Mapping net blotch resistance in ‘Nomini’ and CIho 2291 barley

Net blotch (Pyrenophora teres) is one of the most devastating diseases of barley (Hordeum vulgare L.) worldwide. Identification of diagnostic molecular markers associated with genes and quantitative trait loci (QTL) for net blotch resistance will facilitate pyramiding of independent genes. Linkage mapping was used to identify chromosomal locations of the independent, dominant genes conditioning net blotch resistance in the winter barley ‘Nomini’ (PI 566929) and spring barley CIho 2291. The F2 populations of 238 and 193 individuals, derived from crosses between the susceptible spring barley parent ‘Hector’ (CIho 15514) and the resistant parents Nomini and CIho 2291, respectively, were used to map the genes governing resistance in the resistant parents. The dominant gene governing resistance in Nomini, temporarily designated Rpt-Nomini, was mapped to a 9.2-cM region of barley chromosome 6H between the flanking microsatellite markers Bmag0344a (r2 = 0.7) and Bmag0103a (r2 = 0.9), which were 6.8 and 2.4 cM away from Rpt-Nomini, respectively. The dominant gene governing resistance in CIho 2291, temporarily designated Rpt-CIho2291, was mapped to a 34.3-cM interval on the distal region of barley chromosome 6H between the flanking microsatellite markers Bmag0173 (r2 = 0.65) and Bmag0500 (r2 = 0.26), which were 9.9 and 24.4 cM away from Rpt-CIho2291, respectively. Identification of the chromosomal location of Rpt-Nomini and Rpt-CIho2291 will facilitate efforts in pyramiding multiple genes for net blotch resistance

Virus infection and grazing exert counteracting influences on survivorship of native bunchgrass seedlings competing with invasive exotics

1.  Invasive annual grasses introduced by European settlers have largely displaced native grassland vegetation in California and now form dense stands that constrain the establishment of native perennial bunchgrass seedlings. Bunchgrass seedlings face additional pressures from both livestock grazing and barley and cereal yellow dwarf viruses (B/CYDVs), which infect both young and established grasses throughout the state. 2.  Previous work suggested that B/CYDVs could mediate apparent competition between invasive exotic grasses and native bunchgrasses in California. 3.  To investigate the potential significance of virus-mediated mortality for early survivorship of bunchgrass seedlings, we compared the separate and combined effects of virus infection, competition and simulated grazing in a field experiment. We infected two species of young bunchgrasses that show different sensitivity to B/CYDV infection, subjected them to competition with three different densities of exotic annuals crossed with two clipping treatments, and monitored their growth and first-year survivorship. 4.  Although virus infection alone did not reduce first-year survivorship, it halved the survivorship of bunchgrasses competing with exotics. Within an environment in which competition strongly reduces seedling survivorship (as in natural grasslands), virus infection therefore has the power to cause additional seedling mortality and alter patterns of establishment. 5.  Surprisingly, clipping did not reduce bunchgrass survivorship further, but rather doubled it and disproportionately increased survivorship of infected bunchgrasses. 6.  Together with previous work, these findings show that B/CYDVs can be potentially powerful elements influencing species interactions in natural grasslands. 7.  More generally, our findings demonstrate the potential significance of multitrophic interactions in virus ecology. Although sometimes treated collectively as plant ‘predators’, viruses and herbivores may exert influences that are distinctly different, even counteracting

Structural equation modeling with heavy tailed distributions

structural model, kurtosis, robust methods, efficiency, power,