Molecular identification and pathogenicity of Rhizoctonia spp. from tobacco growing areas in northwestern Argentina

Abstract

In Argentina, more than 60 % of the tobacco crops are grown in the northwestern part of the country and where Rhizoctonia solani leads to a reduction in crop yield and quality. In this study, 35 isolates of Rhizoctonia were obtained from 32 tobacco fields in northwestern Argentina and characterized by both morphological and molecular approaches. Based on the variability in the ITS region, isolates were identified as R. solani (80 %), Waitea circinata var. zeae (Rhizoctonia zeae) (8 %) and binucleate Rhizoctonia (8 %). Most isolates of R. solani belonged to the anastomosis groups (AGs) AG 4 HG-I (44 %), AG 2-1 (41 %) and AG 4 HG-III (13 %). Isolates of binucleate Rhizoctonia belonged to AG-F and AG-P of Ceratobasidium sp. Morphological variability was higher within isolates of AG 2-1 and AG 4 HG-III than within those of AG 4 HG-I. Aggressiveness of the isolates towards tobacco seedlings was assessed in the greenhouse.Isolates of AG 2-1 were the most aggressive on leaves, causing target spot, whereas isolates of AG 4 HG-I were the most aggressive on stems and roots, causing damping-off.

Molecular identification and pathogenicity of Rhizoctonia spp. recovered from seed and soil samples of the main bean growing area of Argentina

“…There are reports of AG 2-1 and AG 7 isolates causing disease in tobacco and cotton (Bacharis et al, 2010;Mercado-Cárdenas et al, 2012), but not on bean plants, as we observed under controlled environment conditions. Moreover, AG 2-1 isolates were found to be associated with damping-off, target spot, and sore shin in tobacco in the same area (Mercado-Cárdenas et al, 2015). Fifty-three and 47% of the Rhizoctonia solani isolates were obtained from seed and soil samples, respectively, suggesting that both, seed and soil-borne inoculum may play a significant role in pathogen dispersal in the region, as reported in other areas worldwide (Naseri and Mousavi, 2015).…”

“…AG 4 isolates have also been reported to be associated with web blight in common bean (Gálvez et al, 1989;Tu et al, 1996;Godoy-Lutz et al, 2003Yang et al, 2007;Dubey et al, 2014). Moreover, R. solani AG 4 can attack other commercial crops including maize and tobacco (Bacharis et al, 2010;Mercado-Cárdenas et al, 2015), which are grown in rotation with bean in northwestern Argentina. Isolates identified as R. solani AG 4 HG-I and AG 4 HG-III were obtained from tobacco plants with sore shin and damping-off symptoms in different fields in the Lerma Valley, Salta province (Mercado-Cárdenas et al, 2015).…”

“…Moreover, R. solani AG 4 can attack other commercial crops including maize and tobacco (Bacharis et al, 2010;Mercado-Cárdenas et al, 2015), which are grown in rotation with bean in northwestern Argentina. Isolates identified as R. solani AG 4 HG-I and AG 4 HG-III were obtained from tobacco plants with sore shin and damping-off symptoms in different fields in the Lerma Valley, Salta province (Mercado-Cárdenas et al, 2015). The use of non-host crops in rotational systems may lead to improved control, thus reducing the incidence of bean root rot.…”

Soil properties related to suppression of Rhizoctonia solani on tobacco fields from northwest Argentina

“…Crop losses of 15% were recorded worldwide from damping off and root rot, and leaf target spot led to a reduction in tobacco yield of 5% (Nicoletti et al , ). R. solani is a component of the soilborne microbial complex that causes yellowing and drying of tobacco plants in northwest Argentina (NWA) and is responsible for a 20% reduction of tobacco production in affected fields (Mercado Cárdenas et al , ). Tobacco is one of the most important agricultural crops for this agro‐ecological area, with over 52% of Argentinean tobacco grown in Salta and Jujuy provinces with a mean yield of 2312 kg ha −1 (Miniagri, ).…”

“…Recently, morphological and molecular approaches have identified and characterized the R. solani AGs that infect tobacco plants in NWA (Mercado Cárdenas, ). Subgroups AG2‐1, AG4‐HGI and AG4‐HGIII were found to be predominant in infected tobacco plants (Mercado Cárdenas et al , ). AG2‐1 was associated with leaf target spot and AG4 produced damping off and root rot diseases, with the subgroup AG4‐HGI being more aggressive than AG4‐HGIII.…”