Factors affecting the competitive ability of triticale (× Triticosecale Wittm. ex A. Camus.) against annual ryegrass (Lolium rigidum Gaudin)

Abstract

<p>Triticale (× <i>Triticosecale</i> Wittm. ex A. Camus.) is a relatively new human-made crop. It is used for both grain harvesting and grazing and is an important contributor to world food security for human beings and livestock. Triticale is ranked as the world’s third most tolerant crop to environmental stresses after rye (<i>Secale cereale </i>L.) and canola (<i>Brassica napus</i> L.) followed by barley (<i>Hordeum</i> vulgare L.) and wheat (<i>Triticum aestivum</i> L.). While wheat suffers significant yield losses worldwide due to many causes, including weed competition, it is thought that triticale may potentially be used as an alternative competitive cereal to help with weed management in wheat-based farming systems.</p> <p>Weed infestation, including annual ryegrass (<i>Lolium rigidum</i> Gaudin), is one of the major problems in cereal cropping systems. It can cause up to 50% yield losses due to competition with crops, particularly wheat. Although herbicides are commonly effective in controlling many weeds in cereal cropping, the issue of herbicide resistance is an increasing concern around the world, especially for ryegrass. Globally, ryegrass is one of at least 42 weed species that have evolved resistance to more than one mode of action of herbicides. Therefore, weed scientists and grain growers are exploring alternative weed management strategies using cultural practices to minimise the reliance on herbicides for weed control. One of these agronomic practices is the selection of competitive cultivars while other factors such as seed rates, row spacing, seed size and manipulating nutrient and soil moisture regimes are also potentially useful. Crop competitive ability has been studied for cereal crops including wheat, barley and rye, but little work has been done on triticale cultivars.</p> <p>This research aimed to identify varietal differences in competitiveness of several triticale cultivars in comparison with two commercial wheat cultivars. It also aimed to examine management factors that can be manipulated to increase the competitive ability of triticale cultivars against weeds, with a focus on annual ryegrass. Several glasshouse experiments as well as a field trial were carried out at the University of New England, Armidale, New South Wales, Australia. In the first experiment, 17 triticale lines and two wheat cultivars were examined to characterise their early growth characteristics. Of those, eight triticale and two wheat cultivars were selected to examine their competitive ability with annual ryegrass in a follow up experiment based on the range of the varietal differences in the first experiment. From those experiments, cultivars with low and high competitiveness were selected for subsequent experiments evaluating the effects of other factors on their competitive ability with ryegrass. Four triticale cultivars and one wheat cultivar (all short season) were used to assess crop: weed plant proportion, sowing rate, row spacing, crop seed size, and soil nutrient and soil moisture regimes.</p> <p>The results obtained showed that triticale and wheat crop cultivars differ significantly in several growth characteristics except root length and root biomass when grown in pots. These phenotypic differences were affected by crop: weed competition, with several cultivars being identified as having the ability to withstand intense ryegrass competition, while others demonstrated poor competitiveness.</p> <p>Under field conditions, sowing rate and row spacing affected crop competitive ability but depended on the growth stage, growth characteristics and crop cultivar. High sowing rate in combination with wide row spacing was the most effective treatment on crop competitive ability with ryegrass for some cultivars, whereas high sowing rate with narrow row spacing was the most effective for the others.</p> <p>The results in Chapter 5 indicate that selecting larger triticale seeds is likely to confer greater competitive advantage against annual ryegrass and presumably other weeds during early growth periods, commonly the most critical time for crops to become established against weeds. Improving crop competitive ability by increasing water and/or nutrient rates may depend on crop cultivar and factors such as weed species, timing and growth stage as well as other environmental conditions. The results also showed that triticale cultivars performed as well or better than several commercial wheat cultivars, which indicates that triticale may be a useful cereal species for weed management approaches based on competitive crops. Selection of suitable cultivars, combined with increased sowing rate and wide row spacing, selecting for large seeds and increasing fertiliser and soil moisture regimes may increase crop growth, and potentially crop competitiveness with weeds, however, other factors such as the species of weed, its growth characteristics, timing and responses to environmental factors are also likely to affect the competitive interactions.</p> <p>This study has provided useful information about the effects of the tested factors on the crop competitive ability of triticale cultivars with weeds. It has confirmed that triticale may be a useful species in weed management compared with wheats. However, further research is needed to examine competitiveness of spring (long season) and winter (short season) cultivars under field conditions, including with weeds other than annual ryegrass. Future experiments under field conditions should be repeated to investigate whether the interaction between crop cultivar and environment is involved in terms of the effect on crop competitive ability with weeds. Those factors include sowing rate, row spacing, seed size and fertiliser and moisture rates. These cultural practices have the potential to enhance weed suppression and minimise the reliance on herbicides by cereal growers in Australia when applied in integrated weed management programs.</p>