Meiotic pairing and morphological and yield characterisation of three advanced lines of hexaploid tritordeum (×Tritordeum martini)

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Abstract

Hexaploid tritordeum [×Tritordeum martinii A. Pujadas (Poaceae) nothosp. nov.; HchHchAABB] resulted from crosses between wild barley (Hordeum chilense Roem et. Schultz) and durum wheat [Triticum turgidum L. ssp. durum (Desf.) Husn.]. Tritordeum (HT) presents interesting agronomic traits that can be transferred to cultivated wheat. Through the years, several HT lines were developed and characterised. Genomic stability and fertility are expected for advanced HT lines with multiple self-fertilisation generations. In this work, we analysed the meiotic chromosomal pairing in pollen mother cells (PMCs) of three advanced lines of hexaploid tritordeum (HT9, HT31 and HT67) after fluorescence in situ hybridisation (FISH) performed with genomic DNA from H. chilense and the bread wheat cloned rDNA sequence, pTa71, as probes, and characterised nine morphological and yield-related traits for three consecutive years in adult plants. As expected, all HT lines showed regular meiotic chromosomal pairing, ensuring plant fertility as previously confirmed by the characterisation of morphological and yield-related traits in adult plants of preceding generations. Globally, tritordeum is interesting for wheat breeding and has potential as an alternative crop.

Controls on use efficiency of plant nutrients along subtropical to alpine gradients on the Tibetan Plateau

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Controls on use efficiency of plant nutrients along subtropical to alpine gradients on the Tibetan Plateau

The data along Tibetan Alpine Vegetation Transects indicate that, to maximize nitrogen use efficiency of canopy production, forest trees tend to have a higher mean residence time of nitrogen in the plants through increased leaf life span, whereas alpine shrubs and grasslands tend to have higher nitrogen productivity through increased below-ground fraction of biomass. Similar patterns are found in phosphorus use efficiency.


Abstract

Question

Knowledge of how nutrient use strategies differ between forest trees and alpine shrubs/grasses is important to understand the mechanisms of vegetation changes from montane forests to alpine shrubs/grasslands along altitudinal gradients. We tested the hypothesis that, to maximize the nitrogen use efficiency (NUE) of canopy production, forest trees tend to have a higher mean residence time (MRT) of nitrogen in the plants through increased leaf life span, whereas alpine shrublands and grasslands tend to have higher nitrogen productivity through increased below-ground biomass fraction. We further tested whether similar patterns are found in phosphorus use efficiency (PUE).

Location

Twenty-one sampling sites along Tibetan Alpine Vegetation Transects (TAVT) at altitudes from 1900 m to 4900 m.

Methods

We measured the maximum biomass of new canopy leaves and twigs and the concentrations of their nutrients N and P and associated ecosystem variables along the TAVT. NUE (PUE) was calculated as the product of nutrient productivity (dry matter production per unit N or P in new canopy leaves and twigs) and MRT (the ratio of foliage nutrient pool to annual nutrient uptake).

Results

With increasing altitude, leaf life span increased in forest trees but decreased in shrublands and grasslands, while below-ground fraction increased when vegetation changed from montane forests to alpine shrubs/grasslands. In forest trees, higher N-MRT and P-MRT and lower P productivity were associated with longer leaf life span and lower below-ground fraction, while N productivity varied little. In alpine shrublands and grasslands, N-MRT, P-MRT and P productivity varied little with leaf life span and below-ground fraction, while N productivity was positively correlated with below-ground fraction.

Conclusions

Our data supported the hypothesis, suggesting that NUE of canopy production would be a measure of changes in ecosystem functioning from montane forests to alpine shrublands and grasslands along altitudinal gradients. The findings provide an insight into the linkage between biogeochemistry and phytogeographic processes across ecosystems.

Seedling recruitment in response to stand composition, interannual climate variability, and soil disturbance in the boreal mixed woods of Canada

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Seedling recruitment in response to stand composition, interannual climate variability, and soil disturbance in the boreal mixed woods of Canada

We found that three important conifer species of the Eastern Canadian boreal mixed woods (white spruce, balsam fir and white cedar) have reduced seedling recruitment during warmer growing seasons, which is not the case for the main deciduous trees (trembling aspen, paper birch) in this ecosystem. This effect could aid the northward migration of temperate deciduous species in a warming climate.


Abstract

Aim

Seedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long-term field experiment (18 years) to study the effects of these factors and their interactions on seedling recruitment.

Location

Our study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis).

Methods

Sixteen 1-m2 seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing-season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model.

Results

Soil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment.

Conclusion

Our findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed-wood ecosystems.

Identification and pathogenicity of Colletotrichum species associated with twig dieback of citrus in Western Australia

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Identification and pathogenicity of Colletotrichum species associated with twig dieback of citrus in Western Australia

Citrus twig dieback in Western Australia was shown to be caused by Colletotrichum gloeosporioides, C. karstii and C. novae-zelandiae.


Abstract

Up to 32 Colletotrichum species have been reported to be associated with pre- or postharvest diseases of citrus globally, while in Australia, six species have been reported to cause citrus leaf and fruit disease. Twig or shoot dieback has recently been observed as an emerging disease in citrus orchards in Western Australia. Colletotrichum species were isolated from diseased twigs showing dieback (withertip) or lesions, with or without gummosis, collected from 12 varieties of orange, mandarin and lemon. Colletotrichum gloeosporioides sensu stricto, Colletotrichum karstii and Colletotrichum novae-zelandiae were identified using a polyphasic approach that included multigene phylogenetic analysis using sequences of internal transcribed spacer and intervening 5.8S nrDNA (ITS), glyceraldehyde-3-phosphate dehydrogenase (gapdh), β-tubulin (tub2), actin (act) and histone (his3) for isolates in the boninense species complex, and Apn2–Mat1–2 intergenic spacer and partial mating type (Mat1–2) (ApMat) and glutamine synthetase (gs) for isolates in the gloeosporioides species complex, as well as morphological characteristics. C. gloeosporioides was the most prevalent species associated with twig dieback in Western Australia, while C. novae-zelandiae was reported for the first time in Australia. Pathogenicity tests on shoot twigs from lemon and orange trees confirmed C. gloeosporioides, C. karstii and C. novae-zelandiae as the cause of twig dieback, with C. gloeosporioides being the most aggressive species. Knowledge of the species causing twig dieback and their lifestyle will assist the development of integrated control methods.

Comparative genomics identifies genetic markers linked to structural variations that differentiate Puccinia graminis tritici and secalis formae speciales

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Comparative genomics identifies genetic markers linked to structural variations that differentiate Puccinia graminis tritici and secalis formae speciales

Newly available genome sequence data were harnessed to design four simple PCR-based assays able to distinguish Puccina graminis formae speciales.


Abstract

Stem rust is a serious disease of many gramineous plants including small grain staples such as wheat, barley, rye and triticale. Separate formae speciales (ff. spp.) of the causal fungus, Puccinia graminis, predominantly infect certain host plant genera. However, despite these taxonomic subdivisions, many P. graminis ff. spp. are genetically too similar to distinguish using existing genetic markers. For those infecting cereals, this is particularly challenging for P. graminis f. sp. tritici (Pgt) and P. graminis f. sp. secalis (Pgs). Herein we harnessed newly available genomic data for 39 Pgt and Pgs isolates and identified four regions of structural variation that were used to design four simple PCR-based assays to distinguish the aforementioned formae speciales. These genomic regions display large presence/absence variation between Pgt and Pgs isolates, and yet a high degree of sequence conservation within shared neighbouring regions, facilitating primer design. We also confirmed lack of amplification in host plant genera analysed, which included assessment of the shared alternate host of Pgt and Pgs, Berberis vulgaris. Accurate classification of P. graminis ff. spp. infections on B. vulgaris is exceptionally valuable to rapidly define plants harbouring P. graminis inoculum when adjacent to cereal crops. Finally, we demonstrated utility of these four genetic markers to correctly distinguish a genetically diverse array of Pgt and Pgs isolates. This strategy could now be readily applied to other pathogens of interest, which will be of increasing value as genomic resources continue to rapidly expand for many key biotic threats to agricultural productivity.