Low Chilling Requirement Research Articles

Effective Categorization of Tolerance to Salt Stress through Clustering Prunus Rootstocks According to Their Physiological Performances

The effects of climate change on traditional stone fruit producing areas, together with the generation of new varieties with lower chilling requirements that allow the cultivation of previously unexplored areas, are setting up a challenging scenario for the establishment of productive orchards that must be more efficient in their capacity to adapt to new edaphoclimatic conditions. In this context, the rootstock breeding programs are a key piece in the agronomic strategy to achieve this adaptation through the development of rootstocks compatible with the new varieties and capable of transferring their tolerance to stress. An effective categorization of phenotypes within the germplasm involved in a plant breeding program is of utmost importance. Through the measurement of physiological parameters in both roots and leaves, tolerance to saline stress (120 mM NaCl) was evaluated in seven Prunus rootstocks whose genetic background included representatives of the subgenera Prunus, Cerasus, and Amygdalus. To group the genotypes according to their physiological performance under salt stress, an agglomerative hierarchical clustering was applied. The genotypes were grouped into three clusters containing rootstocks very sensitive (‘Mazzard F12/1’), moderately tolerant (‘Maxma 60’, ‘Cab6P’ and ‘AGAF 0204-09’), and tolerant (‘Mariana 2624’, ‘Garnem’ and ‘Colt’) to salt stress. ‘Mariana 2624’, a plum-based rootstock, was identified as the most tolerant Prunus rootstock. The information reported is valuable both in the productive context, for the selection of the most appropriate rootstocks to establish an orchard, and in the context of plant breeding programs, when choosing parents with outstanding traits to obtain progenies tolerant to salt stress.

Enhancing the sustainability of Mediterranean olive groves through adaptation measures to climate change using modelling and response surfaces

Some adaptation measures in response to the severe impacts of climate change on Mediterranean olive orchards were evaluated under a wide range of weather conditions. For this task, a decision support system for improving resources management by the integration of the AdaptaOlive simulation model, perturbed climate and impact and adaptation response surfaces for the model output analysis was developed. Thus, the introduction of irrigation (considering different irrigation strategies such as full demand, regulated deficit irrigation or irrigation support), the implementation of cultivars with lower chilling requirements, the modification of orchard density and an increase in irrigation efficiency were evaluated under current and future weather conditions.Optimal sustainable and environmentally friendly adaptation measures varied depending on the local weather conditions. Thus, the introduction of irrigation provided excellent results under dry and cool winter weather conditions. Cultivars with low chilling requirements reduced flowering failure associated with the lack of chill accumulation and registered optimal performance under mild winter conditions. This adaptation measure played a critical role under these weather conditions, even more so than measures focused on preventing water stress as irrigation. Finally, increasing orchard density was appropriate in non-water-limited areas with cool winter conditions.This study confirms the great importance of integrating crop modelling and tools for model output analysis into the assessment of site-specific adaptation measures to climate change, in order to ensure the sustainability of Mediterranean agricultural systems under semi-arid conditions.

Low Chilling Requirement Apple Cultivars as a Potential Genomic Resource for Improving Heat Stress Tolerance During Global Warming

Low Chilling Requirement Apple Cultivars as a Potential Genomic Resource for Improving Heat Stress Tolerance During Global Warming

‘lucía myrtea’ and ‘victoria myrtea’: Two New Japanese Plum Cultivars with Low Chilling Requirements, Early Ripening, and High-quality Fruit for the Fresh Market

"‘lucía myrtea’ and ‘victoria myrtea’: Two New Japanese Plum Cultivars with Low Chilling Requirements, Early Ripening, and High-quality Fruit for the Fresh Market" published on Nov 2021 by American Society for Horticultural Science.

High-quality reference genome and annotation aids understanding of berry development for evergreen blueberry (Vaccinium darrowii)

Vaccinium darrowii Camp (2n = 2x = 24) is a native North American blueberry species and an important source of traits such as low chill requirement in commercial southern highbush blueberry breeding (Vaccinium corymbosum, 2n = 4x = 48). We present a chromosomal-scale genome of V. darrowii generated by the combination of PacBio sequencing and high throughput chromatin conformation capture (Hi–C) scaffolding technologies, yielding a total length of 1.06 Gigabases (Gb). Over 97.8% of the genome sequences are scaffolded into 24 chromosomes representing the two haplotypes. The primary haplotype assembly of V. darrowii contains 34,809 protein-coding genes. Comparison to a V. corymbosum haplotype assembly reveals high collinearity between the two genomes with small intrachromosomal rearrangements in eight chromosome pairs. With small RNA sequencing, the annotation was further expanded to include more than 200,000 small RNA loci and 638 microRNAs expressed in berry tissues. Transcriptome analysis across fruit development stages indicates that genes involved in photosynthesis are downregulated, while genes involved in flavonoid and anthocyanin biosynthesis are significantly increased at the late stage of berry ripening. A high-quality reference genome and accompanying annotation of V. darrowii is a significant new resource for assessing the evergreen blueberry contribution to the breeding of southern highbush blueberries.

Characterization of strawberry genotypes with low chilling requirement for cultivation in tropical regions

Although strawberry can be cultivated in all types of climate, it grows best in temperate climates, limiting its cultivation in certain countries or regions with tropical or subtropical climates. The objective of this study was to verify the genetic diversity of 34 pre-selected day-neutral strawberry genotypes in humid tropical and subtropical conditions through characterization of morpho-agronomic characteristics and molecular markers. The selection was based on qualitative and quantitative morpho-agronomic traits, using the Gower algorithm. Molecular characterization was performed with AFLP markers, using four combinations of selective primers. Six representative variables were subjected to principal component analysis (PCA) and the Mulamba and Mock selection index. Soluble solids and luminosity of the outer part of the fruit did not differ among genotypes but presented values ​​above those usually found. AFLP markers detected 80% polymorphism, confirming high genetic variability among genotypes. Clustering based on molecular and agronomic data separated the genotypes into three groups, and the Mulamba and Mock index did not select individuals derived from 'Albion' or RVFS06. PCA highlighted the genotypes RVCA16M-1, RVDA11M-3, RVDA11M-4, and RVDA11M-25 as superior for most of the evaluated traits compared with the commercial cultivars 'Albion' and 'Monterey'. The PCA and selection index results indicate the reliability of the multivariate analysis for selecting superior strawberry genotypes for cultivation in tropical regions. Of the 34 genotypes analyzed, four stood out with potential for immediate cultivation.

High-quality genome assembly of 'Cuiguan' pear (Pyrus pyrifolia) as a reference genome for identifying regulatory genes and epigenetic modifications responsible for bud dormancy

Dormancy-associated MADS-box (DAM) genes serve as crucial regulators of the endodormancy cycle in rosaceous plants. Although pear DAM genes have been identified previously, the lack of a high-quality reference genome and techniques to study gene function have prevented accurate genome-wide analysis and functional verification of such genes. Additionally, the contribution of other genes to the regulation of endodormancy release remains poorly understood. In this study, a high-quality genome assembly for 'Cuiguan' pear (Pyrus pyrifolia), which is a leading cultivar with a low chilling requirement cultivated in China, was constructed using PacBio and Hi-C technologies. Using this genome sequence, we revealed that pear DAM genes were tandemly clustered on Chr8 and Chr15 and were differentially expressed in the buds between 'Cuiguan' and the high-chilling-requirement cultivar 'Suli' during the dormancy cycle. Using a virus-induced gene silencing system, we determined the repressive effects of DAM genes on bud break. Several novel genes potentially involved in the regulation of endodormancy release were identified by RNA sequencing and H3K4me3 chromatin immunoprecipitation sequencing analyses of 'Suli' buds during artificial chilling using the new reference genome. Our findings enrich the knowledge of the regulatory mechanism underlying endodormancy release and chilling requirements and provide a foundation for the practical regulation of dormancy release in fruit trees as an adaptation to climate change.

Bud break accompanies with the enhanced activities of hemicellulase and pectinase and the mobilization of cell wall thickenings in Persian walnut bud scales

The endo-dormant bud scales of walnut have storage parenchyma cells with thickened walls. During bud dormancy release, cell wall hydrolytic enzymes mobilize pectin and hemicellulose reserves of these cells to fuel bud break. Cell wall hydrolytic enzymes might define specific stages of bud dormancy release. Bud dormancy release is important in woody plants as it is linked to final biomass and yield. This process requires enzyme activities which affect the bud cell wall physico-chemical properties, however, little information is available. Accordingly, the activities of some cell wall hydrolytic enzymes were studied during endo-dormancy release in lateral buds of two Persian walnut (Juglans regia L.) cultivars having low (‘Serr’) and high (‘Hartley’) chilling requirements (CRs). Buds were collected monthly from the leaf shedding stage (November) till bud break and used for enzymatic analysis. In both cultivars, the activities of 1,4-β-D-glucanase, xylanase, mannanase and pectinase increased during dormancy release. In ‘Serr’, first rises in mannanase and pectinase activities occurred before transition to eco-dormancy (January) and the second rises occurred before bud break (March). Similarly, in ‘Hartley’, first rise in mannanase activity observed before transition to eco-dormancy (February) and the second rise before bud break (April). ‘Serr’ buds also displayed significant increase in the activities of hemicellulases and pectinase earlier than ‘Hartley’, however, the latter showed quantitatively higher means for the enzymatic activities. Endo-dormant bud scales had very thick-walled storage parenchyma cells which turned into thinner-walled ones during bud break, suggesting cell wall polysaccharide mobilization by hemicellulases and pectinases. Thus, the activation of cell wall hydrolytic enzymes during endo-dormancy release may contribute to the bud scale cell wall carbohydrate reserve mobilization and/or growth-associated wall relaxation in preparation for bud break. Furthermore, buds from low CR plants may show earlier activation of cell wall-loosening mechanisms during dormancy release.

Assessment of Chilling Requirement and Threshold Temperature of a Low Chill Pear (Pyrus communis L.) Germplasm in the Mediterranean Area

In temperate climates, bud break and shoot and flower emission of deciduous fruit tree species are regulated by precise chilling and heating requirements. To investigate this aspect, sixty-one accessions of European pear (Pyrus communis L.) collected in Sicily were phenotyped for three consecutive years for harvest date, bud sprouting and blooming to determine both the chilling requirements and the threshold temperature using the Chill Days model. The whole germplasm collection was grown in two different experimental fields located at 10 and 850 m above sea level representing two Mediterranean-type climates in which pear is commonly cultivated. Results revealed a mean threshold temperature of 6.70 and 8.10 °C for the two experimental fields, respectively, with a mean chilling requirement ranging from −103 and −120 days. Through this approach, novel insights were gained on the differences in chilling requirement for early flowering cultivars to overcome dormancy. Furthermore, to better dissect differences in chilling requirement between accessions, the sprouting bud rate of six cultivars was assessed on excised twigs stored at 4 ± 0.1 °C from 300 to 900 h followed by a period at 25 ± 0.1 °C varying from seven to twenty-eight days. Results of both experiments highlighted that Sicilian pear germplasm is characterized by a low chilling requirement compared to other pear germplasm, making Sicilian local accessions valuable candidates to be used for selecting novel cultivars, coupling their low chilling requirements with other traits of agronomical interest.

Exploring low-chill genotypes of Persian walnut (Juglans regia L.) in west of Iran

Climate change may cause a significant decline in winter chill over the coming decades and is becoming an important issue for walnut (Juglans regia L.) breeding programs to address. The current study was conducted to identify superior walnut genotypes with low-chilling requirements in western Iran (Ilam province). In the first step, approximately 200 walnut trees of seed-origin were pre-selected based on a questionnaire. Based on this primary evaluation for phenotypic and horticultural traits, 55 of the 200 genotypes were selected for further study. Morphological and phenological traits of these 55 were evaluated for two consecutive years and 11 genotypes were selected as superior. These superior genotypes were moderate to late-leafing with high yield, lateral fruitfulness, thin shells, and light to extra light kernel color. Nut weight, kernel weight and kernel percentage of the 11 superior genotypes ranged between 12.6–15.9 g, 6.9–8.2 g, and 49.7–62.0%, respectively. These superior genotypes had high levels of protein (13.3–18.2%), oil (55.3–65.9%) and PUFAs content. Assessment of chilling requirement of these superior genotypes showed that eight (IrIlZg1, IrIlZg13, IrIlZg7, IrIlZg12, IrIlAa92, IrIlAa47, IrIlAa48 and IrIlAa27) had significantly lower chilling requirements than the cultivar ‘Chandler’. Although having low-chill requirements, these genotypes were moderate to late-leafing. This may be due to their high heat requirement, since chilling requirement together with heat accumulation determines the leafing and flowering date. In conclusion, the selected low chilling requirement genotypes having moderate to late leafing could be used in walnut breeding programs to release commercial cultivars which are suitable for areas with spring frost concerns and expected future loss of winter chill due to climate change.

County-Specific Chill Hours Accumulation in South Carolina

Winter chilling is critical for most temperate fruits and perennial plants during the winter season. Most fruit and nut trees require a prolonged period of chilling to break their dormant stage and bloom when spring arrives. This research’s primary objective was to calculate the chill hour’s accumulation in each county in South Carolina based on the historical hourly air temperature data for the last ten years (2010-2020). The chilling hours model used to calculate the daily chill hours was based on the number of hours when the air temperature was between 32°F to 45°F (0 to 7.2°C). The total chill hours for each county were then determined by accumulating the daily chill hours from October to June. Our results showed that among the different counties in South Carolina, on average Laurens County had the most prolonged chill hours (1419 hrs). The chill hours were higher between November to March, and counties near the coastal regions had fewer chill hours than the counties in the inland areas. For example, Beaufort, Charleston, Berkeley, Horry, and Dorchester counties that are located near the coastal region had fewer chill hours. In contrast, counties located in the inland areas like Laurens, Chester, Lancaster, and York recorded the most prolonged chill hours. Our results suggest that selecting high chilling requirement crops for the inland areas and low chilling requirement crops for coastal areas would be appropriate. Farmers in South Carolina can use this information to plan their crop selection and management.

Viability of temperate fruit tree varieties in Spain under climate change according to chilling accumulation

Fruit trees stop their growth over the coldest period of the year to avoid damage. To resume their growth and for successful fruit production, they need to accumulate winter chill. It is expected that global warming will diminish winter chill availability with potentially negative impacts on the viability and yield of these crops. The objective of this study was to assess the viability of seven tree crops among the most relevant in peninsular Spain and the Balearic Islands. For this purpose, chilling requirements were gathered from the literature to define a requirement range for each tree crop encompassing most of the varieties used in Spain. Then the bias-adjusted outputs of an ensemble of 10 regional climate models under the two representative concentration pathways (RCPs), 4.5 and 8.5, were used to feed a chilling model for calculating chill accumulation. The ensemble's outcome agreement index was applied to each combination of chill requirement and climate ensemble to assess crop viability. This was done by testing the hypothesis that the winter chill accumulation will be greater than the safe winter chill for the 2021–2050 (near future) and 2071–2100 (far future) periods and for both RCPs. A future reduction in the safe winter chill areas is projected with high agreement in climate projections across peninsular Spain and the Balearic Islands independently of the RCP or future period. The crops studied would be viable in the near future period as long as varieties with low chilling requirements are used. These varieties, however, would not be adequate in the far future in some currently highly productive regions, where the situation would become more severe, especially under the RCP8.5 scenario. In these cases, adaptation would be possible by shifting the crop to adjacent areas together with careful variety selection in terms of chilling requirements. The results indicate that the RCP8.5 scenario in the far future has an especially negative impact on the crops analysed, calling for resolute mitigation measures to guarantee tree crop production and food security. Recommendations for adaptation, with low uncertainty regarding climate projections, were included here, using actual tree varieties, thereby facilitating interpretation and on-field application for farmers and agricultural technicians.

Requerimento de frio de cultivares de pessegueiro e recomendação de cultivo no Rio Grande do Sul

O pessegueiro apresenta um período de dormência no outono/inverno, superado pelo acúmulo de horas de frio (HF), variável com a cultivar. O objetivo desse trabalho foi quantificar a necessidade de frio na dormência de 18 cultivares de pessegueiro. Estacas de ‘Flor da Prince’, ‘Planalto’, ‘Vanguarda’, ‘Robidoux’, ‘Fascínio’, ‘Cerrito’, ‘Libra’, ‘Chimarrita’, ‘Atenas’, ‘Maciel’, ‘Kampai’, ‘Granada’, ‘Santa Aurea’, ‘Barbosa’, ‘Della Nona’, ‘Mandinho’, ‘Bonão’ e ‘Baby Gold’ foram coletadas a campo em abril/2019. Submeteu-se as estacas em câmaras incubadoras a 7,2°C e dois tempos de frio (200 e 400 HF). Após cada tempo de frio, transferiu-se as estacas para 20ºC para indução da brotação das gemas. Estratificou-se as cultivares quanto a exigência de frio em três classes: baixa (≤200 HF), média (201-400 HF) e alta (>400 HF). Relacionou-se a exigência de frio das cultivares com as datas de brotação e colheita a campo e zoneou-se as cultivares às regiões ecofisiográficas do RS, baseado no mapa de HF. ‘Flor da Prince’, ‘Vanguarda’, ‘Mandinho’, ‘Libra’, ‘Kampai’, ‘Granada’, ‘Bonão’ e ‘Cerrito’ necessitaram ≤200 HF para superar a dormência. ‘Fascínio’, ‘Baby Gold’, ‘Atenas’, ‘Maciel’, ‘Santa Aurea’ e ‘Chimarrita’ necessitaram de 201-400 HF. ‘Barbosa’, ‘Planalto’, ‘Della Nona’ e ‘Robidoux’ necessitaram >400 HF. As datas de brotação e colheita das cultivares a campo relacionaram-se com a exigência de frio dos genótipos. As cultivares de baixa exigência podem ser cultivadas em todo o Estado; as de média exigência limitam-se ao cultivo apenas na fronteira oeste; e as de alta exigência são recomendadas principalmente para Serra Gaúcha, Campos de Cima da Serra, parte do Planalto Médio e da Serra do Sudeste.

Improving crucial details and selecting the optimal model for evaluating the chilling requirement of Paeonia lactiflora Pall. at low latitudes during four winters

The countless perennial plants face severe problems associated with insufficient chilling accumulation and obstacles to dormancy release in warm-winter climates as a result of increased global warming. These problems hinder the ability of these plants to grow in low-latitude regions and consequently reduce their economic values. “The southward planting of herbaceous peony” (Paeonia lactiflora Pall.) is a representative example of promoting the expansion of temperate plants into subtropical and even tropical regions. Evaluating the chilling requirement (CR) of herbaceous peony and then selecting or breeding new cultivars that have substantial low-CR traits are important for peony cultivation and popularization at low latitudes. In this study, natural and controlled chilling treatments and CR evaluations were conducted for the southernmost cultivated Chinese peony, ‘Hang Baishao’, initially during three winters. The start times of the evaluations and the assessment criteria for the CR fulfillments were specifically defined, after which five models were used to evaluate the CR of ‘Hang Baishao’. According to the stability of the CR value during the three years, the availability of overlaps among the three-year CR ranges, and the correlations between the CR values and the morphological data, the Utah (UT) model was identified as the optimal model and was subsequently used to evaluate five other northern peony cultivars. The results indicate that ‘Hang Baishao’ and ‘Qihua Lushuang’ were representative cultivars with a low CR, while ‘Zhuguang’ represented a typical cultivar with a high CR. The dependability of the UT model was further confirmed by evaluating the CR of ‘Hang Baishao’ and ‘Zhuguang’ during a fourth winter. This study constitutes an integrated research strategy on CRs on the basis of multiyear observations, multi-treatment experiments, multi-detail definitions and multi-cultivar validations, and the results could provide new perspectives for studies on economic plants that undergo winter dormancy in low-latitude regions.

New Varieties of Blueberry Released by US in 2018 and Analysis of Breeding Trends

In 2018, the United States Department of Agriculture (USDA-ARS), the Clemson University, and the University of California jointly announced 40 new varieties of blueberry, including 12 varieties of northern highbush blueberry, 21 varieties of southern highbush blueberry, and 7 varieties of ornamental blueberry. Based on the analysis of the comprehensive characteristics of the announced blueberry varieties, this paper summarizes the current development trend of global blueberry breeding. The results have been shown that: 1) the cultivation of southern highbush blueberry is still the main direction of blueberry breeding, and the number of new ornamental blueberry varieties has increased. 2) The main breeding direction for northern highbush blueberry is to cultivate new varieties with early maturity, large fruit, hard texture, and good storability. 3) The breeding trend of blueberries in the southern highbush blueberry is mainly focused on cultivating new cultivars with the low chilling requirement and have comprehensive characteristics such as early maturity, large fruit, and good fruit quality. 4) The main direction of ornamental blueberry breeding is to pay attention to the diversification of fruit color and the leaf color that changes with the season for use in Garden potted plants and landscaping. 5) In recent years, China has made rapid progress in blueberry breeding except for the traditional breeding countries such as Europe and America. The breeding trend described in this paper will point out the direction for blueberry breeding in China in the future and have important practical reference value.

Chilling accumulation in fruit trees in Spain under climate change

Abstract. Growing trees are quite vulnerable to cold temperatures. To minimise the effect of these cold temperatures, they stop their growth over the coldest months of the year, a state called dormancy. In particular, endodormancy requires accumulating chilling temperatures to finish this sort of dormancy. The accumulation of cool temperatures according to specific rules is called chilling accumulation, and each tree species and variety has specific chilling requirements for correct plant development. Under global warming, it is expected that the fulfilment of the chilling requirements to break dormancy in fruit trees could be compromised. In this study, the impact of climate change on the chilling accumulation over peninsular Spain and the Balearic Islands was assessed. For this purpose, bias-adjusted results of 10 regional climate models (RCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5 were used as inputs of four different models for calculating chilling accumulation, and the results for each model were individually compared for the 2021–2050 and 2071–2100 future periods under both RCPs. These results project a generalised reduction in chilling accumulation regardless of the RCP, future period or chilling calculation model used, with higher reductions for the 2071–2100 period and the RCP8.5 scenario. The projected winter chill decrease may threaten the viability of some tree crops and varieties in some areas where the crop is currently grown, but also shows scope for varieties with lower chilling requirements. The results are relevant for planning future tree plantations under climate change, supporting adaptation of spatial distribution of tree crops and varieties in Spain.

Southern Highbush Blueberry Cultivars from the University of Florida

Southern highbush blueberries combine the fruit quality and productivity of highbush blueberries with the low chilling requirement necessary to produce a crop in the Florida climate. Written by J. G. Williamson, D. A. Phillips, P. M. Lyrene, and P. R. Munoz and published by the UF/IFAS Horticultural Sciences Department, this 13-page major revision describes current and historical southern highbush blueberry cultivars released by the University of Florida. http://edis.ifas.ufl.edu/hs1245

Spring Is Coming: Genetic Analyses of the Bud Break Date Locus Reveal Candidate Genes From the Cold Perception Pathway to Dormancy Release in Apple (Malus × domestica Borkh.).

Chilling requirement (CR) for bud dormancy completion determines the time of bud break in apple (Malus × domestica Borkh.). The molecular control of bud dormancy is highly heritable, suggesting a strong genetic control of the trait. An available Infinium II SNP platform for genotyping containing 8,788 single nucleotide polymorphic markers was employed, and linkage maps were constructed in a F1 cross from the low CR M13/91 and the moderate CR cv. Fred Hough. These maps were used to identify quantitative trait loci (QTL) for bud break date as a trait related to dormancy release. A major QTL for bud break was detected at the beginning of linkage group 9 (LG9). This QTL remained stable during seven seasons in two different growing sites. To increase mapping efficiency in detecting contributing genes underlying this QTL, 182 additional SNP markers located at the locus for bud break were used. Combining linkage mapping and structural characterization of the region, the high proportion of the phenotypic variance in the trait explained by the QTL is related to the coincident positioning of Arabidopsis orthologs for ICE1, FLC, and PRE1 protein-coding genes. The proximity of these genes from the most explanatory markers of this QTL for bud break suggests potential genetic additive effects, reinforcing the hypothesis of inter-dependent mechanisms controlling dormancy induction and release in apple trees.

Genetic variability in a Brazilian apple germplasm collection with low chilling requirements.

The apple (Malus domestica Borkh) originally evolved to require temperatures below 7.2 °C for the induction of budding and flowering. In Brazil, breeders have overcome the climate barrier and developed the cultivars Anabela, Julieta, Carícia, and Eva, with low chilling requirements and good yield characteristics. These cultivars are grown in many warmer climate countries in South America, Africa, and the Middle East. The apple germplasm collection that originated these cultivars has several genotypes with pedigrees for a low chilling requirement. Knowledge of the variability and genetic relationships among these genotypes may be useful in the development of superior new cultivars. In this work, we first selected the best ISSR (inter-simple sequence repeat) primers for genetic studies in apple, and then we used the selected primers to evaluate the genetic variability of the apple germplasm collection at the Instituto Agronômico do Paraná. The evaluation of 42 ISSR primers in 10 apple genotypes allowed us to select the best nine primers based on the polymorphic information content (PIC) and resolving power (RP) indexes. The primer selection step was robust since the dendrogram obtained with the nine selected primers was the same as the one obtained using all 26 polymorphic primers. Primer selection using PIC and RP indexes allowed us to save about 60% of time and costs in the genetic variability study. The nine ISSR primers showed high levels of genetic variability in the 60 apple genotypes evaluated. The relevance of the primer selection step is discussed from the perspective of saving time and money in germplasm characterization. The high genetic variability and the genetic relationships among the genotypes are discussed from the perspective of the development of new apple cultivars, mainly aiming for a low chilling requirement that can better adapt to current climatic conditions or those that may arise with global warming.

‘SCS425 Luiza’: new apple cultivar with medium chilling requirement and resistant to glomerella leaf spot (colletotrichum spp.)

Abstract Apple is one of the main agribusiness products of temperate-zone fruits in Southern Brazil. More than 90% of apple production is obtained from only two apple cultivars – Gala and Fuji and their mutations. These apple varieties are insufficiently adapted to the regional climate and ‘Gala’ and its mutations are also susceptible to glomerella leaf spot – GLS, currently the main apple disease in Brazil. ‘SCS425 Luiza’ cultivar was developed by Epagri / Estação Experimental Caçador, aiming to offer to the production chain an early apple variety better adapted to the environmental conditions of Southern Brazil and resistant to GLS. ‘SCS425 Luiza’ cultivar was obtained by artificial hybridization carried out in 2001 using the cultivars Imperatriz and Cripps Pink as parents. ‘SCS425 Luiza’ has lower chilling requirement compared to ‘Galaxy’, higher flowering precocity and yield potential at least equivalent to ‘Galaxy’. It produces fruits with skin finish, flavor and flesh texture adequate for the Brazilian market and storability similar to ‘Galaxy’ apples when harvested at the same maturity.