This disease was reported for the first time from North Carolina in 1907. Since that date it has been observed and recorded from several other states. It is common in New York on apples, but so far as known no other fruit is affected. There are no careful observations on record with respect to differences in the susceptibility of varieties. The disease is known as the spongy Dry Rot and the Volutella rot. The former name is usually given preference.
The affected area may involve a large portion of the fruit, although the lesions begin as small specks scattered over the surface (Fig. 35). Frequently rotten areas enlarge toward each other, finally fusing into large spots (Fig. 35, right). The younger portion of a diseased area is brown, but the older central portion is coal black. The surface of an affected area is dotted with fruiting pustules (Fig. 35, left); these are largest in the central region of the spot and are evident within a quarter of an inch of the margin. If examined with a hand-lens, stiff dark - brown hairs may be observed protruding from the fruiting bodies.
Fig. 35. - Spongy Dry Rot; various stages of development.
These constitute an important diagnostic sign of the disease. The affected tissue is spongy and dry, whence the name spongy Dry Rot.
This apple Rot is caused by the fungus Volutella fructi. Within the fruiting bodies mentioned above conidia are produced. These germinate in a manner similar to the process exhibited by the spores of other fungi. The germtubes enter the apple-fruit through injuries of various kinds. Within the flesh mycelium develops profusely and after a few days the rot is evident. Before a lesion has attained a very great diameter the fruiting bodies appear. Mycelium develops abundantly beneath the cuticle and soon a mycelial cushion is formed. This continues its growth until the skin is ruptured and the structure protrudes. Certain hyphae grow erect and parallel to each other; these are the conidiophores. On the tip of each stalk a conidium is borne. From a single fruiting body several hundred spores may be produced. These are scattered to other fruits and thus new infections arise. Intermingled with the conidiophores are dark-brown, hair - like spines called setae. So far as known the setae play no part in the propagation of the fungus. They serve, however, to distinguish this pathogene on the apple. It is as yet unknown where and in what condition the pathogene passes the winter. The assumption is, that it lives vegetatively in fallen fruits and possibly on decaying debris of various kinds. Infection does not occur, apparently, before the late summer. Lesions develop most commonly on fallen and stored fruits. The disease seems to be highly favored by conditions that prevail in an uncultivated orchard where the weeds and grass abound; here plenty of moisture is available to the parasite.
In the absence of experimental data little can be recommended for the control of the spongy Dry Rot. The disease is not widely destructive and in even those regions where it is most serious it is doubtful whether special treatment is necessary to satisfactory control. Fruit in orchards that are given the standard care may be expected to suffer but little from this disease.
Stevens, F. L., and Hall, J. G. Some apple diseases. The Volutella rot. North Carolina Agr. Exp. Sta. Bul. 196: 41 - 48. 1907.
Smith, R. I., and Stevens, F. L. Insect and fungous diseases of apple and pear. Volutella rot. North Carolina Agr. Exp. Sta. Bul. 206: 104 - 107. 1910.
Stevens, F. L., and Hall, J. G. An apple rot due to Volutella. Journ. Myc. 13: 94 - 99. 1907.
Duggar, B. M. Spongy dry rot fungus of apple. In Fungous Diseases of Plants, p. 316. 1909.