Using virtual plants to analyse the light-foraging efficiency of a low-density cotton crop.

BACKGROUND AND AIMS: Cotton shows a marked plasticity vs. density in terms of branch development and geometry, internode elongation and leaf expansion. This paper proposes interpretations for observed plasticity in terms of light quantity and quality. METHODS: 3-D virtual plants were reconstructed from field observations and 3-D digitization and were used to simulate the light regime in cotton stands of different densities. KEY RESULTS: All densities showed the same linear relationship between LAI and the sum of light intercepted by the canopy, from seedling emergence up to flowering. Simulated R : FR ratio profiles can very likely explain (1) the longer first internodes on main stem and branches and (2) the azimuthal re-orientation of branches toward the inter-row. CONCLUSIONS: Simulation tools were used to analyse plant plasticity in terms of light quantity and quality. The methodology applied here at the stand scale will now be continued at the plant scale to further strengthen the above hypotheses.

Wine contamination by ochratoxin A in relation to vine environment.

Since 2006, a new EC regulation has imposed 2.0 microg/l as the upper limit for OTA concentration in wines (CR 1881/2006). OTA production results from a harmful combination of skin lesions and favourable conditions for A. carbonarius growth, namely the air temperature and humidity, and the berry sugar content. The aim of our research was to highlight in vivo interaction between the number of damaged berries and the conditions for fungus development in relation to OTA concentration in wine. A survey carried out on the 2005 production from 156 vineyards bordering on the French Mediterranean enabled a link to be made between information on crop management, vineyard characteristics, meteorological data and the OTA concentration in wine. With humid air conditions during the susceptible berry period of 20 days before harvest, combined with a large number of damaged berries and a temperature conducive to both fungus growth and OTA production, critical levels of OTA concentration in wine were observed. Within the range of average daily air temperatures investigated, from 17.2 to 22.8 degrees C, during the susceptible berry period, 21 degrees C appeared to be the lower limit below which fungus growth and OTA production were not sufficient to result in critical levels of OTA concentration in wine. In our experiment, an average daily air temperature under 21 degrees C corresponded to an average minimum daily air temperature under 15 degrees C, below which fungus growth stopped under in vitro conditions. The importance of the berry sugar content before harvest was also demonstrated and our results suggest that the risk of wine contamination by OTA might be predicted from the number of damaged berries and the berry sugar content, along with climate monitoring.