Efficacy of Plant Extracts in Controlling Seed Fungal Infections and Enhancing Germination of Annual Wi̇ld Ri̇ce: Oryza nivara in Sri̇ Lanka

Abstract

Wild genetic resources of rice play a crucial role in improving climate-resilient rice. Among them, Oryza nivara is closely related to the cultivated rice. Poor germination ability, prolonged time for germination followed by fungal infections, uneven germination, and strong dormancy are certain practical constraints in adopting O. nivara seeds in research programs. This study aims to assess the antifungal effects of plant leaf extracts on reducing fungal infections and improving the germination percentage of O. nivara seeds. Four aqueous plant extracts from fresh leaves of Zingiber zerumbet, Guava (Psidium guajava L.), Cinnamon (Cinnamomum verum), and Cassia alata, with the 1:1 (100 g leaf crushed in 100 ml water) and 1:2 (100 g leaf crushed in 200 ml water) in 15 min, standard fungicide solution (S) (2gL^-1 of Manganese ethylene-bis-dithiocarbamate), a control using distilled water (C), have been employed with a total of 16 treatments. The experiment was conducted in a completely randomized design with 10 seeds per replicate and 3 replicates for one treatment. Husked and dehusked seeds were treated for 24hr, incubated at 36 °C, and assessed every two days. Optimal germination occurred after 10 days. Data were analysed using one-way ANOVA (p<0.05) and Tukey's HSD test. Seeds with husks failed to germinate and showed no fungal contamination, with all treatments showing that dehusking is compulsory to induce germination. The best germination % was recorded in treatments with both ratios of Zingiber zerumbet (1:1=7.33±0.33^cd; 1:2=8.00±0.0^d) and Cinnamon 1:2 (7.33±0.33^cd) compared to the control (C) and standard (S) (C=5.33±0.33^b and S=6.67±0.33^c), respectively. The least germination rates (1:1=2.67^a±0.33 and 1:2=2.00±0.0^a) were observed in C. alata treatments, inferring negative effects on germination. Moreover, Z. zerumbet (1:1 and 1:2), P. guajava L. (1:1), and C. verum (1:1) exhibited the lowest fungal infection, while C. alata (1:1) demonstrated the highest mean fungal seed infection (7.33±0.33^d) than the control (C=3.00±0.0^c) and the standard (S=1.00±0.58^b). Z. zerumbet bioactive compounds, especially zerumbone, enhanced antifungal activity and seedling growth. Additionally, C. alata exhibits allelopathic effects that inhibit seed germination. Previous O. nivara germination studies reported low rates of 23.11% (dehusking) and 15.56% (dry heat). Our study achieved significantly higher rates (73.3-80%). Overall, both ratios of Z. zerumbet could be recommended as the best leaf extract to minimize fungal attack while increasing germination ability of O. nivara seeds.

Keywords:  Antimicrobial properties, Aqueous extracts, Microbial infection, Sustainable, Wild rice