Métodos de detecção de Leifsonia xyli subsp. xyli e efeito da termoterapia na brotação das gemas de diferentes variedades de cana-de-açúcar

Ratoon stunting disease [Leifsonia xyli subsp xyli (Lxx)] is one of the main diseases of sugarcane and it is of difficult detection in the field. Its spread to uninfected plants and into new areas occurs exclusively through contaminated planting material or mechanically. Thermotherapy at a 52oC/30 min regime is broadly employed in Brazil for producing healthy seed cane. Another recommended regime (50oC/2h) has not been commonly used in Brazil. The purposes of this research were to examine the efficacy of different methods of detection of Lxx in 4-9 months-old plants in cane varieties having different periods of maturity and the effect of thermotherapy (50oC/2h) on bud germination including a consideration on the location of individual buds in the stalks. Microscopy was the best method allowing the detection of Lxx in plants of all ages whereas identification of Lxx in infected plants through dot blot and PCR methods, performed according to published protocols, failed for all treatments. A modification of the dot blot test involving the use of concentrated cane sap was successful in improving the method, allowing the identification of Lxx in infected nine-month old plants. Thermotherapy at a regime of 50oC/2h did not completely eradicate Lxx from infected planting material. This regime was harmful for the germination of buds in var. RB935744 but not for vars RB855156 and RB867515. It increased the percentage of germination of basal buds of RB867515 and decreased that of apical and mid length buds of RB935744.