there was no phytotoxic effect influenced by An and Ba Eos on plants and garlic production.
3.5. Field study
Differences between the initial and final sclerotia density in each treatment were calculated. Significant differences within the slopes (1) of the lineal regression of each treatment equation were analyzed (Table 5). The treatment Ip (0.6 L/L Ip) was no different from the control treatment, showing the highest slopes. This result confirmed that there was no effect of the synthetic fungicide on the production of sclerotia by the fungi. Minambres˜ et al. (2010) found that Ip had no effect on soil sclerotia density. Similar effects were observed for An (600 and 900 L/L) and Ba (600 L/L); no significant differences were found between these samples. According to their slopes, moderate sclerotia inhibition was shown by An and Ba (600 L/L) when combined with Ip (0.6 L/L). However, the best sclerotia inhibition was observed in the combinations of An or Ba (900 L/L) with Ip 0.6 L/L. These combinations not only showed the lowest slopes of sclerotia production but also confirm the synergistic effect of these EOs with Ip.
In addition, the antifungal effect of each treatment on white rot progress was evaluated by calculating area below the disease progress curve (ABDPC) (Table 5). Significant differences were found in ABDPC for all treatments (p < 0.05). The highest values observed were for the control and Ip samples. The combinations Ip with An (0.6 L/L + 900 L/L) and Ip with Ba (0.6 L/L + 900 L/L) had the lowest ABDPC values, being significantly different to the rest of the samples. All other treatments showed intermediate ABDPC values. Our results are in accordance with those observed by Zewide et al. (2007), who reported lower ABCDPC and sclerotia density in garlic crops treated when a synthetic fungicide was applied to the soil.
4. Conclusion
The management of plant diseases with natural compounds is highly needed nowadays. The results of this study evidence that the antifungal power of non-phytotoxic EOs can be used to reduce doses of synthetic compounds that are applied to garlic crop. Anisillo and bay EOs have both moderate antifungal activity but no phytotoxic effect. Moreover, some combinations of these EOs with Ip can reduce the fungicide dose by up to 40% due to the synergistic interactions taking place. Therefore, these EOs are a novel alternative to control “white rot” caused by S. cepivorum and can be applied with Ip not only to reduce the amount of chemical fungicide in the soil, but also to reduce the disease incidence and the sclerotia density after white rot disease. Moreover, the persistence of fungicides and the amount of money spent on them can be reduced. Future studies are needed to adjust the applied concentrations