Francisco Xavier Ribeiro do Vale

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

Effect of Rice Growth Stages and Silicon on Sheath Blight Development

ABSTRACT The objective of this study was to determine the effect of silicon (Si) and rice growth stages on tissue susceptibility to sheath blight (Rhizoctonia solani Kühn) under controlled conditions. Rice plants (cv. Rio Formoso) were grown in pots containing low-Si soil amended with Si at 0, 0.48, 0.96, 1.44, and 1.92 g pot(-1) and inoculated with R. solani at the following days after emergence: 45 (four-leaf stage), 65 (eight-leaf stage), 85 (tillering), 117 (booting), and 130 (panicle exsertion). For plants inoculated with R. solani at all growth stages, Si concentration in straw increased as rate of Si increased from 0 to 1.92 g pot(-1). Concentration of calcium in the straw did not differ among plant growth stages. Although incubation period was not affected by the amount of Si added to the soil, this variable was shorter at booting and panicle exsertion stages. As the rates of Si increased in the soil, the total number of sheath blight lesions on sheaths and total area under the relative lesion extension curve decreased at all plant growth stages. The severity of sheath blight was lower at booting and panicle exsertion stages as the rates of Si increased in the soil. In general, plants grown in Si-nonamended pots and inoculated with R. solani were more vulnerable to infection at all growth stages, but especially at 45 days after emergence. Plant dry weights for inoculated plants increased as the Si rates increased from 0 to 1.92 g pot(-1). The greatest dry weight increases occurred for plants inoculated at booting and panicle exsertion stages. Si fertilization is a promising method for controlling sheath blight in areas where soil is Si deficient and when cultivars that exhibit an acceptable level of resistance to sheath blight are not available for commercial use.

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.

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.

Previsão da requeima da batateira

This experiment was carried out on a potato (Solanum tuberosum) crop to evaluate a prediction system to control late blight caused by Phytophthora infestans. The trial was conducted from May to September 1998 using the cultivar Bintje. Dimethomorph, cymoxanil, mancozeb and chorothalonil were associated with different spraying schemes, based on the modified Wallin (1962) prediction system and on the traditional late blight control system. The prediction schemes tested consisted of accumulated disease severity values (DSV) of 12, 14, and 16. The traditional late blight control consisted of weekly applications of fungicides starting two weeks after plant emergence, while those defined by the prediction system were carried out based on the DSV accumulated throughout the experiment. Descriptive and diagrammatic scales were used to assess late blight severity. The efficiency of the spray schemes was compared with the area below the curve of disease progress and tuber yield. The treatments based on the prediction scheme were as efficient as the weekly calendar program in reducing disease intensity. Disease severity values of 12 and 14 allowed reduction in the number of sprays without significantly affecting the control level of the disease and tuber yield. The use of the systemic fungicide alone, based on the prediction scheme, resulted in high disease intensity; the use of protective fungicides at weekly intervals gave intermediate control similar to the weekly spray calendar. The prediction schemes based on DSV of 14 reduced dimethomorph sprays without any yield loss.

Relationships between angular leaf spot, healthy leaf area, effective leaf area and yield of Phaseolus vulgaris

Three field experiments were carried out with the bean cultivar Carioca Comum to investigate the relationships among visual and virtual severity of angular leaf spot (caused by Phaeoisariopsis griseola), area under visual and virtual disease progress curves (AUDPC), healthy leaf area index on any given day (HLAI), healthy leaf area duration (HAD), healthy leaf area absorption (HAA), effective leaf area duration (ELAD), effective leaf area absorption (ELAA) and yield of Phaseolus vulgaris. To obtain a wide range of disease severities, the plots were sprayed with fungicide at different stages of plant growth (before, during and after flowering). Visual and virtual severity and AUDPC showed no significant correlation with yield. However, HAD, HAA, ELAD and ELAA were significantly correlated with yield. Variables that considered the effective leaf area (ELAD and ELAA) provided similar or better coefficients of determination (R2) than those that considered the remaining green leaf area only (HAD and HAA). Single-point models with HLAI, effective leaf area index (ELAI), intercepted radiation by healthy leaf area (HRI) and intercepted radiation by effective leaf area (EHRI) to estimate yield at various times during the crop season were developed. The slope of the relationship between yield and HLAI, ELAI, HRI and EHRI proved to be stable, regardless of planting date and bean growth stage (from R6 to R8).

Controle da ferrugem do cafeeiro com base no valor de severidade

O presente trabalho teve por objetivo avaliar o controle da ferrugem do cafeeiro (Coffea arabica) baseando-se no valor de severidade, calculado em funcao das variaveis meteorologicas, molhamento foliar e temperatura media durante o periodo de molhamento. Foram escolhidas duas lavouras de cafe da cultivar Catuai Vermelho, uma com alta carga pendente de frutos (101,5 sacas beneficiadas/ha), com seis anos de idade, localizada no municipio de Coimbra, a 680 m de altitude, na regiao da Zona da Mata de Minas Gerais; e a outra, com carga media de frutos (22,4 sacas beneficiadas/ha), com nove anos de idade, localizada no municipio de Carmo do Paranaiba, a 850 m de altitude, na regiao do Alto Paranaiba do Estado de Minas Gerais. Em Coimbra, quando o valor de severidade da ferrugem (VSF) foi igual a 30, foram feitas duas pulverizacoes com fungicida sistemico, igualando-se as duas aplicacoes de fungicida sistemico do calendario. Em Carmo do Paranaiba, o VSF igual a 49 recomendou apenas uma unica pulverizacao; todos os outros tratamentos demandaram duas aplicacoes de fungicidas sistemicos. A incidencia final de folhas doentes na colheita (11,0%) para todos os tratamentos, nao atingiu o nivel de dano economico ao cafeeiro. Nao houve diferenca na eficiencia de controle dos tratamentos baseados no calendario (duas aplicacoes de fungicidas sistemicos e quatro aplicacoes de fungicida cuprico), duas aplicacoes de fungicida sistemico baseadas na incidencia da doenca (10%) e o sistema baseado no VSF. Portanto, o sistema baseado no VSF foi tao eficiente quanto o calendario, para o controle da ferrugem do cafeeiro, porem com economia de uma pulverizacao, na lavoura com carga media de frutos (Carmo do Paranaiba).

Effects of angular leaf spot and rust on leaf gas exchange and yield of common bean (Phaseolus vulgaris)

Isolated and interactive effects of angular leaf spot (caused by Phaeoisariopsis griseola) and rust (caused by Uromyces appendiculatus) on leaf gas exchange and yield was studied in common bean (Phaseolus vulgaris L. cv. Carioca) plants. Gas exchange was measured on 37, 44, 51, and 58 d after planting using a portable photosynthesis system. The inoculation of plants with P. griseola (P), U. appendiculatus (U), and the combination of both pathogens (P+U) caused a significant reduction of net photosynthetic rate (PN) and yield. The reduction of stomatal conductance (gs), PN, and yield was higher under P and combination of P+U than under U treatment. By effect of U, the reduction on yield was higher than the reductions on gas exchange parameters. On the treatment P+U, a reduction of 23 % in PN and a correspondent reduction of 32 % in yield was observed. The interactive effects of the pathogens on yield could be explained in part by the decreases in gs and in PN of diseased bean leaves. The combined effect of both diseases on yield and gas exchange parameters suggests an antagonistic interaction.

Utilization of the cropgro-soybean model to estimate yield loss caused by Asian rust in cultivars with different cycle

In recent years, crop models have increasingly been used to simulate agricultural features. The DSSAT (Decision Support System for Agrotechnology Transfer) is an important tool in modeling growth; however, one of its limitations is related to the unac- counted-for effect of diseases. Therefore, the goals of this study were to calibrate and validate the CSM CROPGRO-Soybean for the soybean cultivars M-SOY 6101 and MG/BR 46 (Conquista), analyze the performance and the effect of Asian soybean rust on these cultivars under the environmental conditions of Vicosa, Minas Gerais, Brazil. The experimental data for the evaluation, testing, and adjustment of the genetic coefficients for the cultivars, M-SOY 6101 and MG/BR 46 (Conquista), were obtained during the 2006/2007, 2007/2008 and 2009/2010 growing seasons. GLUE (Generalized Likelihood Uncertainty Estimation) was used for the estimation of the genetic coefficients, and pedotransfer functions have been utilized to estimate the physical characteristics of the soil. For all of the sowing dates, the early season cultivar, M-SOY 6101, exhibited a lower variance in yield, which represents more stability with regard to the interannual climate variability, i.e., the farmers who use this cultivar will have in 50% of the crop years analyzed, a higher yield than a late-season cultivar. The MG/BR 46 (Conquista) cultivar demonstrated a greater probability of obtaining higher yield in years with favorable weather conditions. However, in the presence of the Asian soybean rust, yield is heavily affected. The early cultivar, M-SOY 6101, showed a lower risk of being affected by the rust and consequently exhibited less yield loss considering the scenario D90 (condensation on the leaf surface occurs when the relative humidity is greater than or equal to 90%), for a sowing date of November 14.

Alterations in Gas Exchange and Oxidative Metabolism in Rice Leaves Infected by Pyricularia oryzae are Attenuated by Silicon.

Rice blast, caused by Pyricularia oryzae, is the most important disease in rice worldwide. This study investigated the effects of silicon (Si) on the photosynthetic gas exchange parameters (net CO2 assimilation rate [A], stomatal conductance to water vapor [gs], internal-to-ambient CO2 concentration ratio [Ci/Ca], and transpiration rate [E]); chlorophyll fluorescence a (Chla) parameters (maximum photochemical efficiency of photosystem II [Fv/Fm], photochemical [qP] and nonphotochemical [NPQ] quenching coefficients, and electron transport rate [ETR]); concentrations of pigments, malondialdehyde (MDA), and hydrogen peroxide (H2O2); and activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and lypoxigenase (LOX) in rice leaves. Rice plants were grown in a nutrient solution containing 0 or 2 mM Si (-Si or +Si, respectively) with and without P. oryzae inoculation. Blast severity decreased with higher foliar Si concentration. The values of A, gs and E were generally higher for the +Si plants in comparison with the -Si plants upon P. oryzae infection. The Fv/Fm, qp, NPQ, and ETR were greater for the +Si plants relative to the -Si plants at 108 and 132 h after inoculation (hai). The values for qp and ETR were significantly higher for the -Si plants in comparison with the +Si plants at 36 hai, and the NPQ was significantly higher for the -Si plants in comparison with the +Si plants at 0 and 36 hai. The concentrations of Chla, Chlb, Chla+b, and carotenoids were significantly greater in the +Si plants relative to the -Si plants. For the -Si plants, the MDA and H2O2 concentrations were significantly higher than those in the +Si plants. The LOX activity was significantly higher in the +Si plants than in the -Si plants. The SOD and GR activities were significantly higher for the -Si plants than in the +Si plants. The CAT and APX activities were significantly higher in the +Si plants than in the -Si plants. The supply of Si contributed to a decrease in blast severity, improved the gas exchange performance, and caused less dysfunction at the photochemical level.