As all living beings, plants are subjected to the attack by different pathogens (bacteria, fungi and viruses) that lead to huge looses in the agriculture worldwide.
Viruses are one of the most damaging biotic stresses affecting crops. In nature, frequently single viral infections (SVI) cause mild or no symptoms, facilitating the spread of viruses by the dispersion of symptomless infected plants. In contrast, in mixed viral infections (MVI), probably the most common, the plant is infected by two or more viruses at the same time. It can lead to synergistic effects, with the resultant disease showing stronger symptoms than with SVI. A successful control of such viral diseases requires epidemiological information regarding their spread (about 80% of all plant viruses are transmitted by insect vectors). Furthermore, MVI might modify virus dissemination parameters by altering the virus-vector-host interactions.
In few cases the importance of MVI is well known, for example in the sweet potato virus disease (SPVD), but in many other cases the scarce knowledge available makes difficult to evaluate the risk represented by MVI. Cucurbits like melon are good examples of this situation: despite the frequent occurrence of MVI (as proved by recent field surveys), only a few in-depth studies have been initiated in this crop until the moment.
A deeper knowledge of the mechanisms involved in the MVI would help to minimize their negative effects on several crops worldwide, increasing the productivity and avoiding looses, leading to direct economic benefits for the society.
MelonMixVir dealt with the plant health challenge posed by MVI in a crop of extreme importance in Europe: melon. The main purpose was to provide scientific-based advice to minimize the damage caused by MVI in melon, with the expected outcome of improving the production and quality of this crop, and accordingly of rising the economic benefits to Europe. We proposed a systematic analysis of pathosystems combining hosts, viruses and vectors to explore the effects caused by their interactions. MelonMixVir general objectives were the following: 1) Pathology of mixed infections: determine the severity and extend of a melon mixed infection, and seek pro-active measures favouring virus control and potential solutions to minimize their damages; 2) Entomology and vectors transmission: analysis of virus transmission by insect vectors (aphids/whiteflies) during a MVI to provide advice and practical approaches to control virus dissemination; 3) Molecular biology and resistance: determine the role of the viral defence system acting during the MVI in melon that could modulate the resistance response of host plants.
We concluded that in the case of a MVI in melon plants by WMV (Watermelon mosaic virus) and CYSDV (Cucurbit yellow stunting disorder virus) there is probably a synergism where WMV benefits of the presence of CYSDV (at least in transmission). The relative amount of each virus is altered by the presence of the other, indicating that somehow they interact inside the plant.
