Boron and TIBA induced physiological and anatomical changes in relation to dry matter partitioning in spring sunflower (Helianthus annuus L.) under delayed sowing

Improper translocation of photoassimilates due to poor differentiation of vascular bundles is reported to result in poor seed set in sunflower (Helianthus annuus L.) especially under high temperature conditions. Furthermore, comprehensive studies for improving vascularisation in sunflower are lacking. Hence, investigations were conducted at the Punjab Agricultural University, Ludhiana, India during spring 2014 and 2015 to evaluate the effect of boron and TIBA on pedicel anatomy and photosynthetic parameters in relation to dry matter accumulation by sunflower. The field experiment was laid-out in split-plot design keeping three sowing dates (January 20—D1, February 10—D2 and March 2—D3) in main plots and eight foliar applications (control, water spray, boron—110, 220, 440 ppm, TIBA—100, 200, 400 ppm) in sub plots with three replications. Delay in sowing caused reduction in photosynthetic parameters and pedicel vascularisation, ultimately resulting into lower biological and seed yield. Foliar spray of boron (220 and 440 ppm) and TIBA (100, 200, 400 ppm) increased the mean length of vascular bundles by 22.9 and 35.5%, and mean width by 34.2 and 39.8% coupled with significant improvement in photosynthetic parameters, and ultimately enhanced seed yield by 13–17% over control. Furthermore, positive correlation of dry matter partitioning to seed with length (|r| = 0.89) as well as width (|r| = 0.93) of vascular bundles indicated the role of boron and TIBA in improving the seed yield via improvement of vascular differentiation. However, plant height and DM partitioning to stem showed highly significant negative correlation with DM partitioning in seed.