Infection Biology of Stagonosporopsis cucurbitacearum in Watermelon and Defence Responses in the Host

Nguyen Thi Thu Nga, Eigil de Neergaard and Hans Jørgen Lyngs Jørgensen ()
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Nguyen Thi Thu Nga: Department of Plant and Environmental Sciences and Copenhagen Plant Science Centre, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
Eigil de Neergaard: Department of Plant and Environmental Sciences and Copenhagen Plant Science Centre, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
Hans Jørgen Lyngs Jørgensen: Department of Plant and Environmental Sciences and Copenhagen Plant Science Centre, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark

Agriculture, 2024, vol. 14, issue 3, 1-15

Abstract: Infection biology and defence responses of watermelon attacked by Stagonosporopsis cucurbitacearum (syn. Didymella bryoniae ) were studied in two genotypes, accessions PI189225 (moderately resistant) and 232-0125/B (susceptible). On intact leaf surfaces, spores started to germinate 14 h after inoculation (hai) with one to three germ tubes, which subsequently developed and formed appressoria. Invasion of the host tissue started at 20 hai by direct penetration from appressoria or occasionally indirectly through stomata. In the susceptible accession, a significantly higher number of direct penetrations were observed than in the moderately resistant. After invasion, hyphal colonisation was restricted in the intercellular spaces in the moderately resistant accession, whereas they developed extensively, causing tissue decay, in the susceptible accession. Macroscopic symptoms were seen in leaves of the moderately resistant accession as small and dry lesions, whereas big, water-soaked lesions developed on the susceptible accession within 48 hai. Investigations of the defence responses of the two accessions showed accumulation of H 2 O 2 at penetration sites beneath appressoria in the moderately resistant, but to a lesser extent in the susceptible accession. Such H 2 O 2 accumulation correlated with a reduction in penetration frequency and a lower level of hyphal growth after infection in the moderately resistant accession. There was a rapid and early increase in total peroxidase as well as β-1,3-glucanase activity in the moderately resistant compared to the susceptible accession. These results indicate that fungal penetration and development in watermelon are inhibited by a consorted action of different responses including accumulation of H 2 O 2 , peroxidase and β-1,3-glucanase.

Keywords: gummy stem blight; microscopy; H 2 O 2; β-1,3-glucanase activity; peroxidase activity; peroxidase isozymes (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2024
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