William Palmore

Publication Date


Advisor(s) - Committee Chair

Larry Elliott, Jeff Jenkins, Hugh Puckett

Degree Program

Department of Biology

Degree Type

Master of Science


Head lettuce, Lactuta sativa var. capitata, is susceptible to a number of economically important diseases, the most frequent being russet spot, rib discoloration, and vascular browning (28), which have been shown by Ceponis and Friedman (7) to be caused by Pseudomonas marginalis. Pseudomonads are common plant pathogens and cause such diseases as halo blight in beans (20), bacterial blight in soybeans (20), and bacterial wilt of the bird-of-paradise (27) and tobacco (24).

Plants that develop symptoms similar to russet of lettuce are oats, infected by Pseudomonas cichorii, and tobacco infected with Pseudomonas tobaci (34). In general, russet symptoms include few to numerous yellow, pink, brown, olive brown or dark brown irregular specks ranging in diameter from 1/16 to 1/8 inch (28). In tobacco these lesions are thought to result from a necrotizing toxin, diamino-dicarboxylic acid, beta-hydroxy-alpha, epsilon-aminopimelic acid, produced by the bacteria (34). In lettuce these lesions result from the bacterial enzymes, protopectinase and pectin depolymerase (7). The red discoloration of lettuce often encountered in grocery stores and home refrigerators has been given the name russet spot, rib discoloration, and tipburn, depending upon where the discoloration occurs (26). These terms are sometimes used interchangeably in the literature.

This investigation was initiated for two purposes: to determine factors which could be responsible for the symptoms which diseased market lettuce develops; and to investigate a preservation procedure that would best control the incidence of this disease.


Agricultural Science | Biology | Horticulture | Life Sciences | Plant Biology | Plant Sciences