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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. (Resume d'auteur)

Field and laboratory studies were conducted from 1993 to 1997 to determine the feasibility of controlling nodding broomrape in sunflower by treating crop seeds with pronamide. Soaking sunflower seeds for 5 min in 50% pronamide solution or coating at the equivalent of 2 kg/ha with pronamide did not impair seed germination or seedling growth, and controlled nodding broomrape 49 to 68% and 51 to 77%, respectively, up to 105 d after planting. Studies of the effect of treated sunflower seeds on germination and seedling growth, at several time intervals after the herbicide application (0, 30, 60, and 90 d after treatment [DAT]), were conducted. Soaking with 50% solution or coating at 2 kg/ha reduced seedling growth by 20 and 24% 60 DAT, respectively, compared with the control. Nomenclature: Pronamide; nodding broomrape, Orobanche cumana Wallr. #3 ORACU; sunflower, Helianthus annuus L. Additional index words: Herbicide seed treatment, parasitic weed. Abbreviations: DAP, days after planting; DAT, days after treat...

Studies were conducted from 1993 through 1995 to determine broomrape control from imazethapyr applied to pea seeds. Soaking seeds for 1 to 10 min in 0.0001% to 1% imazethapyr (Pursuit-10) solutions or coating seeds with imazethapyr at 0.025 to 0.30 mg/g (herbicide/seed, equivalent to 5 to 60 g/ha for a seeding rate of 200 kg/ha) did not affect seed germination or crop emergence and growth. Broomrape control with imazethapyr applied by coating seed at 0.1 to 0.2 mg/g (herbicide/seed, 20 to 40 g/ha) or by soaking seeds for 5 min in 0.1% to to 1% imazethapyr solution was from 75 to 80% and 50 to 70%, respectively. Pea biomass and seed yield increased, compared to broomrape-infested nontreated control, when pea seeds were treated with imazethapyr and imazapyr at 5 g/ha was applied late postemergence, as a result of the excellent broomrape control. Nomenclature: Imazethapyr, 2[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; broomrape, Orobanche crenata Forsk. # 3 ORACR; pea, Pisum sativum L.

Potential antagonists ofFusarium solani f. sp.pisi (Fsp) were selected from soil samples with varying degrees of receptivity to this pathogen. They were tested against Fsp isolate 48 (Fs48), in increasingly complex systems. Most species testedin vitro were able to antagonize Fs48. No relation could be establishedin vitro between the receptivity of the soil from which an isolate originated and its antagonism to Fs48. In soils naturally infested with pea root rot pathogens, which were stored humid at 4°C for a period longer than a year, various isolates ofFusarium, Gliocladium andPenicillium spp. were able to reduce root rot. After sterilization of these soils, onlyGliocladium roseum isolates, added at 105 conidia g−1 dry soil, significantly reduced disease severity and prevented root weight losses caused by Fs48 at 104 conidia g−1 dry soil. In soils in which the biota were activated by growing peas before the assays, doses of 106 and 107 ofG. roseum were required to reduce root rot. In these soils, the antagonistic effects of fluorescent pseudomonad strains from soil of low receptivity to Fsp were variable. Some strains of fluorescent pseudomonads, from soil moderately receptive to Fsp and from highly infested soils, were also able to reduce root rot. Disease suppression by pseudomonad strains was more evident in the absence than in the presence ofAphanomyces euteiches in the root rot pathogen complex. The role of receptiveness of the soil with regard to potential antagonists is discussed.

Summary: Resume: Zusammenfassung Field experiments were conducted from 1989 to 1992 to determine the effects of pre-emergence herbicides in sunflower (Helianthus armuus L.) on: (1) the control of Orobanche cemua Loefl. (broomrape) and (2) crop damage and crop yield. Herbicides tested belong to the imidazolinone, sulfonylurea and substituted amide families. Imazethapy r (20–40 g ha−1), imazapy r (12.5–25 gha−1) and chlorsulfuron (4–6 gha−1) controlled broomrape efficiently without crop injury. With good O. cernua control and good crop tolerance, sunflower seed yield from these treatments were generally similar to the non-infested checks and higher than the infestedchecks. Imazaquin (20–40 gha−1), triasulfuron(4gha−1), pdmisulfuron(3g ha−1), acetochlor (4–4 kg ha−1) and metazachlor (2 kg ha−1) were less effective. Imazamethabenz (200–600 g ha−1) and metolachlor (3–3 kg ha−1) were ineffective. Wetconditions aftercropsowing considerably decreased O. cemua control with pre-emergence herbicides probably caused by enhanced degradation. Des herbicides de prelevee pour la lutte contre Vorobanche (Orobanche cemua Loefl.) dans le toumesol (Helianthus annuus L.) Des experimentations au champ ont ete conduites de 1989 a 1992 pour determiner les effets d'herbicides de pre1evee du toumesol sun (a) la destruction de l'orobanche (Orobanche cernua Loefl.) et (b) la phytotoxcite sur la culture. Les herbicides testes appartenaient aux imidazolinones, aux sulfonylurdes et aux amides substituees. L'imazethapyr (20 a 40 gha−1), l'imazapyr (12,5 a25gha−1)et le chlorsulfuron (4 a 6 gha−1) detruisaient efficacement l'orobanche sans occasionner de phytotoxidt6 sur la culture. Dans ces conditions, les rendements etaient generalement semblables a ceux des temoins non infestes et superieurs a ceux des temoins infestes. L'imazaquin (20 a 40 g ha−1), le triasulfuron (4 gha−1), le primisulfuron (3 g ha−1), lacetolachlor (4,4 kg ha−1) et le metazachlor (2 kg ha−1) etaient moins efficaces. L'imazamethabenz (200 a 600 g ha−1) et le metolachlor (3,3 kg ha−1) etaient inefficaces. Des conditions humides aprfes le semis diminuaient considerablement la destruction de O. cemua par les herbicides de prelevee, probablement a cause d'une degradation plus elevee. Vorauflaufherbigide zur Bekdmpfung der Sommerwurz Orobanche cemua Loefl. in Sonnenblume (Helianthus annuus L.) Zwischen 1989 und 1992 wurden in Sonnenblume Feldversuche zur Wirkung von Vorauflaufherbiziden aus den Gruppen der Imidazolinone, Sulfonylharnstoffe und substitutierten Amide auf die Sommerwurz Orobanche cernua und auf Kulturpflanzenschaden sowie den Ertrag durchgefuhrt. Mit Imazethapyr (20 bis 40 g ha−1), Imazapyr (12,5 bis 25 g ha−1) und Chlorsulfuron (4 bis 6 g ha−1) lieβ sich die Sommerwurz wirksam bekampfen, ohne daβ Schaden an der Sonnenblume auftraten, und die Ertrage waren allgemein ahnlich oder hoher als bei der nichtparasitierten Kontrolle. Imazaquin (20 bis 40 ha−1), Triasulfuron (4 g ha−1).Primisulfuron (3 g ha −1). Acetochlor (4,4 kg ha −1 und Metazachlor (2 kg ha −1) waren weniger wirksam. Imazamethabenz (200 bis 600 g ha−1) und Metolachlor (3,3 kg ha−1) hatten keine Wirkung. Bei Niederschlagen nach der Saat der Sonnenblume war die Bekampfung der Sommerwurz mit Vorauflaufherbiziden vermutlich wegen verstarkten Abbaus erheblich schwacher.

The effects of sublethal heat treatments on heat resistance were studied forFusarium oxysporum f.sp.dianthi (Fod) andVerticillium dahliae (Vd), one isolate of each pathogen. Treatments of propagule suspensions of Fod at 55°C and of Vd at 45°C for 30 min were survived by less than 0.001% and 0.01% of the propagules, respectively. Pretreatment of suspensions of Fod at 45°C increased survival of the 55°C treatment up to 0.73% of the propagules and pretreatment of suspensions of Vd at 40°C increased survival of the 45°C treatment up to 0.40%. Induction of heat resistance was dependent on duration of the exposure to the sublethal temperature. With Fod, this duration was shorter for propagules from old cultures than for those from young cultures. Pretreatment at 45°C of a suspension of an 1-week-old culture of Fod induced resistance when lasting 30 min or longer, but not when 20 min or shorter. With Vd, the duration of the pretreatment inducing heat resistance depended on type of culture — white or black — due to differences in microsclerotia formation. Implications of induced heat resistance for control of plant diseases by thermotherapy are discussed.

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 GR(24) 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.

8 pages, 2 tables, 2 figures, [14C]-Imazethapyr was applied as a seed treatment and at plant pre-emergence and post-emergence to peas (Pisum sativum L.) parasitized by Orobanche crenata Forsk. Herbicide uptake increased with time regardless of the application method. Uptake reached about 98%, 89%, 81% and 94% of the total herbicide applied for the seed coating, seed soaking, pre-emergence and post-emergence treatments respectively. Herbicide translocation within the host plants consistently differed between O. crenata-infected and non-infected plants. High levels of 14C activity were accumulated by parasitic plants from the host. In non-infected pea plants, pods were stronger sinks for imazethapyr than the other parts of the plant, regardless of the application method. The herbicide distribution in the pea plant: O. crenata complex showed the same pattern regardless of the application methods. However, accumulation of radioactivity in the parasite was lower with pre-emergence and post-emergence application than with the seed treatments. In addition, radioactivity concentration in O. crenata plants was slightly higher when [14C]-imazethapyr was applied to pea seeds by coating than by soaking.

5 pages, 2 figures, 4 tables, Field studies were conducted at nine locations in southern Spain during 2 yr to develop models of nodding broomrape competition with sunflower and to establish economic thresholds. At each location, 30 to 35 small plots, each consisting of three sunflower plants, were chosen at random. The infection severity (BIS, no. of emerged broomrapes per sunflower plant) varied from 0 to 35. Plots were harvested at maturity to assess several sunflower and broomrape population variables. The percent sunflower yield reduction averaged over locations due to broomrape was estimated by the equation: % SYR= 1.7 × BIS (r² = 0.92). Crop yield loss per BIS unit increased with the expected yield and was estimated to be about 25, 50, and 75 kg ha-¹ for yields of 1000, 2000, and 3000 kg ha⁻¹, respectively. A consistent relationship could be established between broomrape-infected sunflower yield, crop and broomrape biomass, and BIS parameters: SSY1 = 0.2259 x PoBio/(1 + 0.0687 x BIS) (r2 = 0.7820). The BIS economic threshold was about 1.5 and 3.5 for control treatment cost of $ 40 ha-1 and potential yields of 2000 and 1000 kg ha-1, respectively., Europen Union (EEC XII-TS2*0124-C) and the Spanish Scientific and Technological Commission (CICYT Agro-Petri 0057/92).