Abstract
ABSTRACT The aim of the research was to evaluate the effectiveness of thermotherapy by humid heat of nodal segments to reduce the incidence of microbial contaminants in the introduction phase of the in vitro propagation of Bambusa vulgaris. Two independent experiments were carried out in a completely randomized design using a 4 × 2 factorial arrangement, four levels of temperature (25, 30, 40 and 50 °C) versus two treatment time intervals (5 or 10 min). Each treatment was composed of nine replications, corresponding to one single-nodal segment obtained from primary or secondary branches, in sucrose-free Murashige and Skoog medium with half the concentration of salts, supplemented with 6.5 g L-1 agar, 50 mg L-1 citric acid, 50 mg L-1 ascorbic acid, 200 mg L-1 chloramphenicol and 2 mg L-1 N6-benzylaminopurine. Isolation of prevalent mold fungi per repetition was conducted, and identification at genus level obtained from microcultures. The treatments corresponding to 50 °C for 5 or 10 min reduced significantly the fungal contamination that occurred at 11% and 0%, respectively, in nodal segments from primary branches, and 0% and 11%, respectively, in those from secondary ones. Fungi of genera Alternaria, Bipolaris and Curvularia were isolated from both types of segment, and Cladosporium from secondary branches only. The lowest percentages of mycelial growth detected in nodal segments submitted to both binomials demonstrated the effectiveness of the technique to reduce fungal contamination despite negative interference on sprouting.
Highlights
IntroductionBamboo (Bambusa vulgaris Schrad., ex J.C. Wendl.), a plant of the family Poaceae, presents as its center of origin Asia, where the greatest diversity of species is found
Dry or wet heat thermotherapy is a viable option in phytosanitary procedures for the control and/or eradication of fungi transmitted by seeds (MANCINI; ROMANAZZI, 2014). In view of this scenario, the objective of this research was to test the efficacy of humid heat thermotherapy on nodal segments of primary and secondary branches of B. vulgaris to reduce contamination during the introduction phase of the micropropagation of the species, as well as to identify at the genus level the fungi which were expressed as contaminants
Any primary branch sprouted when the secondary ones are formed will be younger than these. If this same phenomenon happens in B. vulgaris, the primary branches would be younger than the secondary ones collected in the same month in which the experiments were installed
Summary
Bamboo (Bambusa vulgaris Schrad., ex J.C. Wendl.), a plant of the family Poaceae, presents as its center of origin Asia, where the greatest diversity of species is found. Studies show the presence of 258 native bamboo species, distributed in two tribes, Olyreae and Bambuseae, and 35 genera in Brazil (FILGUEIRAS et al, 2015). The country stands out for its potential for exploration of the grass because it is the one of the New World countries with the greatest diversity of species but mainly for encouraging the development of its culture through Law 12.484 of 2011 which instituted the National Policy for Incentives for the Sustainable Management and Cultivation of Bamboo – PNMCB (TORRES; HOULLOU; SOUZA, 2016). The largest commercial planting area in the world exceeds 108 km and is distributed among the Brazilian states of Maranhão, Paraíba and Pernambuco (GENEROSO, 2014)
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