Seedling Resistance Research Articles

Drought Resistance and Heavy Metal Adsorption Capacity of Mulberry in Alpine Regions

Mulberry is an important perennial economic crop. It is the pursuit of modern mulberry breeders to continuously improve the drought resistance and heavy metal adsorption capacity of mulberry varieties. In this paper, three excellent mulberry varieties were introduced and cultivated in the alpine region, and the drought resistance of mulberry seedlings under different drought degrees and different days of drought was analysed. The root powder of mulberry seedlings was ground and dissolved by combining physical and chemical methods. The heavy metal ions are taken as an example. The heavy metal adsorption capacity of the root powder of mulberry seedlings under different initial ion concentrations and different pH values is analysed. The experimental results show that the drought resistance of different varieties is different. The concentration of heavy metal ions and pH value can only be achieved.

Quantitative Inheritance of Sclerotinia Stem Rot Resistance in Brassica napus and Relationship to Cotyledon and Leaf Resistances

Sclerotinia sclerotiorum is a necrotrophic fungus causing devastating stem rot and associated yield losses of canola/rapeseed (Brassica napus) worldwide, including in Australia. Developing host resistance against Sclerotinia stem rot is critical if this disease in canola/rapeseed is to be successfully managed, as cultural or chemical control options provide only partial or sporadic control. Three B. napus breeding populations, C2, C5 and C6, including the parents, F1, F2, BC1P1, and BC2P2, were used in a field study with an objective of exploring the inheritance pattern of disease resistance (based on stem lesion length [SLL]) and the genetic relationships of disease with stem diameter (SD) or days to first flowering (DTF), and to compare these new adult plant stem resistances against S. sclerotiorum with those of seedling (cotyledon and leaf) resistances in earlier studies. Heritability (broad sense) of SLL was 0.57 and 0.73 for population C2 at 3 and 5 weeks postinoculation and 0.21 for population C5 at 5weeks postinoculation. Additive genetic variance was evident within all 3 populations for DTF but not for SD. Narrow-sense heritability for DTF was 0.48 (C2), 0.42 (C5), and 0.32 (C6). SD, DTF, and SLL were all inherited independently, with no significant genetic covariance between traits in bivariate analysis. Genetic variance for SLL in populations C2 and C5 was entirely nonadditive, and there was significant nonadditive genetic covariance of SLL at 3 and 5 weeks postinoculation. Generation means analysis in population C2 supported the conclusion that complex epistatic interactions controlled SLL. Several C2 and C5 progeny showed high adult plant stem resistance, which may be critical in developing enhanced stem resistance in canola/rapeseed. Although population C6 showed no genetic variation for SLL resistance in this study, it showed significant nonadditive genetic variance at the cotyledon and leaf stages in earlier studies. We conclude that host resistance varies across different plant growth stages, and breeding must be targeted for resistance at each growth stage. In populations C2, C5, and C6, resistance to S. sclerotiorum in stem, leaf, and cotyledon was always controlled by nonadditive effects such as complex epistasis or dominance. Overall, our findings in relation to the quantitative inheritance of Sclerotinia stem rot resistance, together with the new high-level resistances identified, will enable breeders to select/develop genotypes with enhanced resistances to S.sclerotiorum.

Cross-adaptation of wheat seedlings in hyperthermia and infection with Bipolaris sorokiniana Shoem

The article presents the results of studies of adaptive reactions of 10-day-old seedlings of wheat varieties Novosibirskaya 18, Novosibirskaya 44, Sibirskaya 21 and Omskaya 18 under combined stress. It was found that the preliminary hyperthermia of the seeds increased the resistance of seedlings by the type of cross-adaptation to the subsequent action of B. sorokiniana (decrease in EC to 71,9 %, DI to 29,7 %, inhibition of biomass accumulation and growth to 95,4 %). The varietal specificity of the formation of adaptive reactions under the combined action of stressors was revealed. The protective effect of hyperthermia is most pronounced in the varieties Novosibirskaya 18 and Omskaya 18.

Screening of Some Ethiopian Wheat Lines Against Stem Rust Races at Seedling Stage

In Ethiopia, stem rust caused by Puccinia graminis f. sp. tritici (Pgt) is one of the most serious wheat diseases. On vulnerable cultivars, it has the ability to cause yield losses of up to 100%. The infection responses of forty-two wheat lines at the seedling stage against eleven isolates of stem rust race TTKSK (Ug99 race), TTRTF, TKTTF (Digalu race), JRCQC, TKKTF, TRTTF, TTTTF, TTKTF, TTKTT, RRTTF, and TKPTF were evaluated in a study. Wheat lines were experimentally infected with urediniospores of the races under controlled conditions at Ambo Plant Protection Research Center in 2021. Against the Pgt races that were examined, different seedling resistance responses were seen. Thirteen wheat lines, WL-1, WL-4, WL-21, WL-35, WL-37, WL-38, WL-41, WL-43, WL-45, WL-48, WL-49, WL-61, WL-64, had low infection types against all races, whereas six wheat lines, WL-26, WL-31, WL-33, WL-47, WL-51, and WL-66, had the resistant wheat lines discovered in this study can be exploited as a source of resistant genes for breeding program.

Evaluation of the source material for the selection of Siberian millet in the conditions of the Lower Volga region

Methods for early diagnosis of drought tolerance in leguminous crops, based on the screening of physiological indices of resistance to stress, are of great importance for the acceler-ated selection of drought tolerant soybean lines. On the basis of the Volga NIISS, laboratory exper-iments were carried out to assess the physiological and biochemical parameters of drought re-sistance of seedlings of promising soybean samples under conditions of osmotic stress. As a result of studying the indicators of seed germination in a sucrose solution and morphophysiological assessment of seedlings of soybean varieties, samples with a high starting growth rate were identified - 156/2014, D-150 and variety Yuzhanka. A strong direct relationship was established between the indices of seed germination on sucrose solution and the index of root length (r = 0.98), between the index of root length and the dynamics of accumulation of free proline under the influence of a stress factor (r = 0.76). According to a comprehensive assessment of the studied samples, it was found that the greatest decrease in growth processes and the smallest accumulation of free proline were noted in samples VNIIOZ-796/11 and Velichava / 2009. Samples D-150, 156/2014 and variety Yu-zhanka were identified as the most drought-resistant.

Evaluation of prospective soybean samples by physiological and biochemical signs of dry resistance

Methods for early diagnosis of drought tolerance in leguminous crops, based on the screening of physiological indices of resistance to stress, are of great importance for the accelerated selection of drought tolerant soybean lines. On the basis of the Volga NIISS, laboratory experiments were carried out to assess the physiological and biochemical parameters of drought re-sistance of seedlings of promising soybean samples under conditions of osmotic stress. As a result of studying the indicators of seed germination in a sucrose solution and morphophysiological assessment of seedlings of soybean varieties, samples with a high starting growth rate were identified - 156/2014, D-150 and variety Yuzhanka. A strong direct relationship was established between the indices of seed germination on sucrose solution and the index of root length (r = 0.98), between the index of root length and the dynamics of accumulation of free proline under the influence of a stress factor (r = 0.76). According to a comprehensive assessment of the studied samples, it was found that the greatest decrease in growth processes and the smallest accumulation of free proline were noted in samples VNIIOZ-796/11 and Velichava / 2009. Samples D-150, 156/2014 and variety Yuzhanka were identified as the most drought-resistant.

The GmXTH1 gene improves drought stress resistance of soybean seedlings.

In order to study the role of GmXTH1 gene in alleviating drought stress, soybean seeds with GmXTH1 gene were transferred by T4 treated with PEG6000 concentration of 0%, 5%, 10%, and 15% respectively. The germination potential, germination rate, germination index, and other indicators were measured. The results showed that the germination potential, germination rate, and germination index of OEA1 and OEA2 strains overexpressed in T4 generation were significantly higher than those of the control material M18. After 0-day, 7-day, and 15-day drought stress, the analysis of seedling phenotypes and root-shoot of different T4 generation transgenic soybean lines showed that under stress conditions, the growth of GmXTH1 overexpression material was generally better than that of the control material M18. The growth of GmXTH1 interference expression material was generally worse than that of the control material M18, with significant differences in plant phenotypes. The root system of GmXTH1 overexpressed material was significantly developed compared with that of the control material M18. The analysis of physiological and biochemical indexes showed that the relative water content and the activity of antioxidant enzymes (superoxide dismutase and peroxidase) of GmXTH1 transgenic soybean material were significantly higher than those of the control material M18, and the accumulation of malondialdehyde was lower under the same stress conditions at seedling stage. Fluorescence quantitative PCR assay showed that the relative expression of GmXTH1 gene in transgenic soybean was significantly increased after drought stress. The results showed that the overexpression of GmXTH1 could increase the total root length, surface area, total projection area, root volume, average diameter, total cross number, and total root tip number, thereby increasing the water intake and reducing the transpiration of water content in leaves, thus reducing the accumulation of MDA and producing more protective enzymes in a more effective and prompt way, reducing cell membrane damage to improve drought resistance of soybean.

Identification of Quantitative Trait Loci for Leaf Rust and Stem Rust Seedling Resistance in Bread Wheat Using a Genome-Wide Association Study.

In recent years, leaf rust (LR) and stem rust (SR) have become a serious threat to bread wheat production in Kazakhstan. Most local cultivars are susceptible to these rusts, which has affected their yield and quality. The development of new cultivars with high productivity and LR and SR disease resistance, including using marker-assisted selection, is becoming an important priority in local breeding projects. Therefore, the search for key genetic factors controlling resistance in all plant stages, including the seedling stage, is of great significance. In this work, we applied a genome-wide association study (GWAS) approach using 212 local bread wheat accessions that were phenotyped for resistance to specific races of Puccinia triticina Eriks. (Pt) and Puccinia graminis f. sp. tritici (Pgt) at the seedling stages. The collection was genotyped using a 20 K Illumina iSelect SNP assay, and 11,150 polymorphic SNP markers were selected for the association mapping. Using a mixed linear model, we identified 11 quantitative trait loci (QTLs) for five out of six specific races of Pt and Pgt. The comparison of the results from this GWAS with those from previously published work showed that nine out of eleven QTLs for LR and SR resistance had been previously reported in a GWAS study at the adult plant stages of wheat growth. Therefore, it was assumed that these nine common identified QTLs were effective for all-stage resistance to LR and SR, and the two other QTLs appear to be novel QTLs. In addition, five out of these nine QTLs that had been identified earlier were found to be associated with yield components, suggesting that they may directly influence the field performance of bread wheat. The identified QTLs, including novel QTLs found in this study, may play an essential role in the breeding process for improving wheat resistance to LR and SR.

Genetic control of juvenile resistance to powdery mildew in spring bread wheat cultivars from the VIR collection

Background. Bread wheat (Triticum aestivum L.) is one of the major food crops of humankind. Powdery mildew, caused by Blumeria graminis f. sp. tritici, is the most destructive foliar disease capable of causing great yield losses in epidemic years. Breeding for resistance to powdery mildew is the most economical and effective way to control this disease. By now, 68 loci were identified to contain more than 90 alleles of resistance to powdery mildew in wheat. However, there is a permanent necessity in finding new sources of resistance.The objective of the present study was to characterize the seedling powdery mildew resistance in some spring bread wheat varieties from the VIR collection and determine the inheritance of powdery mildew resistance in these accessions.Materials and methods. The powdery mildew resistant varieties ‘SW Kungsjet’ (k-66036), ‘SW Kronjet’ (k-66097), ‘Boett’ (k-66353), ‘Batalj’ (k-67116), ‘Stilett’ (k-67119) ‘Pasteur’ (k-66093) were crossed with a resistant line ‘Wembley 14.31’ (k-62557) containing the Pm12 gene, and with ‘SW Milljet’ (k-64434); the variety ‘Sibirka Yartsevskaya’ (k-38587) was used as a susceptible parent and control. The hybrid populations F2 were inoculated with the fungus population from local field and evaluated. The powdery mildew population manifested virulence to Pm1a, Pm2, Pm3a-f, Pm4a-b, Pm5a, Pm6, Pm7, Pm8, Pm9, Pm10, Pm11, Pm16, Pm19, Pm28, and avirulence to Pm12. The degree of resistance was assessed on days 8 and 10 after the inoculation using the Mains and Dietz scale (Mains, Dietz, 1930). The castrated flowers in the spikes were pollinated using the twell-method (Merezhko et al., 1973). Chi-squared for goodness of fit test was used to determine deviation of the observed data from the theoretically expected segregation.Results. According phytopathological and genetic tests, juvenile resistance in the varieties ‘SW Kungsjet’, ‘SW Kronjet’, ‘Boett’, ‘Batalj’, ‘Stilett’ and ‘Pasteur’ is controlled by dominant genes, which differ from Pm1a, Pm2, Pm3a-f, Pm4a-b, Pm5a, Pm6, Pm7, Pm8, Pm9, Pm10, Pm11, Pm12, Pm16, Pm19, and Pm28. The varieties ‘SW Milljet’, ‘SW Kronjet’ and ‘Pasteur’ had identical resistance genes. Genetic control of juvenile resistance to powdery mildew in ‘Batalj’, ‘Boett’, ‘Stilett’, ‘SW Milljet’, ‘SW Kungsjet’, ‘Pasteur’ was governed by different genes.Conclusions. The varieties ‘SW Kungsjet’, ‘SW Kronjet’, ‘Boett’ have been maintaining adult and seedling resistance since 2005, and ‘Batalj’, ‘Stilett’ and ‘Pasteur’ since 2017. Seedling resistance of these varieties to local powdery mildew population is controlled by dominant genes. A high degree of resistance was displayed by ‘SW Kungsjet’ and ‘SW Kronjet’ in the Novosibirsk Province, while ‘SW Kungsjet’ was resistant to mildew populations of Tatarstan. The variety ‘Pasteur’ manifested seedling resistance to leaf rust, and ‘SW Kungsjet’ was resistant to loose smut. By summing all the results, it may be suggested that the varieties ‘SW Kungsjet’, ‘SW Kronjet’, ‘Boett’, ‘Batalj’, ‘Stilett’ and ‘Pasteur can serve as good donors of powdery mildew resistance in wheat breeding.

Quantitative Trait Loci Mapping of Adult Plant and Seedling Resistance to Stripe Rust (Puccinia striiformis Westend.) in a Multiparent Advanced Generation Intercross Wheat Population.

Stripe rust caused by the biotrophic fungus Puccinia striiformis Westend. is one of the most important diseases of wheat worldwide, causing high yield and quality losses. Growing resistant cultivars is the most efficient way to control stripe rust, both economically and ecologically. Known resistance genes are already present in numerous cultivars worldwide. However, their effectiveness is limited to certain races within a rust population and the emergence of stripe rust races being virulent against common resistance genes forces the demand for new sources of resistance. Multiparent advanced generation intercross (MAGIC) populations have proven to be a powerful tool to carry out genetic studies on economically important traits. In this study, interval mapping was performed to map quantitative trait loci (QTL) for stripe rust resistance in the Bavarian MAGIC wheat population, comprising 394 F6 : 8 recombinant inbred lines (RILs). Phenotypic evaluation of the RILs was carried out for adult plant resistance in field trials at three locations across three years and for seedling resistance in a growth chamber. In total, 21 QTL for stripe rust resistance corresponding to 13 distinct chromosomal regions were detected, of which two may represent putatively new QTL located on wheat chromosomes 3D and 7D.

NLR diversity and candidate fusiform rust resistance genes in loblolly pine

Resistance to fusiform rust disease in loblolly pine (Pinus taeda) is a classic gene-for-gene system. Early resistance gene mapping in the P. taeda family 10-5 identified RAPD markers for a major fusiform rust resistance gene, Fr1. More recently, single nucleotide polymorphism (SNP) markers associated with resistance were mapped to a full-length gene model in the loblolly pine genome encoding for a nucleotide-binding site leucine-rich repeat (NLR) protein. NLR genes are one of the most abundant gene families in plant genomes and are involved in effector-triggered immunity. Inter- and intraspecies studies of NLR gene diversity and expression have resulted in improved disease resistance. To characterize NLR gene diversity and discover potential resistance genes, we assembled de novo transcriptomes from 92 loblolly genotypes from across the natural range of the species. In these transcriptomes, we identified novel NLR transcripts that are not present in the loblolly pine reference genome and found significant geographic diversity of NLR genes providing evidence of gene family evolution. We designed capture probes for these NLRs to identify and map SNPs that stably cosegregate with resistance to the SC20-21 isolate of Cronartium quercuum f.sp. fusiforme (Cqf) in half-sib progeny of the 10-5 family. We identified 10 SNPs and 2 quantitative trait loci associated with resistance to SC20-21 Cqf. The geographic diversity of NLR genes provides evidence of NLR gene family evolution in loblolly pine. The SNPs associated with rust resistance provide a resource to enhance breeding and deployment of resistant pine seedlings.

Transcriptome Analysis of Eucalyptus grandis Implicates Brassinosteroid Signaling in Defense Against Myrtle Rust (Austropuccinia psidii)

Eucalyptus grandis, in its native Australian range, varies in resistance to Austropuccinia psidii (syn. Puccinia psidii). The biotrophic rust fungus, A. psidii is the causal agent of myrtle rust and poses a serious threat to Australian biodiversity. The pathogen produces yellow pustules of urediniospores on young leaves and shoots, resulting in shoot tip dieback, stunted growth, and death. Dissecting the underlying mechanisms of resistance against this pathogen will contribute to improved breeding and control strategies to mitigate its devastating effects. The aim of this study was to determine the molecular dialogue between E. grandis and A. psidii, using an RNA-sequencing approach. Resistant and susceptible E. grandis seedlings grown from seed collected across its natural range were inoculated with the pandemic biotype of A. psidii. The leaf tissue was harvested at 12-h post inoculation (hpi), 1-day post inoculation (dpi), 2-dpi and 5-dpi and subjected to RNA-sequencing using Illumina 50 bp PE reads to a depth of 40 million reads per sample. Differential gene expression and gene ontology enrichment indicated that the resistant seedlings showed controlled, coordinated responses with a hypersensitive response, while the susceptible seedlings showed no systemic response against myrtle rust. Brassinosteroid signaling was apparent as an enriched term in the resistant interaction at 2-dpi, suggesting an important role of this phytohormone in defense against the pathogen. Brassinosteroid mediated signaling genes were also among the candidate genes within two major disease resistance loci (Puccinia psidii resistance), Ppr3 and Ppr5. While brassinosteroids have been tagged as positive regulators in other plant disease resistance interactions, this is the first report in the Eucalyptus – Austropuccinia psidii interaction. Furthermore, several putative resistance genes, underlying known resistance loci and implicated in the interaction have been identified and highlighted for future functional studies. This study provided further insights into the molecular interactions between E. grandis and A. psidii, contributing to our understanding of this pathosystem.

Determination of the Seedling Reactions of Some Turkish Bread and Durum Wheat Cultivars to Stem Rust Races TTTTF, RTTTC and RTTTF

Seedling resistance of 46 bread wheat and 14 durum wheat cultivars grown commonly in Turkey to stem rust races TTTTF, RTTTC, and RTTTF, the most common races in the Kastamonu region of Turkey, was determined under greenhouse conditions. Bread wheat cultivars Tahirova 2000, Yıldırım, Alpu 2001, Canik 2003 and Basri Bey 95 were found to be resistant to three stem rust races. Durum wheat cultivars Sarı Çanak 98 and Fırat 93 were resistant to stem rust race TTTTF. Durum wheat cultivars Eminbey, Altıntaş 95, Zühre and Sarı Çanak 98 were resistant to stem rust race RTTTC whereas durum wheat cultivars Eminbey, Altıntaş 95, İmren, Yelken 2000 and Zühre exhibited resistant reaction to stem rust race RTTTF. The majority of the wheat cultivars tested showed susceptible reactions to these stem rust races.

Identification of Winter Habit Bread Wheat Landraces in the National Small Grains Collection with Resistance to Emerging Stem Rust Pathogen Variants.

Wheat stem rust caused by Puccinia graminis f. sp. tritici is a widespread and recurring threat to wheat production. Emerging P. graminis f. sp. tritici variants are rapidly overcoming major gene resistance deployed in wheat cultivars and new sources of race-nonspecific resistance are urgently needed. The National Small Grains Collection (NSGC) contains thousands of wheat landrace accessions that may harbor unique and broadly effective sources of resistance to emerging P. graminis f. sp. tritici variants. All NSGC available facultative and winter-habit bread wheat landraces were tested in a field nursery in St. Paul, Minnesota, against a bulk collection of six common U.S. P. graminis f. sp. tritici races. Infection response and severity data were collected on 9,192 landrace accessions at the soft-dough stage and resistant accessions were derived from single spikes. Derived accessions were tested in St. Paul a second time to confirm resistance and in a field nursery in Njoro, Kenya against emerging races of P. graminis f. sp. tritici with virulence to many known resistance genes including Sr24, Sr31, Sr38, and SrTmp. Accessions resistant in the St. Paul field were also tested at the seedling stage with up to 13 P. graminis f. sp. tritici races, including TTKSK and TKTTF, and with 19 molecular markers linked with known stem rust resistance genes or genes associated with modern breeding practices. Forty-five accessions were resistant in both U.S. and Kenya field nurseries and lacked alleles linked with known stem rust resistance genes. Accessions with either moderate or strong resistance in the U.S. and Kenya field nurseries and with novel seedling resistance will be prioritized for further study.

Tea Plants With Gray Blight Have Altered Root Exudates That Recruit a Beneficial Rhizosphere Microbiome to Prime Immunity Against Aboveground Pathogen Infection.

Tea gray blight disease and its existing control measures have had a negative impact on the sustainable development of tea gardens. However, our knowledge of safe and effective biological control measures is limited. It is critical to explore beneficial microbial communities in the tea rhizosphere for the control of tea gray blight. In this study, we prepared conditioned soil by inoculating Pseudopestalotiopsis camelliae-sinensis on tea seedling leaves. Thereafter, we examined the growth performance and disease resistance of fresh tea seedlings grown in conditioned and control soils. Next, the rhizosphere microbial community and root exudates of tea seedlings infected by the pathogen were analyzed. In addition, we also evaluated the effects of the rhizosphere microbial community and root exudates induced by pathogens on the performance of tea seedlings. The results showed that tea seedlings grown in conditioned soil had lower disease index values and higher growth vigor. Soil microbiome analysis revealed that the fungal and bacterial communities of the rhizosphere were altered upon infection with Ps. camelliae-sinensis. Genus-level analysis showed that the abundance of the fungi Trichoderma, Penicillium, and Gliocladiopsis and the bacteria Pseudomonas, Streptomyces, Bacillus, and Burkholderia were significantly (p < 0.05) increased in the conditioned soil. Through isolation, culture, and inoculation tests, we found that most isolates from the induced microbial genera could inhibit the infection of tea gray blight pathogen and promote tea seedling growth. The results of root exudate analysis showed that infected tea seedlings exhibited significantly higher exudate levels of phenolic acids and flavonoids and lower exudate levels of amino acids and organic acids. Exogenously applied phenolic acids and flavonoids suppressed gray blight disease by regulating the rhizosphere microbial community. In summary, our findings suggest that tea plants with gray blight can recruit beneficial rhizosphere microorganisms by altering their root exudates, thereby improving the disease resistance of tea plants growing in the same soil.

Osmotic regulation and chlorophyll fluorescence characteristics in leaves of wheat seedlings under different salt stresses

The damage mechanism of salt stress on plants has attracted much attention. In order to reveal the damage mechanism of different salt stresses, we compared osmotic regulation and photosynthetic characteristics of seedlings of wheat cultivar Xianhan 3 under sodium salt (150 mmol·L-1) and calcium salt (5, 30 mmol·L-1) treatments alone or in combination. The results showed that sodium salt or calcium salt stress alone significantly inhibited the growth of roots and stems, but increased the amount of soluble sugar and proline, regulatory energy-dissipated electron yield, non-photochemical quenching and relative content of zeaxanthin contents in leaves. In contrast, salt treatments alone significantly decreased the levels of chlorophyll a and chlorophyll b, maximum photochemical efficiency, PSⅡ photochemical efficiency, photochemical quenching and photosynthetic electron transport efficiency. Furthermore, the inhibition of wheat seedling growth was more sensitive to calcium salt than to sodium salt stress, whereas the decreases of chlorophyll content and chlorophyll fluorescence parameters were more prominent in response to sodium salt stress. Except for the amount of soluble protein, lutein and the relative level of zeaxanthin, the changes of other parameters in the leaves due to sodium salt stress were effectively blocked by the application of low calcium concentration, but further increased by the presence of high calcium salt concentration. Taken together, sodium or calcium salt stress alone significantly inhibited seedling growth. The toxicity of sodium salt to wheat seedlings was effectively alleviated by low calcium concentration, but was aggravated by high calcium concentration, which were associated with the changes of photosynthetic pigment content, light energy capture, and photosynthetic electron transport process in the leaves of wheat seedlings. Moreover, osmotic regulators played an important role in enhancing the resistance of wheat seedlings to sodium or/and calcium environment.

Effects of different arbuscular mycorrhizal fungi mediated by different methods on the growth and drought resistance of Cinnamomum migao seedlings in a karst region

Effects of different arbuscular mycorrhizal fungi mediated by different methods on the growth and drought resistance of Cinnamomum migao seedlings in a karst region

English

A shade house experiment was conducted in Saudi Arabia to evaluate the impact of a mixture of three arbuscular mycorrhiza fungi (AMF) namely Funneliformis mosseae, Rhizophagus intraradices and Claroideoglomus etunicatum, a bacterium Bacillus subtilis, and their combinations on the growth and drought resistance potential of Acacia torilis seedlings under moderate and water deficit-stress. Thus, inoculants treatments (AMF, Bacillus subtilis, AMF+Bacillus, and control) and several watering intervals (1, 2, 3 and 4 weeks) were applied. Inoculation of AMF and Bacillus to A. tortilis seedlings found effective in terms of improved seedling growth. AMF and combined inoculation resulted in a larger shoot (shoot fresh and dry weights, seedling height, leaf number, leaf area) and root development (root fresh and dry weights, root length, root surface area, and root volume) as compared to the non-inoculated seedlings. Single inoculants of B. subtilis, showed better improvement in 1- and 2-week watering intervals compared to the control. Inoculated seedlings showed lower proline accumulation than non-inoculated seedlings, and thus improved seedling resistance to water deficit-stress. Mycorrhizal and mixed inoculation enhanced the amount of chlorophyll in the seedling’s leaves. Furthermore, seedlings with AMF and co-inoculants showed better drought tolerance even at 3- and 4-week watering intervals. © 2021 Friends Science Publishers

Characterization of the Powdery Mildew Resistance Gene in Wheat Breeding Line KN0816 and Its Evaluation in Marker-Assisted Selection.

Wheat powdery mildew, caused by Blumeria graminis (DC.) Speer f. sp. tritici is a destructive disease seriously threatening yield and quality of common wheat (Triticum aestivum L., 2n=6x=42, AABBDD). Characterization of resistance genes against powdery mildew is useful in parental selection and for developing disease-resistant cultivars. Chinese wheat breeding line KN0816 has superior agronomic performance and resistance to powdery mildew at all growth stages. Genetic analysis using populations of KN0816 crossed with different susceptible parents indicated that a single dominant gene, tentatively designated PmKN0816, conferred seedling resistance to different B. graminis f. sp. tritici isolates. Using a bulked segregant analysis, PmKN0816 was mapped to the Pm6 interval on chromosome arm 2BL using polymorphic markers linked to the cataloged genes Pm6, Pm52, and Pm64, and flanked by the markers CISSR02g-6 and CIT02g-2, both with genetic distances of 0.7 cM. Analysis of closely linked molecular markers indicated that the marker alleles of PmKN0816 differed from those of other powdery mildew resistance genes on 2BL, including Pm6, Pm33, Pm51, Pm64, and PmQ. Based on the genetic and physical locations and response pattern to different B. graminis f. sp. tritici isolates, PmKN0816 is most likely a new powdery mildew resistance gene and possesses effective resistance to all the 14 tested B. graminis f. sp. tritici isolates. In view of the elite agronomic performance of KN0816 combined with the resistance, PmKN0816 is expected to become a valuable resistance gene in wheat breeding. To transfer PmKN0816 to different genetic backgrounds using marker-assisted selection (MAS), closely linked markers of PmKN0816 were evaluated, and four of them (CIT02g-2, CISSR02g-6, CIT02g-10, and CIT02g-17) were confirmed to be applicable for MAS in different genetic backgrounds.

Warm wheat does not rust - how wheat resists stripe rust when temperatures rise.

Stripe rust is a destructive wheat disease that is estimated to cause 5.47 million tonnes of wheat loss per year (Beddow et al., 2015). The fungus that causes the disease, Puccinia striiformis f. sp. tritici (Pst), occurs in all wheat-growing regions of the world but causes more problems in cooler climates. One reason for this is that the fungus requires relatively low temperatures for spore germination, growth, and sporulation. But some wheat plants also have a defense mechanism against Pst that only operates under high temperatures. Two types of temperature-sensitive defense mechanisms are known: high-temperature seedling plant resistance and high-temperature adult plant resistance. When grown under high-temperature conditions, wheat varieties with such a defense mechanism are resistant against Pst. Because high-temperature resistance provides immunity to all Pst races, understanding the genetic basis of this defense mechanism might be valuable for breeding. Over the last decades, breeders have developed resistant cultivars by deploying race-specific resistance genes. Race-specific resistant cultivars have limited durability because pathogens evolve quickly. In the case of Pst, new races have overcome most of the known race-specific resistance genes (Fu et al., 2009). Therefore, breeding for non-race-specific resistance such as high-temperature resistance might be a more durable solution in the fight against stripe rust. Xiaoping Hu, Professor of Plant Pathology at Northwest Agricultural and Forestry University in Yangling, China, is trying to understand the molecular mechanisms involved in high-temperature resistance in seedlings. His research group performed transcriptomic analysis on the resistant cultivar Xiaoyan 6 that had been inoculated with Pst and grown under high temperatures. Among the differentially expressed genes, they found a gene encoding a cysteine-rich receptor-like kinase that they designated TaCRK10. In this issue of The Plant Journal, the researchers investigated the role of this gene (Wang et al., 2021). To investigate if TaCRK10 is involved in resistance to Pst, the authors performed virus-induced gene silencing (VIGS) in the Xiaoyan 6 cultivar and inoculated the TaCRK10-silenced plants with Pst. When plants started to show symptoms of stripe rust, they were divided into two groups. One group was placed under high-temperature conditions (20°C) for 24 h, whereas the other group was kept at normal temperatures (16°C). In the TaCRK10-silenced plants grown under high temperatures, there was abundant spore formation on the leaves, whereas non-silenced plants showed only limited sporulation. Under normal temperatures, control plants and silenced plants did not show differences. These results suggest that TaCRK10 is required for high-temperature seedling plant resistance to Pst in the Xiaoyan 6 cultivar. Furthermore, when they overexpressed TaCRK10 from Xiaoyan 6 in the susceptible wheat cultivar Fielder, then inoculated the overexpression lines with Pst, sporulation was much lower than in wild-type plants. Interestingly, the overexpression lines were resistant against Pst when grown at normal temperatures. Further analysis of these lines revealed expression of genes involved in the salicylic acid defense pathway as well as accumulation of reactive oxygen species (ROS), which are common signs of an immunity response. To deduce the molecular action of TaCRK10, the authors performed a yeast-two-hybrid assay using a library constructed from Pst-infected leaves of the Xiaoyan 6 cultivar grown at high temperature. They found that TaCRK10 interacted with the histone variant TaH2A.1. Because TaCRK10 contains a serine/threonine kinase-like domain, the authors wondered if TaCRK10 might phosphorylate histone TaH2A.1. To test this, the researchers produced recombinantly expressed proteins and mixed them in the presence of ATP. Using an electrophoresis technique that separates phosphorylated and non-phosphorylated proteins followed by Western blot analysis, they found that TaH2A.1 was indeed phosphorylated in the presence of TaCRK10. To find out if H2A.1 is involved in high-temperature seedling plant resistance to Pst, the authors used VIGS to silence the histone variant. Subsequent inoculation experiments showed that sporulation was higher on TaH2A.1-silenced plants at both normal and high temperatures than on non-silenced plants. Hence, TaH2A.1 appears to be involved in wheat resistance to Pst (Figure). Xiaoping Hu wants to better understand the TaCRK10-TaH2A.1 pathway by identifying the phosphorylation sites on H2A.1 on which CRK10 acts and to determine if phosphorylation of TaH2A.1 plays a role in high-temperature resistance to stripe rust in seedlings. He explains that the findings might be used to develop wheat varieties with a durable resistance against Pst. Overexpression of CRK10 from Xiaoyan 6 in the susceptible variety Fielder resulted in plants that were resistant to the pathogen grown at normal temperatures, showing that susceptible cultivars can become resistant in this way, but also that constitutive overexpression of the allele leads to resistance that is no longer dependent on temperature.