in international differentiating series of rice cultivars for determination of pathotypes. After, the same isolates were inoculated in the rice cultivar IRGA 424 to evaluate resistance to fungicide Bim® 750 BR (Tricyclazole - 250 g/ha) that was applied 24 and 48 hours after pathogen inoculation (hai). Leaf blast severity and infection efficiency were evaluated 9 days after inoculation (dai), latency period (2 dai) and sporulation intensity (7 dai). Nine different pathotypes were identified, predominantly as IA group. The latent period of isolates occurred between from 48 to 120 h. The application of tricyclazole, 24 hai reduced disease severity with the exception of the isolate Py 7.1. The great variability of the pathogen allowed for adaptation to this molecule and can increase its aggressiveness and should be considered to guide the integrated management of the disease.

Contrasting genetic structure between two begomoviruses infecting the same leguminous hosts.

Begomoviruses are whitefly-transmitted, ssDNA plant viruses and are among the most damaging pathogens causing epidemics in economically important crops worldwide. Wild/non-cultivated plants play a crucial epidemiological role, acting as begomovirus reservoirs and as 'mixing vessels' where recombination can occur. Previous work suggests a higher degree of genetic variability in begomovirus populations from non-cultivated hosts compared with cultivated hosts. To assess this supposed host effect on the genetic variability of begomovirus populations, cultivated (common bean, Phaseolus vulgaris, and lima bean, Phaseolus lunatus) and non-cultivated (Macroptilium lathyroides) legume hosts were sampled from two regions of Brazil. A total of 212 full-length DNA-A genome segments were sequenced from samples collected between 2005 and 2012, and populations of the begomoviruses Bean golden mosaic virus (BGMV) and Macroptilium yellow spot virus (MaYSV) were obtained. We found, for each begomovirus species, similar genetic variation between populations infecting cultivated and non-cultivated hosts, indicating that the presumed genetic variability of the host did not a priori affect viral variability. We observed a higher degree of genetic variation in isolates from MaYSV populations than BGMV populations, which was explained by numerous recombination events in MaYSV. MaYSV and BGMV showed distinct distributions of genetic variation, with the BGMV population (but not MaYSV) being structured by both host and geography.

Use of the IRAP marker to study genetic variability in Pseudocercospora fijiensis populations.

Pseudocercospora fijiensis is the etiological agent of black Sigatoka, which is currently considered as one of the most destructive banana diseases in all locations where it occurs. It is estimated that a large portion of the P. fijiensis genome consists of transposable elements, which allows researchers to use transposon-based molecular markers in the analysis of genetic variability in populations of this pathogen. In this context, the inter-retrotransposon-amplified polymorphism (IRAP) was used to study the genetic variability in P. fijiensis populations from different hosts and different geographical origins in Brazil. A total of 22 loci were amplified and 77.3 % showed a polymorphism. Cluster analysis revealed two major groups in Brazil. The observed genetic diversity (H E) was 0.22, and through molecular analysis of variance, it was determined that the greatest genetic variability occurs within populations. The discriminant analysis of principal components revealed no structuring related to the geographical origin of culture of the host. The IRAP-based marker system is a suitable tool for the study of genetic variability in P. fijiensis.

Novel and highly diverse fungal endophytes in soybean revealed by the consortium of two different techniques.

Fungal endophytes were isolated from the leaves of soybean cultivars in Brazil using two different isolation techniques - fragment plating and the innovative dilution-to-extinction culturing - to increase the species richness, frequency of isolates and diversity. A total of 241 morphospecies were obtained corresponding to 62 taxa that were identified by analysis of the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA). The Phylum Ascomycota predominated, representing 99% and 95.2% of isolates in the Monsoy and Conquista cultivars, respectively, whereas the Phylum Basidiomycota represented 1% and 4.8% of isolates, respectively. The genera Ampelomyces, Annulohypoxylon, Guignardia, Leptospora, Magnaporthe, Ophiognomonia, Paraconiothyrium, Phaeosphaeriopsis, Rhodotorula, Sporobolomyces, and Xylaria for the first time were isolated from soybean; this suggests that soybean harbours novel and highly diverse fungi. The yeasts genera Rhodotorula and Sporobolomyces (subphylum Pucciniomycotina) represent the Phylum Basidiomycota. The species richness was greater when both isolation techniques were used. The diversity of fungal endophytes was similar in both cultivars when the same isolation technique was used except for Hill's index, N1. The use of ITS region sequences allowed the isolates to be grouped according to Order, Class and Phylum. Ampelomyces, Chaetomium, and Phoma glomerata are endophytic species that may play potential roles in the biological control of soybean pathogens. This study is one of the first to apply extinction-culturing to isolate fungal endophytes in plant leaves, thus contributing to the development and improvement of this technique for future studies.

Seleção de bactérias endofíticas de tomateiro como potenciais agentes de biocontrole e de promoção de crescimento / Screening of endophytic bacteria isolated from tomato plants as potencial biocontrol agents and growth promotion

Quarenta isolados bacterianos endofíticos de plantas sadias de tomateiro foram avaliados quanto à sua potencialidade como agentes de biocontrole de doenças do tomateiro. Foi realizada, em casa de vegetação, uma seleção massal utilizando-se Pseudomonas syringae pv. tomato e Alternaria solani, como patógenos desafiantes. Com base na média do número de lesões por planta, quatro isolados foram selecionados como potenciais agentes de biocontrole dessas enfermidades fúngica e bacteriana do tomateiro. Esses isolados foram identificados, por meio do sequenciamento do gene 16S do DNA ribossômico, como Acinetobacter johnsonii (UFV-E05), Serratia marcescens (UFV-E13), Sinorhizobium sp. (UFV-E25) e Bacillus megaterium (UFV-E26). Os mesmos isolados selecionados para o biocontrole também foram avaliados quanto à sua capacidade de promover o crescimento em plantas e somente S. marcescens (UFV-E13) proporcionou aumento na altura das plantas.

Forty isolates of endophytic bacteria obtained from healthy tomato plants were tested for their potential as biocontrol agents of tomato diseases. A massal screening was performed at greenhouse using Pseudomonas syringae pv. tomato and Alternaria solani as challenging pathogens. Based on the average number of lesions per plant, four isolates were selected as potential agents of biocontrol of these tomato diseases caused by fungi and bacteria. These isolates were identified by 16S ribosomal DNA sequence analysis as Acinetobacter johnsonii (UFV-E05), Serratia marcescens (UFV-E13), Sinorhizobium sp. (UFV-E25) and Bacillus megaterium (UFV-E26). The four endophytes selected for biocontrol were also evaluated for their ability of promoting plant growth and only S. marcescens (UFV-E13) presented increase in the height of the plants.

Inheritance of resistance to Phytophthora infestans (Peronosporales, Pythiaceae) in a new source of resistance in tomato (Solanum sp. (formerly Lycopersicon sp.), Solanales, Solanaceae)

In Brazil, no commercial tomato (Solanum lycopersicum L. formerly Lycopersicon esculentum Mill.) varieties are available which are resistant to the late blight, one of the most important tomato diseases, produced by the phytopathogenic oomycete Phytophthora infestans. The wild tomato (Solanum habrochaites Knapp & Spooner, formerly Lycopersicon hirsutum Dunal) shows resistance to P. infestans, because of which we investigated an interspecific cross between S. lycopersicum cv. Santa Clara and S. habrochaites accession BGH 6902 maintained at the Horticultural Germplasm Bank at the Federal University of Viçosa (Banco de Germoplasma de Horticultura (BGH), Universidade Federal de Viçosa (UFV), Viçosa, Minas Gerais, Brazil) The genitors, F1, F2, BC1 and BC2 were used to study the inheritance of resistance to P. infestans and to estimate the genetic parameters associated with resistance. Analysis of the area under the disease progress curve (AUDPC) indicated that inheritance is polygenic and that dominance controls character, whereas mean analysis showed that the additive effect was the most important. Although the character presents variability, the heritability is low which generates the need to better control the environment to obtain success with the selection.