Anne Sitarama Prabhu

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.

Phenotypic virulence analysis of Pyricularia grisea isolates from Brazilian upland rice cultivars

Foi conduzido um estudo de virulencia fenotipica da populacao de Pyricularia grisea, coletada de 10 cultivares de arroz de terras altas, em tres locais distintos, objetivando determinar o grau de similaridade entre virulencia fenotipica de isolados, a composicao de racas fisiologicas e seu padrao de virulencia nas cultivares de arroz. Identificaram-se 16 racas, com base no tipo de reacao nas oito diferenciadoras internacionais, das quais IB-9 e IB-41 foram as predominantes. A frequencia de virulencia foi alta nas cultivares IAC47 e IAC165 entre as de ciclo medio e precoce, respectivamente. A frequencia dos isolados virulentos nas cultivares de terras altas foi maior (51,1%) do que nas cultivares irrigadas (21,8%). Ambos os isolados virulentos e avirulentos as linhas isogenicas estavam presentes na populacao de P. grisea testada. Dos72 isolados estudados, 94,4% foram virulentos aos genes Pi-3 e Pi-4a. A frequencia de virulencia foi relativamente baixa, em ordem decrescente, em Pi-1, Pi-4b e Pi-2. Ocoeficiente de similaridade variou de 0,28 a1,0 entre as diferentes racas dos isolados. O coeficiente de similaridade entre os isolados pertencentes ao grupo IB9 variou de 0,56 a1,0. Considerando o coeficiente de similaridade de 0,81, 72% dos isolados IB-9 apresentaram o mesmo padrao de virulencia.

Rice Ratooning Management Practices for Higher Yields

Rice is one of the worlds most important cereal crops and rice ratooning is one of the potential technologies to increase rice production. Based on land and water management, rice ecosystem is mainly divided into lowland, upland and deep water or floating rice. Rice ratooning is mainly practiced on lowland rice ecosystem. Ratooning provides higher resource use efficiency per unit time and per unit land area. However, better yield of ratoon crop is possible by adopting appropriate management practices for main crop as well as for ratoon crop. These management practices include land preparation, adequate plant density and spacing, use of appropriate cultivars, water management, application of adequate rate of fertilizers, appropriate height of cutting, and control of diseases, insects and weeds.

Relationship between panicle blast severity and mineral nutrient content of plant tissue in upland rice

Abstract Panicle blast (Pyricularia grisea) in upland rice causes significant yield losses depending upon the environmental conditions and nutritional status of the plant at the grain‐filling stage. Four field experiments were conducted to evaluate the influence of mineral nutrients on panicle blast of four upland rice genotypes on an oxisol. Panicle blast severities of four genotypes were related to nutrient concentrations in panicle tissues. Nitrogen (N), phosphorus (P), and magnesium (Mg) contents in tissue were significantly (P<0.01) and positively correlated, whereas potassium (K) and calcium (Ca) were negatively correlated with panicle blast severity. While the relationship between tissue N concentration and disease severity was quadratic, it was linear for K concentration. The correlation between tissue contents of N and P were positive and highly significant (r=0.75 P<0.001). Micronutrient tissue concentrations were not significantly correlated to panicle blast severities except for zinc (Zn). The...

Cultivar response to fungicide application in relation to rice blast control, productivity and sustainability (1)

(2) Abstract - Four field trials were conducted, from 1995 to 1997, with the objective of studying the response of four upland cultivars to foliar fungicide application in relation to panicle blast control, grain yield and sustainability. Differential disease control and yield response of cultivars to fungicide treat- ment were obtained. Losses in grain yield of cultivars IAC 202, Caiapo, Rio Paranaiba and Araguaia due to panicle blast were 44.8%, 27.4%, 24.4% and 18.2%, respectively. Two applications of tricyclazole or benomyl controlled panicle blast, as indicated by lower values of disease progress curve and relative panicle blast severity, and increased grain yield of the cultivar IAC 202. The losses in 100 panicle grain weight and grain yield were significantly reduced by 22.3% and 25.1% in IAC 202 and 23.6% and 20.5% in Caiapo, respectively, with two sprays of tricyclazole. Sustainable value index for yield was maximum with two applications of tricyclazole (0.59), followed by one application at booting (0.46) and at heading (0.40) in cultivar IAC 202. Results showed no yield response of the cultivars Rio Paranaiba and Araguaia to fungicide applications for panicle blast control.

An Unprecedented Outbreak of Rice Blast on a Newly Released Cultivar BRS Colosso in Brazil

Rice blast occurred in epidemic proportions on a newly released upland rice cultivar BRS Colosso, in the rice growing season 2004/2005. Twenty isolates were collected from the affected panicles of the cultivar BRS Colosso from three different States, two pathotypes IB-1 and IB-17 were identified. They were classified into thirteen Brazilian pathotypes based on the reaction pattern on eight upland rice cultivars, utilized as local differentials. Differences in aggressiveness of the isolates on the cultivar BRS Colosso were evident. Ten highly aggressive isolates were used to determine the partial resistance to leaf blast in the BRS Colosso and BRS Bonanca. There was no significant isolate x cultivar interaction for partial resistance. The mean leaf blast severity was significantly higher in BRS Colosso than in BRS Bonanca. Inoculation of culms with the same ten isolates showed cultivar x isolate interaction. Some isolates were more aggressive showing severe culm blast. There was no correlation among the aggressiveness of the isolates on leaf and culm. The disease outbreak in BRS Colosso could be attributed to the absence of adequate degree of partial resistance, the preexistence of compatible pathotypes IB-1 and IB-17 and their dissemination through seed.

Resistance spectra of six elite breeding lines of upland rice to Pyricularia grisea

O objetivo deste trabalho foi avaliar o espectro de resistencia de seis linhagens elites de arroz de terras altas, desenvolvidas para maior produtividade e qualidade superior de graos, atraves de testes de inoculacao em casa de vegetacao e no campo. Nos testes de inoculacao, foram utilizados 96 isolados de Pyricularia grisea, sendo 46 provenientes da cultivar Primavera, 31 da cultivar Maravilha e 19 de seis linhagens elites. Os patotipos internacionais IC-1 e IB-9, e os patotipos brasileiros BD-16 foram identificados como mais frequentes entre os isolados coletados da cultivar Primavera. Os isolados da cultivar Maravilha pertenceram a quatro patotipos internacionais e a 11 patotipos brasileiros com predominância de IB-9, IB-49, BB-1 e BB-21, respectivamente. Enquanto as linhagens CNAs 8711 e CNAs 8983 apresentaram reacoes de resistencia para todos os isolados oriundos da cultivar Maravilha, CNAs 8983 mostrou reacao suscetivel para tres isolados de Primavera, pertencentes ao patotipo IC-1. A maioria dos isolados que apresentaram reacoes compativeis com a cultivar Primavera foram incompativeis com a cultivar Maravilha e vice-versa. As avaliacoes no campo mostraram diferencas significativas entre as linhagens com relacao a area sob curva de progresso da brusone nas folhas. Os isolados de P. grisea que apresentaram reacoes diferenciais nas linhagens podem ser utilizados para a piramidacao de genes em novas cultivares de arroz de terras altas.

Genetic and phenotypic diversity of Magnaporthe oryzae from leaves and panicles of rice in commercial fields in the State of Goiás, Brazil

Genetic and phenotypic structure of Magnaporthe oryzae populations of two upland rice cultivars was determined. Monoconidial isolates were obtained from rice blast affected fields, four from cv. BRS Bonanca and four from cv. Primavera, in Goias State (2001-2003). The pathotypes IB-41 and IB-9 were predominant in both leaf and panicle isolates of BRS Bonanca and IF-1 in Primavera. A great majority of pathotypes were common to both leaf and panicle subpopulations of Bonanca (42.8%) and Primavera (66.6%). The ANOVA of virulence data showed high variability within population of each cultivar. There was no significant difference in virulence pattern of isolates from leaves and panicles, independent of collection site and cultivar. The molecular characterization of isolates was done employing the rep-PCR analysis with two primer sequences from Pot2. The genetic analysis of 538 isolates showed a high genotypic diversity in both leaf and panicle pathogen populations with 103 haplotypes in Bonanca and 49 in Primavera. The migration of pathotypes from leaves to panicles in each field was 70.8% and 36.6% for Primavera and BRS Bonanca, respectively. The diversity of M. oryzae population was influenced by cultivar of origin. A great amount of population diversity was encountered within the same field.

Development of blast resistant somaclones of the upland rice cultivar araguaia

O grau de resistencia a brusone da cultivar de arroz (Oryza sativa) Araguaia tem decrescido ao longo dos anos, resultando em prejuizos significativos na produtividade. O objetivo principal deste estudo foi obter somaclones resistentes a brusone (Pyricularia grisea), adaptando os metodos de selecao em casa de vegetacao e de campo. Foram avaliadas plantas regeneradas (R1) de paniculas imaturas da cultivar Araguaia nas geracoes R2 a R6 para resistencia a brusone e caracteristicas agronomicas. O metodo de avaliacao e selecao de plantas envolveu avaliacoes de populacoes segregantes e linhagens fixadas, em condicoes naturais de infeccao no campo, e infeccoes artificiais em casa de vegetacao com duas racas prevalecentes de P. grisea IB-1 e IB-9. Foram obtidos somaclones com resistencia vertical e progresso lento de brusone. Vinte de 31 somaclones desenvolvidos com alto grau de resistencia vertical e tipo de planta em leque apresentaram estabilidade da resistencia no campo e nos viveiros de brusone na geracao R6. No procedimento de selecao em casa de vegetacao com duas racas especificas, foram obtidos 44 somaclones com progresso lento de brusone, as quais nao diferiram da Araguaia quanto ao tipo de planta e potencial de produtividade.

Silicon reduces brown spot severity and grain discoloration on several rice genotypes

This study aimed to investigate the effect of silicon (Si) on the reduction of brown spot severity (BSS), caused by Bipolaris oryzae, and grain discoloration in several rice genotypes. An experiment was conducted in a greenhouse where eight genotypes were evaluated for their response to Si rates and decrease on BSS. The relationship between Si rates and BSS was linear negative. Additionally, a field experiment was conducted including forty-eight genotypes which were grown in upland conditions and evaluated for their response to Si rates and reduction on grain discoloration. The relationship between Si rates and grain discoloration was quadratic negative. Weight of filled grains per panicle increased as the Si rates in the soil increased. Genotypic differences for Si concentration in husk were evident for both non-amended and Si-amended plots. While the Si concentration in husk increased to all genotypes, there was no relationship between grain discoloration and Si concentration in husk for plants from non-amended and Si-amended plots. The genotype CAN-7024 with the highest resistance to leaf brown spot also showed the lowest grain discoloration in comparison to the genotypes Casado and Caqui.