Potassium Influence on Susceptibility of Bermudagrass to Helminthosporium cynodontis Toxin

Abstract

Inadequate K fertilization of bermudagrass, Cynodon dactylon (L.) Pers., can lead to stand loss and increased disease symptoms. This study was conducted to determine the relationship between fungal leaf spot (Helminthosporium cynodontis Marig.) susceptibility and K status of hybrid bermudagrass ‘Grazer’ and ‘Tifton 78’ bermudagrass were grown in washed sand under six K fertilization rates (10, 30, 70, 100, 200, and 400 mg kg−1) in a greenhouse. Plants were clipped three times at 28‐d intervals and the K concentration in the tissue was determined. Prior to the final clipping, 4 mL of culture filtrate containing toxin (CFT) produced by H. cynodontis was sprayed in a fine mist on each plant. Plants were rated for disease severity according to leaf spot coverage after approximately 36 h. A curvilinear relationship was observed between disease severity and tissue K concentration. Leaf spotting increased when tissue K levels decreased below about 25 g/kg. Tifton 78 was more resistant than Grazer to CFT. Tifton 78 maintained higher tissue K levels at all fertilization rates due to lower biomass production and comparable amounts of K removed. Varietal differences should be considered when determining proper K fertilization rates from tissue analysis.

Soil‐Fertility Principles for Warm‐Season Perennial Forages and Sustainable Pasture Production

“…Forage crops require similar amounts of K as N. Low K availability is often associated with stand mortality and increased incidence of pest and diseases (Matocha and Smith, 1980; Richardson and Croughan, 1989). Intensively managed hay production systems require application of K removed in the forage to sustain crop yields.…”

Potassium Influences Forage Bermudagrass Yield and Fungal Leaf Disease Severity in Mississippi

“…Likewise, soil-test K in September 2009 was lower in plots previously fertilized with 9 than 18 Mg litter/ha (30 vs. 38 mg/kg, P < 0.05). These levels of soil K, which are categorized in the very low or low indices based on five southern states that employ the Mehlich-3 extractant (19), strongly suggest rapid annual changes in soil K influenced bermudagrass K nutrition and hence, its susceptibility to fungal diseases (1,15). Indeed, during 2 years of ryegrass-bermudagrass hay production the levels of soil K decreased progressively from approximately 108 mg/kg in September of 2007 to approximately 42 mg/kg in April of 2009 and to 34 mg/kg in September of 2009 ( Fig.…”

“…They reported an inverse, curvilinear relationship between tissue K and disease severity, and a large decrease in severity between 0 and 112 kg K/ha with slight or no decrease in the disease when tissue K levels exceeded approximately 8.0 g/kg. In a similar greenhouse trial, bermudagrass was grown using six K fertilization rates, sprayed with a culture filtrate of B. cynodontis , and evaluated for leaf necrosis caused by a toxin (15). These authors also observed a curvilinear relationship between severity of symptoms and tissue K levels, and they identified a threshold level of K for reduction in symptoms of approximately 25 g/kg, as well as cultivar differences in disease severity at similar levels of tissue K.…”

“…These pathogens were formerly considered to be Helminthosporium spp. (2,9,15,20), and are collectively referred to as dematiaceous hyphomycetes because pigmented asexual spores are produced directly on vegetative mycelium without specialized reproductive structures (3). Dematiaceous hyphomycetous pathogens always occurred in complexes of up to eight species of proven pathogenicity, rather than individually, on bermudagrass at animal waste application sites in Mississippi (11,12).…”

Efeito da idade de corte sobre a produção, composição químico-bromatológica, digestibilidade >i<in vitro>/i< e teor de ácido cianídrico de >i<Cynodon dactylon>/i< (L.) Pers. cv. Florakirk

“…O cálcio aumenta a resistência à doenças provavelmente devido ao seu efeito na composição da parede celular, tomando-a mais resistente à penetração por patógenos (Agrios, 1988 , indicando que a análise de tecido e fertilização potássica adequada podem ser usadas como prevenção para reduzir problemas com doenças em grama bermuda. Matocha & Smith (1980) também observaram, em condições de campo, relação entre a severidade de mancha foliar e o nível de K no tecido de grama bermuda Coastal (C. dacty/on), porém o nível crítico de K no tecido foi 6 g kg-\ inferior ao observado por Richardson & Croughan (1989).…”