THE BACTERIAL DISEASES that cause spotting and wilting are most important during the growing period, but sometimes they continue to develop after harvest and cause damage in storage or at the market. The wilt diseases cause discoloration of the internal tissues and are often not discovered until the vegetable is cut when it is prepared for food. The symptoms of the more important of these diseases are:

Tomato Bacterial spot (caused by Xanthomonas vesicatoria): Spots on mature green fruit are brownish-black, elevated, scabby areas, one-eighth to one-fourth inch in diameter, with feathered or irregular margins. Old spots are sunken, gray, or bleached and the affected skin is dry, paper-like, and ragged. Spots are superficial and do not develop into soft rot.

Bacterial speck (Pseudomonas tomato): Causes dark brown, slightly raised specks, one thirty-second to one-sixteenth inch in diameter, with definite margins. Spots are superficial and decay does not follow.

Bacterial canker (Corynebacterium michiganense): Spots on mature green fruit are light brown to brown, slightly raised circular areas, about one-sixteenth to one-eighth inch in diameter. They are surrounded by a characteristic white halo. Spots are superficial and do not develop into soft rot.

Beans Common blight (Xanthomonas phaseoli) and halo blight (Pseudomonas phaseolicola): Cause circular to irregular-shaped, watery or greasy-appearing spots on the pods. The margin of the common blight spots becomes almost brick red as the spots become older. A yellowish crust of bacterial ooze is sometimes evident on the common blight spots and a grayish-white crust on the halo blight spots.

Peas Bacterial blight (Pseudomonas pisi): Pod spots in the early stages are small and water-soaked. In more advanced stages they are larger, slightly sunken, greasy, or water-soaked, irregular-shaped, and have gray or grayish-brown centers.

Cucumbers Bacterial spot (Pseudomonas lachrymans): Spots on cucumbers start as minute, circular, water-soaked areas. Later the affected tissues dry and crack and the centers of the spots become sunken and chalky white in color. A gummy exudate is sometimes present on the spots. A breakdown and soft rot frequently follow.

Cauliflower and Cabbage Leaf spot (Pseudomonas maculicola) Leaf spots are water-soaked at first and then become brownish or purplish gray. They coalesce and become elongated as they enlarge and give the leaf a ragged appearance. Spots on the cauliflower head are small, gray to brown, and affect both the epidermis and deeper tissues. Later develops into soft rot.

Black rot (Xanthomonas campestris): Causes yellowing of the leaves and blackening of the veins. Leaves shed from stalk. Often followed by soft rot.

Celery Bacterial blight (Pseudomonas apii): Causes numerous small irregular-shaped spots on the leaflets. Spots are yellow at first, but later are rusty brown with a yellow border or halo.

Stone fruits Bacterial spot (Xanthomonas pruni): Fruit spots at first are small, circular, and light brown. Later they enlarge, darken, dry out, and crack. A viscid, yellowish, gummy exudate is sometimes present on the lesions.

Lemon Black pit (Xanthomonas citri): Fruit spots are sunken, roughly circular, one-fourth to one-half inch in diameter, brown at first and later black. The white part of the peel beneath the pits collapses and turns light brown to reddish brown.

Potato Ring rot (Corynebacterium sepedonicum): Causes odorless decay that is confined at first to vicinity of vascular ring of the potato. Affected tissues are cream-colored to pale lemon yellow and have a soft cheesy texture. Starts at stolon attachment and progresses through vascular system to the eyes. Causes characteristic cracking that extends into the vascular ring. Soft rot frequently follows.

Brown rot (Pseudomonas solanacearum): May cause a slight depression at the stolon attachment. Sometimes shows as a grayish discolored patch on surface of potato. Causes moist brown discoloration and slight softening of the vascular ring. A gray sticky bacterial Ooze often exudes from the vascular tissue. Later the interior becomes soft brown and only the shell of the potato holds it together.

Fruits and vegetables affected with bacterial spot and wilt diseases at harvest should be carefully graded and sorted to eliminate all that show symptoms of disease and then should be refrigerated promptly to retard development on the apparently sound produce. They should be used as promptly as possible after they are removed from the refrigerated storage.

WILSON L. SMITH, JR., is a pathologist in the division of handling, transportation, and storage, Bureau of Plant Industry, Soils, and Agricultural Engineering, at Beltsville, Md. He has higher degrees from the University of Maryland and Cornell University. His major research studies have concerned bacterial diseases of plants.

B. A. FRIEDMAN is a pathologist at the Market Pathology Laboratory of the division of handling, transportation, and storage of horticultural crops in New York City. He obtained his doctorate in bacteriology at New York University.

Blue mold rot on lemon.