Molecular diagnosis of super elongation disease in field and laboratory grown cassava (Manihot esculenta Crantz) plants
Keywords:Cassava, gibberellin A4, super-elongation disease, Bermuda grass
AbstractThe fungal pathogen Sphaceloma manihoticola Bitanc. & Jenkins produces large amounts of gibberellin GA4 during the late stages of Super-elongation disease (SED) in infected cassava plants, due to the expression of the Smp450-2 gene. Laboratory grown cassava plants were inoculated with a suspension of S. manihoticola; DNA was extracted over a 21-day period and then amplified via PCR using SPM primers designed from the Smp450-2 gene. In laboratory grown cassava, late stage SED symptoms were not observed. However, SPM primers were able to amplify a 602bp DNA fragment extracted from both laboratory grown and field cultivated cassava plants; although late stages of SED were not observed in planta. In addition, field grown cassava displaying differential SED symptoms such as cankers on stems and necrotic leaf lesions, produced variations in band intensities when DNA from these tissues was amplified with SPM primers. Therefore, this method may be used to diagnose and measure disease severity in cassava showing symptoms of SED. Assessment of disease severity in cassava by use of molecular markers is important in management of local planting material and in continuous assessment of SED tolerant varieties of cassava which are widely distributed in the Caribbean region. Moreover, the presence of S. manihoticola in infected plant tissues was also detected by these primers targeting the gene AM 886290.1 of S. manihoticola in the grassy weed Bermuda grass (Cynodon dactylon L).