Effect of Oxygen, Carbon Dioxide, and Ethylene on Growth, Sporulation, and Production of Microsclerotia by Verticillium dahliae

IOANNOU, N., R. W. SCHNEIDER, and R. G. GROGAN. 1977. Effect of oxygen, carbon dioxide, and ethylene on growth, sporulation, and production of microsclerotia by Verticillium dahliae. Phytopathology 67: 645-650. Verticillium dahliae cultured in decreasing 02 (20.9 to 17.5% of maximum and very few conidia were produced. The 0.06%) and nearly constant CO2 (about 0.03%) production of MS decreased progressively with each decrease concentrations, produced maximum radial growth and in 02 and corresponding increase in CO2 concentration, and sporulation at 1.9 and 2.7% 02, respectively; growth was nil was completely inhibited at 10% 02 and 11% CO2. Infected at 0.06% 02. The production of microsclerotia (MS) was tomato stems exposed to normal air, 10% 02 and 11% C0 2, maximum at 20.9% 02 and decreased progressively with each or 2.5% 02 and 20% CO2, produced the maximum, 10% of the decrease in 02 concentration. Under constant 02 (17-18%) maximum, and no MS, respectively. Infected stems, that and increasing CO2 concentrations (ranging from 0.03 to were exposed to the inhibitory gas mixtures for 10 days, 20.9%), maximum radial growth and sporulation were resumed production of MS after return to normal air, and produced at 6.2 and 0.03% C0 2, respectively. In 20.9% CO 2, produced within 10 days about 30-40% of the numbers of MS radial growth was essentially the same as at 0.03%, but produced by stems exposed continuously to normal air. sporulation was reduced to about 20% of the maximum. The Exposure of cultures to ethylene concentrations ranging production of MS decreased with each increase in C0 2 from 0 to 35 l~liters/liter did not affect growth, sporulation, concentration and was completely inhibited at about 12.2% or MS production. Microsclerotia produced under the CO2. Under different mixtures of 02 and CO2, ranging from different atmospheres were equally viable. Also, MS 20.9% 02 and 0.03% CO2 to 0.5% 02 and 20.5% CO2, radial produced under normal air, and then exposed to low 02 and growth was maximum at 16.5% 02 and 4.5% CO2, whereas high CO 2 concentrations for up to 3 mo, survived as well as conidia and MS production were maximum in normal air. MS exposed continuously to normal air. Under 0.5% 02 and 20.5% CO2, radial growth was reduced to Additional key words: tomato, vascular wilt disease, microbial ecology, soilborne pathogens. Although various investigators (4, 5, 13, 14, 15, 23) cotton plugs. Luck (13) reported that MS did not develop have reported on the influence of aeration on growth and when the CO2 content was lower than that in normal air survival of Verticihlium dahliae Kleb., detailed studies on and suggested that CO2 fixation was involved in the this subject are lacking. Menzies (14) and Nadakavukaren formation of MS. (15) reported that microsclerotia (MS) were eliminated Production of MS by V. dahliae was inhibited in from soil by flooding and they attributed this to the infected tomato stems incubated in saturated soil (10). In induced anaerobiosis. Wilhelm (23) and Green (5) preliminary experiments, when test tubes were filled with reported that the population of V. dahliae in soils sterilized quartz sand and saturated with liquid medium decreased with increasing depth, and that the heaviest containing conidia of V. dahliae, MS formed only on top infestation was located in the upper 30 cm of soil. of the sand and around air bubbles trapped at various Although aeration was not discussed at length by these depths within the sand. These observations and the authors, Green (5) suggested that the abrupt reduction of reports by others led us to examine the effect of various inoculum in soil at depths below 30 to 45 cm concentrations of 02 and CO2 on the growth, sporulation, corresponded "to the lower limits of the partially oxidized MS development, and survival of V. dahliae. Ethylene, a topsoil of most of the soils sampled." Brinkerhoff (4) volatile factor recently implicated in soil fungistasis (18) suggested that low 02 concentrations inhibited the and in soil biology generally (19), also was examined in formation of MS because MS did not develop in infected relation to its effects on growth, sporulation, and cotton leaves incubated in sealed glass jars, but were production of MS by V. dahliae. The effect of the aboveformed abundantly in leaves incubated in jars closed with mentioned gases on the production of MS was given Copyright © 1977 The American Phytopathological Society, 3340 particular emphasis. A preliminary report of this study Pilot Knob Road, St. Paul, MN 55121. All rights reserved, has been published (9).