Characterization of a Phytoplasma Associated with Frogskin Disease in Cassava

Abstract

Cassava frogskin disease (CFSD) is an economically important root disease of cassava (Manihot esculenta) in Colombia and other South American countries, including Brazil, Venezuela, Peru, Costa Rica, and Panama. The roots of severely affected plants are thin, making them unsuitable for consumption. In Colombia, phytoplasma infections were confirmed in 35 of 39 genotypes exhibiting mild or severe CFSD symptoms either by direct or nested polymerase chain reaction (PCR) assays employing ribosomal (r)RNA operon primer pairs. The CFSD-associated phytoplasmas were identified as group 16SrIII strains by restriction fragment length polymorphism (RFLP) and sequence analyses of amplified rDNA products, and results were corroborated by PCRs employing group 16SrIII-specific rRNA gene or ribosomal protein (rp) gene primers. Collectively, RFLP analyses indicated that CFSD strains differed from all phytoplasmas described previously in group 16SrIII and, on this basis, the strains were tentatively assigned to new ribosomal and ribosomal protein subgroups 16SrIII-L and rpIII-H, respectively. This is the first molecular identification of a phytoplasma associated with CFSD in cassava in Colombia.

The underestimated diversity of phytoplasmas in Latin America

“…Such differential distribution of phytoplasmas is probably due to the diversity and preferential distribution of their insect vectors. While some leafhopper vectors of phytoplasma, such as species of Dalbulus, have been detected in all Latin American countries (Nault, 1980(Nault, , 1983, others, such as Amplicephalus curtulus, have been detected only in Chile and Colombia (Alvarez et al, 2009;Arismendi et al, 2014).…”

Cleaning cassava genotypes infected with cassava frogskin disease via in vitro shoot tip culture

“…Other biotic constrains, such as mites, insects, and many diseases as root rot, cassava bacterial blight, Cassava vein mosaic virus (CsVMV), Cassava common mosaic virus (CsCMV), and cassava frogskin disease (CFSD), have caused severe restrictions on cassava production in Latin America (Calvert and Thresh, 2002;López et al, 2006;Carvajal-Yepes et al, 2014;Souza et al, 2014). The CFSD directly affects the starch, root quality and thus crop yield of cassava (Calvert and Thresh, 2002;Alvarez et al, 2009).…”

“…The etiology of CFSD is complex because some authors attribute the disease to different species off viruses, such as Cassava frogskin-associated virus (CsFSaV; Reoviridae/ Oryzavirus), Cassava torrado-like virus (CsTLV; Secoviridae/Torradovirus), Cassava new alphaflexivirus (CsNAV; Alphaflexiviridae/Potexvirus), and Cassava polero-like virus (CsPLV; Luteoviridae/Polerovirus) (Carvajal-Yepes et al, 2014), and also with phytoplasma belongings to the 16SrIII-L (Alvarez et al, 2009;Oliveira et al, 2014) and 16SrIII-A (Souza et al, 2014) subgroups.…”

“…Plants infected with this disease usually have no symptoms on the aerial part; while the tuberous root exhibited a woody appearance, thickened cork-like peel with opaque aspect, and coalescent lip-like slits in a honeycomb pattern; whereas severe affected plants do not show formation of tuberous roots, due to the abscence of starch accumulations (Calvert and Thresh, 2002;Alvarez et al, 2009;Carvajal-Yepes et al, 2014). Calvert and Thresh (2002) pointed out that, in some situations, certain genotypes of cassava mosaic symptoms can develop on leaves and stems near the ground can be slightly swollen.…”

“…Controlling CFSD involves the removal of diseased plants, the sanitization of tools with sodium hypochlorite, the use of healthy cuttings, the establishment phytosanitary quarantine and the adoption of measures to prevent its spread, especially to areas free of the disease (Calvert and Thresh, 2002;Alvarez et al, 2009). As cassava is a vegetatively propagated plant, the accumulation of phytoplasma and/or virus in cuttings is recurrent, resulting in losses in root yield that can reach 90% (Alvarez et al, 2009) and, in extreme cases, 100% (Oliveira EJ, unpublished results).…”