Elucidating the Use of Refrigeration as a Method for Short-Term Preservation of Urediniospores from the Coffee Leaf Rust Pathogen, <i>Hemileia vastatrix</i> , In Vitro

Coffee leaf rust (CLR), the most devastating disease of arabica coffee (Coffea arabica L.), is caused by Hemileia vastatrix Berk &amp; Br. It is currently impossible to culture the obligate parasite, so methods for preserving urediniospore viability are important for researchers that may not have easy access to sources of inoculum. This study tested the storage of detached, CLR-infected coffee leaves in a conventional refrigerator as a means of preserving the viability of urediniospores for several weeks. Two experiments were conducted to assess the efficacy of the method: one comparing the viability of lab-grown H. vastatrix stored at 4°C and 25°C over the course of 2 weeks and a second experiment comparing the germination rate of samples over 3 weeks using field samples collected from 6 coffee farms on Hawai‘i Island, HI, USA. The results demonstrated that storage of infected coffee leaves at 4°C preserves urediniospores better than storage at 25°C over time, with the mean area under the germination rate curve being greater for the 4°C treatment compared to 25°C (0.851 vs 0.549). The average germination rate across all farms 3 weeks after collection was 45.5%, demonstrating that the method worked equally well with field samples. This H. vastatrix urediniospore preservation method offers a low-cost and simple way to maintain spore viability and extend inoculum availability for up to 3 weeks. This method is particularly useful for researchers that do not have easy access to H. vastatrix urediniospores or have a limited budget.