THE ANATOMIC RESPONSES OF DAUCUS CAROTA TO THE ASTER YELLOWS VIRUS

Abstract

Struckmeyer, B. Esther. (U. Wisconsin, Madison.) The anatomic responses of Daucus carota to the aster yellows virus. Amer. Jour. Bot. 50(9): 959–963. Ilus. 1963.—The leaves, petioles, and roots of carrots (Daucus carota) displaying aster yellows virus in the field and those infected with the aster yellows virus inoculated by the 6‐spotted leafhopper were examined anatomically. Compared to the uninoculated, the young infected leaves displayed fewer layers of palisade cells and larger spongy parenchyma cells with a more compact arrangement. Mature leaves of infected plants sometimes were undulated and had few chloroplasts, many of which appeared fragmented. Hypertrophy and hyperplasia in the phloem tissue were associated with some necrosis and obliteration of cells. Long, needle‐shaped crystalline inclusion bodies were present in the phloem in the leaves and roots. Most of the vascular bundles of the petiole were abnormal. Malformations included proliferating phloem cells, which in some instances almost encircled the bundle, hyperplasia of the phloem, hypertrophy of the parenchyma, and considerable necrosis and obliteration of these cells. Other responses included the division into 3 or 4 rows of the large outer phloem parenchyma by parallel walls so that a cambium‐like layer was simulated. The tissue enclosed by this layer divided and underwent considerable necrosis and gummosis. Lacunae were found between the phloem bundle cap and the older phloem. Some of the cells in the phloem tissue differentiated into bundles with xylem. Numerous, short, lateral roots were conspicuous on the main root. The most noticeable response of the root tissue to this malady was hyperplasia and hypertrophy of the phloem followed by cellular disorganization, necrosis, and obliteration of cells. Some sieve tubes, companion cells, and parenchyma contained a gumlike deposit.