Nitrogen-induced changes in morphological development and bacterial susceptibility of Belgian endive (Cichorium intybus L.) are genotype-dependent

Nitrogen is known to modulate plant development and resistance to pathogens . Four selected lines (Alg, NS1, NR1 and NR2) of chicory (Cichorium intybus L.) were grown on low (0.6 mM) and high (3 mM) NO3- nutrition in order to study the effect of N on the expression of three traits, namely, shoot/root ratio, chicon morphology and resistance to soft rot caused by Erwinia sp. For all genotypes, increasing N supply led to a higher shoot/root ratio, re sulting from an increased shoot biomass but with no effect on root growth. In contrast, the effect of N on chicon morphology and resistance to bacteri a was genotype-dependent and we distinguished two groups of lines according to their phenotypic characteristics. In the group consisting of NR1 and NR 2, increasing NO3- supply during the vegetative phase made the chicon morph ology switch from an opened to a closed type while resistance to bacteria w as not affected by N supply. In the NS1 and Alg group, the effect of N on c hicon morphology was the opposite to that observed in the NR1-NR2 group whi le NS1 and Alg exhibited a partial resistance to Erwinia sp., only expressi ng soft-rot disease when the N supply reached 3 mM. Characterization by DNA amplification fingerprinting (DAF) allowed the generation of 110 polymorph ic bands and confirmed that the lines NR1 and NR2, on the one hand, and NS1 and Alg, on the other hand, belong to two distinct genetic groups. The DAF results indicate that chicon morphology and partial resistance to Erwinia sp. are complex traits which would be amenable to quantitative trait loci a nalysis. The split growth phase of chicory means that any changes in chicon related to N supply during vegetative growth were mediated by a root-origi nating signal. No variation in root carbon content among genotypes and NO3- treatments was observed. In contrast, differences in root N content reveal ed the same grouping of the chicory lines, NR1 and NR2 being systematically richer in amino acids and NO3- than NS1 and Alg. However, no correlation e xisted between N compounds and chicon morphology or pathology if all genoty pes were considered together. Thus, the effect of N on plant development an d pathology as well as putative identified signals might be specific for a genotype. Our study indicates that it is necessary to consider the genetic variability within a species in any signalling-pathway research.