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Summary Density:yield loss models rely on fixed coefficients, parameterized from a particular site and season to predict the impact of weeds on crop yields. However, the empiricism of this approach and failure to incorporate environmental effects, has major biological and economic implications. In this study, seasonal variability in wheat yield loss and associated economic costs from Avena spp. were quantitated. A competition experiment at Wagga Wagga, NSW, showed large seasonal differences in wheat yield loss from densities of Avena spp. across 2 years. Gross margins, simulated over a 51-year period, decreased as Avena spp. density increased and were more variable at low crop densities and higher weed densities. For example, at a density of 200 Avena spp. plants m-2 , coefficient of variation in crop gross margin (CV ) was $AUS 47 ha-1 for a crop density of 200 wheat plants m-2 compared with a CV of $AUS 75 ha-1 for a crop density of 50 wheat plants m-2 . The value of yield loss predictions will be vastly improved by making parameter values in yield loss models a function of seasonal factors such as rainfall. [ABSTRACT FROM AUTHOR]

The relative competitive advantage of 12 commercially available wheat varieties was examined against Lolium rigidum Gaud. at a number of sites from 1995 to 1997 in south-eastern Australia. Nearly all the variation in crop grain yield was attributable to the variety × environment effects (81%), with only 4% due to variety × weed × environment effects. Some varieties exhibited an environment-specific competitive advantage, for example Katunga, Dollarbird and Hartog, whereas others like Shrike, Rosella and Janz were relatively poorly competitive in some situations. The introduction of greater genetic variability into wheat is required to significantly increase competitiveness. Alternatively, manipulating crop agronomy, such as increasing crop seeding rate, may be a practical alternative. The grain yield of weed-free wheat was highly positively correlated with grain yield of the weedy plots, suggesting that local adaptation is important for strong competitiveness, and that wheat breeders in southern Australia may be inadvertently selecting for competitive advantage with weeds when selecting for other traits such as early vigour. The varieties which showed competitive yield advantage also suppressed L. rigidum. A combination of short-term agronomic manipulations and a longer-term breeding effort is needed for increasing wheat competitiveness, and the increasing importance of herbicide-resistant weeds may facilitate this process. [ABSTRACT FROM AUTHOR]

The competitive abilities of a wide range of genotypes of wheat (Triticum aestivum L.) and durum wheat (Triticum durum Desf.) against Lolium rigidum Gaud. (annual ryegrass) were examined to determine the potential for breeders to select strongly competitive varieties. Considerable potential within the wheat genome to breed varieties with greater competitive ability was demonstrated. In 1993, 250 genotypes from around the world were screened and in 1994 a subset of 45 (mainly Australian) genotypes were further examined. A uniform density of L. rigidum reduced grain yield of wheat by up to about 80% in 1993 and to 50% in 1994, depending on wheat genotype. Reduction in grain yield was correlated with L. rigidum dry matter. Wheats varied in competitive ability with source, and durum wheats were less competitive than T. aestivum. The ‘old’ standard wheat varieties (released between 1880 and 1950) suppressed the weed more than all the current varieties, with the exception of eight F1 hybrids. A doubling of the crop seeding rate of 10 of the genotypes in 1994 reduced the biomass of L. rigidum by an average of 25% compared with the standard seeding rate. Ranking of competitive ability of varieties at high density was consistent at both seeding rates. The strongly competitive genotypes had high early biomass accumulation, large numbers of tillers, and were tall with extensive leaf display. The potential for breeding enhanced competitive ability in wheat is discussed. [ABSTRACT FROM AUTHOR]

The competitive abilities of eight winter crops were compared against Lolium rigidum Gaud, (annual ryegrass), an important weed of southern Australia, as a potential strategy to suppress weeds and reduce dependence on herbicides. Two cultivars of each species were chosen to represent the range of competitive ability within each crop and grown in field experiments in 1992 and 1993. The order of decreasing competitive ability (with the ranges of percentage yield reduction from L. rigidum at 300 plants m-2 in parenthesis) was as follows: oats (Avena saliva L.), 2–14%; cereal rye (Secale cereale L.), 14–20%; and triticale (X Triticosecale), 5–24%; followed by oilseed rape, (Brassica napus L.), 9–30%; spring wheat (Triticum aestivum L.), 22–40%; spring barley (Hordeum vulgare L.), 10–55%; and, lastly, field pea (Pisum sativum L.), 100%, and lupin (Lupinus angustifolius L.), 100%. Differences in competitive ability of cultivars within each species were identified, but competition was strongly influenced by seasonal conditions. Competition for nutrients (N, P and K) and light was demonstrated. L. rigidum dry matter and seed production were negatively correlated with grain yield of the weedy crops. More competitive crops offer the potential to suppress grass weeds while maintaining acceptable grain yields. Ways of improving the competitive abilities of grain legume crops are discussed. [ABSTRACT FROM AUTHOR]

Features a study that discussed the key methodological obstacles in designing and selecting an appropriate screening bioessay and commonly used screening bioessays for assessing allelopathic potential in crop germplasm. Information on the allelopathy process; Review of achievements in the genetic control of allelopathy and in the development of allelopathic varieties for weed management; Use of laboratory bioassay to investigate the possible involvement of allelopathy.

Presents a study to understand the genetic control of crop alleopathic activity. Genes which might be involved in regulating the production and exudation of allelochemicals; Use of plant biotechnology to help reveal the genetics of this trait; Use of the genes for weed suppression and management.

Solanum elaeagnifolium is a weed of national significance in Australia. However, the genetic diversity of S. elaeagnifolium is poorly understood. Four amplified fragment length polymorphism primer combinations were utilised to investigate the genetic variation and structure of 187 S. elaeagnifolium individuals collected from 94 locations in Australia. High genetic diversity was found, with an average Jaccard's genetic similarity at 0.26. Individuals were assigned to two genetic clusters or considered as admixed according to their membership coefficient value ( q) calculated by Bayesian model-based genetic structure analysis. This suggested that Australian S. elaeagnifolium may have originated from two distinct gene pools. These results were further supported by principal co-ordinates analysis. Large spatial groups of individuals assigning to these two gene pools were found in western Victoria and south-western New South Wales ( NSW) and northern NSW, which correlated well with the early records of S. elaeagnifolium in both regions. The high genetic diversity found here could add difficulties to effective control of S. elaeagnifolium across regions. [ABSTRACT FROM AUTHOR]

Solanum elaeagnifolium (silverleaf nightshade) is an invasive perennial weed in Australia, with aerial growth commencing in spring from either the perennial root system or the soil seedbank, with senescence occurring in autumn. A total of 642 S. elaeagnifolium individuals were collected at flowering from 92 locations in south-eastern Australia to study morphological variation and its implications for management. Large morphological variation was found between individuals from different locations. Leaf length, width and area ranged from 1.44 to 10.6 cm, 0.39 to 4.09 cm and 0.41 to 25.8 cm2 respectively. Plants from higher rainfall regions were significantly taller and had larger leaves, suggesting a possible correlation between rainfall and morphology. Scanning electron microscopy comparison of leaf surfaces showed lower trichome and stomatal densities on the adaxial surface (67.0 ± 3.3 trichomes mm−2 and 603.4 ± 29.2 stomata mm−2 respectively) than on the abaxial surface (131.9 ± 7.2 trichomes mm−2 and 813.7 ± 30.5 stomata mm−2 respectively). The morphological plasticity of S. elaeagnifolium highlighted in this study could probably contribute to its adaptability and partly explain its establishment and continuing expansion in Australia. [ABSTRACT FROM AUTHOR]

Z hu XC , W u HW , R aman H , L emerle D , S tanton R & B urrows GE (2012). Evaluation of simple sequence repeat (SSR) markers from Solanum crop species for Solanum elaeagnifolium. Weed Research 52, 217-223. Summary Molecular markers specific for Solanum elaeagnifolium (silverleaf nightshade) are currently not available. A total of 35 simple sequence repeat (SSR) primer pairs from potato ( Solanum tuberosum), tomato ( S. lycopersicum) and eggplant ( S. melongena) were tested for cross-species transferability in S. elaeagnifolium. Among them, 13 primer pairs successfully produced alleles (bands). The polymorphism information content ranged from 0 to 0.84. The transferable rate of SSR from potato, tomato and eggplant to S. elaeagnifolium was 20%, 40% and 46% respectively. SSR analysis revealed high level of genetic diversity among 40 individuals collected within a paddock. Highly polymorphic and transferable cross-species SSR markers would be useful for determining the extent of genetic diversity in S. elaeagnifolium populations. [ABSTRACT FROM AUTHOR]