THE INFLUENCE OF DARKNESS ON THE RESISTANCE OF PEACH ROOTSTOCK 'NEMAGUARD' TO MELOIDOGYNE INCOGNITA

Abstract

A study was carried out to investigate the effect of light and darkness on the resistance of the peach rootstock 'Nemaguard' to Meloidogyne incognita. Varying lengths of darkness were applied at different times after nematode inoculation to establish the effect of increasing levels of root-knot infestation as well as the effect of increasing periods of darkness. When the nematode inoculated plants were completely shaded for four days or more, gall formation on the roots was observed; phenylalanine-ammonia-lyase (PAL) level in the roots decreased significantly and the content of soluble phenols decreased in the roots but increased in the leaves. If the plants were subsequently uncovered, the small galls previously formed during the darkening time disappeared; the PAL level increased greatly in comparison with that in natural condition; the content of soluble phenols did not change evidently. The peroxidase isozyme pattern of the roots did not show clear difference between the two treatments: a specific anionic band observed in the leaves of the shaded plants is postulated to be related to hydrolysis from insoluble phenols to soluble ones. The mechanism of the plant resistance to nematode is discussed.