Marta Cristina Corsi de Filippi

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.

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.

Chapter 18 Silicon from rice disease control perspective in Brazil

Rice blast and grain discoloration are mainly responsible for significant losses in grain yield and quality both in upland and irrigated ecosystems in Brazil. Rice ( Oryza sativa L.) planting in rotation with soybean in extensive, contiguous areas and high input technology provided a conductive environment to diseases which were hitherto unimportant, such as sheath blight in irrigated rice and take-all in upland rice. Even though varietal resistance constitutes a major component in rice disease management, it should be integrated with long-term benefits of silicon (Si) fertilization. A field study conducted with genotypes showing wide variability for grain discoloration and different rates of SiO 2 showed promising results. Initial greenhouse inoculation tests are encouraging in controlling leaf blast at the vegetative phase with Si. The logical extension of firmly established existing concepts on Si and rice disease management should rely on multidisciplinary approach and inter-institutional collaboration. Extensive on-farm trials at hot spot locations for diseases will compliment the experimental results and increase the speed and efficacy in accomplishing the desired goals.

Inheritance of blast resistance in rice to two Pyricularia grisea races, IB-1 and IB-9

Seven sources of resistance to the two predominant races IB-1 and IB-9 of the rice blast pathogen Pyricularia grisea were selected based on leaf blast reaction in tests conducted under controlled greenhouse conditions. Crosses involving resistant and susceptible parents were made to study the inheritance of the disease reaction for different sources of resistance. The F1 and F2 progenies of all crosses, including backcrosses to resistant and susceptible parents, were tested for reaction to leaf blast. The data showed that resistance is controlled by one to three genes that segregate independently in most of the donors. Non-allelic interaction among resistance genes, including dominant epistasis, was identified.

Occurrence of crown sheath rot caused by Gaeumannomyces graminis var. graminis, a new rice disease in Brazil.

Crown sheath rot also known as black sheath rot has been found to occur in upland rice (Oryza sativa) in the municipalities of Unai (MG), Palmeiras(GO), Itaberai (GO), Humaita (AM) and in flooded rice in the States of Goias, Tocantins and Rio Grande de Sul. The causal agent was identified as Gaeumannomyces graminis var. graminis based on morphological and cultural characteristics of the fungus as well as pathogenicity tests conducted utilizing different Brazilian isolates. This constitutes the first report of the disease occurrence in rice in Brazil.

Expression of resistance in rice hybrids to Pyricularia grisea

Thirty-nine rice (Oryza sativa) hybrids and their restorers were assessed for vertical resistance to Pyricularia grisea in the rice blast nursery, and in artificial inoculation tests with two pathotypes, under controlled greenhouse conditions. The hybrids were developed from cytoplasmic genetic male sterile lines 046I and IR 58025A, derived from WA cytoplasm. In the rice blast nursery all hybrids showed susceptible reaction varying from 5 to 9. Compatible and incompatible leaf blast reactions of hybrids to two pathotypes, IC-1 and IB-45, were observed in inoculation tests. A majority of the hybrids were resistant when the restorer was resistant. However, seven of the 25 F1 hybrids exhibited susceptible reactions even when one of the parents was resistant to a pathotype. The partial resistance of 11 hybrids and their parents that showed compatible reactions to two pathotypes was analyzed. Differential interaction between isolates and genotypes was observed for partial resistance in relation to both disease severity and lesion number indicating the specific nature of partial resistance.

Cytological aspects of incompatible and compatible interactions between rice, wheat and the blast pathogen Pyricularia oryzae

Blast, caused by the fungus Pyricularia oryzae, is an important disease affecting rice and wheat yield worldwide. This study investigated the cytological aspects of incompatible (non-host resistance) and compatible (host resistance) rice- (R_Po) and wheat- (W_Po) Pyricularia oryzae isolate interactions. Inoculations of rice and wheat with the R_Po and W_Po isolates of P. oryzae, respectively, were expected to be compatible interactions (host resistance), whereas inoculations of rice and wheat with the W_Po and R_Po isolates of P. oryzae, respectively, were considered to be incompatible interactions (non-host resistance). For the compatible interactions (rice-R_Po and wheat-W_Po), fungal hyphae penetrated and colonized the epidermal cells and also invaded many neighboring cells. By contrast, in the case of the incompatible interactions (rice-W_Po and wheat-R_Po), fungal hyphae were not able to penetrate nor colonize the epidermal cells, but when penetration did occur, the hyphae were restricted to the first-invaded epidermal cell. The frequency of appressorial sites exhibiting infection hyphae within the epidermal cell underlying an appressorium was greater in the case of the compatible interactions. By contrast, unsuccessful penetrations with cytoplasmic granulation occurred with high frequency in the incompatible wheat-R_Po and rice-W_Po interactions and the number of necrotic epidermal cells underlying the appressorium was low for the rice-W_Po interaction as well as for the wheat- R_Po interaction, where no symptoms of necrosis were exhibited. However, the opposite was observed for the compatible interactions. The present study presents cytological features associated with incompatible and compatible rice- and wheat-P. oryzae interactions that may be useful to studies involving variability, coevolution, diagnosis, and regulation of quarantine or even in a rice or wheat breeding program whose aim is to transfer genes involved in non-host resistance to host resistance due to similarities in downstream mechanisms.

CONTROLE QUÍMICO DA BRUSONE EM ARROZ DE TERRAS ALTAS: EFEITOS NOS FUNGOS NÃO ALVOS DO FILOPLANO

Upland rice blast significantly affects yield, requiring one or two fungicides applications to control it. However, the effect of fungicides on beneficial fungi and on fungi not targeted by rice phylloplane are unknown. This study aimed to evaluate the effect of fungicides on panicle blast control, on fungi not targeted by rice phylloplane, and to study the antibiosis of fungi not targeted by M. oryzae . A field experiment was conducted by using two cultivars (Primavera and Bonanca), four fungicides (trifloxistrobina + propiconazol, azoxistrobina, tebuconazol, and triciclazol) and a control, with a randomized blocks design, in a split-plot scheme, and four replications. The panicle blast severity, leaf chlorophyll content, number of colony-forming units cm - ² of leaf area, and antibiosis were assessed. The Primavera cultivar showed higher panicle blast severity than Bonanca. The fungicides azoxistrobina and trifloxistrobina + propiconazol significantly differed from the control, showing the lowest panicle blast severities. The fungicides did not affect the chlorophyll content, but differences were noticed between the cultivars. The fungicides tebuconazol, trifloxistrobina + propiconazol, and azoxistrobina significantly reduced the phylloplane fungi, concerning the control. The triciclazol did not differ from the control, showing the highest number of colony-forming units cm - ² of leaf area. Among the four fungi tested, only Epicoccum sp. showed antagonism to M. oryzae .

Influência da adubação nitrogenada, época de plantio e aerosporos sobre a severidade da mancha de grãos em arroz de terras altas

Grain discoloration (GD) is ranked second among the most economically important rice diseases. The influence of nitrogen levels, planting date and air spora concentration on the disease severity was studied in the field. GD severity in the rice cultivar BRS Bonanca was assessed on two planting dates (30/11/2006 and 21/12/2006), using five nitrogen levels (0, 30, 60, 120 and 240 kg of N.ha-1) and a randomized split plot block design with three replicates. The effect of N level on GD severity was not significant. The correlation between GD severity and empty spikelets was positive and significant. The fungus population in the air (air spora) was quantified using the volumetric trap Rotorod Sampler from panicle emergence to maturation. Grain discoloration linearly increased with time (r = 0.98; P < 0.01), but the same did not occur with the total number of fungi, which varied from 0.23 to 2.97 spores/liter of air/minute. The fungi present in the air in decreasing order of spore concentration were Nigrospora sp., Pyricularia oryzae, Pithomyces sp., Alternaria sp., Cercospora sp., Fusarium sp., Curvularia sp. and Bipolaris sp. These fungi, Phoma sp. and others were also detected in the seed health testing. The correlation between the quantity of spores of P. oryzae and other fungi was linear and positive (r=0.80, P < 0.01). The number of spores increased with the increase in relative humidity and exponentially decreased with the increase in maximum temperature.