Wild Poaceae Research Articles

Halophytic Bacterial Endophyte Microbiome from Coastal Desert-Adapted Wild Poaceae Alleviates Salinity Stress in the Common Wheat Triticum aestivum L.

Abiotic stresses threaten the strategic crops of Poaceae (Gramineae) worldwide. Habitat-adapted microbiome of wild plants has the potential to alleviate abiotic stresses in alternate hosts. Persian Gulf's coastal deserts are colonized by halophyte plants hosting habitat-adapted halophytic microbiota. Here, endophytic bacteria from wild Poaceae in coastal deserts of the north Persian Gulf at Hormozgan province, Iran, were isolated and screened for mitigating salinity stress in wheat. Accordingly, seven dominant species of wild Poaceae in the region, i.e., Aeloropus lagopoides, Aeloropus litiralis, Chrysopogon aucheri, Cymbopogon olivieri, Desmostachya sp., Halopayrum mucronatum, and Sporbuls arabicus, were explored. In total, 367 endophytic bacteria were isolated, 90 of which tolerated 2.5-M NaCl. Of these, 38 strains were selected based on their bioactivity and applied for in vitro wheat-interaction assays under 250-mM NaCl stress. Five superior strains promoted seed germination and growth indices in rain-fed winter wheat cv. Sardari, i.e., Bacillus subtilis B14, B19, & B27, Bacillus sp. B21, and Bacillus licheniformis Ba38. In planta assays in saline soil (2.7 dS m-1) using the superior strains indicated that Bacillus sp. B21 and Bacillus licheniformis Ba38 increased germination and root and shoot lengths and their dry and fresh weights in wheat seedlings. Moreover, phenolics and flavonoids contents of wheat seedlingswere influenced by endophyte application. Thus, the coastal desert-adapted microbiome of wild Poaceae could alleviate abiotic stress and promote growth in cultivated species of Poaceae, such as wheat.

A question of rite—pearl millet consumption at Nok culture sites, Nigeria (second/first millennium BC)

The Nok culture in central Nigeria, dated 1500–1 cal bc, is known for its famous terracotta sculptures. We here present a study on > 11,000 botanical macro-remains from 50 sites, including 343 samples from Nok contexts and 22 samples dating between cal ad 100 and 400, after the end of the Nok culture. With 9,220 remains, pearl millet (Cenchrus americanus (L.) Morrone, syn. Pennisetum glaucum (L.) R.Br.) is dominant in the Nok samples, followed by cowpea (Vigna unguiculata (L.) Walp.), Canarium schweinfurthii Engl., Nauclea latifolia Sm. (syn. Sarcocephalus latifolius (Sm.) E.A.Bruce), wild fruit trees and wild Poaceae. The pearl millet remains consist exclusively of charred caryopses; chaff remains are completely absent. Because we studied all size fractions, including the small 0.5 mm fractions usually containing the involucres, bristles and husks, the absence of pearl millet chaff is real, excluding a methodological explanation, and distinguishes Nok from contemporary other West African sites. We propose that most excavated Nok sites were consumer sites where clean grain was brought in from outside and consumed in a ritual context connected with feasting. This is in line with the archaeological evidence from the larger excavated sites with stone-pot arrangements that are interpreted as ritual places related to mortuary practices. In addition to the known southward branches of pearl millet diffusion from the Sahara we propose a new, hitherto unknown branch directly from the central Sahara to the central Nigerian savannas.

Pest categorisation of High Plains wheat mosaic virus.

The EFSA Panel on Plant Health conducted a pest categorisation of High Plains wheat mosaic virus (HPWMoV) for the EU territory. The identity of HPWMoV, a member of the genus Emaravirus (family Fimoviridae), is well established and reliable identification methods are available. The pathogen is not included in the EU Commission Implementing Regulation 2019/2072. HPWMoV has been reported from Argentina, Australia, Canada, Ukraine and USA, and it is not known to be present in the EU. HPWMoV infects plant species of the family Poaceae (i.e. wheat, maize and several other cultivated or wild Poaceae species). It is the causal agent of High Plains disease of wheat and maize, inducing symptoms ranging from mild to severe mosaic, chlorosis and necrosis in wheat, and chlorotic streaks in maize plants. The virus is transmitted by the wheat curl mite Aceria tosichella, which is present in the EU. HPWMoV transmission via seeds was reported to occur in sweet corn. Sweet corn seeds for sowing were identified as the most relevant pathway for entry of HPWMoV into the EU. Seeds from other hosts and viruliferous wheat curl mites were identified as entry pathways associated with uncertainties. Machinery not appropriately cleaned may move infected seeds and/or parts of cereals infested by viruliferous mites. Cultivated and wild hosts of HPWMoV are distributed across the EU. Would the pest enter and establish in the EU territory, economic impact on the production of cultivated hosts is expected. Phytosanitary measures are available to prevent entry and spread of the virus in the EU. HPWMoV fulfils the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

A Detailed Ecological Exploration of the Distribution Patterns of Wild Poaceae from the Jhelum District (Punjab), Pakistan

The purpose of this study was to investigate the taxonomic diversity, richness, and distribution patterns of Poaceae in relation to abiotic factors in the Jhelum district of the Pakistan Himalayas. We used a random sampling technique from 80 grids within 240 sites with a rich diversity of wild grasses and 720 quadrates in triplets from each site across the Jhelum district between 2019 and 2021 to collect data on grass species and the associated environmental factors and conditions. After evaluating the important value index for each plant taxa and for the environmental data, we analyzed the data using ordination and cluster analysis techniques. Fifty-two Poaceae taxa from twenty-nine genera were recorded within the study area. From a total of 52 recorded Poaceae species, 45 were native and 7 were invasive species. The life form (biological) showed the dominancy of 27 therophyte species, followed by 24 hemicryptophyte species, and 1 geophyte species. Microphyll had the leading leaf size spectra (27 species), followed by nanophyll (12 species), macrophyll (10 species), and leptophyll (3 species). The trend of the life cycle was the maximum (27 spp.) during the monsoon season, followed by spring (11 spp.), winter (8 spp.), and summer (6 spp.). The leading genera were Setaria with 9.61% of the species, followed by Panicum, Cenchrus, and Brachiaria with 7.69% of the species. Aristida and Echinochloa made up 5.76% of the species while Chrysopogon, Digitaria, Eragrostis, Pennisetum, and Poa made up 3.84% of the species. Other genera recorded single species. The leaf size spectra of grasses were dominated by microphylls (50%) followed by nanophylls (23.07%), macrophylls (19.23%), and leptophylls (7.69%). On the basis of the importance value index, the most dominant species was Cynodon dactylon (68), followed by Dichanthium annulatum (58), Brachiaria ramose (38), Dactyloctenium aegyptium (37), Eleusine indica (35), Saccharum bengalense (33), and Cenchrus biflorus (28). Two-way cluster analyses classified the grasses into three plant community associations based on the indicator plant species. Soil parameters as subsamples were tested for moisture, pH, EC, OM, macronutrients (CaCO3, N, P, and K), and saturation while the ordination analysis revealed that they had a significant (p ≤ 0.002) effect on vegetation associations. Overall, this study contributes to a better understanding of the influence of environmental factors on the composition and associations of grass species and the development of scientifically informed management solutions for the ecological restoration of degraded habitats in this Himalayan region.

New species of Colletotrichum from wild Poaceae and Cyperaceae plants in Iran

ABSTRACT Twenty-two Colletotrichum strains were isolated from anthracnose symptoms or leaf spots on leaves of various wild Poaceae and Cyperaceae plants collected in three provinces of Iran and tentatively identified as belonging to the Graminicola species complex based on morphology. All strains were studied via a polyphasic approach combining colony characteristics, morphology and phylogeny inferred from multi-locus sequences, including the nuc rDNA ITS1-5.8S-ITS2 (ITS), partial sequences of the β-tubulin (tub2), actin (act), manganese superoxide dismutase 2 (sod2), DNA lyase 2 (apn2) genes, a 200-bp intron of the glyceraldehyde-3-phosphate dehydrogenase (gapdh), and the intergenic spacer between the apn2 gene and the mat1 idiomorph (apn2/mat1). Six species were distinguished, including three new species, namely C. caspicum, C. persicum, and C. sacchari, and three previously described species, C. cereale, C. nicholsonii and C. sublineola. Comprehensive morphological descriptions and illustrations are provided for all species. Furthermore, this study provided new insights into the distribution and host range of known species.

A Regulatory Network of Heat Shock Modules-Photosynthesis-Redox Systems in Response to Cold Stress Across a Latitudinal Gradient in Bermudagrass.

Bermudagrass (Cynodon dactylon Pers.) is a wild Poaceae turfgrass with various genotypes and phenotypes. In this study, 16 wild bermudagrass germplasms were collected from 16 different sites along latitudinal gradients, and different temperature treatments were compiled and used for physiological and transcriptome analysis. To explore the correlation between the key differentially expressed genes and physiological indicators, a total of 14,654 DEGs were integrated from the comparison of different temperature treatments and used for weighted gene co-expression network analysis. Through comparative transcriptome analysis and gene annotation, the results showed that differential gene expression profiles in networks are associated with the plant growth, photosystem, redox system, and transcriptional regulation to cold stress in bermudagrass. In particular, genes encoding HSP70/90 and HsfA3/A8 are not only regulated by temperature stress, but also directly or indirectly interplay with the processes of peroxide scavenging and chlorophyll synthesis under cold stress. Besides, through a weight evaluation analysis of various physiological indexes, we identified an accession of wild bermudagrass with relatively strong cold resistance. These results provide important clues and resources to further study the responses to low-temperature stress in bermudagrass.

Comparison of the Virome of Quarantined Sugarcane Varieties and the Virome of Grasses Growing near the Quarantine Station.

Visacane is a sugarcane quarantine station located in the South of France, far away from sugarcane growing areas. Visacane imports up to 100 sugarcane varieties per year, using safe control and confinement measures of plants and their wastes to prevent any risk of pathogen spread outside of the facilities. Viruses hosted by the imported material are either known or unknown to cause disease in cultivated sugarcane. Poaceae viruses occurring in plants surrounding the quarantine glasshouse are currently unknown. These viruses could be considered as a source of new sugarcane infections and potentially cause new sugarcane diseases in cases of confinement barrier failure. The aim of this study was to compare the plant virome inside and outside of the quarantine station to identify potential confinement failures and risks of cross infections. Leaves from quarantined sugarcane varieties and from wild Poaceae growing near the quarantine were collected and processed by a metagenomics approach based on virion-associated nucleic acids extraction and library preparation for Illumina sequencing. While viruses belonging to the same virus genus or family were identified in the sugarcane quarantine and its surroundings, no virus species was detected in both environments. Based on the data obtained in this study, no virus movement between quarantined sugarcane and nearby grassland has occurred so far, and the confinement procedures of Visacane appear to be properly implemented.

Identification, molecular and biological characterization of two novel secovirids in wild grass species in Belgium

High throughput sequencing was performed on virion-associated nucleic acids (VANA) from a pool of fifty asymptomatic rough bluegrasses (Poa trivialis L.) collected in a Belgian grazed pasture. Bioinformatics analyses produced some contigs presenting similarities with secovirid genomes, in particular nepoviruses and waikaviruses. Three distinct positive-sense single-stranded RNAs including 5’ and 3’ UTR were reconstructed and they represented two novel viruses infecting rough bluegrass, for which the provisional names poaceae Liege nepovirus A (PoLNVA, 7298 nt for RNA1 and 4263 nt for RNA2) and poaceae Liege virus 1 (PoLV1, 11,623 nt) were proposed. Compared to other Secoviridae members, the highest amino acid identity reached 90.7 % and 66.7 % between PoLNVA and nepoviruses for the Pro-Pol and CP regions respectively, while PoLV1 presented the highest amino acid identity with waikaviruses but with lower identities, i.e. 41.2 % for Pro-Pol and 25.8 % for CP regions, far below the ICTV demarcation criteria for novel secovirid. Based on sequence identity and phylogenetic analyses, PoLNVA was proposed to belong to the genus Nepovirus and PoLV1 as an unclassified secovirids. Detection of the two novel viruses was confirmed in high prevalence in rough bluegrass and ten other wild Poaceae species (Agropyron repens, Agrostis capillaris, Apera spica-venti, Anthoxanthum odoratum, Cynosorus cristatus, Festuca rubra, Holcus lanatus, Lolium perenne, Phleum bertolini and Phleum pratense) by RT-PCR and Sanger sequencing, revealing a diverse host range within Poaceae for these novel secovirids. Seed transmission was evaluated and confirmed for PoLNVA.

Key root traits of Poaceae for adaptation to soil water gradients.

Summary Drought and flooding are contrasting abiotic stressors for plants. Evidence is accumulating for root anatomical traits being essential for the adaptation to drought or flooding. However, an integrated approach to comprehensively understand root anatomical traits has not yet been established.Here we analysed the root anatomical traits of 18 wild Poaceae species differing in adaptation to a range of soil water content. Regression model analyses revealed the optimal anatomical traits that were required by the plants to adapt to low or high soil water content.While the area and number of each root tissue (e.g. stele, cortex, xylem or aerenchyma) were not strongly correlated to the soil water content, the ratio of the root tissue areas (cortex to stele ratio (CSR), xylem to stele ratio (XSR) and aerenchyma to cortex ratio (ACR)) could fully explain the adaptations of the wild Poaceae species to the soil water gradients.Our results demonstrate that the optimal anatomical traits for the adaptations to soil water content can be determined by three indices (i.e. CSR, XSR and ACR), and thus we propose that these root anatomical indices can be used to improve the tolerance of crops to drought and flooding stresses.

Sorghum mastrevirus-associated alphasatellites: new geminialphasatellites associated with an African streak mastrevirus infecting wild Poaceae plants on Reunion Island.

Nine complete nucleotide sequences of geminialphasatellites (subfamily Geminialphasatellitinae, family Alphasatellitidae) recovered from the wild Poaceae Sorghum arundinaceum collected in Reunion are described and analyzed. While the helper geminivirus was identified as an isolate of maize streak virus (genus Mastrevirus, family Geminiviridae), the geminialphasatellite genomes were most closely related to, and shared ~63% identity with, clecrusatellites. Even though the geminialphasatellite molecules lack an adenine rich-region, they have the typical size of geminialphasatellites, encode a replication-associated protein in the virion sense, and have probable stem-loop structures at their virion-strand origins of replication. According to the proposed geminialphasatellite species and genus demarcation thresholds (88% and 70% nucleotide identity, respectively), the genomes identified here represent a new species (within a new genus) for which we propose the name "Sorghum mastrevirus-associated alphasatellite" (genus "Sorgasalphasatellite").

Holocene climate change and its influence on early agriculture in the Nile Delta, Egypt

To investigate how Holocene climate patterns influenced the development of early Egyptian agriculture at the archaeological site of Sais on the Nile Delta, we conducted a palynological study. Seven palynological zones were defined to reveal Holocene climate fluctuations. Zone I (ca. 9000–7000 cal yr BP) was a period of warming climate, succeeded by a progressive drying climate phase in Zones II–VII (ca. 7000–2000 cal yr BP). Pollen records indicate Nile flooding prevailed before 7000 years ago, making the study area uninhabitable, before it later developed into a wetland setting. The earliest farming started at ca. 6700 cal yr BP, as indicated by the abrupt appearance of cereal (Poaceae > 35 μm), during a time of climate warming (Zone III), This material can be differentiated from wild Poaceae (<35 μm), which occurs throughout the profile, indicating the cereal was introduced to this area for agriculture. Results further reveal the transformation of human activities, from passive adaptation to climate, to actively remolding the environment against the background of long-term drying. During the early farming stage (ca. 6700–5500 cal yr BP), climate-human indicators were synchronous in distribution, suggesting lower pressure from climate change on population growth; however, this reversed from ca. 5500 cal yr BP, as intensive agriculture was required to meet shortages of natural resources during climate drying. Perhaps, the best evidence for adaptation is the increased abundance of Azolla from ca. 4000 years ago, a fern that favours growing in still-water bodies, hinting that much more irrigation was required at the time to sustain societal development.

Phytoplasmas in Poaceae species: a threat to the most important cereal crops in Europe

Phytoplasmas are phytopathogenic bacteria from the class Mollicutes. Cereal diseases caused by these microorganisms contribute to serious economic losses. Infected plants change the colour of their aboveground parts and are stunted. Bacteria also damage the root system and cause plant necrosis. The ears are deformed, which leads to sterility and reduced grain yield. The disease can cause on average about 50%, and in some cases up to 90% loss in yield. Wheat, oats and barley are susceptible to phytoplasmas from the ribosomal group 16SrI. Bacteria from ribosomal groups 16SrI and 16SrXII infect maize. Phytoplasmas are transmitted to cereals by insects, mainly species representing the Cicadellidae family, e.g. Psammottetix striatus (L.), Dalbulus maidis (DeLong & Wolcott), Macrosteles laevis (Ribaut) and the Cixiidae family e.g. Reptalus panzeri (Low). In addition, many studies have suggested that wild Poaceae plants may be a reservoir of phytoplasmas in the environment. The occurrence of diverse phytoplasmas in Poaceae species worldwide indicates an ongoing threat towards cereal crops in Europe.

Exploring the diversity of Poaceae-infecting mastreviruses on Reunion Island using a viral metagenomics-based approach

Mostly found in Africa and its surrounding islands, African streak viruses (AfSV) represent the largest group of known mastreviruses. Of the thirteen AfSV species that are known to infect either cultivated or wild Poaceae plant species, six have been identified on Reunion Island. To better characterize AfSV diversity on this island, we undertook a survey of a small agroecosystem using a new metagenomics-based approach involving rolling circle amplification with random PCR amplification tagging (RCA-RA-PCR), high-throughput sequencing (Illumina HiSeq) and the mastrevirus reads classification using phylogenetic placement. Mastreviruses that likely belong to three new species were discovered and full genome sequences of these were determined by Sanger sequencing. The geminivirus-focused metagenomics approach we applied in this study was useful in both the detection of known and novel mastreviruses. The results confirm that Reunion Island is indeed a hotspot of AfSV diversity and that many of the mastrevirus species have likely been introduced multiple times. Applying a similar approach in other natural and agricultural environments should yield sufficient detail on the composition and diversity of geminivirus communities to precipitate major advances in our understanding of the ecology and the evolutionary history of this important group of viruses.

Differential responses to phosphorus availability in the halophytes Aeluropus Littoralis, Catapodium rigidum, and Hordeum maritimum

ABSTRACTThe objective of this experiment was to explore the variability of response to phosphorus (P) availability in three fodder Poaceae species native of saline biotopes, Aeluropus littoralis, Catapodium rigidum, and Hordeum maritimum. The behavior of these wild species has been compared to that of a cultivated one, Hordeum vulgare. Plants were grown in plastic pots filled with inert sand. The experiment was carried out in a greenhouse with six P levels: 0, 5, 15, 60, 180, and 360 µM P concentration supplied as KH2PO4. Results showed that the growth of the four species is strongly affected by the low phosphorus availability in the medium. Furthermore, to reach 80% of their maximum yield expressed as shoot dry weight (DW), a soil phosphorus concentration of approximately 40 µM P concentration is sufficient for Hordeum maritimum, whereas approximately 66, 120, and 132 µM P concentration are needed for C. rigidum, A. littoralis, and Hordeum vulgare plants, respectively. Thus, our results showed that spontaneous species are more tolerant to P deficiency than cultivated barley. The relative performance of the three wild Poaceae species is likely related to their capacity to maintain higher P acquisition efficiency (PAE) under low P concentration conditions. These native Poaceae species may therefore represent genetic resources for the improvement of barley.

The aeropalynology of Es-Sénia airport, Oran, northwest Algeria

A continuous study of atmospheric pollen in Oran Province, northwest Algeria, using the Cour method was undertaken between April 2004 and April 2006. A pollen-collecting device was placed in the meteorological station at Es-Sénia airport, near Oran city. It was found that the pollen harvest during the first year was 4230 grains, which is significantly higher than that in the second year which produced 2258 grains. These data gave a mean annual index of 3246 pollen grains, 99.7% of which were positively identified. Pollen from herbaceous plants (69.5%) proved significantly more abundant than arboreal and shrub pollen (27.9 and 2.3% respectively). The pollen types identified, in decreasing order of abundance, were Chenopodiaceae/Amaranthaceae, Plantago, Olea, wild Poaceae, Lygeum, Cupressaceae, Urticaceae, Quercus, Pinus, total Asteraceae, Eucalyptus, Brassicaceae, Casuarina, Pistacia, Arecaceae, Apiaceae, Thymeleaceae and Rumex. The abundance range was Chenopodiaceae/Amaranthaceae (41.4%) to Rumex (0.6%). The winter pollen spectrum largely comprised Arecaceae and Cupressaceae. Pollination during spring included most taxa, i.e. total Asteraceae, Brassicaceae, Chenopodiaceae/Amaranthaceae, Lygeum, Olea, Pinus, Pistacia, Plantago, wild Poaceae, Quercus, Rumex and Urticaceae. During the summer Apiaceae and Eucalyptus both pollinated, and Casuarina pollen was largely produced in autumn. A significant correspondence between the airborne pollen spectrum and the vegetation of the region was established.

POLLEN AND SPORE DISTRIBUTION IN THE SURFACE SEDIMENTS OF THE NORTHERN SOUTH CHINA SEA AND THEIR TRANSPORTATION

45 pollen samples were collected from the surface sediments of the northern South China Sea,ranging from the continental shelf,the slope to the deep basin.The spatial distribution of pollen abundance indicates that the Pearl River may be the major transporter of pollen and spores to the sea.In general,pollen and spore concentrations decrease gradually with the distance from the Pearl River mouth.However,there is another relatively high value area to the east of Hainan Island,that is consistent with the assumption that nearby lands may be the major pollen source area,but rivers act as the most important carriers. Fern spores are obviously more than pollen grains,and also show a similar distribution pattern that the concentration decreases with distance from the Pearl River mouth.However,the percentage value increases with the distance from the shores.This pattern indicates that although inflow rivers may have carried most spores in,the dispersal ability of fern spores in the seawater is much better than that of pollen grains. Abundant Pinus pollen grains in the northern SCS probably came from the widely distributed Pinus massoniana in the inland areas of China.Other coniferous pollen was rarely found,while Podocarpus was well represented.Most common pollen taxa from subtropical and tropical broadleaved forests were dominated by evergreen Quercus and Castanopsis,of which pollen percentage was higher than that of other plants.Other subtropical and tropical tree pollen taxa were usually represented only by few pollen grains,indicating their low representation.Pollen of the widely distributed shrubs in the temperate regions was also not common.Phyllocladus pollen from Southeast Asia was frequently observed.Herb pollen,especially wild Poaceae and Cyperaceae,is common in the samples near the shore.

Genetic structure and clonal diversity of an introduced pest in Chile, the cereal aphid Sitobion avenae

In Chile, the aphid Sitobion avenae is of recent introduction, lives on cultivated and wild Poaceae, and is thought to reproduce by permanent parthenogenesis. In order to study the genetic variability and population structure of this species, five microsatellite loci were typed from individual aphids collected from different cultivated and wild host plants, from different geographical zones, and years. Chilean populations showed a high degree of heterozygosity and a low genetic variability across regions and years, with four predominant genotypes representing nearly 90% of the sample. This pattern of low clonal diversity and high heterozygosity was interpreted as the result of recent founder events from a few asexually reproducing genotypes. Most geographical and temporal variation observed in the genetic composition resulted from fluctuations of a few predominant clones. In addition, comparisons of the genotypes found in Chile with those described in earlier surveys of S. avenae populations in Western Europe led us to identify 'superclones' with large geographical distribution and high ecological success, and to make a preliminary exploration of the putative origin(s) of S. avenae individuals introduced to Chile.

Multivariate statistical and other approaches for the separation of cereal from wild Poaceae pollen using a large Holocene dataset

The separation of the pollen of wild Poaceae species from that of domesticated cereal crops is of considerable importance to palynologists studying Holocene vegetational and agricultural change. Studies of the characteristics of modern pollen populations indicate that it may be possible to distinguish cereal pollen from that of many (but not all) undomesticated Poaceae species, though there are few detailed investigations into the applicability of such studies to palaeoecological samples. This paper assesses the reliability of available keys for identifying sub-fossil grass pollen using a large Holocene dataset obtained from a series of well-dated profiles from lowland Yorkshire, England. Pollen within the dataset is classified using the keys of Andersen (Danmarks Geol Undersogelse, Arbog, 1978, 69–92, 1979) and Kuster (1988), and the resulting identifications are compared. The possibilities of combining the two approaches and employing the multivariate statistical techniques of principal component and discriminant analysis to achieve greater confidence of identification are then investigated. Finally, the findings of the above analyses are used to discuss the interpretation of incidences of large Poaceae pollen (i.e. >37 μm grain diameter as measured in silicone oil) within the palynological record, particularly during prehistory. The outcomes of this study will be of relevance to other investigations in which careful identification of large grass pollen is desirable, but where preservation or other factors prohibit accurate or confident identification of pollen surface pattern.

EFFECT OF HOST DEFENSE CHEMICALS ON CLONAL DISTRIBUTION AND PERFORMANCE OF DIFFERENT GENOTYPES OF THE CEREAL APHID Sitobion avenae

Five microsatellite loci were used to study the genetic variability and population structure of Sitobion avenae (Hemiptera: Aphididae) on some of its host plants. Individuals were collected in Chile from different cultivated and wild Poaceae. Forty-four multilocus genotypes were found among the 1052 aphids analyzed, of which four represented nearly 90% of the sample. No specialist genotypes were found, although some preferred hosts endowed with chemical defenses, i.e., hydroxamic acids (Hx), while others preferred comparatively undefended hosts. Performances of some predominant and some rare genotypes were evaluated on plants differing in their Hx levels. Significant differences in performance were found among clones, the two most common genotypes showing no differences in performance among all hosts tested, and the rare genotypes showing enhanced performance on the host with highest Hx level. A hypothesis is proposed whereby the appearance of rarer genotypes is in part related to the presence of Hx.

DIBOA in wild Poaceae: sources of resistance to the Russian wheat aphid (Diuraphis noxia) and the greenbug (Schizaphis graminum).

Hydroxamic acids are secondary metabolites typical of Poaceae that play a role in cereal resistance against pests and pathogens. The content of the hydroxamic acid aglucones DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one) and DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) was evaluated in wild Poaceae belonging to the tribes Triticeae (genera Hordeum and Elymus) and Aveneae (genera Deschampsia and Phalaris). The concentration of DIBOA in seedling extracts of the wild barleys Hordeum chilense, H. brevisubulatum subsp. violaceum and H. bulbosum was negatively correlated with parameters related to performance of the cereal aphids Schizaphis graminum and Diuraphis noxia. The relevance of the results obtained for breeding programs aimed at increasing cereal resistance against aphids is discussed.