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Terminal velocity of fall of Didymella exitialis ascospores in air
Notes and brief articles DODMAN,R. L. &FLENTJE,N. T . (1970). The mechanism and physiology of plant penetration by Rhizoctonia solani. In Rhizoctonia solani : Biology and Pathology (ed. J. R. Parmeter, Ir), pp. 149-160. Berkeley : University of California Press. FLENTJE, N. T . (1957). Studies on Pelliculariafilamenrosa (Pat.) Rogers. III. Host penetration and resistance,and strain specialization. Transactions of the British Mycological Society 40, 322-336.
MURRAY, D. I. L. (1981). Rhizocronia solani causing barley stunt disorder. Transactions of the British Mycologi cal Society 76, 383-395.
NAYKAYAMA, T . ( 1940). A study of the infectionof cotton seedlings by Rhizoctonia solani. Annals of the Phytopathological Society of Japan 10, 93-103 .
OGOSHI, A. ( 1975). Studies on the anastomosis groups of Rhizocronia solani Kuhn. Japan Agricultural Research Quarterly 9, 198-2°3.
GLADDERS, P. & COLEy-SMITH, J. R. (1977). Infection cushion formation in Rhizoctonia tuliparum . Transactions of the British Mycological Society 68, 115-118.
GLADDERS, P. & CoLEY-SMITH, J. R . (1979). Host infection by Rhizoctonia tuliparum , Transactions of the British Mycological Society 7'1., 251-260.
PARMETER, J. R., JR, SHERWOOD, R. T. & PLATT, W. D. (1969). Anastomosis grouping among isolates of Thanatephorus cucumeris. Phytopathology 59, 1270-1278.
RUPPEL, E. G . ( 1973). Histopathology of resistant and susceptiblesugarbeet rootsinoculatedwith Rhizoctonia solani. Phytopathology 6], 123-126.
TERMINAL VELOCITY OF FALL OF DIDYMELLA EXITIALIS ASCOSPORES IN AIR BY P . H. GREGORY, JOHN LACEY AND B. P. R. VITTAL
Rothamsted Experimental Station, Harpenden, Herts, England Didymella exitialis (M oreau) E. Muller is of interest as both a possible allergen and plant pathogen. Its ascospores may occur in dense concentrations in the air near barley fields (Frankland & Gregory, 1973)· It was abundant in late summer of 1981 and the opportunity was taken to determine the terminal velocity of fall of its ascospores in air. The terminal velocity is of interest as it affects deposition of the spores on vegetation and in the respiratory tract . The ascospores measure 12-14 x 4'o-5'5Ilm and are ellipsoid or somewhat biconic (P un ithalingam, 1979), hence the terminal velocity cannot be calculated from Stoke's formula for small spheres. Tests were made with a sedimentation chamber consisting of a vertical cylinder used in an earlier study of the terminal velocity of basidiospores of Lycoperdon giganteum as described by Gregory & Henden (1976 ). After generating a spore cloud in the chamber, samples of air were removed at intervals by aspiration through a Cascade Impactor (May, 1945) . This sampling method allows two simultaneous estimates of terminal velocity in a single experiment : (1) by inertial separation at the successive jets of the Cascade Impactor; and (2) by sedimentation based on measuring the rate of dieaway of concentration of the spore cloud. The Cascade Impactor consists of four jets of decreasing width arranged in a series (' Cascade '), each jet impinging on the sticky surface of a glass slide which can be scanned under the microscope. The largest particles are deposited at the first and widest jet, and with an aerosol of uniformly sized particles, from the proportions deposited at each of Trans . Br . Mycol. Soc . 79 (2), (1982).
the jets (numbered 1 to 4), the terminal velocity by inertial separation can be estimated using a calibration diagram (G regory & Henden, 1976). Decay of concentration by sedimentation with time is measured from the total number of spores collected from each successive sample. Several hundred dry infected leaves were collected from barley fields; groups of four or five leaves were knotted at intervals along a string several metres long, dipped in water momentarily and immediately transferred to the top of the sedimentation chamber and left for 30 min to discharge ascospores (the optimum time determined from previous tests ). Then the string was removed from the chamber after partly raising the lid. The air in the chamber was stirred by convection with a pan of warm water placed beneath the chamber to warm the floor . This avoided the use of a fan, which had caused loss of spores to the chamber wall by centrifugal rotation of the air in previous experiments (Gregory & Henden, 1976). At intervals during the half hour after withdrawing the leaves, samples of air were drawn from the middle of the chamber through the Cascade Impactor, operated at the standard rate of 17'51 min-I, to monitor the decay of concentration due to ascospores sedimenting under gravity to the floor of the chamber. At the start 15 s samples (4'38 1) were withdrawn, but as concentration decreased larger samples were taken (T able 1). Estimates of terminal velocity based on inertial separation in the Cascade Impactor are shown in Table 1 . Spores were deposited at jets 1 and 2 only, none penetrated to jets 3 and 4. The distribution
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Notes and brief articles Table
1.
Decreasing concentration of Didymella exitialis ascospores in sedimentation, chamber, inertial and sedimentation methods
Time from start (s) Experimental data ° No, of ascospores in jet 1 212 in jet 2 686 Volume sampled (I) 4'3 8 No, of ascospores I-I of air at jet 1 4 8 '4 at jet 2 156'6 Total 205'0 Terminal velocity by inertial method: percentage spores penetrating jet 1 76'4 Equivalent unit density smooth sphere (pm) 11'0 Corresponding v, (mm S-I) 3'6 Terminal velocity by sedimentation method: correction factor for volume removed in sampling 1'0 Corrected number of ascospores I-I 2°5'0
3°0
600
9°0
69 406 4'38
24 224 5'83
12 120 5'83
15'75 92'69 108'44
4'12 38 '4 2 4 2'54
2'06 20'60 22'66
4 27 17'5 0'23 1'54 1'77
Mean 85'5
90'3
90'9
87'1
9'6 3'0
9'0 2,8
8,8 2'3
9'5 3'0
1'02
1'04
1'06
1'08
110'5
of spores between jets 1 and 2 indicated a terminal velocity of 2'94 mm S-I, Estimates based on die-away of the original concentration are conveniently obtained by plotting numbers of spores trapped on a logarithmic scale against linear time (Fig, 1), Corrections were made for depletion of the original concentration due to removal of samples, and concentrations are plotted at the mid-point of the sampling time, The die-away curve is a good approximation to a straight line, and the linear regression coefficient calculated from the combined counts from jets 1 + 2 against time gives b = -()"00112. Thus the time taken for the concentration to decrease to one-tenth of its initial value (to I) was 885 s (14'75 min), With the settling chamber used (Gregory & Henden, 1976), terminal velocity, V s = 1842/tol mm S-I, hence VB = 2'08 mm S-I, Thus there is a discrepancy of 50 '/0 between the two methods when applied to Didymella exitialis, even using the data from the same spore deposits, Provisionally v" = 2 mm S-1 is considered more reliable, This discrepancy contrasts strongly with the agreement between the two methods shown by the earlier work with the nearly spherical basidiospores of L. giganteum. However, a similar discrep-
Trans, Br. Mycol. Soc, 79 (2), (1982),
1800
44'2
24'0
81 '4 10'0 2'94
1'9 1
ancy was found by Gregory & Henden (unpubl.) with the highly elongate ascospores of Gaeumannomyces graminis measuring 70-100 x 4,um (Dennis, 1960). These unexplained discrepancies need further research. One of us (B. P, R, V.) is grateful to the Royal Society of London for an award under the Commonwealth Bursaries Scheme to work at Rothamsted. REFERENCES DENNIS, R. W, G, (1960). 'British Cup Fungi and their Allies, London: Ray Society Publications, FRANKLAND, A. W. & GREGORY, P, H. (1973), Allergenic and agricultural implications of airborne ascospore concentrations from a fungus, Didymella exitialis. Nature, London 245, 336-337.
GREGORY, P. H, & HENDEN, D, R, (1976), Terminal velocity of basidiospores of the giant puftball (Lycoperdon giganteum), Transactions of the British Mycological Society 67, 39
Printed in Great Britain
MURRAY, D. I. L. (1981). Rhizocronia solani causing barley stunt disorder. Transactions of the British Mycologi cal Society 76, 383-395.
NAYKAYAMA, T . ( 1940). A study of the infectionof cotton seedlings by Rhizoctonia solani. Annals of the Phytopathological Society of Japan 10, 93-103 .
OGOSHI, A. ( 1975). Studies on the anastomosis groups of Rhizocronia solani Kuhn. Japan Agricultural Research Quarterly 9, 198-2°3.
GLADDERS, P. & COLEy-SMITH, J. R. (1977). Infection cushion formation in Rhizoctonia tuliparum . Transactions of the British Mycological Society 68, 115-118.
GLADDERS, P. & CoLEY-SMITH, J. R . (1979). Host infection by Rhizoctonia tuliparum , Transactions of the British Mycological Society 7'1., 251-260.
PARMETER, J. R., JR, SHERWOOD, R. T. & PLATT, W. D. (1969). Anastomosis grouping among isolates of Thanatephorus cucumeris. Phytopathology 59, 1270-1278.
RUPPEL, E. G . ( 1973). Histopathology of resistant and susceptiblesugarbeet rootsinoculatedwith Rhizoctonia solani. Phytopathology 6], 123-126.
TERMINAL VELOCITY OF FALL OF DIDYMELLA EXITIALIS ASCOSPORES IN AIR BY P . H. GREGORY, JOHN LACEY AND B. P. R. VITTAL
Rothamsted Experimental Station, Harpenden, Herts, England Didymella exitialis (M oreau) E. Muller is of interest as both a possible allergen and plant pathogen. Its ascospores may occur in dense concentrations in the air near barley fields (Frankland & Gregory, 1973)· It was abundant in late summer of 1981 and the opportunity was taken to determine the terminal velocity of fall of its ascospores in air. The terminal velocity is of interest as it affects deposition of the spores on vegetation and in the respiratory tract . The ascospores measure 12-14 x 4'o-5'5Ilm and are ellipsoid or somewhat biconic (P un ithalingam, 1979), hence the terminal velocity cannot be calculated from Stoke's formula for small spheres. Tests were made with a sedimentation chamber consisting of a vertical cylinder used in an earlier study of the terminal velocity of basidiospores of Lycoperdon giganteum as described by Gregory & Henden (1976 ). After generating a spore cloud in the chamber, samples of air were removed at intervals by aspiration through a Cascade Impactor (May, 1945) . This sampling method allows two simultaneous estimates of terminal velocity in a single experiment : (1) by inertial separation at the successive jets of the Cascade Impactor; and (2) by sedimentation based on measuring the rate of dieaway of concentration of the spore cloud. The Cascade Impactor consists of four jets of decreasing width arranged in a series (' Cascade '), each jet impinging on the sticky surface of a glass slide which can be scanned under the microscope. The largest particles are deposited at the first and widest jet, and with an aerosol of uniformly sized particles, from the proportions deposited at each of Trans . Br . Mycol. Soc . 79 (2), (1982).
the jets (numbered 1 to 4), the terminal velocity by inertial separation can be estimated using a calibration diagram (G regory & Henden, 1976). Decay of concentration by sedimentation with time is measured from the total number of spores collected from each successive sample. Several hundred dry infected leaves were collected from barley fields; groups of four or five leaves were knotted at intervals along a string several metres long, dipped in water momentarily and immediately transferred to the top of the sedimentation chamber and left for 30 min to discharge ascospores (the optimum time determined from previous tests ). Then the string was removed from the chamber after partly raising the lid. The air in the chamber was stirred by convection with a pan of warm water placed beneath the chamber to warm the floor . This avoided the use of a fan, which had caused loss of spores to the chamber wall by centrifugal rotation of the air in previous experiments (Gregory & Henden, 1976). At intervals during the half hour after withdrawing the leaves, samples of air were drawn from the middle of the chamber through the Cascade Impactor, operated at the standard rate of 17'51 min-I, to monitor the decay of concentration due to ascospores sedimenting under gravity to the floor of the chamber. At the start 15 s samples (4'38 1) were withdrawn, but as concentration decreased larger samples were taken (T able 1). Estimates of terminal velocity based on inertial separation in the Cascade Impactor are shown in Table 1 . Spores were deposited at jets 1 and 2 only, none penetrated to jets 3 and 4. The distribution
Printed in Great Britain
Notes and brief articles Table
1.
Decreasing concentration of Didymella exitialis ascospores in sedimentation, chamber, inertial and sedimentation methods
Time from start (s) Experimental data ° No, of ascospores in jet 1 212 in jet 2 686 Volume sampled (I) 4'3 8 No, of ascospores I-I of air at jet 1 4 8 '4 at jet 2 156'6 Total 205'0 Terminal velocity by inertial method: percentage spores penetrating jet 1 76'4 Equivalent unit density smooth sphere (pm) 11'0 Corresponding v, (mm S-I) 3'6 Terminal velocity by sedimentation method: correction factor for volume removed in sampling 1'0 Corrected number of ascospores I-I 2°5'0
3°0
600
9°0
69 406 4'38
24 224 5'83
12 120 5'83
15'75 92'69 108'44
4'12 38 '4 2 4 2'54
2'06 20'60 22'66
4 27 17'5 0'23 1'54 1'77
Mean 85'5
90'3
90'9
87'1
9'6 3'0
9'0 2,8
8,8 2'3
9'5 3'0
1'02
1'04
1'06
1'08
110'5
of spores between jets 1 and 2 indicated a terminal velocity of 2'94 mm S-I, Estimates based on die-away of the original concentration are conveniently obtained by plotting numbers of spores trapped on a logarithmic scale against linear time (Fig, 1), Corrections were made for depletion of the original concentration due to removal of samples, and concentrations are plotted at the mid-point of the sampling time, The die-away curve is a good approximation to a straight line, and the linear regression coefficient calculated from the combined counts from jets 1 + 2 against time gives b = -()"00112. Thus the time taken for the concentration to decrease to one-tenth of its initial value (to I) was 885 s (14'75 min), With the settling chamber used (Gregory & Henden, 1976), terminal velocity, V s = 1842/tol mm S-I, hence VB = 2'08 mm S-I, Thus there is a discrepancy of 50 '/0 between the two methods when applied to Didymella exitialis, even using the data from the same spore deposits, Provisionally v" = 2 mm S-1 is considered more reliable, This discrepancy contrasts strongly with the agreement between the two methods shown by the earlier work with the nearly spherical basidiospores of L. giganteum. However, a similar discrep-
Trans, Br. Mycol. Soc, 79 (2), (1982),
1800
44'2
24'0
81 '4 10'0 2'94
1'9 1
ancy was found by Gregory & Henden (unpubl.) with the highly elongate ascospores of Gaeumannomyces graminis measuring 70-100 x 4,um (Dennis, 1960). These unexplained discrepancies need further research. One of us (B. P, R, V.) is grateful to the Royal Society of London for an award under the Commonwealth Bursaries Scheme to work at Rothamsted. REFERENCES DENNIS, R. W, G, (1960). 'British Cup Fungi and their Allies, London: Ray Society Publications, FRANKLAND, A. W. & GREGORY, P, H. (1973), Allergenic and agricultural implications of airborne ascospore concentrations from a fungus, Didymella exitialis. Nature, London 245, 336-337.
GREGORY, P. H, & HENDEN, D, R, (1976), Terminal velocity of basidiospores of the giant puftball (Lycoperdon giganteum), Transactions of the British Mycological Society 67, 39
Printed in Great Britain