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Cultivar Mixtures

How many cultivars make a good mixture?

The number of cultivars in the mixture can influence the disease control benefit achieved from it. Mundt (1994) showed that increasing the number of cultivars up to 5 gave a trend towards decreasing the severity of stripe rust on wheat (see table), but with potentially diminishing returns beyond 3 or 4 cultivar components. Newton et al. (1997), as shown in the figure below, obtained similar results in the control of scald on winter barley.

Percent reduction of stripe rust severity (relative to mean of component cultivars in pure stand) for wheat cultivar mixtures tested in field plots at three locations (from Mundt, 1994).
Components in mixture	Number of mixtures	Mean^a
2	10	31
3	10	42
4	5	49
5	1	48
Mean of all mixtures		39
^a Mean over three locations and 3-4 replications per location.

Change in scald severity in mixtures of winter barley cultivars compared as influenced by the number of component cultivars (adapted from Newton et al., 1997). Click image for an enlarged view.

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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