Raquitismo-das-soqueiras: métodos de diagnose, influência da idade da cana-de-açúcar para detecção e efeito da termoterapia em dois títulos de Leifsonia xyli subsp. xyli

Abstract

Ratoon stunt (RSD), caused by Leifsonia xyli subsp. xyli (Lxx), is considered the main sugarcane disease for directly affecting yield crop. The disease is disseminated in all cultivars and states of the Country; still, little information under Brazilian conditions is available. The most recommended method in Brazil for RSD control are diagnostic test and thermotherapy of seedcanes. The serological diagnostic test is employed for the conventional billet planting while the PCR-based technique is preferred for the presprouted seedcane (MPB). Two combinations of thermotherapy are employed: 52°C/30min and 50°C/2h, the first higher treatment performance as well as higher failure to eliminate Lxx. Although Lxx titer may affect thermotherapy efficiency more data is sitll necessary on its importance for each of the thermotherapy combination. Also, more information is needed on early Lxx detection when contaminated seedcane is employed. Therefore, this work aimed at the following objectives: (a) determine the thermotherapy efficacy in seedcanes contaminated with different Lxx titer; (b) examine the interaction between sugacane age and Lxx detection; (c) evaluate the efficiency of serological and molecular detection technique on different ages of sugarcane. The experiment was carried out in field with six diseased treatments formed by two untreated ones with two distinct Lxx titer, and four treated with two combinations of thermotherapy and Lxx titer. Data collection started at seventh month after treatment, when sap extraction was possible and after that, monthly. Data showed: (a) thermotherapy was an important measure of RSD control, regardless the sampling age of plants, Lxx titer, and diagnostic technique; (b) both thermotherapy combination showed Lxx elimination failure; (c) Lxx was already detected in seven month plant regardless the Lxx titer; (d) failure of the thermotherapy was identified by both diagnostic techniques.