Short Communication (I JOURNAL OF PLANT PHYSIOLOGY An Arbuscular Mycorrhizal Fungus (Glomus mosseae) Induces a Defence-like Response in Rubber Tree (Hevea brasiliensis) Roots

International audienceThe specific activities of cinnamyl alcohol dehydrogenase (EC 1.1.1.-) and cell wall-bound peroxidases (EC 1.11.1.-) were enhanced in roots of Hevea brasiliensis 2 weeks after inoculation with Glomus mosseae, simultaneously with an increased lignin content. However, no scopoletin accumulation was observed by this time. These defence-like reactions were caused by the first penetration of the AM fungus but they were transient

Growth and gas exchange responses of Hevea brasiliensis seedlings to inoculation with Glomus mosseae

International audienc

An Arbuscular Mycorrhizal Fungus (Glomus mosseae) Induces a Defence-like Response in Rubber Tree (Hevea brasiliensis) Roots

International audienceThe specific activities of cinnamyl alcohol dehydrogenase (EC 1.1.1.-) and cell wall-bound peroxidases (EC 1.11.1.-) were enhanced in roots of Hevea brasiliensis 2 weeks after inoculation with Glomus mosseae, simultaneously with an increased lignin content. However, no scopoletin accumulation was observed by this time. These defence-like reactions were caused by the first penetration of the AM fungus but they were transient

A new method to obtain monozoosporangial isolates of sunflower downy mildew (Plasmopara halstedii)

A new method to obtain monozoosporangial strains was applied on 9 pathotypes of Plasmopara halstedii (100, 300, 304, 314, 700, 704, 710, 707 and 714), the parasite causing sunflower downy mildew. Single zoosporangia were isolated from the surface of agar medium and placed on leaf disks on solid Knop medium. The best fungal development was obtained with leaf disks taken from the first pair of sunflower leaves when these measured from 5 to 8cm in length. The percentage success rate in obtaining monozoosporangial strains varied from 1.4 to 7.4% according to race. The percentage of disks showing sporulation depends on spore viability, the physiological state of leaves and the receptivity of the sunflower genotype. This method enabled us to confirm the presence of a new downy mildew pathotype in France: race 707

Variation in form and size of Plasmopara halstedii (sunflower downy mildew) zoosporangia

Zoosporangia form and size were studied on a collection of 94 strains of Plasmopara halstedii (sunflower downy mildew). Both oval and round forms were present in all strains analysed. The proportion of two forms varied significantly according to strain and plant age but more especially to host plant genotype. Whatever the strain or host genotype, oval zoosporangia were larger than round ones, but there was no relation between the proportion of the oval form and mean zoosporangia size. There was no relation between zoosporangia form or size and race virulence profiles or aggressiveness criteria, with the possible exception of zoosporangia size and sporulation density. It is concluded that, for this obligate parasite, although form and size of zoosporangia depend on pathogen strain, these characters also vary according to growth conditions of Plasmopara halstedii, in particular to the genotype of the plant host

A Method to Measure Aggressiveness of Plasmopara halstedii (Sunflower Downy Mildew)

For the first time, a method was used to measure aggressiveness of two Plasmopara halstedii races (100 and 710), the parasite causing sunflower downy mildew. Two sunflower lines showing different levels of quantitative resistance were used to measure two aggressiveness criteria: latent period and sporulation density. A strain of race 100 had a shorter latent period and greater sporulation density than a strain of race 710. The sunflower inbred line BT, rather susceptible in the field, presented a greater sporulation density and a shorter latent period than another inbred line FU, which shows greater resistance in the field. These results indicated that race 100 was more aggressive than race 710. The behaviour in the field of the two inbred lines was confirmed in the laboratory observations

Variation in aggressiveness of Plasmopara halstedii (sunflower downy mildew) (vol 116, pg 247, 2009)

absen

Impact of major gene resistance management for sunflower on fitness of

Changes in virulence of Plasmopara halstedii populations under different major gene (Pl) management strategies were studied over 5 years continuous cropping of one sunflower hybrid under netting cages. Strategies were monoculture of forms of the hybrid with 1 gene or with combinations of 2 genes, alternation of different genes, and mixtures of several different forms of the hybrid. Monoculture with single resistance genes led to loss of efficient resistance after 3 years, with high levels of disease and increased variability of the pathogen, whatever the Pl gene used. Combinations of genes, alternation and mixtures gave longer term control of downy mildew. In particular, combinations of resistance genes coming from both female and male parents of the hybrid (such that even impurities had a resistance gene) gave the best control and least variation in pathogen virulence. Results are discussed with the object of durable control of downy mildew by all methods available

Impact of major gene resistance management for sunflower on fitness of Plasmopara halstedii (downy mildew) populations

Changes in virulence of Plasmopara halstedii populations under different major gene (Pl) management strategies were studied over 5 years continuous cropping of one sunflower hybrid under netting cages. Strategies were monoculture of forms of the hybrid with 1 gene or with combinations of 2 genes, alternation of different genes, and mixtures of several different forms of the hybrid. Monoculture with single resistance genes led to loss of efficient resistance after 3 years, with high levels of disease and increased variability of the pathogen, whatever the Pl gene used. Combinations of genes, alternation and mixtures gave longer term control of downy mildew. In particular, combinations of resistance genes coming from both female and male parents of the hybrid (such that even impurities had a resistance gene) gave the best control and least variation in pathogen virulence. Results are discussed with the object of durable control of downy mildew by all methods available