Cereal variety and species mixtures in practice, with emphasis on disease resistance Maria Finckh, Edward Gacek, Henriette Goyeau, Christian Lannou, Ueli Merz, Christopher Mundt, Lisa Munk, Jadwiga Nadziak, Adrian Newton, Claude de Vallavieille-Pope, et al. To cite this version: Maria Finckh, Edward Gacek, Henriette Goyeau, Christian Lannou, Ueli Merz, et al.. Cereal variety and species mixtures in practice, with emphasis on disease resistance. Agronomie, EDP Sciences, 2000, 20 (7), pp.813-837. 10.1051/agro:2000177. hal-00886081 HAL Id: hal-00886081 https://hal.archives-ouvertes.fr/hal-00886081 Submitted on 1 Jan 2000 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Agronomie 20 (2000) 813–837 813 © INRA, EDP Sciences 2000 Original article Cereal variety and species mixtures in practice, with emphasis on disease resistance Maria R. FINCKHa*, Edward S. GACEKb, Henriette GOYEAUc, Christian LANNOUc, Ueli MERZd, Christopher C. MUNDTe, Lisa MUNKf, Jadwiga NADZIAKg, Adrian C. NEWTONh, Claude de VALLAVIEILLE-POPEc, Martin S. WOLFEi a Dept. of Ecol. Plant Protection, University of Kassel, Nordbahnhofstr. 1a, 37213 Witzenhausen, Germany b National Office for Cultivar Testing, 63022 Slupia Wielka, Poland c Laboratoire de Pathologie Végétale, BP 01, 78850 Thiverval-Grignon, France d Institute of Plant Sciences, Swiss Federal Institute of Technology, Universitästsstr. 2, 8092 Zürich, Switzerland e Dept. Botany and Plant Pathology, Cordley 2082, Oregon State University, Corvallis, OR 97331-2902, USA f Dept. of Plant Biology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark g Exptl. Plant Breeding Station IHAR, 46233 Bakow, Poland h Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK i Wakelyns Agroforestry, Fressingfield, Eye, IP21 5SD, UK (Received 3 March 2000; revised 22 May 2000; accepted 3 August 2000) Abstract – Variety mixtures can provide functional diversity that limits pathogen and pest expansion, and that makes use of knowledge about interactions between hosts and their pests and pathogens to direct pathogen evolution. Indeed, one of the most powerful ways both to reduce the risk of resistance break-down and to still make use of defeated resis- tance genes is to use cereal variety and species mixtures. The most important mechanisms reducing disease in variety and species mixtures are barrier and frequency effects, and induced resistance. Differential adaptation, i.e. adaptation within races to specific host genotypic backgrounds, may prevent the rapid evolution of complex pathotypes in mix- tures. Mixtures generally stabilise yields and yield losses due to disease; abiotic stresses are also better buffered than in pure stands. When mixture components are carefully put together, product quality can be enhanced or at least equal that of the pure stands. Mixture use in practice worldwide is reviewed. functional diversity / induced resistance / differential adaptation / yield stability / evolutionary plant breeding Résumé – Les mélanges de variétés et les mélanges interspécifiques de céréales dans la pratique. Les variétés en mélanges, de par leur diversité génétique, limitent le développement des épidémies et des ravageurs. Cette diversité peut être organisée selon notre connaissance des interactions hôte – agent pathogène pour influer sur l’évolution des Communicated by Hanne Østergård (Roskilde, Denmark) * Correspondence and reprints [email protected] Plant Genetics and Breeding 814 M.R. Finckh et al. populations parasites. La culture de variétés en mélange ou de mélanges interspécifiques est une des méthodes les plus efficaces à la fois pour limiter le risque de contournement des résistances, et pour utiliser avec bénéfice des résistances déjà contournées. Les principaux facteurs de réduction de la sévérité des épidémies dans les mélanges sont les effets de barrière, la proportion de plantes sensibles et la résistance induite. L’adaptation d’isolats de même race au fond géné- tique d’un hôte, ou adaptation différentielle, pourrait ralentir la sélection de races complexes dans les mélanges. D’une façon générale, les mélanges stabilisent les rendements. Le risque de pertes de rendement dues aux stress biotiques et abiotiques est plus limité dans un mélange que dans une culture pure. Un choix judicieux des composants du mélange peut permettre d’obtenir une qualité du produit de récolte équivalente ou supérieure à celle d’une culture pure. L’utilisa- tion des mélanges au niveau mondial est discuté. diversité fonctionnelle / résistance induite / adaptation différentielle / stabilité du rendement / amélioration génétique 1. Introduction But the reason(s) for the mixture advantage were not known. From the mid-nineteenth century on, plant Up to the last two hundred years, agricultural breeding, mechanisation and other factors such as systems were based on crop varieties and landraces inorganic fertilisers and pesticides evolved rapidly, that were genetically heterogeneous. Some of the allowing for and leading to a massive concentra- heterogeneity would have been selected conscious- tion on monoculture and all contributing to weed, ly, but much of it would have arisen through natur- pest and disease problems in different ways. al selection or random events. It is impossible now ‘Monoculture’ refers usually to the continuous use to gauge the extent to which the overall hetero- of a single crop species over a large area. However, geneity would have been useful as a buffer against with respect to plant pathogens and pests it is the effects of diseases, pests, weeds and other envi- important to differentiate between monoculture at ronmental variables. Monoculture may have been the level of species, variety or resistance genes common but only at the species level. For example, [29]. For example, within a species there may be the major rotation in European agriculture was many different genotypes with different resistances wheat – barley or oats or beans – fallow. to a specific pest or pathogen and great variation with respect to competitiveness with weeds and During the agricultural revolution of the 17th other crops. Within modern varieties there is usual- and 18th centuries, there were major developments ly little diversity for resistance or morphological that included an increase in diversity among crop traits. species, the introduction and development of clover-based cropping systems, and directed selec- Resistance gene monocultures are more difficult tion and multiplication of superior plant genotypes. to conceptualise. Many different varieties may By the middle of the 19th century, Charles Darwin exist, but with the same resistance (or susceptibili- [23] was able to report: ty) gene(s). For example, in the late 1960’s, virtu- ally all hybrid maize varieties in the southeastern “It has been experimentally proved, that if a plot US possessed the cytoplasmatically inherited of ground be sown with one species of grass, and a Texas male sterility. Unfortunately, this trait is similar plot be sown with several distinct genera of closely linked to susceptibility to certain strains of grasses, a greater number of plants and a greater the pathogen Cochliobolus carbonum (syn. weight of dry herbage can be raised in the latter Helminthosporium maydis). The monoculture for than in the former case. The same has been found susceptibility (even though different varieties had to hold good when one variety and several mixed been planted) led to selection for these strains and varieties of wheat have been sown on equal spaces in 1970 the pathogen caused more than 1 billion of ground.” (=109) $US in losses [90]. Cereal variety and species mixtures 815 As a consequence of the use of large-scale resis- pathogen propagules). In addition, autoinfec- tance gene monocultures, varietal resistance, par- tion (i.e. infection of the same genotype) is ticularly to air-borne plant pathogens, has to be effectively reduced; renewed continuously because of the strong selec- (3) Selection in the host population for more com- tion for pathogen genotypes able to overcome petitive and/or more resistant genotypes can resistance [11, 46, 48, 71, 85, 94]. Routine applica- reduce (or sometimes increase) overall disease tions of synthetic inputs, including multiple fungi- severity; cides, have become necessary in cereal production in Europe and the US. (4) Competitive interactions among host plants may affect plant susceptibility; Starting in the 1920s, some breeders and pathol- ogists maintained and developed the notion that the (5) Pathogens non-virulent on a host genotype may disease problems caused by monoculture could be induce resistance reactions that work against avoided or alleviated by retaining functional diver- virulent races; sity within the cereal crop. This means, the diversi- (6) Interactions among pathogen races (e.g. com- ty that limits pathogen and pest expansion and that petition for available host tissue) may reduce is designed to make use of knowledge about inter- disease severity.