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Cultivar Selection Is an Effective and Economic Strategy for Managing Charcoal Rot of Strawberry in Florida

    Authors and Affiliations
    • Juliana S. Baggio1
    • Leandro G. Cordova2
    • Teresa E. Seijo1
    • Joseph W. Noling3
    • Vance M. Whitaker1
    • Natalia A. Peres1
    1. 1University of Florida, Gulf Coast Research and Education Center, Wimauma, FL 33598
    2. 2Corteva Agriscience, Indianapolis, IN 46268
    3. 3University of Florida, Citrus Research and Education Center, Lake Alfred, FL 33850


    Macrophomina phaseolina, the causal agent of charcoal rot, is a soilborne pathogen that affects strawberry crowns leading to plant wilt and collapse. Disease management involves a combination of physical, cultural, and chemical methods. Field trials were conducted for 10 consecutive Florida seasons (2010–11 to 2019–20) to determine the susceptibility of strawberry cultivars to charcoal rot and the effect of cultivar selection on disease and to estimate the economic impact of cultivar selection on disease management. Six cultivars grown commercially in Florida were chosen and grouped as highly susceptible (HS) (‘Strawberry Festival’ and ‘Treasure’), susceptible (S) (‘Florida Radiance’ and ‘Florida Beauty’), and moderately resistant (MR) (Sensation ‘Florida127’ and Winterstar ‘FL05-107’) according to their susceptibility levels. After a primary analysis of the individual trials, a network meta-analysis was conducted to estimate and compare the final disease incidence and the disease progress rate of each susceptibility group. The economic impact of charcoal rot on strawberry production and gross revenue was estimated based on plant production functions, weekly fruit prices, and disease progress over time with parameters obtained via the meta-analytical models. Disease incidence was reduced by 91.5 and 77.3%, respectively, when the MR and S cultivar groups were adopted instead of the HS group. There was a 62.5% reduction in the disease incidence when the MR group was used instead of the S group. Significant differences in disease progress rates were also observed when the MR and S groups were adopted instead of the HS group. Therefore, the adoption of more resistant cultivars is an effective strategy when incorporated into a charcoal rot integrated management program and can significantly impact growers’ revenue by reducing disease incidence, preventing yield loss, and, consequently, minimizing economic losses.

    Strawberry (Fragaria × ananassa Duch.) is an economically important fruit crop in the United States, with a total production of 1.3 million tons across 20,000 ha in 2018 (FAOSTAT 2020). Florida is the second largest strawberry producer in the country, with an economic impact on the community exceeding $700 million (FSGA 2020). The estimated cost of strawberry production in Florida is close to US$75,000 per hectare (Guan et al. 2017).

    Florida strawberry production is an annual system. Transplants, obtained from nurseries located primarily in California, North Carolina, and Canada, are transplanted to plastic-mulched raised beds from late September through mid-October (Whitaker et al. 2019a). Fruit production commonly occurs from November to March, with the most profitable harvests during the early season (November to January). After the end of strawberry production at many commercial farms, the plastic and drip tapes are removed, the beds are leveled, and the soil is tilled. Cover crops might be planted to increase the organic matter content of the soil (Yu et al. 2018). On some commercial farms, plastic-mulched beds are reutilized, either for cultivating secondary crops, such as those in the Cucurbitaceae and Solanaceae, or for a second strawberry crop the next fall (Baggio et al. 2021).

    Diseases, mainly caused by fungal pathogens, comprise one of the major threats encountered by the Florida strawberry industry. Among them, Macrophomina phaseolina (Tassi) Goidanich, a causal agent of charcoal rot, can cause severe losses. The pathogen colonizes the vascular tissues of the strawberry crowns, and symptoms are usually characterized by reddish-brown discoloration in these tissues, leading to wilting and collapse of older leaves and eventual death of the whole plant (Avilés et al. 2008; Mertely et al. 2005; Zveibil and Freeman 2005). Without appropriate management, charcoal rot can cause >80% plant mortality in commercial production fields under favorable conditions (Baggio et al. 2021). In this situation, yields are severely affected, and strawberry growers can experience serious economic impacts because current options for crop insurance are not affordable (Rosa and Johnson 2019).

    M. phaseolina survives as microsclerotia, which are resistant structures found in the soil and crop debris, which serve as a source of inoculum. Plant infection occurs by microsclerotia germination and penetration mainly through the roots, but the fungus can also be dispersed aboveground by water and cause infection through the aerial parts of the strawberry plant (Baggio et al. 2019; Dhingra and Sinclair 1975; Zveibil et al. 2012). Air and soil temperatures ranging from 28 to 35°C, dry and sandy soils, and the repeated cultivation of a susceptible host (i.e., strawberry) are conducive to disease development, pathogen survival, and increasing soil populations (Dhingra and Sinclair 1978; Short et al. 1978). Because of high production costs, some Florida strawberry growers have been reusing plastic-mulched beds and drip irrigation systems for a second season and maintaining dead plants from the previous season on the beds until new transplants arrive in the fall. This new practice has contributed to an increase in M. phaseolina inoculum in production fields, even though soil fumigants might be used as a crop termination treatment at the end of the season (Baggio et al. 2019).

    Management of charcoal rot depends greatly on the reduction of the M. phaseolina population. For years, the disease was efficiently and almost exclusively managed with preplant soil fumigation with methyl bromide; however, because its use was completely banned for strawberry fruit production in the United States in 2016 (Gareau 2017), charcoal rot management has become a challenge for the strawberry industry worldwide (Mertely et al. 2005; Zveibil and Freeman 2005). Over the past three strawberry seasons in Florida, the number of strawberry samples infected with M. phaseolina submitted to the University of Florida’s Gulf Coast Research and Education Center (UF-GCREC) Diagnostic Clinic has increased three-fold, from <10% to approximately 30%. Moreover, the number of commercial farms reporting problems with charcoal rot has also increased markedly during the same period.

    Preplant soil fumigation is still the predominant control method adopted by Florida strawberry growers for the control of M. phaseolina. However, the alternative broad-spectrum fumigants currently available (e.g., allyl isothiocyanate [AITC], chloropicrin with 1,3-dichloropropene, metam potassium, metam sodium) are not as effective as methyl bromide for reducing the pathogen population and controlling disease (Baggio et al. 2018; Chamorro et al. 2016). In addition to fall fumigation, crop termination using fumigants at the end of the strawberry season has become a usual practice among growers who have reported issues with soilborne pathogens, nematodes, and weeds, especially if the grower is planning to reuse the plastic the following season (Baggio et al. 2021; Khatri et al. 2020; Noling 2015). The lower efficacy of these fumigants is cause by intrinsic chemical characteristics that limit their movement and diffusion through the soil profile (Porter et al. 2004). Moreover, there are no effective postplanting fungicides currently available to control M. phaseolina on strawberry (Mertely et al. 2017a, b, 2020).

    Because of the persistent survival of M. phaseolina in soil and crop debris, and because of the limitations of chemical control to mitigate yield impacts of charcoal rot in strawberry production, the industry needs effective physical and cultural strategies for integrated management of charcoal rot. For instance, the adoption of a white-stripe center on black plastic mulches could reduce charcoal rot incidence by decreasing soil temperature and minimizing heat stress of transplants during the establishment period (Baggio et al. 2021). Physical removal of strawberry crop residue could decrease M. phaseolina populations in the soil, especially in areas with high amounts of inoculum, at the expense of significantly increasing production costs (Baggio et al. 2021).

    An additional strategy to manage charcoal rot would be to adopt the use of less susceptible strawberry cultivars (Peres et al. 2018; Sánchez et al. 2016; Winslow et al. 2017). Host resistance is a very common tool for the management of diseases caused by bacteria and viruses, where chemical control might not be as efficient. The screening of cultivars from Israel, Florida, and California for charcoal rot susceptibility has already been performed (Holmes et al. 2020; Nelson 2018; Pickel et al. 2020; Seijo et al. 2020; Winslow et al. 2017). However, the effect of cultivar selection on the reduction of charcoal rot incidence and development and its economic impact on strawberry production have never been investigated.

    Therefore, the objectives of this study were as follows: to determine the susceptibility of Florida strawberry cultivars to charcoal rot; to assess the effects of cultivar selection on charcoal rot by performing a multivariate meta-analysis of 10 cultivar trials conducted from 2010 to 2020 in Florida; and to estimate the economic impact of disease management via cultivar selection.

    Materials and Methods

    Florida cultivar susceptibility to charcoal rot: experimental design and data collection.

    To determine the susceptibility of strawberry cultivars to charcoal rot, trials were conducted in strawberry fields at the Gulf Coast Research and Education Center (GCREC) in Wimauma, FL, during 10 consecutive strawberry seasons (2010–2011 to 2019–2020). Bare-root green-top strawberry plants were transplanted between late September and mid-October to 1,3-dichloropropene (97.5%, Telone II, Corteva Agriscience, 168 kg/ha) fumigated, raised beds (91 m long × 71 cm wide, 15 and 18 cm high at the edges and center, respectively, spaced 1.2 m between bed centers) covered with 0.03-mm-thick virtually impermeable black film (Blockade, Berry Plastics, Evansville, IN) with a single drip tape (Chapin drip tape-BTF Jain Irrigation Inc, Fresno, CA) 2.5 cm deep at the center of the bed. Transplants were planted in two staggered rows (38 cm apart) per bed with 38 or 30 cm between plants within each row during the 2010–11 to 2015–16 seasons and during the 2016–17 to 2019–20 seasons, respectively. Transplants were overhead-irrigated during daylight hours for approximately 10 days during establishment and then irrigated and fertilized through drip tape throughout the season. Four plots of each cultivar containing 10 plants per plot (except for the 2010–2011 season: 20 plants) were arranged in a randomized complete block design, with each replication in a separate bed. Plants were inoculated with a mixture of three M. phaseolina isolates originated from symptomatic strawberry plants collected in commercial fields and maintained at the UF-GCREC culture collection following two procedures. During the first five seasons (2010–2011 to 2014–2015), 5 ml of corn cob pieces (Kay-kob pet litter, KayTee, Chilton, WI) infested with M. phaseolina (Baggio et al. 2018; Chamorro et al. 2016) were placed in the transplant hole just before planting. During the last five strawberry seasons (2015–2016 to 2019–2020), transplants with roots trimmed to approximately 7 cm in length were root-dip–inoculated in a microsclerotia suspension for 20 seconds before planting. Inoculum was produced by homogenizing 40 potato dextrose agar (PDA, Difco) plates containing the pathogen colonies grown at 30°C in the dark for 2 weeks in a blender with 1600 ml deionized water; the volume was increased to 8 liters with 0.25% water agar medium (2 liters per replication). Isolates 01-179, 02-200, and 05-27, collected in 2001, 2002, and 2005, respectively, were used during the 2010–11 to 2015–16 seasons. During the 2016–17 and 2017–18 seasons, isolate 05-27 was replaced by isolate 09-95, collected in 2009. During the 2018–19 and 2019–20 seasons, isolate 01-179 was replaced by isolate 16-369, collected in 2016. Plants were monitored for the development of typical charcoal rot symptoms, such as wilting and collapse of older leaves with eventual death of the entire plant, every 2 weeks for 4 to 6 months or weekly for 7 to 12 weeks (corn cob and root dip inoculations, respectively). Isolations from symptomatic tissues were performed to confirm the causal agent. Disease incidence was expressed as the proportion (percentage) of the total number of wilting and collapsed plants in relation to the total number of plants.

    Meta-analysis of cultivar selection effects on charcoal rot incidence and disease progress rate.

    Based on the average final disease incidence obtained during the field trials (Table 1), cultivars were organized in three susceptibility groups, highly susceptible (HS; >50% disease incidence), susceptible (S; 25 to 50% disease incidence), and moderately resistant (MR; <25% disease incidence) to charcoal rot; these groups were used in the meta-analysis. Following methodology described by Madden et al. (2016) and Cordova et al. (2017, 2019), a network meta-analysis was performed for two response variables: final disease incidence and disease progress rate. During the first stage of the analysis, strawberry cultivars were grouped based on their level of susceptibility to charcoal rot, hereafter referred to by their susceptibility group. A primary analysis of individual trials was performed to quantify the effects of the susceptibility groups on the two response variables. The means of the final disease incidence for each cultivar and susceptibility group were analyzed in a generalized linear mixed model using PROC GLIMMIX in SAS 9.4 (SAS Institute Inc., Cary, NC). The disease progress rate and intercept parameters were estimated using a monomolecular model with PROC MIXED according to Baggio et al. (2019). The means for the disease progress rate for each susceptibility group in each study were analyzed using PROC GLIMMIX. Following the primary analysis, in which the mean effect sizes and estimated within-study variability were obtained, a multivariate meta-analysis with random effects was conducted to estimate and compare the final disease incidence and disease progress rate of each susceptibility group. The three groups were compared during the 10 seasons, except for the 2010–11 strawberry season, when no MR cultivar was evaluated during the experiment. The effect size for the meta-analysis was the difference in the response variables between each susceptibility group: MR versus HS, MR versus S, and S versus HS. For the final disease incidence and disease progress rate, respectively, the contrast estimate was the ratio of the natural logarithm of the charcoal rot incidence (proportion), presented as the incidence difference (IncidenceD), and the difference between progress rates (day−1). The within-study and among-study variance and weight were calculated, and meta-analysis was performed using PROC MIXED procedure following the methods of Cordova et al. (2017) and Madden et al. (2016).

    Table 1. Final disease incidence (%) of strawberry cultivars with different levels of susceptibility to charcoal rot caused by Macrophomina phaseolina during 10 consecutive strawberry seasons (2010–2011 to 2019–2020)

    Economic impact of cultivar selection on the management of charcoal rot.

    The economic impact of charcoal rot on strawberry production and gross revenue under different cultivar susceptibility scenarios was estimated for the 2014–15, 2015–16, 2016–17, and 2018–19 seasons. Fruit production (total yield) was estimated during trials conducted at UF-GCREC for cultivars Strawberry Festival (HS), Florida Radiance (S), and Sensation Florida127 (MR). Harvests were performed twice per week for 3 to 4 months at research plots, and yield data were expressed as the number of total flats (3.6 kg of fruit per flat) per hectare. Average weekly flat prices were calculated from a survey of commercial farms in Florida performed by the Florida Strawberry Growers Association (FSGA; data not published). The weekly production values and average flat prices were used to calculate the cumulative value (i.e., gross revenue) per plant on a weekly basis for the entire season. The overall economic impact of charcoal rot under increasing levels of disease incidence and progress was estimated for HS, S, and MR strawberry cultivars. Disease progress over time and weekly incidence were estimated for each susceptibility group using the monomolecular model:


    in which y is the disease incidence, t is the time (days after planting), y0 is a parameter related to the disease incidence at time t = 0, and r is the disease progress rate (day−1) (Madden et al. 2007). The progress rate and intercept parameters were estimated by the meta-analytical models fitted to the data from the 10 seasonal trials. Based on the percentage of predicted weekly disease incidence, we calculated the number of plants that were not producing each week because of charcoal rot and how much these weekly plant losses would impact the overall gross revenue. For each susceptibility group, the cost of losing a plant to charcoal rot was calculated weekly as the lost production value (i.e., seasonal plant value minus the cumulative value up to the week lost), because when a plant showed charcoal rot symptoms (wilting and collapse of older leaves with eventual death of the entire plant), it would not produce for the remainder of the season.


    Florida cultivar susceptibility to charcoal rot.

    Six strawberry cultivars commercially important (past or present) to the Florida production were selected from trials conducted over a 10-year period based on the highest, intermediate, and lowest levels of charcoal rot incidence and production traits (Table 1). Cultivars Strawberry Festival, Treasure, and Florida Radiance were used during the 10 seasons; WinterstarFL05-107’ was planted during every season except the first; Sensation ‘Florida127’ was not used during the first two seasons; and ‘Florida Beauty’ was planted during the last four seasons. The final disease incidence averages across seasons for HS cultivars Strawberry Festival and Treasure were 62.4 and 76.8%, respectively. Cultivars Florida Radiance and Florida Beauty had averages of 40.7 and 45.6% final charcoal rot incidence, respectively, and comprised the S group. Finally, disease incidences for Sensation ‘Florida127’and Winterstar ‘FL05-107’ were 21.9 and 21.1%, respectively, and they were included in the MR group.

    Effect of cultivar susceptibility on charcoal rot incidence and disease progress rate.

    The IncidenceD between the MR and HS groups was significantly different from zero for all the cultivar trials except trial number 5 (season 2014–2015), indicating a significative reduction in charcoal rot incidence for the MR group in comparison with the HS group (Fig. 1A). For the S and HS groups, IncidenceD was significantly different from zero for only 3 of the 10 trials; however, the overall mean value from the meta-analysis indicated a significant disease incidence reduction for the S group compared with the HS group (Table 2 and Fig. 1B). The IncidenceD between the MR and S groups was significantly different from zero for five out of nine trials, and the overall mean denoted a significative decrease in charcoal rot incidence for the MR group compared with the S group (Table 2 and Fig. 1C).

    Fig. 1.

    Fig. 1. Forest plot of the log ratio of the disease incidence of strawberry cultivars with different susceptibility levels to charcoal rot caused by Macrophomina phaseolina of 10 trials during consecutive strawberry seasons (2010–11 to 2019–20). A, Moderately resistant (MR) versus highly susceptible (HS). B, Susceptible (S) versus highly susceptible (HS). C, Moderately resistant (MR) versus susceptible (S) cultivars.

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    Table 2. Fit of a multivariate meta-analytical model to charcoal rot incidence (IncidenceD) and progress rate (RateD) based on differences among strawberry cultivars with different levels of susceptibility (moderately resistant, susceptible, and highly susceptible) to charcoal rot caused by Macrophomina phaseolina

    Across the 10 trials, the final disease incidence means recorded for the HS, S, and MR groups were 60.0, 13.6, and 5.1%, respectively (data not shown). The adoption of MR and S groups instead of the HS cultivar groups reduced the disease incidence by averages of 91.5 and 77.3%, respectively (Table 2). In other words, a 50% disease incidence using an HS cultivar was reduced to 4.3% using an MR cultivar, and to 11.4% using an S cultivar. The use of the MR groups instead of the S group reduced the disease incidence by 62.5% (Table 2) or, in a situation of 50% charcoal rot incidence using an S cultivar, the disease incidence was reduced to 18.8% when using an MR cultivar.

    Disease progress rates across the 10 trials were 0.058, 0.035, and 0.017 day−1 for the HS, S, and MR groups, respectively. Significant differences between disease progress rates (RateD) were observed when the MR and S groups were adopted instead of the HS group (Table 2). Conversely, no significant difference (P = 0.1367) between the MR and S groups was noticed (Table 2). Based on the predicted models, charcoal rot epidemics were delayed approximately 40 days when the MR cultivars were used instead of HS cultivars (Fig. 2). Moreover, at the beginning of harvesting season (mid-December), approximately 70 days after planting, the charcoal rot predicted incidence values for the MR, S, and HS groups were 15.4, 74.7, and 94.5%, respectively, and may increase to 78.9, 98.5, and 99.9%, respectively, toward the end of the season in March (Fig. 2).

    Fig. 2.

    Fig. 2. Disease progress curves over the strawberry season for moderately resistant (MR), susceptible (S), and highly susceptible (HS) cultivars estimated by the meta-analytical models fitted to the combined data from 10 seasonal trials obtained during the meta-analysis. Final disease incidences predicted by the model were 78.9, 98.5, and 99.9% for MR, S, and HS cultivars, respectively. Orange stripe: beginning of the harvest season.

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    Economic impact of cultivar selection on the management of charcoal rot.

    Because of the similar results obtained for the 2014–15, 2015–16, and 2016–17 seasons, and because of the atypical conditions (reduced yield) during the 2018–19 season, only the assessment for the 2016–17 season is presented (Fig. 3). Total fruit yield for cultivars Sensation Florida127 (MR), Florida Radiance (S), and Strawberry Festival (HS) were 29,435, 28,501, and 23,367 kg/ha, respectively. Based on weekly fruit yields and weekly prices, the total gross revenue for these cultivars were US$87,031, 80,804, and 61,101 per hectare, respectively. At a planting density of 40,333 plants/ha, the average seasonal US$ values per plant for each of the susceptibility groups, determined based on the total gross revenue and number of plants per hectare, were US$2.16, 2.00, and 1.51, respectively.

    Fig. 3.

    Fig. 3. Estimated economic impact of charcoal rot on strawberry production gross revenue (US$ value of lost plants per hectare) for cultivars Sensation Florida127 (moderately resistant [MR]), Florida Radiance (susceptible [S]), and Strawberry Festival (highly susceptible [HS]) over the harvest season based on weekly disease incidence and plant value. Impacts were determined for the 2016–17 strawberry season and used average weekly prices and fruit production functions from each cultivar susceptibility group by considering 40,333 plants/hectare. Disease progress over time and weekly incidence were estimated using the monomolecular model y = 1−(1−y0)exp(−rt) with parameters obtained during the meta-analysis. Overall plant value lost (US$) was determined based on the incidence of charcoal rot and weekly value of each plant for each susceptibility group of cultivars and seasonal production and pricing. Seasonal plant value was determined based on the total gross revenue and number of plants per hectare for MR, S, and HS cultivars: US$2.16, 2.00, and 1.51 per plant, respectively.

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    When we combined the estimate of the charcoal rot disease incidence of each susceptibility group with economic values of individual plants for each week, we were able to assess the impact of plant loss on the gross revenue throughout the season (Fig. 3). Because of the high incidence levels of charcoal rot in the beginning of the season for S and HS cultivar groups (Fig. 2), cultivation of these groups instead of the MR group generated higher plant and economic losses (Fig. 3). For example, approximately 60 days after planting (first month into harvesting season), gross revenue losses of approximately US$2100, 52,600, and 55,700 per hectare were observed for MR, S, and HS cultivar groups, respectively (Fig. 3).


    This study demonstrated that the adoption of MR strawberry cultivars was an effective nonchemical strategy for managing charcoal rot in Florida strawberry fields. We were able to identify differences in the susceptibility of strawberry cultivars to M. phaseolina and estimate the economic impact of cultivar selection on disease management.

    Reduced disease incidence and progression over time for less susceptible cultivars could be associated with host–pathogen interaction characteristics because significantly less pathogen DNA was detected in these cultivars when compared with highly susceptible cultivars during a previous study (Winslow et al. 2017). However, no complete resistance to charcoal rot was observed during our studies, which was in agreement with other studies (Holmes et al. 2020; Sánchez et al. 2016; Winslow et al. 2017). The cultivar Strawberry Festival was classified as highly susceptible, as previously reported during a screening study of >90 U.S. strawberry cultivars (Winslow et al. 2017). Conversely, during greenhouse studies performed in Chile, ‘Florida Radiance’, marketed outside the United States as ‘Florida Fortuna’, was more susceptible to charcoal rot than ‘Strawberry Festival’ and showed high disease severity, significant reduction in the dry weight of plants, and plant mortality >70% (Sánchez et al. 2016). However, our studies, which were conducted over a 10-year period in field conditions, demonstrated that ‘Florida Radiance’ was less susceptible than ‘Strawberry Festival’.

    During this study, comparisons among different susceptibility groups of cultivars to charcoal rot were also investigated. The meta-analysis of the outcomes of 10 field trials showed that the adoption of MR and S cultivar groups reduced the charcoal rot incidence and plant loss (mortality) and increased gross revenue when compared with the HS group. Although significant, this difference was less pronounced between the S and HS groups.

    Variations in the disease response were observed throughout the trials, probably because of the use of isolates differing in their aggressiveness to strawberry (Baggio et al. 2019), differences in environmental conditions among the growing seasons, and different inoculation methods. In fact, the higher incidence and faster disease development observed during the latter five seasons, regardless of the cultivar, might be related to the more aggressive inoculation method, whereby trimmed roots were dipped in microsclerotia suspension. The combination of isolates with different levels of aggressiveness has been reported to be a useful strategy for resistance screens because moderately aggressive isolates could differentiate between cultivars with low or moderate resistance, whereas aggressive isolates could be used to differentiate between cultivars with high levels of resistance (Fang et al. 2012; MacKenzie et al. 2006). Moreover, differences in the environment can influence the expression of different mechanisms involved in the resistance to charcoal rot (Coser et al. 2017; Nelson 2018). However, these variations are accounted for by the meta-analysis, which combines results from multiple trials and evaluates the effects of treatments or the relationships among variables (Madden and Paul 2011).

    Estimated yield and weekly strawberry prices were used together with the estimated disease progress curve parameters from the meta-analysis to assess the economic impact on gross revenue of using certain group of cultivars at different charcoal rot occurrence scenarios. Because the 10 trials were usually finalized before the end of the commercial strawberry seasons (March or April), the final incidences obtained for March (Figs. 2 and 3) were based on disease progress curves predicted by the meta-analytical models. Although strawberry growers select cultivars based on their desirable agronomic and market traits, strawberries are not marketed to the general public with their cultivar identity. Therefore, strawberry prices are not typically different among cultivars. Fluctuations of strawberry fruit prices within and among Florida strawberry seasons depend on several factors: the percentage of acreage planted with a certain cultivar; market competition, especially with Mexico and California; and timing of the peak of fruit production, which is related to environment conditions, cultivar agronomic traits, and diseases; all of these can drastically influence weekly strawberry prices. Because of the high crop value and the same or similar costs for transplants of the cultivars, the adoption of a more resistant cultivar would likely minimize yield losses and, thus, cumulative economic losses during the production season. For example, considering a production cost of $75,000 per hectare (Guan et al. 2017), a loss of >$50,000 because of charcoal rot caused by the use of HS and S cultivars represents a significant economic impact on strawberry production and gross revenue. Therefore, the use of less susceptible cultivars could minimize losses.

    The most predominant strawberry cultivars currently used by Florida growers are Florida Brilliance, Sensation Florida127, and Florida Radiance, representing 52, 29, and 9% of planted hectares during the 2019–20 season (Whitaker and Agehara 2020). Despite being easy to harvest, producing very attractive fruit with a long shelf life, and being the predominant cultivar for years, ‘Strawberry Festival’ is HS to charcoal rot and is rarely used today by growers, mainly because of its later production and lower yields (Chandler et al. 2000). This is consistent with the lower total gross revenues and value per plant and higher economic losses because of premature plant loss to charcoal rot early during the season observed in this study. The other two cultivars selected for harvest data during this study, Florida Radiance (S) and Sensation Florida127 (MR), both produced earlier and higher yields; therefore, they had larger total revenues and values per plant (Whitaker et al. 2017a, 2019b). Fortunately, because of the MR profile of cultivar Florida127 regarding charcoal rot, the final incidence values are lower and development of the epidemic is delayed. For example, near the start of harvest, 50 days after planting, the charcoal rot incidence values of HS and S cultivars are already >80 and >50%, respectively, whereas the epidemic has yet to develop in MR cultivars. When an epidemic occurs, the disease incidence is usually relatively low. Therefore, planting these cultivars in areas with a history of charcoal rot would decrease the economic impact of charcoal rot on gross revenue. Moreover, the delay in disease development would enhance the benefits of cultivars that produce early during the season, thus increasing the economic return for crop investment during the early season, when strawberry prices are usually higher.

    Two of the three cultivars that currently dominate commercial strawberry production in Florida, Sensation Florida127 and Florida Brilliance, are MR to charcoal rot (Whitaker et al. 2017a, 2018a). Similar to Sensation ‘Florida127’, ‘Florida Brilliance’ produces earlier and higher yields desired by growers (Whitaker et al. 2018a). Both cultivars could be used to help minimize the economic impact of charcoal rot. However, the MR cultivar Winterstar FL05-107 produces inconsistent quality and lower yields than current cultivars (Whitaker et al. 2018b); therefore, it has not been grown widely.

    Unfortunately, there are no cultivars resistant to all the diseases that affect Florida strawberry. For example, Sensation ‘Florida127’, ‘Florida Brilliance’ and ‘Florida Radiance’ are susceptible to Phytophthora crown rot, which is caused by Phytophthora spp., which are usually harbored by asymptomatic nursery transplants transported to production fields (Pettitt and Pegg 1994; Whitaker et al. 2017a, 2019b). An alternative would be the adoption of cultivars less resistant to charcoal rot, such as ‘Florida Beauty’, for example, which is reported to be more resistant to Phytophthora crown rot (Whitaker et al. 2017b). Although disease progress rates of MR and S cultivars are not significantly different, disease usually starts earlier with an S cultivar. Therefore, the selection of cultivars should be based on the disease history of production fields.

    Thankfully, for the management of charcoal rot, HS cultivars are no longer widely used in Florida, and even Florida Radiance (S) is disappearing from production in favor of Florida Brilliance. Although the inoculation methods used were aggressive, they simulated naturally occurring epidemics observed in areas with high levels of inoculum and disease pressure. In fact, in commercial fields affected by charcoal rot during the 2017 to 2018 Florida season, when preplanting soil fumigation was not performed, the disease incidence for ‘Florida Radiance’ was close to 60% during the early season (Baggio et al. 2021).

    Our results demonstrated in a quantitative manner that the adoption of strawberry cultivars MR to charcoal rot reduced disease development and plant loss (mortality), minimized but did not eliminate yield reduction, and, consequently, reduced the economic impact on strawberry production revenue. Therefore, the use of MR cultivars should be considered a valuable tool to incorporate in integrated disease management programs for charcoal rot.


    We thank all staff, students, and interns for field assistance and collecting data from these trials over the years.

    The author(s) declare no conflict of interest.

    Literature Cited

    The author(s) declare no conflict of interest.

    Funding: This research was supported by the Florida Agricultural Experiment Station and the Florida Strawberry Research and Education Foundation.