Florida Agricultural Experiment Station


lation experiments have shown that a large number of species
and varieties, hybrids and wild relatives of Citrus are more or
less susceptible to canker.
 SYMPTOMS OF CANKER
 Canker may attack any part of the tree above the ground
although the leaves, twigs, young branches, and fruits are most
commonly infected and these parts chiefly while still fairly
young and tender. The distinguishing feature of the disease as
 S observed in the field is the characteristic spotting
 produced on the foliage, twigs, and fruits.






 Fig. 12.-Canker on young twig of trifoliate orange.

 On the leaves, canker first appears as small watery, trans-
lucent spots usually of a darker green color than the surround-
ing tissue and with raised, convex surfaces. The spots, which
may appear on either surface of the leaf, usually become evident
on the lower one first. As the disease advances, the surfaces of
the spots become white or grayish and finally rupture, exposing
a light brown, spongy central mass developed in a crater-like
formation of the ruptured epidermis. Such spots usually become
surrounded by a yellowish halo, which persists in very old lesions.
The size, color, and abundance of the lesions vary somewhat on
the different kinds of citrus trees attacked (Fig. 11). For ex-
ample, the lesions are largest on grapefruit leaves, on which they
may be nearly 1/2 inch in diameter, and are usually not quite so
large on leaves of the sweet orange. On the leaves of limes and
lemons, they are much smaller, frequently not being more than
1/8 inch in diameter. Old lesions become brown and corky and
may even appear pinkish or dark-colored on account of becoming
overgrown by saprophytic fungi.
 On the Twigs, Branches, and Roots:-Lesions on the twigs
are common on the more susceptible kinds of Citrus, such as the
grapefruit, trifoliate orange, lime, and sweet orange varieties.
The spots on young twigs are like those on the leaves and
fruit (Fig. 12). On the older twigs they are more prominent