LAUSR

Sugarcane white leaf (SCWL) is one of the major sugarcane diseases in the Asian continent associated with phytoplasmas. It occurs in all sugarcane-growing areas of Sri Lanka, causing substantial economic losses. However, subgroup level identification has been not reported so far for the phytoplasma strains associated with this disease in Sri Lanka. In the present study, the geographical distribution of phytoplasma strains associated with SCWL in Sri Lanka, identification of their weed reservoirs and ribosomal subgroup analysis based on phytoplasma 16S rRNA gene were carried out. A total of 27 SCWL samples representing six main sugarcane-growing areas of Sri Lanka and six samples of two grass species (Cynodon dactylon and Brachiaria distachya) showing putative symptoms of phytoplasma were analyzed. A nested PCR product of 1.2 kb size was consistently amplified in all the symptomatic samples with primers amplifying the 16S rRNA gene. A higher level of sequence identity from 99.03 to 100% was shared among the 16S rRNA gene sequences of all tested SCWL phytoplasma strains. Both Bermudagrass white leaf (BGWL) and Brachiaria grass white leaf (BraWL) phytoplasma strains shared 97.5–98.1% identity of their 16S rRNA gene with SCWL strains. The 16S rRNA gene sequence comparisons and virtual RFLP analysis of SCWL, BGWL, and BraWL phytoplasma isolates allowed their affiliations with ‘Candidatus Phytoplasma sacchari’ (16SrXI-B subgroup) with SCWL and ‘Ca. P. cynodontis’ (16SrXIV-A subgroup) with the grasses samples. The phytoplasma subgroup 16SrXI-B was identified as the most widespread SCWL phytoplasma subgroup in commercial sugarcane varieties in Sri Lanka.