Cultivar Mixtures | APSnet Education Center

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Cultivar Mixtures

Crops and diseases suited to cultivar mixtures

The effectiveness of cultivar mixtures has been demonstrated most commonly for foliar diseases of small grains in which host plants are small and for which there is frequent inoculum exchange among host genotypes. The effectiveness of cultivar mixtures in the control of foliar diseases of plants is related to the probability that pathogen propagules will fail to encounter susceptible tissues. Following Garrett and Mundt (1999) there are several inherent characteristics of each specific plant disease that affect this probability:

Size of genotype unit area (click here for more information)

Steepness of dispersal gradient (click here for more information)

Ultimate lesion size (click here for more information)

Pathogen generation time

Degree of host specialization (click here for more information)

Inherent characteristics of plant pathosystems that predict whether or not mixtures of cultivars will provide disease suppression. (from Garrett and Mundt, 1999).
Host	Pathogen	Small host genotype unit area	Shallow dispersal gradient	Small lesion size	Short pathogen generation time	Strong host specialization
Coffee	Hemileia vastatrix	-	+	+	-	+
Pepper	Xanthomonas campestris	-	-	-	+	+
Potato	Phytophthora infestans	-	+	-	+	+
Rice	Magnaporthe oryzae	+	+	+	+	+
Wheat	Blumeria graminis	+	+	+	+	+
Wheat	Puccinia triticina (formerly P. recondita)	+	+	+	-	+
Wheat	Puccinia striiformis	+	+	-	-	+
Wheat	Mycosphaerell graminicola	+	-	-	-	-
Wheat	Rhizoctonia cerealis	+	-	-	-	-
+ Characteristic favors disease suppression by cultivar mixtures - Characteristic does not favor disease suppression by cultivar mixtures.

	Uredinia of Hemileia vastatrix, causal agent of coffee rust. (Used by permission from J.R. Baker) Click image to enlarge.
	White sporangia and sporangiophores of Phytophthora infestans, causal agent of late blight, at the margins of necrotic potato leaf lesions. (Courtesy R.V. James) Click image to enlarge.
	Mature rice blast lesions showing necrotic borders caused by Magnaporthe grisea. (Courtesy J.M. Bonman) Click image to enlarge.

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Contents

Introduction

What is a cultivar mixture?

Mechanisms by which cultivar mixtures suppress disease

Effect of cultivar mixtures on epidemic development

Effect of Cultivar mixtures on the evolution of pathogen races or pathotypes

Crops and diseases suited to cultivar mixtures

Use of cultivar mixtures to manage multiple diseases

How many cultivars make a good mixture?

Reported successes with cultivar mixtures

Agronomic considerations

References