A conceptual model for the development of Phytophthora disease in Quercus robur

Here, a conceptual model is presented for the development of Phytophthora disease in pedunculate oak. The model is presented using the causal loop diagram tool and gives an overview of how various abiotic and biotic factors, such as soil moisture, nutrient availability and mycorrhizal colonization, may affect the reproduction and the infective capacity of soil-borne Phytophthora species, the susceptibility of the host and subsequent disease development. It is suggested that the link between the root damage caused by Phytophthora species and overall tree vitality is in the assimilation and allocation of carbon within the plants. The potential impact of environmental factors on these processes is discussed. The model is presented with reference to scenarios related to variation in soil moisture and nutrient availability. The need for species-specific validation of the model and the implications of the model are discussed

Genetics and Genomics of Carrot Biotic Stress

International audienceCarrot (Daucus carota ssp. sativus) production can be affected by a wide range of pests and pathogens. At least five diseases of carrot are caused by bacterial pathogens, 36 by fungal and oomycete pathogens, two by phytoplasmas, and 13 by viruses; and seven genera of nematodes and two genera of parasitic plants affect carrot. In addition, numerous insect and mite pests can cause losses. There have been extensive efforts to select carrot cultivars with partial or complete resistance to many of these pathogens and pests, and to identify wild species with resistance to specific biotic stresses for introgression into breeding populations and commercial cultivars. For some pathogens and pests, significant advances have been made at identifying resistance and mapping that resistance to the carrot genome. For others, resistance has been identified, but the genetic basis is yet to be determined. For a majority of these diverse stresses, however, there has been little success at identifying highly effective resistance and understanding the genetic basis of resistance. The diversity of stresses as well as interactions among these pests and pathogens can complicate efforts to develop cultivars with resistance to all key biotic stresses in a region that also meet market and consumer expectations. New approaches to identifying resistant material and speeding traditional breeding are being developed with molecular breeding tools, including simple sequence repeat markers and deep-coverage libraries of the carrot genome. These valuable genomic resources will enhance efforts to identify and breed for resistance to carrot pests and pathogens