Improving drought tolerance in okra by exogenous application of biofertilizer, plant growth regulator, and miniral nutrient | |
| Author | Sainam Udpuay |
| Call Number | AIT Diss no.AS-24-01 |
| Subject(s) | Plants--Drought tolerance Vesicular-arbuscular mycorrhizas Mycorrhizal fungi Silicon |
| 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 |
| Series Statement | Dissertation ; no. AS-24-01 |
| Abstract | Water scarcity is increasing over time adversely affecting plant growth and crop productivity. Okra [Abelmoschus esculentus (L.) Moench], an annual vegetable crop belonging to Malvaceae family, is valued as a nutritious vegetable and oil crop used in the paper, oil, culinary, and pharmaceutical industries. It is commercially grown in many parts of the world, such as South and Southeast Asia, including Thailand. However, drought stress can have a negative impact on the growth of okra plants, hindering seed germination and affecting the plant’s physiological and biochemical functions. Water shortage can cause damage to the cell membrane, reduce water content in the plant, and decrease the photosynthesis rate. Lower pod yield and dry matter partitioning of drought-exposed okra plants have been reported due to poor assimilate transport, membrane damage, and biochemical alteration. To address the problem of water scarcity, a shift in perspective from optimizing production per unit area to maximizing production per unit of water consumption (increase in water use efficiency) is needed. In the first greenhouse experiment, 17 of the most popular okra genotypes were evaluated for their drought tolerance ability where plants were subjected to two water regimes of well-watered (WW) and water-deficit (WD; withholding irrigation for 10 days) at the vegetative stage. A significant variation among genotypes was observed in terms of growth and physio-biochemical response (15–70% reduction in shoot dry matter at WD compared with WW for different genotypes, 45% average reduction in membrane stability index for all genotypes, 62–89% reduction in net photosynthetic rate at WD compared with WW for different genotypes, and 7–146% increase in crop water stress index at WD compared with WW for different genotypes). Based on Ward’s multivariate cluster analyses of growth and physio-biochemical traits, the tested genotypes were classified into drought tolerant, moderately drought tolerant, and drought sensitive ones. Among the 17 tested genotypes, five genotypes (Four Compass 443, Green Nam Tao, Dark Green Okra No.5, Maejo 70, and Jusco) were found drought tolerant, six genotypes (Dow Morakot, King Star, Queen Star, Hisao, Bhalsar, and Maejo 49) were found moderately drought tolerant, while the remaining six genotypes (Best Green 5, TVRC 064, River Green No.1, Taratip, Lucky Five 473, and Chia Tai) were found drought sensitive. This study provides a base for okra growers to select the most feasible genotype for their areas based on the condition of irrigation water availability. The findings will also serve as firsthand information for the plant breeders to screen the newly-released genotypes for their drought tolerance ability. In the second polyhouse experiment, a factorial pot experiment, consisting of eight biofertilizer treatments applied as a soil drench (autoclaved inoculum [control], and inoculation with arbuscular mycorrhizal fungi [AMF], phosphate-solubilizing fungi [PSF], plant growth-promoting rhizobacteria [PGPR], AMF + PSF, AMF + PGPR, PGPR + PSF, and AMF + PSF + PGPR) and three soil moisture regimes (50%, 75%, and 100% field capacity [FC]), was carried out. The results indicated that decreasing soil moisture level severely affected growth and fruit yield of okra. The application of microbial biofertilizer effectively enhanced growth, fruit yield, and physio-biochemical traits of okra under different soil moisture levels. Among the selected biofertilizer treatments, co-inoculation of AMF and PGPR exhibited promising results in improving growth and productivity of the okra plants at 75% and 100% FC. Co-inoculation of AMF and PGPR significantly increased shoot dry matter (51%), root dry matter (73%), fruit yield (113%), and irrigation water productivity (122%) of okra compared with the non-inoculated plants across soil moisture levels. In addition, a significant reduction in accumulation of free proline (31%) compared with the non-inoculated plants was observed for the same biofertilizer combination. It is recommended to apply AMF and PGPR in combination to improve okra yield and water productivity under drought stress.In the third polyhouse experiment, a factorial experiment arranged under completely randomized design with three factors consisting of soil incorporation of two soluble silicon (Si) doses (0 and 60 kg ha–1 ) applied in the form of monosilicic acid, foliar spray of four types of plant growth regulators (PGRs) (control, 6-benzyladenine [BA] at 100 mg L–1 , naphthalene acetic acid [NAA] at 40 mg L–1 , and salicylic acid [SA] at 2 mM), and three soil moisture levels (50%, 75%, and 100% FC) was conducted. Results revealed that reducing soil moisture level to 50% FC from 100% FC caused up to 60%, 77%, 61%, 44%, and 87% reduction in leaf area, root dry matter, fruit yield, irrigation water productivity, and net photosynthetic rate, respectively. Exogenous application of Si at 60 kg ha–1 outperformed the control plants at all soil moisture levels by increasing shoot dry matter up to 33% and stomatal conductance up to 125%, along with a significant increase in fruit yield, irrigation water productivity, and other evaluated physiological traits. Among the PGRs applied in this study, SA was comparatively better than others resulting in 33–119%, 10–41%, and 17–19% increase in fruit yield, irrigation water productivity, and net photosynthetic rate compared with the control plants across soil moisture levels and Si doses. The combined application of Si and SA was even more effective than their individual application. Among the PGRs, plants grown with SA had the highest performance and resulted in an increase of 33–119% and 10– 41% in fruit yield and irrigation water productivity, respectively, across Si doses and soil moisture levels. The tolerance of okra plants to drought stress can be further improved by a combined exogenous application of Si (60 kg ha–1 ) as a soil amendment and SA (2 mM) as a foliar spray, and are thus recommended for okra cultivation under water-scarce conditions. |
| Year | 2024 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AS-24-01 |
| 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) | Anal, Anil Kumar;Zulfiqar, Farhad; |
| Scholarship Donor(s) | AIT Scholarships;Ministry of Agriculture and Cooperatives (MOAC), Thailand; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2024 |