Seed priming with growth regulators modulates production, physiology and antioxidant defense of Indian squash (Praecitrullus fistulosus) under semi-arid conditions.

Indian squash (Praecitrullus fistulosus) crop faces heat and drought during its growth that is considered the most important abiotic stress in semi-arid areas. Seed priming with growth regulators enhances stress tolerance; hence, mitigates the adverse effects of unpredictable stresses due to adverse weather conditions. This two-year (2019 and 2020) study was conducted to infer the role of seed priming in improving heat tolerance of Indian squash (cultivar Sahavi) through improvement in physiological and antioxidant defense systems. Six treatments that included no priming (control), hydropriming, priming with indole acetic acid (IAA) at 100 mg L-1, salicylic acid (SA) at 50 mg L-1, ascorbic acid (AA) at 100 mg L-1 and thiourea at 500 mg L-1 each for 06 hours) were included in the study. Results revealed that priming with AA and SA significantly (P ≤ 0.05) enhanced germination (39 and 47%), germination index (57 and 58%), plant height (23 and 22%), vine length (15 and 14%), number of fruits per plant (62%), fruit weight per plant (66 and 67%), economic yield (32%), photosynthesis rate (18 and 17%), protein content (10%), proline (23%), glycine betaine (3%), malondialdehyde content (11 and 10%) and catalase activity (24%) compared to control treatment. Furthermore, seed priming with AA and SA significantly (P ≤ 0.05) shortened the mean germination time (25 and 28%) compared to the control. The results indicated that AA and SA had significant potential to mitigate adverse effects of heat stress in Indian squash. Findings from this study showed that seed priming with AA and SA promoted heat-stress tolerance and enhanced growth and productivity of Indian squash.

The impact of aqueous and N-hexane extracts of three Fabaceae species on seed germination and seedling growth of some broadleaved weed species.

Weed infestation is a persistent problem for centuries and continues to be major yield reducing issue in modern agriculture. Chemical weed control through herbicides results in numerous ecological, environmental, and health-related issues. Moreover, numerous herbicides have evolved resistance against available herbicides. Plant extracts are regarded as an alternative to herbicides and a good weed management option. The use of plant extracts is environmentally safe and could solve the problem of herbicide resistance. Therefore, laboratory and wire house experiments were conducted to evaluate the phytotoxic potential of three Fabaceae species, i.e., Cassia occidentalis L. (Coffee senna), Sesbania sesban (L.) Merr. (Common sesban) and Melilotus alba Medik. (White sweetclover) against seed germination and seedling growth of some broadleaved weed species. Firstly, N-hexane and aqueous extracts of these species were assessed for their phytotoxic effect against lettuce (Lactuca sativa L.). The extracts found more potent were further tested against germination and seedling growth of four broadleaved weed species, i.e., Parthenium hysterophorus L. (Santa-Maria), Trianthema portulacastrum L. (Pigweed), Melilotus indica L (Indian sweetclover). and Rumex dentatus L. (Toothed dock) in Petri dish and pot experiments. Aqueous extracts of all species were more toxic than their N-hexane forms for seed germination and seedling growth of lettuce; therefore, aqueous extracts were assessed for their phytotoxic potential against four broadleaved weed species. Aqueous extracts of all species proved phytotoxic against T. portulacastrum, P. hysterophorus, M. indica and R. dentatus and retarder their germination by 57, 90, 100 and 58%, respectively. Nevertheless, foliar spray of C. occidentalis extract was the most effective against T. portulacastrum as it reduced its dry biomass by 72%, while M. alba was effective against P. hysterophorus, R. dentatus and M. indica and reduced their dry biomass by 55, 68 and 81%, respectively. It is concluded that aqueous extracts of M. alba, S. sesban and C. occidentalis could be used to retard seed germination of T. portulacastrum, P. hysterophorus, M. indica and R. dentatus. Similarly, aqueous extracts of C. occidentalis can be used to suppress dry biomass of T. portulacastrum, and those of M. alba against P. hysterophorus, R. dentatus. However, use of these extracts needs their thorough testing under field conditions.

Photosynthesis research under climate change.

Increasing global population and climate change uncertainties have compelled increased photosynthetic efficiency and yields to ensure food security over the coming decades. Potentially, genetic manipulation and minimization of carbon or energy losses can be ideal to boost photosynthetic efficiency or crop productivity. Despite significant efforts, limited success has been achieved. There is a need for thorough improvement in key photosynthetic limiting factors, such as stomatal conductance, mesophyll conductance, biochemical capacity combined with Rubisco, the Calvin-Benson cycle, thylakoid membrane electron transport, nonphotochemical quenching, and carbon metabolism or fixation pathways. In addition, the mechanistic basis for the enhancement in photosynthetic adaptation to environmental variables such as light intensity, temperature and elevated CO2 requires further investigation. This review sheds light on strategies to improve plant photosynthesis by targeting these intrinsic photosynthetic limitations and external environmental factors.

Drought Tolerance of Soybean (Glycine max L. Merr.) by Improved Photosynthetic Characteristics and an Efficient Antioxidant Enzyme Activities Under a Split-Root System.

Water deficiency significantly affects photosynthetic characteristics. However, there is little information about variations in antioxidant enzyme activities and photosynthetic characteristics of soybean under imbalanced water deficit conditions (WDC). We therefore investigated the changes in photosynthetic and chlorophyll fluorescence characteristics, total soluble protein, Rubisco activity (RA), and enzymatic activities of two soybean varieties subjected to four different types of imbalanced WDC under a split-root system. The results indicated that the response of both cultivars was significant for all the measured parameters and the degree of response differed between cultivars under imbalanced WDC. The maximum values of enzymatic activities (SOD, CAT, GR, APX, and POD), chlorophyll fluorescence (Fv/Fm, qP, ɸPSII, and ETR), proline, RA, and total soluble protein were obtained with a drought-tolerant cultivar (ND-12). Among imbalanced WDC, the enhanced net photosynthesis, transpiration, and stomatal conductance rates in T2 allowed the production of higher total soluble protein after 5 days of stress, which compensated for the negative effects of imbalanced WDC. Treatment T4 exhibited greater potential for proline accumulation than treatment T1 at 0, 1, 3, and 5 days after treatment, thus showing the severity of the water stress conditions. In addition, the chlorophyll fluorescence values of FvFm, ɸPSII, qP, and ETR decreased as the imbalanced WDC increased, with lower values noted under treatment T4. Soybean plants grown in imbalanced WDC (T2, T3, and T4) exhibited signs of oxidative stress such as decreased chlorophyll content. Nevertheless, soybean plants developed their antioxidative defense-mechanisms, including the accelerated activities of these enzymes. Comparatively, the leaves of soybean plants in T2 displayed lower antioxidative enzymes activities than the leaves of T4 plants showing that soybean plants experienced less WDC in T2 compared to in T4. We therefore suggest that appropriate soybean cultivars and T2 treatments could mitigate abiotic stresses under imbalanced WDC, especially in intercropping.

Changes in morphology, chlorophyll fluorescence performance and Rubisco activity of soybean in response to foliar application of ionic titanium under normal light and shade environment.

Titanium (Ti) is considered an essential element for plant growth; however, its role in crop performance through stimulating the activities of certain enzymes, enhancing chlorophyll content and photosynthesis, and improving crop morphology and growth requires more study. We therefore conducted a laboratory experiments to study the effects of ionic Ti application on morphology, growth, biomass distribution, chlorophyll fluorescence performance and Rubisco activity of soybean (Glycine max L.) under normal light (NL) and shade conditions (SC). In this study, we sprayed soybean plants with five different levels of ionic Ti (T1 = 0, T2 = 1.25, T3 = 2.5, T4 = 5 and T5 = 10 mg Ti Plant-1) through foliar application method. Our results show that with increasing moderate (2.5 mg Ti Plant-1) Ti concentration, the chlorophyll pigments (chlorophyll [Chl] a, b, carotenoid [Car]), plant biomass, photochemical efficiency of photosystem II (Fv/Fm), and electron transport rate (ETR) of soybean increased, but higher levels (5-10 mg Ti Plant-1), resulted in leaf anatomical and chloroplast structural disruptions under both NL and SC. Soybean plants showed maximum biomass, leaf area, leaf thickness, Chl a, b, Car, Rubisco activity, Fv/Fm and ETR for T3 at 2.5 mg Ti Plant-1; however, declined significantly for T5 at high concentration of 10 mg Plant-1. In NL, the application of 2.5 mg Ti Plant-1 (T3) increased the Chl a, b, and total Chl contents 40, 20, and 27% as compared to control treatment (T1). In SC, the application of 1.25 mg Ti mg Plant-1 (T2) increased the Chl a, b, and total Chl contents 38, 19, and 14% as compared to control treatment. In NL, the Fv/Fm, qP, PSII, and ETR were higher in the T3 treatment over the T1 (control) by 7, 0.3, 16, and 16%, respectively. In SC, the Fv/Fm, qP, PSII, and ETR were higher in the T3 treatment over the T1 (control) by 5, 5, 19, and 19%, respectively. Moreover, Rubisco activity was at peak (55 and 6% increase under NL and SC) at 2.5 mg Ti Plant-1and decreased with increasing Ti concentration, reaching the lowest at 10 mg Ti Plant-1, which indicates that leaf cells were damaged as observed in the leaf anatomy. We concluded that ionic Ti expresses a hormesis effect: at lower concentrations, promoting soybean growth, however, at higher concentrations, suppressing soybean growth both under NL and SC. We therefore suggest that under different light stress conditions, Ti application could serve to mitigate abiotic stresses, especially in intercropping systems.

Tree species as a potential source of bio-herbicides for controlling Parthenium hysterophorus L.

To assess the herbicidal potential of Eugenia jambolana Lam., Ricinus communis L., Ziziphus jujuba L. and Ziziphus mauritiana L. against noxious weed Parthenium hysterophorus L., germination bioassay using their 1%, 2%, 3%, 4% and 5% (w/v) and seedling growth bioassay using their 5% (w/v) (on dry weight basis) aqueous leaf extracts (ALE) were conducted. ALE of R. communis showed maximum reductions in germination percentage (79%), germination index (89%) and seedling biomass (88%) as well as maximum delays in mean germination time (211%) and time to 50% germination (265%) of parthenium whereas maximum reductions in its seedling length (47%) and seedling vigour index (97%) were shown by Z. mauritiana. Reciprocal dose-response relationship by probit regression analysis revealed that LC50 values of R. communis and Z. mauritiana are 1.04% and 1.44%, respectively. Therefore, R. communis and Z. mauritiana are potential sources of bio-herbicides against this weed.