Cultivar Mixtures for the Simultaneous Management of Multiple Diseases: Tan Spot and Leaf Rust of Wheat

Abstract

Because of differences in life histories between Puccinia triticina, a highly specialized, polycyclic, windborne pathogen with a shallow dispersal gradient, and Pyrenophora tritici-repentis, a residue-borne pathogen with a steep dispersal gradient, wheat mixtures are expected to be more effective at controlling leaf rust than tan spot. The objectives of this research were to determine the effect of two-cultivar mixtures with varying proportions and different pathogen resistance profiles on the severity of tan spot and leaf rust, to evaluate yield of the mixtures in the presence or absence of disease, and to directly compare the relative effectiveness of cultivar mixing for tan spot versus leaf rust. In a field experiment at two sites in Kansas over two growing seasons, winter wheat cvs. Jagger and 2145, which have differential resistance reactions to leaf rust and tan spot, each were planted in proportions of 0.25, 0.50, 0.75, and 1.00. Plots were inoculated with each pathogen alone, both pathogens, treated with a fungicide, or exposed to ambient conditions. For both diseases for all siteyears, severity decreased substantially on the susceptible cultivar as the proportion of that cultivar decreased in mixture. Mixtures were significantly more effective at reducing leaf rust than tan spot in three of four site-years. Mixtures generally yielded the same as the weighted mean of components in monoculture although, in two of three site-years, at least one fungicide-treated and one diseased mixture each yielded higher than expected values. Although this particular mixture produced only modest yield benefits, the potential for simultaneous reductions in tan spot and leaf rust was demonstrated.

Wheat Variety Selection to Maximize Returns and Minimize Risk: An Application of Portfolio Theory

“…Wheat mixtures are also commonly grown in the Pacific Northwest (Mundt, 2002). Cox et al (2004) provided evidence that cultivar mixtures can increase yield and reduce yield variability.…”

Mistura de cultivares de dois componentes no manejo de múltiplas doenças do trigo

“…Para a ferrugem da folha, em que há resistência genética completa na cultivar Fundacep horizonte, o efeito das misturas foi mais pronunciado do que para as doenças onde a variação na suscetibilidade é devido à resistência parcial, como para mancha amarela e giberela. Cox et al (2004) também observaram maior efeito da mistura de variedades na redução da severidade da ferrugem da folha do que para a mancha amarela. Segundo os autores, esse efeito deve estar relacionado com as características de cada doença como o número de ciclos secundários, a forma de dispersão do patógeno e o nível de especificidade ao hospedeiro.…”

“…A estratégia consiste essencialmente na mistura de cultivares que variam em muitas características incluindo resistência a doenças, mas que têm similaridade suficiente para serem cultivadas juntas (Wolfe, 1985). O manejo de doenças com mistura de cultivares foi reportada como eficiente para diversas doenças como a brusone do arroz (Raboin et al, 2012), oídio da cevada (Finckh et al, 1999), mancha amarela e ferrugem da folha do trigo (Cox et al, 2004), antracnose do feijoeiro (Ntahimpera et al, 1996).…”

Genetic Vulnerability of Modern Crop Cultivars: Causes, Mechanism and Remedies

“…mixtures of several similar pure lines having different genes for disease and insect pest resistance, in self-pollinated crops, may be expected to tolerate diseases and insect pests attacks better than their pure components (Marshal, 1977;Rajaram and Dubin, 1977;Trenbath, 1977;Simmonds, 1979;Zadoks and Schein, 1979;Welish, 1981). Mixtures with appropriate resistance genes could also help to reduce severities of multiple pathogens (Cox et al, 2004).…”