Watanachai Lontom

Screening for salt-tolerance plants has been carried out to enhance yield production. Consequently, the physiological and growth parameters were performed. These methods are labor-intensive and destructive. Nowadays, non-destructive thermography has been used for detecting infrared radiation under water stress. However, monitoring progressive leaf temperature under salt stress conditions has rarely been reported in rice (Oryza sativa L.) This study aims to monitor salt stress response in ‘Pokkali’ rice seedlings using infrared radiation (IR) thermography together with physiological and growth parameters. Twenty-six-day-old ‘Pokkali’ rice seedlings, standard salt tolerant, were subjected to 80, 120, and 160 mM NaCl for 8 d under hydroponic conditions. Our study found that NaCl condition influences the emission of infrared radiation and the elevation in leaf temperature. Notably, seedlings exposed to 160 mM NaCl after 8 d exhibited significantly higher temperature changes (5.21 °C), and higher crop water stress index (CWSI). Likewise, we observed lower reductions in transpiration rate (88.19%), stomatal conductance (92.78%), and photosynthetic rate (70.99%). Together, the correlation matrix revealed a strong relationship between CWSI and leaf gas exchange parameters, including photosynthetic rate, transpiration rate, and stomatal conductance. Additionally, IR-thermal indices and some physiological parameters contributed to the segregation between control and salt stress groups. Therefore, the simple thermal imaging technique can effectively monitor salt stress responses at various NaCl concentrations in the ‘Pokkali’ rice. The application of IR-thermography will be applied to various abiotic stressors and different rice cultivars in the future.

In the current study, the influence of silicon (Si) on KDML 105 rice plants exposed to drought and salt stress was observed. The 28-days old rice plants were arranged into control, drought, and salinity conditions. The drought and salinity conditions were achieved by addition of 20% W/W polyethylene glycol 6000 and 120 mM NaCl to the nutrient solution, respectively. Si was concurrently applied in all groups by adding 0, 1.5, 2.0, and 2.5 mM Na2SiO3. The results showed that some growth and physiological parameters were positively changed by the Si-application. The relative water content was significantly improved in the 1.5 mM Si-supplemented drought group and the 2.0 mM Si-supplemented salt group. Additionally, Si at 2.0 mM significantly improved photosynthetic activity in the rice and slightly reduced plant temperature under salt stress. Moreover, exogenous Si ameliorated NaCl toxicity from the sodium-potassium ratio decline. The results suggested that 2.0 mM silicon was a proper concentration to recover plants exposed to abiotic stress.

Photosynthetic performance and biomass at different growth stages of the salt-sensitive KDML105 rice cultivar, three improved lines (RD73, CSSL8-94, and TSKC1-144), and the salt-tolerant standard genotype (Pokkali) were investigated under non-saline, semi-saline, and the heavy-saline field conditions in the northeast of Thailand. In the non-saline field, net photosynthesis rates (P_n) of all genotypes remained high from the early vegetative stage to the milky stage and then dramatically reduced at maturity. In contrast, in both saline fields, P_n was the highest at the early vegetative stage and continuously declining until maturity. Leaf chlorophyll content remained high from the early vegetative to milky stage then reduced at maturity for all three field conditions. During the reproductive phase, P_n of KDML105 and the improved lines were reduced by 4–17% in the heavy-saline field, while that of Pokkali was increased (11–19% increase over that of the non-saline). Pokkali also showed a prominent increase in water use efficiency (WUE) under salinity. Nevertheless, rice leaves under saline conditions maintained the PSII integrity, as indicated by the pre-dawn values of maximum quantum yield of PSII photochemistry (F_v/F_m) of higher than 0.8. Pokkali under the semi-saline and the heavy-saline conditions exhibited 51% and 27% increases in final biomass, and 64% and 42% increases in filled grain weight plant⁻¹, respectively. In the semi-saline condition, RD73, TSKC1-144, CSSL8-94, and KDML105 showed moderate salt tolerance by displaying 24%, 18.6%, 15%, and 11.3% increases in final biomass, and 24%, 4%, 13%, and 6% increases in filled grain weight plant⁻¹, respectively. In contrast, in the heavy-saline field, final biomass of RD73, KDML105, CSSL8-94, and TSKC1-144 showed 48%, 45%, 38%, and 36% reductions from that in the non-saline field, while the filled grain weight plant⁻¹ were reduced by 45%, 58%, 35%, and 32%, respectively. This indicated that the improved lines carrying drought- and/or salt-tolerance genes achieved an increased salt tolerance level than the parental elite cultivar, KDML105.

Drought is one of the important problems that drastically affect sugarcane production in several countries. The objective of this research was to investigate the effects of early drought stress on physiological parameters and agronomic traits of six sugarcane genotypes under field conditions. The experiment was arranged in a split plot in a completely randomized block design with three replications. The main plot was represented by three different water regimes: field capacity (FC), ½FC and rain-fed (RF), whereas the subplot consisted of six sugarcane genotypes: KK3 (drought tolerant), Q117 (drought tolerant), LK92-11 (drought susceptible), Ths98-271 (S. spontaneum), KK08-214 (the F1 hybrid derived from S. spontaneum × S. officinarum) and E08-4-019 (the F1 hybrid derived from Erianthus sp. × S. officinarum). The six sugarcane genotypes were subjected to three irrigation treatments. The 45-day-old plants of all sugarcane genotypes were exposed to drought by withholding water for 72 days. Certain photosynthetic parameters were measured in the leaves of four-month-old plants. Certain cane yield parameters were measured in the 12-month-old plants. The results showed that early drought stress decreased the maximum quantum yield of PSII efficiency, net photosynthetic rate, transpiration rate and stomatal conductance. Drought stress significantly (p ≤ 0.01) decreased cane yield. The cane yield and sugar yield of KK3 were significantly (p ≤ 0.01) higher than those of the other genotypes. The wild-type sugarcane and the F1 hybrids derived from the wild and commercial sugarcane could maintain better photosynthetic performance while encountering early drought stress.