Importance of determining infection by Phytophthora spp. in raspberry collapses in long-cane system

M.F. Roque, E. Diogo, M. Mota, P.B. Oliveira
Root rot disease caused by Phytophthora spp. severely affects raspberry production, causing plant decline and death, and is present in all temperate regions of the world. Premature chlorosis, wilting and collapse of fruiting canes, low emergence and survival of primocanes, and red-brown necrosis in the root cortex are some recurrent symptoms. In this study, ‘Sapphire’ long-term long-canes from an English nursery (KS) and three Dutch nurseries (AD; BS; TY) with first year vegetative growth in two pot volumes (1.8 and 4.7 L) and exit from the cold storage in three dates (July 7, July 23 and August 12, 2020) were analysed. For detection of Phytophthora spp. three samples were randomly collected per treatment at end of production cycle: nursery of origin, pot volume and plant collapse state (not collapsed, collapsing and collapsed), making a total of 45 samples. Each sample consisted of five sub-samples of roots from different plants and different areas of clod collected in the same tunnel. The samples were kept moist at room temperature until their analysis in laboratory. After incubation in water for up to a week and observation with a stereo microscope it was found that all plants collapsing or collapsed were infected with Phytophthora spp. Long-canes with symptoms of collapsing showed the highest percentage of infection, a phase where water and nutrients assimilation by roots is high. In collapsed plants Phytophthora spp. was always found, however, with a slower percentage of infection, most probably because the roots were already heavily degraded or dead. In symptomless plants, only five samples were positive for the presence of Phytophthora spp. Results showed that long-cane collapse is strongly associated to infection of the root system by Phytophthora spp., however, it is necessary to consider other factors which induce stress to long-canes, such as high temperatures in summer (35 to 40°C), the excess of cooling hours during cold storage (more than 1000 h) and the conditions of growth and development of tray plants and primocanes in nursery (compass, vessel volume, watering, fertilization, etc.). Pot volume had no clear effect on the infection.
Roque, M.F., Diogo, E., Mota, M. and Oliveira, P.B. (2023). Importance of determining infection by Phytophthora spp. in raspberry collapses in long-cane system. Acta Hortic. 1381, 157-162
DOI: 10.17660/ActaHortic.2023.1381.21
decline, disease, root rot, oomycete, growth development

Acta Horticulturae