چكيده لاتين :
Introduction: Drought stress is one of the most important limiting factors for plant growth in the arid and semi-arid regions. This stress affecting crop production such as maize (Zea mays L.). Maize can play an important role in providing forage for silage animals, especially in the winter season in most parts of Iran due to high production capability . The application of plant growth regulators such as jasmonic acid and humic acid is one of the fastest ways to increase crop tolerance to environmental stresses viz. drought stress. The role of these acids is to prevent aging and falling of leaves, hormonal effects and improve nutrient uptake, which leads to increase of root and shoot biomass. Due to the expansion of industrial livestock, maize silage supply is essential. On the other hand, maize pollination and grain filling occur in the summer season and it overlaps with the peak of water limitation. Thus, in this experiment, the effect of jasmonic acid and humic acid on morpho-physiological characteristics and water use efficiency of forage maize under drought stress were studied.
Materials and Methods: In order to investigate the effects of jasmonic acid and humic acid to mitigate the impact of drought stress during pollination of forage maize (KSC 704), an experiment was conducted in research farm of the Shahrekord University, in 2016. The experiment was performed as a split plot in a randomized complete block design with three replicates. The treatments consisted of different levels of drought stress (no drought stress (field capacity), moderate drought stress (0.75 field capacity) and severe stress (0.50 field capacity)) as main plots and plant growth regulators (without hormone, jasmonic acid and humic acid) as sub plots. In no hormone condition, distilled water was used. Foliar application was done 10 mM jasmonic acid and humic acid content of 1500 grams per hectare before maize flowering. The volume of water consumed for each irrigation was measured by contour system. In this experiment leaf relative water content (RWC), proline, chlorophyll content, carotenoids, leaf area index (LAI), leaf weight, stem weight, ear weight, forage yield and water use efficiency (WUE) were measured. The analysis of data was performed using SAS software. Mean comparisons of study characteristics were done by LSD test at the 5% probability level.
Results and Discussion: The results showed that the relative water content, proline, chlorophyll, carotenoids, leaf area index, shoot weight, ear weight, forage yield and water use efficiency were affected by drought stress conditions. Although drought stress was reduced forage yield and related traits, the use of jasmonic acid compared to the control and humic acid under mild stress was significantly increased relative water content (61.1 and 39.3 %, respectively), leaf weight (60.4 and 41.8%, respectively), stem (14.8 and 25.12%, respectively), ear weight (13 and 23.8%, respectively), proline content (16 and 32.1 %, respectively), forage yield (24.4 and 24.2%, respectively). Under severe stress conditions, jasmonic acid significantly increased relative water content of leaf, weight of leaf, weight of stem and leaf area index. Under severe drought stress, jasmonic acid and humic acid had no significant difference. It was observed that under non-stress conditions, jasmonic acid wasn’t effective on water use efficiency and humic acid showed a negative effect. Under moderate drought stress, jasmonic acid was effective with increase 21.15 %, in moderating drought stress for maize and under severe stress jasmonic acid and humic acid had no significant effect.
Conclusion: According to the results, the occurrence of drought stress during pollination has a significant effect on maize yield. So that the severe drought stress (50% soil moisture depletion) leads to decrease in yield of maize forage due to decrease weight of leaf and ear. Although the most positive results of the use of growth regulators on maize yield were obtained under non-stress (full irrigation), the effect of moderate drought stress was mainly observed on forage production on jasmonic acid. The positive effect of foliar application of jasmonic acid in reducing the damage of drought stress and increasing of water use efficiency under moderate drought stress indicated that the use of this hormone could be useful in increasing production and quality of maize silage.
