Differential competitive ability of morphologically diverse spring wheat genotypes

Non-Peer ReviewedSixteen genotypes of common spring wheat (T. aestivum) were grown under conditions of simulated weed competition at Saskatoon in 1991 and 1992. Weeds consisted of cultivated oat (Avena sativa cv. Waldern) and Oriental mustard (Brassica juncea cv. Cutlass) sown at two densities (48 and 96 seeds m2 per weed species), and a weed free control. Seedling establishment, % ground cover, and seed yield for all three species was recorded as was wheat tiller number, spike number, maximum height, LAI (Ieaf area index), leaf orientation, and flag leaf length and size. Significant (p =0.01) weed rate by genotype interactions involving changes in genotype rank were detected for grain yield, indicating differences in competitive ability existed among the wheat genotypes. The highest yielding genotypes under weed free conditions were not necessarily the highest yielding under weedy conditions. Yield reductions averaged over two weed densities ranged from 36 to 52 %. Genotypes which exhibited lower yield reductions also showed greater suppression of weed growth. Although competitive genotypes were generally taller than non-competitive genotypes, other traits such as tillering capacity and leaf length were important determinants of competitive ability

The need to breed crop varieties suitable for organic farming, using wheat, tomato and broccoli as examples: A review

It is estimated that more than 95% of organic production is based on crop varieties that were bred for the conventional high-input sector. Recent studies have shown that such varieties lack important traits required under organic and low-input production conditions. This is primarily due to selection in conventional breeding programmes being carried out in the background of high inorganic fertilizer and crop protection inputs. Also, some of the traits (e.g., semi-dwarf genes) that were introduced to address problems like lodging in cereals in high-input systems were shown to have negative side-effects (reduced resistance to diseases such as Septoria, lower protein content and poorer nutrient-use efficiency) on the performance of varieties under organic and low-input agronomic conditions. This review paper, using wheat, tomato and broccoli as examples, describes (1) the main traits required under low-input conditions, (2) current breeding programmes for organic, low-input agriculture, (3) currently available breeding and/or selection approaches, and (4) the benefits and potential negative side-effects of different breeding methodologies and their relative acceptability under organic farming principles. © 2010 Royal Netherlands Society for Agricultural Sciences. Published by Elsevier B.V. All rights reserved