Vegetative development of Plectranthus ornatus Codd under two growth environments, three fertilization doses and in vitro effect of its ethanolic extract on plant pathogenic fungi

Abstract

Looking for alternative methods to control plan pathogens includes, not only to study the effectiveness of plant extracts, but also to evaluate the propagating conditions, to guarantee the supply of enough plant material for the extracts production. To study the effect of light on vegetative development of P. ornatus, an experiment was conducted using shoot-propagated plants, grown in 2 kg poliethilene bags, placed under two environments: transparent-roof canopy and total sun light exposure. In each environment, three doses of a 15-15-15 fertilizer were applied to the plants: 0, 5 y 10 g·plant^-1. Ten plants per treatment and a complete randomized design were used. Evaluations were performed at days 0 and 37 of the following variables: length of main stem, number and length of branches; and at day 45 leaf thickness. The amount of light received was measured at the beginning of the experiment. Secondary metabolite groups were determined and the effect of the ethanolic extract was evaluated on the mycelial growth of the fungi Fusarium oxysporum f. sp. phaseoli, Macrophomina phaseolina and Colletotrichum gloeosporioides. Significant differences were found between environments but not fertilizing doses for branch length and leaf thickness. Alkaloids were higher in plants growing under transparent-roof canopy, while anthraquinones, phenols and flavonoids were higher under total sun light exposure. The three fungi were fully susceptible to 10 % concentration of the plant extract; only C. gloeosporioides was susceptible to 5 and 2.5 % concentration. Results show that P. ornatus plants should be grown under total sun light exposure for a better green mass and MS production.