Role of Trehalose Synthesis in Ralstonia syzygii subsp. indonesiensis PW1001 in Inducing Hypersensitive Response on Eggplant (Solanum melongena cv. Senryo-nigou)

Ralstonia syzygii subsp. indonesiensis (Rsi, former name: Ralstonia solanacearum phylotype IV) PW1001, a causal agent of potato wilt disease, induces hypersensitive response (HR) on its non-host eggplant (Solanum melongena cv. Senryo-nigou). The disaccharide trehalose is involved in abiotic and biotic stress tolerance in many organisms. We found that trehalose is required for eliciting HR on eggplant by plant pathogen Rsi PW1001. In R. solanacearum, it is known that the OtsA/OtsB pathway is the dominant trehalose synthesis pathway, and otsA and otsB encode trehalose-6-phosphate (T6P) synthase and T6P phosphatase, respectively. We generated otsA and otsB mutant strains and found that these mutant strains reduced the bacterial trehalose concentration and HR induction on eggplant leaves compared to wild-type. Trehalose functions intracellularly in Rsi PW1001 because addition of exogenous trehalose did not affect the HR level and ion leakage. Requirement of trehalose in HR induction is not common in R. solanacearum species complex because mutation of otsA in Ralstonia pseudosolanacearum (former name: Ralstonia solanacearum phylotype I) RS1002 did not affect HR on the leaves of its non-host tobacco and wild eggplant Solanum torvum. Further, we also found that each otsA and otsB mutant had reduced ability to grow in a medium containing NaCl and sucrose, indicating that trehalose also has an important role in osmotic stress tolerance.

Identification and pathogenicity of Fusarium spp. associated with tuber dry rot and wilt of potato in Algeria

Fusarium is one of the most important genera of phytopathogenic fungi, causing potato wilt in the field and potato tuber dry rot during storage. The objectives of this study were to identify Fusarium species associated with both potato diseases in different growing regions in Algeria, and to assess their pathogenicity. Among the 152 isolates collected from symptomatic potato plants and tubers in different provinces in Algeria, 13 species of Fusarium and Neocosmospora were identified. Among these three species were isolated only from plants showing symptoms of Fusarium potato wilt (F. oxysporum, F. venenatum, Neocosmospora solani). Two species (F. culmorum, N. tonkinensis) and an isolate of Neocosmospora sp. were found exclusively in tubers with potato dry rot and the remaining ones (F. redolens, F. cf. tricinctum, F. sambucinum, F. cf. incarnatum-equiseti, F. nygamai, F. brachygibbosum and N. falciformis) were associated with both sample types. Fusarium sambucinum was the most frequent species (52.6% of isolates). Fusarium oxysporum and F. nygamai isolates were the most aggressive in the potato wilt pathogenicity test, and F. sambucinum isolates were the most aggressive in the potato tuber pathogenicity test. This is the first study identifying and characterizing potato dry rot and potato wilt pathogens in Algeria.

Вредоносность патокомплекса Fusarium – Alternaria в посадках картофеля

Статья посвящена описанию особо опасной болезни картофеля сопряженному трахеомикозному увяданию, вызываемому патокомплексом грибов родов Fusarium и Alternaria на фоне контрастных метеоусловий: обильные осадки (две декады) и засушливые условия (две декады). Заболевание ведет к критическим потерям урожая картофеля. Защитные мероприятия против данного заболевания картофеля должны сочетать нормированное орошение при установлении засушливой погоды не менее 710 суток с применением смесей биопрепаратов и органоминеральных удобрений.The paper is devoted to very dangerous potato disease combined potato wilt caused with pathocomplex of fungi from genera Fusarium and Alternaria on the base of contrasted meteorological conditions: strong rains (during two decades) and dried conditions (during also two decades). The disease leads to crucial potato yield loss. Protective measures against this disease should include scheduled irrigation at dried weather not less than for 710 days with application of mixtures of biopreparations and organic mineralized fertilizers.