Dactylarin

Root-knot nematodes belonging to the genus Meloidogyne are agriculturally important pests, and biocontrol strategies offer safer alternatives for their management. In the present study, two fungal species from Indian soils were identified as Arthrobotrys thaumasia and Tolypocladium cylindrosporum based on morphological characteristics and further confirmed using molecular markers. In vitro evaluation of A. thaumasia against M. incognita and Caenorhabditis elegans showed 82 and 73% parasitism, respectively, whereas T. cylindrosporum gave 65.2 and 57.7% parasitism, respectively. Similarly, culture filtrates of A. thaumasia caused 57.7 and 53.7% mortality of M. incognita and C. elegans, respectively, whereas T. cylindrosporum caused higher mortality of 87.3 and 64%, respectively. Besides, greenhouse evaluation of both fungi against M. incognita infecting tomato significantly reduced nematode disease burden reflecting parasitic success measured as the total number of galls, egg masses, eggs per egg mass, and derived nematode multiplication factor. Application of A. thaumasia and T. cylindrosporum reduced nematode multiplication factor by 80 and 95%, respectively, compared with control. General metabolite profiling of tested fungi using gas chromatography-mass spectrometry and ultra-performance liquid chromatography-quadrupole/time of flight mass spectrometry reported for the first time here showed presence of various volatile and non-volatile compounds with nematicidal activity, viz., trimethyl-heptadiene, methyl-hexadecanol, dodecadienal, decane, terpendole E, dodecane, acetamido-6-anthraquinone, and hexadecanol. Also, other compounds such as undecane, dibutyl-disulfide, octadecenal, paganin, talathermophilin, dactylarin, tolypyridone A, tolypyridone B, pyridoxatin, and destruxin were identified, reported in the literature to possess antibacterial, antifungal, and insecticidal properties. This is the first report of the occurrence of both fungi from India and pioneer demonstration of T. cylindrosporum for root-knot nematode management.

Cytotoxic effect of dactylarin on Ehrlich ascites carcinoma cells is caused by the inhibition of some SH-dependent glycolytic enzymes, especially of hexokinase (EC 2.7.1.1), glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) and 6-phosphofructokinase (EC 2.7.1.11). Dactylarin interacts with thiols, which explains its inhibitory effectiveness on the above glycolytic enzymes.

The metabolites of the predacious fungus Dactylaria lutea ROUTIEN include the anthraquinone macrosporin (2) and three hydroxylated 1,2,3,4-tetrahydro derivatives of this anthraquinone, altersolanol A (5), altersolanol B (4) and dactylariol (6). The structure and relative configuration of dactylariol are established from spectroscopic studies, and its absolute configuration is proposed as 1R, 2R, 3R by virtue of its co-occurrence with altersolanol B. Dactylarin, suggested by other authors to have the structure (1), is shown to be identical with altersolanol B (4).