Extension of localized freeze injury in barley by acute post-thaw bacterial disease

Abstract

A distinctive pattern of injury restricted to the roots and lower crown occurred in barley plants frozen at high water content (4). Degenerative changes progressed toward the crown meristems during the recovery period. Excising the injured root tissues before they deteriorated improved recovery (6). Incubated freeze-injured tissues were bioassayed to detect agents that inhibit growth or lyse cells with the following results. 1. 1. Agents inhibitory to the growth of plant cells and to B. subtilis developed in freeze-injured roots within a few hours of postfreezing incubation. Maximum activity occurred within 1 day and persisted for 4 days of incubation. 2. 2. Freeze-injured tissue from plants grown, frozen, and incubated aseptically did not develop lytic or inhibitory activity nor did freeze-injured roots of normal plants have lytic or inhibitory agents when assayed immediately after thawing. 3. 3. Development of lytic and inhibitory activity correlated with increase of bacterial population in the incubated tissue. 4. 4. The principle bacteria were Pseudomonads. 5. 5. Attempts to isolate a toxic substance were not successful. However, it was possible to destroy the toxin by treatment with heat or KOH without killing the bacteria, which when reassayed on B.s./PDA were still toxin producers. 6. 6. Chemical disinfectants applied at the time of thawing improved recovery. Post-thaw tissue degeneration can be restricted to localized freeze injuries by control of disease microorganisms. Freeze-injured tissues stimulate proliferation of latent bacteria present in the healthy root tissue. As infection spreads, bacteria lyse healthy cells surrounding the primary freeze injury. Plant recovery is impaired when noninjured meristem essential for recovery becomes infected.