PATHOGEN AGENTS IN MEDITERRANEAN PROCESSING TOMATOES AND THEIR GENETIC MONITORING

In areas where tomatoes have been grown for some years, plots are heavily contaminated by soil fungi. The fungi and bacteria which attack the leaves and fruits in damp years cause serious epidemics which reduce yields and have an adverse effect on the quality of the fruit.

Over recent years, several viruses transmitted by insects have resulted in the destruction of plots. The Cucumber Mosaic Virus (CMV), transmitted by aphids, is probably responsible for the most considerable losses, especially under the form of necrosis in southern Italy. The Tomato Spotted Wilt Virus (TSWV), which has been present for many years in the Mediterranean Basin, is the cause of extensive outbreaks since this area was infested by the Californian thrips, Frankliniella occidentalis, which is a much more active vector of the virus than the Thrips tabaci which was formerly prevalent in the region.

A large number of animal parasites affect canning tomato. In the earth, these are mainly gall nematodes and wireworms. The aerial parts of the plants are often colonized by spider mites, tomato russet mites and the fruits attacked by caterpillars.

Over recent years, several books and brochures have been written on tomato diseases. For this reason, this presentation will deal principally with the genetic curbing methods applied to tomato crops to be used for industrial processing and the advances to be expected from this approach.

It is now possible to grown fixed varieties or Fl hybrids which possess resistance to several of the following pathogenic agents: Verticillium dahliae, Fusarium oxysporum f. sp. lycopersici, Stemphylium spp., Phytophthora infestans, Pseudomonas tomato and Meloïdogyne spp.

Breeding programmes currently underway allow us to hope that the next few years will see the arrival of varieties with resistance to Pyrenochaeta lycopersici, Leveillula taurica, Corynebacterium michiganense, Tomato Spotted Wilt Virus and Tomato Yellow Leaf Curl Virus.

As most resistances which are currently useable are dominant or semi- dominant, it is probable that breeders will attempt to combine them in F1 hybrids. Food industry tomato F1 hybrids carrying resistances to 5 pathogen agents are already on the market.