RESUMEN
As the world population grows, there is a pressing need to improve productivity from water use in irrigated and rain-fed agriculture. Foliar diseases have been reported to decrease crop water-use efficiency (WUE) substantially, yet the effects of plant pathogens are seldom considered when methods to improve WUE are debated. We review the effects of foliar pathogens on plant water relations and the consequences for WUE. The effects reported vary between host and pathogen species and between host genotypes. Some general patterns emerge however. Higher fungi and oomycetes cause physical disruption to the cuticle and stomata, and also cause impairment of stomatal closing in the dark. Higher fungi and viruses are associated with impairment of stomatal opening in the light. A number of toxins produced by bacteria and higher fungi have been identified that impair stomatal function. Deleterious effects are not limited to compatible plant-pathogen interactions. Resistant and non-host interactions have been shown to result in stomatal impairment in light and dark conditions. Mitigation of these effects through selection of favourable resistance responses could be an important breeding target in the future. The challenges for researchers are to understand how the effects reported from work under controlled conditions translate to crops in the field, and to elucidate underlying mechanisms.
Asunto(s)
Productos Agrícolas/microbiología , Productos Agrícolas/fisiología , Enfermedades de las Plantas/microbiología , Hojas de la Planta/microbiología , Agua/metabolismo , Agricultura , Productos Agrícolas/efectos de la radiación , Interacciones Huésped-Patógeno , Luz , Fotosíntesis , Inmunidad de la Planta , Hojas de la Planta/fisiología , Hojas de la Planta/efectos de la radiación , Estomas de Plantas/microbiología , Estomas de Plantas/fisiología , Estomas de Plantas/efectos de la radiación , Transpiración de PlantasRESUMEN
BACKGROUND: A new fungicide resistance risk assessment method is described, based on traits (of pathogens, fungicides and agronomic systems) that are associated with rapid or slow occurrence of resistance. Candidate traits tested for their predictive value were those for which there was a mechanistic rationale that they could be determinants of the rate of resistance evolution. RESULTS: A dataset of 61 European cases of resistance against single-site-acting fungicides was assembled. For each case, the number of years from product introduction to first detection of resistance (the FDR time) was quantified - varying from 2 to 24 years. Short and long predicted FDR times represent high and low resistance risk respectively. Regression analysis identified traits that were statistically associated with FDR time. A model combining these traits explained 61% of the variation in FDR time. Validation showed that this predictive power was highly unlikely to have occurred by chance. CONCLUSION: Unlike previous methods, trait-based risk assessment can be used to assess resistance risk for fungicides with new modes of action, when there is no prior knowledge of resistance behaviour. Risk predictions using the new method provide a more reliable basis for resistance management decisions. © 2014 Society of Chemical Industry.
Asunto(s)
Agricultura/métodos , Evolución Biológica , Farmacorresistencia Fúngica , Hongos/efectos de los fármacos , Fungicidas Industriales/farmacología , Modelos Biológicos , Medición de RiesgoRESUMEN
BACKGROUND: In the European Union, assessments of resistance risk are required by the regulatory authorities for each fungicide product and are used to guide the extent of anti-resistance strategies. This paper reports an evaluation of a widely used 'risk matrix', to determine its predictive value. Sixty-seven unique cases of fungicide resistance in Europe were identified for testing the risk assessment scheme, where each case was the first occurrence of resistance in a pathogen species against a fungicide group. RESULTS: In most cases, high-, moderate- and low-risk categories for fungicide, pathogen and agronomic systems were each associated with significant differences in the number of years from fungicide introduction to the first detection of resistance (FDR time). The combined risk, calculated by multiplying the individual risk factors using the risk matrix, had useful predictive power (72.8% of FDR time variance accounted for; VAF) for all fungicides, but only limited predictive power (25.8% VAF) for single-site acting fungicides (the predominant type). CONCLUSION: The resistance risk matrix has significant, but limited, predictive value. New fungicide modes of action, or pathogens that have become newly prevalent, cannot be assigned to risk categories until new methods of resistance risk assessment are developed.
Asunto(s)
Farmacorresistencia Fúngica , Fungicidas Industriales/farmacología , Productos Agrícolas , Unión Europea , Hongos , Enfermedades de las Plantas/microbiología , Medición de Riesgo/métodosRESUMEN
Rhizomania is a soil-borne disease that occurs throughout the major sugar beet growing regions of the world, causing severe yield losses in the absence of effective control measures. It is caused by Beet necrotic yellow vein virus (BNYVV), which is transmitted by the obligate root-infecting parasite Polymyxa betae. BNYVV has a multipartite RNA genome with all natural isolates containing four RNA species, although some isolates have a fifth RNA. The larger RNA1 and RNA2 contain the housekeeping genes of the virus and are always required for infection, whereas the smaller RNAs are involved in pathogenicity and vector transmission. RNA5-containing isolates are restricted to Asia and some parts of Europe, and these isolates tend to be more aggressive. With no acceptable pesticides available to restrict the vector, the control of rhizomania is now achieved almost exclusively through the use of resistant cultivars. A single dominant resistance gene, Rz1, has been used to manage the disease worldwide in recent years, although this gene confers only partial resistance. More recently, new variants of BNYVV have evolved (both with and without RNA5) that are able to cause significant yield penalties on resistant cultivars. These isolates are not yet widespread, but their appearance has resulted in accelerated searches for new sources of resistance to both the virus and the vector. Combined virus and vector resistance, achieved either by conventional or transgenic breeding, offers the sugar beet industry a new approach in its continuing struggle against rhizomania.