Assessment of Phytoplasma titer variation across white leaf disease severity levels in sugarcane varieties cultivated in four selected regions of Sri Lanka

Abstract

Sugarcane White Leaf Disease (WLD) is one of the major threats to the sugarcane industry in Sri Lanka. This study was conducted to investigate the phytoplasma titer variability of WLD in different sugarcane varieties grown in four different sugarcane growing areas, namely, Pelwatta, Ethimale, Siyambalanduwa and Hingurana in Sri Lanka. Healthy (severity level 0), initial (1-2 white color strips emerge in the leaf lamina), middle (50% of the leaf lamina covered by white color streaks) and severe stages (entire leaf lamina is white colour) were considered as the selected WLD severity levels. Genomic DNA was extracted from the leaf samples using CTAB method. The presence of the causal agent phytoplasma was determined by the standard PCR method using two phytoplasma specific primers (SPP1 and SPP2). The quantification of amplified phytoplasma DNA was evaluated using BlasTaqTm 2X qPCR assay. Almost all four of the examined locations exhibited similar levels of disease severity. The disease incidence level in the four tested locations had a range of 23% to 26%. Among the tested sugarcane varieties in four locations, WLD phytoplasma abundance was significantly higher (P < 0.05) in Ethimale SL 98 2524 with a phytoplasma abundance level of 888344.957 106 254072.449 106 μM, followed by Hingurana, Co 775 with a phytoplasma abundance level of 20.444 106 6.011 106 μM. In Pelwatta, variety SL 00 652 had the significantly highest phytoplasma abundance level of 182.168 106 49.010 106 μM. In Siyambalanduwa the variety SL 10 950 and SL 10 979 were the most susceptible varieties. The lowest abundance levels with no significant differences were observed in varieties of SL 00 354, SL 96 128, SL 10 904 and SL 10 1123. The healthy stage of all the tested varieties recorded a phytoplasma abundance level within a range of 0.000000416 μM to 0.00619 μM. In Ethimale SL 98 2524, Hingurana SL 00 652 and Co 775, Pelwatta SL 00 652 and in Siyambalanduwa SL 10 950 and SL 10 979 were identified as the most susceptible varieties for WLD in terms of phytoplasma titer levels.