Gossypii Var Research Articles

Endophytic Fungi Inoculation Reduces Ramulosis Severity in Gossypium hirsutum Plants.

Biotic stress in cotton plants caused by the phytopathogenic fungus Colletotrichum gossypii var. cephalosporioides triggers symptoms of ramulosis, a disease characterized by necrotic spots on young leaves, followed by death of the affected branch's apical meristem, plant growth paralysis, and stimulation of lateral bud production. Severe cases of ramulosis can cause up to 85% yield losses in cotton plantations. Currently, this disease is controlled exclusively by using fungicides. However, few studies have focused on biological alternatives for mitigating the effects of contamination by C. gossypii var. cephalosporioides on cotton plants. Thus, the hypothesis raised is that endophytic fungi isolated from an Arecaceae species (Butia purpurascens), endemic to the Cerrado biome, have the potential to reduce physiological damage caused by ramulosis, decreasing its severity in these plants. This hypothesis was tested using plants grown from seeds contaminated with the pathogen and inoculated with strains of Gibberella moniliformis (BP10EF), Hamigera insecticola (BP33EF), Codinaeopsis sp. (BP328EF), G. moniliformis (BP335EF), and Aspergillus sp. (BP340EF). C. gossypii var. cephalosporioides is a leaf pathogen; thus, the evaluations were focused on leaf parameters: gas exchange, chlorophyll a fluorescence, and oxidative metabolism. The hypothesis that inoculation with endophytic strains can mitigate physiological and photochemical damage caused by ramulosis in cotton was confirmed, as the fungi improved plant growth and stomatal index and density, increased net photosynthetic rate (A) and carboxylation efficiency (A/Ci), and decreased photochemical stress (ABS/RC and DI0/RC) and oxidative stress by reducing enzyme activity (CAT, SOD, and APX) and the synthesis of malondialdehyde (MDA). Control plants developed leaves with a low adaxial stomatal index and density to reduce colonization of leaf tissues by C. gossypii var. cephalosporioides due to the absence of fungal antagonism. The Codinaeopsis sp. strain BP328EF can efficiently inhibit C. gossypii var. cephalosporioides in vitro (81.11% relative inhibition), improve gas exchange parameters, reduce photochemical stress of chlorophyll-a, and decrease lipid peroxidation in attacked leaves. Thus, BP328EF should be further evaluated for its potential effect as a biological alternative for enhancing the resistance of G. hirsutum plants and minimizing yield losses caused by C. gossypii var. cephalosporioides.

Morphocultural and pathogenic characterization of Colletotrichum gossypii and Colletotrichum gossypii var. cephalosporioides under different temperatures

ABSTRACT Considering the importance of identifying Colletotrichum species associated with cotton plants, this study aimed to characterize the morphological and pathogenic isolates of C. gossypii var. cephalosporioides and C. gossypii under different temperatures. Five isolates of C. gossypii var. cephalosporioides and C. gossypii were incubated at 20, 25 and 30 °C. The cultural characteristics data were analyzed through ANOVA and the means compared by the Tukey test. There were differences between the isolates of the two species concerning mycelial growth and sporulation at different temperatures. Temperatures between 20 to 30 °C increased the length of conidia but did not influence the width, whereas between 25 and 30 °C, there was the highest mycelial growth. Colletotrichum gossypii expressed anthracnose symptoms, and ramulosis symptoms were observed only in plants inoculated with C. gossypii var. cephalosporioides.

Systematic studies of the subgenus Crewella of Ceratina (Hymenoptera, Apidae, Xylocopinae), with a revision of the species occurring in Argentina

The subgenus Crewella Cockerell of Ceratina Latreille is found only in the Neotropical region, with maximal diversity in South America. A morphological study of the species in the subgenus led to the recognition of five species groups, based on several characteristics of the head, the first metasomal tergum, and the female sixth metasomal tergum. A key to the species-groups is presented. The following new species are described: C. dalyana , from Colombia, C. amazonica , C. crassipunctata , and C. foveinasis from Peru, C. duplocarinata , C. guaranitica , and C. lobata from Argentina, C. acuminata from Brazil and Paraguay, and C. carbonaria from Argentina and Brazil. Lectotypes are designated for C . brunneipes Friese, C . diligens Smith, and C . vernoniae Schrottky. The following are new synonyms: C . brunneipes Friese, 1910 of C . maculifrons Smith, 1854, and C . gossypii var. asuncionis Strand, 1910 of C . gossypii Schrottky, 1907. A revision of the species in Argentina, with a key to species, is presented.

Systematic studies of the subgenus Crewella of Ceratina (Hymenoptera, Apidae, Xylocopinae), with a revision of the species occurring in Argentina

The subgenus Crewella Cockerell of Ceratina Latreille is found only in the Neotropical region, with maximal diversity in South America. A morphological study of the species in the subgenus led to the recognition of five species groups, based on several characteristics of the head, the first metasomal tergum, and the female sixth metasomal tergum. A key to the species-groups is presented. The following new species are described: C. dalyana , from Colombia, C. amazonica , C. crassipunctata , and C. foveinasis from Peru, C. duplocarinata , C. guaranitica , and C. lobata from Argentina, C. acuminata from Brazil and Paraguay, and C. carbonaria from Argentina and Brazil. Lectotypes are designated for C . brunneipes Friese, C . diligens Smith, and C . vernoniae Schrottky. The following are new synonyms: C . brunneipes Friese, 1910 of C . maculifrons Smith, 1854, and C . gossypii var. asuncionis Strand, 1910 of C . gossypii Schrottky, 1907. A revision of the species in Argentina, with a key to species, is presented.

BACTERIA FOR COTTON PLANT PROTECTION: DISEASE CONTROL, CROP YIELD AND FIBER QUALITY1

ABSTRACT Ramulosis (Colletotrichum gossypii var. cephalosporioides) is an important fungal disease of cotton in Brazil, exclusively controlled by fungicide application. Therefore, sustainable management of ramulosis is essential. This work aimed to evaluate the potential of three bacterial strains, Bacillus amyloliquefaciens (UFLA285), Bacillus velezensis (UFLA401), and Paenibacillus lentimorbus (MEN2), for the biocontrol of ramulosis in cotton and their effects on yield and fiber quality. Seed treatment (ST), foliar spray, and soil drenching application methods were used (separately or combined) under greenhouse and field conditions. Chemical treatments recommended against ramulosis and water were used as controls. Under greenhouse conditions all strains reduced the disease incidence. While B. velezensis UFLA401 and P. lentimorbus MEN2 reduced the incidence by 56.6% and 45.7%, respectively, independent of the application method, B. amyloliquefaciens UFLA285 reduced the disease by about 60% when applied as a foliar spray or ST + foliar spray. Two field trials were performed and all bacterial strains reduced ramulosis incidence. In the first year, B. velezensis UFLA401 sprayed on the plants reduced incidence by 22.3% and ST + two foliar sprays resulted in the best performance, decreasing ramulosis by 57%. In both seasons the yield increased by using either bacterial or chemical treatments compared to the water control. The combination B. velezensis UFLA401 and P. lentimorbus MEN2 sprays provided better fiber quality than chemical treatment. Therefore, Bacillus sp. (UFLA285 and UFLA401) and P. lentimorbus MEN2 are potential tools to reduce ramulosis, increase cotton yield and fiber quality.

Specificity and sensibility of primer pair in the detection of Colletotrichum gossypii var. cephalosporioides in cotton seeds by PCR technique

Abstract: Cotton Ramulosis (Gossypium hirsutum) is an important disease affecting cotton plantations in Brazil, and its causal agent, Colletotrichum gossypiivar.cephalosporioides(Cgc), according to the Brazilian phytosanitary authority, was considered a regulated non quarantine pest. It makes this microorganism subject to standardization in seed certification programs. The current seed health testing for detecting that pathogen in seed samples does not provide reliable results for routine analysis. On this paper, attempts were made to design specific primers for detection of Cgc associated with cotton seed. Two primer sets were selected based on the analysis of a multiple alignment of gene’s sequence encoding the glyceraldehyde 3-phosphate dehydrogenase from Cgc, C. gossypii and reference strains of the C. gloeosporioides species complex. The conserved sites unique to Cgc strains were used to design specific fragment of 140 bp. The primer specificity was confirmed by using other fungi. The primers produced a detectable band of target DNA of Cgc in all inoculum potentials of the pathogen artificially inoculated by the water restriction technique. The developed primer pair represents, therefore, a reliable and rapid mean to diagnose the Ramulosis agent in cotton seed.

Field resistance of advanced breeding lines of upland cotton to ramulosis caused by Colletotrichum gossypii var. cephalosporioides

Cotton ramulosis caused by Colletotrichum gossypii var. cephalosporioides is the main disease in the cotton growing areas of South America. Commercially available cultivars do not exhibit ramulosis resistance and thus it is necessary to identify sources of resistance. This study evaluated the Colombian LCER collection of advanced breeding lines (ABLs) of Upland cotton for ramulosis resistance. LCER is composed of F6 lines derived from crosses between lines with African and Colombian ancestry (LC collection) and high yielding cultivars from USA, Brazil and Africa adapted to the monsoon and savanna climate of the Colombian Caribbean. Disease development was measured thirteen weeks after planting using a qualitative scale designed for high levels of ramulosis intensity (absence of healthy plants and high proportions of dwarf plants for susceptible cultivars). A ramulosis resistant scale (RSC) was developed from these disease assessments to evaluate the ABLs across environments. Thirteen ABLs exhibited ramulosis resistance. Fourteen ABLs were classed as susceptible cultivars, while the remaining 30 exhibited intermediate levels of resistance. Half of the individuals in susceptible ABLs exhibited dwarfism symptoms while the plant population in resistant cultivars showed lower percentage of dwarfism (<1%) and sprouting (around 50%). Thirty seven ABLs representing the range of disease responses were evaluated at a second location. Multifactor ANOVA revealed that resistance measured as RSC scores can be used to evaluate genotypes across environments to identify sources of resistance. These resistant ABLs can be released as new resistant cultivars for the Caribbean or used as parents in breeding programs.

Near infrared hyperspectral images and pattern recognition techniques used to identify etiological agents of cotton anthracnose and ramulosis

Hyperspectral imaging near infrared (HSI-NIR) has the potential to be used as a non-destructive approach for the analysis of new microbiological matrices of agriculture interest. This article describes a new method for accurately and rapidly classifying the etiological agents Colletotrichum gossypii (CG) and C. gossypii var. cephalosporioides (CGC) grown in a culture medium, using scattering reflectance HSI-NIR and multivariate pattern recognition analysis. Five strains of CG and 46 strains of CGC were used. CG and CGC strains were grown on Czapek-agar medium at 25 °C under a 12-hour photoperiod for 15 days. Molecular identification was performed as a reference for the CG and CGC classes by polymerase chain reaction of the intergenic spacer region of rDNA. The scattering coefficient µs and the absorption coefficient µa were obtained, which resulted in a µs value for CG of 1.37 × 1019 and for CGC of 5.83 × 10–11. These results showed that the use of the standard normal variate was no longer essential and reduced the spectral range from 1000–2500 nm to 1000–1381 nm. The results evidenced two type II errors for the CG 457-2 and CGC 39 samples in the soft independent modelling model of the analogy model. There were no classification errors using the algorithm of the successive projections for variable selection in linear discriminant analysis (SPA-LDA). A parallel validation of the results obtained with SPA-LDA was performed using a box plot analysis with the 11 variables selected by SPA, in which there were no outliers for the HSI-NIR models. The new HSI-NIR and SPA-LDA procedures for the classification of CG and CGC etiological agents are noted for their greater analytical speed, accuracy, simplicity, lower cost and non-destructive nature.

Evaluation of inoculum potential of pathogens in seeds: relation to physiological quality and DNA quantification by qPCR

Abstract: Given what is already known in regard to seed health and the availability of molecular methods for detection of the pathogens Stenocarpella maydis and Stenocarpella macrospora in maize seeds, Colletotrichum gossypii var. cephalosporioides in cotton seeds, and Corynespora cassiicola in soybean seeds, the aim of this study was to evaluate seed vigor according to different inoculum potentials. The fungus isolates were inoculated on seeds by the technique of water restriction, through which different inoculum potentials are obtained, corresponding to times of seed exposure of 0, 24, 48, and 96 hours for maize and cotton seeds, and 0, 36, 108, and 144 hours for soybean seeds. The seeds were subjected to germination, electrical conductivity, health, and qPCR tests. Results of the blotter test showed that in most pathosystems, there was a higher incidence of the fungi with an increase in inoculum potential. A decrease in germination percentage was observed in all species as inoculum potential increased, as well as further degradation of seed membranes. The qPCR test confirmed that the most damaged seeds in the tests had higher presence of the pathogens.

Dynamics of cotton ramulosis epidemics caused by Colletotrichum gossypii var. cephalosporioides in Colombia

The main cotton growing regions in South America are affected by Colletotrichum gossypii var. cephalosporioides (Cgc). The most severe epidemics provoke considerable yield reductions linked to meristem necrosis, over-sprouting, branching and stunting. The Sinu Valley is the greatest cotton producer in Colombia and is heavily affected by this disease. Using data from field trials conducted in 2012, 2013 and 2014 in a naturally infested area covering 15 planting dates, we attempted to identify weather variables linked to ramulosis epidemics. Cotton planting season in the Sinu Valley runs from August to November, with higher rainfall intensity and frequency for crops planted earlier at the season while decreasing as the meridional winter solstice is approached. Rainfall, temperature and RH variables were significantly correlated with disease development (measured as AUDPS for ramulosis infection intensity). Rainfall alone was able to explain the majority of variation in ramulosis development across all the testing planting dates. A linear regression model was fitted for this association between ramulosis development and accumulated rainfall. Disease development is higher in the early planting dates (mid-August to September) while the disease is absent in crops established at October.

Inducing resistance in cotton against Colletotrichum gossypii var. cephalosporioides with essential oils

This study aimed to evaluate the potential of essential oils of rosemary ( Rosmarinus officinalis ), baccharis ( Baccharis trimera ), lemon grass ( Cymbopogon citratus ), basil ( Ocimum basilicum ) and eucalyptus ( Corymbia citriodora ) in inducing resistance in cotton plants against C. gossypii var. cephalosporioides . The inductive effect of the essential oils was evaluated in plants growing in pots in the environment, which were treated with 1% essential oil at 47 days of age. 24 hours after elicitor treatment the plants were inoculated with a suspension of 1.5 x 10 5 conidia mL -1 of C. gossypii var. cephalosporioides . Five evaluations were performed disease and calculated the area under the disease progress curve. All essential oils showed potential for inducing resistance against cotton C. gossypii var. cephalosporioides .

The recombinant pea defensin Drr230a is active against impacting soybean and cotton pathogenic fungi from the genera Fusarium, Colletotrichum and Phakopsora.

Plant defensins are antifungal peptides produced by the innate immune system plants developed to circumvent fungal infection. The defensin Drr230a, originally isolated from pea, has been previously shown to be active against various entomopathogenic and phytopathogenic fungi. In the present study, the activity of a yeast-expressed recombinant Drr230a protein (rDrr230a) was tested against impacting soybean and cotton fungi. First, the gene was subcloned into the yeast expression vector pPICZαA and expressed in Pichia pastoris. Resulting rDrr230a exhibited in vitro activity against fungal growth and spore germination of Fusarium tucumaniae, which causes soybean sudden death syndrome, and against Colletotrichum gossypii var. cephalosporioides, which causes cotton ramulosis. The rDrr230a IC50 corresponding to inhibition of fungal growth of F. tucumaniae and C. gossypii var. cephalosporioides was 7.67 and 0.84 µM, respectively, demonstrating moderate activity against F. tucumaniae and high potency against C. gossypii var. cephalosporioides. Additionally, rDrr230a at 25 ng/µl (3.83 µM) resulted in 100 % inhibition of spore germination of both fungi, demonstrating that rDrr230a affects fungal development since spore germination. Moreover, rDrr230a at 3 µg/µl (460.12 µM) inhibited 100 % of in vitro spore germination of the obligatory biotrophic fungus Phakopsora pachyrhizi, which causes Asian soybean rust. Interestingly, rDrr230a substantially decreased the severity of Asian rust, as demonstrated by in planta assay. To our knowledge, this is the first report of a plant defensin active against an obligatory biotrophic phytopathogenic fungus. Results revealed the potential of rDrr230a as a candidate to be used in plant genetic engineering to control relevant cotton and soybean fungal diseases.

Mixed inheritance in the genetic control of ramulosis (Colletotrichum gossypii var. cephalosporioides) resistance in cotton.

Ramulosis is one of the most aggressive diseases in cotton, and understanding the genetic control of its resistance is imperative for selecting superior cotton genotypes in breeding programs. This study analyzed the inheritance pattern of this resistance using chi-square goodness-of-fit tests to determine the phenotypic proportions of the F2 generation, and a mixed inheritance approach to jointly model major gene and polygenes effects. F1, F2, Rc1, and Rc2 generations were obtained by crossing resistant (BRS Facual, CNPA 2984, or CNPA 2043) and susceptible (Delta Opal, CNPA 999, or CNPA 2161) genotypes, and were assessed under field conditions with artificial inoculation of the pathogen (Colletotrichum gossypii var. cephalosporioides). Genetic control of the trait varied among the crossings. For Delta Opal x BRS Facual and CNPA 2161 x BRS Facual, phenotypic segregations in the F2 generation did not differ from the expected proportions for the hypothesis of duplicate genes (15:1). For Delta Opal x CNPA 2043, the segregation did not differ from the expected proportions for dominant recessive epistasis (13:3). The hypothesis of genetic control by one major gene was supported only for the Delta Opal x CNPA 2043 crossing. Three other crossings showed evidence of polygenes in the inheritance of the trait. In conclusion, major genes and polygenes are likely involved in the genetic control of ramulosis resistance in cotton.

Screening of Endospore-Forming Bacteria for Cotton Seed Treatment against Bacterial Blight and Damping-off

Under conventional seed treatment, reports of efficacy loss or activity on nontarget microorganisms foster the search for sustainable disease management alternatives. Biological seed treatment has been meeting these requirements and exerts benefits that go beyond plant health. Looking for those alternatives, 368 Endospore-forming bacterial strains were screened for the control of bacterial blight and damping-off, caused by Xanhomonas axonopodis pv. malvacearum and Colletotrichum gossypii var. cephalosporioides, respectively. From the sampled sites, the strains with the highest bacterial blight and damping-off control were obtained from Primavera do Leste and Campo Verde (MT), respectively. Those had the potential to control both diseases were obtained from Primavera do Leste. Consistent disease control with seed treatment was found with two strains: Bacillus subtilis UFLA285 and Paenibacillus lentimorbus MEN2 with disease symptoms reduced by 45 and 56%, respectively for damping-off and 26 and 76%, respectively for bacterial blight. Therefore beneficial bacteria are a plausible alternative for a sustainable disease control in cotton.

English

The use of DNA sequences analysis has been an important mean to distinguish and to identify populations of organisms at different levels. By molecular markers several complex organisms have been successful detected in plants for distinct aims. Ribosomal DNA (rDNA) has been used to evaluate genetic variability, microorganism phylogeny and to develop specific primers for detection of plant pathogens in plant tissues. In this study, the objective was to characterize isolates of Colletotrichum gossypii var. cephalosporioides and Colletotrichum gossypii , collected in different regions of Brazil, by analyzing the nucleotide sequence of rDNA regions. ITS1, ITS2, and the intervening 5.8S gene were amplified by PCR and their sequences compared to each other and to those from other species registered in the GenBank. The rDNA of isolates associated with Gossypium spp. showed sequence identities ranging from 96 to 100% in the ITS1 region, 98 to 100% in the 5.8S gene, and 97 to 100% in the ITS2 region. The sequences were submitted to UPGMA analysis, and according to the phylogenetic trees, the C . gossypii var. cephalosporioides and C. gossypii species clustered together along with isolates of Glomerella cingulata from mango and papaya, and thus no distinction could be made between isolates of those organisms.

The etiological agent of cotton ramulosis represents a single phylogenetic lineage within the Colletotrichum gloeosporioides species complex

Ramulosis of cotton, caused by Colletotrichum gossypii var. cephalosporioides (CGC), is an important disease of cotton in Brazil. The main objective of this work was to test whether CGC is a phylogenetic species inside the Colletotrichum gloeosporioides species complex. A Bayesian inference phylogenetic analysis of a combined ITS and TUB2 dataset was conducted with 21 strains identified as CGC and five strains of Colletotrichum gossypii (CG), associated with cotton anthracnose, obtained from diseased plants from different regions of Brazil. All CGC strains formed a highly supported lineage inside the clade of Colletotrichum theobromicola, a member of the C. gloeosporioides species complex. CG strains formed another lineage in the same clade. These findings were supported by a second analysis conducted with three genes (ITS+TUB2+GAPDH) and a subset of five CGC and three CG strains. During pathogenicity tests, all five CGC strains tested induced typical symptoms of ramulosis on inoculated plants, including foliar necrosis, death of apical meristems and over sprouting. Plants inoculated with CG strains exhibited foliar necrotic spots two months after inoculation. These results give phylogenetic support for the placement of CGC in the C. gloeosporioides species complex, and the distinction between the ramulosis and anthracnose pathogens of cotton in Brazil.

Capacidade fotossintética de plantas de algodoeiro infectadas por ramulose e supridas com silício

Nas plantas atacadas por patógenos ocorrem danos nas células do mesofilo, colonização dos espaços intra e intercelulares e fechamento de estômatos, afetando a transpiração, influxo do CO2 e taxa fotossintética. O uso de silício (Si) é importante para reduzir a intensidade de inúmeras doenças em várias espécies de plantas, além de ter um efeito positivo sobre a capacidade fotossintética. Objetivou-se com este estudo investigar o efeito do Si sobre a capacidade fotossintética de plantas de algodoeiro das cultivares BRS Araçá e FM 993 infectadas por Colletotrichum gossypii var. cephalosporioides supridas (+Si) ou não (-Si) com Si. Avaliaram-se as variáveis de trocas gasosas: taxa de assimilação líquida de carbono (A), condutância estomática (g s), transpiração (E), razão entre a concentração interna e ambiente de CO2 (Ci/Ca), a eficiência instantânea no uso da água (A/E) e a concentração de pigmentos. Houve redução de A, g s, fixação de carbono, concentrações de clorofila a (cl a), clorofila b (cl b) e carotenoides, matéria seca total (MST) e aumento na E e na A/E. Com o fornecimento de Si, as plantas das duas cultivares de algodoeiro aumentaram a A devido ao aumento na g s e na fixação de CO2, além de no uso mais eficiente da água. O suprimento de Si aumentou as concentrações de cl a, cl b e carotenoides e MST nas duas cultivares. O Si afetou a fisiologia das plantas de algodoeiro infectadas por C. gossypii var. cephalosporioides, aumentando a resistência à ramulose devido a incrementos na capacidade fotossintética, na concentração de pigmentos e no acúmulo de biomassa.

Estabilidade fenotípica, um complemento relevante na avaliação e classificação de genótipos de algodoeiro para resistência a doenças

Neste trabalho é formulado um conceito mais abrangente da resistência a patógenos em genótipos de algodoeiro, mediante inclusão, nos critérios de avaliação, da estabilidade fenotípica desse atributo, quando se consideram ambientes com intensidades diversas de ocorrência das doenças. Para fundamentar o método, um estudo foi realizado com base em dados obtidos em experimentos efetuados, para avaliação de genótipos com respeito à murcha de Fusarium (Fusarium oxysporum f. vasinfectum), mancha-angular (Xanthomonas citri subsp. malvacearum), ramulose (Colletotrichum gossypii var. cephalosporioides), mancha de Ramularia (Ramularia areola) e aos nematoides Meloidogyne incognita e Rotylenchulus reniformis. Interações genótipos X: ambientes significativas ocorreram em todos esses casos, dando margem a análises subsequentes de estabilidade fenotípica da resistência ou tolerância a esses patógenos. Diferenças notáveis foram observadas quanto a essa característica, e mediante associação dela com um parâmetro expressivo do pior desempenho nas avaliações realizadas, foi possível conferir previsibilidade e classificações mais seguras da reação dos genótipos à incidência das doenças consideradas.

Progresso da ramulose em campo a partir de sementes de algodoeiro inoculadas com Colletotrichum gossypii var. cephalosporioides

Objetivou-se avaliar a severidade e o progresso da ramulose no campo a partir de diferentes tempos de exposição das sementes de algodoeiro ao fungo Colletotrichum gossypii var. cephalosporioides. O experimento foi conduzido com cinco tratamentos e quatro repetições. Os tratamentos foram compostos por parcelas contendo 5% de sementes inoculadas nos tempos 0, 36, 72, 96 e 108 h de exposição ao patógeno. As avaliações foram feitas dos 46 dias até os 111 dias após a semeadura e os dados transformados para área abaixo da curva de progresso da incidência (AACPI) e da severidade (AACPS) da doença. Observou-se que a incidência de C. gossypii var. cephalosporioides cresceu de acordo com o aumento do tempo de exposição das sementes ao patógeno, chegando a 99% de incidência no tempo 108 h. Por outro lado, houve redução na germinação das sementes conforme o aumento no tempo de exposição, de 99%, no tempo 36 horas, para 92%, no tempo 108 horas. A AACPI e a AACPS da doença foram maiores com o aumento do tempo de exposição das sementes ao patógeno, observando-se o progresso da incidência (93,1%) e da severidade (42,5%) no maior tempo de exposição das sementes (108 h) em relação à testemunha.

Efeito de restritores hídricos sobre a germinação, comprimento da radícula e níveis de detecção de Colletotrichum gossypii var. cephalosporioides em sementes de algodão

O fungo Colletotrichum gossypii var. cephalosporioides, agente causal da ramulose do algodoeiro, é transmitido pela semente que se constitui em uma das mais importantes fontes de inóculo inicial e de introdução da doença em áreas indenes. Para que se possa identificar sua presença em lotes de sementes, é importante que se empreguem métodos de detecção rápidos e seguros. O mais empregado é o do papel de filtro, que se baseia na avaliação de sinais do patógeno desenvolvidos sobre as sementes, seguida da sua identificação morfológica. O método apresenta a desvantagem do crescimento das plântulas no período de incubação das sementes que pode favorecer o desenvolvimento de outros fungos e prejudicar a caracterização do patógeno. Para minimizar este problema vem sendo empregada a técnica da restrição hídrica. O presente trabalho teve como objetivo avaliar o efeito de três solutos em dois potenciais osmóticos, comparados ao tratamento padrão de água destilada, ao congelamento e ao 2,4 D, sobre a germinação, comprimento da radícula e detecção do agente causal da ramulose, durante o teste de sanidade. Os solutos Manitol e NaCl foram mais eficientes em inibir a germinação e favorecer a incidência do patógeno no potencial osmótico de -0,8 MPa. O KCl mostrou-se eficiente em inibir a germinação nos dois potenciais osmóticos testados, -0,6 e -0,8 MPa, porém reduziu a incidência do patógeno no potencial de -0,8 MPa. Os solutos Manitol, nos potenciais osmóticos de -0,8 e -0,6 MPa e o NaCl no potencial osmótico de -0,8 foram eficientes em reduzir o comprimento da radícula, sem interferir negativamente nos níveis de detecção de C. gossypii var. cephalosporioides, podendo ser recomendados para uso em análises sanitárias de rotina.