Formation of phytoalexins within and outside lesions of Botrytis cinerea in French bean leaves

Rapidly spreading lesions and lesions restricted in size developed in primary leaves of French bean (Phaseolus vulgaris) in response to infection byBotrytis cinera isolates BC-1 and BC-5, respectively. These isolates caused similar differential lesions in leaves of cucumber, flax, lettuce and tomato. To determine whether phytoalexin accumulation was correlated with the resistant reaction in bean leaves, accumulation of phytoalexins was examined in necrotic areas of both types of lesions and in their surrounding green tissues. Phaseollin was the predominant phytoalexin, both inside and outside lesions, whereas phaseollidin and sometimes also phaseollinisoflavan were always present in lower concentrations. Phaseollin accumulated earlier and to higher levels within and around lesions of isolate BC-5 than of isolate BC-1. Relatively low concentrations of phaseollin were detected in the more remote green areas, including the petiole, of leaves bearing a spreading lesion. The phaseollin metabolite, 6a-hydroxyphaseollin, was found only inside lesions and in a narrow zone around lesions of both types. The authors consider the possibility that the differing concentrations of phytoalexins in the infected tissues are not a determining factor for the differential interactions betweenB. cinerea and bean leaves, but are rather the result of it.     

Phytoalexin production in French bean leaves infected by botrytis cinerea

French bean (Phaseolus vulgaris) leaves were inoculated with three pathogenic and two nonpathogenic isolates ofBotrytis cinerea and the infected tissues, containing either spreading lesions or lesions limited in size, were investigated for the presence of phytoalexins. In most cases phaseollin, phaseollidin, phaseollinisoflavan, the phaseollin metabolite, 6a-hydroxyphaseollin, and a few unidentified antifungal compounds were found; phaseollin was predominant. The concentration of phaseollin accumulating in leaves infected by the nonpathogenic isolate BC-5 was about twice as high as that in infections produced by pathogenic isolates. In contrast, leaves infected by the nonpathogenic isolate BC-6 only contained low concentrations of phaseollin.Our data do not provide strong evidence that phaseollin is the principal factor that limits lesion development.Samenvatting Bladeren van boon (Phaseolus vulgaris) werden geïnoculeerd met drie pathogene en twee niet-pathogene isolaten vanBotrytis cinerea, als gevolg waarvan zich uitbreidende lesies, resp lesies van beperkte omvang ontstonden. Deze lesies werden samen met een omringend groen gedeelte onderzocht op de aanwezigheid van fytoalexinen. Hiertoe werden deze stoffen geëxtraheerd uit drooggevroren bladmateriaal, en gezuiverd m.b.v. kolomchromatografie over Sephadex LH-20 (Tabel 1) en dunnelaag-chromatografie (Tabel 2). Kwantitatieve analyse vond plaats d.m.v. in situdensitometrie.In de meeste gevallen werden phaseolline, phaseollidine, phaseollineïsoflavaan, een omzettingsprodukt van phaseolline, nl. 6a-hydroxyphaseolline, en enkele onbekende fungitoxische stoffen aangetoond (Fig. 1). Phaseolline was het meest voorkomende fytoalexine (Fig. 2 en 3). De concentratie van phaseolline in bladeren geinfecteerd met het niet-pathogene isolaat BC-5 was ongeveer tweemaal zo hoog als in bladeren geïnfecteerd met een pathogeen isolaat (isolaat BC-1, BC-3 en BC-4). Daarentegen bevatten bladeren die met het niet-pathogene isolaat BC-6 waren geinfecteerd slechts lage concentraties phaseolline.De hoeveelheden phaseolline en 6a-hydroxyphaseolline, omgerekend per lesie, namen snel toe in zich uitbreidende lesies van isolaat BC-1, terwijl de toenamesnelheid van deze stoffen afnam in lesies van isolaat BC-5, die beperkt van omvang bleven (Fig. 4).De resultaten geven geen duidelijke aanwijzingen dat phaseolline de belangrijkste remmende factor zou zijn bij het beperkt blijven van lesies.