Acidification of the culture medium as a strategy to control endophytic contaminations in Prunus spp. rootstocks cultured in GreenTray TIS bioreactor

Overgrowth of endophytes in some in vitro cultures may disrupt the normal shoot tip growth and proliferation, being necessary to obtain endophytes-free cultures to achieve a normal plant micropropagation process. To remove these contaminations from the culture medium, antibiotics are commonly added to the culture medium. However, its use in plant production must be urgently reduced because of the current restrictions imposed by the European Union. For that purpose, the effect of acidic low (pH 3) and neutral (pH 7) pH was tested in the GreenTray® TIS bioreactor as an alternative to control endophytes growth without affecting the micropropagation of the Prunus rootstock RP-20 explants. The results demonstrated that culture at pH 3 did not affect the number of shoots, shoot FW, shoot length and the amount of chlorophyll pigments, but significantly reduced endophytes population. The identification also revealed that Roseomonas mucosa, Microbacterium oxydans, Bacillus subtilis and Luteibacter yeojuensis were the bacterial isolates responsible of those contaminations. These results might suppose a real breakthrough in the in vitro tissue culture field, although more research is required to meet the pH requirements for the different plant species and other endophytic.