
Pumpkins and squashes (
The type and selection of a rootstock greatly influence the growth, yield, and fruit quality of the scion plant (King
Cucumber (
Since the seedlings are more prone to environmental extremities, the tolerance can be exactly and efficiently examined in the early developmental stage. Also, screening at the later developmental stages is difficult as it requires a lot of space and resources input and time-consuming. Therefore, developing a selection strategy using seedlings at the early developmental stage enables quick, efficient, and reproducible assessment of low-temperature tolerance. Screening at the early seedling stage has already been reported for other crops, including tomatoes (Cao
To address this issue, we aimed to establish a selection strategy to assess the low-temperature tolerance at the early developmental stage. By this strategy, in a short span of time, we could select the low-temperature tolerant pumpkin germplasms, which further could be used as a bloomless rootstock for cucumber. To develop the optimal conditions for screening, we used different types of seedlings (excised or non-excised), different growth conditions, and stress durations. Furthermore, we also examined the grafting compatibility and growth of grafted plants to select low-temperature tolerant and grafting-com-patible pumpkin germplasm as breeding material to use as a rootstock for cucumber grafting.
A total of 291 accessions from NPGS (National Plant Germplasm System, USDA) and 357 accessions from the National Agrobiodiversity Center (RDA, Republic of Korea) were collected for this study. From the 648 accessions, upon preliminary screening in unheated nursey for two years, we selected candidate low-temperature tolerant accessions based on root fresh weight (RFW) in comparison with the known commercial chilling tolerant cultivars “Heukjong” (
Table 1 . List of selected accessions of
Species | Accession/variety (company) | Country of origin |
---|---|---|
S81009 | Rep. of Korea | |
S81015 | Rep. of Korea | |
S81230 | China | |
S81328 | Rep. of Korea | |
S81635 | United States | |
"Nunbusyeo" (Takii Korea) | ||
"Shintoza" (Farm Hannong) | ||
"Heukjong" (Farm Hannong) |
All of the seeds used in the study were harvested within a year and stored in the low-temperature. For germination, all selected lines were sown in a 40 port connected tray (54.0 × 28.0 × 5.0 cm) filled with commercial soil mixture (Baroke No.2, Seoul Bio Co., Ltd). 1 week old post-ge-rminated seedlings with fully developed cotyledons were used as starting materials for the different experiments. We devised 4 different experiments (Fig. 1) for evaluating the low-temperature stress responses, as shown below. For all experiments, we performed in three replicates. For control purpose, we grew the same entries in unstressed condition (25°C/15°C, 16 hours light/8 hours dark). The relative humidity of the chamber was about 85%, and after excision, a transparent plastic lid was covered and sealed using a kitchen wrap to maintain the relative humidity, and irrigation was not performed until the end of the experiment. All unstressed controls grown at the normal temperature were raised in the same condition as stress-treated seedlings except for the low-temperature treatment.
The seedlings were excised to remove the roots, and the hypocotyls were planted in the artificial soil. The excised seedlings were cultured for 3 weeks at alternating temperature of 17°C/7°C (8 hours light/16 hours dark), under an LED lamp (Red:Blue = 2:1, 150 µmol m–2 s–1) as a light source (Fig. 2). After 3 weeks of low-temperature treatment, the shoots and roots growth were investigated.
For Exp. 2, all seedling growth conditions are the same as Exp. 1. But in Exp. 2, we prolonged the low-temperature treatment duration to 6 weeks from 3 weeks to examine the effects of longer treatment on the shoot and root growth.
The growth conditions of Exp. 3 are the same as Exp. 2. But unlike Exp. 2, in Exp. 3 we used intact seedlings without excision and incubated at the low-temperature for 6 weeks.
In order to evaluate low-temperature tolerance more accurately, we adopted the pot cultivation method to allow the plants to attain full growth potential. For this, seedlings were raised in 40 port connected trays and then were transplanted in a plastic pot (height 7.7 cm, 350 mL) and cultured at the low-temperature. The treatment conditions in Exp. 4 were the same as Exp. 1. Plants were irrigated when the soil surface became dry to maintain adequate soil moisture.
In order to evaluate the low-temperature tolerance of grafted cucumber seedlings according to the pumpkin accessions and varieties, “Nakdongcheongjang” (Farm Hannong), a Chinese long green variety, was used as the scion. Cucumbers and the rootstock entries were sprouted at 30°C and sown in 105 port connected trays, and 10 days after sowing, when the first true leaves of cucumbers emerged, they were grafted using “Root Removed Single Cotyledon Ordinary Splice Grafting” (RRSCOSG) method. Rootstocks were sown 3 days after sowing of cucumbers to obtain a hypocotyl of a suitable size for grafting. 40-port connected tray (54.0 × 28.0 × 5.0 cm) was filled with soil, and after sufficient watering, the grafted seedlings were transplanted, covered with a transparent plastic lid, and sealed with kitchen wrap to maintain relative humidity for 7 days. The temperature during the initial graft-take period was 28°C/20°C (16 hours light/8 hours dark) and was lowered to 24°C/20°C after 3 days of grafting. Later, the grafted seedlings were transferred and continued to grow at low-temperature (17°C/7°C 8 hours light/16 hours dark) for 8 weeks. After the designated treatment at control and stress conditions, the plant height (PH), number of leaves (NoL), number of internodes (NoInt), fresh and dry weight of the cucumber plants were investigated.
Statistical analysis was performed using the R program Version 4.1.2. Correlation coefficients were computed to assess the relationships of various traits between seedling growth. All data were statistically analyzed by analysis of variance (ANOVA), and Duncan’s test was performed at
We monitored the root growth patterns of a tolerant pumpkin cultivar “Heukjong” and a sensitive cultivar “Nunbusyeo” seedlings to examine their differential growth responses to the different ambient temperatures. In order to minimize the effect of germination vigor and to attain uniformity, we used excised seedlings without roots at the cotyledonary stage, first and second true leaf stage, and then transferred them to the different ambient temperatures. Upon transfer to different temperatures, we counted their newly formed roots at different time intervals (10, 15, 20, 25 days after excision (DAE)) as a growth response index. Under the unstressed condition, the susceptible cultivar “Nunbusyeo” developed a higher number of roots compared to the tolerant cultivar “Heukjong” (Fig. 3A and 3C). Conversely, the tolerant cultivar “Heukjong” developed a greater number of roots in the stress condition than in the control condition after 20 days of excision (Fig. 3C and 3D). Under the low-tem-perature treatment, we did not observe any significant difference in the number of newly formed roots among “Heukjong” and “Nunbusyeo” until 20 DAE. Interestingly, after 20 days of low-temperature treatment, “Heukjong” seedlings excised at the cotyledonary stage showed more dramatic increase in the number of newly formed roots than that of excised seedlings at the first and second true leaf stage. On average, cotyledonary excised “Heukjong” seedlings showed 27.1 number of roots at 25 DAE. On the other hand, “Nunbusyeo” showed only 18.9 number of roots. Together, we observed seedling excision carried out at the cotyledonary stage and low-temperature treatment for 20-25 days was ideal for the screening procedure to distinguish between low-tem-perature tolerant and susceptible cultivars.
We applied the identified testing conditions shown in Fig. 3B and 3D to different pumpkin accessions and commercial varieties to identify low-temperature tolerant lines. The root weight of “Heukjong” and “Nunbusyeo” did not show a significant difference at room temperature, but there was a significant difference under the low-tempe-rature. In our experiment under low-temperature stress, as expectedly, “Heukjong” showed the highest RFW, and “Nunbusyeo” showed the lowest RFW. Among the pumpkin accessions examined, we found that “S81015” showed the highest RFW under the low-temperature (Fig. 4). Hence, we considered “S81015” as one of the promising low-temperature tolerant lines. Similarly, “S81328” also showed higher RFW under low-temperature stress after “S81015” and it was thought to be a candidate low-tem-perature tolerant germplasm.
When we compared the results obtained from Exp. 2 and 3, we found the higher shoot fresh weight (SFW) in all accession except for “S81009” and “S81230” in Exp. 2. Similarly, we found higher RFW in “S81328”, “S81635”, “Nunbusyeo”, and “Heukjong” cultivars in Exp. 2 compared to their RFW in Exp. 3 (Table 2). When we treated the non-excised seedlings with low-temperature in 40 port connected tray (Exp. 3), we found the lowest RFW in “S81635” and “Nunbusyeo”. Additionally, we found many seedlings were got rotten and eventually died.
Table 2 . Comparison of plant growth indexes of the
Species | Accession/variety | Exp. 2z) | Exp. 3 | Exp. 4 | ||||||
---|---|---|---|---|---|---|---|---|---|---|
RFWy) (g) | SFW (g) | RFW (g) | SFW (g) | PH (cm) | NoInt | NoL | RFW (g) | SFW (g) | ||
S81009 | 0.39 ± 0.20bc | 3.40 ± 0.62c | 0.65 ± 0.12bc | 3.47 ± 0.58b | 134.49 ± 17.55cd | 4.9 ± 2.1bc | 5.6 ± 2.7c | 0.70 ± 0.13bcd | 5.97 ± 1.86d | |
S81015 | 0.29 ± 0.23bcd | 3.63 ± 0.70c | 0.72 ± 0.15ab | 2.51 ± 0.51c | 121.24 ± 47.75d | 4.3 ± 2.1c | 6.9 ± 1.3bc | 0.90 ± 0.18b | 6.84 ± 1.05d | |
S81230 | 0.01 ± 0.02e | 1.69 ± 0.64d | 0.56 ± 0.28cd | 3.87 ± 0.61b | 223.76 ± 30.62b | 6.3 ± 2.4bc | 6.7 ± 0.5bc | 0.86 ± 0.22b | 15.79 ± 0.89b | |
S81328 | 0.48 ± 0.21b | 5.18 ± 1.24b | 0.45 ± 0.10d | 3.94 ± 1.19b | 160.04 ± 28.24c | 4.6 ± 2.2c | 5.9 ± 2.2c | 0.46 ± 0.12cd | 7.11 ± 2.47d | |
S81635 | 0.12 ± 0.05de | 1.80 ± 0.78d | 0.03 ± 0.03f | 0.74 ± 0.19e | 167.58 ± 21.40c | 7.1 ± 2.0b | 7.3 ± 1.7bc | 0.73 ± 0.19bc | 11.04 ± 3.83c | |
“Nunbusyeo” | 0.22 ± 0.10cde | 1.89 ± 0.67d | 0.16 ± 0.04ef | 1.64 ± 0.45d | 75.21 ± 8.28e | 5.0 ± 2.2bc | 5.0 ± 2.2c | 0.39 ± 0.13d | 4.34 ± 2.00d | |
“Shintoza” | 0.16 ± 0.13de | 3.37 ± 0.83c | 0.28 ± 0.04e | 2.01 ± 0.81cd | 161.89 ± 33.67c | 6.4 ± 2.1bc | 8.6 ± 2.4b | 2.09 ± 0.48a | 16.33 ± 3.18b | |
“Heukjong” | 1.09 ± 0.29a | 7.48 ± 1.56a | 0.85 ± 0.13a | 5.66 ± 0.87a | 360.43 ± 55.39a | 10.7 ± 1.8a | 12.0 ± 1.8a | 2.38 ± 0.53a | 22.94 ± 3.04a |
Values are presented as mean ± standard deviation. Different letters indicate significant differences, as calculated statistically by Duncan’s multiple range test. z)Exp. 2: Low-temperature treatment for 6 weeks after seedling excision using 40 port connected tray, Exp. 3: Low-temperature treatment for 6 weeks on non-excised seedling using 40 port connected tray, Exp. 4: Low-temperature treatment for 6 weeks on non-excised seedling using single pot. y)RFW: Root fresh weight, SFW: Shoot fresh weight, PH: Plant height, NoInt: Number of internodes, NoL: Number of leaves.
To observe the seedling growth indexes more accurately, we cultured the non-excised seedlings in a bigger pot (Exp. 4). We observed the seedlings grew more robustly in Exp. 4 than that in Exp. 3. This might be due to the more of the growth space and water availability. We measured PH, NoInt, NoL, RFW, and SFW. As expected, the tolerant cultivar “Heukjong” displayed superior growth in terms of PH, NoInt, NoL, RFW, and SFW compared to all other cultivars and germplasms tested. Among the pumpkin accessions,” S81015” (0.90 g) and “S81230” (0.86 g) displayed higher RFW, whereas “S81328” (0.46 g) displayed the lowest RFW (Table 2). Interestingly, the higher RFW we observed in “S81015” at Exp. 4 also resembled its RFW recorded in Exp. 1, despite the more insufficient growth space and culture time. The growth pattern of tolerant and susceptible germplasms under low-temperature stress was more apparent when grown in bigger pots. When we extrapolate the growth patterns, growth of the tolerant “S81015” under the low-temperature stress is more vivid than that of the others. The growth rate at the control condition (25°C/15°C) did not significantly correlate with the growth rates under the stress condition. There was a significant correlation between all indexes we considered for evaluating low-temperature tolerance experiments with the RFW of Exp. 1. Specifically, the correlation coefficient of the RFW of Exp. 1 was high with Exp. 2 (
Table 3 . Correlation coefficient between growth indexs in the different low-temperature screening experiments.
25°C/18°C RFWy) | Exp. 1z) RFW | Exp. 2 | Exp. 3 | Exp. 4 | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
RFW | SFW | RFW | SFW | PH | NoInt | NoL | RFW | |||||||
Exp. 1 | RFW | 0.41 | - | |||||||||||
Exp. 2 | RFW | 0.25 | 0.92** | - | ||||||||||
SFW | 0.32 | 0.91** | 0.94*** | - | ||||||||||
Exp. 3 | RFW | 0.64 | 0.71* | 0.62 | 0.66 | - | ||||||||
SFW | 0.23 | 0.75* | 0.74* | 0.77* | 0.84** | - | ||||||||
Exp. 4 | PH | 0.05 | 0.80* | 0.68 | 0.67 | 0.53 | 0.74* | - | ||||||
NoInt | -0.02 | 0.72* | 0.62 | 0.53 | 0.23 | 0.45 | 0.90** | - | ||||||
NoL | 0.30 | 0.84** | 0.67 | 0.69 | 0.41 | 0.49 | 0.87** | 0.91** | - | |||||
RFW | 0.48 | 0.71* | 0.53 | 0.59 | 0.37 | 0.41 | 0.72* | 0.77* | 0.92** | - | ||||
SFW | 0.13 | 0.64 | 0.43 | 0.47 | 0.32 | 0.50 | 0.90** | 0.89** | 0.91** | 0.87** |
z)Exp. 1: Low-temperature treatment for 3 weeks after seedling excision using 40-port connected tray, Exp. 2: Low-temperature treatment for 6 weeks after seedling excision using 40 port connected tray, Exp. 3: Low-temperature treatment for 6 weeks on non-excised seedling using 40 port connected tray, Exp. 4: Low-temperature treatment for 6 weeks on non-excised seedling using single pot. y)RFW: Root fresh weight, SFW: Shoot fresh weight, PH: Plant height, NoInt: Number of internodes, NoL: Number of leaves.
Further, we also examined the low-temperature tole-rance of grafted cucumbers after grafting with the pumpkin accessions as rootstocks. As a positive control, cucumbers were self-grafted, assuming it has the highest grafting compatibility. Upon grafting, we measured PH, NoL and SFW, shoot dry weight (SDW). For data precision, we omitted the data of the accessions if the sample number of survived grafted plant is less than three. The “Heuk-jong”-grafted, “Shintoza”-grafted and self-grafted cucum-ber plants displayed comparable growth patterns under the unstressed condition. The SDW of “Heukjong”-grafted cucumber (3.77 g) showed the highest, followed by that of self-grafted cucumber (3.45 g). Similarly, the self-grafted cucumber displayed the highest SFW (37.68 g) followed by “S81635”-grafted cucumber (34.78 g) and “Heuk-jong”-grafted cucumber (33.55 g). Under stress condition, we found that the success rate of grafting and survival rate was very low. “S81230” showed a high growth rate in Exp. 4, but displayed a low survival rate upon grafting, which suggests that the grafting compatibility can be varied, and all the tolerant cultivars cannot be useful as a compatible rootstock. However, “Heukjong”-grafted cucumber had the highest SDW (0.79 g) and SFW (5.71 g). Consistent with the previous experiments, the tolerant cultivar “S81015” also outperformed with better grafting compa-tibility than other pumpkin germplasms. Accordingly, the “S81015”-grafted cucumber conferred 0.51 g of SDW and 2.41 g of SFW followed by “S81009”-grafted cucumber with 0.41 g of SDW and 3.04 g of SFW (Table 4). Notably, compared to shoot weight, the plant height is not a reliable stress tolerance indicator as some of the pumpkin lines also grew taller than the tolerant commercial varieties.
Table 4 . Comparison of growth indexes of grafted cucumbers under two temperature conditions according to the
Species | Accession/variety | 25°C/18°C | 17°C/7°C | ||||||
---|---|---|---|---|---|---|---|---|---|
PHz) (cm) | No. L | SFW (g) | SDW (g) | PH (cm) | No. L | SFW (g) | SDW (g) | ||
S81009 | 45.67 ± 8.75a | 10.3 ± 2.9ab | 27.78 ± 3.35b | 2.57 ± 0.07a | 61.16 ± 18.08a | 4.0 ± 1.0b | 3.04 ± 0.26b | 0.41 ± 0.02bc | |
S81015 | 89.33 ± 60.75a | 12.7 ± 4.0a | 31.21 ± 3.68ab | 3.42 ± 0.63a | 59.72 ± 5.03a | 3.0 ± 1.0b | 2.41 ± 0.95bc | 0.51 ± 0.02b | |
S81230 | NA | NA | NA | NA | NA | NA | NA | NA | |
S81328 | 57.67 ± 11.36a | 11.3 ± 0.6ab | 30.62 ± 3.50ab | 2.69 ± 0.11a | 70.15 ± 6.60a | 3.3 ± 1.2b | 2.06 ± 0.28bc | 0.42 ± 0.09bc | |
S81635 | 62.33 ± 17.76a | 11.0 ± 1.7ab | 34.78 ± 5.77ab | 3.07 ± 0.55a | 53.28 ± 5.35a | 4.0 ± 1.0b | 2.35 ± 0.68bc | 0.37 ± 0.10cd | |
"Nunbusyeo" | NA | NA | NA | NA | 35.36 ± 9.34b | 3.3 ± 2.1b | 1.78 ± 0.60c | 0.28 ± 0.07d | |
"Shintoza" | 52.17 ± 21.57a | 8.3 ± 1.5b | 32.95 ± 4.58ab | 3.20 ± 1.25a | 66.49 ± 6.45a | 8.0 ± 1.0a | 6.06 ± 0.27a | 0.76 ± 0.06a | |
"Heukjong" | 73.67 ± 0.76a | 10.0 ± 1.0ab | 33.55 ± 3.00ab | 3.77 ± 0.58a | 58.80 ± 5.99a | 7.3 ± 0.6a | 5.71 ± 0.80a | 0.79 ± 0.07a | |
70.50 ± 14.93a | 11.7 ± 1.2ab | 37.68 ± 0.96a | 3.45 ± 1.04a | NA | NA | NA | NA |
Values are presented as mean ± standard deviation. Different letters indicate significant differences, as calculated statistically by Duncan’s multiple range test. z)PH: Plant height, No.L: Numbers of leaves, SFW: Shoot fresh weight, SDW: Shoot dry weight.
To correlate the growth indexes (PH, NoL, SDW, SFW) under control and stress condition upon grafting among the experiments, we found the pumpkin RFW of Exp. 4 was highly correlated with the NoL (
Table 5 . Correlation analysis between root growth in four low-temperature screening experiments and growth indexes of grafted cucumbers under the two temperature conditions.
Grafted cucumber | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|
25°C/18°C | 17°C/7°C | |||||||||
PHz) | No.L | SFW | SDW | PH | No.L | SFW | SDW | |||
Pumpkin | Control | RFW | 0.39 | -0.01 | -0.31 | 0.41 | 0.26 | 0.29 | 0.45 | 0.55 |
Exp. 1y) | RFW | 0.49 | -0.04 | 0.22 | 0.75 | 0.23 | 0.49 | 0.57 | 0.71 | |
Exp. 2 | RFW | 0.25 | -0.06 | 0.02 | 0.48 | 0.21 | 0.37 | 0.43 | 0.53 | |
Exp. 3 | RFW | 0.41 | 0.22 | -0.45 | 0.35 | 0.41 | 0.15 | 0.32 | 0.49 | |
Exp. 4 | RFW | 0.12 | -0.66 | 0.47 | 0.75 | 0.33 | 0.94** | 0.97*** | 0.97*** |
z)PH: Plant height, No.L: Number of leaves, SFW: Shoot fresh weight, SDW: Shoot dry weight. y)Exp. 1: Low-temperature treatment for 3 weeks after seedling excision using 40-port connected tray, Exp. 2: Low-temperature treatment for 6 weeks after seedling excision using 40 port connected tray, Exp. 3: Low-temperature treatment for 6 weeks on non-excised seedling using 40 port connected tray, Exp. 4: Low-temperature treatment for 6 weeks on non-excised seedling using single pot.
In this study, we tried to develop a quantifiable in-house screening method which can be applied for assessing the low-temperature stress responses in pumpkin (
In our study, while comparing the growth rates of the selected germplasms and varieties, we found the figleaf gourd (
In an effort to identify earliest developmental stage of pumpkin seedling for screening, seedlings were excised in different stages (cotyledonary, 1st true leaf, and 2nd true leaf) and treated with varied ambient conditions at different time intervals. Likewise, we considered the root weight as the most important selection index for selecting low-tem-perature tolerant rootstock as a root crop. Since seed fidelity and germination vigor greatly affect the root growth rate of seedling, the root growth was compared at 2 different temperature conditions upon excision of roots to rule out the influence of the roots that formed during germination. After excision, the amount of newly regenerated roots under unstressed condition was not correlated with that of stressed condition (Table 3). We found out that excision can make it easier to compare the root regeneration ability in case of using limited space. Also, we suggest that root regeneration ability under the low-temperature can be used as a direct selection criterion that can evaluate intrinsic low-temperature tolerance of pumpkin rootstocks, according to the high correlation coefficient between Exp. 1 and 4. Additionally, since RRSCOSG method is generally applied for cucumber grafting, in which rootstock roots are also removed, excision in screening procedure can be applied for a preliminary test on regeneration ability of new roots.
In comparison to the plant growth stage, the root regeneration ability showed a phenotypic difference under low-temperature stress when the excision was held. “Heukjong” seedling excised at cotyledonary stage had lower root forming ability than that of other stages until 15 days pass, but showed a conspicuous increase from 20 DAE. Similarly, the “Nunbusyeo” seedling excised at the cotyledonary stage displayed the highest number of roots on 25 DAE (Fig. 3). This result might be due to the differential rooting ability depending on the developmental stage. Similar to this hypothesis, Bae
In this study, considering the fact that the rootstock has a significant influence on the growth of scion, it was assumed that the root growth rate was appropriate as a valid indicator for the selection of the rootstock. Low-temperature significantly influence the metabolism of plants, such as photosynthesis, respiration, and absorption of nutrients and water. Especially, it has been reported that the temperature of the rhizosphere has a great effect on the growth of the shoot. Previous reports also had shown that the net photosynthetic rate and photochemical efficiency of PSII decreased sharply when the soil temperature was 15°C or less (Ahn
Among the growth indicators of grafted cucumber plants, the shoot weight showed the most similar tendency to that of Exp. 1 (Table 4 and 5). As expected, we found that the SFW of self-grafted seedlings was the highest under unstressed conditions. Similarly, In the case of SDW, “Heukjong” was higher than that of self-grafted seedlings, but it was not statistically significant. This appears to be due to the vigorous root growth of figleaf gourd. Among the pumpkin accessions, “S81015” was identified as a low-temperature tolerant line, and it also improved the low-temperature tolerance of the grafted cucumbers. Some pumpkin accessions showed different growth rates of grafted seedlings compared to the plant itself. It is estimated that the strength of low-temperature tolerance after grafting is affected by compatibility. It is thought that the selection of uniform seedlings after true leaf emergence for pot cultivation acted as a factor in that the growth rate of non-excision pot cultivation showed the highest correlation with grafted seedlings under low-temperature conditions. On the other hand, in the case of excised seedlings, it was thought that it was relatively difficult to select seedlings with even vigor before the appearance of the true leaves. Overall, effective low-temperature tolerance screening was possible by treating low-temperature for 3 weeks after excision.
We expect the indoor low-temperature tolerance screening method developed through this study can be effectively used for breeding of bloomless rootstocks for cucumber. It is considered highly effective as a selection method because the root growth rate, which is a key trait of rootstock, was used as a selection index. As the allelic diversity for low-temperature tolerance in the commercial bloomless rootstock cultivars is narrow, we need to find novel pumpkin resources that can render a higher level of tolerance (Yolcu
This study was supported by a grant (project no. PJ01350903) from the National Institute of Horticultural Herbal Sciences, Rural Development Administration.
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