Podridão vermelha do sisal: progresso da doença em diferentes temperaturas e controle biológico utilizando misturas de bactérias

Abstract

Sisal (Agave sisalana Perrine ex Engelm) is cultivated in the semi-arid regions of Brazil, and has been pointed out as the main hard fiber worldwide and an important source of income for this region. Sisal bole rot disease is the most important disease of this crop, reaching all cultivated areas in Bahia State, Brazil, with average incidences varying between 5 and 40 %. The combination of bacteria selected as potential biological control agents may represent a strategy to control this disease. The effect of temperature on the patossystem Aspergillus niger - Agave sisalana is still unknown. This work aimed to study bacteria and their combination in the control of sisal bole rot disease in plants under field conditions and to study the effect of temperature on growth and sporulation of A. niger and on disease progression. Paenibacillus sp., Bacillus pumilus, Brevibacterium sp., Serratia rubidae, Bacillus sp. (2 isolates) and their combinations presented antagonism against A. niger, significantly inhibiting mycelium growth and spore germination. Under field conditions these bacteria and their combinations promoted a significant reduction in the incidence and severity of bole rot disease, with control efficiency above 70 %. Disease control with the combinations of bacteria was not superior to that obtained with the individual bacterial isolates. The optimum temperature for growth and sporulation of A. niger was 28°C. At temperatures between 24 and 42°C, bole rot disease incidence and plant mortality reached 100 %, while at temperatures between 12 and 18°C, disease incidence varied from 5 to 45 % and disease severity varied from 0.25 to 17.3 %. The pathogen seems to be well adapted to the temperatures of the semi-arid region.