Strategische kennis voor de preventie van bacterieziekten in de pootaardappelteelt: eindverslag : AF18034

Samenvatting

Research was conducted to infections of a (PB1-) potato crop grown from minitubers with blackleg causing soft rot Pectobacteriaceae (BL-SRP). For this, an enrichment multiplex TaqMan assay (EM-TaqMan assay) was developed, allowing to detect the various BL-SRP variants simultaneously with a sensitivity of 10-100 cells per gram plant material. During four growing seasons (2019- 2022) PB1 crops were surveyed. Plant tissues (leaves, stems and tubers) were collected and analyzed using the EM-TaqMan assay. During wet growing seasons relatively high infection incidences were found both in leaves (8%) and tubers (≤ 42%), in particular with a virulent haplotype of P. brasiliense. During dry seasons, only low incidences were found. It was found that P. brasiliense is able to enter a VBNC-state in the presence of cupper ions (CuSO4). However, we were unable to find conditions to let the cells multiply again. Therefore we have no indications that VBNC play a role in the epidemiology of P. brasiliense. The role of potential infection sources was studied. BL-SRP were not found in rain water, but 2.3% of the sampled insects at a PB crop were contaminated with BL-SRP, indicating that insects may be important in the transmission of BL-SRP from an infection source to a PB1 crop. Inoculum deposited on haulms poses a high risk for tuber infections. This was studied by spray inoculation of haulms of young potato plants with different densities (102 – 109 cfu per plant) of a virulent, rifampicin resistant mutant of P. brasiliense. In a wet growing season, low densities could already result in haulm infections while all plants yielded infected tubers. In a dry year only at the highest inoculum densities haulm infections were found, but tuber infections even at the lowest densities. Analysis conducted at the NAK to the role of environmental factors on the infection level of seed potatoes were done using data of seed lots tested in high classes in the period 2015-2018. Characteristics pointing to vertical infections (mother to daughter tubers) such as class/generation of a seed lot, shows a strong relationship with the presence of SRP in the daughter tubers. There is a difference in the infection risk between cultivars. Conditions positively related to the risk on horizontal transmission (infections from the environment) are soil characteristics, relative humidity, precipitation at the end of the growing season, and soil saturation, while temperature during the growing season shows a negative correlation with the presence of BL-SRP in daughter tubers.