Analysis of plant and fungal transcripts from resistant and susceptible phenotypes of Leptospermum scoparium challenged by Austropuccinia psidii.

Austropuccinia psidii is the causal pathogen of myrtle rust disease of Myrtaceae. To gain understanding of the initial infection process, gene expression in germinating Austropuccinia psidii urediniospores and in Leptospermum scoparium inoculated leaves were investigated via analyses of RNAseq samples taken 24 and 48 hours post inoculation (hpi). Principal component analyses of transformed transcript count data revealed differential gene expression between the uninoculated L. scoparium control plants that correlated with the three plant leaf resistance phenotypes (immunity, hypersensitive response and susceptibility). Gene expression in the immune resistant plants did not significantly change in response to fungal inoculation, while susceptible plants showed differential expression of genes in response to fungal challenge. A putative disease resistance gene, jg24539.t1, was identified in the L. scoparium hypersensitive response phenotype family. Expression of this gene may be associated with the phenotype and could be important for further understanding the plant hypersensitive response to A. psidii challenge. Differential expression of pathogen genes was found between samples taken 24 and 48 hpi, but there were no significant differences in pathogen gene expression that were associated with the three different plant leaf resistance phenotypes. There was a significant decrease in the abundance of fungal transcripts encoding three putative effectors and a putative carbohydrate-active enzyme between 24 and 48 hpi, suggesting that the encoded proteins are important during the initial phase of infection. These transcripts, or their translated proteins, may be potential targets to impede the early phases of fungal infection by this wide-host range obligate biotrophic basidiomycete.

A synoptic review of plant disease epidemics and outbreaks published in 2022.

This scientometric study reviews the scientific literature and CABI distribution records published in 2022 to find evidence of major disease outbreaks and first reports of pathogens in new locations or on new hosts. This is the second time we have done this, and this study builds on our work documenting and analysing reports from 2021. Pathogens with three or more articles identified in 2022 literature were: Xylella fastidiosa, Bursaphelenchus xylophilus, Meloidogyne species complexes, Candidatus Liberibacter asiaticus, Raffaelea lauricola, Fusarium oxysporum formae specialis and Puccinia graminis f. sp. tritici. Our review of CABI distribution records found 29 pathogens with confirmed first reports in 2022. Pathogens with four or more first reports were: Meloidogyne species complexes, Pantoea ananatis, grapevine red globe virus and Thekopsora minima. Analysis of the proportion of new distribution records from 2022 indicated that grapevine red globe virus, sweet potato chlorotic stunt virus and Ca. Phytoplasma vitis may have been actively spreading. As we saw last year, there was little overlap between the pathogens identified by reviewing scientific literature versus distribution records. Strikingly, too, there was also no overlap between species assessed to be actively spreading in this year's study and those identified last year. In general, introduction of new pathogens and outbreaks of extant pathogens threaten food security and ecosystem services. Continued monitoring of these threats is essential to support phytosanitary measures intended to prevent pathogen introductions and management of threats within a country.

Hiding in Plain Sight: A Widespread Native Perennial Harbors Diverse Haplotypes of 'Candidatus Liberibacter solanacearum' and Its Potato Psyllid Vector.

The unculturable bacterium 'Candidatus Liberibacter solanacearum' (CLso) is responsible for a growing number of emerging crop diseases. However, we know little about the diversity and ecology of CLso and its psyllid vectors outside of agricultural systems, which limits our ability to manage crop disease and understand the impacts this pathogen may have on wild plants in natural ecosystems. In North America, CLso is transmitted to crops by the native potato psyllid (Bactericera cockerelli). However, the geographic and host plant range of the potato psyllid and CLso beyond the borders of agriculture are not well understood. A recent study of historic herbarium specimens revealed that a unique haplotype of CLso was present infecting populations of the native perennial Solanum umbelliferum in California decades before CLso was first detected in crops. We hypothesized that this haplotype and other potentially novel CLso variants are still present in S. umbelliferum populations. To test this, we surveyed populations of S. umbelliferum in Southern California for CLso and potato psyllid vectors. We found multiple haplotypes of CLso and the potato psyllid associated with these populations, with none of these genetic variants having been previously reported in California crops. These results suggest that CLso and its psyllid vectors are much more widespread and diverse in North American natural plant communities than suggested by data collected solely from crops and weeds in agricultural fields. Further characterization of these apparently asymptomatic haplotypes will facilitate comparison with disease-causing variants and provide insights into the continued emergence and spread of CLso.

Monitoring Genetic Erosion of Aromatic and Medicinal Plant Species in Alentejo (South Portugal).

The main goal of this work was to study the genetic erosion risk of plants with aromatic, medicinal and gastronomic applications in Portugal, particularly in the Alentejo region. The target species were coriander (Coriandrum sativum L.), hart's pennyroyal (Mentha cervina L.) and pennyroyal (Mentha pulegium L.). The methodology involved direct observations and surveys (2002/2003 and 2011). The GE formula applied in Hammer's studies was used to estimate genetic erosion. The main factors causing genetic erosion were the primary drivers of biodiversity loss: habitat loss, invasive species, and overexploitation influenced by human intervention such as the clearing of watercourses, vegetation control, grazing and desertification. The results indicate a reduction in individuals per species in Alentejo, with a net erosion loss of 11% for M. pulegium, 32% for M. cervina and 33% for C. sativum. The overall loss of accessions (genetic erosion risk) was higher in cultivated accessions (33%) than in wild accessions (11%), with an annual genetic erosion rate of 3.7% and 1.2%, respectively. The annual risk of genetic erosion for M. pulegium accessions collected in a natural habitat was 0.6%, which is much lower than the 3.7% for M. cervina. These results consolidate the importance of collecting and conserving genetic resources.

Molecular Epidemiology of Ralstonia pseudosolanacearum Phylotype I Strains in the Southwest Indian Ocean Region and Their Relatedness to African Strains.

The increasing requirement for developing tools enabling fine strain traceability responsible for epidemics is tightly linked with the need to understand factors shaping pathogen populations and their environmental interactions. Bacterial wilt caused by the Ralstonia solanacearum species complex (RSSC) is one of the most important plant diseases in tropical and subtropical regions. Sadly, little, outdated, or no information on its epidemiology is reported in the literature, although alarming outbreaks are regularly reported as disasters. A large set of phylotype I isolates (n = 2,608) was retrieved from diseased plants in fields across the Southwest Indian Ocean (SWIO) and Africa. This collection enabled further assessment of the epidemiological discriminating power of the previously published RS1-MLVA14 scheme. Thirteen markers were validated and characterized as not equally informative. Most had little infra-sequevar polymorphism, and their performance depended on the sequevar. Strong correlation was found with a previous multilocus sequence typing scheme. However, 2 to 3% of sequevars were not correctly assigned through endoglucanase gene sequence. Discriminant analysis of principal components (DAPC) revealed four groups with strong phylogenetic relatedness to sequevars 31, 33, and 18. Phylotype I-31 isolates were highly prevalent in the SWIO and Africa, but their dissemination pathways remain unclear. Tanzania and Mauritius showed the greatest diversity of RSSC strains, as the four DAPC groups were retrieved. Mauritius was the sole territory harboring a vast phylogenetic diversity and all DAPC groups. More research is still needed to understand the high prevalence of phylotype I-31 at such a large geographic scale.

Do plant communities show constant final yield?

Total biomass production of plant monocultures growing over a range of densities and harvested after a period of growth increases monotonically with density and then levels out at higher densities. This pattern is called constant final yield (CFY) and is considered one of the most general phenomena in plant ecology. If CFY applies to plant communities, it would be a key to understanding and predicting many community-level phenomena. We tested two primary hypotheses experimentally: (1) Mixtures of several species show CFY. (2) If so, the proportion of biomass production by the component species in a mixture does not change at densities above the density that reaches CFY. We performed a series of glasshouse experiments over 3 years using a "community density series," in which the overall density of five species was varied while their proportions remained unchanged. In the first experiment, we grew a mixture of annual and perennial herbaceous species in mesocosms, and all species were also grown in monocultures at the corresponding densities. A similar experiment was performed in the second and third years, but only with annuals. A third experiment with mixtures only was performed in pots over 2 years. In all cases, aboveground biomass was harvested, separated by species, dried, and weighed. Perennials with underground storage organs produced maximum aboveground biomass at low or intermediate densities. In the second experiment, two of the species produced maximum biomass at the second-highest density in monoculture, while mixtures of all five species showed classical CFY behavior, and the contribution of the species to the mixture changed very little above the lowest density producing CFY. The results of the third experiment were also consistent with the hypotheses. In conclusion, CFY in aboveground biomass production was observed in communities of annual species, and the contribution of the individual species was relatively insensitive to an increase in density above that reaching CFY, i.e., competitive performance of the species changed with density until CFY was reached. Evidence for CFY was stronger in mixture than in monoculture. Coexistence theory must include density as well as frequency dependence if densities are below CFY.

Unraveling the Host-Selective Toxic Interaction of Cassiicolin with Lipid Membranes and Its Cytotoxicity.

Cassiicolin (Cas), a toxin produced by Corynespora cassiicola, is responsible for Corynespora leaf fall disease in susceptible rubber trees. Currently, the molecular mechanisms of the cytotoxicity of Cas and its host selectivity have not been fully elucidated. Here, we analyzed the binding of Cas1 and Cas2 to membranes consisting of different plant lipids and their membrane disruption activities. Using high-speed atomic force microscopy and confocal microscopy, we reveal that the binding and disruption activities of Cas1 and Cas2 on lipid membranes are strongly dependent on the specific plant lipids. The negative phospholipids, glycerolipids, and sterols are more sensitive to membrane damage caused by Cas1 and Cas2 than neutral phospholipids and betaine lipids. Mature Cas1 and Cas2 play an essential role in causing membrane disruption. Cytotoxicity tests on rubber leaves of Rubber Research Institute of Vietnam (RRIV) 1, RRIV 4, and Prang Besar (PB) 255 clones suggest that the toxins cause necrosis of rubber leaves, except for the strong resistance of PB 255 against Cas2. Cryogenic scanning electron microscopy analyses of necrotic leaf tissues treated with Cas1 confirm that cytoplasmic membranes are vulnerable to the toxin. Thus, the host selectivity of Cas toxin is attained by the lipid-dependent binding activity of Cas to the membrane, and the cytotoxicity of Cas arises from its ability to form biofilm-like structures and to disrupt specific membranes.

Plant Diversity Conservation Challenges and Prospects-The Perspective of Botanic Gardens and the Millennium Seed Bank.

There is a pressing need to conserve plant diversity to prevent extinctions and to enable sustainable use of plant material by current and future generations. Here, we review the contribution that living collections and seed banks based in botanic gardens around the world make to wild plant conservation and to tackling global challenges. We focus in particular on the work of Botanic Gardens Conservation International and the Millennium Seed Bank of the Royal Botanic Gardens, Kew, with its associated global Partnership. The advantages and limitations of conservation of plant diversity as both living material and seed collections are reviewed, and the need for additional research and conservation measures, such as cryopreservation, to enable the long-term conservation of 'exceptional species' is discussed. We highlight the importance of networks and sharing access to data and plant material. The skill sets found within botanic gardens and seed banks complement each other and enable the development of integrated conservation (linking in situ and ex situ efforts). Using a number of case studies we demonstrate how botanic gardens and seed banks support integrated conservation and research for agriculture and food security, restoration and reforestation, as well as supporting local livelihoods.

Quadrat-based monitoring of desert grassland vegetation at the Jornada Experimental Range, New Mexico, 1915-2016.

The data set covers a 101-yr period (1915-2016) of quadrat-based plant sampling at the Jornada Experimental Range in southern New Mexico. At each sampling event, a pantograph was used to record the location and perimeter of living plants within permanent quadrats. Basal area was recorded for perennial grass species, canopy cover area was recorded for shrub species, and all other perennial species were recorded as point data. The data set includes 122 1 × 1 m permanent quadrats, although not all quadrats were sampled in each year of the study and there is a gap in monitoring from 1980 to 1995. These data provide a unique opportunity to investigate changes in the plant community over 100 yr of variation in precipitation and other environmental conditions. We provide the following data and data formats: (1) the digitized maps in shapefile format; (2) a data table containing coordinates (x, y) of perennial species within quadrats, including cover area for grasses and shrubs; (3) a data table of counts of annual plant individuals per quadrat; (4) a species list indicating growth form and habit of recorded species; (5) a table of dates when each quadrat was sampled; (6) a table of the pasture each quadrat was located within (note that pasture boundaries have changed over time); (7) a table of depth to petrocalcic layer measurements taken at quadrat locations; (8) a table of particle size analysis of soil samples taken at quadrat locations; (9) a table of topographic characteristics of quadrat locations (e.g., concave or convex topography). Pantograph sampling is currently conducted at 5-yr intervals by USDA-ARS staff, and new data will be added periodically to the EDI Data Portal Repository (see section V.E.2). This information is released under the Creative Commons license-Attribution-CC BY and the consumer of these data is required to cite it appropriately in any publication that results from its use.

Centre-periphery approaches based on geography, ecology and historical climate stability: what explains the variation in morphological traits of Bulnesia sarmientoi?

BACKGROUND AND AIMS: The centre-periphery hypothesis posits that higher species performance is expected in geographic and ecological centres rather than in peripheral populations. However, this is not the commonly found pattern; therefore, alternative approaches, including the historical dimension of species geographical ranges, should be explored. Morphological functional traits are fundamental determinants of species performance, commonly related to environmental stability and productivity. We tested whether or not historical processes may have shaped variations in tree and leaf traits of the Chaco tree Bulnesia sarmientoi. METHODS: Morphological variation patterns were analysed from three centre-periphery approaches: geographical, ecological and historical. Tree (stem and canopy) and leaf (leaf size and specific leaf area) traits were measured in 24 populations across the species range. A principal component analysis was performed on morphological traits to obtain synthetic variables. Linear mixed-effects models were used to test which of the implemented centre-periphery approaches significantly explained trait spatial patterns. KEY RESULTS: The patterns retrieved from the three centre-periphery approaches were not concordant. The historical approach revealed that trees were shorter in centre populations than in the periphery. Significant differences in leaf traits were observed between the geographical centre and the periphery, mainly due to low specific leaf area values towards the geographical centre. We did not find any pattern associated with the ecological centre-periphery approach. CONCLUSIONS: The decoupled response between leaf and tree traits suggests that these sets of traits respond differently to processes occurring at different times. The geographical and historical approaches showed centres with extreme environments in relation to their respective peripheries, but the historical centre has also been a climatically stable area since the Last Glacial Maximum. The historical approach allowed for the recovery of historical processes underlying variation in tree traits, highlighting that centre-periphery delimitations should be based on a multi-approach framework.

Population Genomics of Plant Viruses: The Ecology and Evolution of Virus Emergence.

The genomics era has revolutionized studies of adaptive evolution by monitoring large numbers of loci throughout the genomes of many individuals. Ideally, the investigation of emergence in plant viruses requires examining the population dynamics of both virus and host, their interactions with each other, with other organisms and the abiotic environment. Genetic mechanisms that affect demographic processes are now being studied with high-throughput technologies, traditional genetics methods, and new computational tools for big-data. In this review, we discuss the utility of these approaches to monitor and detect changes in virus populations within cells and individuals, and over wider areas across species and communities of ecosystems. The advent of genomics in virology has fostered a multidisciplinary approach to tackling disease risk. The ability to make sense of the information now generated in this integrated setting is by far the most substantial obstacle to the ultimate goal of plant virology to minimize the threats to food security posed by disease. To achieve this goal, it is imperative to understand and forecast how populations respond to future changes in complex natural systems.

Detection and Molecular Characterization of 'Candidatus Liberibacter asiaticus' and Citrus Tristeza Virus Associated with Citrus Decline in Bhutan.

Citrus, mainly mandarin (Citrus reticulata Blanco), is an economically important fruit crop in Bhutan. Despite having favorable agroclimatic conditions for citrus cultivation, the early decline of fruit-bearing orchards coupled with low crop productivity is a major concern among citrus growers. During a recent survey, an association of 'Candidatus Liberibacter asiaticus' (citrus greening) and citrus tristeza virus (CTV), either singly or as mixed infections in declined citrus trees, was recorded in all four major citrus-growing districts (Tsirang, Dagana, Zhemgang, and Sarpang). Using PCR-based diagnosis, a higher incidence of citrus greening (27.45%) and tristeza (70.58%) was observed in symptomatic field samples. Detection and characterization of 'Ca. L. asiaticus' was performed based on the 16S ribosomal DNA, prophage gene, 50S ribosomal rplA-rplJ gene, and tandem repeats of the CLIBASIA_01645 locus. Similarly, the coat protein, p23, and p18 genes were used as genetic markers for the detection and characterization of Bhutanese CTV. The 'Ca. L. asiaticus' isolates from Bhutan segregated into classes II and III based on the CLIBASIA_01645 locus, analogous to Indian isolates from the northeast region and Term-A based on the CLIBASIA_05610 locus. CTV isolates of Bhutan were observed as closely related to the VT strain, which is considered to be the most devastating. To the best of our knowledge, this is the first study on molecular characterization of 'Ca. L. asiaticus' and CTV isolates and their association with citrus decline in Bhutan.

Molecular Phylogenomics and Population Structure of Phytophthora pluvialis.

Phytophthora pluvialis is an oomycete that was first isolated from soil, water, and tree foliage in mixed Douglas-fir-tanoak forests of the U.S. Pacific Northwest (PNW). It was then identified as the causal agent of red needle cast of radiata pine (Pinus radiata) in New Zealand (NZ). Genotyping-by-sequencing was used to obtain 1,543 single nucleotide polymorphisms across 145 P. pluvialis isolates to characterize the population structure in the PNW and NZ. We tested the hypothesis that P. pluvialis was introduced to NZ from the PNW using genetic distance measurements and population structure analyses among locations between countries. The low genetic distance, population heterozygosity, and lack of geographic structure in NZ suggest a single colonization event from the United States followed by clonal expansion in NZ. The PNW Coast Range was proposed as a presumptive center of origin of the currently known distribution of P. pluvialis based on its geographic range and position as the central cluster in a minimum spanning network. The Coastal cluster of isolates were located at the root of every U.S. cluster and emerged earlier than all NZ clusters. The Coastal cluster had the highest degree of heterozygosity (Hs = 0.254) and median pairwise genetic distance (0.093) relative to any other cluster. Finally, the rapid host diversification between closely related isolates of P. pluvialis in NZ indicate that this pathogen has the potential to infect a broader range of hosts than is currently recognized.

Evolution and Adaptation of Forest and Crop Pathogens in the Anthropocene.

Anthropocene marks the era when human activity is making a significant impact on earth, its ecological and biogeographical systems. The domestication and intensification of agricultural and forest production systems have had a large impact on plant and tree health. Some pathogens benefitted from these human activities and have evolved and adapted in response to the expansion of crop and forest systems, resulting in global outbreaks. Global pathogen genomics data including population genomics and high-quality reference assemblies are crucial for understanding the evolution and adaptation of pathogens. Crops and forest trees have remarkably different characteristics, such as reproductive time and the level of domestication. They also have different production systems for disease management with more intensive management in crops than forest trees. By comparing and contrasting results from pathogen population genomic studies done on widely different agricultural and forest production systems, we can improve our understanding of pathogen evolution and adaptation to different selection pressures. We find that in spite of these differences, similar processes such as hybridization, host jumps, selection, specialization, and clonal expansion are shaping the pathogen populations in both crops and forest trees. We propose some solutions to reduce these impacts and lower the probability of global pathogen outbreaks so that we can envision better management strategies to sustain global food production as well as ecosystem services.

Population Genomics of Bacterial Plant Pathogens.

Population genomics is transforming our understanding of pathogen biology and evolution, and contributing to the prevention and management of disease in diverse crops. We provide an overview of key methods in bacterial population genomics and describe recent work focusing on three topics of critical importance to plant pathology: (i) resolving pathogen origins and transmission pathways during outbreak events, (ii) identifying the genetic basis of host specificity and virulence, and (iii) understanding how pathogens evolve in response to changing agricultural practices.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

An early evaluation of translocation actions for endangered plant species on Mediterranean islands.

In situ conservation is widely considered a primary conservation strategy. Plant translocation, specifically, represents an important tool for reducing the extinction risk of threatened species. However, thus far, few documented translocations have been carried out in the Mediterranean islands. The Care-Mediflora project, carried out on six Mediterranean islands, tackles both short- and long-term needs for the insular endangered plants through in situ and ex situ conservation actions. The project approach is based on using ex situ activities as a tool to improve in situ conservation of threatened plant species. Fifty island plants (representing 45 taxa) were selected for translocations using common criteria. During the translocations, several approaches were used, which differed in site selection method, origin of genetic material, type of propagative material, planting method, and more. Although only preliminary data are available, some general lessons can be learned from the experience of the Care-Mediflora project. Among the factors restricting the implementation of translocations, limited financial resources appear to be the most important. Specific preliminary management actions, sometimes to be reiterated after translocation, increase the overall cost, but often are necessary for translocation success. Translocation using juvenile/reproductive plants produces better results over the short term, although seeds may provide good results over the long run (to be assessed in the future). Regardless, plant translocation success can only be detected over long periods; therefore, proper evaluation of plant translocations requires a long-term monitoring protocol. Care-Mediflora project represents the first attempt to combine the existing approaches in a common plant conservation strategy specifically focusing on the Mediterranean islands.

Plant epigenetic mechanisms: role in abiotic stress and their generational heritability.

Plants have evolved various defense mechanisms including morphological adaptations, cellular pathways, specific signalling molecules and inherent immunity to endure various abiotic stresses during different growth stages. Most of the defense mechanisms are controlled by stress-responsive genes by transcribing and translating specific genes. However, certain modifications of DNA and chromatin along with small RNA-based mechanisms have also been reported to regulate the expression of stress-responsive genes and constitute another line of defense for plants in their struggle against stresses. More recently, studies have suggested that these modifications are heritable to the future generations as well, thereby indicating their possible role in the evolutionary mechanisms related to abiotic stresses.

Effects of habitat degradation, microsite, and seed density on the persistence of two native herbs in a subtropical shrubland.

PREMISE OF THE STUDY: Species in degraded ecosystems may interact differently with their surroundings from those under historic conditions. Understanding factors affecting variation in early life history stages of plants is fundamental to assessing their persistence in intact and degraded habitats, and the value of degraded lands. We evaluated the effect of seed density on the seed dynamics of two herbaceous species (annual, biennial), and considered how seed availability may influence population dynamics in different habitats (degraded, intact Florida scrub) and microsites (bare sand, leaf litter, shrub). METHODS: We used data on responses to experimental treatments (seed removal, seedling emergence, establishment) and models to evaluate how effects of these factors may change over time since the last disturbance. KEY RESULTS: Probability of any seed removal, emergence, and establishment per unit increased with seed density, although proportion removal for Chamaecrista fasciculata, proportion emergence for Balduina angustifolia, and proportion establishment for both species decreased with density. When animals were given selective access to seeds, invertebrates were primarily responsible for seed removal of both study species. Models with dynamics changing with time-since-disturbance for both species predicted that population growth may decrease slightly if local available seed density increases. CONCLUSIONS: Detailed demographic comparisons of populations in intact and degraded conditions can be used to understand the way that environmental conditions (habitat, microsite) combine with seed density effects to influence population dynamics of herb species. Degraded habitat may act as a transitional state in a trajectory toward intact conditions for some species, or as refugia for other native species.

Incidence and severity of white mold for soybean under different cultural practices and local meteorological conditions / Incidência e severidade de mofo-branco em soja sob diferentes práticas culturais e condições meteorológicas locais

The Sclerotinia sclerotiorum (Lib.) de Bary fungus is a necrotrophic and polyphagous pathogen with soybean crop as one of its most important hosts. However in order to occur epidemics caused by such a pathogen it is necessary that the climatic conditions, mainly air temperature and relative humidity be favorable to the occurrence and development of the disease. The current research aimed to assess the incidence and severity of S. sclerotiorum in soybean plants grown in Arapoti, PR, Brazil, as a function of different plant populations, row spacing, and microclimate. The experiment was conducted in a naturally infested area. The experimental design adopted was a randomized block in a factorial combination with 4 row spacing (0.35, 0.45, 0.60, 0.75 m) and 4 plant populations (150, 200, 250; 300 thousand plants per hectare), totaling 16 treatments and 4 replications. Throughout the current study we performed 4 assessments of incidence and severity. Local climatic conditions were favorable for the incidence and severity of the pathogen. Mean air temperature, rainfall, relative humidity and leaf wetness duration, monitored during all experimental period, favored the development of the pathogen in the experimental field. Yield and 100 seed weight did not show fluctuations as a function of variations on the incidence and severity of white mold in soybean crop fields. Nevertheless, crop yield was higher under a reduced spacing, whereas the 100 seed weight showed the highest values under the lowest plant population treatment.

O fungo Sclerotinia sclerotiorum (Lib.) de Bary é um patógeno necrotrófico, polífago que tem a planta da soja como um dos seus principais hospedeiros. Porém, para que ocorram epidemias em decorrência desse patógeno é necessário que as condições climáticas, principalmente de umidade e temperatura do ar, sejam favoráveis para a ocorrência e o desenvolvimento da doença. O presente trabalho teve como objetivo avaliar a incidência e severidade de S. sclerotiorum em plantas de soja cultivadas em Arapoti, PR, Brasil, em função de diferentes densidades populacionais, espaçamentos entrelinhas e microclima. O experimento foi conduzido em área naturalmente infestada. O delineamento experimental adotado foi o de blocos casualizados em esquema fatorial, combinando 4 espaçamentos entrelinhas (0,35; 0,45; 0,60; 0,75 metros) e 4 densidades populacionais (150, 200, 250, 300 mil plantas ha-1), totalizando 16 tratamentos e 4 repetições. Ao longo do experimento foram efetuadas 4 avaliações de incidência e severidade. A temperatura média do ar, precipitação, umidade relativa do ar e a duração do molhamento foliar, monitoradas durante todo o período experimental, foram favoráveis para o desenvolvimento do patógeno na área experimental. A produção e a massa de 1000 grãos não apresentaram oscilações em função das variações nos níveis de incidência e severidade de mofo-branco na cultura da soja cultivada na condição climática estudada. Contudo, a produtividade da cultura foi maior nos tratamentos com espaçamentos reduzidos. Já a massa de 1000 grãos apresentou maiores valores em tratamentos com reduzida densidade populacional.

Physiological potential of bean seeds as a function of population densities on winter crop season, in northern Minas Gerais / Desempenho fisiológico de sementes de feijão-comum cultivado em diferentes densidades populacionais na safra de inverno, no norte de Minas Gerais

For adapting well to various soil and climatic conditions in Brazil and the tradition of high consumption, bean plays a key role in feeding the population. Despite the different environmental conditions, there are few specific cultivars for each planting season, particularly when aimed at the production of quality seeds. The objective of this study was to evaluate the physiological potential of bean seeds from five population densities, under the edafoclimatic conditions of Janaúba, northern Minas Gerais. The experiment was conducted on winter crop season, with planting in August 2011. The experimental design was a randomized block in 3 x 5 factorial, with four replicates. The treatments consisted of three cultivars of common bean with different growth types (Ouro Vermelho, Ouro Negro and BRSMG Madrepérola), and five densities (100, 200, 300, 400 and 500 thousand plants ha-1). Seeds were evaluated for water content, germination and vigor (tests of first count, seedling emergence, emergence speed and accelerated aging). From the results, it can be concluded that the bean seeds of the cultivar Ouro Negro present superior physiological potential in relation to the cultivars Ouro Vermelho and BRSMG Madrepérola. Increasing the sowing density up to 300 thousand plants ha-1 is suitable for the production of bean seeds on winter crop season, representing a good alternative for cultivation in the region.

Por se adaptar bem às mais variadas condições edafoclimáticas do Brasil e pela alta tradição de consumo, o feijoeiro desempenha papel fundamental na alimentação da população brasileira. Apesar das condições ambientais distintas, existem poucas cultivares específicas para cada época de plantio, principalmente quando visa à produção de sementes de qualidade. Objetivou-se com este trabalho avaliar o desempenho fisiológico de sementes de feijão-comum cultivado em cinco densidades populacionais, nas condições edafoclimáticas de Janaúba, Norte de Minas Gerais. O experimento foi conduzido na safra de inverno, com plantio em agosto de 2011. O delineamento experimental utilizado foi em blocos casualizados, em esquema fatorial 3 x 5, com quatro repetições. Os tratamentos consistiram em três cultivares de feijão-comum de diferentes tipos de crescimento (Ouro Vermelho, Ouro Negro e BRSMG Madrepérola), e cinco densidades populacionais (100, 200, 300, 400 e 500 mil plantas ha-1). As sementes foram avaliadas quanto ao teor de água, à germinação e ao vigor (testes de primeira contagem, emergência de plântulas, índice de velocidade de emergência e envelhecimento acelerado). Diante dos resultados, conclui-se que as sementes de feijão da cultivar Ouro Negro apresentam desempenho fisiológico superior em comparação com as cultivares Ouro Vermelho e BRSMG Madrepérola. O aumento da densidade de semeadura até 300 mil plantas ha-1 é adequado para a produção de sementes de feijão na safra de inverno, representando boa alternativa para o cultivo na região.