Selecting the superior late-leafing genotypes of Persian walnut (Juglans regia L.) using morphological and pomological evaluations

BACKGROUND

Late-spring frost is one of the major factors limiting and reducing yield of Persian walnut (Juglans regia L.) in temperate regions, including Iran. Therefore, in the present study, seedling-originated genotypes of walnut were investigated to identify late-leafing genotypes with high-quality kernels for direct cultivation in orchards or as parents in breeding programs. In the first step, the variation of the selected trees was investigated in terms of traits related to phenology, vegetation, and fruit. In the second step, late-leafing trees were identified and their traits related to kernel quality were investigated to identify superior genotypes.

RESULTS

Strong variabilities were exhibited among the studied genotypes based on the traits recorded. The genotypes showed high variation based on dates of leafing, full male flowering date, and full female flowering date, including very early, early, moderate, and late. After recording the leafing date, 21 late-leaf genotypes were identified and evaluated to select the superiors among them in terms of kernel quantity and quality. Among them, the values of nut-related traits ranged as follows: nut length: 30.12-49.74 mm, nut width: 29.31-37.17 mm, nut weight: 8.77-16.47 g, and shell thickness: 1.15-2.25 mm. The values of kernel-related traits ranged as follows: kernel length: 22.35-35.73 mm, kernel width: 21.79-29.03 mm, kernel weight: 3.22-8.17 g, and kernel percentage: 35.08-53.95%.

CONCLUSIONS

According to the ideal values and situations of commercial characteristics of walnut, twelve promising late-leafing genotypes (No. 9, 13, 32, 33, 72, 77, 78, 82, 83, 86, 92, and 98) were identified and are recommended for cultivation in orchards.

Estimating late spring frost-induced growth anomalies in European beech forests in Italy

Weather extremes and extreme climate events, like late spring frosts, are expected to increase in frequency and duration during the next decades. Although spring phenology of European beech is well adapted to escape freeze damages on longer time scales, the effects of occasional late spring frosts (LSF) are among the main climatic damages to these forests to such an extent that they limit beech distribution and elevation range, especially at its southern margin. The aim of this work was to evaluate the short-term effects of two consecutive LSF events occurred in 2016 and 2017 in Italy on the beech forest vegetation activity. Remotely sensed land surface temperature (LST) data were used to detect the pixels where LSF occurred, while enhanced vegetation index (EVI) data were used to quantify LSF effects by computing a spring vegetation activity anomaly index (sAI). In 2016 and 2017, the LSF covered, respectively, about 29% and 32% of the total Italian beech-dominated area. The two LSF widely differed in their spatial patterns and their effects. In 2016, the pixels belonging to the sAI classes with the highest spring anomalies were also those where prolonged LSF occur, while, in 2017, the pixels belonging to the highest sAI classes were those that underwent the shorter (but probably more intense) LSF events. Under scenarios of increased frequency risk of repeated LSF, the proposed methodology may represent an automatic and low-cost tool both for monitoring and predicting European beech growth patterns.

Frost controls spring phenology of juvenile Smith fir along elevational gradients on the southeastern Tibetan Plateau

Impacts of climatic means on spring phenology are well documented, whereas the role of climatic variance, such as occurrence of spring frosts, has long been neglected. A large elevational gradient of forests on the southeastern Tibetan Plateau provides an ideal platform to explore correlates of spring phenology and environmental factors. We tested the hypothesis that spring frost was a major factor regulating the timing of bud-leaf phenology by combining 5 years of in situ phenological observations of Abies georgei var. smithii with concurrent air temperature data along two altitudinal gradients. Mean lapse rate for the onset of bud swelling and leaf unfolding was 3.1 ± 0.5 days/100 m and 3.0 ± 0.6 days/100 m, respectively. Random forest analysis and conditional inference trees revealed that the frequency of freezing events was a critical factor in determining the timing of bud swelling, independent of topographic differences, varying accumulation of chilling days, and degree-days. In contrast, the onset of leaf unfolding was primarily controlled by the bud swelling onset. Thus, the timing of bud swelling and leaf unfolding appear to be controlled directly and indirectly, respectively, by spring frost. Using space-for-time substitution, the frequency of spring freezing events decreased by 7.1 days with 1 °C of warming. This study provides evidence for impacts of late spring frosts on spring phenology, which have been underappreciated in research on phenological sensitivity to climate but should be included in phenology models. Fewer spring freezing events with warming have important implications for the upward migration of alpine forests and treelines.

Production, pomological and nutraceutical properties of apricot

Apricot (Prunus sp.) is an important fruit crop worldwide. Despite recent advances in apricot research, much is still to be done to improve its productivity and environmental adaptability. The availability of wild apricot germplasms with economically interesting traits is a strong incentive to increase research panels toward improving its economic, environmental and nutritional characteristics. New technologies and genomic studies have generated a large amount of raw data that the mining and exploitation can help decrypt the biology of apricot and enhance its agronomic values. Here, we outline recent findings in relation to apricot production, pomological and nutraceutical properties. In particular, we retrace its origin from central Asia and the path it took to attain Europe and other production areas around the Mediterranean basin while locating it in the rosaceae family and referring to its genetic diversities and new attempts of classification. The production, nutritional, and nutraceutical importance of apricot are recapped in an easy readable and comparable way. We also highlight and discuss the effects of late frost damages on apricot production over different growth stages, from swollen buds to green fruits formation. Issues related to the length of production season and biotic and abiotic environmental challenges are also discussed with future perspective on how to lengthen the production season without compromising the fruit quality and productivity.

Transcriptome profiling of fully open flowers in a frost-tolerant almond genotype in response to freezing stress

Spring frost is a major limiting abiotic stress for the cultivation of almonds [Prunus dulcis (Mill.)] in Mediterranean areas or the Middle East. Spring frost, in particular, damages almond fully open flowers, resulting to significant reduction in yield. Little is known about the genetic factors expressed after frost stress in Prunus spp. as well as in almond fully open flowers. Here, we provide the molecular signature of pistils of fully open flowers from a frost-tolerant almond genotype. The level of frost tolerance in this genotype was determined for all three flowering stages and was confirmed by comparing it to two other cultivars using several physiological analyses. Afterwards, comprehensive expression profiling of genes expressed in fully open flowers was performed after being exposed to frost temperatures (during post-thaw period). Clean reads, 27,104,070 and 32,730,772, were obtained for non-frost-treated and frost-treated (FT) libraries, respectively. A total of 62.24 Mb was assembled, generating 50,896 unigenes and 66,906 transcripts. Therefore, 863 upregulated genes and 555 downregulated genes were identified in the FT library. Functional annotation showed that most of the upregulated genes were related to various biological processes involved in responding to abiotic stress. For the first time, a highly expressed cold-shock protein was identified in the reproductive organ of fruit trees. The expression of six genes was validated by RT-PCR. As the first comprehensive analysis of open flowers in a frost-tolerant almond genotype, this study represents a key step toward the molecular breeding of fruit tree species for frost tolerance.

Spring frost vulnerability of sweet cherries under controlled conditions

Spring frost is a significant production hazard in nearly all temperate fruit-growing regions. Sweet cherries are among the first fruit varieties starting their development in spring and therefore highly susceptible to late frost. Temperatures at which injuries are likely to occur are widely published, but their origin and determination methods are not well documented. In this study, a standardized method was used to investigate critical frost temperatures for the sweet cherry cultivar 'Summit' under controlled conditions. Twigs were sampled at four development stages ("side green," "green tip," "open cluster," "full bloom") and subjected to three frost temperatures (-2.5, -5.0, -10.0 °C). The main advantage of this method, compared to other approaches, was that the exposition period and the time interval required to reach the target temperature were always constant (2 h). Furthermore, then, the twigs were placed in a climate chamber until full bloom, before the examination of the flowers and not further developed buds started. For the first two sampling stages (side green, green tip), the number of buds found in open cluster, "first white," and full bloom at the evaluation date decreased with the strength of the frost treatment. The flower organs showed different levels of cold hardiness and became more vulnerable in more advanced development stages. In this paper, we developed four empirical functions which allow calculating possible frost damages on sweet cherry buds or flowers at the investigated development stages. These equations can help farmers to estimate possible frost damages on cherry buds due to frost events. However, it is necessary to validate the critical temperatures obtained in laboratory with some field observations.