Characterization of Fungi Associated with Olive Fruit Rot and Olive Oil Degradation in Crete, Southern Greece

Abstract

In November 2019, a severe outbreak of fruit rot was observed in olive orchards in Crete, southern Greece. Symptoms appeared primarily on fruits and stalks, resembling those caused by anthracnose. Typical symptoms were fruit rot, shrinkage and mummification, associated commonly with stalk discoloration and fruit drop. Disease incidence was estimated up to 100% in some cases and an unprecedented increase in olive oil acidity reaching up to 8% (percentage of oleic acid) in severely affected olive groves was recorded. Thirty-two olive groves were then surveyed, and samples of fruit, stalk, leaf and shoot were collected. Visual, stereoscopic and microscopic observations revealed several fungi belonging to the genera Alternaria, Botryosphaeria, Capnodium, Colletotrichum, Fusarium and Pseudocercospora. Fungal infection in fruits was commonly associated with concomitant infestation by the olive fruit fly Bactrocera oleae along with increased air temperature and relative humidity conditions that prevailed in October-November 2019. Twenty representative fungal strains isolated from symptomatic fruits and stalks were characterized by morphological, physiological and molecular analyses. By rDNA-ITS region and EF1-α gene sequencing analysis, these isolates were identified as Alternaria spp., A. infectoria, Botryosphaeria dothidea, Colletotrichum boninense sensu lato, Fusarium lateritium, F. solani species complex and Stemphylium amaranthi. Pathogenicity tests on punctured fruits revealed that all isolates were pathogenic; however F. solani isolates along with B. dothidea were the most virulent and wounds were necessary for efficient fungal infection. Moreover, as little as 10 spores of F. solani were sufficient of causing significant infection in punctured fruits. Fusarium solani was also capable of infecting olive fruits in the presence of B. oleae, with no additional wounding, in artificial inoculation experiments. Moreover, it was capable of colonizing and affecting olive blossoms. Further analyses in olive oil extracted from fruits artificially inoculated with F. solani indicated a significant increase in oil acidity, K232, K270 and peroxide value, whereas total phenols content was significantly decreased. To the best of our knowledge, this is the first report of Fusarium solani associated with olive fruit rot and olive oil degradation worldwide.

Rapid real-time quantitative colorimetric LAMP methodology for field detection of Verticillium dahliae in crude olive-plant samples

“…Note that in the previous study the RAPD LAMP assay was evaluated by bare-eye detection of the color change after 60 min of reaction time (Moradi et al, 2014) as opposed to the 35 min required in the case of qcLAMP. In the present study, the non-target pathogens Stemphylium amaranthi, Fusarium lateritium, Colletotrichum boninense, F. solani, Alternaria sp., A. infectoria, Botryosphaeria dothidea and Colletotrichum gloesporioides with frequent presence in olive branches and leaves (Markakis et al, 2021) were not amplified proving the specificity of the present assay (Fig. 2d).…”

Good Agricultural Practices Related to Water and Soil as a Means of Adaptation of Mediterranean Olive Growing to Extreme Climate-Water Conditions

“…Both T1 and T2 treatments gave the lowest yields during 2019. This reflects the great impact of combined pest and disease problems that significantly reduced olive oil production in Crete during that year [35]. Although pest and disease control was not included in the GAPs schedule applied in the present study, yield in T2 was less affected than in T1.…”

First report of the Fusarium arthrosporioides/avenaceum complex causing olive fruit rot in Italy

“…Recently, F. solani and F. lateritium have been reported as causal agents of olive fruit rot in Greece (Markakis et al., 2021), but as far as we know, this is the first report of olive rot caused by F. arthrosporioides/avenaceum in Italy and globally, suggesting that different species belonging to the Fusarium genus can cause fruit rotting and that their specific role remains to be investigated.…”

“…As reported by Yli-Mattila et al ( 2022), these two species, part of the F. tricinctum species complex (FTSC), are not distinguishable morphologically nor by phylogenetic analysis, even based on sequences of multiple marker genes (Lombard et al, 2022). Recently, F. solani and F. lateritium have been reported as causal agents of olive fruit rot in Greece (Markakis et al, 2021), but as far as we know, this is the first report of olive rot caused by F. arthrosporioides/avenaceum in Italy and globally, suggesting that different species belonging to the Fusarium genus can cause fruit rotting and that their specific role remains to be investigated.…”

“…Fruit symptoms on naturally infected olive fruit.Pathogenicity tests were performed using pure cultures of isolate FUS10. Healthy olives were surface sterilised and inoculated with mycelial plugs(Markakis et al, 2021), with or without artificial wounding, while olive fruits inoculated with only sterile PDA plugs served as a control. After inoculation, the fruits were placed in sterile boxes and kept at 25• C and 100% relative humidity.…”