Effect of pea canopy architecture on splash dispersal of Mycosphaerella pinodes conidia

Abstract

To investigate the hypothesis that disrupting pathogen movement within the plant canopy could slow the development of aschochyta blight, the effect of pea canopy architecture on splash dispersal of Mycosphaerella pinodes -conidia was studied in controlled conditions using a rainfall simulator generating rain events (2 mm) in still air. In intra-plant dispersal experiments, a source constituted by a semi-leafless pea plant with a single infectious lesion (108 pycnidia per cm 2 of lesion, 1685 conidia per pycnidium) was placed in the middle of eight healthy target plants. Spore deposition was estimated by the number of lesions that developed on each stipule of the source (auto-deposition) and target (allodeposition) plants after incubation. Rates of deposition on the source and target plants were 0·53 and 0·47, respectively. On the source plant, most of the spores were splashed downwards, with few spores remaining at the infectious node and very few spores moving upwards. In inter-plant dispersal experiments, potted plants were grouped to constitute 1-m 2 canopies. A range of canopy architectures was achieved by using different plant densities and growth stages. A suspension of conidia was placed in the centre of each canopy. Resulting horizontal dispersal gradients were generally described by a negative exponential model. Canopies with a leaf area index (LAI) greater than 0·48 produced gradients with slopes that were not significantly different. A less dense canopy (LAI 0·36) produced a significantly steeper slope. Half-distances were short and ranged between 1·6 and 6·5 cm. The barrier rate, calculated as the ratio of the mean number of lesions assessed on isolated plants to the mean number of lesions assessed on plants in canopies, increased with increasing canopy LAI.

Effect and underlying mechanisms of pea-cereal intercropping on the epidemic development of ascochyta blight

“…The number of lesions was counted on those stipules that had been present on the day of the splash experiment. Under similar experimental conditions, Schoeny et al (2008) showed that the age of the stipules (i.e. their position along the stem) did not bias lesion counts.…”

“…As previously described by Schoeny et al (2008), rainfall was generated by an oscillating nozzle (Deltalab, Tec Jet SS 6560) positioned at a height of 3.8 m in a closed shed. Displacement was at constant speed with a sweep angle of 180°, providing a rainfall intensity of 40 mm h −1 .…”

“…LAI (dimensionless) is the ratio of the total leaf area of the canopy (m 2 ) divided by the area of ground covered by the canopy (m 2 ). The total leaf area of each canopy was calculated by multiplying the number of plants constituting the canopy by the number of leaves per plant and the mean leaf area (7.48 cm 2 ) (Schoeny et al 2008). …”

“…Under field conditions, Le May et al (2009) showed that spring pea cultivars with different architectural features (stem height, branching ability, standing ability) but similar levels of susceptibility to ascochyta blight displayed differences in disease progress on leaves. Under controlled conditions, Schoeny et al (2008) demonstrated that the leaf area index of a pea canopy could influence the splash dispersal of M. pinodes conidia.…”

Current knowledge on plant/canopy architectural traits that reduce the expression and development of epidemics

“…The pathogens may be characterised by several trophic status (from biotrophic to necrotrophic) and the observed symptoms may affect only one or several organs (leaf, stem, flower, fruit and grains). Schoeny et al (2008) showed the relationship between the leaf area index (LAI) and the horizontal dispersal gradient of Mycosphaerella pinodes pycniospores on pea. The leaves density measured through the LAI had an effect on the barrier rate increasing with canopy LAI.…”