Interactive roles of fire seasons and biological invasions in the short‐term dynamics of tropical savannas

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Interactive roles of fire seasons and biological invasions in the short-term dynamics of tropical savannas

The interactive effects of altered fire regimes and biological invasions on biodiversity are still poorly known. Using experimental data, we show that the identity of invasive species played a stronger role as a driver of change of savanna communities in Brazil. Communities invaded by Melinis minutiflora gained more species and were more temporally variable than those invaded by Urochloa brizantha.


Abstract

Aim

Changes in fire regimes and biological invasions are major threats to tropical savannas. Fire is a key driver of community composition in these ecosystems and can be used as a management tool to control some invasive alien species, while being advantageous to native ones. However, we still do not fully comprehend the interactive effects of these threats on native plant communities. Here, we conducted an experiment in southeastern Brazil to investigate how variation in the composition of native communities invaded either by Melinis minutiflora or Urochloa brizantha is affected by fire in different seasons: early-dry season, mid-dry season and late-dry season in comparison to fire suppression.

Location

Itirapina, state of São Paulo, southeastern Brazil (22°14′07″S 47°53′07″W).

Results

The effects of fire seasons and invasive species were independent for species richness but interactive for species gains and losses. In general, the identity of the invasive species was a key factor driving community dynamics, with fire seasons playing a weaker role. Invaded communities changed gradually over time and the major changes happened over longer time lags. Communities invaded by M. minutiflora gained more species than those invaded by U. brizantha. Thus, communities invaded by M. minutiflora also had more variation in their species richness through time than those invaded by U. brizantha.

Conclusions

Although biological invasions and fire seasons interacted as drivers of change in native savanna communities, the identity of the invasive species played a stronger role. Communities invaded by M. minutiflora gained more species and were more variable than those invaded by U. brizantha.

Environmental drivers of wheat yield variability across China’s production regions: Insights from field experiments

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Abstract

Wheat crops underpin contemporary global food security. Predominant wheat production zones in China include the Huang-Huai-Hai-Plain and the Mid-Lower Reaches of the Yangtze River, although climatic effects on productive potential across these regions vary markedly in space and time. Here, we conducted field experiments during the wheat season of 2015–2018 to examine environmental effects on growth, with fertilization and irrigation provided at levels ensuring that nutrient and water stress exposure was minimal. Yields in Huang-Huai-Hai-Plain and the Mid-Lower Reaches of the Yangtze River averaged 8950 and 4818 kg ha−1, respectively. Yield variation across regions was primarily related to spike number per unit area and grain number per spike. Maturity biomass was higher in Huang-Huai-Hai-Plain; this translated into higher grain yields. Lower temperature and longer growing duration between emergence and jointing in Huang-Huai-Hai-Plain afforded higher tillering and spike numbers, whereas higher growth rates from jointing to maturity resulted in higher biomass production in Huang-Huai-Hai-Plain compare with the Mid-Lower Reaches of Yangtze River. Growth rate, grain numbers and yield were positively correlated with the ratio of daily intercepted solar radiation to mean temperature during jointing to anthesis, termed photothermal quotient. Collectively, our results suggest that growth rate accounted for more variation in biomass production compared with growth duration, and the photothermal conditions in the Mid-Lower Reaches of the Yangtze River were restrictive for spike development and yield formation. Our results help disentangle drivers of crop growth through the development of agro-environmental conceptual frameworks, enabling a better understanding of yield variability in space and time.

Ecophysiological mechanisms underlying the positive relationship between seed protein concentration and yield in soybean under field heat and drought stress

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Abstract

A positive relationship between protein concentration and yield has been documented in different combinations of genotype and environment, often under potential conditions. However, the ecophysiological bases underlying this positive relationship under heat stress (HS) and drought stress (DS) during seed filling are still lacking. Our objective was to evaluate the relationship between seed protein content and concentration with yield in field experiments exposed to HS, DS and HS × DS interaction during the seed filling. Two field experiments were conducted and assimilates accumulation, remobilization and redistribution patterns were analysed in high and low seed protein soybean genotypes. The crop was exposed to four treatments: control (ambient temperature and soil water content near field capacity), HS (episodes above 32°C, 6 h d−1) during 15 days, DS (soil water content ≤25% of field capacity) during the whole seed filling and HS × DS. Significant and positive relationships between seed protein content and concentration with yield were observed across treatments and genotypes. Under DS and HS × DS, assimilates available during the seed filling decreased, and assimilates remobilization and partition to seeds were limited, responses significantly associated with seed protein content and concentration, and yield reductions. Furthermore, we demonstrated here that the high leaf N content at the beginning of seed filling, the short early reproductive phase duration, the high source to sink ratio and the high dry matter stem remobilization capacity, as well as the low seed number and high seed weight are intrinsic characteristics of the high protein genotype that could be associated with its high seed protein content and concentration and yield under stressful conditions. This knowledge is key to develop soybean management strategies to improve seed protein level and yield under contrasting productive scenarios.

Shared quantitative trait loci underlying root biomass and phenology in wheat (Triticum aestivum L.)

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Abstract

In this study, we investigated the genetic mapping of root biomass and root/shoot ratio. We utilized a large (n = 345) bi-parental recombinant inbred line (RIL) population from the ‘Penny’ × ‘Yecora-Rojo’ cross to investigate the partitioning of biomass above- and belowground and to identify the quantitative trait loci (QTL) that influence root biomass and root/shoot ratio. Genotyping of 345 RILs by using genotyping by sequencing produced 2918 single-nucleotide polymorphism markers by which a genome-wide map of 3507 cM was constructed. Phenotyping was conducted in an augmented design with large pots in controlled environment. We identified two significant QTL regions, QRt.peye-5A and QRt.peye-5B, which control root biomass and the root/shoot ratio. QRt.peye-5A, marking a 3.15 Mbp region on chromosome 5A, explained 11% of variations in root biomass and 9.5% of variations in root/shoot ratio, with the narrow region harbouring 28 genes. QRt.peye-5B, marking a 12.2 Mbp region on chromosome 5B, explained 7% of variations in root/shoot ratio and harbours 104 genes. The root/shoot ratio enhancing alleles at QRt.peye-5A and QRt.peye-5B come from ‘Penny’ and ‘Yecora-Rojo’ respectively. These QTL regions contains genes such as the two MADS box transcription factors on the 5A QTL that are candidate genes for Vrn1 locus, and other genes previously postulated for root traits such as a COBRA-like COBL2 and landmark hormonal responses genes such as IAA16, IAA4 and BRI1, DREB2A-INTERACTING PROTEIN2 (DRIP2) and bHLH92 which has a role in amelioration of stress conditions.

Halo‐hydromorphism alters nitrogen fertilization responses of tall wheatgrass pastures: Capture and use of resources, tiller dynamics and forage production

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Abstract

Halo-hydromorphism limits productivity in approximately 100 million hectares worldwide. Tall wheatgrass (Thinopyrum ponticum) is a species widely used in these environments for its seeding potential, being the addition of nitrogen a considered technological tool to increase forage quality and production. The objective of the study was to determine the impact of nitrogen fertilization on the capture and use of resources (radiation, water and nitrogen) in a cool season perennial sward growing in contrasting halo-hydromorphic conditions. Cultivated pastures from three independent sites were used. Sites were described according to the degree of halo-hydromorphism using soil salinity and water table attributes (salinity and depth) as environmental indicators: low HHM site [electrical conductivity (EC1:2.5) 0.97 dS/m; water table salinity 2.03 dS/m; depth 85 cm], intermediate HHM site (EC1:2.5 3.86 dS/m; water table salinity 7.40 dS/m; depth 134 cm) and high HHM site (EC1:2.5 4.49 dS/m; water table salinity 7.85 dS/m; depth 31 cm). At each site, a late spring regrowth (~750°Cd) was studied by applying two treatments (n = 5): without (N0) and nitrogen fertilization (N150; 150 kg/ha of nitrogen in the form of urea). The response of tall wheatgrass to nitrogen fertilization in halo-hydromorphic conditions depends on soil salinity and water table attributes. N150 treatments production was twice as high as in N0 in low HHM and intermediate HHM environments (from 1750 to 3500 kgDM/ha and from 1080 to 1985 kgDM/ha, respectively). Meanwhile, in high HHM conditions, forage production was only 40% higher when nitrogen was added (from 625 to 870 kgDM/ha). In low HHM the higher N150 production was related to tiller density and size, whereas in intermediate HHM and high HHM was linked only to tiller size. In N150 treatments, the nitrogen nutrition index was negatively affected with the increase in HHM conditions (0.77, 0.62 and 0.55 for low HHM, intermediate HHM and high HHM, respectively). Instead, nitrogen nutrition index of N0 was similar in all the environments (~0.42). In N150, forage production capacity analysed in terms of radiation and water use efficiency (RUE and WUE, respectively) was similar in low HHM and intermediate HHM environments (RUE ~0.81 gDM/Mj and WUE ~13 kgDM/mm). These findings emphasize the importance of conducting analyses based on resource use and capture to understand productive responses to the increase in growth-limiting factors. Furthermore, they contribute to the identification of environments suitable for nitrogen fertilization.

Morphology, phylogeny and pathogenicity of fungal species associated with leaf blight and stem canker of Theobroma cacao in Malaysia

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Morphology, phylogeny and pathogenicity of fungal species associated with leaf blight and stem canker of Theobroma cacao in Malaysia

Leaf blight of Theobroma cacao in Malaysia was found to be caused by Diaporthe tulliensis and Neopestalotiopsis clavispora while stem canker was caused by D. tulliensis, Fusarium proliferatum and Fusarium solani.


Abstract

Malaysia stands prominently among Asia's key cocoa-producing countries. In the cocoa season of 2022–2023, Malaysia demonstrated its contribution to the industry, with an estimated production of around 364,000 tonnes of cacao bean grindings. Nonetheless, fungal diseases pose undeniable challenges to the cocoa sector. Extensive sampling conducted between September 2018 and March 2019 across multiple states in Malaysia revealed concerning symptoms of leaf blight and stem canker affecting Theobroma cacao plants. The aim of this study was to identify and characterize fungal species associated with leaf blight and stem canker of T. cacao in Malaysia through morphological, molecular and pathogenicity analyses. Morphological and molecular phylogenetic analyses using multiple DNA regions (rDNA internal transcribed spacer [ITS], TEF1 and TUB2) were performed and identified 40 fungal isolates found in this study as Diaporthe tulliensis (17 isolates), Fusarium solani (seven isolates), Fusarium proliferatum (six isolates) and Neopestalotiopsis clavispora (10 isolates). Pathogenicity tests with mycelial plugs and wound treatments showed that D. tulliensis and N. clavispora were responsible for causing leaf blight whereas D. tulliensis, F. solani and F. proliferatum caused stem canker of T. cacao. The present study provides insights into disease aetiology and symptomatology that may be useful in planning effective disease management for the host plant.

The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

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The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

Pathogenicity on lychee and population genomics show that taxa in the gloeosporioides species complex are predominantly clonal, and symptoms and host range are linked to genotype.


Abstract

Lychee pepper spot, a field disease affecting lychee fruit skin, pedicels and petioles, is caused by Colletotrichum siamense, a fungal pathogen within the gloeosporioides species complex. Members of Colletotrichum from the gloeosporioides species complex and occasionally those from the acutatum species complex also cause postharvest anthracnose of lychee. Pepper spot was first described in Australia many years after anthracnose on lychee was first described, giving rise to the hypothesis that a novel species or strain within the gloeosporioides species complex causes pepper spot. In the present study, 19 isolates of Colletotrichum spp., collected from pepper spot and anthracnose symptoms on lychee fruit, representing 13 different genotypes across five species, were inoculated onto lychee fruit in the field or on detached fruit in the laboratory, to understand more about their pathogenic diversity. We found that symptoms were specific to genotype of the pathogen, as three genetically similar isolates of C. siamense consistently caused pepper spot and anthracnose, whilst other isolates caused anthracnose only. Cross-inoculation studies on detached fruit of lychee, banana, avocado and mango also provided some evidence of host specialization in isolates of C. siamense infecting lychee in Australia. Our experiments provided further evidence that detached fruit assays cannot be used as a reliable proxy for field inoculation studies. This research confirms that C. siamense is a causal agent of both lychee pepper spot and lychee anthracnose in Australia, and Colletotrichum alienum and Colletotrichum queenslandicum are reported as causal agents of anthracnose of lychee for the first time.