Laércio Zambolim

Influence of silicon on sheath blight of rice in Brazil

The effect of silicon (Si) on sheath blight (Rhizoctonia solani K . uhn) of rice was studied under greenhouse conditions. The predominant commercial rice cultivars ‘BR-IRGA409’, ‘Metica-1’, ‘EPA GRI-109’, ‘Rio Formoso’, ‘Java ! and ‘CICA-8’, were grown in pots containing low-Si soil amended with 0, 0.48, 0.96, 1.44 or 1.92 g Si pot � 1 . Plants were inoculated at the maximum tillering stage. For all cultivars, Si concentration in straw increased more than 60% as the rates of Si increased from 0 to 1.92 g pot � 1 . Incubation period of R. solani was slightly prolonged with increasing Si rates and ranged from 53 to 64 h depending upon the cultivar. Total number of sheath blight lesions, total area under the relative lesion extension progress curve, severity of sheath blight, and the highest relative lesion height on the main tiller decreased by 37%, 40%, 52% and 24%, respectively, as the rate of Si increased from 0 to 1.92 g pot � 1 . Silicon may offer a viable method to control sheath blight in areas where soil is deficient in Si and

Effects of Angular Leaf Spot and Rust on Yield Loss of Phaseolus vulgaris

ABSTRACT Three field experiments were conducted in 1997, 1998, and 1999 to investigate the effects of angular leaf spot and rust, separately or combined, on host growth and yield of individual bean plants (Phaseolus vulgaris). In each experiment, three treatments were established by inoculating cv. Carioca with Phaeoisariopsis griseola, Uromyces appendiculatus, or with both pathogens. An additional control treatment was not inoculated, but was sprayed with a fungicide. In the 1997 and 1999 experiments, angular leaf spot reached higher disease levels than rust, whereas in 1998, rust was more severe than angular leaf spot. Host growth, expressed as healthy leaf area duration (HAD), and yield were the highest in 1997 and lowest in 1998. In each experiment, the treatments did not differ significantly to the area under leaf area progress curve, HAD, and healthy leaf area absorption (HAA). All inoculated treatments had significantly more severe disease and less yield than the control treatment. Based on the analysis of 60 plants in each experiment, yield was not related to the areas under disease progress curve for either or both diseases. In 1997 and 1999, yield was related to HAD (R(2) = 0.57 and 0.43) and HAA(R(2) = 0.60 and 0.55). Based on the combined analysis of all 36 plots, angular leaf spot reduced the leaf area because of defoliation, whereas rust did not affect the leaf area. Rust reduced yield more than four times that of angular leaf spot, although the decrease in photosynthesis to angular leaf spot was twice that of rust.

Concepts in plant disease resistance

Resistance to nearly all pathogens occurs abundantly in our crops. Much of the resistance exploited by breeders is of the major gene type. Polygenic resistance, although used much less, is even more abundantly available. Many types of resistance are highly elusive, the pathogen apparently adapting very easily them. Other types of resistance, the so-called durable resistance, remain effective much longer. The elusive resistance is invariably of the monogenic type and usually of the hypersensitive type directed against specialised pathogens. Race-specificity is not the cause of elusive resistance but the consequence of it. Understanding acquired resistance may open interesting approaches to control pathogens. This is even truer for molecular techniques, which already represent an enourmously wide range of possibilities. Resistance obtained through transformation is often of the quantitative type and may be durable in most cases.

Foliar application of potassium silicate reduces the intensity of soybean rust.

This study aimed to determine if potassium silicate (KSi) sprays could reduce the intensity of soybean rust. In the field experiment 1, soybean plants were sprayed with KSi (pH 10.5) at rates of 8, 20, 40 and 60 g/L. In the field experiment 2, with the same treatments, the pH of the KSi solutions was 5.5. In experiment 3, the treatments were KSi (40 g/L, pH 10.5), potassium hydroxide (KOH) (6.5 g/L,pH10.5), epoxiconazole + pyraclostrobin, and control. In experiment 4, the treatments were the same as in experiment 3, but the pH of the KSi and KOH solutions was adjusted to 5.5. Plants sprayed with water served as a control treatment for all field experiments. Plants were artificially inoculated with Phakopsora pachyrhizi before the application of products. Even though there was no relationship between silicon (Si) concentration in leaf tissue and KSi rates, Si concentration increased by 67% and 73% respectively above the control, when averaged across all KSi rates for experiments 1 and 2. The relationship between the severity of soybean rust and KSi rates atpH10.5 and 5.5 was, respectively, linear and quadratic. Soybean rust severity at the highest KSi rate (pH 5.5) was70%less than the control. In experiments 3 and 4, the highest disease severity was observed on the control treatment which differed from other treatments. The application of KSi at pH of 10.5 (Exp. 3) and 5.5 (Exp. 4) decreased soybean rust severity by 36% and 43%, respectively, over the control. No significant difference in disease severity was found between KSi and KOH treatments, but they were significantly different, regardless of pH used, from the epoxiconazole + pyraclostrobin treatment. In greenhouse experiments, Si concentration in leaf tissue was higher with the application of KSi, regardless of the pH of the solutions, as compared with water spray. Soybean rust severity and the number of pustules were higher on leaves of plants sprayed with water, as well as on those sprayed with phosphoric acid + NaOH, and phosphoric acid + KOH, when compared with the application of KSi. There was no difference between the KSi and KOH treatments, regardless of the pH, and epoxiconazole + pyraclostrobin sprays for disease severity and number of pustules. This is the first study where field and greenhouse experiments have demonstrated a reduction of soybean rust intensity with foliar application of KSi. This information may be valuable in areas where soybean is grown as a monoculture, and where high yielding but susceptible cultivars cannot be grown because of the occurrence of frequent severe epidemics.

Influência da nutrição mineral na intensidade da mancha-de-olho-pardo em mudas de cafeeiro

The experiment was carried out at the coffee nursery of the Universide Federal de Vicosa, in Vicosa, MG, Brazil, using nutrient circulating solution to evaluate the intensity of brown-eye spot (Cercospora coffeicola), variety Catuai Vermelho, as a function of N and K. Acompletely randomized design with 16 treatments, three replicates, and two plants per plot was used in a factorial with four levels of K (3, 5, 7 and 9mmol/L) combined with four levels of N (3, 7, 11 and 15mmol/L). After seven inoculations and evaluations, the plants were picked. Total dry matter production, total leaf area, and the area below the curve of progress (AACP) for the total number of leaves were not influenced by the levels of K, but increased with increasing levels of N. There was increase in AACP areas for the number of lesions per leaf and defoliation, with the increase of K levels, and a reduction of N levels. The increase in K levels reduced the Ca and Cu leaf contents, indicating possible relation between its contents and the increase of the disease. The P, Mg, Mn, and Fe leaf contents were not influenced by the K levels, and had a small reduction with increased N contents in the nutrient solution, increasing thereafter.

Manejo de doenças de plantas em cultivo protegido

Plant disease management in greenhouse crops Crop production based on plasticulture has allowed substantial gains in yields for many horticultural crops. In the greenhouse, crop production may be more easily optimized and plants may be better exploited for their maximum yields. However, this may increase the impact of some biotic and abiotic diseases. Less important diseases may become highly destructive in crops cultivated in the greenhouse. Indeed, in some cases disease management may become more complex in the greenhouse than in the field. Disease management in greenhouse cropping systems requires flexibility and great efforts for integration of available control measures.

White mold intensity on common bean in response to plant density, irrigation frequency, grass mulching, Trichoderma spp., and fungicide

The purpose of this study was to evaluate the efficiency of integrated managements on white mold control on common bean. Initially, in vitro testing was made to assess the antagonism of 11 Trichoderma isolates against Sclerotinia sclerotiorum and to investigate fungicides (fluazinam and procymidone) inhibitory effects on those fungi. In two field experiments the following combinations were tested: irrigation frequencies (seven or 14 days), plant densities (six or 12 plants per meter), and three disease controls (untreated control, fungicide or Trichoderma spp.). In a third experiment plant densities were replaced by grass mulching treatments (with or without mulching). Fluazinam was applied at 45 and 55 days after emergence (DAE). The antagonists T. harzianum (experiments 1 and 3) and T. stromatica (experiment 2) were applied through sprinkler irrigation at 10 and 25 DAE, respectively. Most of the Trichoderma spp. were effective against the pathogen in vitro. Fluazinam was more toxic than procymidone to both the pathogen and the antagonist. Fungicide applications increased yield between 32 % and 41 %. In field one application of Trichoderma spp. did not reduce disease intensity and did not increase yield. The reduction from 12 to six plants per meter did not decrease yield, and disease severity diminished in one of the two experiments. It is concluded that of the strategies for white mold control just reduction of plant density and applications of fungicide were efficient.

Doenças do milho causadas por fungos do gênero Stenocarpella

Stemocarpella macrospora and S. maydis may cause seed rot, seedling blight, stem and ear rot and leaf spot in corn. Normally these fungi are the main grain rot causal agent when ears are infected. The damage caused exclusively by Stenocarpella has not yet been determined. The pathogens are found in practically all maize-growing regions of Brazil. The major disease intensity occurs under corn monoculture, mainly in small farms and fields for seed production where corn is continuously cultivated. Corn debris and infected seed are the primary source of inoculum. The inoculum, consisting of conidia produced in plant debris, is disseminated at short distance by wind and rain splash. Long distance dissemination occurs by seeds. Plant infection may occur systemically with inoculum coming from seeds, as mycelium, and/or through direct penetration of leaf sheats, foliar blade, peduncle and ear husks, from spore deposition, germination and penetration. The optimal temperature for mycelial growth and conidial germination is between 23 and 28 oC for both fungi. The main strategies to control these diseases are based on the elimination and/or reduction of primary inoculum, the use of healthy seed, seed treatment with fungicide of the benzimidazoles group and crop rotation. There is little information about disease resistance in commercial hybrids in Brazil. Balance of soil fertility and avoidance of high plant population may also help to reduce the infection.

Syntheses, crystal structure, spectroscopic characterization and antifungal activity of new N-R-sulfonyldithiocarbimate metal complexes.

Five new compounds with the general formula of (Bu(4)N)(2)[M(RSO(2)NCS(2))(2)], where Bu(4)N=tetrabutylammonium cation, (M=Ni, R=4-FC(6)H(4)) (1), (M=Zn, R=4-FC(6)H(4), 4-ClC(6)H(4), 4-BrC(6)H(4), 4-IC(6)H(4)), (2), (3), (4) and (5), respectively, were obtained by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate (RSO(2)N=CS(2)K(2)) with nickel(II) chloride hexahydrate or zinc(II) acetate dihydrate in metanol:water 1:1. The elemental analyses and the IR data are consistent with the formation of the expected bis(dithiocarbimato)metal(II) complexes. The (1)H and (13)C NMR spectra showed the signals for the tetrabutylammonium cation and the dithiocarbimate moieties. The compounds 1, 2 and 5 were also characterized by X-ray diffraction techniques. The nickel(II) is coordinated by two N-4-fluorophenylsulphonyldithiocarbimato(2-) ligands forming a planar coordination. The zinc(II) exhibits distorted tetrahedral configuration in compounds 2 and 5 due to the chelation effect of two sulfur atoms of the N-R-sulfonyldithiocarbimate ligands. The antifungal activities of the compounds were tested in vitro against Colletotrichum gloeosporioides, an important fungus that causes the plant disease known as anthracnose in fruit trees. All the complexes were active.

Dispersão Vertical e Horizontal de Conídios de Stenocarpella macrospora e Stenocarpella maydis

Vertical and horizontal dispersion of conidia of Stenocarpella macrospora and Stenocarpella maydis Experiments were carried out in the field to quantify airborne dispersal of Stenocarpella maydis and S. macrospora conidia from naturally infected corn (Zea mays) straw. The data indicated that 93% and 88% of the total number of sampled conidia of S. maydis and S. macrospora, respectively, were trapped during the day, differing statistically from the night period. The number of sampled conidia of both fungi, was inversely proportional to the vertical and horizontal distance of spore traps from the inoculum source. Conidia were collected up to a height of 2.0 m and up to 120.0 m from the inoculum source. In both experiments, the frequency and the number of collected spores were the highest at a height of 25.0 cm and at a distance of 20.0 m from the inoculum source. Conidia was dispersed in the air as individual spores and/or grouped in cirri and not essentially associated to rain splashes.