Further evidence of the association of a phytoplasma and a virus with yellow leaf syndrome in sugarcane

Using the polymerase chain reaction (PCR), reverse-transcriptase–PCR (RT–PCR) and double-antibody-sandwich enzyme-linked immunosorbent assay (DAS–ELISA), a phytoplasma (sugarcane yellows phytoplasma, ScYP) and a virus (Sugarcane yellow leaf virus, ScYLV) were detected in sugarcane with yellow leaf syndrome (YLS) in Mauritius. Samples were collected from clones undergoing quarantine, in a variety-collection plot and in commercial fields. A 1·25 kb DNA fragment encoding the phytoplasma 16S rRNA was consistently amplified by nested PCR. Of 134 samples with and without symptoms derived from 113 varieties, 111 were infected by either ScYLV or ScYP. The phytoplasma was detected in 63 samples by PCR. Restriction fragment-length polymorphism (RFLP) analysis of the phytoplasma 16S rDNA amplified product indicated that sugarcane yellows phytoplasma group III, which is related to Western X phytoplasma, is present in Mauritius. ScYLV was detected by RT–PCR and ELISA. The virus was more widely distributed than the phytoplasma, and was found in 70 and 100 samples by ELISA and RT–PCR, respectively. There was a significant correlation between the presence of the phytoplasma and YLS symptoms, while such correlation was not significant for ScYLV detected by RT–PCR. ELISA was less sensitive than RT–PCR for detection of ScYLV. Forty-one samples were coinfected with both microorganisms. Eighty-five per cent of the samples displayed symptoms when ScYLV and SCYP coexisted, while 55 and 38% were observed when ScYP or ScYLV, respectively, was present alone. The results indicate that the presence of both organisms enhanced the syndrome.