Wheat (Triticum aestivum L.) Allelopathy and its Implications for Weed Management and Rhizosphere Ecology

Studies were carried out to evaluate the allelopathic potential of four hexaploid wheat (Triticum aestivum L.) cultivars (Millat-2011, AARI-2011, Lasani-2008 and Faisalabad2008) at different growth stages tillering (Z30), anthesis (Z60) and maturity (Z90). The objectives were to ascertain wheat allelopathic potential to suppress emergence and establishment of important grassy and broad-leaved weed species and characterize soil microbial dynamics and enzyme activities under wheat allelopathy. The overall goal was to characterize the variability in wheat allelopathic potential with respect to plant age, cultivarspecific differences, and relevance to soil functional diversity. One field experiment and four wire-house experiments were carried out at the Student Research Area, University of Agriculture, Faisalabad. Field Experiments: The soil at the experimental site belongs to the Lyallpur Soil Series (USDA classification-Aridisol-fine-silty, mixed, hyperthermic Ustalfic, Haplargid; FAO classification -Haplic Yermosols). Wheat cultivars were sown in 4 m × 10 m field plots, and were maintained either weedy or weed free. Fallow plots (without wheat) were used as a control. Trials were laid out in randomized complete block design with four replications. Data were collected on crop growth, weed density and dry biomass, soil chemical and biological properties. Herbage of wheat cultivars was collected at tillering, anthesis and maturity for biochemical analysis. Weed densities were significantly lower in plots sown with wheat than in control plots. Floristic composition of weeds varied significantly among wheat cultivars and between years. A total of seven broad leaf (swine cress, lambsquarters, blue pimpernel, field bind weed, sweet clover, fathen, fumitory and broadleaf dock), three grassy weeds (canarygrass, and bermudagrass) and one sedge (purple nutsedge) belonging to seven distinct families (Poaceae, Chenopodiaceae, Brassicaceae, Primulaceae, Cyperaceae, Fabaceae and Convolvulaceae) were identified. Summed dominance ratios of the weeds were in the order: swine cress > lambsquarters > blue pimpernel > canarygrass > field bind weed > purple nutsedge > sweet clover during 2011-12, and swine cress > blue pimpernel > lambsquarters > canarygrass > field bind weed > purple nutsedge > sweet clover during 2012-13. Summed dominance ratios changed during the growing season due mainly to variation in emergence timing of different weeds; sweet clover emerged at 60 days after sowing (DAS) and broadleaf dock at 75 DAS during 2011-12. Sweet clover and broadleaf dock were identified at 45 and 60 DAS during 2012-13, although during 2011-12, these weeds were absent at these times. Total weed dry biomass at 45 DAS ranged from 0.81-1.39 g m -2 during 2011-12 and 0.45-0.83 g m -2 during 2012-13 in plots sown with wheat compared to 13.02 g m -2 and 2.78 g m -2 in fallow plots, for respective years. At 105 DAS, total weed dry biomass was significantly lower (4.96-14.13 g m -2 and 5.02-6.11 g m -2 ) in wheat-sown plots than fallow plots (109.38 and 183.24 g m -2 ) during 2011-12 and 2012-13, respectively. HPLC profile of allelochemicals revealed that wheat herbage contained eight compounds: gallic acid, p-hydroxybenzoic acid, syringic acid, ferulic acid, vanillic acid, protocatechuic acid, p-coumaric acid and benzoic acid. Concentrations of these allelochemicals varied among wheat cultivars and with stage of growth. Concentration of total allelochemicals in