Botrytone, a New Naphthalenone Pentaketide Produced by Botrytis fabae, the Causal Agent of Chocolate Spot Disease on Vicia faba

Abstract

A strain of Botrytis fabae isolated from faba bean (Vicia faba L.) plants displaying clear chocolate spot disease symptoms produced phytotoxic metabolites in vitro. The phytotoxins isolated from the culture filtrate organic extract were characterized by spectroscopic and optical methods. A new naphthalenone pentaketide, named botrytone, was isolated and characterized as (4R)-3,4-dihydro-4,5,8-trihydroxy-1(2H)-naphthalenone together with other well-known closely related naphthalenones such as regiolone and cis- and trans-3,4-dihydro-2,4,8-trihydroxynaphthalen-1(2H)-ones. When tested on leaves of the host plant, with the cis- and trans-3,4-dihydro-2,4,8-trihydroxynaphthalen-1(2H)-ones assayed in mixture, regiolone demonstrated the highest level of phytotoxicity together with cis- and trans-3,4-dihydro-2,4,8-trihydroxynaphthalen-1(2H)-ones. Botrytone showed moderate phytotoxic activity at 1 mg/mL and was still phytotoxic at 0.5 mg/mL.

Cyclobotryoxide, a Phytotoxic Metabolite Produced by the Plurivorous Pathogen Neofusicoccum australe

“…In fact, they belong to a group of well-known phytotoxins produced by pathogenic fungi for different agrarian crops such as scytalone, isosclerone, botrytone, and cis-and trans-3,4dihydro-2,4,8-trihydroxynaphthalenones. 32,33 When assayed on the leaves of different plant species at different concentrations, compounds 1 and 3−6 showed varying degrees of phytotoxicity. The toxicity data obtained in the leaf-puncture bioassay on holm oak, cork oak, and grapevine cv.…”

Regiolone and Isosclerone, Two Enantiomeric Phytotoxic Naphthalenone Pentaketides: Computational Assignment of Absolute Configuration and Its Relationship with Phytotoxic Activity

“…The fungus was grown on modified Czapek medium as recently reported. [1] P. aleophilum was isolated from esca-infected grapevine cv. Sangiovese plants collected from a field in Tuscany.…”

“…[9] Extraction and Purification of Phytotoxic Naphthalenone Pentaketides: The lyophilized culture filtrates (3.5 L) of B. fabae as well as that of P. aleophilum (7.0 L) were dissolved in 1 / 10 of the initial volume with distilled water and extracted with ethyl acetate as previously reported. [1,9] The organic extracts were combined, dried (Na 2 SO 4 ), and concentrated under reduced pressure to yield a brown solid residue. The residue (427.0 mg) obtained from the B. fabae culture filtrates was purified by chromatography on a silica gel column (CHCl 3 /2-propanol, 9:1) to give nine homogeneous fractions.…”

“…The residue (36.0 mg) of the second fraction was further purified by TLC on silica gel (CHCl 3 /2-propanol, 94:6) to yield regiolone [(-)-1, 22.0 mg, 6.3 mg L -1 ]. [1] The residue (375.0 mg) obtained from P. aleophilum culture filtrates was purified by chromatography on a silica gel column (CHCl 3 /2-propanol, 9:1) to give 12 homogeneous fractions. The residue (60.0 mg) of combined fractions 4-6 was further purified by TLC on silica gel (CHCl 3 /2-propanol, 98:2) to yield isosclerone [(+)-1, 2.8 mg, 0.4 mg L -1 ].…”

“…[1] The dihydroxynaphthalenone 1 has been found in both enantiomeric forms in a number of fungi and plants, the (-)-1 enantiomer being commonly named as regiolone and the (+)-1 isomer called isosclerone (Scheme 1). Regiolone was first isolated from the walnut tree (Juglans regia L.) that grows throughout the Himalayas of India and Nepal, different extracts of which have been used in folk medicine.…”