Pear Cultivars Research Articles

Comparison of the blossom and shoot susceptibility of European and Asian pear cultivars to Pseudomonas syringae pv. syringae

Comparison of the blossom and shoot susceptibility of European and Asian pear cultivars to Pseudomonas syringae pv. syringae

New approaches in pear preservation: Putrescine and modified atmosphere packaging applications to maintain fruit quality during cold storage

AbstractPear (P. communis L.), which is a climacteric fruit species, has a very short storage and shelf life, and significant losses occur due to high metabolic activity and the fruit's respiration rate after harvest. Therefore, preventing or reducing post‐harvest quality losses in pear is one of the most basic problems awaiting solution. In this study, we planned for this purpose; the fruits of the Ankara pear cultivar treated with modified atmosphere packaging (MAP), putrescine (1 mM), and MAP + putrescine were stored for 120 days at 1°C and 90 ± 5% relative humidity. The quality analyses and measurements, such as weight loss, decay rate, fruit firmness, soluble solids content (SSC), titratable acidity (TA), total phenolic compounds, antioxidant capacity, organic acids, and specific phenolic compounds, were performed on the 30th, 60th, 90th, and 120th days. Weight loss and decay ratios were lower for putrescine and putrescine + MAP‐applied fruit. With these applications, the softening of the fruit was slowed down, and the increasing SSC in the fruit and the decreasing TA rates were lower, and thus the ripening of the fruit was delayed. Changes in individual phenolic content and organic acids were lower in MAP and putrescine‐applied fruit. The study revealed that MAP and putrescine applications in pear can be used effectively to maintain fruit quality after harvest.

Comparative Analysis of Transcriptomes to Identify Genes during Bud Dormancy of Pyrus pyrifolia ‘Huanghua’

The study of pear dormancy mechanisms is currently a major research area in pear production and has high economic significance for agricultural production. We selected the southern sand pear cultivar Pyrus pyrifolia ‘Huanghua’ as the test material to study the pear dormancy process through microscopic observation of pear flower buds. The endodormancy period is abbreviated as D_bud. Similarly, the endodormancy release initiation period and the ecodormancy period are referred to as DB_bud and G_bud, respectively. Meanwhile, RNA sequencing was used to obtain the gene expression profile of Pyrus pyrifolia ‘Huanghua’ flower buds. The RNA sequencing results indicated that there were 224 differentially expressed genes (DEGs) in endodormancy (D) vs. endodormancy release initiation period (DB), while 975 were identified between endodormancy and ecodormancy (G). Finally, a total of 868 DEGs were found in the DB vs. G comparison. The expression levels of the genes Pbr009498.1 (LAX1-1), Pbr012348.1 (LAX1-2), Pbr021158.1 (GH35), and Pbr031621.1 (LAX2) encoding IAA were significantly higher during the DB_bud than during the D_bud. The expression level of Pbr025864.2 (IAA13) during the D_bud was significantly higher than the DB_bud and G_bud. The Pbr041942.1 (GID1B) gene also showed a significant increase during ecodormancy. Taken together, these results suggest that these genes, annotated as LAX1, GH35, LAX2, IAA13, and GID1C, are involved in endodormancy maintenance and in the transition from endodormancy to ecodormancy in Pyrus pyrifolia ‘Huanghua’.

Excluding sunscald from long-term storage of ‘Granny Smith’ apples

Sunscald is a postharvest apple and pear peel disorder primarily caused by excessive light exposure during the growing season. Symptoms are not apparent at-harvest but develop during storage as superficial brown or gray discolored patches on the exposed portion of the apple. A novel protocol using hyperspectral imaging (HSI) was developed to identify apples at- harvest that are more likely to develop the disorder and reduce sunscald in the cold chain by eliminating at-risk apples from long-term storage. PLS-DA and LOGISTIC models and an index summarizing the chlorophyll to carotenoid ratio were tested for this purpose using two populations selected for different sun exposure levels and four populations harvested from whole trees. The accuracy of models varied seasonally. However, detection of sunburn and estimation of sunscald risk based on index values was a more consistent approach. Summarizing peel area according to this index was the basis for categorizing whole apples as rejected (sunburned), high (sunscald) risk, or low-risk. Categorization segregated apples nearly entirely into these categories with only an insignificant frequency of misclassification. The frequency of high-risk apples without sunburn symptoms in the populations harvested from whole trees fell below 20 %, although actual sunscald incidence within this category ranged from 55 % to 81 % among populations harvested from whole trees, highlighting that other factors beyond elevated sun exposure contribute to sunscald incidence. The classification model for low and high-risk categories had an accuracy of 83–93 % in four independent populations, with 99.9 % sensitivity to classify non-sunscalded fruit into the low-risk category. Sorting by sunburn presence and sunscald risk allows for apples that have sunburn symptoms to be excluded and those that are marketable but most likely to develop sunscald to be pushed to market rather than storage. With the appropriate source/sensor array, this approach is readily adaptable to sorting lines or even robotic harvesters. Challenges include adapting this approach for other apple and pear cultivars and extending capabilities for additional uses, including sorting fruit into additional categories representative of relative sunlight exposure.

The effect of postharvest low oxygen treatments on sensory evaluation in some pear cultivars under different storage technologies

The effect of postharvest low oxygen treatments on sensory evaluation in some pear cultivars under different storage technologies

Mediterranean Wild Pear Fruits as a Neglected but Valuable Source of Phenolic Compounds

The genus Pyrus has a long history in Sardinia (Italy), where two wild pear species (P. spinosa Forssk. and P. pyraster (L.) Burgsd.) and Pyrus communis L. cultivars are extensively distributed. Even if neglected, these taxa represent well-adapted key resources for redesigning sustainable farming systems. This report aims at shedding light on the phenolic fingerprint and antioxidant properties of wild pear fruits and comparing their traits with those of the studied pear cultivar germplasm (PCG). Fruits of wild pear species were collected, and flesh, peel, and core subsamples were analyzed. Moreover, available data from previous research on PCG were analyzed. The contents of total phenolics (TotP), total flavonoids (TotF), and condensed tannins (CT), as well as the antioxidant capacity, were similar in the flesh of the two wild species. However, P. spinosa had significantly higher values of TotP (89 g GAE kg−1 DM) and CT (33 g DE kg−1 DM) in the peel. Eleven individual phenolic compounds were identified and quantified in the fruit flesh, 14 in both peel and core. For both wild species, arbutin and chlorogenic acid were the main phenolic compounds, followed by the quercetin glycosides. Comparing the antioxidant capacity and TotF fruit flesh values of wild pears with those of PCG, the latter resulted up to 15-fold lower. The wild types showed unique metabolite profiles. Results support novel insights on the phytochemicals of wild pear fruits.

The results of the evaluation of the compatibility of pear cultivars with dwarf rootstocks of VNIISPK breeding for intensive fruit production technologies in Central Russia

The results of the evaluation of the compatibility of pear cultivars with dwarf rootstocks of VNIISPK breeding for intensive fruit production technologies in Central Russia

Valorization of a Local Italian Pear (Pyrus communis L. cv. ‘Petrucina’)

In recent decades, the food production chain has undergone transformations that have profoundly affected the way food is supplied, causing changes in the quality of the final products. Moreover, biodiversity is seriously threatened worldwide, and the valorization of local germplasm is a priority goal for most sectorial policies in Europe and elsewhere. Southern Italy and the Mediterranean basin present a vast heritage of fruit tree cultivars that is gradually being lost. Through this work, we aim to valorize a well-adapted local pear cultivar named Petrucina from the Salento area (southeastern Italy, Apulia region), which has never been studied before in detail. With this aim, the nutritional and nutraceutical features of pear flesh were characterized and compared with a reference pear cultivar that is widespread and well-known in Europe (cv. ‘Conference’). Petrucina fruits have shown a peculiar aromatic compound profile, and a content of up to 398.3, 30.9, and 4.7 mg/100 g FW of malic acid, citric acid, and ascorbic acid, respectively, much higher than that of Conference fruits. Additionally, Petrucina flesh presents a more than triple total phenolic content and an antioxidant activity more than double that of Conference, making Petrucina a true functional food that deserves wide appreciation.

Morphological Evaluation of Pear cvs. Santa Maria, Williams, and Deveci Grafted onto Clonal and Seedling Rootstocks

This research was conducted to determine the effects of quince clonal rootstocks [Quince BA29 (BA29) and Quince A (QA)], pear clonal rootstocks [FOX9, FOX11, OHxF333, OHxF87 and FAROLD40] and European pear seedling rootstocks on the morphological characteristics of 'Santa Maria', 'Williams', and 'Deveci' pear cultivars in Bafra (Samsun) ecological conditions in the research years of 2021 and 2022. Morphological characteristics, such as rootstock diameter (mm), trunk diameter (mm), trunk cross-sectional area (cm2), tree height (cm), crown dimensions (width, length, height and volume), leaf stalk length (cm), leaf stalk thickness (mm), leaf dimensions (width, length, area), annual shoot length (cm), node numbers and internode length (cm) were examined in the study. Results of the study revealed significant variation in the case of research years on most morphological attributes; generally, the values were higher in the research year 2022 than in 2021. It has been determined that the effect of rootstocks on all the morphological characteristics was significant except for leaf stalk thickness. The highest morphological values were obtained from OHxF333, FOX11, and FAROLD40 compared to the other rootstocks, and the lowest values were recorded in FOX9, OHxF87, and seedling rootstocks, respectively. Considering the cultivars' effect on the evaluated morphological traits, the highest leaf characteristics, and internode length in the annual shoots were acquired from the 'Santa Maria' cultivar, but all other attributes were higher in the 'Deveci' cultivar. The ' Williams ' cultivar recorded almost all the lowest morphological values. The highest trunk cross-sectional area was determined in the 'Deveci'/OHxF333 (38.63 cm2) and the lowest in the 'Williams'/FOX9 (4.95 cm2). The longest annual shoots were determined in the 'Deveci'/FOX11 (43.05 cm) and the shortest in the 'Williams'/Seedling (16.11 cm). The highest leaf area was observed from the 'Santa Maria'/BA29 (21.11 cm2) and 'Santa Maria'/FOX11 (20.95 cm2) combinations. According to the results of the research, it was determined that OHxF333 rootstock among the evaluated rootstocks performed morphologically better than the others. FOX9 and OHxF87 pear clone rootstocks showed very poor performance compared to other rootstocks.

Profiling of soluble sugar compositions in mature fruits of a diverse pear (Pyrus spp.) germplasm by UPLC

Soluble sugars play a vital role as taste components in fruits, significantly contributing to fruit quality. Here, we employed ultraperformance liquid chromatography (UPLC) to determine the sugar composition of mature pear fruits from 142 cultivars. The results revealed that fructose, sorbitol, glucose, and sucrose were the primary soluble sugars present in pear fruit, and Pyrus pyrifolia (China) exhibited the highest total sugar content, followed by Pyrus ussuriensis, Pyrus bretschneideri, Pyrus communis, and Pyrus pyrifolia (Japanese and Korean (J&K)), Pyrus sinkiangensis, and the Hybrid Breeding (HB) cultivars. Furthermore, our study uncovered that the sampling time of these pear cultivars has a significant positive correlation with the content of sorbitol and glucose, respectively. Additionally, the soluble sugar content varied among pear fruits originating from different geographic positions, and the pear cultivars originating from the South China group presented the highest content of soluble sugar. In conclusion, these findings can provide valuable phenotypic data for studying sugar genetics and can also aid in selecting suitable parent cultivars in pear breeding programs.

Genetic and molecular regulation of chilling requirements in pear: breeding for climate change resilience.

Pear (Pyrus spp.) is a deciduous fruit tree that requires exposure to sufficient chilling hours during the winter to establish dormancy, followed by favorable heat conditions during the spring for normal vegetative and floral budbreak. In contrast to most temperate woody species, apples and pears of the Rosaceae family are insensitive to photoperiod, and low temperature is the major factor that induces growth cessation and dormancy. Most European pear (Pyrus Communis L.) cultivars need to be grown in regions with high chilling unit (CU) accumulation to ensure early vegetative budbreak. Adequate vegetative budbreak time will ensure suitable metabolite accumulation, such as sugars, to support fruit set and vegetative development, providing the necessary metabolites for optimal fruit set and development. Many regions that were suitable for pear production suffer from a reduction in CU accumulation. According to climate prediction models, many temperate regions currently suitable for pear cultivation will experience a similar accumulation of CUs as observed in Mediterranean regions. Consequently, the Mediterranean region can serve as a suitable location for conducting pear breeding trials aimed at developing cultivars that will thrive in temperate regions in the decades to come. Due to recent climatic changes, bud dormancy attracts more attention, and several studies have been carried out aiming to discover the genetic and physiological factors associated with dormancy in deciduous fruit trees, including pears, along with their related biosynthetic pathways. In this review, current knowledge of the genetic mechanisms associated with bud dormancy in European pear and other Pyrus species is summarized, along with metabolites and physiological factors affecting dormancy establishment and release and chilling requirement determination. The genetic and physiological insights gained into the factors regulating pear dormancy phase transition and determining chilling requirements can accelerate the development of new pear cultivars better suited to both current and predicted future climatic conditions.

Reactive Oxygen Species and Salicylic Acid Mediate the Responses of Pear to Venturia nashicola Infection

Reactive oxygen species (ROS) and salicylic acid (SA) are essential signaling molecules in plant cells that participate in responses to biotic and abiotic stresses. Changes in ROS and SA signals during interactions between pear and the pear scab pathogen Venturia nashicola remain unclear. Herein, we analyzed the roles of ROS in the signal transduction pathway of pear scab resistance using the highly resistant Huangguan and susceptible Xuehua cultivars of pear (Pyrus bretschneideri Rehd). Protoplasts, calluses, and leaves were obtained from 14-year-old pear trees and treated with V. nashicola for different periods. The results showed that ROS rapidly accumulated in protoplasts of both cultivars within a 120-min treatment period, but the fluorescence intensity of ROS differed between cultivars. The H2O2 content in fruit-derived calluses of Huangguan peaked at 48 h post-infection at levels 1.85 times higher than those in Xuehua. Induction of H2O2 by V. nashicola in Huangguan was more intense than in Xuehua over a 96-h treatment period. At 96 h post-infection, the malondialdehyde content in leaves of Huangguan was significantly lower than in Xuehua, while the activities of superoxide dismutase, peroxidase, and catalase, and the relative expression levels of PbMnSOD, PbPOD, and PbCAT genes were higher in Huangguan than Xuehua. V. nashicola infection also caused a continuous increase in the leaf SA content of Huangguan, which was 6.76 times higher than in Xuehua at 96 h post-infection, and V. nashicola exposure upregulated the expression of PbPAL, PbICS, PbPR1, and PbPR5. In summary, both ROS and SA participated in the responses of pear trees to V. nashicola infection and played vital roles in the signal transduction pathway of pear scab resistance.

Nondestructive detection of SSC in multiple pear (Pyrus pyrifolia Nakai) cultivars using Vis-NIR spectroscopy coupled with the Grad-CAM method

Vis-NIR spectroscopy coupled with chemometric models is frequently used for pear soluble solid content (SSC) prediction. However, the model robustness is challenged by the variations in pear cultivars. This study explored the feasibility of developing universal models for predicting SSC of multiple pear varieties to improve the model's generalizability. The mature fruits of 6 pear cultivars with green skin (Pyrus pyrifolia Nakai cv. ‘Cuiyu’, ‘Sucui No.1’ and ‘Cuiguan’) and brown skin (Pyrus pyrifolia Nakai cv. ‘Hosui’,’Syusui’ and ‘Wakahikari’) were used to establish single-cultivar models and multi-cultivar universal models using convolutional neural network (CNN), partial least square (PLS), and support vector regression (SVR) approaches. Multi-cultivar universal models were built using full spectra and important variables extracted by gradient-weighted class activation mapping (Grad-CAM), respectively. The universal models based on important variables obtained satisfactory performances with RMSEPs of 0.76, 0.59, 0.80, 1.64, 0.98, and 1.03°Brix on 6 cultivars, respectively.

Transcriptomic Database Analysis of Magnesium Transporter (MGT) Gene Family in Pear (Pyrus bretschneideri) Revealed Its Role in Reproductive Stage Development

The membrane proteins of the magnesium transporter (MGT) family are essential to Mg homeostasis. However, there has not been a comprehensive study of MGT in pear. The 17 MGT that were renamed to PbMGT1–17 in this study were found in the pear genome database. Phylogenetically, PbMGT proteins were categorized into three groups, namely NIPA, MRS2, and CorA. The majority of PbMGT were hydrophobic proteins situated on the chloroplast, according to the characterization study. Members of the same group shared comparable conserved motifs and gene structure, as revealed by motif and exon/intron analysis. The application of gene ontology (GO) and cis-elements has demonstrated that PbMGT genes exhibit a high degree of sensitivity to stressors and take part in chloroplast development and Mg+ ion transport. It was discovered by tissue-specific expression analysis that PbMGT genes might have a role in the development of organs. The critical significance of PbMGT was shown through comprehensive expression in five pear cultivars at various fruit developmental stages. The PbMGT5 gene was significantly expressed throughout fruit development, suggesting a role in the setting and ripening processes of pear fruits. For the first time, our research brought attention to the function of PbMGT genes as they relate to fruit development. Our research is likely to serve as an incentive for the development of pear breeding initiatives in the future.

Assessment of SSC and soluble sugar content of three pear cultivars during storage using dielectric method

This study aims to develop models for predicting soluble solids content (SSC) and soluble sugar content of three different pear cultivars. The samples' SSC and soluble sugar content, as well as the dielectric spectra in the frequency range of 20–4500 MHz were first collected, then the dielectric penetration depth was analyzed using one-way ANOVA method, and finally the accuracy of different models for predicting SSC and soluble sugar contents including partial least squares regression (PLSR), support vector machine (SVM), back propagation - artificial neural network (BP-ANN), and extreme learning machines (ELM) were compared. Results showed that the mean dielectric spectra of three pear cultivars presented similar trends. The dielectric penetration depth in the researched frequency range reached the maximum sugar content determination depth (intact pears: 20 mm; pulp: 17 mm). The correlations between glucose and dielectric spectra under specific frequency for 'Yulu' (determination coefficient: R2 = 0.88) and 'Korla' (R2 = 0.94) pears were the highest, while in terms of 'Xuehua' pear, the correlation was relatively lower (R2 ≤ 0.64). The Rp2 (R2 of prediction set) of the optimal sugar prediction model based on the dielectric spectra of intact pear and pear pulp were successively between 0.77–0.88 and 0.85–0.93. This research proved the feasibility of predicting sugar content in different pear cultivars using dielectric spectra.

Comparative transcriptome profiling and co-expression network analysis uncover the key genes associated with pear petal defense responses against Monilinia laxa infection.

Pear brown rot and blossom blight caused by Monilinia laxa seriously affect pear production worldwide. Here, we compared the transcriptomic profiles of petals after inoculation with M. laxa using two pear cultivars with different levels of sensitivity to disease (Sissy, a relatively tolerant cultivar, and Kristalli, a highly susceptible cultivar). Physiological indexes were also monitored in the petals of both cultivars at 2 h and 48 h after infection (2 HAI and 48 HAI). RNA-seq data and weighted gene co-expression network analysis (WGCNA) allowed the identification of key genes and pathways involved in immune- and defense-related responses that were specific for each cultivar in a time-dependent manner. In particular, in the Kristalli cultivar, a significant transcriptome reprogramming occurred early at 2 HAI and was accompanied either by suppression of key differentially expressed genes (DEGs) involved in the modulation of any defense responses or by activation of DEGs acting as sensitivity factors promoting susceptibility. In contrast to the considerably high number of DEGs induced early in the Kristalli cultivar, upregulation of specific DEGs involved in pathogen perception and signal transduction, biosynthesis of secondary and primary metabolism, and other defense-related responses was delayed in the Sissy cultivar, occurring at 48 HAI. The WGCNA highlighted one module that was significantly and highly correlated to the relatively tolerant cultivar. Six hub genes were identified within this module, including three WRKY transcription factor-encoding genes: WRKY 65 (pycom05g27470), WRKY 71 (pycom10g22220), and WRKY28 (pycom17g13130), which may play a crucial role in enhancing the tolerance of pear petals to M. laxa. Our results will provide insights into the interplay of the molecular mechanisms underlying immune responses of petals at the pear-M. laxa pathosystem.

Effects of 1-methylcyclopropene on skin greasiness and quality of 'Yuluxiang’ pear during storage at 20°C

During storage at 20°C, specific pear cultivars may exhibit a greasy texture and decline in quality due to fruit senescence. Among these varieties, 'Yuluxiang’ is particularly susceptible to peel greasiness, resulting in significant economic losses. Therefore, there is an urgent need for a preservative that can effectively inhibit the development of greasiness. Previous studies have demonstrated the efficacy of 1-methylcyclopropene (1-MCP) in extending the storage period of fruits. We hypothesize that it may also influence the occurrence of postharvest peel greasiness in the 'Yuluxiang’ pears. In this study, we treated 'Yuluxiang’ pears with 1-MCP. We stored them at 20°C while analyzing the composition and morphology of the surface waxes, recording enzyme activities related to wax synthesis, and measuring indicators associated with fruit storage quality and physiological characteristics. The results demonstrate that prolonged storage at 20°C leads to a rapid increase in skin greasiness, consistent with the observed elevations in L*, greasiness score, and the content of total wax and greasy wax components. Moreover, there were indications that cuticular waxes underwent melting, resulting in the formation of an amorphous structure. In comparison to controls, the application of 1-MCP significantly inhibited increments in L* values as well as grease scores while also reducing accumulation rates for oily waxes throughout most stages over its shelf period, additionally delaying transitions from flaky-wax structures towards their amorphous counterparts. During the initial 7 d of storage, several enzymes involved in the biosynthesis and metabolism of greasy wax components, including lipoxygenase (LOX), phospholipase D (PLD), and β-ketoacyl-CoA synthase (KCS), exhibited an increase followed by a subsequent decline. The activity of LOX during early shelf life (0–7 d) and the KCS activity during middle to late shelf life (14–21 d) were significantly suppressed by 1-MCP. Additionally, 1-MCP effectively maintained firmness, total soluble solid (TSS) and titratable acid (TA) contents, peroxidase (POD), and phenylalanine ammonia-lyase (PAL) activities while inhibiting vitamin C degradation and weight loss. Furthermore, it restrained polyphenol oxidase (PPO) activity, ethylene production, and respiration rate increase. These findings demonstrate that 1-MCP not only delays the onset of peel greasiness but also preserves the overall storage quality of 'Yuluxiang’ pear at a temperature of 20°C. This study presents a novel approach for developing new preservatives to inhibit pear fruit peel greasiness and provides a theoretical foundation for further research on pear fruit preservation.

The Biophysical Properties of the Fruit Cuticles of Six Pear Cultivars during Postharvest Ripening

Pears are abundant in bioactive compounds, which exert favorable effects on human health. The biophysical attributes of fruit cuticles are pivotal in determining fruit quality, storability, and susceptibility to mold growth. This study aimed to elucidate the biophysical properties of six pear cultivars, ‘Conference’, ‘Celina’, ‘Abate Fetel’, ‘Packham’s Triumph’, ‘Sweet Sensation’, and ‘Williams’. Two maturity stages, unripe and fully ripened, were investigated. Furthermore, the efficacy of trimethyl-chitosan-coated pear surfaces in preventing Penicillium expansum (P. expansum) growth was assessed. Basic maturity indices (CIE color, ethylene evolution, firmness, soluble solids), cuticle contact angle, roughness, and zeta potential were analyzed. Surface roughness was measured using an optical profilometer, hydrophobicity was measured via profilometry, and zeta potential was quantified using an electrokinetic analyzer. The ‘Celina’ cultivar exhibited the highest roughness, whereas ‘Williams’ had the lowest roughness. All the cultivars’ cuticles demonstrated hydrophilic characteristics, with contact angles ranging between 65° and 90°. For pH values exceeding 3.5, all pear surfaces exhibited a negative zeta potential. P. expansum growth was the slowest on the ‘Packham’s Triumph’ and ‘Conference’ cultivars. Treatment with trimethyl chitosan effectively inhibited P. expansum growth in the initial hours of incubation. In conclusion, diverse pear cultivars manifest distinct biophysical surface properties and varying susceptibility to P. expansum growth. The growth of P. expansum correlates positively with roughness, contact angle, and zeta potential. These differences can significantly impact shelf life potential and the overall postharvest quality of pears.

Protein/Lipid ratio of pollen biases the visitation of bumblebees (Bombus ignitus Smith) to male-fertile cultivars of the Japanese pear (Pyrus pyrifolia Nakai).

Bees have been known to visit the male-fertile cultivars of self-incompatible flowering plants more frequently than the male-sterile cultivars, but the origin of this preference is poorly understood. Here, we demonstrate that this preference is driven by the higher protein/lipid ratio of male-fertile pollen compared with male-sterile pollen by way of two caged-behavioral assays with six cultivars. In the first assay, flower-naïve bumblebees (Bombus ignitus Smith) showed a significantly higher flower-visitation rate to male-fertile cultivars (pollen germination rate > 55%; > 14 visits/10 min) of the Japanese pear (Pyrus pyrifolia Nakai) than male-sterile cultivars (pollen germination rate ≤ 20%; > 6 visits/10 min). In the second, bees still preferred the anthers of male-fertile cultivars (5-9 visits/10 min) more than those of male-sterile ones (less than 1 visit in 10 min) even in the absence of all other organs (i.e., petals, pistil, nectar), indicating that pollen is responsible for the preference. We then analyzed the macronutrient content of the pollen and its visual cues, and found that the bee preference was highly correlated with the protein/lipid ratio (0.3-1.6) but not color variables such as (a)chromatic contrast, intensity, and spectral purity. We conclude that the protein/lipid ratio influences the foraging behavior of the bumblebees likely by serving as (1) a chemotactile cue while antennating, (2) a gustatory cue after intake, and (3) an olfactory cue. In addition, the low bee visitation rate to poorly viable pollen could be due to its low protein/lipid ratio.

Metabolic alterations in pear cultivars during storage at ambient conditions

Patharnakh’ (PN) (Pyrus pyrifolia Burm. Nakai) and ‘Punjab Beauty’ (PB) [Pyrus communis L. × Pyrus pyrifolia Burm. Nakai] are the leading low-chill pear cultivars of the subtropics of India. Diurnal temperature and relative humidity during the fruit harvest period are high, which considerably affects the shelf life of fruits. Fruits of ‘PN’ and ‘PB’ pear harvested at physiological maturity were stored for 16 days at ambient temperature, and the effects of the storage day interval on physical and qualitative parameters were studied. Both cultivars showed reductions in fruit firmness, physiological weight loss, total soluble solids, and juice acid content during storage. Activities of fruit softening enzymes such as polygalacturonase (PG), pectin methylesterase (PME), and cellulase were enhanced, whereas those of superoxide dismutase (SOD) were reduced during storage. Fruit firmness was negatively correlated with polygalacturonase, pectin methylesterase, PPO, and cellulase enzymes in both cultivars. In both cultivars, the increased browning of the fruit during storage was negatively correlated with total phenolic content and positively correlated with polyphenol oxidase activity during storage. ‘Patharnakh’ and ‘Punjab Beauty’ fruits maintain desirable quality parameters up to 6–12 days and 4–8 days, respectively, during storage at ambient conditions.