Rhopalosiphum padi Feeding � Attempted Symptomatic Defence Mechanisms in Barley Leaves Include Wound Callose Deposition?

Abstract

The deposition of callose and the damage-related symptoms subsequently expressed by infested plants were investigated after feeding on barley leaves by bird cherry-oat aphid (BCA), Rhopalosiphum padi L. Feeding by this aphid does not result in appearance of visible damage to the plants, provided the feeding population is small. Using aniline blue fluorochrome, we confirmed that whilst low feeding density (5 aphids) results in appearance of wound callose in sieve tubes, this only occurs after 14d of feeding, when the feeding population had increased. Continued feeding results in progressively more callose deposition and by 21d, severe damage has been caused. In contrast, feeding by larger populations (50 adult aphids), results in the appearance of wound callose within 72h, in longitudinal and cross veins. We suggest that this wounding response appears to play a role in the appearance of golden yellow streak symptoms reported to occur in leaves where BCA feeding density was high.