HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hill, J. H. Articles by Grau, C. R. Search for Related Content PubMed Articles by Hill, J. H. Articles by Grau, C. R. Agricola Articles by Hill, J. H. Articles by Grau, C. R. Related Collections Soybean Pest Management Systems Plant Disease

CROP BREEDING & GENETICS

Identification of Field Tolerance to Bean Pod Mottle and Soybean Mosaic Viruses in Soybean

^a Dept. of Plant Pathology, Iowa State Univ., Ames, IA 50011
^b Dept. of Plant Pathology, Univ. of Wisconsin, Madison, WI 53706

^* Corresponding author (johnhill{at}iastate.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Development of a method to identify field tolerance to bean pod mottle and soybean mosaic viruses (BPMV and SMV) in soybean [Glycine max (L.) Merr.] allowed evaluation of 33 soybean accessions for field response to BPMV and SMV. Based on measurement of parameters that included relative level of virus antigen in seed and mottling of soybean seed coats, three accessions showed tolerance to SMV and BPMV (PI 561353, M90-18411, PI 507353), eight were tolerant to SMV (MN 1301, M92-160047, M91-113037, PI 423826A, A99-216031, NE 3001, U96-2408, Colfax), and four were tolerant to BPMV (PI 184042, M93-326056, M95-255017, Spansoy 201). Treatment of seed with the insecticide imidacloprid (1-[(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine) did not effect disease control. The relative level of virus antigen in seed harvested from experimental plots was shown to correlate significantly with virus incidence in plots. The data suggest that quantitative assay of virus seed antigen may provide a useful estimate of relative virus incidence in test plots and aid identification of field tolerance to seed-borne viruses.

Abbreviations: BPMV, bean pod mottle virus • ELISA, enzyme-linked immunosorbent assay • OD, optical density • SMV, soybean mosaic virus

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
BEGINNING IN 1998, BPMV has become an increasing problem for soybean producers in the north central United States. Recently, Giesler et al. have summarized properties of the virus as well as its pathology to soybeans (Giesler et al., 2002). Since the late 1990s, losses due to the disease have included reduced yield and seed quality conferred by mottling of soybean seed coats or hilum bleeding. The principal insect vector of the virus is the bean leaf beetle (Cerotoma trifurcata) (Hopkins and Mueller, 1984). A low level of transmission through soybean seed may also occur (Krell et al., 2003).

One solution for disease control has been developed and depends on well-timed insecticides to manage bean leaf beetle populations. (Krell et al., 2004). However, the most effective long-term method for control of disease caused by virus infection is host plant resistance. Resistance to BPMV has not been reported for commercially available cultivars of Glycine max. Ross (1986) previously reported resistance of four soybean germplasm lines that exhibit mild symptoms after mechanical inoculation with BPMV. A recent report, using mechanical inoculation of 115 accessions of G. max soybeans with BPMV in the greenhouse, has identified 11 accessions that expressed mild symptoms of virus infection. All accessions, however, became systemically infected, and field performance of these lines was not reported (Zheng et al., 2005). In the same report, 12 accessions of G. tomentilla did not become systemically infected with BPMV. However, incorporation of this resistance into G. max is hampered by the difficulty of making interspecific crosses. Recent evaluation of 52 U.S. ancestral accessions found no resistance to BPMV (Zheng et al., 2005). Personal observations as well as those reported by growers suggest that soybean cultivars vary significantly in response to disease caused by BPMV, and that severity of leaf symptoms does not positively correlate with the presence of BPMV. Therefore, since leaf symptoms could not be reliably used, an alternative approach explored the potential for resistance or tolerance. Studies were established to search for field tolerance under conditions of high disease incidence. Under these conditions, tolerant accessions may have reduced virus incidence resulting in higher yields and improved seed quality. No controlled inoculation of plants was employed, and all spread of endemic virus occurred through activity of insect vectors naturally present at experimental locations.

Since primary grower concerns are centered on reductions in yield and seed quality, the measurement of field tolerance included data on yield and evaluation of seeds harvested from soybeans grown where virus disease was present. Since seed quality can be negatively impacted by discoloration or mottling (hilum bleeding) of seed coats, assessment of seed quality for purposes of this study included the percentage of seed with mottled seed coats, as well as the relative amount of virus antigen in a seed sample. Percentage of seed with mottled seed coats and the amount of virus antigen were the basis for development of a virus seed index (Krell et al., 2005).

Compounding the difficulty of identification of tolerance to BPMV was presence of SMV, whose symptoms are difficult to differentiate from those of BPMV in the field (Hill, 1999). Associated with infection by SMV is mottling of soybean seed coats, which is indistinguishable from that caused by BPMV. Similar to BPMV, the virus is also transmitted through seed but at potentially higher levels (Hill, 1999). Further, infection of soybean plants by both viruses can cause synergism (Calvert and Ghabrial, 1983). For SMV, resistance to a variety of SMV strains is differentially conferred by three resistance genes, Rsv1, Rsv3, and Rsv4 (Hill, 1999).

Since an efficient vector of SMV (Hill et al., 2001) was increasingly prevalent after 2001 (Lee Burrows et al., 2005, Ragsdale et al., 2004, Wedberg et al., 2001), the possibility that SMV could be an important part of the virus disease complex in experimental plots to identify virus disease resistance was evident. Therefore, soybean accessions were also screened for field tolerance to SMV in the last two of the three years the study was conducted, using methods similar to those used for BPMV. The objective of this study was to determine if a method to identify field tolerance to BPMV and/or SMV could be developed. In the process, several candidate soybean accessions were identified.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Experimental Field Design
For the initial studies, a set of cultivars was selected from plots to evaluate lines for resistance to brown stem rot [Phialophora gregata (Allington and Chamberlain) W. Gams]. In 2001 and 2002, the cultivars were planted at the Arlington Agricultural Experiment Station, Columbia County, WI, and near Janesville, Rock County, WI. For the 2002 trials only, seed of an additional set of the same cultivars was treated with the insecticide imidacloprid (Gaucho 4F, 29.6 mL/22.7 kg; Gustafson, Marsing, ID, and Bayer CropScience, Research Triangle Park, NC). Additional accessions, cultivars, breeding lines, and plant introductions were evaluated for reaction to BPMV and SMV. The expanded set of accessions, based on field and greenhouse results (Grau, unpublished), were added to the trial at Rock County in 2002, and the experiment was repeated in 2003 at the West Madison Agricultural Experiment Station, Dane County, WI.

Individual plots were planted at 3.0 m x 7.6 m, and four rows were spaced 76 cm apart. Plots were managed for weeds using standard agronomic practices. The previous year's crop was corn at all Rock County locations and soybean at the Columbia County and Dane County locations. A randomized complete block design with three to four replications was used at each location.

To determine virus incidence, the most fully expanded terminal trifoliolate leaf was collected from each of 20 plants chosen randomly in each plot, and each leaf was assayed separately by enzyme-linked immunosorbent assay (ELISA). Leaves were immediately placed on ice for transport and stored at –20°C until assayed for BPMV and SMV. In 2001, samples were collected at soybean growth stages (Fehr and Caviness, 1977) V5/V6, R2, and R5 at both locations. An additional sampling time was added in 2002, with samples being collected at soybean growth stages V1, V5/R2, R3/R4, and R6 at both locations. Sampling at the Dane County site in 2003 was intensified to seven times during the growing season, including soybean growth stages V1, V5, R2, R3, R4, R5, and R6/7. Protocols previously described (Krell et al., 2003) or diagnostic kits from Agdia (Elkhart, IN) were used for the ELISA. Leaf samples were extracted using 0.05 M phosphate buffer, pH 7.2 (Sigma, St. Louis, MO). Absorbance at 405 nm (generally greater than 0.80) was measured using an EL 800 Universal Microplate Reader (Bio-Tek, Winooski, VT).

Plots were also visually assessed for virus symptoms three times in 2001 at both locations, starting when symptoms began to appear. Symptoms attributed to viruses were rated visually in each plot by estimating the percentage of symptomatic tissue visible at the top of the plant canopy. In 2002, the Columbia County site was assessed three times and Rock county was assessed five times beginning at growth stages R2/R3. Virus assessment in 2003 at Dane County began at growth stages R3/4 and was done weekly for 4 wk. Only data from the last sampling date are shown.

Seed Analyses
Samples of 100 seeds were evaluated from each replicate to determine the percentage of seed coat discoloration for a soybean seed sample. Any seed showing brown or black seed coat discoloration was counted as mottled. The relative amount of BPMV or SMV antigen in a sample of 100 seeds was determined by ELISA in a manner similar to that previously described (Krell et al., 2005). In summary, batches of 100 seeds were ground at setting no. 6 for 1 min in 100 mL of 0.05 M sodium borate, pH 7.2, with a Brinkmann Polytron homogenizer and model PT 20 ST probe generator (Brinkman Instruments, Westbury, NJ). Extracts were squeezed through two layers of cheesecloth and 0.1-mL samples were used per well. Positive and negative controls were included in each ELISA plate. Optical density (OD) at 405 nm was recorded at six timed intervals during a 20- to 150-min period after addition of the enzyme substrate. The mean OD₄₀₅ of four replicate wells was used to generate a regression equation that relates hydrolysis time to OD. A standard hydrolysis time of 60 min after substrate addition was used to calculate the OD that corresponds to the amount of virus antigen in each homogenized seed sample (sample OD). A similar calculation was made for the negative healthy seed control (negative control OD). For each ELISA plate, the relative virus antigen content of each sample was calculated as relative amount of virus antigen in seed sample = (sample OD)/(negative control OD plus two standard deviations). Therefore, calculated values of virus antigen in seed samples are relative to 1.0, which designates no detectable antigen. Similar to a previous report, sample well-to-well variation was less than 5%, and regression equations yielded coefficient of determination (R²) values greater than 0.99 (Krell et al., 2005).

The number calculated as the product of percentage seed coat mottling and relative antigen was arbitrarily defined as the "virus seed index" for each seed sample. Using this criterion, a seed sample with a low virus index was regarded as superior in quality to a sample with a high virus index. To obtain an overall assessment of tolerance to both BPMV and SMV, a virus seed index was also calculated as the sum of the seed index for each virus.

Data Analyses
Differences between virus index, relative antigen content, seed coat mottling, seed yield, and percentage symptomatic plants were analyzed using the general linear model procedure (SAS Institute, Inc., 1999). Differences generating significant F-value differences were further compared by examining the least significant difference.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
The initial experiments were established in 2001 at two sites using a set of soybean cultivars (Table 1). The mean value of relative BPMV antigen for all cultivars was significantly higher (t test, P < 0.01) at the Rock County site (mean = 3.8) than at the Columbia County site (mean = 1.0). This was supported by observation of few bean leaf beetles at the Columbia County site as compared to the Rock County site and virus incidence data (not shown), based on ELISA of leaf samples, collected at growth stage R5, that showed mean incidence (mean = 100%) of BPMV significantly greater (t test, P < 0.01) at Rock County than at Columbia County (mean = 0.0%). Apparent viruslike symptoms observed at the Columbia County site (Table 1) were presumably due to presence of SMV, where mean incidence was 18% as compared to 4% at Rock County.

Tests were conducted at the Dane County location in 2003 where both bean leaf beetles and soybean aphids were present (data not shown). Consistent with this observation, ELISA of leaf samples collected from soybean plants at R6/7 showed both SMV and BPMV were detected but that mean incidence (mean = 43.1%) of SMV was significantly different (P < 0.01) than that of BPMV (mean = 4.8%). In agreement with these data, the mean relative antigen for all cultivars in the set of commercial cultivars used in the 2001 and 2002 tests was 1.7 and 2.8 for BPMV and SMV, respectively (Table 3).

The expanded set of soybean accessions was evaluated where BPMV was prevalent at Rock County in 2002, and where SMV was prevalent at the Dane County location in 2003 (Table 4). Mean relative BPMV antigen for all accessions at Rock County in 2002 was 6.8 and was 1.1 for SMV. In contrast, mean relative SMV antigen (mean = 2.6) was higher than mean relative BPMV antigen (mean = 1.7) at Dane County in 2003. Again, both the virus incidence data (2002: mean BPMV = 98.7%, SMV = 0.0%; 2003: mean BPMV = 6.6%, SMV = 32.5%) and relative virus antigen were a reflection of the insect vector prevalent at each location (data not shown).

Based on both relative antigen level in seed and virus incidence, as determined by ELISA of leaf samples, Rock County in 2001 and 2002 were sites most appropriate to characterize soybean accessions for tolerance to BPMV. Columbia County in 2002 and Dane County in 2003 were locations to characterize soybean accessions for tolerance to SMV. The biological variability that occurs within years and locations, due in part to different insect vector populations that influence which virus is most prevalent at a location, dictates comparative yearly evaluation of accessions at each location for the traits measured.

The results from this study reveal that it is not practical to establish rigid quantitative limits to identify accessions that are field tolerant or sensitive to virus infection. In this study, specific attention was directed toward both seed mottling and relative virus antigen. This is illustrated by data for Mycogen 5261 whose percentage of mottled seed ranged from 9.7% to 27.5% in the years 2001–2003 (Tables 1–3). Relative to the accessions in the test, the Mycogen 5261 ranks among the lowest two in 2001 to 2002 and lowest three in 2003 for percentage of seed coat mottling. However, in 2001 seed from the Mycogen 5261 had the highest relative antigen content of those tested at the Rock County location for BPMV, and, in 2002 and 2003, it ranked fifth highest for BPMV. In contrast, data for H2494 show that it is low for relative BPMV antigen at Rock County in 2001 and 2002, years in which incidence of BPMV was high at this location. However, in 2002 the percentage of mottled seed was high at this site. This was unlikely due to SMV, since relative SMV antigen was low in 2002 at this location. Factors other than virus infection are known to cause mottling of soybean seed coats (Srinivasan and Arihara, 1994; Takahashi and Abe, 1994; Takahashi et al., 1996; Cober et al., 1998).

In more extensive tests of a larger set of soybean accessions (Table 4), the high BPMV relative antigen content in 2002 of accessions PI 398311, SD97-456, U96-2408, and A99-216031 did not suggest they were tolerant to BPMV (Table 5), even though the percentage of mottled seed in these lines was in the lower half of those lines tested (Table 4). In contrast, seed from Bell and SD96-755 were highly mottled, making them unacceptable for consideration as tolerant (Table 5), but contained a relatively low BPMV antigen content in 2002 (Table 4). The data affirm previous reports (Krell et al., 2005) that mottling is an unreliable indicator of virus presence in seed. If mottling is used as a sole selection criterion for tolerance, selection of an accession that may have high levels of virus antigen but low percentage of seed-coat mottling could increase the potential risk through seed transmission for introduction of virus into a field the following growing season.

All accessions in this study (Tables 1–4) were placed into groups based on their response in the field trials (Table 5). Initially, accessions that had a relatively low virus seed index were selected as having potential field tolerance to one or both viruses. Then, examination of the components of the seed index allowed accessions with specific tolerance to one or both viruses to be identified. Accessions that had both a low mottling percentage and antigen content were regarded as superior. Our assessment suggested at least three accessions were tolerant to both SMV and BPMV, while eight accessions were tolerant to SMV and four were tolerant to BPMV. Others in the test were unacceptable due to either consistent or occasional occurrence of some combination of high antigen value and/or percentage of seed coat mottling. Placement into a group is obviously dependent on the selection criteria used by the investigator.

Due to the wide range of seed yield potential among the accessions in the test, meaningful comparisons of seed yield with relative virus antigen level is impractical. For example, seed yield of LN 98-4446 was higher that that of PI 507353; conversely, LN 98-4446 has a higher relative antigen content than PI 507353 (Table 4).

The data confirm anecdotal evidence that leaf symptoms are an unreliable selection criterion for resistance. For example, LN 98-4446 showed virtually no leaf symptoms in the field. However, it had high BPMV and SMV seed antigen levels in 2002 and 2003, respectively (Table 4), demonstrating no positive association of virus incidence with evident symptoms.

Both BPMV and SMV were easily detected in seeds from the same plot in 2003 (Tables 3 and 4). This raises concern for the synergistic interaction of BPMV with SMV and is expected to be a future problem when inoculum and vectors of both viruses are present. Increased titer of BPMV in SMV-infected plants may result in increased levels of BPMV antigen in some accessions (Anjos et al., 1992). The significant increase in loss of seed yield potential when soybeans are infected by both viruses (Ross, 1969) argues for incorporation of virus resistance into soybeans used for commercial production.

The results demonstrate that interpretation of data to identify field tolerance to virus disease requires correct identification of viruses prevalent at the field site where the test is conducted. This becomes particularly critical when two viruses, with different insect vectors, cause similar phenotypic symptoms. Therefore, in this study it was important to monitor incidence of both BPMV and SMV at the experimental sites. This was especially important in 2002 and 2003 when both soybean aphids and bean leaf beetles were prevalent, but sometimes in different geographic areas.

The seed-borne nature of both viruses suggested that one criterion to identify field tolerance might be the relative amount of virus antigen in seed lots harvested from plants in experimental plots. The approach described is designed to screen large numbers of lines for tolerance to BPMV and SMV. The concept may also be useful for other viruses that are seed-borne. Specificity of the antisera allows discrimination of two viruses with closely similar symptoms. Initial screening, under conditions of high disease incidence, allows selection of lines with acceptable seed yield potential and seed with relatively low mottling percentage (e.g., <25%). Subsequent evaluation of the selected lines for relative antigen content may be easily mechanized. Vector prevalence parallels incidence of SMV or BPMV, and the relative amount of virus antigen in seed lots correlates significantly with virus incidence in plots from which the seed was harvested.

This is believed to be the first report of field tolerance to BPMV in G. max, for which no resistance genes have been identified (Wang et al., 2005; Zheng et al., 2005). Subsequent incorporation of naturally occurring resistance genes to SMV into BPMV field tolerant cultivars may eliminate potential for synergism between the two viruses and yield more effective management tactics for disease caused by these two viruses.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
This study was supported, in part, by the North Central Soybean Research Program, the Iowa Soybean Promotion Board, and the Wisconsin Soybean Marketing Board.

Received for publication August 8, 2006.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 

• Anjos, R.J., U. Jarlfors, and S.A. Ghabrial. 1992. Soybean mosaic potyvirus enhances the titer of two comoviruses in dually infected soybean plants. Phytopathology 82:1022–1027.
• Calvert, L.A., and S.A. Ghabrial. 1983. Enhancement by soybean mosaic virus of bean pod mottle virus titer in doubly infected soybean. Phytopathology 73:992–997.
• Cober, E.R., G.R. Ablett, R.K. Buzzel, B.M. Luzzi, V. Poysa, A.S. Sahota, and H.D. Voldeng. 1998. Imperfect yellow hilum color in soybean is conditioned by II rr TT. Crop Sci. 38:940–941.[Abstract/Free Full Text]
• Cullen, E.M., J. Gaska, and B. Jensen. 2003. Bean leaf beetle control with seed treatments [Online]. Available at http://soybean.uwex.edu/library/soybean/grain/Insects/Aphids/documents/bean_leaf_beetle_control.pdf (verified 14 Nov. 2006). University of Wisconsin Extension, Madison.
• Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Spec. Rep. 80. Iowa Agric. Home Econ. Exp. Stn., Iowa State Univ., Ames.
• Giesler, L.J., S.A. Ghabrial, T.E. Hunt, and J.H. Hill. 2002. Bean pod mottle virus. A threat to U.S. soybean production. Plant Dis. 86:1280–1289.
• Hill, J.H. 1999. Soybean mosaic virus. In Soybean disease compendium. APS Press, St. Paul, MN.
• Hill, J.H., R. Alleman, D.B. Hogg, and C.R. Grau. 2001. First report of transmission of soybean mosaic and alfalfa mosaic viruses by Aphis glycines in the New World. Plant Dis. 85:561.
• Hopkins, J.D., and A.J. Mueller. 1984. Effect of bean pod mottle virus on soybean yield. J. Econ. Entomol. 77:943–947.
• Krell, R.K., L.P. Pedigo, J.H. Hill, and M.E. Rice. 2003. Potential primary inoculum sources of bean pod mottle virus in Iowa. Plant Dis. 87:1416–1422.
• Krell, R.K., L.P. Pedigo, J.H. Hill, and M.E. Rice. 2004. Bean leaf beetle (Coleoptera: Chrysomelidae) management for reduction of bean pod mottle virus. J. Econ. Entomol. 97:192–202.[ISI][Medline]
• Krell, R.K., L.P. Pedigo, M.E. Rice, M.E. Westgate, and J.H. Hill. 2005. Using planting date to manage bean pod mottle virus in soybean. Crop Prot. 24:909–914.[CrossRef]
• Lee Burrows, M.E., C.M. Boerboom, J.M. Gaska, and C.R. Grau. 2005. The relationship between Aphis glycines and soybean mosaic virus incidence in different pest management systems. Plant Dis. 89:926–934.
• Ragsdale, D.W., D.J. Voegtlin, and R.J. O'Neil. 2004. Soybean aphid biology in North America. Ann. Entomol. Soc. Am. 97:204–208.[CrossRef]
• Ross, J. 1969. Effect of time and sequence of inoculation of soybeans with soybean mosaic and bean pod mottle viruses on yields and seed characters. Phytopathology 59:1404–1408.
• Ross, J. 1986. Registration of four soybean germplasm lines resistant to bean pod mottle virus. Crop Sci. 6:210.
• SAS Institute, Inc. 1999. User's manual, version 8.0. SAS Institute, Inc., Cary, NC.
• Srinivasan, A., and J. Arihara. 1994. Soybean seed discoloration and cracking in response to low temperatures during early reproductive growth. Crop Sci. 34:1611–1617.[Abstract/Free Full Text]
• Takahashi, R., and J. Abe. 1994. Genetic and linkage analysis of low temperature-induced browning in soybean seed coats. J. Hered. 85:447–450.[Abstract/Free Full Text]
• Takahashi, R., J. Asanuma, and S. Asanuma. 1996. Association of T gene with chilling tolerance in soybean. Crop Sci. 36:559–562.[Abstract/Free Full Text]
• Wang, Y., H.A. Hobbs, C.B. Hill, L.L. Domier, G.L. Hartman, and R.L. Nelson. 2005. Evaluation of ancestral lines of U.S. soybean cultivars for resistance to four soybean viruses. Crop Sci. 45:639–644.[Abstract/Free Full Text]
• Wedberg, J.L., C.R. Grau, N.C. Kurtzweil, J.M. Gaska, D.B. Hogg, and T.H. Klubertanz. 2001. Lessons on soybean aphid in 2000 and 2001. Proc. Wisconsin Fertilizer, Aglime, Pest Manage. Conf. 40:256–261.
• Zheng, C., P. Chen, T. Hymowitz, S. Wickizer, and R. Gergerich. 2005. Evaluation of Glycine species for resistance to bean pod mottle virus. Crop Prot. 24:49–56.[CrossRef]

This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hill, J. H. Articles by Grau, C. R. Search for Related Content PubMed Articles by Hill, J. H. Articles by Grau, C. R. Agricola Articles by Hill, J. H. Articles by Grau, C. R. Related Collections Soybean Pest Management Systems Plant Disease