Susceptibility of different types of banana planting materials to Panama disease in the Canary Islands

Rhizomes and `bits' have been used traditionally as banana planting materials in the Canary Islands. Since the beginning of the commercial conversion during the early 1990s from cv. Dwarf Cavendish to cv. Grande Naine (both M. Acuminata Colla, AAA), there exists in the Canaries a controversy on the supposed higher susceptibility to Panama disease of in vitro planting materials compared to traditional rhizomes and bits. In this paper were summarized finished research done to clarify this issue (a glasshouse trial using rhizomes, bits and in vitro plants of Dwarf Cavendish and Grande Naine, and a field trial using the same planting materials derived from several clones of Dwarf Cavendish and Grande Naine) and present preliminary results of two on-going trials designed to continue evaluating the behavior of these types of planting materials; in the first trial, bit descendants of nine clones from the INIBAP International Musa Testing Program II (IMTPII) are being used to compare behavior with that of the parental in vitro plants tested earlier in the Program; the second is a field trial of the above-mentioned three types of planting materials cultivated in large containers, using three substrates and several treatments. Results of the glasshouse trial indicated a higher susceptibility of in vitro plants to Panama disease. However, as the trial was conducted under controlled-environment conditions with a low number of experimental units, the results needed further validation. In the field trial of the three types of planting material from different clones and local selections, no significant differences in severity of rhizomes symptoms were found between the types of planting materials tested but there were significant differences among the in vitro planting material derived from local selections; these results are considered non-condusive. However, as field trials usually require several repetitions in order to obtain definite results. Regarding the on-going trials, the preliminary results of the IMTP II bit descendants suggested a similar or slightly higher severity of external symptoms for some clones but less severity for others when compared with the parental in vitro plants used in the IMTP II trial. In the factorial trial, height evolution was used as an indirect measure of disease severity: in vitro plants were significantly shorter than bits and were the first to show external symptoms, at 45-days after transplanting