The effects of uneven, patchy cultivar mixtures on disease control and yield in winter barley

Crops that feed the world 4. Barley: a resilient crop? Strengths and weaknesses in the context of food security

“…Furthermore, by mixing elite lines with contrasting traits, particularly disease resistance, yields exceeding the mean of the components and as good as the best component can frequently be achieved. Crude or patchy mixtures are as or more effective than homogeneous mixtures, eliminating the cost of special mixing (Newton and Guy 2009). Disease can be reduced considerably by a combination of three effects: the barrier of resistant plants, reduced density of susceptible plants, and induced resistance (Chin and Wolfe 1984), achieving reductions of up to 75% in the case of scald/Rhynchosporium .…”

Control of foliar diseases in barley: towards an integrated approach

“…The problem of low levels of disease control or yield increase is particularly prevalent in spring barley (Newton and Thomas 1992, Newton et al 2002, Mercer et al 2006), but in winter barley yield increases of up to 17% have been achieved on both small (Day 1984, Newton et al 2002 and large plot scales (Newton and Guy 2009). This difference may be attributable to lower disease levels and the shorter and less stressed season in spring barley, but equally may be due to germplasm differences as Paynter and Hills (2007) generally found no overall yield increases or disease control using current Australian winter barley germplasm.…”

“…Numerous cultivars were used, but most used the same resistance and yet it was still a success. Patchy mixed sowing has also been found to both reduce disease and increase yield more than homogeneous mixed sowings even in the absence of disease, but controlling the 'patchiness' at a field scale could be problematic (Newton and Guy 2009). However, this work clearly shows that crude patchiness was easy to deploy in practice, as no pre-mixing of seed was necessary, and whilst it didn't always result in big yield increases, it did deliver disease reduction and the same or more yield than homogeneously pre-mixed seed.…”

Plant Disease Control through the use of Variety Mixtures

“…In spring barley, the level of disease control or yield increase demonstrated has often been only moderate (Newton & Thomas, 1992;Newton et al, 2002;Mercer et al, 2006), but in winter barley yield increases of up to 17% have been achieved on both small (Day, 1984;Newton et al, 1998) and large plot scales (Newton & Guy, 2008). The difference between the spring and winter crops of barley may be attributable to lower disease levels and the shorter and less stressed season in the former case.…”

“…For rhynchosporium (R. secalis) on winter barley, the optimum GUA or patch size was determined at about 4 m 2 in one study (Newton & Begg, 2008), which lead to experiments to determine whether a patchy arrangement of component cultivars might be better than homogeneous mixing even within fi elds. Patchy sowing was found to both reduce disease and increase yield more than homogeneous sowings compared with the mean of monocultures sown alongside, even in the absence of disease (Newton & Guy 2008). Controlling the spatial nature of the 'patchiness' at a fi eld scale could be problematic but this work clearly shows that crude patchiness was easy to deploy in practice, as no pre-mixing of seed was necessary, and whilst it didn't always result in big yield increases, it did deliver disease reduction and the same or more yield than homogeneously pre-mixed seed.…”