Growth attributes
At the panicle initiation stage, plant growth regulators and moisture stress were imposed; before that, all agronomic procedures were similar for all treatment. Therefore, there is no significant difference in the effects of foliar spray and moisture stress treatments on rice development during active tillering and panicle initiation. When there is no moisture stress (conventional irrigation), taller plants were observed during the flowering and harvesting periods (Fig 3). If irrigation was applied a day after the ponded water at a depth of 5 cm disappeared, the height of the rice plants increased. In the absence of moisture stress, the crop may have increased meristematic cell activity and cell elongation, which would have increased the stem’s growth rate and, consequently, the rice plant’s height
(Chowdhury et al., 2014). When moisture stress at the panicle initiation stage, shorter plant heights were noted. According to
Thangaraj et al., (1998), applying moisture stress to rice at any stage of growth before anthesis drastically decreased plant height. When it came to the foliar application of growth-regulating substances, 1% potassium silicate spraying was comparable to 2% seaweed extract in terms of increasing plant height. This may be explained by the fact that silicon encourages upright leaves, which raises photosynthetic capability and raises plant height.
Mrudhula and Krishna, (2020) found similar outcomes while growing rice in saline soil.
The highest number of tillers per hill
-1 was observed in moisture stress-free control (conventional irrigation) among the different moisture stress treatments. This was followed by moisture stress during the flowering stage. This could be due to adequate aeration, which promoted greater nutrient uptake and higher plant growth and tiller formation by facilitating the absorption of more nutrients. These findings align with those of
Hameed et al., (2011). At the flowering and harvest stages, a 1% potassium silicate foliar spray resulted in a significantly higher number of tillers hill-1 in terms of growth-regulating compounds. It was comparable to 2% seaweed extract foliar spray. This might have led to more cell division activity, which improves plant establishment and tillers formation. Plants with silicon deposits have more upright leaves. Silicon has a synergistic effect with other nutrients, making the nutrients available to the plant. These findings are consistent with those of
(Punniyamoorthi, et al., 2024). In the current study, the total number of tillers generally reduced where moisture stress was imposed. However, it is possible to overcome this with proper supplementation of stress management strategies. This was also in agreement with the findings of
Vijayalakshmi and Nagarajan, (1994).
The moisture stress-free control group showed the highest Leaf Area Index (LAI) among the different moisture stress treatments (Fig 4). Several factors could contribute to the higher LAI under one day after disappearance (DAD) of ponded water at a 5 cm depth of rice irrigation, including increased nutrient uptake, favourable moisture regimes, delayed leaf senescence and a greater photosynthetic rate. Moisture stress during the panicle initiation stage resulted in lower LAI. This might be due to a loss of cell turgor, leading to reduced cell enlargement and less transport of assimilates from the leaves to the developing sink. The decrease in LAI during the panicle initiation stage was caused by a rapid decline in leaf elongation combined with increased leaf senescence, as found by
Lilley and Fukai, (1994). Regarding foliar growth regulator application, spraying 1% potassium silicate increased LAI, which was comparable to 2% seaweed extract. This could be attributed to their beneficial role in cell division and elongation, resulting in increased LAI
(Li et al., 2008). The combination of 1% potassium silicate and moisture stress-free control resulted in a higher LAI. A moisture stress-free control using 2% seaweed extract was the next highest. Maintaining elevated LAI was positively impacted by potassium silicate application, especially in stressful conditions. At the panicle initiation stage, lower LAI was observed under moisture stress in addition to the control (no spray).
DMP increased steadily with each growth stage and peaked at harvest. Without moisture stress (conventional irrigation), there was increased DMP (Fig 5). Dry matter accumulation could have increased because of sufficient nutrient availability and a larger photosynthetic surface area, leading to rapid accumulation. These findings align with those of
Hameed et al., (2011). Decreased DMP was observed with moisture stress at panicle initation stage, likely because poor moisture availability affects photosynthetic rate, water and nutrient uptake and photo assimilate transport. Lower dry matter production was a result of moisture stress inhibiting plant growth, leaf number, leaf size and tillers (
Ashraf and Ragavan, 2019). Increased DMP was recorded with foliar application of one percent potassium silicate and two percent seaweed extract under moisture stress. This might be because Silicon (Si) promotes growth, strengthens rice culms and increases resistance and photosynthesis. Similar findings were reported by
Ashraf et al., (2024). At harvest, there was a significant interaction between moisture stress and foliar spraying of growth-regulating chemicals. DMP increased when combining moisture stress-free control (standard irrigation) with 1% potassium silicate spraying and then with moisture stress-free control plus 2% seaweed extract.
Physiological and biochemical parameters
Chlorophyll index
The total chlorophyll content of the plant influenced its photosynthetic rate, which in turn affected biomass production and yield. Stress-induced reduction in leaf chlorophyll content could be attributed to reduced biosynthesis or accelerated pigment degradation. The plants were not under moisture stress, showed a higher chlorophyll index (SPAD). The reduced chlorophyll index during moisture at panicle initiation stage was tabulated in Table 1. According the finding of
Jahan et al., (2014), moisture stress decreased the amount of chlorophyll in leaves, which suppressed crop output by reducing CO2 assimilation. The levels of chlorophyll ‘a’, chlorophyll ‘b’ and total chlorophyll were significantly reduced by moisture stress. Conversely, under moisture stress conditions, there would be degradation in pigment composition, which induced a decrease in chlorophyll content
(Khairi et al., 2015). Among the foliar applications of growth-regulating compounds, increased chlorophyll index (SPAD) was observed with one percent potassium silicate, followed by seaweed extract at 2%. This might be due to the improvement in chlorophyll content. Various studies indicated that plant growth regulators increased the chlorophyll content when under moisture stress.
Relative leaf water content
One of the most important indicators of plant water stress is relative leaf water content (RWLC), which indicated ability of the plants to preserve tissue water status in the face of moisture stress. The relative leaf water level of the moisture stress-free control was higher than that of the other moisture stress treatments and moisture stress during the flowering stage came next was tabulated in Table 2. Under situations of moisture stress, yield was significantly impacted by rapid early development and the maintenance of RWLC at a reasonably high level during the reproductive period. Further, at the panicle initiation stage, a reduced relative water content was noted in response to moisture stress.
Khairi et al., (2015) noted a similar result. Under conditions of moisture stress, foliar treatment of 1% potassium silicate preserved the leaf cells’ high relative water content status. Nonetheless, this was comparable to using 2% seaweed extract topically. Osmotic adjustment may be the cause of this and growth regulators’ positive effects may be connected to an increase in photosynthetic equipment, which in turn boosted the production of osmotic solutes during drought
(Ashraf et al., 2021).
Proline content
The concentration of proline varied significantly based on the type of moisture stress and growth-regulating chemicals were applied. At the panicle initiation stage, proline content was higher under moisture stress, but lower without moisture stress free control. Among the growth-regulating compounds sprayed, one percent potassium silicate resulted in lower proline content was tabulated in Table 3. This could be because growth-regulating substances minimized stress effects, leading to less proline. According to
Ashraf et al., (2020), using Si can reduce transpiration loss by up to 30%. Silicon lowers water loss by helping the plant maintain its ideal transpiration rate. However, proline content was higher in the absolute control. Proline serves as a compatible solute and protects cytoplasmic enzymes and structures. The main reason for increased proline concentration during moisture stress might be the reduced incorporation of the continuously synthesized amino acid, proline, during its synthesis.
Catalase activity
Catalase enzyme activity gradually increased at different growth stages, as indicated by the trend of decreasing H
2O
2 levels
(Ashraf et al., 2020a). Catalase is one important enzyme that removes H
2O
2 from the mitochondria and microorganisms
(Shigeoka et al., 2002). Drought may be the cause of the maximum catalase activity observed in the current investigation, which occurred with moisture stress at the panicle start stage was tabulated in Table 4. According to
Sultana et al., (2001), moisture stress enhanced catalytic activity by 30% during the reproductive stage and 35% during the vegetative stage. Catalase activity was shown to be reduced when 1% potassium silicate was sprayed. Under abiotic stress circumstances, catalase (CAT), a significant and potent antioxidant enzyme, counteracted the effect of H
2O
2 and shielded plants from harm. In general, this enzyme is regarded as an H
2O
2 scavenger that helps lessen oxidative damage
(Reddy et al., 2004).
Soluble protein
In the current study, the control that was not under any moisture stress had a greater soluble protein content, whereas moisture stress at the panicle initiation stage had the lowest soluble protein content. Both a decrease in enzyme synthesis and the breakdown of accessible soluble protein in plants may be responsible for the drop in soluble protein concentration was tabulated in Table 5. However, the presence of binding inhibitors inside the catalytic region is the reason for the reduction in rubisco activity
(Parry et al., 1999 and
Ashraf et al., 2018). The rubisco enzyme is degraded by abiotic stress, as shown by a decrease in soluble protein in leaves. The foliar spray of 1% potassium silicate produced the highest amount of soluble protein among the moisture stress management treatments, followed by 2% seaweed extract.
Grain and straw yield
The moisture stress-free treatment led to higher grain and straw yields was tabulated in Table 6. This might be due to a higher fertility percentage, more grain panicles and more productive tillers. Additionally, the fields’ rotating irrigation (watering and drying) increases soil aeration, root development and nutrient availability during crop growth, while also reducing weed growth. These factors all contributed to enhanced yield components and greater rice output. The results are in line of
Ceesay et al., (2006) and
Ashraf et al., (2020), who discovered that repeated cycles of wetting and drying enhanced rice plant growth by boosting nutrient availability, leading to increased yields of grain and straw. Moisture stress during panicle initiation had a greater negative impact on rice yield than during flowering.
Grain and straw yields were increases under 1% potassium silicate foliar spray. However, this was comparable with foliar spray of 2% seaweed extract. This could be due to the fact that applying silicon to upland paddy increased plant sturdiness and allowed it to grow erect without lodging. The plant’s erect position exposed it to sunlight, which increased photosynthetic activity and organic constituent assimilation. These assimilates lower the prevalence of pests and diseases while simultaneously promoting crop growth and development. The crop produces a profitable yield of rice by growing quickly and using the soil’s nutrients and moisture. The results align with the findings of
Patil et al., (2018) and
Ashraf and Ragavan, (2021). The yield of grain and straw was significantly impacted by both moisture stress and the foliar application of growth-regulating substances. Grain production was raised by combining foliar spray of 1% potassium silicate with moisture stress-free control. This was followed by a 2% foliar spraying of seaweed extract to minimize moisture stress. The foliar application of silicon levels led to a considerable increase in straw yield. This may be explained by silicon’s ability to boost photosynthetic activity and the effectiveness of water and nutrient utilization. In the end, this leads to better vegetative development. The number of tillers per hill and plant height were the main factors associated with higher straw output. Plant sections that accumulate silicon have better tolerance to biotic and abiotic stressors and less lodging. It’s possible that each of these elements helped to increase the amount of straw produced.
Singh et al., (2008) reported similar results.
