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ASHS 2024 Annual Conference

 

Rapid-screening Bioassay Assessing Potential Allelopathic Influence on Spinach by Aqueous Extract from Fresh, Whole-plant Sorghum-sudangrass Tissue

Authors:
Kenneth W. Pierce College of Interdisciplinary Studies—Environmental Science/Agriculture, Tennessee Technological University, Box 5034, Cookeville, TN 38505, USA

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Michael P. Nattrass School of Agriculture, Tennessee Technological University, Box 5034, Cookeville, TN 38505, USA

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Abstract

Cover crops are defined as crops grown primarily for agroecosystem improvement rather than for market or sale. The use of cover crops to decrease the negative effects of weeds and improve soil and ecosystem health is increasing, but unanticipated allelopathic responses to those cover crops by subsequent crops is sometimes a problem. Allelopathy is broadly defined as the biochemical interactions between all types of plants, including microorganisms. Because allelopathic effects include both inhibitory and stimulatory responses and may be species- and cultivar-specific, a method of rapidly screening donor and recipient crops for allelopathic interactions is needed. The objective of this research was to evaluate a growth chamber bioassay for rapidly screening spinach (Spinacia oleracea L.) cultivars for allelopathic interactions with an aqueous extract from fresh whole-plant tissue of sorghum-sudangrass [Sorghum bicolor (L.) Moench; SSG] cultivars. The bioassay exposed the seed of 10 spinach cultivars to the aqueous extract of three cultivars of SSG during the imbibition and germination processes and evaluated the consequent root and stem development. Compared with the control, the extract from all three SSG cultivars decreased the root length of all spinach cultivars. A subsequent field screen where spinach cultivars were planted into decomposing SSG residue resulted in a similar pattern of growth suppression. These results demonstrate that the growth chamber bioassay is suitable for predicting allelopathic interactions between cultivars of SSG and cultivars of spinach and can be used by growers for making cultivar selection decisions when spinach follows SSG in a cropping sequence. This rapid-screening growth chamber bioassay protocol eliminates many of the environmental and other challenges frequently associated with field trials and may be adaptable for predicting allelopathic interactions among other cover crops, weeds, and subsequent market crops.

Allelopathy is broadly defined as the “biochemical interactions between all types of plants, including microorganisms” (Rice 1984). Although the term is used most often in a negative context to describe inhibitory effects, the general concept of allelopathy incorporates stimulatory effects as well (Cheema et al. 2013). An allelopathic effect can be described as enhancement or suppression of growth of one organism, usually a plant referred to as the “target” or “receiver,” by another organism, the “donor,” as a result of the phytochemical compounds and secondary metabolites it produces and releases.

Allelopathic interactions are found in both managed agronomic and natural ecosystems (Chou 1999). Allelochemical production is influenced by both genetic and environmental factors that can produce various agroecological effects, which include enhanced microbial activity, improved soil health, decreased weed infestation, and increased forage and crop yields (Trezzi et al. 2016). The release of allelopathic compounds from donor plants may occur from the leaves in which rainfall leaches the compounds into the soil through root exudation, volatilization, and even the death and decay or microbial degradation of the plant (Ross and Lembi 2009; Shah et al. 2016). The latter is a common method of release when cover crops are incorporated into the soil. Residue management may be a key factor in taking maximum advantage of allelopathic properties (Langeroodi et al. 2018; Wortman et al. 2013).

Cover crops.

Cover crops, which include those for green manure, are generally defined as crops grown primarily for soil or agroecosystem improvement rather than for market or sale (Wszelaki and Broughton 2012). A variety of plant types and species can be used as cover crops, and the selection of the appropriate cover crop depends on the intended benefit and subsequent crop and growing practices. Cover crops include both cool-season and warm-season annuals, perennials, grasses, legumes, nonlegumes, and mixtures of two or more species. Seeding dates vary by species and geographic location. Cover crops are typically ended before or soon after seeding the main crop, such as spinach, via chemical or various mechanical means (Dorn et al. 2013; Hoorman 2009). The termination date and method are determined by factors such as crop rotation, climate, the C-to-N ratio (C:N), as well as residue management goals (SARE 2012). In addition to chemical (herbicide) treatments, termination options may include mowing, incorporation, rolling–crimping, tillage, or grazing.

Importance of sorghum-sudangrass.

SSG [Sorghum bicolor (L.) Moench] is classified as a warm-season annual grass adapted to a wide variety of soil and climate conditions that is frequently used as a summer cover crop (Baldwin and Creamer 2006; SARE 2012). It is high-yielding, producing up to 27.3 Mg⋅ha−1 of dry biomass (Hoorman 2009). As a cover crop, SSG can be mowed, rolled, or crimped to provide mulch for weed suppression and moisture retention. As a green manure crop, it can be incorporated into the soil to increase the organic matter content. Jabran (2017) stated that Sorghum species are essential agronomic crops with strong allelopathic potential that can be exploited for weed control in other field crops.

The allelopathic effects of SSG have been documented for several market crops and weed species, with the expression of allelopathy and the degree of effect varying with cultivar or genotype (Besancon et al. 2020), growth stage, growing environment (Dayan 2006), and cropping system (Jabran et al. 2015). Sorghum-sudangrass allelopathy can decrease yields of subsequent crops that are direct-seeded or grown from transplants (Finney et al. 2009). Sorgoleone (hydrophobic p-benzoquinone), several phenolics, and dhurrin (a cyanogenic glycoside) have been identified as allelopathic compounds isolated from sorghum. All Sorghum genotypes produce sorgoleone to some extent, and it is phytotoxic to a wide range of plant species (Weston et al. 2013). The aerial parts of sorghum produce mostly phenolic compounds, whereas the sorgoleone is produced by and exuded from the root hairs.

Importance of spinach.

Spinach (Spinacia oleracea L.) is an important leafy and highly nutritious vegetable crop that is in increasing demand because of its consumption versatility. Much is consumed fresh, but it is also cooked alone and used as a component in other prepared dishes (Morelock and Correll 2008). Furthermore, it preserves well and can be easily processed, canned, and frozen. According to the US Department of Agriculture, National Agricultural Statistics Service vegetables annual summary of 2021, the United States produced almost 314,679 metric tons of spinach valued at US$496 million (US Department of Agriculture, National Agricultural Statistics Service 2022).

Spinach as a market crop is typically direct-seeded into the field and is regularly grown by both organic and conventional producers. Spinach is suspected to have been first domesticated in what is Iran today, but the precise timeline and migration paths are unclear (Ribera et al. 2020). Although many cultivars exist, spinach is described according to one of three leaf textures: savoy, (wrinkled), smooth, or semi-savoy. Savoy leaf-type cultivars are sometimes preferred for shipping and packing because they result in less compaction during transport (Ribera et al. 2020). Smooth leaf cultivars are preferred for canning and freezing because they are easier to clean (Ma et al. 2016). However, leaf type does not affect acceptance for freeze-dried spinach (Wisakowsky et al. 1977), and all three leaf types are suitable and acceptable for fresh market sales.

In recent years, spinach nutritive research has expanded beyond basic vitamin and mineral content to include other compounds identified as phytochemicals and bioactives that exhibit antioxidative, anti-inflammatory, and hepatoprotective effects when consumed by humans (Ramaiyan et al. 2020; Roberts and Moreau 2016). Several previous studies demonstrated greater leaf accumulation of nitrates in savoy than in smooth types (Barker et al. 1974; Olday et al. 1976). More recently, Hayes et al. (2020) observed a significant correlation between beta-carotene bioavailability and leaf texture, with the smooth cultivars providing higher relative content. These studies suggest that other traits, such as allelopathic sensitivity, may also be correlated with leaf texture.

The gene pool that influences the spinach leaf texture has remained relatively small compared with that of many other crops (Ribera et al. 2020). Although breeding efforts have focused on yield and disease resistance (Pandey and Kalloo 1993), future cultivar development and selection efforts will need to emphasize performance in heat and drought stress situations. Climate change is predicted to have an impact on global spinach production, with warmer temperatures and perhaps the related salt stress posing major challenges. To date, little breeding work has been performed to address abiotic stress associated with climate change, and that is expected to expand because the quantity of available wild types has recently increased (Ribera et al. 2021). Access to those accessions for breeding purposes will likely lead to additional cultivars with improved agro-morphological characteristics, and those cultivars will eventually need to be evaluated for potential allelopathic interactions with other crops.

With the understanding that the allelopathic interactions may be cultivar-specific, and that cultivars may represent different leaf phenotypes, the cultivars selected for the present experiments include representatives from each leaf type. Cultivars representing both hybrid and open-pollinated seed production were also specifically selected for inclusion in the study.

Potential benefits of performing the germination screening bioassay.

Research has shown that allelopathic effects and interactions are species-specific (Hong and Hu 2007; Jabran 2017), and that monocots may react differently than dicots to a specific allelochemical. Research with oats (Avena sp.) demonstrated that allelopathic effects and interactions may be cultivar-specific (Fay and Duke 1977). Xuan et al. (2003) reported cultivar-specific responses with alfalfa (Medicago sativa L.). Putnam and Duke (1974) suggested that many of the major world crops may have, at one point, produced allelopathic compounds to aid in survival and competition, but the characteristic may have been lost or diminished during domestication. Consequently, screening collections of cultivated varieties and wild accessions for allelopathic potential may identify valuable germplasm for breeders to use for developing crops that resist the negative impact of weeds, or that may be useful for developing bioherbicides. Therefore, it is important to develop a relatively rapid-screening bioassay protocol for evaluating specific cultivar or accession allelopathic sensitivity within species. Such screening protocols should also be useful to breeders using marker-assisted selection technology to evaluate spinach performance under adverse allelopathic influences (Morelock and Correll 2008).

Growth chamber bioassays can help differentiate the effects of simple competition from the effects of allelopathic interactions that can be very difficult to partition in a field setting (Elmore 1985). Because allelopathic effects are based on composition and concentration (Amb and Ahluwalia 2016), growth chamber bioassays must simulate typical field incorporation rates. However, a significant advantage of growth chamber bioassays is that they can be conducted any time of the year without the environmental and other challenges associated with field trials. To our knowledge, research regarding screening bioassays for allelopathic interactions among SSG and spinach cultivars is lacking.

Objectives.

The objectives of this study were to develop a bioassay protocol for rapidly screening spinach cultivars for allelopathic interactions with an aqueous extract from fresh whole-plant tissue from SSG cultivars, evaluate 10 popular spinach cultivars for allelopathic interactions with three commonly available cultivars of SSG, and correlate the bioassay results to field observations.

Materials and Methods

The foundation of this research was based on a concept for screening a soybean seed sample for the expression of the Roundup Ready™ (glyphosate tolerance) gene. The specific bioassay was first published by Iowa State University (Goggi and Stahr 1997), and it was later adapted by the Association of Official Seed Analysts (AOSA) for seed testing officials and the commercial seed testing industry (AOSA 2001). The protocol involves examining the shoots and radicles of seed that have been exposed to a 0.82% active ingredient (a.i.) of glyphosate during the imbibition and germination process. The seedlings demonstrating the presence of the glyphosate tolerance gene appear normal, whereas those without the gene appear stunted and abnormal with very little, if any, secondary root development.

Since Dayan et al. (2009, 2010) described the primary mode of action of sorgoleone, a primary allelopathic constituent of SSG, as inhibiting photosynthesis in germinating seedlings, the rationale for this potential allelopathic screening protocol is that the sensitivity of spinach seedlings to allelopathic compounds in the aqueous extract of the SSG might be evaluated through techniques similar to that for glyphosate gene expression.

SSG planting and growth.

Outdoor plots were selected at Tennessee Tech University’s Shipley Farm (36°11′051″ N, 85°32′0″ W) and seeded with three SSG cultivars: FSG 214 Brown Mid-Rib 6 (BMR), Greengrazer V (GGV), and Sugar Graze 2 (SG2). Plots were seeded on 10 Jun 2022, with a no-till seed drill calibrated to sow 50 kg⋅ha−1 with a planting depth of 2.5 cm. A 60-cm buffer to provide distinct separation between the SSG cultivars and an adjacent control plot were maintained vegetation-free via mechanical removal or chemical applications of a 1% glyphosate herbicide solution (Fig. 1). A sample report of the Mountview silt loam showed that the plot soil pH was 5.6 with 2.25% organic matter content, with major and minor nutrients at sufficient levels for adequate plant growth.

Fig. 1.
Fig. 1.

Field plot source of sorghum-sudangrass tissue used for the fresh, whole-plant, aqueous extract and location of field screening of nine spinach cultivars.

Citation: HortScience 58, 10; 10.21273/HORTSCI17158-23

SSG extraction for growth chamber bioassays.

Twenty whole plants of each SSG cultivar were carefully removed from the plots 40 d after planting (DAP), and as much of the soil as possible was removed without rinsing or damaging the roots of the plants. The fresh biomass was weighed, cut into small pieces, and placed in a Waring blender with distilled water at a rate of 10.5 g of fresh plant material per 100 mL of distilled water. The biomass rate was based on field incorporation (to a depth of 15 cm) calculations for dry matter yields reported by Hoorman (2009) adjusted to include the unwashed root system and for plant moisture content. The plant material was pulverized in the blender on the medium (#5) setting for 10 min. To remove solids from the extract, a two-step filtration process consisting of cheesecloth, followed by Whatman #1 filter paper, was used. The extract appeared as a green or brownish liquid (Fig. 2). The extract was refrigerated at 2 °C until use.

Fig. 2.
Fig. 2.

Filtered, fresh, whole-plant, aqueous sorghum-sudangrass extract.

Citation: HortScience 58, 10; 10.21273/HORTSCI17158-23

Spinach selection and growth chamber bioassays.

A panel of 10 common spinach cultivars were selected for screening bioassays that represented the savoy, smooth, and semi-savoy leaf characteristics (Table 1). The cultivars also represented both hybrid and open-pollinated seed production techniques. Growth chamber bioassays consisting of 10 seeds each of the 10 cultivars were conducted between two standard germination towels (Anchor Paper Co., St. Paul, MN, USA) according to the AOSA rules for testing seed (AOSA 2001). The previously prepared plant extract was removed from refrigeration and allowed to reach room temperature (∼22 °C). Approximately 15 mL of the extract (treatment) was required to saturate two towels. One layer of the saturated germination towel was placed on a layer of wax-coated paper and identified with the appropriate treatment and planting date (Fig. 3). Seed were placed in a single row in the center of the towel and covered with the second saturated towel. The edges of the waxed paper were folded over the two layers of towels and loosely rolled into a cylinder and secured with a rubber band at the bottom. The outside of each roll was labeled with the SSG treatment, replication number, and spinach cultivar (Fig. 4). Rolls were placed upright in cylindrical polypropylene containers designated for the BMR, GGV, and SG2 treatments; then, they were covered with polyethylene film to help retain moisture and contain any volatile organic compounds from the extract. Ten spinach cultivars were represented in each container. Distilled water was used in a similar manner as a control and placed in a separate container. Then, polypropylene containers were placed in a growth chamber set at a constant 15 °C (Fig. 5). At 14 DAP, the number of seeds that had germinated, root length, and shoot length were recorded for each seedling (Fig. 6). There were three replications of each assay in a split plot design with the SSG cultivar treatment as the main plot and the spinach cultivar as the subplot. The statistical analysis was performed using the general linear model procedure, with multiple comparisons made using least square means and mean separation using Duncan’s multiple range test at α = 0.05 (SAS version 9.4; SAS Institute Inc., Cary, NC, USA).

Table 1.

Spinach (Spinacia oleracea L.) cultivar names, pollination method, and leaf types of the cultivars screened for allelopathic interactions with the aqueous extract from fresh sorghum-sudangrass [Sorghum bicolor (L.) Moench] tissue.

Table 1.
Fig. 3.
Fig. 3.

Ten spinach seed placed in a single row on standard weight germination paper saturated with the sorghum-sudangrass treatment.

Citation: HortScience 58, 10; 10.21273/HORTSCI17158-23

Fig. 4.
Fig. 4.

Each roll was labeled with the sorghum-sudangrass treatment, replication number, and spinach cultivar.

Citation: HortScience 58, 10; 10.21273/HORTSCI17158-23

Fig. 5.
Fig. 5.

Ten spinach cultivars in each polypropylene container covered with polyethylene film and placed in a growth chamber set for a constant 15 °C.

Citation: HortScience 58, 10; 10.21273/HORTSCI17158-23

Fig. 6.
Fig. 6.

Example of Acadia spinach in distilled water control compared to Greengrazer V sorghum-sudangrass extract 14 d after planting.

Citation: HortScience 58, 10; 10.21273/HORTSCI17158-23

Field screening of spinach in SSG residue.

Portions of the same plots from which the whole plants were taken and an adjacent control plot with no vegetation were used for field screening a panel of nine spinach cultivars. To end the SSG to prepare for planting, the plots were crimped on 15 Aug 2022, and the residue was incorporated on 23 Sep 2022. Aboveground biomass was ∼1.6 kg/m2 incorporated to a depth of 15 cm. Final seedbed preparation occurred on 28 Sep 2022, and planting occurred the next day. Spinach seed were planted at a depth of 1.25 cm on 5-cm centers to provide 20 seed per row. There were three rows (replications) of each spinach cultivar per treatment in a randomized complete block design. Plots were irrigated immediately after planting with the equivalent of ∼0.6 cm of rainfall. The number of emerged seedlings were recorded at 14, 21, 28, and 35 DAP, and a final count was made at 42 DAP. A statistical analysis was performed using the general linear model procedure with mean separation using Duncan’s multiple range test at α = 0.05 (SAS version 9.4; SAS Institute Inc., Cary, NC, USA).

Results and Discussion

Growth chamber bioassay results.

When grouped and analyzed collectively according to leaf type, all SSG treatments decreased the overall seedling lengths compared with the control (Table 2). The BMR treatment decreased seedling length of the smooth leaf types (P < 0.001). Seedling length was not different between the three SSG treatments for the savoy and semi-savoy leaf types.

Table 2.

Mean seedling length response of spinach (Spinacia oleracea L.) by leaf type to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 2.

During comparisons of the overall seedling length of the selected cultivars grouped according to pollination techniques used during seed production, all SSG treatments decreased the overall seedling lengths compared with the control (P < 0.001) (Table 3). Of the three SSG treatments, BMR showed the greatest effect; it decreased the mean seedling length response by 26.4% in both hybrid and open pollinated cultivars. There was no significant difference between the GGV and SG2 treatments when the spinach cultivars were grouped according to pollination techniques.

Table 3.

Mean seedling length response of spinach (Spinacia oleracea L.) by pollination technique to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 3.

Several significant observations were noted among the individual spinach cultivars within each leaf type. Compared with the control, the total seedling length for all spinach cultivars was decreased by each of the three SSG cultivar treatments (P < 0.001) (Tables 4 and 7). However, the response was cultivar-specific for both the SSG donors and spinach recipients. These observations are consistent with cultivar-specific responses described for other crop allelopathic interactions (Fay and Duke 1977; Xuan et al. 2003).

Table 4.

Mean savoy and semi-savoy leaf-type spinach (Spinacia oleracea L.) cultivar seedling length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 4.

For example, ‘Tundra’ seedling length was decreased more by SG2 than BMR, whereas ‘Gazelle’ and ‘Reflect’ seedling lengths were decreased more by BMR than by SG2. A similar trend can be observed in the root length responses (Tables 5 and 8). Compared with the control, all SSG treatments decreased root lengths of all spinach cultivars (P < 0.001). As with the overall seedling length, ‘Tundra’ root length was decreased more by SG2 than by BMR, whereas ‘Gazelle and ‘Reflect’ were decreased more by BMR than by SG2 treatments (P < 0.001). None of the stem lengths was decreased by any of the SSG treatments (Tables 6 and 9). In the case of ‘Matador’, stem length seemed to be enhanced by the GGV and SG2 treatments compared with the control. Mean germination was relatively unaffected by the SSG treatments compared with the control (Tables 10 and 11). Table 12 summarizes the seedling length response of each spinach cultivar to each of the treatments in the growth chamber bioassay. The response to the control demonstrates that growth rate differences exist between the spinach cultivars, which may be caused by genetics, seedling vigor, or seed quality. Responses of the spinach cultivars to the specific treatments shown in Table 12 can be used by growers to select the cultivar that is least sensitive to the allelopathic effects of a specific SSG cultivar. For example, if a grower chooses to plant spinach in BMR SSG residue, then ‘Tundra’ is recommended and ‘Gazelle’ should be avoided. Likewise, for planting into SG2 SSG residue, ‘Reflect’ would be a better cultivar selection than ‘Tundra’ or ‘Acadia’.

Table 5.

Mean savoy and semi-savoy leaf-type spinach (Spinacia oleracea L.) cultivar root length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 5.
Table 6.

Mean savoy and semi-savoy leaf-type spinach (Spinacia oleracea L.) cultivar stem length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay 14 at d after planting.

Table 6.
Table 7.

Mean smooth leaf-type spinach (Spinacia oleracea L.) cultivar seedling length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 7.
Table 8.

Mean smooth leaf-type spinach (Spinacia oleracea L.) cultivar root length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 8.
Table 9.

Mean smooth leaf-type spinach (Spinacia oleracea L.) cultivar stem length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay 14 d after planting.

Table 9.
Table 10.

Mean savoy and semi-savoy leaf-type spinach (Spinacia oleracea L.) cultivar germination percentage response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 10.
Table 11.

Mean smooth leaf-type spinach (Spinacia oleracea L.) cultivar germination percentage response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 11.
Table 12.

Mean spinach (Spinacia oleracea L.) cultivar seedling length response to fresh, whole-plant, aqueous extract of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars in a growth chamber bioassay at 14 d after planting.

Table 12.

Field screening results of spinach in SSG residue.

This component of the experiment was designed to evaluate the predictive correlation between the growth chamber bioassays using the fresh, whole-plant, aqueous extract and an actual field environment. Although the number of emerged seedlings were recorded at 14, 21, 28, 35, and 42 DAP, only the counts at 21 DAP (Tables 13 and 14) and 42 DAP (Tables 15 and 16) are shown. In accordance with the protocols of the AOSA (2001), 21 DAP represents the time by which most anticipated germination has occurred during an official seed germination test. Bessin et al. (2021) suggests 42 DAP as the potential first harvest of field-planted spinach.

Table 13.

Mean savoy and semi-savoy leaf-type spinach (Spinacia oleracea L.) cultivar survival percentage response to field-incorporated residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars at 21 d after planting.

Table 13.
Table 14.

Mean smooth leaf type spinach (Spinacia oleracea L.) cultivar survival percentage response to field-incorporated residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars 21 d after planting.

Table 14.
Table 15.

Mean savoy and semi-savoy leaf-type spinach (Spinacia oleracea L.) cultivar survival percentage response to field-incorporated residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars 42 d after planting.

Table 15.
Table 16.

Mean smooth leaf-type spinach (Spinacia oleracea L.) cultivar survival percentage response to field-incorporated residue of sorghum-sudangrass [Sorghum bicolor (L.) Moench] cultivars 42 d after planting.

Table 16.

Assuming the spinach seed are healthy and viable, the anticipated seedling emergence in a field environment can be 60% to 80% of the total number of seeds planted (OSU 2010). Initial mean emergence in the control plot during this experiment ranged from 45.0% to 66.7%, which was somewhat lower than expected and may have negatively affected the planned comparisons. The total number of emerged seedlings fluctuated over the course of the experiment as some seedlings declined and died, whereas additional seedlings emerged. Progressive decline and death in the treatments were somewhat expected in the treatments because Guenzi (1967) noted that decomposing sorghum residues exhibited phytotoxic effects on wheat for up to 16 weeks after soil incorporation.

The overall suppressive allelopathic effects of the SSG treatments observed in the growth chamber bioassays were also observed in the field screen. Seedling emergence and survival for all spinach cultivars were decreased by each of the three SSG cultivar treatments compared with the control (P < 0.001). As in the growth chamber bioassays, the response to the allelopathic effect of the decomposing SSG residue was both cultivar donor-specific and cultivar recipient-specific. The differing effects of the SSG cultivars on spinach cultivar performance was consistent with the genetic influences described by Besancon et al. (2020). Of the three treatments, the decomposing BMR residue seemed to suppress the growth most and should be avoided as a summer cover crop if a fall crop of spinach is planned. Decreased germination and decreased survival of the spinach in the field setting compared with the growth chamber bioassays further highlight the need and importance of rapid screening growth chamber bioassays that are unaffected by weather and other environmental factors.

Conclusions

An aqueous extract from fresh whole-plant SSG tissue can be used to screen for potential allelopathic interactions between cultivars of SSG and cultivars of spinach. The screening observations are consistent with the literature demonstrating that allelopathic interactions may be cultivar-specific (Fay and Duke 1977; Xuan et al. 2003) and can be used by growers for making cultivar selection decisions when spinach follows SSG in a cropping sequence. This rapid-screening growth chamber bioassay protocol eliminates many of the environmental and other challenges frequently associated with field trials, and it may be adaptable for predicting allelopathic interactions among other cover crops, weeds, and subsequent market crops.

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  • Langeroodi A, Radicetti E, Campiglia E. 2018. How cover crop residue management and herbicide rate affect weed management and yield of tomato (Solanum lycopersicon L.) crop. Renewable Agric Food Syst. https://doi.org/10.1017/ S1742170518000054.

  • Ma J, Shi A, Mou B, Evans M, Clark J, Motes D, Correll J, Xiong H, Qin J, Chitwood J, Weng Y. 2016. Association mapping of leaf traits in spinach (Spinacia oleracea L.). Plant Breed. 135:399404.

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  • Morelock T, Correll J. 2008. Spinach. In: Prohens J, Nuez F (eds). Vegetables I. Handbook of plant breeding. Springer, New York, NY, USA.

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    • Export Citation
  • Ramaiyan B, Kour J, Nayik G, Anand N, Alam M. 2020. Spinach (Spinacia oleracea L.), p 159–173. In: Ahmad Nayik G, Gull A (eds). Antioxidants in vegetables and nuts: Properties and health benefits. Springer, New York, NY, USA.

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  • Ribera A, Van Treuren R, Kik C, Bai Y, Wolters A. 2021. On the origin and dispersal of cultivated spinach (Spinacia oleracea L.). Genet Resources Crop Evol. 68:10231032.

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  • US Department of Agriculture, National Agricultural Statistics Service. 2022. Vegetables 2021 Summary (February 2022) ISSN: 0884-6413.

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    • Export Citation
  • Wszelaki A, Broughton S. 2012. Cover crops and green manures. Publication W235-G. University of Tennessee Extension, Knoxville, TN, USA.

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    • Search Google Scholar
    • Export Citation
  • Fig. 1.

    Field plot source of sorghum-sudangrass tissue used for the fresh, whole-plant, aqueous extract and location of field screening of nine spinach cultivars.

  • Fig. 2.

    Filtered, fresh, whole-plant, aqueous sorghum-sudangrass extract.

  • Fig. 3.

    Ten spinach seed placed in a single row on standard weight germination paper saturated with the sorghum-sudangrass treatment.

  • Fig. 4.

    Each roll was labeled with the sorghum-sudangrass treatment, replication number, and spinach cultivar.

  • Fig. 5.

    Ten spinach cultivars in each polypropylene container covered with polyethylene film and placed in a growth chamber set for a constant 15 °C.

  • Fig. 6.

    Example of Acadia spinach in distilled water control compared to Greengrazer V sorghum-sudangrass extract 14 d after planting.

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  • Hoorman J. 2009. Using cover crops to improve soil and water quality. ANR-57. Ohio State University Extension, Lima, OH, USA.

  • Jabran K. 2017. Manipulation of allelopathic crops for weed control. Springer International Publishing, New York, NY, USA. https://doi.org/10.1007/978-3-319-53186-1_1.

  • Jabran K, Mahajan G, Sardana V, Chauhan B. 2015. Allelopathy for weed control in agricultural systems. Crop Prot. 72:5765.

  • Langeroodi A, Radicetti E, Campiglia E. 2018. How cover crop residue management and herbicide rate affect weed management and yield of tomato (Solanum lycopersicon L.) crop. Renewable Agric Food Syst. https://doi.org/10.1017/ S1742170518000054.

  • Ma J, Shi A, Mou B, Evans M, Clark J, Motes D, Correll J, Xiong H, Qin J, Chitwood J, Weng Y. 2016. Association mapping of leaf traits in spinach (Spinacia oleracea L.). Plant Breed. 135:399404.

    • Search Google Scholar
    • Export Citation
  • Morelock T, Correll J. 2008. Spinach. In: Prohens J, Nuez F (eds). Vegetables I. Handbook of plant breeding. Springer, New York, NY, USA.

  • Olday F, Barker A, Maynard D. 1976. A physiological basis for different patterns of nitrate accumulation in two spinach cultivars. J Am Soc Hortic Sci. 101(3):217219. https://doi.org/10.21273/JASHS.101.3.217.

    • Search Google Scholar
    • Export Citation
  • Oregon State University (OSU). 15 February 2010. Oregon vegetables: Spinach. https://horticulture.oregonstate.edu/oregon-vegetables/spinach-0. [accessed 2 Sep 2022].

  • Pandey S, Kalloo G. 1993. Spinach: Spinacia oleracea L., p 325–336. In: Kalloo G, Bergh B (eds). Genetic improvement of vegetable crops. Pergamon Press, Tarrytown, NY, USA.

  • Putnam A, Duke W. 1974. Biological suppression of weeds: Evidence for allelopathy in accessions of cucumber. Science. 185:370372. https://doi.org/10.1126/science.185.4148.370.

    • Search Google Scholar
    • Export Citation
  • Ramaiyan B, Kour J, Nayik G, Anand N, Alam M. 2020. Spinach (Spinacia oleracea L.), p 159–173. In: Ahmad Nayik G, Gull A (eds). Antioxidants in vegetables and nuts: Properties and health benefits. Springer, New York, NY, USA.

  • Ribera A, Bai Y, Wolters A, Van Treuren R, Kik C. 2020. A review on the genetic resources, domestication and breeding history of spinach (Spinacia oleracea L.). Euphytica. 216:48.

    • Search Google Scholar
    • Export Citation
  • Ribera A, Van Treuren R, Kik C, Bai Y, Wolters A. 2021. On the origin and dispersal of cultivated spinach (Spinacia oleracea L.). Genet Resources Crop Evol. 68:10231032.

    • Search Google Scholar
    • Export Citation
  • Rice E. 1984. Introduction, p 1–7. In: Allelopathy (2nd ed). Academic Press, Inc., Orlando, FL, USA.

  • Roberts J, Moreau R. 2016. Functional properties of spinach (Spinacia oleracea L.) phytochemicals and bioactives. Food Funct. 7:33373353.

    • Search Google Scholar
    • Export Citation
  • Ross M, Lembi C. 2009. Applied weed science: Including the ecology and management of invasive plants (3rd ed). Pearson Education, Inc., Upper Saddle River, NJ, USA.

  • Shah A, Iqbal J, Ullah A, Yang G, Yousaf M, Fahad S, Tanveer M, Hassan W, Tung S, Wang L, Khan A, Wu Y. 2016. Allelopathic potential of oil seed crops in production of crops: A review. Environ Sci Pollut Res Int. 23:1485414867.

    • Search Google Scholar
    • Export Citation
  • Sustainable Agriculture Research & Education (SARE). 2012. Managing cover crops profitably (3rd ed). Handbook Series, Book 9. University of Maryland, College Park, MD, USA.

  • Trezzi M, Vidal R, Balbinot A Jr, von Hertwig Bittencourt H, daSilva Souza Filho A. 2016. Allelopathy: Driving mechanisms governing its activity in agriculture. J Plant Interact. 11(1):5360.

    • Search Google Scholar
    • Export Citation
  • US Department of Agriculture, National Agricultural Statistics Service. 2022. Vegetables 2021 Summary (February 2022) ISSN: 0884-6413.

  • Weston L, Alsaadawi I, Baerson S. 2013. Sorghum allelopathy—From ecosystem to molecule. J Chem Ecol. 39:142153.

  • Wisakowsky E, Burns E, Smith M. 1977. Factors affecting the quality of freeze-dried compressed spinach. J Food Sci. 42(3):782783.

  • Wortman S, Francis C, Bernards M, Blankenship E, Lindquist J. 2013. Mechanical termination of diverse cover crop mixtures for improved weed suppression in organic cropping systems. Weed Sci. 61(1):162170.

    • Search Google Scholar
    • Export Citation
  • Wszelaki A, Broughton S. 2012. Cover crops and green manures. Publication W235-G. University of Tennessee Extension, Knoxville, TN, USA.

  • Xuan T, Tsuzuki E, Terao H, Matsuo M, Khanh T. 2003. Correlation between growth inhibitory exhibition and suspected allelochemicals (phenolic compounds) in the extract of alfalfa (Medicago sativa L.). Plant Prod Sci. 6(3):165171.

    • Search Google Scholar
    • Export Citation
Kenneth W. Pierce College of Interdisciplinary Studies—Environmental Science/Agriculture, Tennessee Technological University, Box 5034, Cookeville, TN 38505, USA

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Michael P. Nattrass School of Agriculture, Tennessee Technological University, Box 5034, Cookeville, TN 38505, USA

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Contributor Notes

K.W.P. is the corresponding author. E-mail: kwpierce@tntech.edu.

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