Selecting tomato (Solanum lycopersycon L.) lines for mycorrhizal competence: a prerequisite for breeding the plants of the future.

Recent breeding programs revealed that it is difficult to select varieties for low-input agriculture by starting from conventional varieties. One of the explanations given for this failing is that conventional varieties, selected under high-input conditions, would have lost genes coding for symbiotic competence. For example, conventional varieties generally show a lower capacity to sustain root symbiosis with naturally occurring arbuscular mycorrhizal fungi (AMF), than needed for low-input agriculture. Such loss in mycorrhizal competence was probably due to breeding in fully fertilized soils, which resulted in the selection for plant genotypes unable to exploit these beneficial microorganisms. Therefore, the goal of our research was to select, among ten mutant lines belonging to a tomato (cv Red Setter) EMS mutant collection, those presenting both a good mycorrhizal competence and a high level of productivity, in order to obtain tomato genotypes adapted to breeding in low-input cropping systems. The wild type line Red Setter, as well as all the 10 mutated ones, showed a characteristic AMF infection dynamics. Some differences were also found in the diversity of root-colonizing AMF taxa. One tomato mutant line was specially mycorrhizal competent, showed high symbiotic precocity and a highly structured symbiotic population. Other mutants were similar to wild type line, and more research is needed to clarify their actual position.