- Email: [email protected]
Acquired resistance to Tobacco mosaic virus transmitted to the progeny of hypersensitive Tobacco
VIROLOGY
124,161-163
(1983)
SHORT
COMMUNICATIONS
Acquired Resistance to Tobacco Mosaic Virus Transmitted to the Progeny of Hypersensitive Tobacco’
D. A. ROBERTS Department of Plant Pathology, University of Florida, Gainesville %?611 Received August 9, 1982; accepted September 27, 1982 Acquired resistance was induced in plants of hypersensitive tobacco (Nicotinnu tdmcum L. “Samsun NN”) with a series of five induction inoculations with tobacco mosaic virus (TMV) at 2-week intervals. Selfed progeny were challenge inoculated with TMV. Lesion diameters in the progeny of induction-inoculated plants were approximately two-thirds those in the progeny of noninoculated control plants. Thus, systemic acquired resistance of hypersensitive tobacco to TMV was seed transmitted. The phenomenon was not genetic, because the progeny acquired resistance only if their parent plants had been repeatedly induction inoculated.
Hypersensitive plants, which localize viruses or other pathogens within necrotic lesions in the inoculated tissues, respond to a second (challenge) inoculation by producing smaller and, sometimes, fewer lesions (I, 2). The hypersensitive reaction after the first (induction) inoculation thus seems to enhance resistance. This systemic acquired resistance (2) to tobacco mosaic virus (TMV) in hypersensitive tobacco (Nicotiana tabacum L. “Samsun NN”) can be induced in leaf initials (3), suggesting that such resistance might also develop in embryos and be transmitted to the progeny. Results of experiments reported below demonstrate the seed transmission of acquired (induced) resistance to TMV in “Samsun NN” tobacco. In each of four experiments, two to four fully expanded leaves of six vigorous, greenhouse-grown plants of Samsun NN Turkish tobacco were inoculated with TMV at 2-week intervals. The fifth and last inoculation was made after the flowering period at about the time of seed formation. Noninoculated and induction-inoculated plants flowered at about the same time. r Florida Agricultural Series No. 3783.
Experiment
Inoculum was prepared by grinding TMVinfected leaves of Samsun Turkish tobacco with a mortar and pestle. The extracted juice was pressed through cheesecloth and diluted lOOO-fold in tap water. Carborundum-dusted leaves were uniformly rubbed with cheesecloth pads saturated with the inoculum, and rubbed leaves were rinsed with water within 5 min of inoculation. Approximately 200 lesions formed in each induction-inoculated leaf. Six uninoculated Samsun NN tobacco plants were kept as controls in each experiment. Although simulated induction inoculation of control plants is sometimes recommended, reliable results have been obtained whether control plants were left untreated or subjected to mock inoculation (1). My experience has also shown no need for simulated inoculation of control plants. Lesion diameter was about the same (2.29 f 0.19 mm) in 20 separate experiments on another aspect of systemic acquired resistance to TMV in Samsun NN tobacco. Consistent results were obtained, regardless of whether the controls were untreated plants (nine experiments) or were plants with Carborundum-dusted leaves that had been rubbed with water (five experiments), water-diluted juice from healthy
Station Journal 161
0042~6822/83/010161-03$03.00/0 Copyright All righta
8 1983 by Academic Press, Inc. of reproduction in any form reserved.
162
SHORT
COMMUNICATIONS
Samsun tobacco plants (four experiments), or with 0.05 M neutral phosphate buffer (two experiments). Seed from induction-inoculated plants were mixed together and kept separate from the batch of seed from control plants. Seed were sown in sterilized Vermiculite, and seedlings from each group were transplanted individually to soil in 4-in pots. Later, 12 plants in each group were selected for uniformity of size and vigor, and the growing tips were removed from all plants for convenience (4). The first two fully expanded leaves of all plants were then inoculated with TMV in juice extracted from systematically infected Samsun Turkish tobacco plants. The crude juice had been diluted lO,OOO-fold in water, so as to induce 50 to 100 lesions in most inoculated leaves. One week later, diameters of 10 randomly selected lesions in each leaf were measured with a calibrated ocular lens in a stereoscopic microscope. I chose reduced lesion size as the criterion for induced systemic acquired resistance because, with TMV in hypersensitive tobacco, reductions in lesion size are more consistent than reduced number of lesions (4) and because there is no correlation between size and number of lesions (5). First-generation selfed progeny plants were tested in the four experiments just described. Second-generation plants were tested in five similar experiments, in three of which plants of the first-generation progeny were inoculated five times at 2week intervals and then plants of the selfed second-generation progeny were challenge inoculated. In the other two experiments, first-generation plants were not induction inoculated, but their selfed progeny were challenge inoculated. Lesions that developed in challenge-inoculated leaves of the first- and secondgeneration progeny of induction-inoculated plants were significantly smaller than those in leaves of control plants (Table 1). Lesion diameter was reduced, on the average, 38% in first-generation progeny and 28% in the progeny of first-generation plants that had been induction inoculated. Lesion diameters in the second-generation progeny were not significantly different
TABLE
1
DIAMETERS (mm) OF VIRAL LESIONS IN PROGENYOF HYPERSENSITIVE TOBACCO PLANTS IN WHICH AcQUIREDRESISTANCE HAD BEEN INDUCEDBY MULTIPLE INOCULATIONS WITH TOBACCO MOSAIC VIRUS” Progeny of inductioninoculated plants
“Resistant” plants Control plants
First generation
Second generation
1.37+ + 0.41 2.20 + 0.35
1.81b + 0.38 2.50 + 0.26
“Numbers are mean diameters of all lesions in each category. Ten lesions were measured in each of 24 leaves of 12 plants in every experiment; four experiments were made with first-generation progeny, three with second-generation ones (progeny of induction-inoculated first-generation plants). *Significantly different by the t test (P < 0.015) from corresponding controls.
from those in the controls in the two experiments in which parent plants had not received induction inoculations. The systemic acquired resistance detected in the selfed progeny of inductioninoculated tobacco plants can be traced to the embryonic tissues of developing seed. Results of experiments reported herein thus confirm that induction of systemic acquired resistance can occur in immature tissues (3). Also, these results are consistent with the idea that inducing substances transported from localized infections enhance a defensive mechanism in target tissues (3, 4). The practical implications of acquired resistance in the progeny of hypersensitive tobacco plants are not yet clear. The enhanced resistance reported herein is far from complete and does not persist beyond the first-generation progeny of inductioninoculated plants. Also, the degree of acquired resistance expressed in progeny plants was less than that usually measured in individual plants receiving both induction and challenge inoculations: whereas lesion diameters were reduced only 28-38% in leaves of progeny plants, reductions of 50% and more are common in plants tested individually (4). Neverthe-
SHORT
COMMUNICATIONS
less, practical applications of induced resistance in progeny plants might become possible if latent defenses, such as precursers of antiviral factors (6), could be activated in embryos of seed formed in plants that are not hypersensitive. Systemic resistance to cucumber mosaic virus has already been induced in susceptible cucumber plants by earlier inoculations of the same plants with tobacco necrosis virus (7). ACKNOWLEDGMENT I thank Lucious J. Mitchell, technical assistance.
Jr., for his reliable
163 REFERENCES
1. Ross, A. F., Virdogy 14,340~358 (1961). 2. HAMILTON, R. I., In “Plant Disease” (J. G. Horsfall and E. B. Cowling, eds.), Vol. V, pp. 279303. Academic Press, New York, 1986. 3. BOZARTH, R. F., and Ross, A. F., virology 24,446455 (1964). 4. ROSS, A. F., In “Viruses of plants” (A. B. R. Beemster and J. Dijkstra, eds.), pp. 127-150. North-Holland, Amsterdam, 1966. 5. ROBERTS, D. A., Proc Am Phytopathd Sot. 2,53 (1976). 6. SELA, I., HAUSCHNER, A., and MOZES, R., Virology 89, l-6 (1978). 7. BERGSTROM, G. C., JOHNSON, M. C., and Ku& J., Phytopathology 72.922-926 (1982).
124,161-163
(1983)
SHORT
COMMUNICATIONS
Acquired Resistance to Tobacco Mosaic Virus Transmitted to the Progeny of Hypersensitive Tobacco’
D. A. ROBERTS Department of Plant Pathology, University of Florida, Gainesville %?611 Received August 9, 1982; accepted September 27, 1982 Acquired resistance was induced in plants of hypersensitive tobacco (Nicotinnu tdmcum L. “Samsun NN”) with a series of five induction inoculations with tobacco mosaic virus (TMV) at 2-week intervals. Selfed progeny were challenge inoculated with TMV. Lesion diameters in the progeny of induction-inoculated plants were approximately two-thirds those in the progeny of noninoculated control plants. Thus, systemic acquired resistance of hypersensitive tobacco to TMV was seed transmitted. The phenomenon was not genetic, because the progeny acquired resistance only if their parent plants had been repeatedly induction inoculated.
Hypersensitive plants, which localize viruses or other pathogens within necrotic lesions in the inoculated tissues, respond to a second (challenge) inoculation by producing smaller and, sometimes, fewer lesions (I, 2). The hypersensitive reaction after the first (induction) inoculation thus seems to enhance resistance. This systemic acquired resistance (2) to tobacco mosaic virus (TMV) in hypersensitive tobacco (Nicotiana tabacum L. “Samsun NN”) can be induced in leaf initials (3), suggesting that such resistance might also develop in embryos and be transmitted to the progeny. Results of experiments reported below demonstrate the seed transmission of acquired (induced) resistance to TMV in “Samsun NN” tobacco. In each of four experiments, two to four fully expanded leaves of six vigorous, greenhouse-grown plants of Samsun NN Turkish tobacco were inoculated with TMV at 2-week intervals. The fifth and last inoculation was made after the flowering period at about the time of seed formation. Noninoculated and induction-inoculated plants flowered at about the same time. r Florida Agricultural Series No. 3783.
Experiment
Inoculum was prepared by grinding TMVinfected leaves of Samsun Turkish tobacco with a mortar and pestle. The extracted juice was pressed through cheesecloth and diluted lOOO-fold in tap water. Carborundum-dusted leaves were uniformly rubbed with cheesecloth pads saturated with the inoculum, and rubbed leaves were rinsed with water within 5 min of inoculation. Approximately 200 lesions formed in each induction-inoculated leaf. Six uninoculated Samsun NN tobacco plants were kept as controls in each experiment. Although simulated induction inoculation of control plants is sometimes recommended, reliable results have been obtained whether control plants were left untreated or subjected to mock inoculation (1). My experience has also shown no need for simulated inoculation of control plants. Lesion diameter was about the same (2.29 f 0.19 mm) in 20 separate experiments on another aspect of systemic acquired resistance to TMV in Samsun NN tobacco. Consistent results were obtained, regardless of whether the controls were untreated plants (nine experiments) or were plants with Carborundum-dusted leaves that had been rubbed with water (five experiments), water-diluted juice from healthy
Station Journal 161
0042~6822/83/010161-03$03.00/0 Copyright All righta
8 1983 by Academic Press, Inc. of reproduction in any form reserved.
162
SHORT
COMMUNICATIONS
Samsun tobacco plants (four experiments), or with 0.05 M neutral phosphate buffer (two experiments). Seed from induction-inoculated plants were mixed together and kept separate from the batch of seed from control plants. Seed were sown in sterilized Vermiculite, and seedlings from each group were transplanted individually to soil in 4-in pots. Later, 12 plants in each group were selected for uniformity of size and vigor, and the growing tips were removed from all plants for convenience (4). The first two fully expanded leaves of all plants were then inoculated with TMV in juice extracted from systematically infected Samsun Turkish tobacco plants. The crude juice had been diluted lO,OOO-fold in water, so as to induce 50 to 100 lesions in most inoculated leaves. One week later, diameters of 10 randomly selected lesions in each leaf were measured with a calibrated ocular lens in a stereoscopic microscope. I chose reduced lesion size as the criterion for induced systemic acquired resistance because, with TMV in hypersensitive tobacco, reductions in lesion size are more consistent than reduced number of lesions (4) and because there is no correlation between size and number of lesions (5). First-generation selfed progeny plants were tested in the four experiments just described. Second-generation plants were tested in five similar experiments, in three of which plants of the first-generation progeny were inoculated five times at 2week intervals and then plants of the selfed second-generation progeny were challenge inoculated. In the other two experiments, first-generation plants were not induction inoculated, but their selfed progeny were challenge inoculated. Lesions that developed in challenge-inoculated leaves of the first- and secondgeneration progeny of induction-inoculated plants were significantly smaller than those in leaves of control plants (Table 1). Lesion diameter was reduced, on the average, 38% in first-generation progeny and 28% in the progeny of first-generation plants that had been induction inoculated. Lesion diameters in the second-generation progeny were not significantly different
TABLE
1
DIAMETERS (mm) OF VIRAL LESIONS IN PROGENYOF HYPERSENSITIVE TOBACCO PLANTS IN WHICH AcQUIREDRESISTANCE HAD BEEN INDUCEDBY MULTIPLE INOCULATIONS WITH TOBACCO MOSAIC VIRUS” Progeny of inductioninoculated plants
“Resistant” plants Control plants
First generation
Second generation
1.37+ + 0.41 2.20 + 0.35
1.81b + 0.38 2.50 + 0.26
“Numbers are mean diameters of all lesions in each category. Ten lesions were measured in each of 24 leaves of 12 plants in every experiment; four experiments were made with first-generation progeny, three with second-generation ones (progeny of induction-inoculated first-generation plants). *Significantly different by the t test (P < 0.015) from corresponding controls.
from those in the controls in the two experiments in which parent plants had not received induction inoculations. The systemic acquired resistance detected in the selfed progeny of inductioninoculated tobacco plants can be traced to the embryonic tissues of developing seed. Results of experiments reported herein thus confirm that induction of systemic acquired resistance can occur in immature tissues (3). Also, these results are consistent with the idea that inducing substances transported from localized infections enhance a defensive mechanism in target tissues (3, 4). The practical implications of acquired resistance in the progeny of hypersensitive tobacco plants are not yet clear. The enhanced resistance reported herein is far from complete and does not persist beyond the first-generation progeny of inductioninoculated plants. Also, the degree of acquired resistance expressed in progeny plants was less than that usually measured in individual plants receiving both induction and challenge inoculations: whereas lesion diameters were reduced only 28-38% in leaves of progeny plants, reductions of 50% and more are common in plants tested individually (4). Neverthe-
SHORT
COMMUNICATIONS
less, practical applications of induced resistance in progeny plants might become possible if latent defenses, such as precursers of antiviral factors (6), could be activated in embryos of seed formed in plants that are not hypersensitive. Systemic resistance to cucumber mosaic virus has already been induced in susceptible cucumber plants by earlier inoculations of the same plants with tobacco necrosis virus (7). ACKNOWLEDGMENT I thank Lucious J. Mitchell, technical assistance.
Jr., for his reliable
163 REFERENCES
1. Ross, A. F., Virdogy 14,340~358 (1961). 2. HAMILTON, R. I., In “Plant Disease” (J. G. Horsfall and E. B. Cowling, eds.), Vol. V, pp. 279303. Academic Press, New York, 1986. 3. BOZARTH, R. F., and Ross, A. F., virology 24,446455 (1964). 4. ROSS, A. F., In “Viruses of plants” (A. B. R. Beemster and J. Dijkstra, eds.), pp. 127-150. North-Holland, Amsterdam, 1966. 5. ROBERTS, D. A., Proc Am Phytopathd Sot. 2,53 (1976). 6. SELA, I., HAUSCHNER, A., and MOZES, R., Virology 89, l-6 (1978). 7. BERGSTROM, G. C., JOHNSON, M. C., and Ku& J., Phytopathology 72.922-926 (1982).