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Previous studies of European populations of the blast fungus ( Magnaporthe oryzae) have shown the existence of five clonal lineages. Three of them were common to different countries, whereas one was specific to Hungary and another was specific to Spain. But these studies were carried out on a limited number of individuals and pointed out a need for more extensive studies in each European rice-growing area. In addition, temporal evolution of M. oryzae populations is also poorly documented. In this study, we focused on Guadalquivir delta region in southern Spain. A total of 186 M. oryzae isolates were collected from various farmer and experimental fields, on diverse cultivars, over the period 1999-2003, and characterized for their genotypic and pathotypic diversity. Five lineages were identified, one of which was detected for the first time in Europe (E6). The E6 lineage, which was collected over the period 2000-2003, became dominant in 2000. Pathotyping confirmed previous results of a narrow diversity for virulence spectrum in European lineages. Five dominant pathotypes were identified, each one corresponding to a single pathotype. Drastic changes in lineage relative frequencies were observed from one year to another. The origin of such changes is discussed. [ABSTRACT FROM AUTHOR]

The interaction of the parasitic plant Orobanche cernua with resistant and susceptible cultivars of Helianthus annuus L. was investigated. Using different bioassays to evaluate the early stages of the parasite life cycle (germination, attachment, penetration, and establishment), differences were observed between O. cernua‐resistant and O. cernua‐susceptible sunflower varieties. Germination of O. cernua seeds in the presence of resistant sunflower roots was approximately half that of germination in the presence of susceptible roots, and germinated seeds displayed enhanced browning symptoms. Parasite radicles or host‐tissue around the contact point turned brown after O. cernua attachment to sunflower roots, especially in the resistant varieties. These observations suggested the possible accumulation of toxic compounds as a defence strategy in the resistant sunflower varieties. Sunflower 7‐hydroxylated simple coumarins may play a defensive role against O. cernua parasitism by preventing successful germination, penetration and/or connection to the host vascular system. This hypothesis is supported by the following data: (i) coumarins inhibited the in vitro germination of O. cernua seeds induced by the strigol analogue GR24 and caused a browning reaction in germinated seeds and (ii) resistant sunflowers accumulated higher levels of coumarins in roots and excreted greater amounts than susceptible varieties in response to O. cernua infection. [ABSTRACT FROM PUBLISHER]

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Despite the tremendous economic impact of broomrapes ( Orobanche spp.) on agriculture in many countries little is known of the pattern of genetic variation within this group of parasitic weeds. The present paper describes the use of RAPD markers for the study of five Orobanche species in agricultural fields in Israel. Pronounced genetic differentiation was found between the species, and RAPD markers were raised for the identification of each of them. Southern-hybridization patterns of RAPD products of the various species were used to confirm the interpretation. The same markers were valid both for broomrapes collected in agricultural fields and for those collected in natural habitats. The validity of the markers found for O. cumana and O. crenata was confirmed on plants of the same species that were collected in Spain. Parsimony analysis of 86 RAPD characters produced a tree that clearly distinguishes between the five studied Orobanche species, separates the two Orobanche species belonging to sect. Trionychon from those belonging to sect. Osproleon, and supports the separation of O. cumana from O. cernua and of O. aegyptiaca from O. ramosa. [ABSTRACT FROM AUTHOR]