Organic and inorganic nitrogen effects on spore production and mycelial growth of Neonectria ditissima in vitro

Nitrogen (N) is known to influence the growth of Neonectria ditissima (N.d.), the causal organism of European canker. In vitro, inorganic N inhibits conidia germination at N concentrations above 0.2 mol/L while, in planta, foliar urea application increased disease expression of leaf scar wounds up to nine-fold. The influence of organic and inorganic N sources on mycelial growth and spore production of N.d. in vitro was investigated. Four organic and six inorganic N sources were tested on agar at concentrations of N between 0 and 0.2 mol/L, with 3 different N.d. isolates. Spore production was generally increased by the addition of low concentrations of N, with varying results at higher concentrations dependent on the N source; however, this also differed among N.d. isolates. Spore production was generally incompletely inhibited at the higher N concentrations tested. However, germination from the resulting conidia decreased, possibly due to morphological changes to the spores. Mycelial growth generally decreased with the addition of N. Understanding the N effect in planta will be further complicated by the physiological plant-N and plant-pathogen interaction processes.