Alfredo Seiiti Urashima

Resistance spectra of wheat cultivars and virulence diversity of Magnaporthe grisea isolates in Brazil

Seventy-two monoconidial isolates of Magnaporthe grisea were obtained from the States of Mato Grosso do Sul and Parana. The isolates were inoculated on seedlings of 20 wheat (Triticum aestivum) cultivars under greenhouse conditions. The virulence diversity of M. grisea was assessed based on compatible and incompatible reactions of leaf blast on wheat cultivars. Fifty-four distinct virulence patterns were identified on test cultivars among the isolates collected from the two wheat growing States. Sixteen of these isolates corresponding to 22.2% showed similar virulence pattern. None of the wheat cultivars was resistant to all isolates of M. grisea, but the cultivars differed in degree of resistance as measured by the relative spectrum of resistance (RSR) and disease index (DI). Among the cultivars the RSR ranged from 0 to 53.3% and DI from 0.4662 to 0.9662 (0 to 1 scale). The wheat cultivar BR18 exhibited a broad resistance spectrum in relation to the rest of the tested cultivars to the isolates of M. grisea, and can be used in wheat resistance breeding.

Reação do trigo à Magnaporthe grisea nos diferentes estádios de desenvolvimento

The blast of wheat (Triticum aestivum) was first reported in the State of Parana in 1986 and has now spread to all the major wheat growing areas of Brazil. The relation between leaf and neck blast resistance was studied utilizing three isolates and 15 wheat varieties. The relationship between incidence of blast in wheat spikes and infection of harvested seeds was examined using inoculation tests with three fungal isolates on five wheat cultivars. The varieties showing susceptible reaction at seedling stage were also susceptible to spike infection. The BH1146 was the sole variety resistant at seedling stage, which subsequently produced a significantly lower the incidence and severity of blast. A high positive correlation was observed between incidence and severity of diseased heads. The percentage of infected seeds was less in varieties exhibiting a resistant reaction to spike infection than in susceptible varieties.

Eficiência da disseminação aérea em Pyricularia grisea

Pyricularia grisea (teleomorph Magnaporthe grisea) infects more than 80 gramineous plants. In Brazil, it attacks important crops like rice and wheat causing blast disease. Recently the disease was reported in triticale, an alternative crop to wheat producers in Southern Sao Paulo state. Airborne conidia are one of the most important way of dissemination, although little reliable information is available on the distance traveled by spores from an inoculum source. The present work aimed to determine by molecular tools the efficiency of aerial dissemination of P. grisea from a known inoculum source. The presence of pathogen clones in fields distant 4, 30 and 1000 meters from an infected field suggested that spores can travel at least these distances.

Triticale and Barley: New Hosts of Magnaporthe Grisea in São Paulo, Brazil — Relationship with Blast of Rice and Wheat

Triticale (X. triticosecale) and barley (Hordeum vulgare) are the most recent crops to be infected by Magnaporthe grisea, the causal agent of blast disease. This is a newly emerging problem in Sao Paulo state where frequent yield losses due to rice and wheat blast already occur. The present work is aimed at examining the relationship among isolates from these four important crops through host range, cross-infectivity and DNA fingerprinting. Data from controlled-environment inoculations revealed that M. grisea from triticale and barley could infect triticale, wheat, barley, oat, and rye but not rice, sorghum, maize, common millet, sugarcane, and Brachiaria brizantha. A positive cross-infection of triticale by wheat and barley isolates was observed. Positive cross-infection was also detected between barley and triticale and wheat. Cross-infection was not possible with rice but rice isolates infected barley, triticale and wheat. Southern hybridization of DNA digested with EcoRI, probed with Pot2 showed similar DNA fingerprints among wheat, triticale, and barley isolates suggesting that the disease on triticale and barley originated from wheat blast pathogen.

Comparação entre métodos de avaliação de transmissão de Pyricularia grisea através de sementes em triticale

Methods to examine transmission of Pyricularia grisea from seeds to seedlings of triticale Triticale (X. triticosecale ) is the most recent host of Magnaporthe grisea (Pyricularia grisea), the causal agent of blast, in Sao Paulo state. Severe yield losses occurred in large areas in the southern part of the state in 2001. It is speculated that seed borne infection played a vital role in the outbreak and dissemination of this disease. Nevertheless, transmission of disease from seeds to seedlings is still a matter of controversy, in both rice (Oryza sativa) bl ast and wheat (Triticum aestivum) blast. One reason for this debate may be associated with the method used in those studies. The present work was designed to examine the seed borne transmission of P. grisea from seeds to seedlings in triticale under different methods using 100% infected seeds and controlled temperature of 21 °C and 12 h cycles of light. The treatments were as followed: a) seeding in sterilized soil; b) moist but not flooded seeding in sterilized soil; c) seeding in water-agar media; d) seeding in filter paper. The treatments were arranged in a randomized block design with four replications. Transmission of P. grisea from seeds to seedlings was found in all methods with two types of symptoms: death of seedlings and symptoms on leaves with no death. The rate of transmission of these symptoms was similar in all methods, suggesting that any of these methods could be used. Healthy seedlings with no visible blast symptoms emerged from infected seeds in all methods.

Efficiency of alternative treatments in the control of Pyricularia grisea in wheat seeds.

The present study aimed to examine alternative methods of control of Pyricularia grisea in wheat seeds, one primary source of blast disease. The treatments sodium hypochlorite (2%; pH11,5; 50C; 10min) and hot water (55oC/5min) were selected after preliminary trials that examined the effect on germination of several reagents, at different concentrations, temperatures and period of submersion. Their efficiency in controlling P. grisea in wheat seeds and its transmission to seedlings was studied in seed lots of 400 in four replications in a randomized block design. The fungal incidence was analyzed through blotter test employing 22oC and photoperiod of 12 h from the second to fourth day, seed germination at the seventh day through visual emergence of germ tube and transmission to seedlings at the seventh and 14th days through identification of P. grisea conidia from necrotic lesions of any aerial tissues. The present data revealed that sodium hypochlorite (pH 11.5/50oC/10min) was effective in controlling P. grisea in wheat seeds because it decreased the initial incidence from 57.7% to 2.25% but with deleterious effect on germination. This treatment reduced the fungal transmission to seedlings from 39.7 to 0.5%.

Análise da segregação de avirulência de Magnaporthe grisea do trigo

A segregacao de avirulencia entre progenies de cruzamento entre isolados de Magnaporthe grisea provenientes de trigo (Triticum aestivum) foi estudada utilizando cinco variedades de trigo. A populacao segregante desse estudo foi formada por 37 progenies resultantes do cruzamento entre dois isolados de campo que diferiram na reacao de avirulencia/virulencia a essas variedades. Os resultados obtidos mostraram que para as variedades CNT 8, BR 17 e OR 1 a relacao avirulencia/virulencia foi de 1:1, demonstrando segregacao de um gene de avirulencia, que foi diferente para cada uma das variedades. A segregacao observada para as variedades BR 31 e Iapar 3 foi de 1:3 avirulencia/virulencia indicando segregacao de um gene de avirulencia e do supressor desse gene de avirulencia. Alem disso, a recombinacao sexual entre isolados de M. grisea em condicoes de laboratorio possibilitou produzir isolados virulentos a todas as variedades podendo ser uma das causas para a quebra de resistencia de variedades resistentes.

Incidência de Leifsonia xyli subsp. xyli em variedades de cana-de-açúcar a serem empregados para multiplicação no estado de São Paulo

The ratoon stunting disease (RSD), caused by Leifsonia xyli subsp xyli (Lxx), is one of the most important sugarcane diseases because of damage it inflicts to yield and its presence in all growing regions of the country. Another fact that makes it important to sugarcane crop is the difficulty of its identification in the field based on external symptoms. Moreover, systemic contaminated stalks and cutting materials are the main source of disease dissemination. The Laboratorio de Genetica Molecular (LAGEM) of UFSCar performs routine diagnostic test for RSD. The objective of the present work was to examine the incidence of Lxx from samples received by the LAGEM between 2005 and 2007. The results showed that RB867515 was the most analyzed variety in every year and that 24 out of 98 varieties showed positive infection for Lxx with percentage varying from 0.4 to 38.9%.

Diversidade da virulência de Pyricularia grisea num local de melhoramento genético de arroz

The objective of this investigation was to examine the virulence diversity of Pyricularia grisea isolates collected from the Experimental Station of IAC, Mococa in the state of Sao Paulo. The composition of races and their compatibility with known resistance genes were studied using the Japanese rice (Oryza sativa) differentials. Fifty single spore isolates were obtained from diseased panicles of rice cultivars IAC 201 and IAC 4440. Two races affecting upland rice cultivar IAC 201, JP 137 and JP 177, and one race (JP 200) affecting the lowland rice cultivar IAC 4440 were identified. The results showed low frequency of physiologic races in this breeding site. While all 25 isolates from IAC 4440 were compatible to one resistance gene, pi-ta2, the isolates from IAC 201 were compatible to seven out of nine known resistance genes in the Japanese rice differentials. Furthermore only one resistance gene (pi-zt) was effective to all isolates of P. grisae collected from rice cultivars IAC 201 and IAC 4440.

Métodos de detecção de Leifsonia xyli subsp. xyli e efeito da termoterapia na brotação das gemas de diferentes variedades de cana-de-açúcar

Ratoon stunting disease [Leifsonia xyli subsp xyli (Lxx)] is one of the main diseases of sugarcane and it is of difficult detection in the field. Its spread to uninfected plants and into new areas occurs exclusively through contaminated planting material or mechanically. Thermotherapy at a 52oC/30 min regime is broadly employed in Brazil for producing healthy seed cane. Another recommended regime (50oC/2h) has not been commonly used in Brazil. The purposes of this research were to examine the efficacy of different methods of detection of Lxx in 4-9 months-old plants in cane varieties having different periods of maturity and the effect of thermotherapy (50oC/2h) on bud germination including a consideration on the location of individual buds in the stalks. Microscopy was the best method allowing the detection of Lxx in plants of all ages whereas identification of Lxx in infected plants through dot blot and PCR methods, performed according to published protocols, failed for all treatments. A modification of the dot blot test involving the use of concentrated cane sap was successful in improving the method, allowing the identification of Lxx in infected nine-month old plants. Thermotherapy at a regime of 50oC/2h did not completely eradicate Lxx from infected planting material. This regime was harmful for the germination of buds in var. RB935744 but not for vars RB855156 and RB867515. It increased the percentage of germination of basal buds of RB867515 and decreased that of apical and mid length buds of RB935744.