W. M. Coutinho

Qualidade sanitária e fisiológica de sementes de milho submetidas a termoterapia e condicionamento fisiológico

Thermotherapy has been used for eliminating fungi on seeds. However, physiological and biochemical alterations, which may occur on seeds following this treatment, have not been thoroughly investigated. In this work, the efficacy of heat treatment (hot water) followed by osmopriming, in the control of fungi associated with maize seeds and its effects on physiological seed quality, was evaluated. The fungi associated with the seeds were detected by the deep-freezing blotter method, and physiological quality was determined by germination, first-germination counting and electric conductivity tests in addition to determination of eletrophoretic patterns of the enzymes: esterase (EST), malate dehidrogenase (MDH) and alcohol dehidrogenase (ADH). The heat treatment used was hot water at 60°C for 5, 10 and 20 minutes. After treatment, a fraction of the seeds was submitted to osmopriming on roll paper soaked in PEG 6000 solution at -1.2 MPa. All heat treatments reduced or eliminated Acremonium strictum on maize seeds. Heat treatments for 10 and 20 minutes reduced significantly the percentage of Fusarium verticillioides. Increasing period of heat treatment raised the values of conductivity and reduced significantly seed germination rate and first-germination counting. Heat treatment for 20 minutes altered the eletrophoretic pattern of esterase and malate dehidrogenase enzymes. Osmopriming did not reverse damage caused by the heat treatments.

Um método simples e rápido de seleção para resistência à murcha-de-fusário em genótipos de algodoeiro

This study describes a new method to screen cotton genotypes for wilt resistance caused by Fusarium oxysporum f. sp. vasinfectum. Cotton genotypes were sown in germination trays (25 mL each cell) with sterilized vermiculite. On the fifth and the seventh days after germination, each seedling was inoculated with a suspension adjusted to 5 x 105 spores/mL. Resistance was evaluated using 1) the area under disease progress curve (AUDPC), for 15 days starting on the tenth day after the first inoculation (DAI); 2) disease severity on the 25th DAI; 3) percent of seedlings showing vascular system browning and 4) percent of seedlings with pathogen in the vascular system on the 25th DAI. No significant differences were found among genotypes Clevewilt 6, Auburn 56-24, Bayou SM-1, Coker 312, Stoneville 132, IAC RM2 and BJ 1302 for AUDPC and disease severity. When considering disease severity, genotypes Auburn 56-24, coker 312 and Bayou SM-1 were more resistant than Deltapine 45A, whereas for AUDPC only Coker 312 and Bayou SM-1 were more resistant than Deltapine 45A. Coker 312 was more resistant than Acala 44 only for disease severity. There was a significant correlation between AUDPC and disease severity, however, due to its ease, the latter index was found to be the best to screen cotton genotypes for fusarium wilt resistance.

Bole rot of sisal caused by Aspergillus niger in Brazil

A ocorrencia da podridao do tronco do sisal, causada por Aspergillus niger, e relatada pela primeira vez no Brasil. A doenca foi observada em campos de producao nos Estados da Bahia, Paraiba e Rio Grande do Norte

Fungitoxicidade de grupos químicos sobre Myrothecium roridum in vitro e sobre a mancha-de-mirotécio em algodoeiro

The objective of this work was to evaluate the toxicity of benzimidazoles, triazoles, strobilurins, isoftalonitrils and ditiocarbamats on Myrothecium roridum conidial germination and micelial growth in vitro, and the myrothecium leaf spot severity on cotton plants. On in vitro tests, fungicides were solubilized in PDA media at the following concentrations: 0.1, 1, 10 and 100 mg L -1 . The toxicity of the products were evaluated by the ED50 rate (required for inhibiting 50% of the conidial germination or mycelial growth). In greenhouse tests, the severity of myrothecium leaf spot was quantified by measuring the leaf area affected by the pathogen in cotton plants sprayed before (preventive) and after (curative) the pathogen inoculation. The fungicides thiophanate methyl, carbendazim, metconazole, thiophanate methyl + chlorothalonil, pyraclostrobin + epoxyconazole, pyraclostrobin + metiran, trifloxystrobin + propiconazole, and tebuconazole were highly efficient (ED50<1 mg L -1 ) or efficient (ED50 between 1 and 10 mg L -1 ) inhibiting conidial germination and mycelial growth of M. roridum isolates. In greenhouse tests, fungicides pyraclostrobin + epoxyconazole, tebuconazole, metconazole, and azoxystrobin + cyproconazole are the most efficient against myrothecium leaf spot disease. Preventive treatment is more efficient than curative.

Fungitoxicidade in vitro de iprodione sobre o crescimento micelial de fungos que se associam a sementes de arroz

Although the southern state of Rio Grande do Sul (RS) is responsible for about 40% of the Brazilian rice yield, its rice growing sector has been facing a crisis which is related, among other factors, to a profile of low competitiveness, high production costs and an average yield which is below the genetic potential of the varieties used. One of the ways which has been used to produce more effective responses to such crises lies in the use of a pre-germinated system, as a way of lowering production costs alongside with increasing productivity and thus enhancing competitiveness. Bearing such considerations in mind, this paper aims at comparing the initial development of rice seedlings of genotypes grown in RS (BR IRGA 409, BR IRGA 410, IRGA 416 e IRGA 417) at different temperatures (20, 25 e 30oC) and evaluating the initial growth of seedlings under aerobic and anaerobic conditions. In the anaerobiosis treatments, the seeds were submerged for 24 hours, then were kept in aerobiosis for 24 hours and were finally kept in anaerobiosis for fourteen days. The results of the tests allowed the conclusion that: a) The BR IRGA 409 genotype is better adapted to early sowing in the anaerobiosis condition when the temperature is 20oC; b) In anaerobiosis, the genotypes showed a more prominent radicular growth at higher temperatures.This experiment aimed to evaluate the iprodione effects on mycelial growth of fungi commonly associated with rice seeds in the state of Minas Gerais, Brazil. Isolates of Alternaria alternata, Aspergillus flavus, Aspergillus niger, Aspergillus ochraceus, Curvularia oryzae, Drechslera oryzae, Gerlachia oryzae, Phoma sorghina and Pyricularia grisea were obtained from rice seeds and mycelial growth measured in PDA medium containing the fungicide at concentrations of 10mg.l-1, 50mg.l-1, 100mg.l-1 and 500mg.l-1, after seven days of incubation. The effect of iprodione was evaluated by calculating ED50 (dose required for inhibiting 50% of the mycelial growth). Iprodione inhibits with high effect (ED50 50mg.l-1) the mycelial growth of P. grisea. The fungi A. niger and A. ochraceus were the most sensitive ones to the fungicide tested with ED50 of 2,5 e 3,1mg.l-1, respectively.

A SSR marker linked to the B 12 gene that confers resistance to race 18 of Xanthomonas axonopodis pv. malvacearum in cotton is also associated with other bacterial blight resistance gene complexes

The SSR marker CIR246, which is linked to the B12 gene that confers resistance to race 18 of Xanthomonas axonopodis pv. malvacearum (Xam), was used to evaluate a series of cotton germplasms that were also tested for their response to inoculation with race 18 of Xam (S-295, Delta Opal, 101-102B, Guazuncho-2, Acala 44, Mebane B1, and Stoneville 2B-S9). The allele associated with resistance was amplified in genotypes that carry the B12 gene (S-295 and Delta Opal) as well as in those that carry B2B3 (101-102B) and B9LB10L (Guazuncho-2), indicating that the molecular marker is able to identify genotypes resistant to the Xam races up to race 18, with resistance genes other than B12.

Use of osmotic solutions for inhibition of sunflower seed germination in blotter test

The aim of this work was to investigate the feasibility of using a water restriction technique with osmotic solutes to control sunflower (Helianthus annuus L.) seed germination in blotter tests. The effects of water potential (-0.8 MPa - Megapascal, -1.0 MPa, -1.2 MPa and -1.4 MPa) of substrates osmotically modified with sodium chloride or mannitol were evaluated for seed germination, radicle length and mycoflora present in the samples. The effects of levels of osmotic potentials ranging from -0.35 MPa to -1.4 MPa were also investigated on mycelial growth of the fungi Alternaria alternata and Alternaria zinniae on PDA medium. All osmotic potentials were able to inhibit or to retard seed germination to the extent that seed examination in stereomicroscope became easier without affecting seed mycoflora associated with the seeds. Mycelial growth of A. alternata was stimulated by all osmotic solutes tested, while mycelial growth of A. zinniae was stimulated by mannitol and reduced by all NaCl osmotic potential levels used.

Prevalence of race 18 of Xanthomonas citri subsp. malvacearum on cotton in Brazil

Cotton bacterial blight caused by Xanthomonas citri subsp. malvacearum (Xcm) is one of the most widely distributed and devastating diseases of cotton (Gossypium spp.) worldwide. Twelve Xcm races have been described in the world, with their relative prevalence varying by country. This study aimed to determine the current frequency and distribution of Xcm races in Brazil. Leaves showing cotton blight symptoms were collected from 12 cotton producing areas in the states of Bahia, Goiás, Mato Grosso and Mato Grosso do Sul. A total of 92 isolates were collected from surveyed areas. Race identification was performed by injection of bacterial suspensions into 10 differential cotton cultivars (Acala 44, Stoneville 2B-S9, Stoneville 20, Mebane B1, 1-10B, 101-102B, Gregg 8, Empire B4, PDX P4 and S-295). All Xcm isolates were characterized as race 18, indicating this to be the prevalent race in Brazil.

Development of a powder formulation of Aspergillus parasiticus for dry inoculation of peanut kernels

The aim of this study was to develop a method for the dry inoculation of Aspergillus parasiticus on peanut kernels for post-harvest studies. Inoculum powder was prepared by adding sterile kaolin powder to A. parasiticus spores developed on filter papers soaked with spore suspension prepared with Czapek medium (5% agar), which were dried at room temperature. Concentrations were adjusted to 5 x 105 and 1 x 106 spores g-1 of kaolin. Varied amounts of the powder inoculum were then used to inoculate 1 kg of peanut kernels. Inoculation was performed by mixing the powder inoculum with the peanut kernels in plastic bags until the kernels were completely covered. The effectiveness of this inoculation method was compared with the common inoculation methods of immersion in aqueous spore suspensions and contamination through contact with fungal colonies growing on culture medium. Fungal growth assay was performed on PDA saline medium, and near-infrared radiation measurements were used to determine peanut kernel moisture content. The dry inoculation technique was effective in inoculating peanut kernels with A. parasiticus, especially at concentrations of 3 x 106 and 4 x 106 spores g-1 per 1 kg of peanut kernels. In contrast to usual methods of inoculation, the dry inoculation technique does not increase the moisture content of inoculated peanut kernels. Thus, the physical state of the peanut kernel remains intact.