Limpeza clonal de videira com cancro-bacteriano e sobrevivência de Xanthomonas campestris pv. viticola em tecidos infectados

Abstract

Bacterial canker (Xanthomonas campestris pv. viticola) (Xcv) caused great damage to the grapevine cultivation in the Vale do Submédio São Francisco. In the first paper techniques of in vitro tissue culture in modified Galzy medium (MGM) were studied in order to eliminate Xcv from ‘Red Globe’ grapevine plants. The first experiment aimed to select the ideal length of apex and axillary’s buds for cultivation in MGM; the second to verify the effect of the thermotherapy (38ºC/four weeks) associated to the MGM cultivation; and the third intended to test antibiotics to eliminate Xcv from explants taken from infected grapevines. All plants obtained without contamination in vitro and culture media contaminated were indexed by using the semi-selective culture media nutrient agar-dextrose-yeast extract-ampicilin (NYDAM) followed by a pathogenicity test. The cultivation of 3 mm explants permitted to obtain plants free of bacteria with regeneration 14.3 times higher than 1 mm explants. The thermotherapy of infected plants associated to the in vitro culture did not eliminate the pathogen. The cultivationof 10 mm explants for 40 days in MGM+cefotaxime (300 mg L-1) eliminated Xcv from grapevine plants. The indexation in NYDAM permitted the visualization of specific Xcv growing. The indexation of in vitro regenerated grapevine plants for Xcv infection by using NYDAM medium is an economic and efficient alternative for production of selected plants. It is known that pruning residues of infected plants abandoned in the grapevine plantations are important source of disease primary inoculum and that burning is recommended as control measure. Thus the second paper investigated the survival of Xcv in infected tissues and the use of composting to eradicate Xcv associated with crop residues. Plants of grapevine “Festival’ were inoculated with a mutant resistant to rifampicin Xcv2Rif and at the time they presented high disease severity, fragmented shoots and entire leaves were placed in mesh bags. These bagswere placed on the surface of microplots in experimental area (experiment 1) and inside compost piles of grapevine pruning residues (experiment 2). The survival of Xcv2Rif in grapevine infected tissue was monitored in the culture medium NYDAM + rifampicin (0,1g L-1) + azoxystrobim (0,16 g L-1), at 8 and 10 days intervals from 1 and 2 experiment setting, respectively. In the experiment 1 tissue decomposition was also evaluated and in the experiment 2, pile temperature curves, phenolyc content, and fungi and bacteria antagonistic to Xcv2Rif were analyzed. The pathogen survived in high densities (104 a 106 CFU g-1) for at least 80 days in grapevine-infected tissues on soil surface. Then grapevine-pruning residues are important inoculum source for other plants in the vineyard. The composting process eliminated Xcv2Rif from crop residues in 10 days due to high temperatures in piles, liberation of phenolyc compounds during the process and microbial antagonism. Therefore the composting is a viable and safemethod to manage pruning residues in grapevine plantations without problems of Xcv survival and without losing of an important source of organic matter for the culture.