Effects of Seedling-Stage Diniconazole Application on Tomato Transplant Quality, Early Growth, and Initial Yield

Diniconazole concentration based leaf development was observed at each stage of seedling growth (Table 1). At 4 weeks after sowing (WAS), the highest concentration (250 mg/L) markedly reduced leaf area, consistent with the role of triazole growth regulators in suppressing gibberellin-mediated cell expansion (Rademacher, 2000). In contrast, 50 and 125 mg/L produced leaf areas comparable to the control. As seedlings progressed into mid-development (5 WAS), treatment wise variability was not pronounced, implying a temporary compensatory growth phase.

Table 1.

Effects of diniconazole concentration on leaf morphological traits and chlorophyll content (SPAD value) of tomato seedlings at different growth stages, raised in a growth chamber at 25°C

During the late nursery stage (6–7 WAS), untreated seedlings exhibited strong reductions in leaf area and premature leaf senescence, likely due to rapid substrate nutrient depletion associated with excessive early vegetative growth. In contrast, diniconazole-treated seedlings maintained greater leaf area, with the 125 mg/L treatment producing the highest leaf area and leaf number. Chlorophyll content followed a similar pattern: SPAD values of untreated seedlings declined steadily, while all diniconazole treatments maintained SPAD values above 50. The enhanced chlorophyll retention, particularly at 125 mg/L, aligns with previous findings that triazoles delay chlorophyll degradation through suppression of GA signaling and protection of chloroplast integrity (Fletcher et al., 2000).

Overall, diniconazole suppressed early leaf expansion but enhanced physiological stability later in the nursery stage.

Diniconazole significantly suppressed shoot elongation in a concentration-dependent manner (Table 2; Fig. 1). Height reduction was the primary sign due to shortened internodes, which is consistent with the inhibition of GA biosynthesis, particularly the suppression of ent-kaurene oxidation by triazole compounds (Davis et al., 1988; Rademacher, 2000). As the height suppressed, stem thickening progressed from 5 WAS onwards, especially at 125 mg/L, resulting in compact seedlings.

Table 2.

Effects of diniconazole concentrations on number of nodes, stem diameter, plant height, and root length of tomato seedlings at different growth stages, raised in a growth chamber at 25°C

Fig. 1.

Representative morphological responses of tomato seedlings raised in a plant growth chamber maintained at 25°C under different diniconazole concentrations (0, 50, 125, and 250 mg/L) from 3 to 7 weeks after treatment.

The shift in assimilate allocation from longitudinal to radial growth reinforces that triazole-induced height control redirects photoassimilates to supportive tissues (Fletcher et al., 2000; Desta and Amare, 2021). By 7 WAS, seedlings treated with 125 mg/L developed more nodes despite being shorter, confirming that the triazole compound reduced internode length without impairing meristematic activity (Jang et al., 2020).

Root growth at a concentration of 125 mg/L was comparable to the control, indicating that moderate diniconazole application did not compromise root system development. This shoot–root balance is agronomically desirable because it enhances post-transplant establishment (Latimer, 1992). Excessive suppression at 250 mg/L, however, diminished overall vigor, likely due to restricted assimilate production and impaired structural development (Choi et al., 2001).

Thus, diniconazole at 125 mg/L effectively suppressed internode elongation while preserving stem diameter and root development, yielding compact, vigorous seedlings ideal for transplanting.

Biomass accumulation was strongly effected by diniconazole concentration (Table 3). At 4 WAS, high-concentration application (250 mg/L) significantly reduced biomass, indicating that excessive suppression of vegetative growth limited assimilate production. As seedlings matured, the 125 mg/L treatment exhibited superior biomass accumulation. By 6 WAS, total fresh weight was approximately one-third greater than the control, and root fresh weight consistently exceeded that of untreated seedlings. By 7 WAS, dry matter accumulation was highest at 125 mg/L, suggesting enhanced tissue density and improved dry matter partitioning.

Table 3.

Effects of diniconazole concentrations on fresh weight, and dry weight of tomato seedlings at different growth stages, raised in a growth chamber at 25°C

These results are consistent with existing studies showing that moderate triazole application increases tissue density and mechanical strength through shifts in assimilate allocation (Fletcher et al., 2000; Niu et al., 2002). In contrast, substantial growth suppression at 250 mg/L, resulted in the lowest biomass throughout development, emphasizing the risk of excessive dosage.

Overall, diniconazole at 125 mg/L resulted in structural robustness and biomass balance in tomato seedlings. Consequently, these seedlings exhibited compact shoot and root growth with sustained vigor, ensuring high transplant quality.

Carry-over effects of diniconazole applied during the nursery stage were evident immediately after transplanting and persisted through early vegetative stage (Table 4). At 1 week after transplanting (WAT), control plants exhibited the smallest leaf area and lowest SPAD values, likely due to the rapid shift toward stem elongation that restricted leaf expansion and photosynthetic capacity. In contrast, seedlings previously treated with 125 mg/L produced significantly greater leaf area and maintained stable SPAD values above 50, indicating superior photosynthetic potential and more stable early growth. These results support findings that moderate height suppression during seedling production improves post-transplant vigor by conserving assimilates for later leaf development (Vavrina and Orzolek, 1993).

Table 4.

Effects of seedling-stage diniconazole treatments on leaf growth and chlorophyll content of tomato plants at different growth stages after transplanting in a greenhouse

From 3 to 5 WAT, all treatments showed increases in leaf number and area; however, diniconazole-treated plants consistently exhibited higher SPAD values, reflecting delayed chlorophyll degradation and enhanced leaf physiological stability. The 125 mg/L treatment produced more leaves and maintained higher chlorophyll content than the control while preventing excessive canopy enlargement. This pattern aligns with the known triazole-mediated reductions in internode elongation and leaf enlargement that promote efficient assimilate allocation to functional leaf tissues (Yun et al., 2007).

By 13 WAT, differences among the control, 50 mg/L, and 125 mg/L treatments had largely diminished, suggesting that these concentrations did not impose long-term restrictions on leaf growth or chlorophyll content. In contrast, the 250 mg/L treatment resulted in decreased leaf number, leaf area, and SPAD values, suggesting impaired leaf development and photosynthetic competence caused by prolonged inhibition of GA biosynthesis (Rademacher, 2000).

Morphological differences established during the nursery period persisted after transplanting and continued to influence stem elongation, radial thickening, and node formation (Table 5; Fig. 2). At 1 WAT, control plants showed pronounced stem elongation, whereas all diniconazole-treated plants remained significantly shorter (23.0–25.5 cm). This persistent height suppression reflects the earlier inhibition of internode extension caused by triazole-mediated GA biosynthesis reduction (Rademacher, 2000).

Table 5.

Effects of seedling-stage diniconazole treatments on number of nodes, basal stem diameter, apical stem diameter, and plant height of tomato plants at different growth stages after transplanting in a greenhouse

Fig. 2.

Morphological characteristics of tomato plants at 13 weeks after transplanting as influenced by different diniconazole concentrations applied during the seedling stage.

By 3 WAT, plants treated with 50 and 125 mg/L had heights similar to the control, but stem diameter remained consistently greater in all diniconazole treatments, indicating sustained allocation of assimilates toward radial growth rather than elongation. Such thickened stems are advantageous for structural strength and hydraulic conductivity, supporting improved long-term vigor.

During the mid-season (5–7 WAT), differences became more pronounced. Plants treated with 250 mg/L developed the thickest stems but remained significantly shorter than all other treatments, reflecting cumulative GA inhibition and reduced metabolic activity, a response previously reported under excessive triazole exposure (Jang et al., 2020). At 13 WAT, the control plants exhibited the greatest height, while the 125 mg/L treatment maintained a compact and agronomically desirable canopy. Node number did not differ among the control, 50 mg/L, and 125 mg/L treatments, indicating that moderate concentrations affected internode elongation but not meristematic activity. Conversely, the 250 mg/L treatment produced fewer nodes, suggesting suppressed meristem function under excessive dosage.

Analogous to nursery stage, 125 mg/L treatment provided the most favorable response, supporting compact growth with enhanced stem diameter and stable node development traits that contribute to improved performance in greenhouse cultivation.

Carry-over effects of diniconazole on reproductive development were substantial and highly concentration dependent (Table 6). At 3 WAT, all diniconazole treatments showed accelerated floral transition compared to the control, with increased numbers of floral primordia and open blooms. The 250 mg/L diniconazole treatment yielded the highest count of early floral structures, indicating that intense vegetative suppression in seedlings diminished competing sinks and promoted earlier reproductive onset, a pattern aligning with growth regulator effects in compact transplants (Zhang et al., 2003).

Table 6.

Effects of seedling-stage diniconazole treatments on number of flowers, number of blooms, and number of fruit sets of tomato plants at different growth stages after transplanting in a greenhouse

Despite this early stimulation, fruit-set efficiency varied widely. Although the 250 mg/L treatment produced many early flower buds, it had relatively low fruit-set rates, while the 50 mg/L treatment achieved the highest fruit set rate at 3 WAT. This indicates that excessive triazole application may reduce assimilate production and transport, limiting the conversion of flowers to fruit, a constraint consistent with known metabolic effects of high triazole concentrations (Rademacher, 2000).

During mid-season (5–7 WAT), fruit set increased across all diniconazole-treated plants producing 2–2.5 times more fruit than the control. The 125 mg/L treatment consistently produced the highest fruit-set numbers at 7 WAT, ascertaining a sustained reproductive advantage beyond the early establishment stage. In contrast, the 250 mg/L treatment did not maintain its initial reproductive stimulation; despite producing abundant floral primordia early, fruit-set retention declined, likely due to limited assimilate supply and cumulative metabolic suppression.

By 9 WAT, treatment effects were fully expressed. Plants treated with 125 mg/L maintained the greatest fruit-set count (14.8 fruits per plant), indicating strong reproductive continuity and sufficient assimilate supply (Yun et al., 2007). Conversely, the 250 mg/L treatment exhibited a major decline in fruit set, reflecting long-term constraints on carbon assimilation and resource allocation (Choi et al., 2001).

Overall, diniconazole imposed distinct responses to various concentrations, during reproductive phase post-transplanting. Moderate application rates enhanced early floral initiation, supported stable mid-season reproductive activity, and ensured sustained fruit-set retention during prolonged greenhouse cultivation. Excessive application (250 mg/L), while stimulating early floral differentiation, ultimately reduced fruit-set efficiency and long-term reproductive performance.

Early yield and harvest earliness were markedly influenced by diniconazole application during the seedling stage, and responses varied strongly with treatment concentration (Table 7; Fig. 3). Among all treatments, 125 mg/L produced the most favorable carry-over effects, leading to the earliest harvest initiation and the greatest cumulative early yield. Yield from the first two trusses reached 663.4 g/plant (20.7 t/ha), representing a 75% increase relative to the untreated control (379.3 g/plant; 11.9 t/ha) which was statistically significant (P < 0.05) (Table 7; Fig. 4). These findings indicate that moderate suppression of vegetative vigor during the nursery stage enhances assimilate partitioning toward reproductive sinks after transplanting, thereby improving early-fruiting performance. Similar improvements in early yield resulting from compact seedling architecture have been reported in tomato and other solanaceous crops (Marcelis, 1996; Kim et al., 2016).

Table 7.

Effects of seedling-stage diniconazole treatments on cumulative fruit number per plant, cumulative fruit weight, mean fruit weight, and estimated yield per hectare of tomato plants at 13 weeks after transplanting under greenhouse conditions

Fig. 3.

Changes in harvest rate of greenhouse-grown tomato plants as influenced by diniconazole concentrations applied during the seedling stage. Harvest rate was determined at 2-week intervals and expressed as the percentage of plants producing marketable fruits relative to the total number of plants per treatment (n = 9).

Fig. 4.

Effects of diniconazole treatments applied during the seedling stage on cumulative fruit number and cumulative yield of tomato plants grown in a greenhouse. Cumulative fruit number and yield were determined from the first and second trusses. Error bars represent the standard error of the mean (n=9).

Although the 250 mg/L treatment produced the highest number of initial fruit sets, its early yield (18.8 t/ha) was lower than that of the 125 mg/L treatment because of reduced mean fruit weight. This responses suggests analogy to previous reports that excessive triazole-induced growth inhibition may accelerate floral induction while restricting assimilate availability during fruit enlargement, thereby reducing final fruit size despite abundant fruit set (Marcelis, 1996; Jang et al., 2020). Across treatments, mean fruit weight varied only modestly (84.9–102.9 g); thus, differences in early yield were primarily driven by variation in fruit set and the timing of harvest onset.

Weekly harvest patterns (Fig. 3) further confirmed the benefits of moderate diniconazole application. Plants treated with 50 and 125 mg/L initiated harvest 2 weeks earlier than both the control and the 250 mg/L treatment. Notably, the 125 mg/L treatment produced the highest proportion (44%) of marketable fruits during week 7 after transplanting, indicating enhanced precocity. These results are consistent with the hypothesis that compact seedlings exhibit greater early reproductive sink strength and more efficient allocation of assimilates to fruit development, particularly during the initial post-transplant period (Talukder et al., 2025).

In contrast, the reduced early yield of the 250 mg/L treatment suggests that excessive inhibition of vegetative growth compromises the sustained supply of assimilates required for early fruit enlargement, even when flower initiation is promoted. Such negative impacts of high triazole concentrations on reproductive productivity have been documented in several horticultural crops (Rademacher, 2000; Jang et al., 2020).

Overall, these results demonstrate that diniconazole application during the seedling stage exerts substantial concentration-dependent carry-over effects on early tomato productivity. Among the treatments examined, 125 mg/L represents to be ideal concentration, simultaneously enhancing harvest earliness and maximizing early cumulative yield.