Impact of Humic Acid on Leaf Carbohydrate Metabolism in Timely and Late Sown Varieties of Wheat (Triticum aestivum L.)

The present study investigated wheat varieties i.e., PBW 725 (timely sown) and PBW 752 (late sown) were sown in randomised block design in PVC cylinders and field conditions at PAU and Bathinda Punjab India. Foliar application of two concentration of humic acid (2 and 4 ppm) was done ten days prior to tillering, booting and flowering stage. The treatment without any spray served as control. At all stages morpho-physiological and biochemical parameters were recorded whereas yield and yield attributes were recorded at maturity. The present study found that foliar spray of 2 and 4 ppm humic acid significantly increased plant height in flowering and grain filling stages. The booting stage exhibited the maximum dry weight (0.089 g) in PBW 752 at 4 ppm dosage. The 4 ppm foliar spray significantly increased the relative growth rate of PBW 725 (15%) at Bathinda. Humic acid reduced membrane damage in PBW 725 and PBW 752 plants at Bathinda, and increased cellular viability (72%) with 4 ppm foliar spray. The chlorophyll a (25.84 µg/g FW), chlorophyll b (10.96 µg/g FW), carotenoids (10.46 µg/g FW), total chlorophyll content (33.5 µg/g FW) along with leaf relative water content (99%) spiked after 4 ppm foliar spray of humic acid. The flowering stage showed an unprecedented value of total soluble sugars for PBW 725 (23.6%) on 4 ppm treatment of humic acid. The study found that starch content (12.9%) increased significantly PBW 752 at Bathinda after 4 ppm of foliar spray of humic acid. The highest α-amylase activity (133.1 nmol of glucose formed 1/min g FW) was observed in PBW 752 at booting stage after 4 ppm of foliar spray of humic acid. On the other hand, foliar spray of humic acid did not depict any significant effect on yield components. Thus, α-amylase activity was augmented by 4 ppm of humic acid at booting stage, which improved the levels of photosynthates, which in turn improved yield attributes.