The extracts of Oxalis barrelieri and Cymbopogon citratus were tested for their antifungal activity against Bipolaris oryzae and Fusarium moniliforme, and use as seed treatment coupled with NaCl treatment to improve the seed germination and the seedlings vigor of treated rice seeds. The significance of the inhibitory activity of the plant extracts against B. oryzae and F moniliforme was type of extract and concentration dependent. The ethanolic extract of C. citratus at 10000 ppm, showed the highest inhibitory effect, with 58.51 and 55.9% growth inhibition of F. moniliforme and B. oryzae, respectively. The rice seeds sorted in 20% NaCl solution had a greater mass (quantify), a germination percentage of 12.5% higher as compared to seeds sorted in with water and 19.5% higher than that of unsorted seeds. A moderate positive and significant linear relationship (Rho (78) = 0.427 **, p <0.01) was shown between weight and germination of rice seeds. The ethanol extracts of O. barrelieri and C. citratus stimulated rice seed germination at comparable degree; 15.15 to 22.06% from the top of paper method and 11.1 to 16.2% from sand method in green house trials. Rice seed treatments at 1% concentration exhibited the best germination and reduced the infestation of B. oryzae and F. moniliforme by 25.25 and 9.83%, respectively. Stressed seeds treated with plant extracts showed less pronounced decrease (5.08 %) in germination compared to untreated stressed seed (25.5%). Sorting of rice seeds with 20% NaCl and/or treatment with ethanol extracts of O. barrelieri and C. citratus showed potential green alternative to reduce seed-borne infestation, improvement of rice vigor and seed germination.

Tomato (Lycopersicon esculentum Mill.) is the most consumed vegetable in the world after potato. In Cameroon, the plant is cultivated in almost all agroecological areas, however, yields remain low due to attacks by various pathogens and insects. Among the pathogens, Fusarium oxysporum f.sp. lycopersici (FOL) is a phytopathogenic fungus responsible for Fusarium wilt, a disease responsible for enormous economic losses. To contribute to the control of this microbial pathogen, the stimulatory effect of the tomato defence system of extracts of some plants in the tomato/FOL interaction was evaluated. Tomato plants were treated with the aqueous extracts (AE) of Callistemon citrinus (C. citrinus), Cymbopogon citratus (C. citratus), and Oxalis barrelieri (O. barrelieri ). After 4 days of spraying with the extracts, the plants were inoculated with a virulent strain of Fusarium oxysporum f.sp. lycopersici (FOL) under controlled conditions. Tomato roots were used to determine the contents of hydrogen peroxide (H2O2), phenols and malondialdehyde (MDA). The activities of the main antioxidant enzymes were also evaluated in tomato roots: catalase (CAT), phenylalanine ammonia lyase (PAL), peroxidase (POX) and superoxide dismutase (SOD). The results showed that treatment of tomato plants with plant extracts and their infection with FOL induced an increase in the contents of H2O2, phenols and MDA in tomato roots; an increase in PAL, POX, SOD activities and a reduction in CAT activity. Our results suggest that the increase and reduction of enzymatic activities, and the increase in the synthesis of some metabolites could mitigate the oxidative damage that takes place during the expansion of the pathogen. Aqueous extracts of C. citrinus, C. citratus and O. barrelieri at 10% (W/V) could be used as natural products to stimulate the tomato defence system against FOL. These results could contribute to the development of natural products to induce tomato resistance against FOL, thus improving productivity, quantity and quality of production.

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