The impact of soil, year and genotypic vigour on the release of allelopathic metabolites by wheat

Abstract

Recurrent selection for increased shoot vigour produced germplasm with enhanced leaf width and leaf area. Genotypes produced in the third cycle of the recurrent selection were top-crossed with two Australian commercial wheat cultivars (Yitpi and Wyalkatchem) generating high vigour lines. Here, in replicated controlled environment experiments and over two years in the field, the effect of the breeding with early shoot vigour on root development, and the presence of secondary allelopathic metabolites and microbially transformed phytotoxic molecules as part of below-ground competitiveness, were examined. The vigour lines were assessed for early root growth and interaction with annual ryegrass, both physical and chemical, in hydroponics and field soil. Breeding lines were compared to Australian commercial cultivars, genotypes of the third cycle of the recurrent selection, the heritage cultivar Federation and triticale. Below-ground, compared to commercial cultivars, the increased vigour lines demonstrated increased competitive ability. In all the experiments, vigorous lines possessed longer total root length and root hair length. In the controlled environment, numerous secondary metabolites, some previously identified to have allelopathic effects on weeds, were detected in the roots and the rhizosphere. In the two-year field study results showed significant differences of secondary phytotoxic metabolite levels between the drier than long-term average 2019 and wetter than average 2020. Contrary to previous results, this work showed increased levels of metabolites and microbial-transformed molecules in the wetter season. However, the genetic variation for early vigour didn’t result in significant differences in the presence of allelopathic molecules.