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The study of the variations in Macrophomina phaseolina, the causal agent of charcoal rot, is critical in understanding the ecology of the isolates and the epidemiology of the diseases they cause. This study sought to identify and characterize M. phaseolina isolates using both molecular and morphological approaches and to determine the virulence of the isolates. Macrophomina phaseolina was isolated from cowpea-diseased stem tissues. Eleven M. phaseolina isolates from the major cowpea growing areas (Manga, Nyankpala, Yendi, Damongo, Tumu, Wa, Akomadan and Ejura) were morphologically and molecularly characterized. DNA of the M. phaseolina isolates were amplified using species-specific PCR primers MpKF1 (5'-CCGCCAGAGGACTATCAAAC-3') and MpKR1 (5'-CGTCCGAAGCGAGGTGTATT-3') and sequencing of the M. phaseolina specific amplicons was obtained. This was followed by searching against the NCBI nucleotide sequence database. Isolates were tested for their pathogenicity on a susceptible cowpea cultivar (IT97K-499-35). Virulence of the M. phaseolina isolates was expressed as the percentage of sown seeds that expressed seed rot and damping-off symptoms 14 days after planting. All isolates were confirmed as M. phaseolina based on the amplicon size obtained, and the sequenced amplicons showed an average of 99% homology to the available M. phaseolina sequences. The radial growth of isolates and the percentage of seed rot and damping off they caused on the IT97K-499-35 cultivar varied significantly. The percentage seed rot and damping off were positively correlated (r = 0.74 and 0.75) with the radial growth and colour intensity of the isolates, respectively. Macrophomina phaseolina infection and disease expression may be predicted by the colour and colour intensity of isolates as well as cowpea genotypes. Isolate Mp_3Mc (dense black colour) was the most virulent while isolate Mp_6Ec (grey colour) was the least virulent, resulting in 76.7% and 26.7% seed rot and damping off, respectively. The three clades resolved through the phylogenetic tree matched the distinct colour types of M. phaseolina which correlated with virulence. Isolates of M. phaseolina are diverse and differ in their pathogenicity. Efforts must be geared towards developing cowpea varieties that have resistance to charcoal rot disease. [ABSTRACT FROM AUTHOR]

Tree-ring data for 1942 - 2013 were used to determine if boreal and subalpine Picea albertiana S. Brown emend. Strong & Hills radial growth rates changed after 1950 in southern Yukon, northwest Canada. The latter year represented the beginning of accelerated atmospheric greenhouse gas accumulation, which has subsequently caused global climate changes. Ring-width chronologies for both boreal and subalpine trees were constructed using 80 trees. Individual ring-width sequences were crossdated, age-detrended, and converted to tree ring-width indices (RWI). In 2013, boreal and subalpine RWI were 41% and 169% greater than in 1950, respectively. In contrast, elevational treeline chronologies in the region typically decreased 20% - 70%. During 1942 - 2013, boreal and subalpine chronologies were significantly, at best modestly (r < |0.36|), and exclusively correlated with either moisture or temperature variables, respectively. Within this same time frame, RWI-climate variable correlates differed between the early and late phases of each chronology. Average pre-1969 or early-phase boreal correlations based on a 19-year moving window reached a maximum of - 0.56. Late-phase chronology correlations typically shifted towards weaker associations with climate variables (typically +0.04 to +0.30). For boreal RWI, 25 of 68 tested climate variables shifted as much as 0.40 - 0.88 correlation coefficient units between the early and late phases of the chronologies. Subalpine RWI were correlated only with July - August precipitation during the early phase of its chronology. These changes suggest responses by spruce to climate have shifted since 1970. The modest 1942 - 2013 RWI-climate variable correlations likely reflect the result of these changing ecological relationships. [ABSTRACT FROM AUTHOR]

Studies of cambial dynamics have been employed to investigate the growth behavior of trees. In these investigations, however, spatial variation in cambial rhythm within the stem is usually not taken into account. This study aims to evaluate the contribution of multiple sampling scales on the cambial dynamics of Cedrela odorata L. (Meliaceae) in different seasons. The effects of slope orientation were also tested. Samples were processed and analyzed with standard plant histology techniques. Data from multiple sampling scales were analyzed with nested ANOVA for each season, and the total variance was partitioned according to the fraction related to each scale. The main sources of variability were associated with the scale of tree and scales smaller than 1 cm. Radial growth was not significantly related to acclivity orientation. Thus, to obtain samples that represent total variability in cambial dynamics, it is preferable to increase the number of sampled trees; to take multiple samples from a few millimetres apart from each other, or to assess multiple histological sections. Samples on scales greater than a few centimetres apart should not be given priority. [ABSTRACT FROM AUTHOR]

We examined modulus of elasticity (MoE) derived from SilviScan in white spruce ( Picea glauca (Moench) Voss) at the site, tree, and ring levels across the Boreal Plains ecozone in Canada. Area-weighted averages of MoE were calculated for juvenile and mature wood and were examined in relation to radial growth, climate, and location. Correlations indicated that there was a negative relationship between radial growth and MoE in the juvenile wood that was detectable at the site and tree levels; however, the relationship weakened in the mature wood, particularly at the site level. Few climate variables were correlated with MoE in juvenile wood, whereas multiple summer and fall climate variables showed a significant correlation with MOE in mature wood. A model describing the radial profile of MoE explained 58% of the variability in MoE, with 10% of the random variability attributed to between-tree differences. Elevation and summer water balance accounted for nearly all of the between-site variability. A decrease in MoE with increasing elevation was noted and has been previously linked to a decrease in cell wall thickness due to a shorter growing season at higher elevations. Integration of the MoE profile model into an individual-tree growth and yield simulator is the next logical step. [ABSTRACT FROM AUTHOR]

Over the period 1883-2013, recruitment of subalpine limber pine ( Pinus flexilis E. James) and Great Basin bristlecone pine ( Pinus longaeva D.K. Bailey) above the upper tree line, below the lower tree line, and across middle-elevation forest borders occurred at localized sites across four mountain ranges in the western Great Basin. A synchronous pulse at all ecotones occurred between 1963 and 2000 (limber pine) and between 1955 and 1978 (bristlecone pine) when pines expanded 225 m beyond forest borders. Little recruitment occurred before this interval or in the 21st century. No obvious environmental factors distinguished recruitment locations from nonrecruitment locations. Where their ranges overlap, limber pine has leapfrogged above bristlecone pine by 300 m. Limber pine tree-ring chronologies, developed to compare radial-growth responses with recruitment, showed dominant pulses of increased growth during the same interval as recruitment. Significant climate correlations of growth and recruitment indicated lead and lag effects as much as 6 years and complex relationships with climate variables, corroborating the importance of cumulative climate effects relative to any single year. Water relations were the most important drivers of growth and recruitment and interacted with growing-season minimum and maximum temperatures. These results underscore the importance of studying ecotones at all margins when evaluating conifer response to climate change. [ABSTRACT FROM AUTHOR]

The auxin-ethylene interaction in regulating root elongation and radial expansion was analysed through the application of the ethylene precursor 1-aminocyclopropane-1- carboxylic acid (ACC) and the synthetic auxin 1-naphthaleneacetic acid (NAA). NAA and ACC, in the concentration range of 0.01-0.1 μmol/L and 1-5 μmol/L, respectively, inhibited root elongation and increased root diameter in a concentration-dependent manner. The inhibitory effect of auxin on root elongation was increased by ethylene applied at low as well as high concentrations. Auxin-induced radial expansion was also enhanced by ethylene, although this effect depended on the level of auxin applied. In the presence of very low exogenous auxin (0.01 μmol/L NAA), ethylene stimulated radial growth at both low and high levels (1-5 μmol/L ACC), whereas the effect of higher auxin concentrations (>0.025 μmol/L NAA) was only enhanced by high ethylene production (5 μmol/L ACC). Interaction was analysed by two-way ANOVA; the results showed that both the effect of each hormone and the interactions responsible for controlling elongation and radial expansion were concentration-dependent. The relative effects of auxin and ethylene on the two growth parameters were also analysed; they showed different types of behaviour. In summary, the results obtained suggest that auxin is the main hormone involved in regulating root growth but that ethylene may modulate its effects. Our research also suggests that root elongation and radial expansion may be independently regulated despite being closely related. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to illustrate how some extreme events could affect forest ecosystems. Forest tree response can be analysed using dendroecological methods, as tree-ring widths are strongly controlled by climatic or biotic events. Years with such events induce similar tree responses and are called pointer years. They can result from extreme climatic events like frost, a heat wave, spring water logging, drought or insect damage… Forest tree species showed contrasting responses to climatic hazards, depending on their sensitivity to water shortage or temperature hardening, as illustrated from our dendrochronological database. For foresters, a drought or a pest disease is an extreme event if visible and durable symptoms are induced (leaf discolouration, leaf loss, perennial organs mortality, tree dieback and mortality). These symptoms here are shown, lagging one or several years behind a climatic or biotic event, from forest decline cases in progress since the 2003 drought or attributed to previous severe droughts or defoliations in France. Tree growth or vitality recovery is illustrated, and the functional interpretation of the long lasting memory of trees is discussed. A coupled approach linking dendrochronology and ecophysiology helps in discussing vulnerability of forest stands, and suggests management advices in order to mitigate extreme drought and cope with selective mortality. [Copyright &y& Elsevier]

Xylem production was studied by repeatedly taking microcore samples from the stems of six tree species growing on the “réserve écologique des Vieux-Arbres”, on Lake Duparquet, Québec, throughout the 1999 growing season. Species examined were paper birch (Betula papyrifera Marsh.), white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) BSP), jack pine (Pinus banksiana Lamb.), red pine (Pinus resinosa Ait.), and eastern white cedar (Thuja occidentalis L.). Onset of xylem cell production was observed in all species by 22 May 1999, and ended as early as mid-July and early August for white spruce and eastern white cedar, respectively. Xylem cell production in the remaining species ended between late August and mid-September. In general, the onset of latewood production ranged from the start of July to the first week of August. Typical sigmoidal curves were characteristic of ring width, number of cells, and number of earlywood cells over the growing season. Completion of the annual growth increment was quickest for white spruce and eastern white cedar, while it continued longest in both pine species. Numerous similarities in xylem production and tree ring formation over the course of the growing season were observed among the six species, suggesting that weather, along with photoperiod, plays a critical role in xylem production. [ABSTRACT FROM AUTHOR]