Effect of foliar application of chitosan and humic acid on yield and yield components of bread wheat under end-season drought stress

Drought is considered one of the most important factors limiting crop performance worldwide. Consumption of humic acid on plants, in addition to soil fertility, increases plant tolerance to drought and soil water holding capacity. Chitosan is also a natural biopolymer modified from chitin and non-toxic, biodegradable, and environmentally friendly substances that acts as a potential stimulant in agriculture. Chitosan and humic acid reduce the negative effects of abiotic stresses. Accordingly, due to the drought crisis in arid and semi-arid regions, in this study, the modulating effect of humic acid and chitosan foliar application on wheat tolerance to drought stress at the end of the season was investigated.

This experiment was performed to study the effect of foliar application of chitosan and humic acid on improving drought tolerance of wheat genotypes in the form of split split plots based on a randomized complete block design with three replications. The main plot includes irrigation treatments at two levels (full irrigation and cessation of irrigation in spike stage), sub-plots including three wheat genotypes including Mihan, CD-93-9, and CD-93-10, and sub-plots including humic acid and chitosan foliar application levels (Zero, 2 g.L-1 of humic acid, 3 ml.L-1 of chitosan and the combination of humic acid and chitosan). The experiment was carried out on a field in Ardabil Agricultural Research Station. Sowing was done in October 2020 with a planting density of 450 seeds per square meter. Chemical fertilizer based on NPK soil test at 50, 100, and 20 kg.ha-1, respectively was added to the soil before planting. Each genotype was planted in 1.5 cm by 7 m plots. The length of each row was 7 m and the distance between the rows was 20 cm and the seeds were sown at a depth of 5 cm. STAR 2.01 statistical software was used to analyze the data including data analysis of variance and comparison of means by LSD method at a 5% probability level.

The results showed that the interaction effect of cultivar × stress × foliar application was significant in all studied traits including plant height, number of seeds per spike, number of spikes, spike length, and grain yield, except the number of tillers per plant and 1000-seed weight. Regarding the number of tillers per plant, the interaction of cultivar × foliar application was significant and for 1000-seed weight, the interaction of cultivar × stress and stress × foliar application was significant. Although there were differences in the response of wheat genotypes to the foliar application under both stress and non-stress conditions, in most traits such as number of tillers, number of seeds per spike, spike length, plant height, and 1000-seed weight, the best result was the simultaneous use of chitosan and humic acid. Was obtained. Also, both under non-stress and under stress conditions, the highest grain yield of the studied genotypes was obtained in simultaneous foliar application of chitosan and humic acid. In general, it can be concluded that the combination of chitosan and humic acid (2 g.L-1 humic acid and 3 ml.L-1 chitosan) significantly showed the best results in increasing the yield and yield components of wheat compared to the control treatment in both non-stress and the end of the season drought stress conditions.

Foliar application of humic acid and chitosan increased and improved the studied traits, both under drought stress and non-stress conditions in wheat genotypes compared to non-foliar application. The maximum number of tillers, number of seeds per spike, number of spikes, spike length, 1000-seed weight, and grain yield were obtained by foliar application of chitosan and humic acid under both full irrigation and stress conditions. Therefore, it is recommended to use simultaneous spraying of chitosan and humic acid to increase tolerance and achieve higher performance. Also, the study of different concentrations of these two substances in combination with each other and at different stages of wheat growth can determine the best dose and time of their consumption in this strategic crop, which is recommended to conduct studies in this regard.