Tetraploid Genotypes Research Articles

Insights Into the Genetic Basis of Blueberry Fruit-Related Traits Using Diploid and Polyploid Models in a GWAS Context

Abstract Polyploidization is an ancient and recurrent process in plant evolution, impacting the diversification of natural populations and plant breeding strategies. Polyploidization occurs in many important crops; however, its effects on inheritance of many agronomic traits are still poorly understood compared with diploid species. Higher levels of allelic dosage or more complex interactions between alleles could affect the phenotype expression. Hence, the present study aimed to dissect the genetic basis of fruit-related traits in autotetraploid blueberries and identify candidate genes affecting phenotypic variation. We performed a genome-wide association study (GWAS) assuming diploid and tetraploid inheritance, encompassing distinct models of gene action (additive, general, different orders of allelic interaction and the corresponding diploidized models). A total of 1,575 southern highbush blueberry individuals from a breeding population of 117 full-sib families were genotyped using sequence capture and next-generation sequencing, and evaluated for eight fruit-related traits. For the diploid allele calling, 77,496 SNPs were detected; while 80,591 SNPs were obtained in tetraploid, with a high degree of overlap (95%) between them. A linear mixed model that accounted for population and family structure was used for the GWAS analyses. By modeling tetraploid genotypes, we detected 15 SNPs significantly associated with five fruit-related traits. Alternatively, seven significant SNPs were detected for only two traits using diploid genotypes, with two SNPs overlapping with the tetraploid scenario. Our results showed that the importance of tetraploid models varied by trait and that the use of diploid models has hindered the detection of SNP-trait associations and, consequently, the genetic architecture of some commercially important traits in autotetraploid species. Furthermore, 14 SNPs co-localized with candidate genes, five of which lead to non-synonymous amino acid changes. The potential functional significance of these SNPs is discussed.

Ploidy and DNA content of cape gooseberry populations grown in southern Brazil

Studies detected chromosomal variability in genotypes of Physalis peruviana L. cultivated in Andean countries, with the existence of diploid and tetraploid genotypes and other variations. Knowledge...

Exploring the metabolic variation between domesticated and wild tetraploid wheat genotypes in response to corn leaf aphid infestation

ABSTRACTInfestation of Triticum (wheat) plants by their pest Rhopalosiphum maidis (corn leaf aphid) causes severe vegetative damage. Despite the agro-economic importance of wheat, the metabolic diversity of Triticum turgidum (tetraploid wheat) in response to aphid attack has not been sufficiently addressed. In this study, we compared the metabolic diversity of two tetraploid wheat genotypes, domesticated and wild emmer. The plants were grown in a control growth room and infested with aphids for 96 h. Our untargeted metabolic analysis performed on plants with and without aphids revealed massive differences between the two genotypes. The targeted metabolic analysis highlighted the differences in the biosynthesis of phytohormones. The aphid progeny was lower in the cultivated durum wheat than in the wild emmer wheat. Overall, these observations emphasize the potential of using the natural diversity of wheat species to better understand the metabolic responses to pest damage.

Morpho-phenology and chromosome number of Iranian Bromus danthoniae Trin. genotypes

ABSTRACT- Bromus danthoniae Trin. is an annual grass species which grows mainly on dry grassy rocky mountain slopes and grassy steppe, and is grazed by many herbivores and recognized as a useful pasture plant. The chromosome number, morphological and anatomical traits of 82 genotypes of B. danthoniae belonging to three sub-taxa were investigated. Twenty-seven quantitative and 20 qualitative morphological traits were evaluated. The results of analysis of variance showed that B. danthoniae genotypes varied significantly for all quantitatively tested traits. Based on cluster analysis, the genotypes were divided into four groups which mostly corresponded to their subspecies identities. According to correlation analysis, lemma length had strong positive correlations with other traits such as awn length (r=0.55**), lemma width (r=0.72**) and caryopsis length (r=0.84**). In addition, lemma width was significantly correlated with the traits like floret number per spikelet (r=0.47**) and caryopsis length (r=0.58**). Based on factor analysis, the first three factors encompass about 51% of total variation. Overall, lemma length and lemma width were the two reliable traits for morphological investigations in this species. The results of chromosome counting showed that B. danthoniae subsp. danthoniae and B. danthoniae var.lanuginusos Roshev. were diploid (2n=2x=14) whereas B. danthoniae subsp. pseudodanthoniae (Drobov) H. Scholz was tetraploid (2n=4x=28). The results of leaf surface anatomy showed that tetraploid genotypes had larger stomata but lower stomatal density than the diploid ones, thus a comprehensive relationship between genome size and guard cell size cannot be ruled out as a plausible explanation for differentiating the ploidy levels. The high morphological variations among the B. danthoniae genotypes explain the habitat distribution of this species and enable us to incorporate this knowledge into practice by exploiting the variation for improvement of pasture production.

Maximization of Markers Linked in Coupling for Tetraploid Potatoes via Monoparental Haploids

Haploid potato populations derived from a single tetraploid donor constitute an efficient strategy to analyze markers segregating from a single donor genotype. Analysis of marker segregation in populations derived from crosses between polysomic tetraploids is complicated by a maximum of eight segregating alleles, multiple dosages of the markers and problems related to linkage analysis of marker segregation in repulsion. Here, we present data on two monoparental haploid populations generated by prickle pollination of two tetraploid cultivars with Solanum phureja and genotyped with the 12.8 k SolCAP single nucleotide polymorphism (SNP) array. We show that in a population of monoparental haploids, the number of biallelic SNP markers segregating in linkage to loci from the tetraploid donor genotype is much larger than in putative crosses of this genotype to a diverse selection of 125 tetraploid cultivars. Although this strategy is more laborious than conventional breeding, the generation of haploid progeny for efficient marker analysis is straightforward if morphological markers and flow cytometry are utilized to select true haploid progeny. The level of introgressed fragments from S. phureja, the haploid inducer, is very low, supporting its suitability for genetic analysis. Mapping with single-dose markers allowed the analysis of quantitative trait loci (QTL) for four phenotypic traits.

Adventitious shoot regeneration from in vitro leaves of Aronia mitschurinii and cotyledons of closely related Pyrinae taxa

The objective of this study was to develop an in vitro shoot regeneration procedure and to evaluate the frequency of adventitious shoot regeneration from: (1) in vitro leaves of a commercial cultivar of Aronia mitschurinii on various media treatments; (2) cotyledons of closely related Pyrinae taxa; and (3) 21 wild Aronia genotypes. Optimum regeneration of leaf explants occurred when they were wounded with two transverse cuts along the midrib and placed on Murashige and Skoog (MS) basal media containing 5 μM indole-3-butyric acid (IBA) and 10 μM thidiazuron (TDZ). TDZ was more effective than 6-benzylaminopurine (BAP) as a cytokinin, and IBA was more effective than the no auxin control, 2,4-dichlorophenoxyacetic acid (2,4-D) and 1-naphthaleneacetic acid (NAA). Regeneration from cotyledons of seven Pyrinae taxa was evaluated using 10 μM BAP in combination with 0.1, 1 and 5 μM NAA. Adventitious shoot formation for A. melanocarpa and P. communis responded best to 1 μM NAA, whereas all other taxa formed a greater number of adventitious shoots on 5 μM NAA. A. mitschurinii cotyledon explants produced a significantly greater number of shoots compared with in vitro leaf explants. The number of shoots forming per cotyledon explant and the percent of explants forming shoots were both significantly different among the 21 Aronia genotypes. Significant differences were observed between the six Aronia taxonomic groups for the number of shoots forming per explant. Diploid and tetraploid Aronia genotypes produced a significantly greater number of shoots per explant than did triploid genotypes. Regenerated shoots were rooted in vitro and plants grew normally in the greenhouse. These results will be useful for future studies using leaf and cotyledon explants for genetic transformation, genome editing and mutation breeding with Aronia and related taxa.

Accumulation of Phenolic Compounds at the Initial Steps of Ontogenesis of Fagopyrum esculentum Plants That Differ in Their Ploidy Levels

Plants of buckwheat Fagopyrum esculentum possessing diploid and tetraploid genotypes were studied at the initial ontogenetic stages. They were compared in their morphophysiological characteristics, accumulation of phenolic compounds (including their main classes—phenylpropanoids and flavonoids), and activity of L-phenylalanine ammonia-lyase. An apparent resemblance in morphophysiological characteristics of seedlings was found between the two specimens, but diploid plants tended to faster linear growth than tetraploid ones. Differences in the accumulation of phenolic compounds in the hypocotyl and cotyledonous leaves were revealed. In most cases, in the course of seedling growth, the changes in phenylalanine ammonialyase activity did not correlate with the changes in the levels of these secondary metabolites. The effects of gene dosage were established towards accumulation of phenylpropanoids and anthocyanins in hypocotyls of seedlings and flavonoid accumulation in cotyledonous leaves. It is concluded that buckwheat seedlings with a tetraploid genotype have higher capacity than diploid seedlings for biosynthesis of phenolics.

Widening the Gene Pool of Sexual Tetraploid Bahiagrass: Generation and Reproductive Characterization of a Sexual Synthetic Tetraploid Population

The improvement of bahiagrass, Paspalum notatum Flüggé, has been inhibited by reduced levels of genetic diversity in sexual tetraploid germplasm. A few experimental sexual tetraploid genotypes (ESTGs) have been generated by chromosome doubling, but these plants typically exhibit low vigor. The objectives of this work were to generate and characterize the ploidy level, mode of reproduction, and fertility of a novel 308 individual sexual synthetic tetraploid population (SSTP) developed by intercrossing 29 sexual F1 hybrids originated by hybridizing several naturally occurring apomictic tetraploids from diverse origin with a few ESTGs. Ploidy levels were determined using flow cytometry, and reproductive modes were evaluated by a molecular assay with apospory‐linked markers and embryo sac observations. The tetraploid level and the sexual mode of reproduction remained stable after two cycles of recombination during the generation of the SSTP. Fertility was evaluated based on seed set under self‐ and open pollination during 3 yr. The SSTP exhibited in average 30.2 and 15.2% seed set under open and self‐pollination, respectively, showing a predominantly cross‐pollination behavior with variable levels of self‐fertility. There were no differences in terms of fertility between the SSTP and the ESTG. The novel tetraploid population behaves as sexual and cross‐pollinated, and it is expected to allow a more efficient genetic improvement under the proposed breeding approaches.

Hybridization of Cultivated Highbush Blueberry with Vaccinium stamineum: Phenotype and Fertility of Backcross1 Populations

Nine F1 hybrids produced by crossing seven tetraploid highbush blueberry cultivars with three tetraploid Vaccinium stamineum genotypes were backcrossed to an array of highbush blueberry cultivars to produce 2500 Backcross1 (BC1) seedlings. Thirty of the most vigorous BC1 plants were intercrossed in a greenhouse. Fertility of the BC1 plants was studied by examining their pollen at 250× and by determining the number of well-developed seeds per pollinated flower after the crosses. Percent well-formed microspores averaged 62.7% for BC1 plants compared with 30.9% for their F1 hybrid parents. Fruit set percentage was high from the BC1 intercrosses, with an average of 9.29 plump seeds per pollinated flower. The 2500 BC1 seedlings in the field were highly variable in vigor, but fewer than 10% were as vigorous as the median vigor of highbush × highbush seedlings. BC1 plants in the field averaged ≈1 month later ripening than highbush × highbush seedlings and berries averaged slightly smaller. Berry clusters were very loose compared with those of highbush. Berry flavor was highly variable from plant to plant, but the berries averaged less sweet and lower in acid than highbush berries. New flavor components not found in highbush seedlings were found in only a few BC1 seedlings. Fresh berries from BC1 plants made bright red juice when crushed in water, whereas berries from most highbush cultivars produced brown to yellow juice/water mixes. Although berry quality in the BC1 population averaged lower than in highbush seedlings, some plants had berry quality as high as typical cultivars. Because V. stamineum is highly drought-tolerant, cultivars bred using V. stamineum introgression could have improved upland adaptation.

Evaluation of resistance to Blumeria graminis (DC.) f. sp. avenae, in Avena murphyi and A. magna genotypes

Powdery mildew is one of the main factors reducing oat yield quality and quantity. New sources of resistance are needed in many breeding programs. The most effective sources of resistance to fungal diseases in cereals have often been found in lower-ploidy species. Thus, tetraploid species could be valuable source of resistance to powdery mildew. The aim of the present study was to identify resistance among tetraploid genotypes that could be used in breeding programmes to increase the level of resistance to powdery mildew in oat. Sixty two Avena magna and 17 A. murphyi accessions were tested and all showed high level of resistance to oat powdery mildew. None of the accessions were completely susceptible to the tested pathogen isolates. Twelve A. magna and six A. murphyi accessions were resistant to all five isolates of the powdery mildew pathogen tested. The rest of the accessions showed a resistant or an intermediate response. The results of the present study show that there are several unexplored resistance sources among A. magna and A. murphyi. Because of the genomic similarity of tetraploid species to hexaploid oats the introduction of the new resistance sources in cultivated oats is promising.

Intraspecific tetraploid hybrids of Paspalum notatum: agronomic evaluation of segregating progeny

For many decades, animal production in southern Brazil has been based on native forage grasses. Paspalum notatum Flugge (bahiagrass) is one of the most frequently used native grass in southern Brazil. The native germplasm of P. notatum is tetraploid and displays apomictic reproduction; hence, chromosome doubling of sexual diploid accessions is required to facilitate hybridization. The main goal of this study was to evaluate forage production and other agronomical evaluation of P. notatum intraspecific hybrids in order to obtain new varieties that could be registered and/or protected and launched as new cultivars in the future. Three tetraploid sexual genotypes were crossed with the ecotypes Bagual and Andre da Rocha. Biomass production (leaf, stem, and inflorescence fractions), plant growth habit, plant height, number of tillers, and frost damage were evaluated in the resulting hybrids. The general combining ability (GCA) and specific combining ability (SCA) were calculated for the six families generated. We evaluated 196 hybrids and the most productive yielded 42 % more total dry mass than the most productive parent (ecotype Bagual), and Bagual production was seven-fold higher than that of cultivar ‘Pensacola’. The highest GCA values were observed for Bagual and Q4205. No correlation was observed between leaf coloration and the frost effect or regrowth in the following winter. Similarly, no correlation between plant growth habit and dry mass production was observed. The reproduction mode of the most productive hybrids are currently being analyzed in larger plots to identify apomictic and sexual genotypes for future registration and protection.

Modern hexaploid wheat differs from diploid and tetraploid ancestors in the importance of stress tolerance versus stress avoidance

Combined high temperature and weak radiation stress negatively influences wheat production. However, related eco-physiological mechanisms across wheat species of different genetic backgrounds are not well documented. A pot-culture experiment was conducted in growth chambers to analyse the prevailing strategies of wheat genotypes with different ploidy levels under combined high temperature and weak radiation (30°C−25°C, 200 µmol m−2 s−1 photosynthetically active radiation (PAR)) stress compared with normal growth conditions (20°C−15°C; 400 µmol m−2 s−1 PAR). The diploid and tetraploid wheat genotypes showed better avoidance ability to high temperature and weak radiation stress than the hexaploids. These diploids and tetraploids produced high vegetative biomass under control conditions but this was reduced substantially under the stress. The adaptive response to avoid the stress was a strong reduction in vegetative organs, mainly leaf area. Consequently, these genotypes produced lower yields. By contrast, modern hexaploid wheat varieties displayed a stronger tolerance to the stress and produced higher yields through greater green leaf area, higher relative leaf water content, and higher proline and soluble sugar contents. The relative importance of these tolerance and avoidance strategies was estimated to account for 60% and 22%, respectively, of the variations in grain yield. Our study demonstrated that modern hexaploid wheat has acquired a greater proportion of tolerance rather than avoidance strategy in response to high temperature and weak radiation stress.

Molecular and biochemical characterization of a potato collection with contrasting tuber carotenoid content

After wheat and rice, potato is the third most important staple food worldwide. A collection of ten tetraploid (Solanum tuberosum) and diploid (S. phureja and S. chacoense) genotypes with contrasting carotenoid content was subjected to molecular characterization with respect to candidate carotenoid loci and metabolic profiling using LC-HRMS. Irrespective of ploidy and taxonomy, tubers of these genotypes fell into three groups: yellow-fleshed, characterized by high levels of epoxy-xanthophylls and xanthophyll esters and by the presence of at least one copy of a dominant allele of the β-Carotene Hydroxylase 2 (CHY2) gene; white-fleshed, characterized by low carotenoid levels and by the presence of recessive chy2 alleles; and orange-fleshed, characterized by high levels of zeaxanthin but low levels of xanthophyll esters, and homozygosity for a Zeaxanthin Epoxidase (ZEP) recessive allele. Novel CHY2 and ZEP alleles were identified in the collection. Multivariate analysis identified several groups of co-regulated non-polar compounds, and resulted in the grouping of the genotypes according to flesh color, suggesting that extensive cross-talk exists between the carotenoid pathway and other metabolite pathways in tubers. Postharvest traits like tuber dormancy and weight loss during storage showed little correlation with tuber carotenoid content, with the exception of zeaxanthin and its esters. Other tuber metabolites, such as glucose, monogalactosyldiacyglycerol (a glycolipid), or suberin precursors, showed instead significant correlations with both traits.

Use of genotyping-by-sequencing to determine the genetic structure in the medicinal plant chamomile, and to identify flowering time and alpha-bisabolol associated SNP-loci by genome-wide association mapping

BackgroundChamomile (Matricaria recutita L.) has a long history of use in herbal medicine with various applications, and the flower heads contain numerous secondary metabolites which are medicinally active.In the major crop plants, next generation sequencing (NGS) approaches are intensely applied to exploit genetic resources, to develop genomic resources and to enhance breeding. Here, genotyping-by-sequencing (GBS) has been used in the non-model medicinal plant chamomile to evaluate the genetic structure of the cultivated varieties/populations, and to perform genome wide association study (GWAS) focusing on genes with large effect on flowering time and the medicinally important alpha-bisabolol content.ResultsGBS analysis allowed the identification of 6495 high-quality SNP-markers in our panel of 91 M. recutita plants from 33 origins (2–4 genotypes each) and 4 M. discoidea plants as outgroup, grown in the greenhouse in Gatersleben, Germany. M. recutita proved to be clearly distinct from the outgroup, as was demonstrated by different cluster and principal coordinate analyses using the SNP-markers. Chamomile genotypes from the same origin were mostly genetically similar. Model-based cluster analysis revealed one large group of tetraploid genotypes with low genetic differentiation including 39 plants from 14 origins. Tetraploids tended to display lower genetic diversity than diploids, probably reflecting their origin by artificial polyploidisation from only a limited set of genetic backgrounds.Analyses of flowering time demonstrated that diploids generally flowered earlier than tetraploids, and the analysis of alpha-bisabolol identified several tetraploid genotypes with a high content. GWAS identified highly significant (P < 0.01) SNPs for flowering time (9) and alpha-bisabolol (71). One sequence harbouring SNPs associated with flowering time was described to play a role in self-pollination in Arabidopsis thaliana, whereas four sequences harbouring SNPs associated with alpha-bisabolol were identified to be involved in plant biotic and abiotic stress response in various plants species.ConclusionsThe first genomic resource for future applications to enhance breeding in chamomile was created, andanalyses of diversity will facilitate the exploitation of these genetic resources. The GWAS data pave the way for future research towards the genetics underlying important traits in chamomile, the identification of marker-trait associations, and development of reliable markers for practical breeding.

Hybridization and heterosis in the Plicatula group of Paspalum

Most forage cultivars released for the genus Paspalum belong to a section named Plicatula. The species of Plicatula are mostly apomictic and consequently the genetic diversity is locked for their genetic improvement. The objectives were to evaluate the crossability, hybrid fertility, heterosis, and genetic distances between apomictic accessions and a sexual genotype of species of Plicatula group of Paspalum. Crosses were made using 22 apomictic tetraploid accessions belonging to 12 different species as pollen donors, and a sexual tetraploid genotype induced by colchicine from a sexual diploid accession of P. plicatulum. Crossability varied between 0 and 16% among crosses. Viable hybrid offspring were recovered from 15 out of 22 crosses. The most successful crosses involved P. guenoarum, P. plicatulum, P. chaseanum, and P. oteroi. Fertility of the sampled hybrids varied between 1.6% for the cross involving P. lenticulare, and 40.1% for an intraspecific cross (P. plicatulum, accession Hojs388). The genetic distance between parents was estimated using amplified fragment-length polymorphism, and it varied between 0.34 and 0.53. There was no correlation between genetic distances and crossability or fertility of the hybrids. Hybrids from the most numerous families were classified for mode of reproduction using flow cytometric seed analysis. The ratio between sexual and apomictic hybrids varied between 0.6:1 and 1.6:1. A selected group of apomictic hybrids were evaluated for several agronomic traits in the field. Heterosis was observed for frost tolerance and cattle preference. The results indicated that gene transfer via hybridization is possible among several species of Plicatula. Superior hybrids for specific traits can be generated and fixed by apomixis.

Genetic Characterisation and Diversity Assessment of Potato Genotypes Using SSR Markers

Information on diversity of genetic materials is vital for choosing parents in a breeding program. The objective of the study was to determine the pattern and level of genetic diversity among the selected 20 tetraploid potato genotypes using 16 SSR markers to identify suitable parents for breeding purposes. The microsatellites showed considerable variation among genotypes and sixty four alleles were amplified by the 16 primer pairs. The number of polymorphic alleles per locus ranged from 2 to 8 with an average of 3.9. The highest number of null alleles was observed was six for genotype Nakpot1. The overall size of the amplified product varied from 48 bp (marker STI0023) to 309 bp (marker STM5121). PIC values ranged from 0.0948 to 0.7832, with an average of 0.4307 per locus. Heterozygosity values ranged from 0.0997 to 0.805 with an average of 0.466919. Significant positive linear correlations were observed between PIC values and number of alleles (r = 0.905); and heterozygosity and number of alleles (r = 0.8659) at p &lt; 0.001. Cluster analysis separated the genotypes into three different groups. The genetic distance between clones ranged from 1 to 5.7. Cruza had the highest genetic distance while the shortest genetic distance was observed between 396026.103 and 396034.104. The microsatellites used in this study provided useful information regarding the variability of the tested genotypes and their selection for breeding purposes.

Interspecific hybridization in Sarcococca supported by analysis of ploidy level, genome size and genetic relationships

Knowledge of ploidy level differences, genome size and genetic relationships between species facilitates interspecific hybridization in ornamentals. For Sarcococca (Buxaceae) only limited (cyto)genetic information is available. The aim of this study was to determine the genome size and chromosome number and to unravel the genetic relationships of a breeder’s collection using AFLP marker analysis. Based on these results, interspecific crosses were made and the efficiency and hybrid status was verified. Two groups of diploid plants (2n = 2x = 24) were observed, with either a genome size of 4.11–4.20 or 7.25–9.63 pg/2C. All the tetraploid genotypes (2n = 4x = 48) had genome sizes ranging from 7.91 to 8.18 pg/2C. In crosses between parents with equal ploidy level and genome size a higher crossing efficiency (on average 58% of the hybridizations resulting in fruits) and more true hybrids (on average 96% of the offspring) were obtained compared to crosses between plants with different genome size and ploidy level (on average 23% fruits and 24% hybrids, respectively). In none of the cross combinations, the ploidy level or genome size was found to be a complete hybridization barrier, although unilateral incongruity was found in some cross combinations. Distant genetic relationships did not hamper the hybridization within Sarcococca genotypes. Our findings will contribute to a more efficient breeding program and a faster achievement of hybrids with an added value.

Species Delimitation in Tetraploid, Apomictic Amelanchier (Rosaceae)

Diversification in Amelanchier tetraploid apomicts differs from that of diploid sexuals and produces groups that are taxonomically difficult. Apomixis facilitates expansion of ecologically successful genotypes into numerous, narrowly distributed, and often minimally distinct microspecies. Residual sexuality in tetraploids creates hybrid swarms and intergradation of taxa. This gene flow is evident in DNA sequences from nuclear and chloroplast regions that record mostly allotetraploid, convoluted histories. Ongoing apomixis in successful tetraploid genotypes fosters their expansion into geographically widespread phenotypic clusters.We delimit such clusters as species and deny species status to microspecies.We demonstrate polyploid complexity and our approach to species delimitation in three taxa of Amelanchier. The tetraploid microspecies A. “rubra” of southeastern Maine, while morphologically distinct, hybridizes with sympatric congeners. Eastern North American A. bartramiana contains diploids and polyploids (tetraploids and a few triploids) that are sometimes morphologically semi-cryptic. We group all ploidy levels in the A. bartramiana agamic complex and recognize as a species the diploid (A. bartramiana). The tetraploid is not given species status because it intergrades extensively with tetraploid congeners, as exemplified by the nothospecies named here, A. ×neglecta. Western North American A. cusickii is tetraploid, mostly distinct morphologically and ecologically, distinct genetically, and merits species status.

Perennial Ryegrass Yield Performance under Abiotic Stress

Breeding of perennial ryegrass (Lolium perenne L.) for forage is mainly aimed at increase in herbage yield. However, abiotic stresses such as drought and winterkill threaten persistence and ability to produce stable aerial biomass of the plant. Field experiments, performed under natural conditions, rather than dissection of abiotic stress factors under artificial or semiartificial conditions, offers opportunity to evaluate the effect of complex of abiotic stresses on the plant performance. The aim of this study was to evaluate the relationship between dry matter yield and tolerance to winter kill and drought of perennial ryegrass ecotypes and cultivars differing in their ploidy level during a 2‐yr period. The field experiment was located in Akademija, Lithuania (55°40′ N, 23°87′ E) in 2015 and 2016. The germplasm consisted of 128 diploid and 25 tetraploid perennial ryegrass populations. Winterkill, spring growth and regrowth after cuts, drought damage, and dry matter yield were assessed. Short periods of lower than −10°C temperatures with slim snow cover determined low damages of the perennial ryegrass after winters. Medium correlation was estimated between drought damages and dry matter yield. Tetraploid genotypes of perennial ryegrass demonstrated higher tolerance to cold and drought stress conditions, better spring growth and regrowth after cuts, and higher dry matter yield.

Morphological and physiological responses of different wheat genotypes to chilling stress: a cue to explain yield loss.

The eco-physiological mechanism of wheat yield loss resulting from chilling stress is a fundamental scientific issue. However, previous studies have focused on hexaploid wheats, and few studies on the morphological and physiological plasticity of wheat plants. Six different wheat genotypes were tested under chilling stress to investigate the physio-morphological parameters as well as the loss of grain yield in growth chambers. Chilling stress resulted in significant loss in grain yield in all genotypes. Under chilling stress, diploid wheats generated zero harvest, and tetraploid genotypes also suffered from a pronounced loss in grain yield, compared with the control group. In contrast, hexaploid genotypes acquired relatively high maintenance rate of grain yield among three species. Diploid and tetraploid wheat genotypes maintained relatively large leaf area and high photosynthetic rates, but they were subjected to significant declines in vascular bundle number and productive tillers as a consequence of the inhibition by sink growth under chilling stress. The hexaploid wheats were found to have relatively low leaf area and photosynthetic rates. These genotypes also stored more soluble carbohydrates and exhibited stronger sink enhancement, ensuring the translocation and redistribution of assimilates. Our findings provided a new theoretical understanding of yield stabilization in the domestication process of wheat genotypes under chilling stress. © 2017 Her Majesty the Queen in Right of Canada. Journal of The Science of Food and Agriculture © 2017 Society of Chemical Industry.