
Chemical herbicides are the cheapest and the most straightforward and successful method used to control weed invasion compared to other traditional and contemporary tactics (Fartyal
There are several effective POST herbicides for soybeans available on the market (Byker
Several previous studies reported the varying effects of bentazone according to the growth stages of soybeans. Wax
In field tests, soybeans were assayed at various growth stages for bentazone response. Wax
Few information is available about bentazone dose-in-duced soybean injury at different growth stages. To determine the reaction of genotypes in soybean breeding, it is necessary to determine the growth stage and bentazone doses through various traits with repeated tests. The objectives of this study were to investigate the performance of tolerant and susceptible soybean accessions in terms of growth stages and bentazone doses on foliar injury and growth performance and to determine the optimal growth stage and application dose of bentazone.
Experiments were conducted at the Kyungpook National University, Daegu, Republic of Korea in 2020 to 2021. Six soybean accessions were chosen from a prior bentazone screening of 430 Korean core collections of cultivated soybeans, including two tolerant accessions (CMJ091 and CMJ416), two moderately tolerant accessions (Daepung and Williams 82), and two susceptible accessions (CMJ169 and Hannam). The six accessions were planted in two replication in a 50-hole plastic tray (10 holes long, five rows wide) containing horticulture soil (Hanareum, Shinsung Mineral, South Korea). Each seed of accessions was planted in the five holes of a row at a depth of 2 cm and thinned to a single seedling after germination. These five plants of each accession in a row represent one replication. The experimental design was a complete block design with three factors: soybean accessions, bentazone doses, and growth stages. Bentazone, Basagran® (a.i. bentazone 40%), was sprayed to soybean plants at a standard field-recommended rate (1X, 1200 grams a.i. per ha) and doubled rate (2X) throughout the VC, V1, and V2 developmental stages (Fehr
The visual injury was scored at five days after treatment (DAT) when there was a maximum injury symptom on the leaves of the reference sensitive genotypes (Suwon 98 and PI 97150) (Ali
On this scale, the represented scores were: 1, no apparent burn spots; 2, few burn spots appeared on the plant leaves, but the plant displayed an average growth; 3, less than half of the plant leaves showed prominent burn spots, and plant growth was slightly affected; 4, more than half of the plant leaves showed noticeable burn spots, and plant growth was seriously affected; and 5, the plant leaves of the whole soybean showed large areas of burn spots and withered.
The average leaf scorch score for each accession was calculated using the following formula:
Average leaf injury = ∑ (LSSi) (Number of plants)/Total number of plants per replication, where LSSi is the level of leaf injury score. Accessions with a visual score of < 2.0, 2.0-3.5, and > 3.5 were considered tolerant, moderately tolerant, and sensitive, respectively.
Following the visual assessment on five DAT, one unifoliate leaf at the VC stage, the first trifoliate leaf from V1 stage, and the second trifoliate leaf from each plant at the V2 stages were taken to generate digital images for leaf necrosis estimation (Fig. 2-4). Leaf samples were collected from each of the five plants in each replication of each accession. The leaves were scanned using a flatbed scanner (Samsung SCX-3405 Laser Multifunction) as soon as they were collected to create digital photographs. The percentage leaf necrosis of the bentazone-treated and control plants was analyzed from the digital images using an open-source software, “Leaf necrosis classifier” (Leaf necrosis classifier, https://lnc.proteomics.ceitec.cz/tutorial). This software worked in a two-step process. The first phase was the creation of a data set using the treated plant's leaf images by indicating the healthy leaf area, damaged leaf area, and image background. The second phase was called the training and evaluation phase, where all images were evaluated based on the previously generated data set in the first phase. It was capable of automatically analyzing a collection of images and providing a quantitative assessment of the percentage of healthy and affected leaves in the samples, as well as a paired output of the original image and segregated out the affected areas overlapped with a red color (Fig. 2-4).
Plant height and above-ground fresh weight were measured at 14 DAT from both the control and treated plants. A ruler was used to measure the height of the plants from the ground to the base of the latest fully developed node. The fresh weight of each plant was measured using an electric balance (Sartorius BS2202S, Germany). To determine the dry weight of the plants, samples were dried in an electric oven. To get reliable results, three independent experiments were conducted in May 2020, May 2021, and June 2021.
A validation test was conducted in August 2021 to confirm the growth stage and bentazone dose for reactions of tolerant, moderately tolerant, and susceptible accessions. Ten soybean accessions of each category (tolerant, moderately tolerant, and susceptible) (Supplementary Table 1) were planted in a plastic tray in two replications. A control was included in each replication to serve as a basis for comparison. The planting methods and design were the same as that described in experiment 1. At the V1 growth stage, the plants in each responsive group were treated with 1X bentazone. Leaf necrosis analysis, visual scoring, and other growth characteristics measurements were identical to those in the previous experiment.
Table 1 . The interaction effects of soybean accessions and bentazone doses on leaf necrosis, visual score, plant height, fresh weight, and dry weight of soybean.
Genotype | Bentazone dose | Leaf necrosis | Visual score | Plant height | Fresh weight | Dry weight | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
(%) | Indexw) | (1-5)v) | Index | (cm) | Index | (g) | Index | (g) | Index | ||||||
CMJ091 | 0X | 2.1dez) | 100 | 1.0g | 100 | 19.4a | 100 | 3.80a | 100 | 0.98a | 100 | ||||
1X | 2.5de | 116 | 1.4f | 140 | 17.8ab | 92 | 3.28abc | 86 | 0.83abc | 85 | |||||
2X | 5.8de | 275 | 1.4e | 136 | 17.0ab | 86 | 3.13abc | 82 | 0.76abc | 78 | |||||
Mean | 3.5 | 1.2 | 18.1 | 3.40 | 0.86 | ||||||||||
CMJ416 | 0X | 1.6e | 100 | 1.0g | 100 | 17.0ab | 100 | 2.89abcde | 100 | 0.69abcd | 100 | ||||
1X | 1.6e | 105 | 1.2f | 117 | 15.6bc | 92 | 2.69abcde | 93 | 0.57bcdef | 83 | |||||
2X | 4.1de | 263 | 1.1fg | 112 | 14.7bcd | 87 | 2.39cdefg | 83 | 0.52cdef | 75 | |||||
Mean | 2.4 | 1.1 | 15.8 | 2.66 | 0.59 | ||||||||||
Daepung | 0X | 2.3de | 100 | 1.0g | 100 | 17.1ab | 100 | 3.65ab | 100 | 0.84a | 100 | ||||
1X | 3.4de | 152 | 2.8c | 276 | 15.9bc | 93 | 3.09abcd | 85 | 0.66bcde | 79 | |||||
2X | 8.3de | 366 | 2.7cd | 267 | 15.2bc | 89 | 2.59abcdef | 71 | 0.57bcdef | 68 | |||||
Mean | 4.8 | 2.1 | 16.1 | 3.11 | 0.69 | ||||||||||
Williams 82 | 0X | 2.0de | 100 | 1.0g | 100 | 16.9abc | 100 | 3.80a | 100 | 0.82abc | 100 | ||||
1X | 4.8de | 235 | 3.0b | 296 | 14.9bc | 88 | 3.15abc | 83 | 0.71abcd | 87 | |||||
2X | 10.4d | 513 | 2.6d | 261 | 14.6bcd | 86 | 2.56bcdefg | 67 | 0.57bcdef | 70 | |||||
Mean | 5.7 | 2.2 | 15.4 | 3.17 | 0.70 | ||||||||||
CMJ169 | 0X | 2.2de | 100 | 1.0g | 100 | 17.8ab | 100 | 3.25abc | 100 | 0.81abc | 100 | ||||
1X | 36.8b | 1,680 | 4.8a | 479 | 14.7bcd | 83 | 1.81efg | 56 | 0.37ef | 46 | |||||
2X | 52.8a | 2,409 | 4.7a | 474 | 13.5cd | 76 | 1.35g | 42 | 0.26f | 32 | |||||
Mean | 30.7 | 3.5 | 15.3 | 2.13 | 0.47 | ||||||||||
Hannam | 0X | 2.0de | 100 | 1.0g | 100 | 11.4de | 100 | 2.67abcde | 100 | 0.62bcde | 100 | ||||
1X | 22.4c | 1,109 | 4.8a | 478 | 10.1e | 89 | 1.87defg | 70 | 0.41def | 66 | |||||
2X | 44.1b | 2,182 | 4.8a | 480 | 9.3e | 82 | 1.37fg | 51 | 0.27f | 44 | |||||
Mean | 22.8 | 3.5 | 10.6 | 1.97 | 0.43 | ||||||||||
Mean | 0X | 2.0 | 100 | 1.0 | 100 | 16.6 | 100 | 3.35 | 100 | 0.79 | 100 | ||||
1X | 11.9 | 587 | 2.9 | 293 | 14.8 | 89 | 2.65 | 79 | 0.59 | 75 | |||||
2X | 20.9 | 1,030 | 2.9 | 288 | 14.0 | 85 | 2.23 | 67 | 0.49 | 62 | |||||
LSD (0.05)y) | 4.1 | 0.3 | 1.0 | 0.32 | 0.08 | ||||||||||
LSD (0.05)x) | 5.1 | 0.4 | 1.1 | 0.44 | 0.11 |
Data combined from three independent tests and three stages.
z)Means having a different letter(s) within a column are significantly different according to
y)LSD (0.05) for comparison the mean of doses.
x)LSD (0.05) for comparison the mean of accessions.
w)Index of all traits was computed relative to 0X treated values, where the performance of 0X dose was considered as 100 percent.
v)Visual score was given in a 1-5 scale, where 1-no apparent burn spots; 2-a few burn spots; 3-less than half burn spots; 4-more than half of the leaves showed spots; 5-the whole soybean leaves showed large areas of burn spots and withered.
Analysis of variance was done for all the parameters using SAS 9.4 with PROC GLM (SAS Institute, Cary, NC, USA, 20132013). With the “LSD.test” function in R, a least significant difference analysis was performed to determine whether there were significant differences across the genotypes, doses, and growth stages for the assessed traits. The Pearson correlation coefficient was calculated and visualized in R using the “Performance Analytics” package (Carl
In this study, the visual injury observed from bentazone doses includes chlorosis, necrosis, and drying of leaves. The severity of leaf injury in this study was influenced by soybean accessions, bentazone doses, and growth stages. The testing time was not significant for leaf necrosis and visual scores, but it was significant for plant height, fresh weight, and dry weight (Supplementary Table 2). The accessions, bentazone doses, and growth stages had significant (
Table 2 . The interaction effects of soybean accession and growth stage as well as the main effect of growth stage on leaf necrosis, visual score, plant height, fresh weight, and dry weight.
Genotype | Growth stage | Leaf necrosis (%) | Visual score (1-5)x) | Plant height (cm) | Fresh weight (g) | Dry weight (g) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Control | Treatment | Indexw) | Control | Treatment | Indexw) | Control | Treatment | Indexw) | ||||||
CMJ091 | VC | 2.5dz) | 1.2c | 16.6bcd | 14.7def | 89a | 3.23abc | 2.59bcdefg | 80a | 0.78abcd | 0.61bcdefg | 78a | ||
V1 | 4.2cd | 1.2c | 20.0ab | 17.2bcd | 86a | 3.7abc | 2.88bcdefg | 78a | 1.00abc | 0.76abcd | 76a | |||
V2 | 3.7cd | 1.1c | 21.7a | 20.3a | 93a | 4.47ab | 4.15a | 93a | 1.16a | 1.01a | 87a | |||
CMJ416 | VC | 1.7d | 1.1c | 13.8cdef | 12.3fgh | 89a | 2.08c | 1.76gh | 85a | 0.45d | 0.388fgh | 86a | ||
V1 | 3.3d | 1.1c | 17.6abc | 14.9cdef | 85a | 3.08bc | 2.69bcdefg | 87a | 0.72abcd | 0.53cdefg | 74a | |||
V2 | 2.3d | 1.1c | 19.5ab | 18.3ab | 94a | 3.5abc | 3.18abcd | 91a | 0.92abcd | 0.72abcdef | 78a | |||
Daepung | VC | 2.7d | 2.1bc | 14.7cde | 13.8efg | 94a | 2.73bc | 1.95defgh | 71a | 0.56cd | 0.42efgh | 75a | ||
V1 | 5.4cd | 2.1bc | 17.3bc | 15.3cde | 88a | 3.68abc | 3.15ancde | 86a | 0.83abcd | 0.63bcdef | 76a | |||
V2 | 5.8cd | 2.2abc | 19.2ab | 17.6abc | 92a | 4.53ab | 3.43abc | 76a | 1.14a | 0.78abc | 68a | |||
Williams 82 | VC | 4.5cd | 2.2bc | 13.8cdef | 12.3fgh | 89a | 2.51bc | 1.87fgh | 75a | 0.58cd | 0.44efgh | 76a | ||
V1 | 6.4bcd | 2.2abc | 17.0bc | 14.9cdef | 88a | 3.68abc | 3.1abcdef | 84a | 0.79abcd | 0.60bcdefg | 76a | |||
V2 | 6.4bcd | 2.2abc | 19.9ab | 17.0bcd | 86a | 5.21a | 3.61ab | 69a | 1.09ab | 0.87ab | 80a | |||
CMJ169 | VC | 34.8a | 3.4ab | 14.8cde | 11.5gh | 78a | 2.49bc | 0.87h | 35a | 0.56cd | 0.19h | 34a | ||
V1 | 22.2ab | 3.5ab | 17.9abc | 13.6efg | 76a | 3.39abc | 1.82gh | 54a | 0.85abcd | 0.36fgh | 42a | |||
V2 | 34.8a | 3.6a | 20.6ab | 17.2bcd | 83a | 3.85abc | 2.04defgh | 53a | 1.01abc | 0.42efgh | 42a | |||
Hannam | VC | 22.0ab | 3.5ab | 9.7f | 8.2i | 85a | 1.89c | 0.78h | 41a | 0.43d | 0.18h | 42a | ||
V1 | 19.3abc | 3.5ab | 11.9ef | 9.6hi | 81a | 2.82bc | 1.90efgh | 67a | 0.64bcd | 0.36fgh | 56a | |||
V2 | 27.3a | 3.5ab | 12.5def | 11.3gh | 90a | 3.30abc | 2.19cdefg | 66a | 0.77abcd | 0.47defgh | 61a | |||
Mean | VC | 11.4 | 2.3 | 13.9 | 12.1 | 87a | 2.49 | 1.64 | 66a | 0.56 | 0.37 | 66a | ||
V1 | 10.1 | 2.3 | 170 | 14.3 | 84a | 3.39 | 2.59 | 76a | 0.80 | 0.53 | 66a | |||
V2 | 13.4 | 2.3 | 18.9 | 16.9 | 89a | 4.14 | 3.10 | 75a | 1.02 | 0.72 | 71a | |||
LSD (0.05)y) | 4.6 | 0.4 | 1.5 | 1.0 | 5.9 | 0.5 | 0.35 | 21 | 0.1 | 0.1 | 22 |
Data combined from three tests and three doses.
z)Means having a different letter(s) within a column are significantly different according to
y)LSD (0.05) for comparison the mean of growth stage.
x)Visual score was given in a 1-5 scale, where 1-no apparent burn spots; 2-a few burn spots; 3-less than half burn spots; 4-more than half of the leaves showed spots; 5-the whole soybean leaves showed large areas of burn spots and withered.
w)Index of all traits were computed relative to control values, where the performance of control was considered as 100 percent.
The analysis of variance showed a significant effect of accessions, bentazone doses, and their interaction to all characteristics examined (
In comparison to the control, tolerant and moderately tolerant accessions, except Williams 82, had no significant difference in leaf injury from the doses; however, the susceptible accessions had more damage when exposed to 2X than those exposed to 1X dose. Overall, the 2X dose caused almost 10 times and twice more necrosis than the control and 1X dose, respectively.
The visual score of the susceptible accessions (3.5) was higher than that of the moderately tolerant (2.1 to 2.2) and tolerant groups (1.1 to 1.2). A significant difference in visual score was present when the 1X and 2X doses were applied to the CMJ091 (tolerant) and Williams 82 (moderately tolerant) accessions, while non-significant differences existed for susceptible accessions (Table 1). The visual score index indicated that the tolerant genotypes had slightly increased visual scores than the control, whereas the moderately tolerant and sensitive genotypes had nearly triple and fivefold the visual scores of the control, respectively. Plant height reduction also increased with the increase in herbicide doses in all the accessions, irrespective of their tolerance. The plant height reduction for the tolerant, moderately tolerant, and susceptible accessions was 8%-14%, 7%-14%, and 11%-24%, respectively. Biomass production was also affected by the herbicide doses. Like the other traits, the biomass production of the herbicide-treated tolerant accessions was not significantly different from that of the control. However, a substantial difference was found in the sensitive accessions, especially when the herbicide dose was doubled (2X). The reduction in the fresh weight of the tolerant, moderately tolerant, and susceptible accessions was 7-18%, 15%-33%, and 30%-58%, respectively. The dry weight reduction also showed a similar pattern, with an order of susceptible > moderately tolerant > tolerant. The tolerant accessions had more average biomass compared to the susceptible accession.
The interaction of the accessions and growth stages was evaluated (Table 2).
The leaf necrosis at the VC, V1, and V2 stages for the tolerant, moderately tolerant, and susceptible accessions showed a similar pattern, with non-significant differences among the three stages within an accession. However, the susceptible accessions had significantly higher leaf necrosis than the tolerant and moderately tolerant accessions in all growth stages. Average over bentazone doses and accessions, all three stages showed no difference in leaf necrosis; however, the V2 stage, which resulted in 13.4% leaf necrosis, showed a relatively higher score than the other stages (Table 2). The tolerant accessions had the lowest visual scores (1.1 to 1.2), whereas the susceptible accessions had the highest (3.5), and the moderately tolerant accessions were in the intermediate (2.1 to 2.2).
The relative indices were 87, 84, and 89 for plant height, 66, 76, and 75 for fresh weight, and 66, 66, and 71 for dry weight for VC, V1, and V2, respectively. There was no significant difference in plant height reduction, fresh weight reduction, and dry weight reduction among the growth stages for overall means and within an accession.
A significant interaction (
Table 3 . The effects of bentazone dose on leaf necrosis, visual score, plant height, fresh weight, and dry weight in relation to the growth.
Growth stage | Bentazone dose | Leaf necrosis | Visual score | Plant height | Fresh weight | Dry weight | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
(%) | Indexx) | (1-5)y) | Index | (cm) | Index | (g) | Index | (g) | Index | ||||||
VC | 0X | 1.4cz) | 100 | 1.0b | 100 | 13.9cd | 100 | 2.49cd | 100 | 0.56cd | 100 | ||||
1X | 12.2abc | 904 | 3.0a | 295 | 12.7cd | 91 | 1.83de | 74 | 0.41de | 73 | |||||
2X | 20.5ab | 1,519 | 2.8a | 281 | 11.6d | 84 | 1.44e | 58 | 0.33e | 59 | |||||
V1 | 0X | 2.8c | 100 | 1.0b | 100 | 17.0ab | 100 | 3.39ab | 100 | 0.81b | 100 | ||||
1X | 8.9bc | 316 | 3.0a | 295 | 14.7bc | 86 | 2.77bc | 82 | 0.58cd | 72 | |||||
2X | 18.6b | 660 | 2.8a | 285 | 13.9cd | 82 | 2.41cd | 71 | 0.49cde | 61 | |||||
V2 | 0X | 1.9c | 100 | 1.0b | 100 | 18.9a | 100 | 4.14a | 100 | 1.02a | 100 | ||||
1X | 14.6ab | 766 | 2.9a | 291 | 17.2a | 91 | 3.35b | 81 | 0.78b | 77 | |||||
2X | 23.6a | 1,235 | 3.0a | 299 | 16.7ab | 88 | 2.84bc | 69 | 0.64bc | 63 |
Data combined from three tests and six genotypes.
z)Means having a different letter(s) within a column are significantly different according to
y)Visual score was given in a 1-5 scale, where 1-no apparent burn spots; 2-a few burn spots; 3-less than half burn spots; 4-more than half of the leaves showed spots; 5-the whole soybean leaves showed large areas of burn spots and withered.
x)Index of all traits was computed relative to 0X treated values, where the performance of 0X dose was considered as 100 percent.
The highest biomass values were observed in the control plants (0X) under the three developmental stages, followed by those in plants treated with 1X and 2X doses (Table 3). No significant differences in fresh weight and dry weight were found within all the growth stages treated with 1X and 2X doses. The index for fresh weight and dry weight of plants treated with 1X and 2X doses at the V1 and V2 stages had a similar pattern. Throughout the stages, the dry weight of plats treated with 2X dose was decreased by around 10% compared to that of plants treated with 1X dose.
Based on experiment 1, it was suggested that 1X dose at the V1 stage would be optimal to screen the reaction of bentazone to soybeans. To validate the performance of the 1X treatment at the V1 stage that may be used to screen the reactions of soybeans to bentazone, a similar study was conducted using previously selected 30 soybean accessions composed of 10 from each category (tolerant, moderately tolerant, and susceptible) (Supplementary Table 1).
The performance of 10 1X bentazone-treated tolerant accessions varied for all the traits studied. The leaf necrosis ranged from 0.6% to 4.3%, with a mean of 2.0%, for the tolerant group, 6.3% to 19.9%, with a mean of 10.7%, in the moderately tolerant group, and 23.4% to 48.0%, with an average of 35.8%, in the susceptible group. The average leaf necrosis in the tolerant group was significantly lower than that in the other two groups.
There was a significant difference in visual scores among the three groups. The visual scores of the tolerant, moderately tolerant, and susceptible accessions were 1.1 (1.0 to 1.3), 3.1 (2.6 to 3.7), and 4.6 (4.0 to 5.0), respectively.
The relative plant height compared with the control for the tolerant, moderately tolerant, and susceptible group was 92% (80% to 106%), 92% (81% to 99%), and 69% (55% to 89%), respectively. The mean reduction in plant height among the three groups was significantly different (Table 4). Three accessions, CMJ342, CMJ091, and CMJ377, in the tolerant group showed less plant height reduction, while Nuriol, Pureun, and Pungsannamul of the moderate group had less reduction in plant height.
Table 4 . The effects of 1X bentazone dose on leaf necrosis, visual score, plant height, fresh and dry weight of the tolerant, moderately tolerant, and susceptible group of soybean accessions treated at the V1 growth stage.
Reaction group | Accession | Leaf necrosis (%) | Visual score (1-5)x) | Plant height | Fresh weight | Dry weight | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Control (cm) | Treatment (cm) | Indexw) | Control (g) | Treatment (g) | Index | Control (g) | Treatment (g) | Index | ||||||
Tolerant | CMJ042 | 2.4 | 1.3 | 19.5 | 17.5 | 90 | 2.00 | 1.62 | 81 | 0.51 | 0.33 | 65 | ||
CMJ101 | 0.6 | 1.0 | 24.1 | 20.6 | 85 | 2.57 | 1.69 | 66 | 0.51 | 0.39 | 77 | |||
CMJ131 | 1.4 | 1.0 | 24.0 | 19.5 | 81 | 2.29 | 1.23 | 54 | 0.47 | 0.24 | 51 | |||
CMJ286 | 0.6 | 1.0 | 23.0 | 18.3 | 80 | 2.27 | 1.19 | 52 | 0.47 | 0.26 | 55 | |||
CMJ342 | 1.5 | 1.2 | 21.2 | 22.4 | 106 | 1.84 | 1.94 | 105 | 0.47 | 0.36 | 77 | |||
CMJ377 | 4.3 | 1.2 | 25.1 | 24.8 | 99 | 2.20 | 1.85 | 84 | 0.50 | 0.38 | 76 | |||
CMJ386 | 1.0 | 1.1 | 22.8 | 21.5 | 94 | 2.29 | 1.80 | 78 | 0.46 | 0.33 | 72 | |||
CMJ091 | 3.1 | 1.2 | 21.1 | 22.0 | 104 | 1.99 | 2.89 | 146 | 0.35 | 0.62 | 176 | |||
Namhae | 2.8 | 1.2 | 21.7 | 19.9 | 91 | 2.34 | 1.64 | 70 | 0.52 | 0.36 | 70 | |||
Socheong | 2.1 | 1.2 | 18.8 | 18.0 | 96 | 2.03 | 1.66 | 82 | 0.58 | 0.43 | 74 | |||
Mean | 2.0cz) | 1.1c | 22.1b | 20.4a | 92a | 2.18a | 1.75a | 80a | 0.48a | 0.37a | 77a | |||
Moderately tolerant | Jungmo3009 | 6.3 | 2.8 | 20.6 | 19.5 | 95 | 3.64 | 1.72 | 47 | 0.87 | 0.41 | 47 | ||
Nuriol | 12.5 | 3.7 | 19.4 | 19.1 | 98 | 1.92 | 1.75 | 91 | 0.54 | 0.44 | 81 | |||
Dagi | 7.0 | 2.6 | 20.8 | 19.6 | 94 | 2.36 | 1.27 | 54 | 0.51 | 0.32 | 63 | |||
Pureun | 19.9 | 3.5 | 17.6 | 17.5 | 99 | 1.98 | 1.69 | 85 | 0.36 | 0.3 | 83 | |||
Pungsanamul | 10.3 | 3.0 | 16.9 | 16.5 | 98 | 1.37 | 1.15 | 84 | 0.27 | 0.23 | 85 | |||
Heugmi | 7.1 | 3.0 | 19.1 | 18.0 | 94 | 1.81 | 1.46 | 81 | 0.33 | 0.28 | 85 | |||
Geomjeongkong 3 | 12.9 | 3.3 | 21.7 | 17.8 | 82 | 2.53 | 1.30 | 51 | 0.36 | 0.24 | 67 | |||
Uram | 7.1 | 2.9 | 22.0 | 19.4 | 88 | 2.15 | 1.61 | 75 | 0.46 | 0.24 | 52 | |||
Daewon | 13.5 | 3.4 | 22.7 | 18.5 | 81 | 2.26 | 1.33 | 59 | 0.38 | 0.22 | 58 | |||
Alchan | 10.8 | 3.2 | 24.5 | 23.3 | 95 | 2.71 | 1.38 | 51 | 0.51 | 0.25 | 49 | |||
Mean | 10.7b | 3.1b | 20.5c | 18.9b | 92a | 2.27a | 1.47b | 64a | 0.46a | 0.29b | 64a | |||
Susceptible | Hannam | 38.5 | 4.5 | 21.4 | 16.9 | 79 | 2.06 | 0.65 | 32 | 0.34 | 0.17 | 50 | ||
Seonam | 48.0 | 5.0 | 29.0 | 18.3 | 63 | 2.58 | 0.60 | 23 | 0.44 | 0.15 | 34 | |||
Dachae | 42.9 | 5.0 | 24.0 | 16.2 | 68 | 2.63 | 0.39 | 15 | 0.39 | 0.09 | 23 | |||
Pokwangkong | 45.6 | 5.0 | 25.2 | 18.4 | 73 | 2.49 | 0.82 | 33 | 0.52 | 0.15 | 29 | |||
Baekchun | 29.4 | 4.5 | 27.3 | 16.7 | 61 | 3.04 | 0.83 | 27 | 0.68 | 0.14 | 21 | |||
CMJ427 | 26.0 | 4.0 | 27.2 | 15.0 | 55 | 2.64 | 0.43 | 16 | 0.50 | 0.14 | 28 | |||
CMJ316 | 28.0 | 4.3 | 25.4 | 16.1 | 64 | 2.83 | 0.64 | 23 | 0.43 | 0.11 | 26 | |||
CMJ185 | 43.5 | 4.8 | 23.9 | 16.3 | 68 | 3.14 | 0.78 | 25 | 0.67 | 0.16 | 24 | |||
CMJ188 | 23.4 | 4.5 | 21.0 | 16.0 | 76 | 1.53 | 0.56 | 37 | 0.45 | 0.08 | 18 | |||
CMJ254 | 32.7 | 4.7 | 20.0 | 17.8 | 89 | 1.51 | 1.33 | 88 | 0.30 | 0.16 | 53 | |||
Mean | 35.8a | 4.6a | 24.4a | 16.8c | 69b | 2.45a | 0.70c | 29b | 0.47a | 0.14c | 29b | |||
LSD (0.05)y) | 4.2 | 0.2 | 1.0 | 1.1 | 10 | 0.29 | 0.25 | 25 | 0.07 | 0.05 | 26 |
z)Means having a different letter(s) within a column are significantly different according to
y)LSD (0.05) for comparison the mean of reaction groups.
x)Visual score was given in a 1-5 scale, where 1-no apparent burn spots; 2-a few burn spots; 3-less than half burn spots; 4-more than half of the leaves showed spots; 5-the whole soybean leaves showed large areas of burn spots and withered.
w)Index of all traits was computed relative to control, where the performance of control was considered as 100 percent.
In the case of fresh weight, a significant difference was also recognized among the three groups. The mean changes in fresh weight were 80% (52%-146%) for the tolerant group, 64% (47%-91%) for the moderately tolerant group, and 29% (15%-88%) for the susceptible group.
Dry weight changes also showed a similar result. The mean changes in dry weight were 77% (51%-176%) for the tolerant group, 64% (47%-85%) for the moderately tolerant group, and 29% (18%-53%) for the susceptible group. Two accessions, CMJ342 and CMJ091, showed less biomass reduction in the tolerant group, and Nuriol, Pureun, and Pungsannamul also showed less reduction in biomass in the moderate group.
A correlation analysis was done to determine the degree to which the characteristics examined was related
(Fig. 5). Leaf necrosis was significantly (r = 0.85,
The determination of bentazone reaction among soybean accessions is needed to develop soybean accessions with bentazone tolerance. Germplasm screening is time-consuming, labor-intensive, and expensive; therefore, it is very important to develop the most effective selection method for plant breeding and genetic studies. Here, an experiment was conducted to suggest a suitable screening stage and bentazone dose with agronomic traits and leaf injury from image analysis. In the selection breeding lines and in the discrimination of tolerant and susceptible accessions, visual scoring is the most commonly used (Anderson
Image analysis is a quantitative technique used to assess plant health that may be compared to appropriate controls. The image analysis-based method was utilized to categorize a wide range of biotic and abiotic foliar stressors in soybean leaflets, thus minimizing the possibility of visual phenotypic misclassification. This practice has gained popularity due to its high accuracy, low instrumentation cost, and less labor-intensive nature. Nowadays, imaging-based phenotyping is extensively employed to detect stress-resistant plants early and to precisely phenotype a large number of individuals to find the underlying genes for stress tolerance (Khirade and Patil 2015; Begum
Correlation analysis was conducted to see the relationship among the traits (Fig. 5). Leaf necrosis was significantly correlated (r = 0.85,
Leaf necrosis varied with the herbicide dose, growth stage, and soybean accessions. Accession by dose showed a significant interaction (
Other researchers also reported that higher doses produced more leaf injury when soybean plants were treated with dicamba and metribuzin (McCown
There was no difference in leaf necrosis and visual scores among the growth stages within the accessions (Table 2), and no difference was also recognized between 1X and 2X doses within the growth stages for leaf necrosis and visual scores. This result means that any early stages can be used to screen tolerance and susceptible genotypes. However, the VC stage only shows two unifoliate leaves (Fehr
Based on the dose-response and growth stage interaction results, it was concluded that 1X bentazone at V1 stage was enough to see proper symptoms for selection. To confirm this, a validation test was conducted (Table 4). Soybean accessions with known reactions to bentazone based on our previous screening with visual scoring were used (not published data). The visual scores ranged from 1.0 to 1.2 for the tolerant group, 2.9 to 3.7 for the moderate group, and 4.0 to 5.0 for the susceptible group. This was well-matched with our criteria; the accession with a visual score of < 2.0, 2.0-3.5, and > 3.5 was considered tolerant, moderately tolerant, and sensitive, respectively. Based on visual scores, leaf necrosis mostly showed lower values in the tolerant group than that in the moderately tolerant and susceptible groups. However, four accessions (Jungmo3009, Dagi, Heugmi, and Uram) in the moderately tolerant group did not show a difference with those in the tolerant group. For example, Jungmo3009 showed no difference with CMJ042, CMJ377, CMJ091, Namhae, and Socheong for leaf necrosis. This result suggested that it is desirable to use leaf necrosis and visual scores to determine the bentazone reactions in soybeans.
The leaf necrosis in tolerant accessions from experiment 1 varied between 2.4% and 3.5% (Table 1), which falls within the range (0.6%-4.3%) of tolerant accessions from our validation study (Table 4). However, the percent leaf necrosis of moderately tolerant and sensitive accessions ranges from 6.3% to 19.9% and 23.4% to 48.0%, respectively, which were higher than the necrosis in a preliminary study. These differences may be due to the differential responses of the different genotypes and environmental conditions in the two experiments. Compared to the preliminary stage test, there was a little high temperature and humidity during the validation study, especially from the days of bentazone treatment to visual scoring and leaf necrosis analysis. This may result in a slight rise in visual scores and plant height in all three groups of soybean accessions. Several previous studies also reported that herbicidal activity increases with increasing temperature and humidity (Wichert
In conclusion, the treatment with 1X bentazone at the V1 growth stage is suitable to screen soybean accessions for bentazone reaction. This result can be used to determine accessions and improve the efficiency of breeding and genetic studies for bentazone reactions.
This research was supported by Kyungpook National University Development Project Research Fund, 2018.
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