Diversity of microorganisms associated with atypical superficial blemishes of potato tubers and pathogenicity assessment

Abstract

Skin blemishes of potato (Solanum tuberosum L.) tubers can cause severe economical losses to production. Some blemishes are due to known pathogens and others whose causes are unknown are called atypical blemishes. The present work aims at determining the origin of superficial atypical blemishes on a set of 204 tubers coming from 12 different French regions producing potato. The diversity of fungi and Streptomyces bacteria associated with blemishes was investigated by systematic isolation followed by identification by sequencing the internal transcribed spacer of the ribosomal DNA for fungi and by sequencing the 16S ribosomal DNA for bacteria. We found a high microbial diversity represented by 349 fungal isolates belonging to at least 47 different species and 21 bacterial strains of Streptomyces sp. The most represented fungi belonged to the genera Fusarium, Rhizoctonia, Alternaria, Penicillium, and Clonostachys. The pathogenicity of representative isolates was assessed in three bioassays; two bioassays based on single inoculations in previously sterilized potting mixture, and one bioassay based on both single and double inoculations under hydroponic conditions. We fulfilled the Koch's postulates for Rhizoctonia solani AG 3 producing sclerotia. For other fungal and bacterial strains, our results did not show any causality or relationship between a single isolate or a complex and the occurrence of the blemishes. Moreover, the observation of irregular polygonal sunken corky lesions (polygonal lesions)-the most frequent atypical blemish-on non-inoculated tubers, suggested that the atypical blemishes could as well be a reaction of the plant to stressful environmental conditions.

Mechanisms and recent advances in biological control mediated through the potato rhizosphere

“…The fungal genera Alternaria, Clonostachys, Fusarium, Penicillium and Rhizoctonia are cited to be commonly encountered in both the rhizosphere and the geocaulosphere of potato (Pieta & Patkowska, 2003; Fiers et al , 2010), and >60 bacterial genera have been identified by culture‐dependant methods in different potato cultivars (Table 1). Three genera, known to mainly contain rhizobacteria species, were consistently identified in each microenvironment: Agrobacterium, Bacillus and Pseudomonas .…”

Seed Potato Production Practices and Quality of Farm Saved Seed Potato in Kiambu and Nyandarua Counties in Kenya

“…Detection of dry rot (Fusarium spp.) and black scurf (Rhizoctonia solani) was done using methods described by [26] and [27] respectively. Three seed tubers per sample were randomly drawn and washed under running tap water.…”

“…Highly viable seed and soil borne inocula of Rhizoctonia solani are carried in the soil or in infected tubers leading to spread of the disease [17,60,61]. Seed tubers infected with dry rot, black scurf and other fungal pathogens causes high storage losses through rotting and reduction in marketability of the ware potato due to formation of blemishes on skin of tubers [26,59,62].…”

Ocorrência de Alternaria alternata (Fr.:Fr.) Keissl. em tubérculos de batata, no Brasil

“…Originária dos Andes e considerada uma das quatro principais espécies cultivadas, a batata (Solanum tuberosum L.) é a base da alimentação da população de diversos países e culturas (Fiers et al 2010).…”

“…Apesar de o fungo A. solani, geralmente, ser retratado como o agente causal da pinta preta (Yanar et al 2011, Leiminger & Hausladen 2012, Weber & Halterman 2012, outras espécies do gênero também podem estar associadas à doença, como A. alternata (Cwalina-Ambroziak & Bogucka 2012) e A. grandis (Rodrigues et al 2010).…”