Preliminary results of herbicidal activity of Salvia spp. against common weeds.

A preliminary study on thirteen Salvia species about the herbicidal activity of their aerial parts exudates for the identification of growth inhibitors with diterpene and triterpene skeletons is reported, as these classes of substances are considered among the lead compounds for new agrochemicals [1]. The selected species were: Salvia namaensis Schinz (a) S. fallax Fernald (b) S. disermas L. (c), S. chamaedryoides Cav. (d), S. confertiflora Pohl. (e), S. x jamensis J.Compton (f), S. buchananii Hedge (g), S. wagneriana Polak (h), S. scabra Linn.fil. (i), S. miniata Fernald (l), S. cacaliaefolia Benth. (m), S. adenophora Fernald (n), S. rutilans Carrière (o). For each species the inhibitory potential against Papaver rhoeas L. was evaluated; commercial seeds of this weed were treated as described in Singh et al, 2005 [2], with DMSO solutions of the exudates at various concentrations (0.2, 0.5, 1.0, 2.0 , 5.0) g/mL. After 1 week, the germinability (%), the seedling growth, the radix length, the cotyledon length, the chlorophyll content [3] were evaluated; all the experiments were conducted in randomized design and were repeated three times. Differences in the activity of various exudates were statistically evaluated using analysis of variance (one-way ANOVA) and Bonferroni’s test. Statistical significance was set at p<0.05. At the exudate concentration of 2.0g/mL, all the tested species significantly differed from the control. h showed the lower anti-germinative activity (30.7%), while d (0.0%), e (0.0%), f (2.7%) showed to be the most active. Among these, the study has primarily been focused on Salvia x jamensis, by evaluating the herbicidal activity of four groups of fractions (a-d) obtained by column chromatography on Sephadex LH20. The germination inhibition was investigated against Papaver rhoeas L. and Avena fatua L., selected as examples of common Dicot and Monocot weeds. Commercial seeds were used for Avena too. ANOVA treatment highlighted that groups c (5.3%, 2g/mL; 0.0%, 5.0g/mL) and d (14.6%, 2g/mL; 0.0%, 5.0g/mL) were the most active against Papaver. The activity of c (3.3%, 2g/mL; 0.0%, 5.0g/mL) was comparable to d (6.8%, 2g/mL; 0.0%, 5.0g/mL) for oat seeds, while it was higher for poppy seeds. Fraction c contained di- and triterpene compounds, previously separated and identified [4]: a new diterpenoid (1: 15, 16-epoxy-cleroda-3-en-7, 10-dihydroxy-12,17; 19,18-diolide), isopimaric acid (2), 14--hydroxy-isopimaric acid (3), 3--hydroxy-isopimaric acid (4), 7,8- dihydrosalviacoccin (5), hautriwaic acid (6) and betulinic acid (7). The activity of these pure compounds was evaluated: 4 (1.6%, 2g/mL; 0.0%, 5.0g/mL, poppy - 26.1%, 2g/mL; 16.2%, 5.0g/mL, oat), 6 (12.3%, 2g/mL; 0.0%, 5.0g/mL, poppy – 22.8%, 2g/mL; 11.8%, 5.0g/mL, oat) and 7 (9.7%, 2g/mL; 0.0%, 5.0g/mL, poppy – 10.3%, 2g/mL; 6.8%, 5.0g/mL, oat) showed comparable activity at the highest level, more against poppy than oat, while 1, 2 and 3 were comparable each other, more against oat than poppy, but had a lower activity. 5 had an intermediate activity. Riferimenti [1] Vyvyan J.R. Tetrahedron, 2002, 58: 1631-1646, [2] H.P. Singh, D.R. Batish, N. Setia, R.K. Kohli. Annals of Applied Biology, 2005, 146: 89-94, [3] H.K. Lichtenthaler Methods in enzymology. 1987, 148: 350-382., [4] A. Bisio, G. Romussi, E. Russo, N. De Tommasi, N. Mascolo, A. Alfieri, M. C. Bonito, C. Cicala Natural Product Communications, 2008.