Preanthesis changes in freeze resistance, relative water content, and ovary growth preempt bud phenology and signify dormancy release of sour cherry floral buds

Physio-Biochemical Insights into the Cold Resistance Variations among Nectarine (Prunus persica (L.) Batsch var. nectarina) Cultivars

Cold stress occurs in late winter and early spring threatens greatly the nectarine industry. In this study, the semi-lethal low temperature (LT50) and thirteen cold resistance related parameters of five nectarine cultivars, including 'Nonglehong little princess' (LP), 'Luyou No. 5' (LY), 'Nonglehong No. 6' (NL), 'Zhongyou No. 20' (ZY) and 'Qiuhongzhu' (QH), were determined. Based on these parameters, they were categorized into high-(HR, including NL and LP), moderate-(MR, including QH) and low-cold resistant (LR, including ZY and LY) groups. The relative water (RW), proline (PRO), soluble sucrose (SS) and soluble protein (SP) contents, and superoxide dismutase (SOD) and peroxidase (POD) activities of HR cultivars were higher while their relative electronic conductivity (RE), malondialdehyde (MDA) and gibberellin acid (GA3) contents and catalase (CAT) activity were lower than other cultivars during natural overwintering. Redundancy analysis revealed that the lowest temperature in a day (LT) and LT50 significantly explains 69.8% and 10.9% of these physiological variables, respectively. Moreover, GA3 and indoleacetic acid (IAA) contents and CAT activity were positively correlated, while PRO, SS, ABA and RW contents were negatively correlated with both LT and LT50. Our study will be helpful in understanding the cold resistance variations of nectarine germplasm resources.

Chilling Requirements of Apricot (Prunus armeniaca L.) Cultivars Using Male Meiosis as a Dormancy Biomarker

Apricot has undergone an important cultivar renewal during the last years in response to productive and commercial changes in the crop. The impact of the sharka disease (plum pox virus) prompted the release of cultivars resistant/tolerant to this virus, leading to a major cultivar renewal worldwide. This has caused high variability in chilling requirements on new releases that remain unknown in many cases. In many apricot-growing areas, the lack of winter chilling is becoming a limiting factor in recent years. To deal with this situation, growers must choose cultivars well adapted to their areas. However, the information available on the agroclimatic requirements of the cultivars is very limited. To fill this gap, in this work, we have characterized the chilling requirements of 13 new apricot cultivars from Europe (France, Greece and Spain) and North America (USA) in two experimental collections in Aragón (Spain). We established the chilling period using male meiosis as a biomarker for endodormancy release over two years. Chilling requirements ranged from 51.9 Chill Portions (CP) to 70.9 CP. Knowing the chilling requirements of cultivars will help growers to select suitable cultivars adapted to the chill availability of their region.

Differential thermal analysis reveals the sensitivity of sweet cherry flower organs to low temperatures

The frequency and severity of spring frosts increase during the budburst in many regions of the world as global warming increases. Variability in the freezing resistance of sweet cherry flower organs during the active growing period has been rarely documented, especially in regard to the sepal, pedicel, receptacle, petal, stamen, and pistil organs of flower at the deacclimation stage. The freezing resistance of flower organs of six sweet cherry cultivars was investigated at regular intervals from the first white stage through the full bloom stage using differential thermal analysis (DTA) for 2019-2020. For most of the cultivars, petal and stamen organs of flower exhibited higher freezing resistance than other flower organs. There were significant differences in frost tolerance among cultivars, and 'Van' and 'Wild Genotype' had a lower level of low temperature exotherms or critical temperatures (LT₅₀ values) in both stages, whereas 'Merton Late' was more sensitive to frost than other cultivars. Additionally, an increase in LT₅₀ values in all cultivars was observed with the progression of the budburst. The results in the present study can increase the certainty of decision-making regarding the timing and methods to increase the air temperature in orchards during spring frost events to prevent frost damage. Larger data sets are required to further validate our results, and future efforts should thus be focused on determining the critical temperatures of flower organs using different measurement techniques.

Male Meiosis as a Biomarker for Endo- to Ecodormancy Transition in Apricot

Dormancy is an adaptive strategy in plants to survive under unfavorable climatic conditions during winter. In temperate regions, most fruit trees need exposure to a certain period of low temperatures to overcome endodormancy. After endodormancy release, exposure to warm temperatures is needed to flower (ecodormancy). Chilling and heat requirements are genetically determined and, therefore, are specific for each species and cultivar. The lack of sufficient winter chilling can cause failures in flowering and fruiting, thereby compromising yield. Thus, the knowledge of the chilling and heat requirements is essential to optimize cultivar selection for different edaphoclimatic conditions. However, the lack of phenological or biological markers linked to the dormant and forcing periods makes it difficult to establish the end of endodormancy. This has led to indirect estimates that are usually not valid in different agroclimatic conditions. The increasing number of milder winters caused by climatic change and the continuous release of new cultivars emphasize the necessity of a proper biological marker linked to the endo- to ecodormancy transition for an accurate estimation of the agroclimatic requirements (AR) of each cultivar. In this work, male meiosis is evaluated as a biomarker to determine endodormancy release and to estimate both chilling and heat requirements in apricot. For this purpose, pollen development was characterized histochemically in 20 cultivars over 8 years, and the developmental stages were related to dormancy. Results were compared to three approaches that indirectly estimate the breaking of dormancy: an experimental methodology by evaluating bud growth in shoots collected periodically throughout the winter months and transferred to forcing chambers over 3 years, and two statistical approaches that relate seasonal temperatures and blooming dates in a series of 11-20 years by correlation and partial least square regression. The results disclose that male meiosis is a possible biomarker to determine the end of endodormancy and estimate AR in apricot.

Creation and Use of Highly Adaptive Productive and Technological Red Currant Genotypes to Improve the Assortment and Introduction into Different Ecological and Geographical Zones

Global climate change with the cyclicity of natural and climatic processes in the growing season of berry plants, causes weakening at the defense system to (a)biotic stressors, which actualize the need for accelerated cultivar-improving breeding. A new hybrid red currant material was obtained and studied by the method of interspecific hybridization. Correlation analysis was used to assess the relationship between adaptively significant and economical and biological traits. To assess intergenotypic variability, hierarchical clustering was used according to the studied features, which allowed combining three standard methods of multidimensional data analysis. Genotypes adapted to different stressors were identified. The genotypes 271-58-24, 44-5-2, 261-65-19, and ‘Jonkheer van Tets’ were found to have a higher ratio of bound water to free water as compared with the others. Moreover, the genotypes of 271-58-24, 261-65-19, 77-1-47, and ‘Jonkheer van Tets’ were found to have less cold damage during the cold periods. The two most productive genotypes were found to be the genotypes 44-5-2, 143-23-35, and 1426-21-80. A dependence of yield on the beginning of differentiation of flower buds, which led to the abundance of flower inflorescences, was revealed. Rapid restoration of leaf hydration ensured successful adaptation of genotypes to the “temperature shock” of the growing season. The genotypes 271-58-24 and ‘Jonkheer van Tets’ were then observed to be far from the test traits and none of these traits were observed to characterize these two genotypes. The genotypes of 261-65-19 and 77-1-47 were then observed to be characterized by their high stability to Cecidophyopsis ribis scores. Genotypes 261-65-19 and 271-58-24, obtained with the participation of ‘Jonkheer van Tets’ as the maternal form, showed sufficient resistance to Pseudopeziza ribis and Cecidophyopsis ribis. Overall results suggested that the hydration recovery of red currant plants is significantly important for a yield improvement. A new cultivar ’Podarok Pobediteliam (genotype 44-5-2) was obtained that meets the requirements of intensive gardening and is characterized by high adaptability, productivity, and technological effectiveness.