Evaluation on Potential Risk of the Emerging Yr5-Virulent Races of Puccinia striiformis f. sp. tritici to 165 Chinese Wheat Cultivars

In 2017, a new race (TSA-6) of the wheat stripe rust pathogen, Puccinia striiformis f. sp. tritici, virulent to resistance gene Yr5 were detected in China. However, whether Chinese wheat cultivars are resistant to the new races was unknown. In this study, two isolates (TSA-6 and TSA-9) with virulence to Yr5 were tested on other wheat Yr gene lines for their avirulence/virulence patterns and used, together with prevalent races CYR32 and CYR34 without the Yr5 virulence, to evaluate 165 major Chinese wheat cultivars for their reactions. Isolates TSA-6 and TSA-9 had similar but different virulence spectra, and therefore should be considered as two different races. Their avirulent/virulence patterns were remarkably different from that of CYR34 but quite similar to that of CYR32. Of the 165 wheat cultivars, 21 had all-stage resistance to TSA-6, 34 to TSA-9, and 20 to both races. Adult-plant resistance (APR) was detected in 35 cultivars to TSA-6 and 27 to TSA-9, but only 3 cultivars showed APR to both new races. Slow rusting resistance was observed in 24 cultivars to TSA-6 and of 33 to TSA-9. Analysis of variance (ANOVA) of disease index indicated a significant difference among cultivars, but not among the four races. Based on the molecular marker data, a low percentage of wheat cultivars carried Yr5, Yr7, Yr10, Yr15, Yr26, and/or YrSP. As TSA-6 and TSA-9 can be a serious threat to wheat production in China, monitoring TSA-6, TSA-9, and other races are continually needed.

Durability of Adult Plant Resistance Gene Yr18 in Partial Resistance Behavior of Wheat (Triticum aestivum) Genotypes with Different Degrees of Tolerance to Stripe Rust Disease, Caused by Puccinia striiformis f. sp. tritici: A Five-Year Study

Adult plant resistance in wheat is an achievement of the breeding objective because of its durability in comparison with race-specific resistance. Partial resistance to wheat stripe rust disease was evaluated under greenhouse and field conditions during the period from 2016 to 2021. Misr 3, Sakha 95, and Giza 171 were the highest effective wheat genotypes against Puccinia striiformis f. sp. tritici races. Under greenhouse genotypes, Sakha 94, Giza 168, and Shandaweel1 were moderately susceptible, had the longest latent period and lowest values of the length of stripes and infection frequency at the adult stage. Partial resistance levels under field conditions were assessed, genotypes Sakha 94, Giza 168, and Shandaweel1 exhibited partial resistance against the disease. Leaf tip necrosis (LTN) was noted positively in three genotypes Sakha 94, Sakha 95, and Shandaweel1. Molecular analyses of Yr18 were performed for csLV34, cssfr1, and cssfr2 markers. Only Sakha 94 and Shandaweel1 proved to carry the Yr18 resistance allele at both phenotypic and genotypic levels. Scanning electron microscopy (SEM) observed that the susceptible genotypes were colonized extensively on leaves, but on the slow-rusting genotype, the pustules were much less in number, diminutive, and poorly sporulation, which is similar to the pustule of NIL Jupateco73 ‘R’.

Molecular and Phenotypic Analysis of Bread Wheat Varieties in Relation to Durable Rust Resistance

Global wheat production is constantly threatened by rust diseases. Identifying resistant genes is a useful tactic to control wheat rust pathogen. Twenty-six wheat varieties were screened with twelve Simple Sequence Repeats (SSR) markers to detect rust resistant genes and the efficacy of genes was validated through field testing. The alleles Lr32, Lr39, Lr50, SrCad and SrWeb were not amplified in the varieties included in this study. The SSR markers indicated that the varieties viz., Chakwal-97, Bakhar-2002 and Lasani-2008 had a combination of 02 slow rusting alleles (Lr46/Yr29 and Yr18/Lr34). The adult plant resistance (APR) allele Yr17 was less prevalent and found only in BWL-97. However, Noshera-96 had a slow rusting combination of Lr67/Yr46 and Lr46/Yr46 alleles. The Lr46/Yr29 identified in 50% of the varieties, Yr18/Lr34 in 19.23%, Lr32 in 11.54%, and multiple APR alleles in 19.32%. Their resistance was validated through a field trap nursery for 3 consecutive seasons. The slow rusting combination of Lr46/Yr29 and Yr18/Lr34 was comparatively more effective than Lr67/Yr46 and Lr46/Yr29 alleles under field conditions. The varieties Yecora-70, Lylpure-73 and Tandojam-83 showed highly susceptible phenotype. The varieties Chakwal-86, Pirsabak-2005, Fareed-2006, and Sehar-2006 showed resistant to moderately resistant phenotype at high-temperature adult-plant stage. The cluster diagram divided the varieties into two distinct clades. The clade II depicted the abundance of APR allele Lr46/Yr29. The varieties contain valuable sources of durable rust resistant alleles that can be exploited to deploy rust resistance in future wheat cultivars. It has been observed that the varieties approved for commercial cultivation after 1990s and onwards contain APR alleles. © 2021 Friends Science Publishers

Wheat Resistance to Stripe and Leaf Rusts Conferred by Introgression of Slow Rusting Resistance Genes

Twenty-three wheat genotypes were evaluated for stripe and leaf rusts, caused by Puccinia striiformis f. sp. tritici and Puccinia triticina f. sp. tritici, respectively, at seedling and adult stages under greenhouses and field conditions during the 2019/2020 and 2020/2021 growing seasons. The race analysis revealed that 250E254 and TTTST races for stripe and leaf rusts, respectively were the most aggressive. Eight wheat genotypes (Misr-3, Misr-4, Giza-171, Gemmeiza-12, Lr34/Yr18, Lr37/Yr17, Lr46/Yr29, and Lr67/Yr46) were resistant to stripe and leaf rusts at seedling and adult stages. This result was confirmed by identifying the resistance genes: Lr34/Yr18, Lr37/Yr17, Lr46/Yr29, and Lr67/Yr46 in these genotypes showing their role in the resistance. Sids-14 and Shandweel-1 genotypes were susceptible to stripe and leaf rusts. Twelve crosses between the two new susceptible wheat genotypes and the three slow rusting genes (Lr34/Yr18, Lr37/Yr17, and Lr67/Yr46) were conducted. The frequency distribution of disease severity (%) in F2 plants of the twelve crosses was ranged from 0 to 80%. Resistant F2 plants were selected and the resistance genes were detected. This study is important for introducing new active resistance genes into the breeding programs and preserving diversity among recently released wheat genotypes.

Mining of Leaf Rust Resistance Genes Content in Egyptian Bread Wheat Collection

Wheat is a major nutritional cereal crop that has economic and strategic value worldwide. The sustainability of this extraordinary crop is facing critical challenges globally, particularly leaf rust disease, which causes endless problems for wheat farmers and countries and negatively affects humanity’s food security. Developing effective marker-assisted selection programs for leaf rust resistance in wheat mainly depends on the availability of deep mining of resistance genes within the germplasm collections. This is the first study that evaluated the leaf rust resistance of 50 Egyptian wheat varieties at the adult plant stage for two successive seasons and identified the absence/presence of 28 leaf rust resistance (Lr) genes within the studied wheat collection. The field evaluation results indicated that most of these varieties demonstrated high to moderate leaf rust resistance levels except Gemmeiza 1, Gemmeiza 9, Giza162, Giza 163, Giza 164, Giza 165, Sids 1, Sids 2, Sids 3, Sakha 62, Sakha 69, Sohag 3 and Bany Swif 4, which showed fast rusting behavior. On the other hand, out of these 28 Lr genes tested against the wheat collection, 21 Lr genes were successfully identified. Out of 15 Lr genes reported conferring the adult plant resistant or slow rusting behavior in wheat, only five genes (Lr13, Lr22a, Lr34, Lr37, and Lr67) were detected within the Egyptian collection. Remarkedly, the genes Lr13, Lr19, Lr20, Lr22a, Lr28, Lr29, Lr32, Lr34, Lr36, Lr47, and Lr60, were found to be the most predominant Lr genes across the 50 Egyptian wheat varieties. The molecular phylogeny results also inferred the same classification of field evaluation, through grouping genotypes characterized by high to moderate leaf rust resistance in one cluster while being highly susceptible in a separate cluster, with few exceptions.

Analysis of miRNA expression associated with the Lr46 gene responsible for APR resistance in wheat (Triticum aestivum L.)

Lr46/Yr29/Pm39 (Lr46) is a gene for slow rusting resistance in wheat. The aim of the study was to analyze the miRNA expression in selected common wheat cultivars carrying resistance genes, Lr46 among others (HN Rod, Pavon‘S’, Myna‘S’, Frontana‘S’, and Sparrow’S’) in response to leaf rust infection caused by Puccinia triticina Erikss. In the Pavon ‘S’, Myna ‘S’, Frontana‘S’, and Sparow‘S’ varieties a product with a length of 242 bp has been identified, which is specific to the Xwmc44 marker linked to the brown rust resistance gene Lr46. In the next step, the differences in the expression of microRNA (miR5085 and miR164) associated with the Lr46 gene, which is responsible for different resistance of selected wheat cultivars to leaf rust, were examined using emulsion PCR (ddPCR). In the experiment, biotic stress was induced in mature plants by infecting them with fungal spores under controlled conditions in a growth chamber. For analysis the plant material was collected before inoculation and 6, 12, 24, and 48 h after inoculation. The experiments also showed that plant infection with Puccinia triticina resulted in an increase in miR164 expression in cultivars carrying the Lr46 gene. The expression of miR164 remained stable in a control cultivar (HN ROD) lacking this gene. This has proved that miR164 can be involved in leaf rust resistance mechanisms.

SOURCES OF BARLEY RESISTANCE TO HELMINTHOSPORIOTIC DISEASES AND THEIR USE IN THE NORTH-EAST FARC

The paper explores 70 samples of spring barley from the collection of WIR under conditions of rather rigid natural infectious helminthosporioses (striped, reticulated and dark brown spotting) in FARC of the North-East in 2018-2019. The spotting was investigated 4-5 times during plants ontogenesis every 10-12 days since the phase 29 on the Cadox scale. The methodology suggested by O.S. Afanasenko (2005) was used to assess the diseases. The nature of vegetative-microbial interactions was evaluated by SCDP (square under the curve of disease progress) and IS (stability index) indicators. During immunological experiment, the authors observed 11 samples resistant to dark brown spotting with lesion rate 10.0-13.0%, SCDP parameters equal 167-223, DUT was 0.18-0.25; 18 samples resistant to reticular spotting (6.0-10.0%, PCRB - 53-103, DUT - 0.18-0.35), and 29 samples characterized by immunity and high resistance to stripe spotting (0-5.0%, SCDP - 10-75). IS - 0.01-0.09). Only 4 samples (Makbo, Kalkul, Buyan and Forward) are characterized by group non-specific resistance to reticulate and dark brown spotting and striate immunity. The longest occurrence period (2-7 days) of dark brown spotting was observed in 8 samples, and reticulum spotting (2-13 days) - in 16 samples. The paper finds out that NCL 95098 (Argentina) had the relatively long occurrence period in terms of dark brown spotting, and varieties from Afghanistan (k-5983) and China (k-2929) to reticulate spotting. Badiory, Makbo, Rodos, and Buyan varieties have equal dynamics of both spotting and slow rusting of diseases in ontogenesis. There is a weak (r = -0.33 - reticulate) and medium (r = -0.58 - dark brown) negative correlation between the latent period and the defeat. The regression equations (y = -0,6071x+6,8571; R2 = 0,917 - dark brown; y = -0,3941x+11,35; R2 = 0,733 - reticulated) show that from infection to the first disease symptoms, their daily increase in trend is 0,61 and 0,39%. Kalkul, NCL 95098, Badioryi and Buyan varieties are seen as effective promising for selection programs to produce high yield adaptive varieties under the conditions of the region. Apart from stability, they are distinguished by the number of productive stems, long, well-grained ears and high productivity.