Effect of water stress on the boron response of wheat genotypes under low boron field conditions

Sterility has emerged as a widespread problem for wheat (Triticum aestivum) production in South and South-east Asia. Whilst boron (B) deficiency is commonly associated with sterility in wheat, the expression of sterility is complicated in rainfed conditions by a number of environmental factors including water stress. A field experiment was conducted to examine the effect of water stress on B response of wheat genotypes on a low B soil (0.087 mg B kg-1soil) at Chiang Mai, Thailand (18°45 N, 99° E) during the dry season from November to March. The experiment consisted of three factors arranged in a split-split plot design with two levels of irrigation: water stress (I–) and full irrigation (I+) in main plots, two levels of B: 0 kg (B0) and 1 kg B ha-1 (B+) as borax in sub plots and four wheat genotypes: SW 41, BL 1022, UP 262 and Sonora 64 in sub–sub plots. Water stress was applied by discontinuing irrigation in I– treatments after the double ridge stage. In all genotypes, above ground biomass was decreased by I–, but not by B deficiency. Significant B×genotype interactions were detected for reproductive growth. SW 41 and BL 1022 strongly responded to added B with relief from B deficiency symptoms at anthesis and improved grain set index (GSI), grains ear-1, ears with grain and grain yield at maturity. By contrast, Sonora 64 could set grain well at B0 and did not show any response to added B with respect to these parameters. Grains ear-1 of SW 41 and BL 1022 was not affected by full irrigation at B0, but were significantly increased when fully irrigated with added B. In all genotypes, B concentration of the flag leaf and the ear at booting and at anthesis was significantly higher in B+, but was not affected by irrigation. Boron × irrigation interactions detected in this study indicate the possibility of the influence of water stress on the severity of wheat sterility in South and South-east Asia.     

An effect of shade on the boron requirement for leaf blade elongation in black gram (Vigna mungo L. Hepper)

The present experiment was undertaken to examine whether shading affects the critical boron (B) concentration for leaf blade elongation in black gram. Six days after germination (D6), black gram seedlings were transferred to 8 pairs of pots containing basal nutrient solution: one pot of each pair contained 1 M H₃BO₃ and the other 10 M H₃BO₃. On D10, one day after the emergence of the first trifoliolate leaf blade (TF₁) and one day before the emergence of TF₂, four pairs of pots were shaded, decreasing the light intensity they received in the glasshouse to about 35% of full sunlight compared with 70% received by the unshaded plants. The response to B supply of dry matter (DM) and elongation rate (LBER) of TF₂ were less pronounced in shaded than in unshaded plants. Critical B concentrations for LBER in TF₂ of black gram were 10 mg B kg^-1DM in shaded and 15 mg B unshaded plants, suggesting that shading may have decreased the B requirement for LBER. Thus the present results suggest that light may need to be considered when setting critical values for the diagnosis of B deficiency in black gram.