Abstract:
Sugarcane smut caused by Sporisorium scitamineum is a devastating disease of sugarcane.
Production of smut-resistant varieties is one of the major objectives in sugarcane breeding
programs in almost all sugarcane-producing countries including Sri Lanka. Since no adequate
scientific information is available, this research was aimed to get an insight on the genetic
variability of sugarcane smut pathogen in Sri Lanka in order to support an effective breeding
program for sugarcane smut disease. The genetic diversity of 83 Sporisorium scitamineum isolates
was comprehensively evaluated in this study. The isolates were collected from 15 different
sugarcane varieties that were grown in seven major sugarcane growing areas of Sri Lanka.
Genomic DNA extracted from the fungal colonies originating from diploid teliospores were
subjected to PCR using bE4 and bE8 specific primers and ITS 4 as well as ITS 1 universal primers.
PCR products were sequenced. Sequence results using both primers showed 99% sequence
similarity among the isolates. Using 16 ISSR primers, we used the inter-simple sequence repeat
(ISSR) polymorphism molecular marker approach. The ISSR primers produced 104 amplified DNA
fragments that are 100% polymorphic. The polymorphic information content (PIC) values ranged
from 0.25 to 0.46 with an average of 0.37, indicating that the collected isolates exhibit a moderate
degree of genetic diversity. Genetic differentiation coefficient (Gst) was estimated to be 0.241,
meaning that only 24% of the total genetic variation originates between populations, while 76%
originates within populations. Gene-flow (Nm) was calculated as 1.572, indicating that gene flow
across populations occurs at a faster rate. The collected isolates clustered into five genetically
distinct groups which did not correspond to their geographical origin. The result of this study
suggests that considerable genetic variation exist among isolates collected from major sugarcane
growing areas in Sri Lanka. Therefore, it is suggested to use a mixture of sugarcane smut isolates
collected from all sugarcane growing areas when screening for smut-resistant sugarcane varieties
for the industry in Sri Lanka to address different adoptive potentials of the isolates.
