Termoterapia e controle biológico para manejo do cancro bacteriano em videira

Abstract

Bacterial canker, caused by Xanthomonas campestris pv. viticola, has been responsible for significant economic losses on the grapevine crop in Brazilian states of Pernambuco and Bahia, located in the São Francisco river Valley. This work evaluated the effect of thermotherapy on cuttings of cultivars Isabel and Red Globe on the viability of plantlets and eradication of X. campestris pv. viticola, and the effect of combination of biological control agents (BCA) and thermotherapy on the pathogen eradication and disease severity reduction. The cuttings were treated at 50, 52 and 54°C during 30, 45 and 60 min, planted, and after 45 days the plantlets were analyzed for growth. The eradication of X. campestris pv. viticola was evaluated at 50 to 52°C and 45, 50 and 60 min by quantifying bacterial populations on cuttings before planting and epidemiological components of bacterial canker, 120 days after planting. Only the temperature of 54°C, mainly during 45 and 60 minutes, affected negatively leaf number, plant height, and length and volume of root system. The bacterial population was reduced in cuttings of both cultivars. No binomial temperature/time was able to eradicate X. campestris pv. viticola, but at 50 and 52°C during 45 to 60 min, canker symptoms on the branches were reduced from 65.5 to 95.9%. To evaluate the combined effect of BCA and thermotherapy, 23 BCA were sprayed on the leaves of 'Red Globe' and 24 h later the pathogen was inoculated. After 40 days, the incubation period and disease severity were evaluated. It was also determined the antibacterial activity of BCA to the pathogen, by testing for antibiotic production, detection of volatile substances, proteases and ammonia. Although not able to eradicate the pathogen, bacterial strains LCB 6, LCB 30, LCB 33, UNEB 27 and RAB 9 (108 CFU/mL), and yeast strains L7, L8 and LF (107 cel/mL) reduced bacterial canker, exhibiting at least one type of antibacterial activity. Two BCA (LCB 6 – Bacillus subtilis and LF - Saccharomyces cerevisiae) were combined with thermotherapy (50 and 52°C for 45, 50 and 60 min). The cuttings were subjected to thermotherapy, followed by immersion during two hours in the suspension of LCB 6 and LF, and the plantlets were sprayed weekly, through 15 weeks. The plantlets were evaluated 120 days after planting. No combination was able to eradicate X. campestris pv. viticola, but some of them reduced the disease severity on leaves and branches. The best results were obtained by combined use of LCB 6 –Bacillus subtilis and thermotherapy at 52°C during 45 min, which is recommended for the integrated management of bacterial canker of grapevine.