Maize growth stage response to waterlogging
The results of this study revealed significant impacts of waterlogging stress on maize growth across all developmental stages. Seven days of waterlogging led to notable reductions in survival percentage, root length and plant height while inducing leaf chlorosis and increasing the number of nodal roots (Table 1). Among the growth stages, the tasseling stage was particularly vulnerable to waterlogging stress, exhibiting the most severe decline in growth performance. When waterlogging stress was imposed at the tasseling stage, the survival rate reached 60.22%. Visual leaf ratings consistently indicate that plants at tasseling exhibit severe chlorosis and reduced plant height, suggesting lower tolerance to waterlogging stress. In addition, by the seventh day of waterlogging, the nodal root length at the tasseling stage measured 37.31 cm, a significant difference from the nodal root lengths observed at other maize growth stages. This significant difference underscores the impact of waterlogging stress on maize growth. In contrast, no significant difference in nodal root numbers were observed at the reproductive stage under non-waterlogged conditions, with values ranging from 33.04 to 37.71. However, nodal root numbers at vegetative growth stages were significantly lower compared to the reproductive stage. This result indicates that the developmental stages of maize are also a factor in the number of nodal roots developed since it is expected that the older growth stages have a higher number of nodal roots. However, it is clearly shown in this result that the development of nodal roots is an adaptive maize response to waterlogging stress.
Waterlogging stress triggered the development of nodal roots, an adaptive response in maize, showcasing the resilience of the plant. Our findings corroborate
Kaur et al., (2020), who reported that maize nodal roots develop as an adaptive response to waterlogging stress. Also, this response, as found by
Kaur et al., (2020), led to increased nodal root formation, especially at the older growth stages. These nodal roots, a mechanism for improved waterlogging tolerance, allow the plant to continue aerobic respiration by accessing atmospheric gases, thereby mitigating the effects of anaerobic stress. This adaptation, also noted by
Esteban and Baldo (2024), aligns with earlier research by
Armstrong and Drew (2002), as cited by
Zaidi et al., (2007), which identified surface rooting as a common strategy in wetland species to withstand flooding. The formation of aerenchyma cells in the root system also helps crops to survive during the waterlogging period
(Duman et al., 2017). In addition to the morphological adaptations, waterlogging stress was observed to induce leaf chlorosis and reduce total leaf chlorophyll content. This was particularly evident at the tasseling stage, where chlorophyll loss was most pronounced, resulting in stunted growth and lower yield. A similar result was also observed in the findings of
Saikia et al., (2021) that greengram chlorophyll declines when exposed to waterlogging. Meanwhile, the induced leaf chlorosis can be attributed to stomatal closure, as
Malik et al., (2001) reported, which limits oxygen and carbon dioxide exchange, thereby decreasing photosynthesis. This finding supports the work of
Lizaso and Ritchie (1997), highlighted the role of abscisic acid (ABA) in regulating stomatal behavior under waterlogged conditions, leading to reduced chlorophyll and premature leaf senescence. Similarly, reduced chlorophyll content due to oxidative stress from waterlogging was observed in studies by
Wang et al., (2012), further explaining the diminished photosynthetic efficiency and growth decline.
Moreover, the tasseling stage experienced marked reductions in yield components such as ear length, diameter, weight, thousand seed weight and kernels per ear (Table 2). These observations suggest that tasseling is the most sensitive stage under waterlogging stress, as corroborated by
Ren et al., (2014), who reported delayed silking and growth retardation under similar conditions. Interestingly, maize plants subjected to waterlogging stress at reproductive stages, particularly during tasseling and silking, experienced the most significant yield reductions, up to 58.30%. This was evidenced by the elongation of the anthesis-silking interval (ASI), which impaired successful pollination and reduced kernel formation. The extended ASI under waterlogged conditions is consistent with previous studies, including those by
Paril et al., (2017), who identified this as a critical factor in yield decline. The reproductive stages’ heightened sensitivity to waterlogging is likely due to the direct impact on reproductive processes, leading to increased barrenness in maize ears, as
Ren et al., (2014) and
Esteban (2024) noted.
The study also highlighted that while maize plants at vegetative stages showed some ability to recover from waterlogging stress, yield reduction was still significant. It shows that waterlogging stress reduced yield from 20.14% to 58.30% depending on the growth stages. Older growth stages exhibited a smaller percentage of yield loss compared to younger ones, aligning with findings by
Shin et al., (2016) and
Esteban (2024), who reported that waterlogging at the early V2 stage resulted in an 80% yield loss, while later stages showed a lesser, but still considerable, yield reduction. This significant yield loss due to waterlogging stress will also imply a monetary loss or income of the farmers.
Furthermore, the analysis revealed that waterlogged maize plants exhibited a reduction in plant height, ear height and leaf area index, which collectively contributed to lower yields. These physiological changes are in line with the work of
Ren et al., (2014), who observed a decrease in dry matter accumulation and distribution under waterlogged conditions. The implications of these findings are significant for maize cultivation in areas prone to waterlogging, as they underscore the importance of selecting waterlogging-tolerant hybrids and adjusting planting schedules to mitigate yield losses, providing actionable solutions for the audience. Farmers can minimize yield losses by improving drainage, adjusting planting schedule to avaoid tasseling during heavy rainfall and selecting maize hybrids with longer nodal roots.
The study confirms that waterlogging at any growth stage significantly impairs maize growth and yield performance, with reproductive stages being the most susceptible. The urgency of the situation is underscored by the critical need for adaptive agricultural practices, including using waterlogging-tolerant maize varieties and optimized agronomic management, to cope with the increasing threat of waterlogging due to climate change. This stress on the importance of the study’s findings invokes a sense of urgency in the audience, reinforcing the need for immediate action.
Inter-phenotypic correlation of maize traits as influenced by waterlogging
The summary Table of significantly correlated maize traits as influenced by seven days of waterlogging is presented in Table 3. The results demonstrate that specific phenotypic traits in maize, particularly leaf greenness and nodal root length, correlate strongly and positively with survival rates under waterlogging stress. This suggests that greener leaves (leaves 2 and 3) and longer nodal roots are indicators of enhanced waterlogging tolerance. As shown in Table 3, leaf visual scores 2 and 3 exhibit significant positive correlations with percentage survival, indicating that greener leaves contributes to higher survival rates. In addition, the negative correlation between leaf visual score 1 (lower greenness) and nodal root length underscores that reduced greenness in younger leaves is associated with shorter root lengths, which may hinder survival in waterlogged conditions. Therefore, maintaining greener leaves and longer nodal roots is a viable criterion for identifying waterlogging-tolerant lines.
Nodal root length is another critical trait positively correlated with percentage survival under waterlogged conditions. This correlation suggests that maize plants with longer nodal roots are better equipped to withstand waterlogging, possibly due to an enhanced capacity for oxygen absorption or improved resilience to water saturation. These findings align with previous studies of
Esteban and Baldo (2024) and
Esteban and Solilap (2016), which identified leaf greenness as a reliable selection criterion for waterlogging tolerance. These results indicate that leaf greenness and nodal root length are integral phenotypic indicators of maize tolerance to waterlogging stress, supporting their use in breeding programs targeting climate resilience.
Furthermore, maize yield components, including ear diameter, length and weight, number of kernels per row and kernel rows per ear, show significant correlations, highlighting that maize yield under stress is governed by multiple traits rather than a single phenotype. This finding emphasizes the complexity of improving yield under adverse conditions like waterlogging. Notably, a strong negative correlation between 1000-seed weight and percentage yield reduction indicates that heavier seeds are associated with lower yield losses, suggesting that seed weight is vital in maintaining yield under stress. The correlations among yield components imply that breeding for waterlogging tolerance must consider multiple traits simultaneously to mitigate yield loss effectively.
The results emphasize the importance of selecting traits such as leaf greenness, nodal root length and key yield components to improve waterlogging tolerance in maize. The strong correlations observed across these traits suggest they are reliable indicators of waterlogging tolerance and crucial for sustaining yield under stress. By integrating these traits into breeding strategies, there is potential to develop maize varieties with enhanced resilience, contributing to more sustainable and climate-adaptive agricultural systems.
