Warm temperatures at bloom reduce fruit set in sweet cherry

Warm springs have often been assumed as a prelude of a good fruit set in temperate fruit tree species. However, recently, evidences have accumulated on erratic fruit set under apparently good and warm springs in Mediterranean conditions. The fact that these observations mainly occurred in sweet cherry (Prunus avium), a species adapted to high latitudes and cold climates raised the question of whether warm temperatures at flowering could have a detrimental effect on fruit set. To evaluate this hypothesis two different sweet cherry cultivars were subjected under field conditions to a slight increase in temperature at bloom over two different years. While the minimum temperature remained stable, the maximum temperature increased 5-7ºC, resulting in a moderate increase of the average temperature of 1-3ºC. This was sufficient to drastically reduce fruit set in both years and cultivars. To know the vulnerable phase to warm temperatures the process was timed back: final fruit set differences were established in the first three weeks following pollination, but the onset of fruiting – when these differences appeared – was tracked back to one week after pollination. The process from pollination to fertilization was examined under both conditions. Fertilization occurred six days after pollination. Higher temperatures accelerated pollen tube growth rate but also reduced the number of growing pollen tubes along the style. In the ovary, the warm treatment accelerated ovule degeneration. These findings alert on the potential negative effect of even slight increases in temperature during cherry blooming, which nowadays – due to global warming trends – is a plausible and realistic scenario under Mediterranean climatic conditions

S-Locus genotyping in Japanese plum by high throughput sequencing using a synthetic S-loci reference sequence

Self-incompatibility in Prunus species is governed by a single locus consisting of two highly multi-allelic and tightly linked genes, one coding for an F-box protein—i.e., SFB in Prunus- controlling the pollen specificity and one coding for an S-RNase gene controlling the pistil specificity. Genotyping the allelic combination in a fruit tree species is an essential procedure both for cross-based breeding and for establishing pollination requirements. Gel-based PCR techniques using primer pairs designed from conserved regions and spanning polymorphic intronic regions are traditionally used for this task. However, with the great advance of massive sequencing techniques and the lowering of sequencing costs, new genotyping-by-sequencing procedures are emerging. The alignment of resequenced individuals to reference genomes, commonly used for polymorphism detection, yields little or no coverage in the S-locus region due to high polymorphism between different alleles within the same species, and cannot be used for this purpose. Using the available sequences of Japanese plum S-loci concatenated in a rosary-like structure as synthetic reference sequence, we describe a procedure to accurately genotype resequenced individuals that allowed the analysis of the S-genotype in 88 Japanese plum cultivars, 74 of them are reported for the first time. In addition to unraveling two new S-alleles from published reference genomes, we identified at least two S-alleles in 74 cultivars. According to their S-allele composition, they were assigned to 22 incompatibility groups, including nine new incompatibility groups reported here for the first time (XXVII-XXXV)

Non-destructive determination of floral staging in cereals using X-ray micro computed tomography (µCT)

Background Accurate floral staging is required to aid research into pollen and flower development, in particular male development. Pollen development is highly sensitive to stress and is critical for crop yields. Research into male development under environmental change is important to help target increased yields. This is hindered in monocots as the flower develops internally in the pseudostem. Floral staging studies therefore typically rely on destructive analysis, such as removal from the plant, fixation, staining and sectioning. This time-consuming analysis therefore prevents follow up studies and analysis past the point of the floral staging. Results This study focuses on using X-ray µCT scanning to allow quick and detailed non-destructive internal 3D phenotypic information to allow accurate staging of Arabidopsis thaliana L. and Barley (Hordeum vulgare L.) flowers. X-ray µCT has previously relied on fixation methods for above ground tissue, therefore two contrast agents (Lugol’s iodine and Bismuth) were observed in Arabidopsis and Barley in planta to circumvent this step. 3D models and 2D slices were generated from the X-ray µCT images providing insightful information normally only available through destructive time-consuming processes such as sectioning and microscopy. Barley growth and development was also monitored over three weeks by X-ray µCT to observe flower development in situ. By measuring spike size in the developing tillers accurate non-destructive staging at the flower and anther stages could be performed; this staging was confirmed using traditional destructive microscopic analysis. Conclusion The use of X-ray micro computed tomography (µCT) scanning of living plant tissue offers immense benefits for plant phenotyping, for successive developmental measurements and for accurate developmental timing for scientific measurements. Nevertheless, X-ray µCT remains underused in plant sciences, especially in above-ground organs, despite its unique potential in delivering detailed non-destructive internal 3D phenotypic information. This work represents a novel application of X-ray µCT that could enhance research undertaken in monocot species to enable effective non-destructive staging and developmental analysis for molecular genetic studies and to determine effects of stresses at particular growth stages

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. Copyright © 2022 Herrera, Lora, Fadón, Hedhly, Alonso, Hormaza and Rodrigo

Reproductive characteristics of citrus rootstocks grown under greenhouse and field environments

The aim of the present study was to evaluate the possible effect of environmental factors on meiosis, meiotic index, pollenviability and in vitro germination of pollen from stock plants of the rootstocks Trifoliate, ‘Swingle’, ‘Troyer’, ‘Fepagro C13’, ‘FepagroC37’ and ‘Fepagro C41’ grown in a protected environment in comparison with stock plants grown in the field. The results showed thatvalues for the characteristics analyzed in 2008, 2009 and 2010 were always higher in the field than in the greenhouse conditions. Inthe field, the average of normal meiotic cells was 60.05%, 44.44% and 60.12%, respectively, and in the greenhouse, 52.75%, 30.95%and 52.82%, respectively. Mean pollen viability in the field was 90.28%, 56.23% and 74.74%, and, in the greenhouse, 64.25%, 41.41%and 66.71%, respectively. As temperature oscillations were higher in the greenhouse than in the field, we suggest that this negativelyaffects the reproductive characteristics analyzed

A transposon surveillance mechanism that safeguards plant male fertility during stress

Although plants are able to withstand a range of environmental conditions, spikes in ambient temperature can impact plant fertility causing reductions in seed yield and notable economic losses 1,2. Therefore, understanding the precise molecular mechanisms that underpin plant fertility under environmental constraints is critical to safeguarding future food production 3. Here, we identified two Argonaute-like proteins whose activities are required to sustain male fertility in maize plants under high temperatures. We found that MALE-ASSOCIATED ARGONAUTE-1 and -2 associate with temperature-induced phased secondary small RNAs in pre-meiotic anthers and are essential to controlling the activity of retrotransposons in male meiocyte initials. Biochemical and structural analyses revealed how male-associated Argonaute activity and its interaction with retrotransposon RNA targets is modulated through the dynamic phosphorylation of a set of highly conserved, surface-located serine residues. Our results demonstrate that an Argonaute-dependent, RNA-guided surveillance mechanism is critical in plants to sustain male fertility under environmentally constrained conditions, by controlling the mutagenic activity of transposons in male germ cells. </p

The effect of temperature on stigmatic receptivity in sweet cherry (Prunus avium L.)

the definitive version is available at: http://www.blackwell-synergy.com/doi/pdf/10.1046/j.1365-3040.2003.01085.xPlant reproduction is highly vulnerable to environmental conditions such as temperature and, consequently, planet warming may have significant consequences on the reproductive phase with serious implication in agricultural crops. Although pollen tube growth is clearly affected by temperature, little information is available on its effect on the female side and on flower receptivity. In this work, the effect of temperature has been evaluated on stigmatic receptivity of sweet cherry in vivo, in the laboratory, and in planta, in the field. Results herein show that temperature has a clear effect on the duration of stigmatic receptivity. Thus, whereas high temperature reduced stigmatic receptivity, low temperature enlarged it. The stigma lost the capacity to offer support first for pollen penetration, second for pollen germination and, finally, for pollen adhesion. The effect of temperature was more pronounced on pollen germination and penetration than on pollen adhesion. High temperature reduced the germination capacity of the pollen as early as the first day after anthesis, a time when no apparent signs of stigma degeneration are apparent. This clear effect of temperature on stigmatic receptivity and pollen performance may have clear implication in crop performance and in establishing screening criteria of best-adapted genotypes.A.H. was supported by AECI and SIA-DGA fellowships and financial support for this work was provided by INIA (project grant RTA 01–103).Peer reviewe