Evaluation of SDHI Fungicides and Host Plant Defense Inducers for the Management of Plant Pathogens in Two Different Cropping Systems

Abstract

Los SDHI y los inductores de defensa de las plantas son alternativas importantes para el manejo de fitopatógenos. Se realizó una evaluación de estas moléculas para Colletotrichum spp. y Erwinia amylovora en manzana y para Calonectria pseudonaviculata (Cps) en boj. Se calculó la DE50 y la sensibilidad de los aislamientos para C. fructicola y C. fioriniae con benzovindiflupyr y penthiopyrad. Además, se observaron correlaciones positivas significativas entre ellos. Así también, se identificaron y caracterizaron genes de SDH para C.fructicola Se calcularon los valores de DE50 de aislados de Cps recolectados dentro y fuera de Carolina del Norte (NC) para cuatro SDHI. Se encontraron correlaciones positivas entre benzovindiflupyr y fluxapyroxad, benzovindiflupyr y penthiopyrad, y penthiopyrad y fluxapyroxad en aislamientos recolectados de NC. En boj, las aplicaciones al suelo de acibenzolar-S-metil mostraron una disminución de la enfermedad. En la manzana, la incidencia del tizón de las flores se redujo con los programas de aspersión de inductores de defensa. La expresión génica de PR-2 y -8 de tejido de hoja de manzano tratado con acibenzolar-S-metil y extracto de Reynoutria sachalinensis aumentó al primer y siete días después de aplicados. Además, Bacillus mycoides aumentó la expresión de PR-1 en uno y siete días.

Succinate dehydrogenase inhibitor (SDHI) fungicides and host plant defense inducers are important alternatives for the management of plant pathogens. SDHIs are single-site fungicides that block the production of energy in fungi by disrupting the electron transport chain in aerobic organisms. Another important fungicide group is the host plant defense inducers whose molecules inhibit or slow the development of pathogens by enhancing the defense system of plants. Several new SDHIs and host plant defense inducers are now available on the market, making them promising tools to be included in the integrated management of new pathosystems. However, an improved understanding of their efficacy and mechanisms need to be studied. Evaluation of these molecules in four pathosystems and two different cropping systems was conducted. In apple, Glomerella leaf spot and bitter rot caused by Colletotrichum spp. and fire blight caused by Erwinia amylovora were evaluated. In boxwood, boxwood blight caused by Calonectria pseudonaviculata was studied. These diseases are causing devastating economic losses in the southeastern US. Nowadays, management of these diseases can be challenging due to resistance and restriction applications. It is necessary to look for more alternatives to be implemented in the integrated pest management of these cropping systems. Therefore, the objectives of this research were to 1) evaluate the effect of four SDHI fungicides for C. fioriniae and C. fructicola by mycelium-growth assay and characterization of sdh genes for C. fructicola, 2) evaluate the effect of four SDHI fungicides for C. pseudonaviculata by mycelium-growth assay, and 3) analyze the effect of host plant defense inducers against boxwood blight and fire blight. Also, evaluate PR gene expression in apple tissue after application of host plant inducers.