In vivo antibacterial activity against 'Rhizobium vitis' and the induction of defense-related genes in grapevines ('Vitis' spp.) by hairy vetch and ryegrass extracts

Water based crude extracts from hairy vetch ('Vicia villosa') and ryegrass ('Lolium perenne') were investigated for their antimicrobial activity against Rhizobium vitis, the causal agent of crown gall of grapevine ('Vitis spp.'), in a greenhouse. A total of 100 ml of each extract (125, 250 and 500 g L-1) prepared from fresh and pounded shoots and roots was applied to grapevine cuttings once every 10 days. The shoot and root extracts displayed remarkable in vivo antibacterial effects, as indicated by reductions in gall formation by R. vitis of 24.97% to 75.02% in 'Kyoho' (susceptible to crown gall) and 100% in 'Campbell Early'(moderately resistant to crown gall) grapevines compared with the untreated control. The expression of several defense-related genes was investigated by quantitative real-time and semi-quantitative RT-PCR in two grapevine cultivars. Treatment with the extracts of hairy vetch and ryegrass led to differential induction of the accumulation of defense-related genes including beta-1,3-glucanase (PR-2), phenylalanine ammonia-lyase (PAL), thaumatin-like protein (TLP), leucine reach-repeat (LRR), polygalacturonase inhibiting protein (PGIP), stilbene synthase (STS) and catalase (CAT). Expression analysis of defense related genes revealed noticeable differences between 'Kyoho' and 'Campbell Early' grapevines. Based on these results, extracts from tested cover crops can act as efficient biological inducers and therefore serve as an alternative strategy for grapevine crown gall protection.