‘Honeycrisp’ Bitter Pit Response to Rootstock and Region under Eastern New York Climatic Conditions

There are still unknown factors at play in the causation of bitter pit in ‘Honeycrisp’ as well as in other apple varieties. To investigate some of these factors, we conducted a survey of 34 ‘Honeycrisp’ orchard blocks distributed across two disparate production regions in eastern New York State, representing a variety of rootstocks, over three growing seasons. Weather, soil, horticultural traits, fruit quality traits, pick timing, leaf and peel minerals were evaluated for their impact on bitter pit (BP) incidence; factors were further evaluated for their interaction with region and rootstock. ‘Honeycrisp’ trees on B.9 rootstock were smaller but with comparable terminal shoot growth when compared to those on M.26 and M.9 rootstocks. B.9 fruits, which had similar fruit size to M.26 and M.9 and had good fruit quality at harvest and after storage, were much less likely to express bitter pit symptoms compared to M.9 and M.26 rootstocks. Not all traits evaluated individually correlated significatively with bitter pit incidence after a period in storage. Depending on rootstock and region, the correlation could be significant in one situation, with no correlation at all in another. In this study, peel Mg/Ca ratio and peel Ca correlated with BP for all three rootstocks, with the strongest correlations associated with the M.9 clones. These same traits correlated with BP for both regions. Pick timing had a significant influence on BP incidence following storage, with later picks offering better bitter pit storage performance. While excessively large fruits, those in the 48 and 56 count size categories, were found to be highly susceptible to BP regardless of rootstock, B.9 BP fruit susceptibility for smaller sizes was found to be size neutral. A PLSR prediction model for each rootstock and each region showed that different variables correlated to BP depending on the situation. Thus, the results could suggest that in addition to the variables considered in this study, there are other less studied factors that can influence the expression of BP symptoms. We strongly suggest that rootstock BP performance be considered a critical parameter when planning a commercial ‘Honeycrisp’ orchard and be evaluated in rootstock breeding and development programs prior to wide commercial release.

Effect of Prohexadione-calcium on the Shoot Growth, Fruits, Endogenous Hormones and Expression of GA-related Genes in ‘Fuji’ Apple (Malus Domestica Borkh.)

The shoot growth of ‘Fuji’ apple is vigorous, which causes a poor lighting condition and a high cost to prune. Prohexadione-calcium (ProCa) has been proven to regulate the shoots growth, fruits and return flowering in apple abroad but there are fewer studies on its effect on the shoot growth, fruits and return flowing in ‘Fuji’ apple in China. Moreover, the mechanism of its action is incompletely understood. So different treatments were applied as foliar sprays to dwarf self-rooted ‘Fubrax Red Fuji ’/M9-T337 trees at 3, 14, 35 and 56 DAPF (Days after petal fall). The results showed that at the end of the growing season, spraying ProCa effectively inhibited the growth of shoots compared to control and one spray of 500 and 750 mg L-1 ProCa, two sprays of 250 mg L-1 ProCa and four sprays of 250 mg L-1 ProCa showed the highest reduction. ProCa had very slight effect on yield, quality and return flowing. During the growing season, two applications of ProCa of 250 mg L-1 on 3 and 14 DAPF significantly reduced the content of GA 1+3 , IAA and ZR but increased the content of ABA in long terminal shoot leaves in at least one time point. The expression patterns of GA-regulated genes showed that ProCa down-regulated MdGA3ox transcript level at 10, 20, 30, 40 and 50 DAPF and down-regulated MdCPS, MdGA20ox, MdRGL1a, MdSLY1 transcripts in at least one time point. This study provided a valuable insight to regulate the vegetative growth of ‘Fuji’ apple and explored the mechanism of ProCa action.

Verification and Modification of a Model to Predict Bitter Pit for ‘Honeycrisp’ Apples

‘Honeycrisp’ (Malus ×domestica) apples were harvested from a total of 17 mid-Atlantic orchards during 2018 and 2019 to verify a previously published bitter pit prediction model. As in the previous study, bitter pit incidence was associated with low calcium (Ca) levels and high ratios of nitrogen (N), potassium (K), and/or magnesium (Mg) to Ca in the fruit peel and excessive terminal shoot growth. The best two-variable model for predicting bitter pit developed with the 2018–19 data set contained boron (B) and the ratio of Mg to Ca (R2 = 0.83), which is different from previous models developed with data from three individual years (2015–17). When used to predict the bitter pit incidence of the 2018–19 data, our previous best model containing the average shoot length (SL) and the ratio of N to Ca underestimated the incidence of bitter pit. The model is probably biased because one or more important variables related to bitter pit have not yet been identified. However, the model is accurate enough to identify orchards with a low incidence of bitter pit.

Ungulate Species and Abundance as well as Environmental Factors Determine the Probability of Terminal Shoot Browsing on Temperate Forest Trees

Ungulate browsing is a major factor influencing tree regeneration. However, it is unclear if the observed increase in ungulate abundance in Central Europe implies increased browsing, and which other factors influence the incidence of browsing. We investigated the impact of forty variables (site, climate, forest and ungulates) on the probability of leader shoot browsing of six tree species which are frequent in Switzerland. The analysis was based on a large dataset including 49 monitoring areas, each containing 25–64 circular plots, in which 10 to 130 cm tall seedlings were repeatedly assessed. Browsing probability was estimated for each plot and year by mixed effects logistic regression and used as a response in random forests to disentangle the influence of the explanatory variables. Browsing probability was positively correlated with ungulate density measures (number culled by hunting or found dead) for all six tree species. Where beyond roe deer, some red deer and/or chamois were present, the browsing probability was higher. Small timber tree stands had less browsing than young growth and thicket stands. Seedlings tended to be more frequently browsed in stands with >80% canopy shading. Browsing increased with increasing understory cover, independent of vegetation category. In conclusion, browsing is a multifactorial phenomenon and ungulate density estimates alone do not explain the whole browsing probability.

Time-coursed transcriptome analysis identifies key expressional regulation in growth cessation and dormancy induced by short days in Paulownia

Maintaining the viability of the apical shoot is critical for continued vertical growth in plants. Terminal shoot of tree species Paulownia cannot regrow in subsequent years. The short day (SD) treatment leads to apical growth cessation and dormancy. To understand the molecular basis of this, we further conducted global RNA-Seq based transcriptomic analysis in apical shoots to check regulation of gene expression. We obtained ~219 million paired-end 125-bp Illumina reads from five time-courses and de novo assembled them to yield 49,054 unigenes. Compared with the untreated control, we identified 1540 differentially expressed genes (DEGs) which were found to involve in 116 metabolic pathways. Expression of 87% of DEGs exhibited switch-on or switch-off pattern, indicating key roles in growth cessation. Most DEGs were enriched in the biological process of gene ontology categories and at later treatment stages. The pathways of auxin and circadian network were most affected and the expression of associated DEGs was characterised. During SD induction, auxin genes IAA, ARF and SAURs were down-regulated and circadian genes including PIF3 and PRR5 were up-regulated. PEPC in photosynthesis was constitutively upregulated, suggesting a still high CO2 concentrating activity; however, the converting CO2 to G3P in the Calvin cycle is low, supported by reduced expression of GAPDH encoding the catalysing enzyme for this step. This indicates a de-coupling point in the carbon fixation. The results help elucidate the molecular mechanisms for SD inducing dormancy and cessation in apical shoots.

Bark necrotic disease in a beech thicket

Symptoms of non-specific bark necroses in beech trees of all ages have lately been described. We investigated the occurrence of bark necrotic disease in beech thicket and health status of the trees. Our objective was to examine how bark necrotic wounds persist and the regenerative potential of young beech thicket. The research experiment was carried out at two isolated localities in the Western Carpathians in the period 2015–2017. A terminal shoot (stem) and a lateral shoot (branch) of each of the 30 sampled beech trees were examined. Young beech stands were affected by the necrotic disease in 87–94% cases (stems 69–83%, branches 33–56%). Shoot diameter and age had a significantly negative linear correlation (P < 0.05) with the development of all analysed disease characteristics on the beech bark. The encouraging finding is a positive regenerative capacity of young beech trees. Over the same period more annual shoots were healed in comparison with those that were newly infected (10.8% on stems and 0.6% on branches).

Influence of Paclobutrazol on Shoot Growth and Flowering in a High-density Pecan Orchard

Paclobutrazol (PBZ) was applied to 6-year-old pecan (Carya illinoinensis) trees as a basal trunk drench (0, 30, 90, and 150 mg·cm−2 trunk cross-sectional area) in Dec. 2012. Terminal shoot growth was retarded for 1 year after a single application of PBZ. The total number of current season shoots showed a significant increase with 30- and 90-mg·cm−2 PBZ treatments. After PBZ application at 30, 60, and 90 mg·cm−2, the percentage of very short shoots (<5 cm) was 32.3%, 36.3%, and 32.3%, respectively, compared with 22.4% on control trees; the percentage of short shoots (5–15 cm) increased to 36.0%, 38.1%, and 43.5%, respectively. The percent of long shoots (>30 cm) was decreased to 7.4%, 5.1%, and 7.6%, respectively, after PBZ application, compared with 18.7% with control. Shoots varying from 5 to 30 cm in length accounted for at least 63.3% of all pistillate inflorescences the following spring.

Effects of plant growth regulators on the in vitro flowering of carnation (Dianthus caryophyllus L.)

The flowering of terminal shoot of carnation has three stages: inflorescence, floral initiation and blooming. Respiration rate increased in the transition from the vegetative growth to the flowering and all the stages of flowering had high respiration rate. Auxin and gibberellin activities, the proportion of auxin to cytokinin increased, and the elongation of inflorescence stem began in the transition from the vegetative growth to floral initiation stage are involved. Auxin and cytokinin activity increased, the proportion of auxin to cytokinin and gibberellin activity decreased in the transition from the floral initiation to blooming stage. Most vegetative shoots became floral buds by two ways: one way induced by auxin with 0.25 mg/LIAA, and the other by cytokinin with 0.25 mg/L BA.