Analysis And Modelling Of The Growth Of Grapevines Affected By Downy And Powdery Mildew

Plant activities, involving physiological processes such as photosynthesis, respiration, stomatal conductance, are strongly affected by pathogen infections, and specific experiments can be set up to investigate single effects. However, the crop responses to pathogen activity can be globally evaluated only analysing growth and development of plants. For these reasons, dynamic crop models offer a valuable framework within which to structure thinking about the interactions between pathogen growth reducing factors and crop growth processes under variable conditions and at several levels of complexity, according to the organisation of considered processes (e.g. molecular, cellular, tissue, organ, plant, crop or even agro-ecosystem) (1). Generally, two modelling approaches have been used to simulate the effect of plant diseases on crop growth: comprehensive and summary. The comprehensive models take into account at more detailed level the processes that regulate growth. They may start at the whole plant level utilising the light profile within the canopy, photosynthesis characteristics of individual leaves, respiration and dry matter partitioning factors. Disease effect can be introduced taking into account many processes, such as tissues consumption, leaf senescence acceleration, stand reduction, light theft, photosynthetic rate reduction etc. The summary models have a simpler approach. To simulate growth they need a fewer parameters such as light interception, radiation use efficiency (RUE) and harvest index. Since dry matter accumulation is calculated as the product of light interception by leaf area and the average RUE, those parameters are the main variables used to characterise the effect of the pathogen on the plant biomass accumulation. Several pests and pathogens affect growth decreasing light interception by leaf area, while they do not affect the average RUE, indicating that the non diseased part of the plant has a normal use of solar radiation. Other pests and pathogens affect both light interception by leaf area and the photosynthetic activity of green leaves suggesting an influence of the pathogen also on the apparently non diseased portion of the leaves (2, 3, 4). The reliability of crop loss simulation is mainly based on the knowledge of the plant-pathosystem. This focuses around the interactions between host and pathogen, with the effect of environmental factors, and it is related to several fields of knowledge that can be considered globally or independently from each other, such as physiology, biochemistry, agrometeorology, pathology, entomology and ecology (5). As concerning grapevine (Vitis vinifera), several studies have been carried out to formulate models for the simulation of crop growth and development (6, 7, 8), and disease infection (9, 10). However few attempts have been made to integrate these models, as well as to evaluate the effects of diseases on the growth responses of crop under different environmental conditions. On these basis, the aims of this work were to analyse under field conditions growth of healthy and diseased grapevines in order to evaluate differences in the rate of organ appearance, dry matter accumulation, leaf area expansion, and to simulate crop responses to fungus infection coupling growth and disease models.