Eficiência de tratamentos alternativos no controle de Pyricularia grisea em sementes de trigo

Abstract

RESUMOO presente trabalho objetivou estudar métodos alternativos de controle de Pyricularia grisea, em sementes de trigo, uma das principais fontes de inóculo da brusone. Após ensaios preliminares para avaliação do efeito dos produtos, em diferentes concentrações, tempos e temperaturas de imersão sobre a germinação das sementes, os tratamentos hipoclorito de sódio (2%; pH 11,5; 50°C; 10 min) e (2%; pH 11,5; 50°C; 10 min) e água quente (55°C/5min) foram selecionados para estudar sua eficiência no controle de P. grisea e transmissão do patógeno para plântula. O delineamento estatístico constou de 400 sementes em 4 repetições em blocos ao acaso. A incidência do fungo foi examinada do 2º. ao 4º. dia através do "blotter test" a 22ºC com fotoperíodo de 12h, a germinação das sementes foi avaliada aos 7 dias através da observação visual da emissão do tubo germinativo e a transmissão aos 7 e 14 dias pela identificação de conídios de P. grisea das lesões necróticas que surgiram em qualquer tecido da parte aérea. Dados do presente estudo revelaram que o tratamento hipoclorito de sódio (pH 11,5/50ºC/ 10min) foi eficiente no controle de P. grisea em sementes de trigo pois reduziu a incidência inicial de 57,7% para 2,25%, mas reduzindo significativamente a germinação para 46%. O tratamento hipoclorito de sódio reduziu a transmissão do patógeno para plântulas de 39,7 para 0,5%. Palavras-chave: Magnaporthe grisea, Triticum aestivum, brusone, controle alternativo, sementes ABSTRACT Efficiency of alternative treatments in the control of Pyricularia grisea in wheat seedsThe 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 (55°C/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 14 th 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%.

Damage of wheat blast on the productivity and quality of seeds as a function of the initial inoculum in the field

“…According to Machado (1994), lots with incidences of P. oryzae above 10% for certified wheat seeds should not be commercialized, which would "condemn" some genotypes studied here, considering the majority of the inoculum doses of the present study. Silva et al (2009) state that in cases of high incidences (these had a 26.7% incidence rate), lots of wheat should be used as grains, being commercialized to Journal of Seed Science, v.39, n.1, p.066-074, 2017 mills, and not as seeds.…”

“…Control measures for blast are still unsatisfactory, which characterizes it as difficult to control (Cruz et al, 2010;Rocha et al, 2014;Coelho et al, 2016). The use of resistance sources constitutes an important alternative, as a function of the low efficiency of the currently used fungicides (Cruz et Journal of Seed Science, v.39, n.1, p.066-074, 2017 Silva et al, 2015).…”

“…Infected wheat seeds may not have symptoms and they may constitute a source of primary inoculum of the disease in the field, generating epidemics by providing initial inoculum to new areas (Coelho et al, 2016), including for the fields of seed production, with serious consequences. Seed planting with P. oryzae was the probable cause for the dissemination of the fungus in wheat from Paraná to Mato Grosso do Sul (Urashima et al, 2007;Silva et al, 2009); and in triticale from Paraná to São Paulo (Medina et al, 2009). Furthermore, with regard to seed quality, the presence of the pathogen may be related to the low germination and low vigor.…”

Rapid emergence of pathogens in agro-ecosystems: global threats to agricultural sustainability and food security

“…The wheat blast disease caused by P. graminis-tritici was first reported in Brazil in 1985 [35] and has since spread across the wheat-growing region of Brazil and into the neighbouring countries of Bolivia, Paraguay and Argentina, causing crop losses of up to 40-100% [36][37][38][39]. Wheat blast is now considered a major quarantine disease and a threat to wheat crops in the USA [40,41] and other wheat-growing regions.…”

Resistance to QoI Fungicides Is Widespread in Brazilian Populations of the Wheat Blast Pathogen Magnaporthe oryzae

“…Wheat blast was first detected in the 1980s in Paraná State (23) and has since spread to wheat-growing regions across central and southern Brazil (1,37) as well as to wheat fields in Bolivia, Argentina, and Paraguay (11) but has not been reported outside of South America (12). The major mechanisms of disease spread over short and long distances are airborne inoculum (42) and movement of infected seed (18).…”