Antifungal potential of extracts from four plants against Acremonium apii and Colletotrichum dematium, two major pathogens of celery (Apium graveolens L.) in Cameroon

In order to contribute to a sustainable control of plant diseases through the use of natural compounds, the antifungal potential of 11 extracts from 4 Cameroonian plants (Ageratum conyzoides, Callistemon citrinus, Cymbopogon citratus and Ocimum gratissimum) was evaluated in vitro against Acremonium apii and Colletotrichum dematium, respectively the causal agents of brown spots and anthracnose diseases of celery (Apium graveolens L.). Inhibition of fungi mycelial growth by essential oils, ethanol and aqueous extracts was assessed by using the supplemented media technique. Essential oils exhibited comparable activities against both fungi with minimum inhibitory concentration between 400 and 6000 ppm. Essential oil from O. gratissimum showed the highest inhibitory activity against both pathogens (400 ppm) followed by C. citratus (700 ppm and 800 ppm against A. apii and C. dematium, respectively), and then C. citrinus (6000 ppm). Ethanol extracts exhibited after the essential oils, the higher inhibitory activity against the two pathogens. Extract of C. citrinus was the most active with reductions of radial growth of 77.68% and 97.16% respectively against A. apii and C. dematium at 10000 ppm. Aqueous extracts at the same concentrations of ethanol extracts had little or no activity against both fungi. The fungitoxic potential of essential oils was higher than the one of the synthetic fungicide used as positive control. Our results suggest a promising potential of essential oils and ethanol extracts for botanicals control of celery fungal pathogens

Chemical composition, antifungal properties and seed treatment potential of essential oil fractions of Callistemon citrinus against two seed-borne fungi of rice: Alternaria padwickii and Bipolaris oryzae

The use of plant extracts with antifungal effects is a plausible alternative solution which is increasingly attracting the attention of researchers worldwide, to address the multiple limitations associated with the use of synthetic agrochemicals. The antifungal potential of essential oils (EO) fractions of Callistemon citrinus, were investigated in vitro by the supplemented media method against Bipolaris oryzae and Alternaria padwickii, two seed-borne fungi of rice in Cameroon. The EO fractions obtained by hydrodistillation of the plant’s fresh and dry leaves inhibited to varying degrees the mycelia growth of the two pathogens. The EO’s fractions obtained from dry leaves were more active than those extracted from fresh leaves. Fractions of EO showed fungicidal effects, with minimum inhibitory concentrations (MIC) varying between 3616 and 7232 μg/ml. The dry leaves EO fraction DF2 exhibited the strongest antifungal activity (MIC = 3616 μg/ml), followed by the fresh leaves fraction FF2 (MIC = 4520 μg/ml) and the total dry leaves EO DM (MIC = 4520 μg/ml), against B. oryzae. Those fractions (DF2, FF2 and DM) also exhibited the highest MIC (MIC = 4520 μg/ml) against Alternaria padwickii. The GC-SM analysis of EO fractions showed that, the antifungal activity was inversely associated to the content of the major bioactive compound 1,8-cineole; 60.67, 66.36 and 86.39% 86.39%; and proportional to α-terpineol; 13.39, 10.52 and 3.5%; for EO fractions DF2, FF2 and MD DM, respectively. Seed treatment of three of rice varieties with fractions DF2, FF2 and DM respectively at the doses of 1.5, 2 and 3.5%, reduced the seed to seedling transmission rate of B. oryzae by 100% and increased the germination rate of these seeds between 2 and 12%. Our results suggest the use of EO from C. citrinus as biofungicides for the treatment of rice seeds infected with B. oryzae and A. padwickii