Two‐component cultivar mixtures reduce rice blast epidemics in an upland agrosystem

Abstract

The effect of two-component rice cultivar mixtures on the control of rice blast disease was studied in three different experiments under rainfed upland conditions in the Madagascar Highlands. The mixtures involved a susceptible cultivar (either susceptible or very susceptible) and a resistant cultivar in different mixture arrangements (random or row mixtures) and with different proportions of the susceptible cultivar (50, 20 and 16AE7%), which were compared to the susceptible cultivar grown in a pure stand. The effect of these mixtures on the incidence and severity of leaf and panicle blast was measured weekly, and on yield and yield components at harvest time. The mixture effect was more efficient in reducing disease with a proportion of 16AE7% susceptible component than with a proportion of 50%. Blast epidemic was significantly reduced in all three experiments. However, under high blast pressure, there was no reduction in the disease by the end of the epidemic and yields of the susceptible cultivar were almost zero whatever the mixture. In two other experiments performed under lower blast pressure, disease incidence and severity were significantly lower in mixtures, and yields of the susceptible cultivars grown in mixtures were higher than those of their respective pure stands. Cultivar mixtures are a promising strategy that could contribute to a more sustainable cultivation of rice under upland conditions in the context of subsistence agriculture in Madagascar, where all cropping operations are manual.

Eight principles of integrated pest management

“…These include the use of mixed cultivars, composite cross-populations (i.e., crop populations obtained by continuously exposing a population rather than individual plants to natural selection), intercropping (i.e., the spatial association of two or more crop species), living mulches, or semi-natural vegetation. Significant disease reduction was obtained by interspacing a rice cultivar susceptible to Magnaporthe oryzae-causing rice blast-with a resistant one (Zhu et al 2000;Raboin et al 2012). Sapoukhina et al (2013) used modeling techniques to demonstrate that mixing wheat cultivars using small proportions of highly resistant ones could more effectively reduce disease severity against multiple diseases while exerting low selective pressure on pathogens.…”

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

“…Esta observação é reforçada quando analisadas as misturas com até 33% da população de indivíduos suscetíveis, nas quais a severidade e incidência das doenças da folha e espiga foram estatisticamente iguais às observadas na cultivar resistente. Esses efeitos na intensidade de doenças também foram reportados em outros estudos de misturas de cultivares no manejo de doenças do trigo (Mundt et al, 1995;Zhou et al, 2014), arroz (Zhu et al, 2000;Raboin et al, 2012) e da batata (Pilet et al, 2006). No caso da requeima da batata, o efeito da mistura de cultivares na área abaixo da curva de progresso da doença foi maior quando associada com aplicações quinzenais ou semanais de fungicidas (Pilet et al, 2006).…”

“…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).…”

Ecological Interactions Within the Biodiversity of Cultivated Systems

“…The combination of these mechanisms helps slow the emergence of pathogenic strains that can circumvent this resistance, as was demonstrated in the case of specific polycyclic leaf diseases like rust or mildew in cereals (Wolfe 1985;Finckh et al 2000;Mundt 2002). This strategy's effectiveness is increased if such resistance is deployed over a large area and over time, as was demonstrated in the case of mildew on spring barley in Eastern and Northern Europe, for septoria and brown rust in winter wheat in France (Mille and de Valavieille-Pope 2001), and for blast on rice in China (Zhu et al 2000) and Madagascar (Raboin et al 2012). This approach, it must be admitted, has been less successful and less convincing in the case of insect pests (Tooker and Frank 2012).…”

“…This type of intervention has been particularly encouraging and fruitful in the case of pathogens, such as those responsible for rust and powdery mildew on wheat or blast on rice (Castilla et al 2003;Cox et al 2004;Finckh et al 2000;Mundt 2002;Zhu et al 2000;de Vallavieille-Pope 2004;Raboin et al 2012).…”