Apple Breeding Research Articles

Screening of Indian wild apple accessions with scab and powdery mildew disease resistant gene specific molecular markers

Investigations on resistance to pathogens within local wild populations is the most efficient way for developing resistant cultivars in breeding programmes. In this study, Indian wild crab apple (Malus baccata Borkh var Himalaica) accessions maintained at two field gene banks in Himachal Pradesh were screened to find out the resistant sources. Individual trees were tested for the presence/absence of Vf, Vrl and Vbj scab resistant and Pl1 and Pl2 mildew resistant genes with eight and one SCAR markers respectively tightly linked to these genes. The potted plants were evaluated after the inoculation of pathogen. All the accessions showed diversity in relation to resistant gene to both the pathogens. All the SCAR markers K08, T06, Al07, Am19, ACS07, ACS09, Z13 and S22 were present in eight crab apple accessions. PLBJ SCAR marker linked with major genes Pl1 and Pl2 was detected in six accessions. Molecular marker assessment results almost corresponded to the data received in pot assay experiments thus were in good agreement. The study confirmed that these accessions carry scab and mildew resistant genes which could play important role in selection of desirable genotypes for apple breeding as well as use as suitable rootstock.

Breeding-oriented evaluation of the progeny of cv. ‘Papirovka tetraploidnaya’ in the Middle Urals

One of the most promising trends in apple breeding is polyploidy. Triploid cultivars show higher fruiting stability and increased self-fertility. The easiest way to obtain triploids is to cross diploid and tetraploid cultivars among themselves. The main limiting factor in this case is a restricted number of initial tetraploid forms whose characteristics affect the quality and prospects of the resulting hybrid progeny.The staff of Sverdlovsk Horticultural Breeding Station in the Middle Urals produced and analyzed 5 hybrid families using cv. ‘Papirovka tetraploidnaya’ as the paternal source; the latter’s pollen was supplied by Acad. E. N. Sedov from the All-Russian Research Institute of Fruit Crop Breeding. Ninety hybrid seedlings were studied.The study showed that ‘Papirovka tetraploidnaya’ with a high degree of probability conveyed the following traits to its progeny: large fruit size, fruit ripening in early summer, midsummer and autumn, loose or medium density of coarse fruit flesh, and nonoutstanding fruit taste (scoring 3.8–4.2 points).

Comparative transcriptome reveals molecular mechanism in apple genotypes differing in CO2 tolerance in CA storage

Internal browning is physiological storage disorder in many apples often associated with high CO2 during controlled atmosphere (CA) storage. However the underlying molecular mechanisms leading to internal browning are poorly understood. This study examined changes in the apple transcriptome associated with internal browning related to high CO2 in CA storage by comparing the responses of a CO2 sensitive cultivar ‘Han Fu’ and the CO2 tolerant cultivar ‘Golden Delicious’. The apples were harvested at optimum maturity for long term storage and stored in a CA of 3 % O2 and 6 % CO2 at 4 ℃ for 60 d. The CO2 sensitive ‘Han Fu’ showed severe browning symptoms within 30 d storage in CA, while no internal browning symptoms were detected in ‘Golden Delicious’ even after 60 d storage under the same storage conditions. PPO activity was higher in ‘Han Fu’ apples after 30 d storage. Differences in the expression profile between cultivars were assessed using RNA-sequencing techniques to identify candidate genes associated with internal browning in a cultivar specific manner. The RNA sequencing results showed that higher expression of the related to apetala 2 (RAP 2) and pyruvate decarboxylase (PDC) encoding genes in ‘Golden Delicious’ apples were associated with higher CO2 tolerance in this cultivar. Conversely, the higher expression of key genes from lactate production (lactate dehydrogenase, LDH), lipid catabolic (patatin-like protein, PLP), polyphenol biosynthesis (phenylalanine ammonia-lyase, PAL), polyphenol oxidase (PPO) were associated with the internal browning development in ‘Han Fu’ apple in CA storage condition. A conceptual model elucidating the molecular mechanism of browning development in ‘Han Fu’ and CO2 acclimation in ‘Golden Delicious’ during storage in CA is proposed. The further elucidation of this mechanism will lead to a theory to optimize cultivar breeding in apple.

Combining genetic resources and elite material populations to improve the accuracy of genomic prediction in apple.

Genomic selection is an attractive strategy for apple breeding that could reduce the length of breeding cycles. A possible limitation to the practical implementation of this approach lies in the creation of a training set large and diverse enough to ensure accurate predictions. In this study, we investigated the potential of combining two available populations, i.e., genetic resources and elite material, in order to obtain a large training set with a high genetic diversity. We compared the predictive ability of genomic predictions within-population, across-population or when combining both populations, and tested a model accounting for population-specific marker effects in this last case. The obtained predictive abilities were moderate to high according to the studied trait and small increases in predictive ability could be obtained for some traits when the two populations were combined into a unique training set. We also investigated the potential of such a training set to predict hybrids resulting from crosses between the two populations, with a focus on the method to design the training set and the best proportion of each population to optimize predictions. The measured predictive abilities were very similar for all the proportions, except for the extreme cases where only one of the two populations was used in the training set, in which case predictive abilities could be lower than when using both populations. Using an optimization algorithm to choose the genotypes in the training set also led to higher predictive abilities than when the genotypes were chosen at random. Our results provide guidelines to initiate breeding programs that use genomic selection when the implementation of the training set is a limitation.

Expression Analysis of AUX/IAA Family Genes in Apple Under Salt Stress.

Members of the auxin/indoleacetic acid (Aux/IAA) gene family in plants are primary auxin-responsive genes that play important roles in many aspects of plant development and in responses to abiotic stress. Recently, 33 Aux/IAA have been identified in the apple genome. The biological responses of MdIAAs to salt stress are still unknown. In this study, Malus zumi, Malus baccata, and Malus × domestica 'Fuji' plantlets were subjected to salt stress by supplementing hydroponic media with NaCl at various concentrations. M. zumi showed the strongest salt resistance, followed by 'Fuji', and M. baccata was the most sensitive to salt stress. Tissue-specific expression profiles of MdIAAs were determined by quantitative real-time polymerase chain reaction. When apple plantlets were subjected to salt stress, most of salt-responsive MdIAAs were up-regulated by 1h, 3h, and 6h in roots, shoot tips, and leaves, respectively. Highly expressed MdIAAs in roots, especially for M. zumi, consisted with the salt tolerance of apple rootstocks. Transgenic apple calli were tolerant to salt stress when over-expressed salt-responsive genes, MdIAA8, -9, and -25. These results provide clues about salt resistance in these three Malus species, which helps apple breeding of salt tolerance by genetic transformation.

Analysis of the state and global trends in the cultivation and breeding of apple trees

The objective of the research is to analyze scientific and technical literature, to identify trends in world production and trends in apple breeding. The article uses official data from the FAO - Food and Agriculture Organization of the United Nations (Statistics Division). In addition, the information from the websites of the Federal State Statistics Service and the Federal State Budgetary Institution "Gossortcommission" - the State Commission for Selection Achievements, Test and Protection - were used. Statistical reports for the period from 2000 to 2019 were taken for analysis. The volume of fruits produced in the world is increasing every year. Apple production is in third place in the world, second only to coffee and olives. The leading apple suppliers are China, USA, Turkey, Poland, Iran, Italy, India, France, Russia, Chile. In 2000-2019 the gross harvest of apples increased from 59 million tons. up to 87 million tons, while the number of cultivated areas decreased from 5.4 to 4.7 million hectares. The main producing regions of this crop are Asia (60.7%), Europe (22.1%), America (12.9%), Africa (3.2%) and Oceania (1.1%). At the same time, the world production of apple trees has significantly stepped towards intensification, thanks to new cultivars and new cultivation technologies. Over the past twenty years, global apple production has grown significantly due to the intensification of production and the introduction of new breeding cultivars.

Trends in Fruit Quality Improvement From 15 Years of Selection in the Apple Breeding Program of Washington State University.

Washington State University's apple breeding program (WABP) was initiated in 1994 to select new apple cultivars with improved eating quality, appearance, and storability that are suitable for production in the main growing regions of the state. Fruit quality is phenotyped using various instrumental measures, such as penetrometers (texture), titrator (acidity), and refractometer (soluble solids concentration; SSC), as well as sensory assessment. The selection regime of WABP occurs in three sequential phases: phase one (P1)—single, unreplicated seedlings at one site, phase two (P2)—replicated selections at three geographically diverse sites, and phase three (P3)—highly replicated elite selections at one to two grower sites. Most of the data collection of WABP occurs in P2. Knowledge of trends/changes associated with advancing selections is essential for understanding the selection criteria and progress of WABP throughout the changing compositions of advancing and culling selections. For each post-harvest trait, P2 data from harvest years 2005 to 2019 were split across sites, and between selections and reference cultivars (e.g., Cripps Pink, Gala, and Honeycrisp). Means of instrumental crispness (Cn) and inner cortex firmness for the advancing selections increased gradually over this period and were significantly higher than those for cultivars. Means of outer cortex firmness measurements were stable for selections but significantly higher than those for cultivars. The average fruit acidity of selections increased marginally over this period and was higher than that of the cultivars. Meanwhile, the average fruit SSCs of selections and cultivars were statistically indistinguishable. These 15-year trends indicate that WABP has been selecting apples with improved eating quality and storability through increased crispness and inner cortex firmness, respectively.

An apple (Malus domestica) AP2/ERF transcription factor modulates carotenoid accumulation

Color is an important trait for horticultural crops. Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health. Here, we identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) transcription factor named MdAP2-34 in apple (Malus domestica Borkh.). MdAP2-34 expression exhibited a close correlation with carotenoid content in ‘Benin Shogun’ and ‘Yanfu 3’ fruit flesh. MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway. The major carotenoid contents of phytoene and β-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin, yet the predominant compound of lutein showed no obvious difference, indicating that MdAP2-34 regulates phytoene and β-carotene accumulation but not lutein. MdPSY2-1 (phytoene synthase 2) is a major gene in the carotenoid biosynthesis pathway in apple fruit, and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34. In addition, overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents. Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple, and this research is valuable for accelerating the apple breeding process.

Cold shock protein 3 plays a negative role in apple drought tolerance by regulating oxidative stress response

As RNA chaperones, cold shock proteins (CSPs) are essential for cold adaptation. Although the functions of CSPs in cold response have been demonstrated in several species, the roles of CSPs in response to drought are largely unknown. Here, we demonstrated that MdCSP3, a downstream target gene of MdMYB88 and MdMYB124, contributes to drought tolerance in apple (Malus × domestica). MdCSP3 responds to various abiotic stresses, including drought, cold, heat, and salt stress. Compared with non-transgenic apple GL-3, the MdCSP3 overexpressing plants exhibit significantly lower drought resistance and a reduced capacity for ROS scavenging by the regulation of antioxidant enzymes SOD, CAT, and POD. Additionally, RNA-seq data shows that MdCSP3 regulates expression of genes involved in oxidative stress response. Taken together, our results demonstrate the functions of MdCSP3 in apple drought tolerance, and this finding provides a new direction for breeding of drought resistant apple.

Duration of the period for creating apple cultivars and tasks on reducing it

The greatest period of time was spent on creating a cultivar at the first stage of breeding in our institution, when we did not have proper experience in apple breeding. For example, in the sixties of the last century, cultivars Pepin Orlovsky, Orlovskaya Zarya, Nizkorosloye and Sinap Orlovsky were created, in which the period from hybridization to inclusion in the State Register of Breeding Achievements allowed for use was 48, 45, 43 and 34 years respectively. With the acquisition of breeding experience in selecting the initial parent cultivars and improving the methods of growing seedlings in the breeding orchard (growing hybrid seedlings in the crown of a semi-dwarf or dwarf rootstock or on insert rootstocks) the period was significantly reduced — to 20 years for such cultivars as Yablochny Spas, Aleksander Boyko, Maslovskoye and a number of others. The first immune domestic cultivar Imrus (immune russian) was created and included in the State Register of Breeding Achievements allowed for use in just 15 years. It took 16 years to create the Rozhdestvenskoye cultivar. Naturally, on average, much less time was spent on the creation of columnar cultivars due to the earlier entry into flowering and fruiting. Due to the fact that high agricultural technology improves the growth processes of hybrid seedlings in the breeding nursery and in the breeding orchard and reduces their juvenile period, it must necessarily be carried out. This report gives a brief production and biological characteristics of the best apple cultivars of the Institute’s breeding. One of the best cultivars immune to scab is the winter cultivar Imrus (immune russian). The cultivar has a rapid fruitfulness and high yield. Its fruit can be stored in the cold storage until mid-March. Veniaminovskoye and Kandil Orlovsky are also valuable immune cultivars. The fruits of Veniaminovskoye are stored in the refrigerator until the end of February; the cultivar is characterized by the dessert quality of the fruit. The advantages of Kandil Orlovsky are also high rapid fruitfulness and productivity. Triploid Aleksander Boyko is immune to scab and has large size of fruit (220 g) and regular fruiting. Columnar cultivars Priokskoye and Poezia are of great interest. Priokskoye is characterized by scab immunity and high productivity. The fruits are characterized by marketability and high consumer qualities. In the refrigerator, the fruits can be stored until February. It took only 18 years to create this cultivar. The columnar scab-immune cultivar Poezia is characterized by high rapid fruitfulness. Its fruits are stored in the refrigerator until February.

BREEDING FRUIT CROPS IN THE TATAR RESEARCH INSTITUTE OF AGRICULTURE

The purpose of the research was to analyze the work on the creation of new varieties of apple, cherry and plum, carried out from 1938 to 2020 in the Tatar Research Institute of Agriculture, as well as the identification of promising crossbreeding combinations and genotypes for use in breeding and transfer to the State variety testing. In the apple breeding orchard, promising seedlings in hybrid families were identified by productivity, taste and size of fruits: Anis Novy×Plodovitoe (1-6-48), Anis Novy×Vityaz(1-7-26, 1-7-27, 1-7-57,1-7-70, 1-7-97), Anis Novy×Ural Souvenir (1-8-88) . In 2021, 4 apple varieties were entered into the State Register of Breeding Achievements of the Russian Federation: Renet Tatarsky, Volzhskaya Krasavitsa, Tenkovskaya and Kamskaya. The apple variety Renet Povolzh’ya is undergoing state variety testing. Promising hybrids 1-1-11, 1-2-11, 1-2-14, 1-10-30, 1-11-6, 1-11-31, 2-2-75,2-2-93 have been selected in sour cherry breeding orchards. In 2015, a new self-fertile variety of Shelangovskaya sour cherry was accepted for State variety testing in the Middle Volga and Volga-Vyatka regions. In 2021, 8 varieties of sour cherries were included in the State Register of Breeding Achievements of the Russian Federation: Krasa Tataria, Zarya Tataria, Shakirovskaya, Truzhenitsa Tataria, Sevastyanovskaya, Tveritinovskaya, Pamyat Sakharova and Obilnaya. In the plum breeding orchard promising hybrid seedlings 1-1-11, 1-1-20, 1-1-47, 1-1-75, 1-1-84, 1-2-36, 1-2-49, 1-2-57, 1-2-60, 1-3-19, 1-3-58, 1-3-86, 1-8-43 and others were selected according to important economic and biological characteristics. In 2021, the State Register of Breeding Achievements of the Russian Federation, admitted for use, included 8 varieties of home-breeding plums of the Tatar Research Institute of Agriculture: 2 varieties of early ripening — Sverkh Rannya, Sineokaya; 6 varieties of medium ripening — Rakitovaya, Renklod Tenkovskiy, Volzhanka, Tenkovskaya Golubka, Kazanskaya and Pamyat Khasanova.

No Evidence of Unexpected Transgenic Insertions in T1190 – A Transgenic Apple Used in Rapid Cycle Breeding – Following Whole Genome Sequencing

Rapid cycle breeding uses transgenic early flowering plants as crossbreed parents to facilitate the shortening of breeding programs for perennial crops with long-lasting juvenility. Rapid cycle breeding in apple was established using the transgenic genotype T1190 expressing the BpMADS4 gene of silver birch. In this study, the genomes of T1190 and its non-transgenic wild-type PinS (F1-offspring of ‘Pinova’ and ‘Idared’) were sequenced by Illumina short-read sequencing in two separate experiments resulting in a mean sequencing depth of 182× for T1190 and 167× for PinS. The sequencing revealed 8,450 reads, which contain sequences of ≥20 bp identical to the plant transformation vector. These reads were assembled into 125 contigs, which were examined to see whether they contained transgenic insertions or if they are not using a five-step procedure. The sequence of one contig represents the known T-DNA insertion on chromosome 4 of T1190. The sequences of the remaining contigs were either equally present in T1190 and PinS, their part with sequence identity to the vector was equally present in apple reference genomes, or they seem to result from endophytic contaminations rather than from additional transgenic insertions. Therefore, we conclude that the transgenic apple plant T1190 contains only one transgenic insertion, located on chromosome 4, and shows no further partial insertions of the transformation vector.Accession Numbers: JQ974028.1.

Porfiry Afanasyevich Dibrova: at the origins of scientific pomiculture in the Urals

Porfiry Afanasyevich Dibrova was one of the first scientists and breeders standing at the origins of scientific pomiculture in the Urals. He was the author of 23 cultivars of apple, six of pear, one of sour cherry, and one of black currant. In the 1940s, he was the leader of collecting missions exploring the local assortment of fruit and berry crops in 50 districts of Sverdlovsk and Molotov (Perm) Provinces, and the Udmurt Republic. P.A. Dibrova was one of the authors of the first standard set of fruit and berry cultivars for the abovementioned areas. He studied regularities in the inheritance of valuable agronomic and biological traits of fruit crops and identified promising sources for apple and pear breeding. He launched the main plant breeding trends in the Middle Urals, now followed by contemporary breeders: the development of highly winter-hardy cultivars of apple and pear with fruiting precocity, stable yields, excellent fruit quality, and improved biochemical composition in fruits.

Alleviation of Postharvest Skin Dimpling of MN55 Apple Fruit and a Possible Association with Apple stem pitting virus

MN55 is an apple (Malus ×domestica Borkh.) cultivar recently released by the University of Minnesota apple breeding program, with fruit marketed in the U.S. as Rave®. When stored for 4 months at 0 to 4 °C, MN55 fruit can develop several storage disorders, including skin dimpling. Skin dimpling incidence was greater for fruit harvested 1 week later than those harvested earlier. Dimpling was not alleviated by prestorage treatments of 1-methylcyclopropene or diphenylamine or by holding fruit at room temperature for 1 day before long-term cold storage. However, dimpling incidence was very low when fruit were stored at 6 to 7 °C. Because viruses have been implicated in other fruit dimpling disorders, the presence of viruses in MN55 leaves and fruit was studied. Apple stem pitting virus (ASPV) was detected by microscopy, reverse transcriptase polymerase chain reaction (RT-PCR) methodology, and high throughput sequencing (HTS) in peel of fruit from MN55 trees that exhibited skin dimpling after 4 months of storage at 0 to 1 °C. ASPV was also detected in supermarket-purchased fruit of other cultivars with noticeable skin dimpling. Although ASPV was not conclusively demonstrated to cause skin dimpling in our work, its prevalence indicates that further investigations are warranted to determine the relationship between viruses and skin deformities in stored apples.

Quantifying apple diversity: A phenomic characterization of Canada’s Apple Biodiversity Collection

Societal Impact StatementA future with a secure and safe food supply requires humanity to preserve and exploit the vast variation available across agricultural plant species. Apples are one of the most widely consumed fruits and provide significant nutritional value worldwide. Here, we characterize key agricultural traits in a diverse collection of apples to provide a foundation for future apple improvement. We show that commercially successful apple varieties capture only a small fraction of apple diversity, and demonstrate that significant improvement is possible by tapping into existing genetic diversity.Summary Here we present a comprehensive evaluation of apple diversity through phenotyping of Canada's Apple Biodiversity Collection (ABC) which contains over 1000 apple accessions. We assessed, over a 4‐year period, more than 20,000 individual apples and quantified variation across 39 phenotypes, including phenology and fruit quality both at harvest and after 3 months of cold storage. We observe that apples in the ABC display a wide range of phenotypic variation that may prove useful for future apple improvement. For example, apples can differ by nearly 61‐fold in weight, 18‐fold in acidity, and 100‐fold in phenolic content. We quantified the dramatic changes to apple physiology that occur during 3 months of cold storage: on average, apples lost 39% of their firmness, 31% of their acidity, and 9% of their weight, but gained 7% in soluble solids. Harvest date, flowering date, and time to ripen were all positively correlated with firmness, which suggests that the developmental pathways that drive phenological events throughout the growing season may play a role in determining an apple's texture. Finally, we show that apple breeding has selected for a significant decline in phenolic content over the past 200 years: apple cultivars released after 1940 had a 30% lower median phenolic content than cultivars released before 1940. The data and analyses presented here not only provide a comprehensive quantification of the range across, and relationships among diverse apple phenotypes, but they also enable genetic mapping studies that will provide the foundation for future apple improvement via genomics‐assisted breeding.

Unraveling a genetic roadmap for improved taste in the domesticated apple

Although taste is an important aspect of fruit quality, an understanding of its genetic control remains elusive in apple and other fruit crops. In this study, we conducted genomic sequence analysis of 497 Malus accessions and revealed erosion of genetic diversity caused by apple breeding and possible independent domestication events of dessert and cider apples. Signatures of selection for fruit acidity and size, but not for fruit sugar content, were detected during the processes of both domestication and improvement. Furthermore, we found that single mutations in major genes affecting fruit taste, including Ma1, MdTDT, and MdSOT2, dramatically decrease malate, citrate, and sorbitol accumulation, respectively, and correspond to important domestication events. Interestingly, Ma1 was identified to have pleiotropic effects on both organic acid content and sugar:acid ratio, suggesting that it plays a vital role in determining fruit taste. Fruit taste is unlikely to have been negatively affected by linkage drag associated with selection for larger fruit that resulted from the pyramiding of multiple genes with minor effects on fruit size. Collectively, our study provides new insights into the genetic basis of fruit quality and its evolutionary roadmap during apple domestication, pinpointing several candidate genes for genetic manipulation of fruit taste in apple.

Genetic Characterization of Domestic Apple Varieties from Tuzla Canton, BiH

Aims: The basic precondition for apple breeding is the genetic diversity of varieties, which implies a large number of different, positive genes that enable adaptation to different weather conditions, resistance to new diseases and pests. One of the reliable sources of genetic diversity are indigenous varieties of Bosnia and Herzegovina. Their genetic identification is the first step in a process that has as its ultimate goal the collection of genetic material. The main goal of this research is to analyze the genetic variability of five indigenous varieties of apple in Tuzla Canton, Bosnia and Herzegovina in terms of contributing to the management of conservation and expansion of existing genetic resources, spreading this material through registered nurseries.
 Study Design: The research included fiveautochthonous apple varieties: "Ovčji nos“ “Dobrić“, "Šarenika“, "Rančica“ and "Petrovača“.
 Place and Duration of Study: Samples of young leaves were collected at the site of Donji Moranjci, City of Srebrenik,Tuzla Canton, Bosnia and Herzegovina in the spring of 2019.
 Methodology: In order to determine the genetic diversity of five indigenous apple varieties were genotyped ten SSR(Simple Sequence Repeats) markers.
 Results: No cases of synonyms or homonyms were found within the analyzed set.The results of the study indicate a pronounced differentiation, ie all five examined varieties represent unique genotypes.
 Conclusion: The examined sets of genotypes possess significant genetic variability, which is important especially when we consider that a relatively small number of samples have been analyzed.

Pyramiding resistance genes and widening the genetic base of the apple (Malus × domestica Borkh.) crop

Apple breeding is active worldwide and yet the apple crop is in a precarious state as it relies on few dominant cultivars and only the Rvi6 (formerly Vf) gene, that confers resistance to scab, has been extensively exploited in the cultivars entered the market in recent years. However, there are some 20 disease resistance genes described in apple and the apple germplasm includes thousands of accessions in the repositories. In this paper, a breeding programme is described, whereby 36 genotypes, including ancient and contemporary apple cultivars, were crossed to produce a new set of selections that combine extensive genetic resources with pyramided resistance genes to several apple diseases, such as scab and powdery mildew. The 110 cross combinations carried out successfully, of the 260 initially planned, produced 7,876 offsprings, reduced to 2,969 after screening with molecular markers associated with five resistance genes. Selections with three or two resistance genes and good agronomic characteristics were kept for further field observations with the aims of creating new cultivars for the market and new parents for future breeding projects

Genome-Wide Identification of Brassinosteroid Signaling Downstream Genes in Nine Rosaceae Species and Analyses of Their Roles in Stem Growth and Stress Response in Apple.

Brassinosteroid signaling downstream genes regulate many important agronomic traits in rice. However, information on such genes is limited in Arabidopsis and Rosaceae species. We identified these genes in Arabidopsis and nine Rosaceae species. They were, respectively, named based on chromosomal locations. Segmental duplication and whole-genome duplication under purifying selection, as determined by Ka/Ks analysis, likely contributed to Rosaceae gene expansion. Apple (Malus domestica), Arabidopsis, and rice genes were generally similar, while several Rosaceae genes differed from their rice homologs in various characteristics, such as gene length, subcellular localization, transmembrane topology, conserved domains, secondary structures, and responses to external signals. The brassinosteroid downstream genes in apple were, respectively, induced or repressed by five phytohormones. Furthermore, these apple downstream genes were differentially expressed in different apple grafting combinations (“Nagafu No. 2”/“Malling 9” and “Nagafu No. 2”/“Nagafu No. 2”) and long–short shoot varieties (“Yanfu No. 6” and “Nagafu No. 2”). Responses of the MdBZR genes to diverse stress signals were examined and candidate hub genes were identified. These findings indicated that several brassinosteroid signaling downstream genes in Rosaceae functionally differed from their rice homologs, and certain apple genes may play roles in plant height and stress responses. This study provided valuable information and presented enriched biological theories on brassinosteroid signaling downstream genes in apple. Identification of such genes serve to help expand apple breeding and growth. This study provides useful information for brassinosteroid signaling downstream genes.

Preliminary genetic mapping of fire blight and European canker resistances in two apple breeding families

Preliminary genetic mapping of fire blight and European canker resistances in two apple breeding families