Induced-Resistance Agents, Silicon Fertilizers, Synthetic Fungicides

Summary: Induced-resistance agents, silicon fertilizers and both together do less well than, as well as and better than synthetic fungicides such as penconazole.

apple (Malus spp.) with symptoms of apple scab disease caused by Venturia inaequalis: University of Georgia Plant Pathology, University of Georgia, Bugwood.org, CC BY 2.0, via Forestry Images

Field trials applied apple and pear scab-controlling silicon (Si) fertilizers, induced-resistance (IR) agents and their combination comparatively to conventional synthetic fungicides, according to an article in Arboriculture & Urban Forestry September 2018.

Field trials by Glynn C. Percival of R.A. Bartlett Tree Research Laboratory broached apple and pear scab because of reduced aesthetics, fruit quality and marketable yields. They commenced with scab fungal symptoms of olive-green spots on leaves or petioles initially and of premature, yellowed leaf drop and deformed, immature fruit drop subsequently. The article Evaluation of Silicon Fertilizers and a Resistance Inducing Agent for Control of Apple and Pear Scab under Field Conditions describes alternatives to synthetic fungicides.

Silicon fertilizers emphasize drought, heavy metal toxicity, lodging and salt resistance; growth; soil penetration by roots; soil-borne and foliar fungal pathogen control; transpiration reduction; and yield.

Induced resistance by fungi-attenuating or weakening biological agents and inorganic potassium and phosphate salt, low-molecular-weight protein and unsaturated fatty acid chemical agents fortify plant defense mechanisms.

The two-year fertilizer- and water-free field trial sites got deltamethrin insecticide treatments every two months from May 2014 to September 2015 and glyphosate weed control treatments. Malus apple and Pyrus communis trial sites had induced-resistance and silicon treatments at bud break, green cluster, 90 percent petal fall and early fruitlet growth stages. Induced-resistance and silicon-nutrition treatments involved 60 observations each of one IR compound, one fungicide and four silicon fertilizers sprayed four times in 10 randomized complete blocks.

Measurements of leaf chlorophyll from comparable-aged leaves at midpoints near their main veins juxtaposed two fully expanded, mature leaves each from crown tops, centers and bases.

The 0.75-hectare (1.85-acre) apple and 0.90-hectare (2.22-acre) peach sites kept aesthetic, defoliated, discolored and yellowed leaf and lesion and percent infected surface fruit scab severity ratings.

Scab outbreaks led to Golden Delicious' respective 4.8 and 5.0 severity ratings Sept. 28, 2014, and Sept. 28, 2015, and to Williams' 3.4 rating both times. Fruit yield and leaf chlorophyll content measure penconazole synthetic fungicide and polyether-modified trisiloxane and salicyladehde as efficacious scab-protectant compounds that minimize fruit and leaf scab severity. The IR agent salicylaldehyde and the Fossil, Rigel, Sil-MATRIX and Sirius silicon fertilizers respectively netted lowest scab-protective compound and highest fruit and leaf silicon content ratings.

Lawrence Datnoff in Baton Rouge, Louisiana, and Renata Resende in Minas Gerais, Brazil, observed silicon nutrition-obtained fungal-resistant barley, corn, grape, peach, rice, rye, strawberry and wheat.

Tsuyoshi Hayasaka in Tsuruoka, Japan, and Sang Gyu Kim in Suwon, South Korea, propose scab-resistant mechanical or physical barriers that cell walls promote through silicon nutrition.

Yanchun Liang and Wanchun Sun in Beijing, China, and Fabríco Á. Rodrigues in Minas Gerais, Brazil, queue up pathogen-resistant silicon-induced lignin, peroxidase, phenolic-compound and phytoalexin accumulation. Development of triazole-insensitive strains results in alternative scab management treatments that replace anti-fungal scab-resistant penconazole schedules at bud break, green cluster, petal fall and early fruitlet. Phenol-based salicylic acid compound and derivative-composed silicon fertilizers and IR agents synthesize bacteria-, fungus-, virus-resistant anti-digestive, anti-microbial, anti-nutritive toxins scarcely toxic to aquatic invertebrates and mammals.

Induced-resistance agents teamed with silicon fertilizers turn alkaloid, phenolic and terpenoid synthesis and cell wall silification into ecosystem-safe, synthetic-competitive fungal pathogen control and low ecosystem toxicity.

pear (Pyrus spp.) fruit with symptoms of pear scab disease caused by Venturia pirina: Howard F. Schwartz, Colorado State University, Bugwood.org, CC BY 3.0, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

apple (Malus spp.) with symptoms of apple scab disease caused by Venturia inaequalis: University of Georgia Plant Pathology, University of Georgia, Bugwood.org, CC BY 2.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1496022

pear (Pyrus spp.) fruit with symptoms of pear scab disease caused by Venturia pirina: Howard F. Schwartz, Colorado State University, Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=5358918

For further information:

Datnoff, L.E.; F.Á. Rodrigues; and K.W. Seebold. 2007. "Silicon and Plant Disease." Pp. 233-246. In: L.E. Datnoff, W.H. Elmer and D.M. Huber, eds., Mineral Nutrition and Plant Disease. St. Paul MN: The American Phytopathological Society.

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayasaka, T.; H. Fujii; and K. Ishiguro. 2008. "The Role of Silicon in Preventing Appressorial Penetration by the Rice Blast Fungus." Phytopathology 98: 1038-1044.

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