Intra-annual growth and mortality of four <Emphasis Type="Italic">Populus</Emphasis> clones in pure and mixed plantings

Intra-annual growth rates were assessed during 3 years for four Populus clones grown in pure and mixed clonal stands at square spacings of 0.5, 1.0 and 1.5 m in western Washington, USA. Height growth rate peaked in August, except at the 0.5-m spacing where it peaked in July and June in years 2 and 3, respectively. Diameter growth rate generally peaked in June. Seasonal growth patterns in mixed clonal stands, relative to those in pure clonal stands, varied by clone. Following early season moisture stress in year 2, growth of a P. balsamifera ssp. trichocarpa clone declined significantly relative to three P. balsamifera ssp. trichocarpa × P. deltoides clones; this trend was most evident at the 0.5-m spacing. During this period of moisture stress, P. balsamifera ssp. trichocarpa had 11 and 36% mortality in pure and mixed stands, respectively, at the 0.5-m spacing; this clone had no mortality at wider spacings during the same period. Although height rankings among clones shifted during the first growing season, rankings at the end of year 1 were very similar to those at the end of year 3.     

Naturally Occurring Scrapie in Southdown Sheep

The purpose of this study was to characterize naturally occurring scrapie in the Southdown breed of sheep. Experimental subjects included 4 Southdown ewes admitted to the University of Missouri, College of Veterinary Medicine Large Animal Clinic. All 4 sheep had signs compatible with clinical scrapie. Cerebrospinal fluid (CSF) cell counts ranged from a low of 1 nucleated cell/microL to high of 4 cells/microL with a median of 3 cells/microL. Cerebrospinal protein concentrations ranged from 26 to 78 mg/dL with a median of 53 mg/dL. Immunoassay of the CSF for the 14-3-3 protein yielded positive results in 3 of the 4 sheep. Sequencing of the prion protein (PrP) gene revealed that all 4 sheep were homozygous for glutamine at codon 171 and, hence, were of the QQ genotype. Histopathologic examination of brain stem tissue sections revealed intracytoplasmic neuronal vacuolation and mild spongiform changes in the gray matter neuropil in all 4 ewes. The diagnosis of scrapie was confirmed by immunohistochemical staining for the abnormal PrP Our results suggest that the genetics of scrapie susceptibility are probably similar in Suffolk and Southdown sheep. Positive immunoassay results for the 14-3-3 protein were observed in 3 of the 4 sheep.     

Perspective: root exudation of herbicides as a novel mode of herbicide resistance in weeds

The evolution of resistance to herbicides in weeds has become a great challenge for global agricultural production. Weeds have evolved resistance to herbicides through many different physiological mechanisms. Some weed species are known to secrete herbicide molecules from roots into the rhizosphere upon being treated. However, root exudation of herbicides as a mechanism of resistance has only recently been identified in two weed species. Root exudation pathways have been investigated in Arabidopsis, and this work suggested that ATP‐binding cassette (ABC) and multidrug and toxic compound extrusion (MATE) transporters play a role in the secretion of primary and secondary plant products from roots. We hypothesize that the mechanisms involved in root exudation of herbicides that result in resistance are mediated by overactive or overexpressed transporters, probably similar to those found for the exudation of primary and secondary compounds from roots. Elucidating the molecular and physiological basis of root exudation in herbicide‐resistant weeds would improve our understanding of the pathways involved in herbicide root secretion mediated by transporters in plants. © 2020 Society of Chemical Industry     

Seedling emergence, growth, and allocation of Oriental bittersweet: effects of seed input, seed bank, and forest floor litter

The establishment of invasive plant populations is controlled by seed input, survival in the soil seed bank, and effects of soil surface disturbance on emergence, growth, and survival. We studied the invasive vine Celastrus orbiculatus Thunb. (Oriental bittersweet) to determine if seedlings in forest understory germinate from the seed bank or from seed rain. We also conducted a greenhouse experiment to investigate the role of leaf litter mass and physical texture on seedling survival, growth, and allocation. In the understory of an invaded mixed hardwood forest, we measured seed input, seedling emergence with seed rain, and seedling emergence without seed rain. Mean seed rain was 168 seeds m⁻²: mean seedling emergence was 107 m⁻², and there was a strong correlation between seed rain and seedling emergence. The ratio of seedlings to seed input (0.61) was close to the seed viability (0.66) leaving very few seeds to enter the seed bank. Seed bank germination under field conditions was low (1 seedling m⁻²). Soil cores were incubated in a greenhouse to determine seed bank viability, and germination from these soil cores did not occur. To determine how litter affects seedling establishment and growth, we measured seedling emergence and biomass allocation in a greenhouse experiment. Seeds were placed below intact and fragmented deciduous leaf litter in amounts ranging from zero to the equivalent of 16 Mg ha⁻¹. Seedling emergence was not affected by fragmented litter, but decreased to <20% as intact litter increased to 16 Mg ha⁻¹. Increasing litter resulted in greater allocation to hypocotyl and less to cotyledon and radicle, and this effect was greater in intact litter. C. orbiculatus seedlings achieve emergence through forest floor litter through plasticity in allocation to hypocotyl growth. The low survival of C. orbiculatus in the seed bank suggests that eradication of seedling advance regeneration and adult plants prior to seed rain may be an effective control strategy. However, the intact forest floor litter of an undisturbed forest will not prevent seedling establishment.     

The effect of environmentally induced stem temperature gradients on transpiration estimates from the heat balance method in two tropical woody species

Commercially available sap flow gauges were used to evaluate the performance of the stem heat balance (SHB) technique for measuring sap flow in coffee (Coffea arabica L. cv. Yellow Catuai) and koa (Acacia koa Gray) plants under greenhouse and field conditions. Transpiration rates measured gravimetrically and with the SHB technique were similar in greenhouse tests, provided that insulation in addition to that supplied by the gauge manufacturer was applied to reduce radiant heating in the vicinity of the sap flow gauges. Unrealistic estimates of transpiration rates were sometimes obtained under both field and greenhouse conditions as a result of negative stem temperature differentials from below to above the gauge heater, even in the absence of power applied to the heaters. It was possible to correct this environmentally induced bias by means of additional stem insulation that minimized the rate of change in stem temperature, or by applying simple corrections using the DeltaT values for unheated gauges operated as blanks. In the field, where dense canopies reduced the radiant energy load on stems, temperature corrections were unnecessary, because DeltaT values in unheated gauges were near zero.     

Cytokine antibody array analysis in brain and periphery of scrapie-infected Tg338 mice

Scrapie is a prion-associated transmissible spongiform encephalopathy (TSE) of sheep and goats, and frequently serves as a comparative model for other prion diseases, such as chronic wasting disease and bovine spongiform encephalopathy. TSEs are unique neurologic disorders that do not appear to be accompanied by robust systemic immunologic responses. mRNA data suggest that cytokines are involved in scrapie progression. In this study, brain tissue, mesenteric lymph nodes, splenic tissue and serum from ovinized mice were screened for 62 cytokine and cytokine-related proteins at pre-clinical and clinical points of infection. Expression patterns were compared to brain histology and clinical presentation. Increased cytokine expression in the brain and periphery were noted in scrapie-positive animals before histologic changes or clinical signs were evident. Of the 62 proteins examined, only IL-10 and TIMP-1 were consistently expressed at increased levels in the serum throughout infection. These cytokines could suggest future targets for biomarkers of infection and may, as well, provide insight into the biologic dynamics of prion-associated neurologic diseases.