Alleviation of salt stress in baby corn through hormonal, chemical, and microbial interventions | |
| Author | Islam, A T M Tanjimul |
| Call Number | AIT Diss no.AS-22-04 |
| Subject(s) | Plants--Effect of salt on Plants--Effect of stress on Salt-tolerant crops Corn |
| Note | A Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Agricultural Systems and Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Soil salinization poses a critical challenge to agroecosystems and is a rising global hazard to the sustainability of agricultural systems by declining the quality and yield of crops, especially in the coastal, arid, and semi-arid regions of the world. Salinity produces a variety of physiological and biochemical changes, including a decrease in soil water potential, ionic disequilibrium, specific ion effects, and an increase in the buildup of reactive oxygen species. Baby corn (Zea mays L.), a popular vegetable crop, can tolerate a moderate level of salinity. However, higher soil salinity is detrimental to its growth and productivity. Baby corn is gaining importance for its enormous processing and export potential. Different mitigation strategies, such as application of salicylic acid (SA) seed priming, silicon (Si) fertilizer, arbuscular mycorrhizal fungi (AMF), and plant growth-promoting rhizobacteria (PGPR), might be used to alleviate salt stress to ensure crop productivity under changing environmental conditions. It was hypothesized that the use of these techniques, either individually or in combination, would be a sustainable management option in maintaining/increasing the yield and quality of this crop grown under salt stress. Therefore, both individual and integrated applications of these techniques were undertaken through a series of polyhouse experiments to evaluate the impacts of these techniques on baby corn grown under salt stress. In the first polyhouse experiment, germination, growth, yield, physiological, and biochemical responses of 11 hybrid baby corn genotypes (Kasetsart 3, PAC 271, PAC 321, PAC 571, SG 17 Super, CP B468, CP B905, WS 111, WS 9103, Chang Daeng 18, and HY 074656) to five levels of NaCl-induced salinity (0.7 [control], 3, 6, 9, and 12 dS m–1 ) were evaluated in a germination trial in petri dishes, followed by a polyhouse study to assess genotypic variation of baby corn genotypes in salinity tolerance. Data on various germination traits, growth, yield, physiological, and biochemical parameters were collected. Increasing salinity level above 6 dS m–1 was equally detrimental for the germination and growth of all tested genotypes. Germination response of Chang Daeng 18 genotype to salt stress was the poorest (22.2% germination rate and 7.7% mean daily germination). Growth, yield, physiological, and sodium (Na+ ) accumulation data revealed that SG 17 Super genotype was the most susceptible to salt stress, whereas PAC 571 was the most tolerant. SG 17 Super had 28% lower shoot dry matter, 54% lower cob yield, 25% less membrane stability index, and 158% more Na+ accumulation compared with PAC 571. All other genotypes were between slightly salt-tolerant to moderately salt-tolerant category, which was also verified by the Hierarchical cluster analysis. Physiological and biochemical parameters, such as free proline, membrane electrolyte leakage, and membrane stability index, as well as ion accumulation parameter, such as Na+ , were the most representative of salt stress. Salinity reduced leaf greenness (SPAD value), while net photosynthetic rate, stomatal conductance, and transpiration rate were not affected. Na+ exclusion and higher K+ /Na+ ratio in leaves of baby corn genotypes correlated well with their higher salinity tolerance, and greater K + /Na+ discrimination was shown by salt-tolerant genotypes. The relative susceptibility of baby corn genotypes to salinity should be taken into consideration for plant breeding programs. The selected salt-tolerant baby corn genotypes have the potential for cultivation in salt-affected soils for better productivity.The second factorial pot experiment, consisting of two baby corn hybrid cultivars (PAC 571: salt-tolerant and SG 17 Super: salt-sensitive), three doses of SA (0 [hydropriming], 1, and 2 mM) applied as a seed priming material, and four levels of salinity (0.7 [control], 6, 9, and 12 dS m–1 ), was conducted to evaluate the impact of SA on baby corn under salt stress. Data on growth, physiological traits, cob yield, and ion content in leaf tissues were collected, which revealed that an increasing salinity level was equally detrimental for the two tested cultivars with varying intensities. At the highest salinity level (12 dS m–1 ), both cultivars produced no cob, and the same salinity level caused a reduction of 67%, 14%, 42%, 87%, and 37% in shoot dry matter, leaf relative water content, membrane stability index, net photosynthetic rate, and leaf potassium content, respectively, compared with the control across cultivars and SA levels. The same salinity level caused about 3-fold, 10-fold, and 6-fold increases in electrolyte leakage, free proline content, and leaf sodium content, respectively. Seed priming with SA was effective, and 1 mM provided more promising results with an increase of 43%, 45%, 5%, and 7% in root dry matter, cob yield, leaf relative water content, and free proline content at 6 dS m–1 than 0 mM SA at the same salinity level. Salt-tolerant cultivar (PAC 571) had significantly higher cob number plant–1 (30%) and cob yield (34%) than salt-sensitive cultivar (SG 17 Super) at 6 dS m–1 . However, there was largely no effect of SA seed priming on other evaluated parameters at 9 and 12 dS m–1 salinity levels. Priming of seeds with 1 mM SA could be a promising approach for baby corn production under a moderate salinity level up to 6 dS m–1 . However, the harmful effects of extreme salinity (9 and 12 dS m–1 ) cannot be completely compensated for SA seed priming. The third factorial polyhouse study, consisting of four soluble Si doses (0, 15, 30, and 60 kg ha–1 ) applied in the form of monosilicic acid, two levels of AMF inoculation (inoculation of AMF [+AMF] and without inoculation of AMF [–AMF]), and three salinity levels (0.7, 6, and 9 dS m–1 ), was conducted to determine the potential combined role of Si and AMF on growth, cob yield, and physio-biochemical traits of baby corn under salt stress. Data on growth, cob yield, physio-biochemical parameters, and leaf ion concentration were collected. The results revealed that rising salinity severely impacted growth and cob yield of baby corn, and the plants were unable to produce any marketable cob at 9 dS m–1 . The same salinity level also caused a significant decrease in membrane stability index (up to 27%) and net photosynthetic rate (up to 73%), along with a drastic increase in Na+ accumulation (up to 323%) across Si doses. Plants supplemented with Si at 60 kg ha–1 exhibited overall better results than other doses (14, 58, and 74% increase in shoot dry matter, cob number per plant, and cob yield compared with 0 kg ha–1 at 0.7 dS m–1 ). The same Si dose (60 kg ha–1 ) caused 13% increase in membrane stability index and 28% decrease in electrolyte leakage at 6 dS m–1 compared with 15 kg ha–1 Si dose. Plants inoculated with AMF outperformed non-inoculated plants for most of the evaluated parameters and caused 100 and 118% increase in cob number per plant and cob yield at 6 dS m–1 . Integrated application of Si (60 kg ha–1 ) and AMF was even more effective for increasing shoot and root dry matter, root colonization, and accumulation of essential ions (K+ , Ca2+, and K+ /Na+ ratio). Therefore, it is recommended to apply 60 kg ha–1 of soluble Si along with AMF for baby corn cultivation in salt-affected soils (up to a maximum of 6 dS m–1 salinity level).The fourth polyhouse experiment, consisting of three Si doses (0, 30, and 60 kg ha–1 ) and three salinity levels (0.7, 4, and 8 dS m–1 ) with (+PGPR) or without (–PGPR) PGPR, was conducted to determine the potential combined role of Si and PGPR on baby corn under salt stress. Increasing salinity was equally detrimental for all plants (61–63 reduction in cob number per plant, 70–79 reduction in cob yield, up to 127% increase in electrolyte leakage, and up to 56% reduction in K+ content at different Si doses) regardless of whether Si and PGPR was applied or not. However, the impact of increasing salinity was generally less profound for plants supplemented with Si or PGPR. The integrated application of Si and PGPR was found more effective than their individual application and caused a significant increase in root dry matter, cob number per plant, stomatal conductance, and free proline accumulation. In addition, Si supplementation at 30 and 60 kg ha–1 along with PGPR inoculation caused a significant reduction in Na+ accumulation in leaves of baby corn compared with non-inoculated plants at the same Si doses. The present results demonstrated a synergistic effect of exogenous application of Si at 60 kg ha–1 and PGPR inoculation on baby corn under salt stress (up to a maximum of 4 dS m–1 ). |
| Year | 2022 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural Systems and Engineering (ASE) |
| Chairperson(s) | Datta, Avishek; |
| Examination Committee(s) | Salin, Krishna R.;Tsusaka, Takuji W.; |
| Scholarship Donor(s) | National Agricultural Technology Program (NATP), Bangladesh Agricultural Research Council, Bangladesh; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2022 |