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. 2015 Oct 16;82(1):184-91.
doi: 10.1128/AEM.02436-15. Print 2016 Jan 1.

Effects of Temperature and Moisture on Development of Fusarium graminearum Perithecia in Maize Stalk Residues

Valentina Manstretta  1 , Vittorio Rossi  2
Affiliations

Effects of Temperature and Moisture on Development of Fusarium graminearum Perithecia in Maize Stalk Residues

Valentina Manstretta et al. Appl Environ Microbiol. .

Abstract

Fusarium graminearum is the predominant component of the Fusarium head blight complex of wheat. F. graminearum ascospores, which initiate head infection, mature in perithecia on crop residues and become airborne. The effects of temperature (T) and moisture on perithecium production and maturation and on ascospore production on maize stalk residues were determined. In the laboratory, perithecia were produced at temperatures between 5 and 30°C (the optimum was 21.7°C) but matured only at 20 and 25°C. Perithecia were produced when relative humidity (RH) was ≥75% but matured only when RH was ≥85%; perithecium production and maturation increased with RH. Equations describing perithecium production and maturation over time as a function of T and RH (R(2) > 0.96) were developed. Maize stalks were also placed outdoors on three substrates: a grass lawn exposed to rain; a constantly wet, spongelike foam exposed to rain; and a grass lawn protected from rain. No perithecia were produced on stalks protected from rain. Perithecium production and maturation were significantly higher on the constantly wet foam than on the intermittently wet lawn (both exposed to rain). Ascospore numbers but not their dispersal patterns were also affected by the substrate.

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Figures

FIG 1
FIG 1
Numbers of Fusarium graminearum perithecia produced per square centimeter of maize stalk (A), percentage of mature perithecia (B), and cumulative number of mature ascospores in perithecia (C) as affected by temperature and days of incubation. Maize stalks were sterilized, inoculated with F. graminearum conidia, and incubated at different constant temperatures (shown on the right, in degrees Celsius). Maturity was evaluated by microscopic observation of crushed perithecia. In panel B, the white arrow indicates when empty perithecia were first observed. Numbers of mature ascospores were determined by suspending perithecia in water and counting the ascospores in the suspension with a hemocytometer; the average numbers of ascospores per perithecium were then calculated. Points are the averages and whiskers the standard errors for 40 values (2 experiments, 2 replicate trays with 10 stalk pieces each).
FIG 2
FIG 2
Observed and predicted production (A) and maturation (B) of Fusarium graminearum perithecia on maize stalks as affected by temperature and days of incubation. The observed values are those shown in Fig. 1, and the predicted values were generated by equation 1 (see Table 1 for equation parameters); the numbers of perithecia per square centimeter of stalk surface were rescaled by dividing each number by the maximum number obtained in the experiment. The line represents the linear fit of observed and predicted values; intercept a = 0.004, slope b = 1.001, R2 = 0.99 (A); a = 0.001, b = 0.991, R2 = 0.99 (B).
FIG 3
FIG 3
Numbers of Fusarium graminearum perithecia produced per square centimeter of maize stalk (A), frequency of mature perithecia (B), and cumulative numbers of mature ascospores in perithecia (C) as affected by constant relative humidity (RH, indicated on the right, in percentages) and days of incubation. Maize stalks were sterilized, inoculated with F. graminearum conidia, and incubated at constant RHs. Maturity was evaluated by microscopic observation of crushed perithecia. The numbers of mature ascospores were determined by suspending perithecia in water and counting the ascospores in the suspension with a hemocytometer; the average numbers of ascospores per perithecium were then calculated. Points are the averages and whiskers the standard errors of 40 values (2 experiments, 2 replicate trays with 10 stalk pieces each).
FIG 4
FIG 4
Observed and predicted production (A) and maturation (B) of Fusarium graminearum perithecia on maize stalks as affected by relative humidity (RH) and days of incubation. The observed values are those shown in Fig. 3, and predicted values were generated by equation 2 (see Table 2 for equation parameters). Numbers of perithecia per square centimeter of stalk surface were rescaled by dividing each number by the maximum number obtained in the experiment. The line represents the linear fit of observed and predicted values; intercept a = −0.008, slope b = 0.983, R2 = 0.96 (A); a = 0.0002, b = 1.017, R2 = 0.99 (B).
FIG 5
FIG 5
Production of Fusarium graminearum perithecia per square centimeter of maize stalk (A) and percentage of mature perithecia (B) in outdoor experiments in 2011 (□) and 2012 (○) (B) as affected by time (day of the year [DOY]) and exposure conditions. Maize stalks were arranged on a grass lawn (white) or on a wet florist foam (black); the stalks were exposed to rain and open air in both treatments, but the foam was always moist while the lawn was moist only during and shortly after rain events. (C) Cumulative numbers of total perithecia (white bars) and mature perithecia (black bars); values indicate the percentages of mature perithecia relative to the total number. Points in panels A and B and bars in panel C are averages of 10 values: two stalk types (artificially inoculated and naturally infested by F. graminearum) and 5 replicates per stalk type. Whiskers in panel C are standard errors of the 10 values.
FIG 6
FIG 6
Cumulative numbers of Fusarium graminearum ascospores trapped over time (DOY) (A) and at the end of the trapping period (B) above maize stalks in outdoor experiments in 2011 (□) and 2012 (○) as affected by exposure conditions. Maize stalks were arranged on a grass lawn (white) or on a wet florist foam (black) as described in the legend to Fig. 5, and spore traps (microscope slides with adhesive tape facing down) were placed 3 to 5 cm above the stalk pieces. Points in panel A and bars in panel C are averages of 10 values: two stalk types (artificially inoculated and naturally infested by F. graminearum) and 5 replicates per stalk type. Whiskers in panel B are standard errors of the 10 values.
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