Degrading enzymes and phytotoxins in Monilinia spp

Abstract

Necrotrophic phytopathogenic fungi secrete degrading enzymes and phytotoxins to penetrate and colonise plant tissues. Since knowledge on the pathogenic processes of brown rot in fruit which becomes infected by Monilinia spp. is limited, we undertook an investigation whose aims were to detect: (i) the degrading enzymes of Monilinia spp. when cultured on media amended with different substrates, and (ii) the phytotoxins which are secreted by Monilinia fructicola, M. fructigena and M. laxa in brown rot-infected fruit. The sporulation and growth of 10 M. fructicola isolates, 9 M. fructigena isolates, and 10 M. laxa isolates plates, which contained 25 mL 2% (w/v) bacteriological agar, 0.67% (w/v) yeast nitrogen base, and 1% (w/v) of one of the following substrates: (1) β1–3 glucan (callose), (2) casein hydrolysate, (3) cutin, (4) methylcellulose, (5) apple pectin, (6) polygalacturonic acid sodium salt, (7) D(+)-sucrose, and (8) xylan were determined in order to detect the degrading enzymes. To look for the phytotoxins, the juice of nectarines that were inoculated with conidial suspensions M. fructicola, M. fructigena and M. laxa were subjected to liquid-liquid extraction with different organic solvents. The extracts were tested for their ability to cause necrosis on nectarine discs and the ones with a positive response were analysed by high performance liquid chromatography with DAD and MS spectrometer detectors and different fractions were collected to delimit metabolites. We found that Monilinia spp. secrete phytotoxins with a molar mass between 329 and 387 g mol−1 and degrading enzymes (cutinases, α-glucosidases, pectin lyases, polygalacturonases, proteases, and xylanases) for penetrating the fruit surface and invading and colonising fruit tissues.