Botrytis cinerea spore balance of a greenhouse rose crop

Abstract

Fungal pathogens are among the most virulent bioagressors of protected crops. For sustainable plant production and to protect the crop against these airborne organisms one must determine their origin, i.e. whether they come from outside the greenhouse or are produced inside it. We considered Botrytis cinerea spore concentration as a particular physical species which is transported by air in the same way as heat, CO 2, water vapour or any tracer gas. We constructed a mass balance of the viable Botrytis spores on the whole-greenhouse volume to assess the inside production of spores and their exchanges. The different elements in the spore balance are considered and are determined experimentally: • spore transfer into or out of the greenhouse is deduced from the difference between the inside and outside spore concentrations, measured by spore traps, multiplied by the whole-greenhouse ventilation rate; • spore deposition on soil and crop and spore impaction on the plants is deduced from observations made using Petri dishes; • inside spore production is the differential term deduced from the whole-greenhouse volume balance. The first measurements and calculations have shown that the presence of insect-proof nets across the greenhouse openings strongly influences the spore balance, as the nets intercept the B. cinerea spores proportionally to the nets’ solidity. Based on wind tunnel experiments, the interception capacity of the nets was quantified and the whole model completed in consequence. These results show the diurnal Botrytis spore balance over 3–4-week periods in the autumn and spring season for a young rose plantation. In agreement with visual observations of B. cinerea sporulation within the greenhouse, it is shown that the origin of the inocula is predominantly internal (2/3 in quantity). However, due to outside climate and greenhouse opening, it can vary widely from one period to another, with a tendency to become predominantly internal as the crop ages.