Field experiments were conducted in western France for two consecutive years to investigate the effect of pea-cereal intercropping on ascochyta blight, a major constraint of field pea production world-wide. Disease pressure was variable in the experiments. Intercropping had almost no effect on disease development on stipules regardless of disease pressure. In contrast, disease severity on pods and stems was substantially reduced in the pea-cereal intercrop compared to the pea monocrop when the epidemic was moderate to severe. Therefore, a pea-cereal intercrop could potentially limit direct yield loss and reduce the quantity of primary inoculum available for subsequent pea crops. Disease reduction was partially explained by a modification of the microclimate within the intercrop canopy, in particular, a reduction in leaf wetness duration during and after flowering. The effect of intercropping on splash dispersal of conidia was investigated under controlled conditions using a rainfall simulator. Total dispersal was reduced by 39 to 78% in pea-wheat canopies compared to pea canopies. These reductions were explained by a reduction in host plant density and a barrier or relay effect of the non-host plants.

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.

Although fiber optic distributed temperature sensing (FO-DTS) has been used in hydrology for the past 10 years to characterize groundwater–streamwater exchanges, it has not been widely applied since the entire annual hydrological cycle has rarely been considered. Properly distinguishing between diffuse and intermittent groundwater inflows requires longer periods (e.g., a few months, 1 year) since punctual changes can be lost over shorter periods. In this study, we collected a large amount of data over a one-year period using a 614 m long cable placed in a stream. We used a framework based on a set of hypotheses approach using thermal contrast between stream temperature and the atmosphere. For each subreach, thermal contrast was normalized using reference points assumed to lie outside of groundwater influence. The concepts and relations developed in this study provide a useful and simple methodology to analyze a large database of stream temperature at high spatial and temporal resolution over a one-year period using FO-DTS. Thus, the study highlighted the importance of streambed topography, since riffles and perched reaches had many fewer inflows than pools. Additionally, the spatial extent of groundwater inflows increased at some locations during high flow. The results were compared to the usual standard deviation of stream temperature calculated over an entire year. The two methods located the same inflows but differed in the mapping of their spatial extent. The temperatures obtained from FO-DTS open perspectives to understand spatial and temporal changes in interactions between groundwater and surface water.

The main objective of the study was to describe the horizontal and vertical distribution of Aphanomyces root rot in a naturally infested pea field.