The cultivated red raspberry (Rubus idaeus) in the genus Rubus subg. Idaeobatus is an economically valued berry crop but its cultivation has been limited by heat in the warm climate regions. Many species in the same subgenus are native to the subtropics and have been considered as potential germplasms for improving heat tolerance of raspberry cultivars. However, their photosynthetic responses to high temperatures and adaptation mechanisms have not been comprehensively exploited. In this study, leaf gas exchange characters of raspberry 'Summer Festival' and three subtropical native species, R. fraxinifolius, R. rosifolius, and R. croceacanthus, were mathematically analyzed. Net photosynthetic assimilation rate (A) and chlorophyll fluorescence against photosynthetic photon flux density (PPFD) and internal carbohydrate concentration (Ci) were measured at 25, 30, and 35 degrees C. Data from the measurements were fitted to modified Farquar, von Cammerer and Berry (FvCB) models and key photosynthetic variables were extracted. Inter- and intra- species differences in A (% Delta A) were quantified by partitioning the total difference into individual and categorized variables using a numerical integration method. The results showed that light saturated A and transpiration (E) of R. idaeus were suppressed at 35 degrees C while both in the subtropical native species sustained or elevated at the high temperature of 30 and 35 degrees C. The two key photosynthetic biochemical variables, maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax), were both increased at high temperatures in all studied taxa. Nevertheless, the superior A of the subtropical species was mainly contributed by the improved diffusional factors, i.e., stomatal conductance (gsc) and mesophyll conductance (gm), in response to elevated temperatures. This study demonstrated that the select subtropical native species better adapt to heat than the cultivated raspberry by maintaining leaf temperature low and photosynthetic efficiency high through consistent gsc and improved gm. The information suggested that for breeding programs targeting on heat tolerance, screening candidate genotypes with photosynthetic diffusional factors should be more efficient than evaluating biochemical factors. The results also provide useful references for raspberry industry to develop cultivation strategies to alleviate the impact from intensifying climate change situations.

The dense trichomes on the abaxial side of the leaves of hybrid grapes might limit the diffusion rates of gas and water vapor, consequently reducing assimilation rate (A). To evaluate the difference in gas exchange efficiency, CO2 response curve (A-C-i curve) and light response curve of mature leaves of 'Riesling' (Vitis vinifera), 'Black Queen' (V. hybrid) and 'Golden Muscat' (V. hybrid) vines were measured. Data were fitted to modified FvCB models and then integrated using a numerical integration approach. At 25 degrees C, A of 'Black Queen' and 'Golden Muscat' were 40 and 38%, respectively, less efficient than that of 'Riesling'. In addition to the diffusional factors, i.e., stomatal and mesophyll conductance, biochemical efficiency, mainly J(max), had an equal or greater contribution to the lower A in hybrid grapes compared to the vinifera at optimal temperatures. Biochemical factors, mainly J(max), contributed 3/4 of the inferior A performance in 'Black Queen', while biochemical and diffusional factors had equal shares to A in 'Golden Muscat'.

Rabbiteye blueberries (Vaccinium virgatum Aiton) cultivated in subtropical climates often display autumn flowering on shoot apices, which offers a potential for off-season berry production. The aim of this study was to elucidate the mechanism of off-season flowering through field observation and gene expression analysis. Field trials from 2018-2020 indicated that apical blooming occurred mainly in non-terminated shoot tips, suggesting that vegetative growing status was necessary for the development of apical flowers. Microstructure of apical buds showed that vegetative growth on shoot tip and apical inflorescence developed simultaneously. To understand the molecular basis of off-season flowering, expression of flowering-related genes, i.e., VcFT, VcCEN, and VcCOL5, in rabbiteye blueberry 'NTU031' and 'Austin' were analyzed. Although most shoots of the two cultivars continued vegetative growth in October, 'NTU031' showed intensive off-season apical flowering from late November while most shoots of 'Austin' terminated with apical growth cessation. In 'NTU031', VcFT expression increased in mid-October with floral meristem development whereas VcCEN and VcCOL5 expression decreased. On the other hand, 'Austin' did not show any significant fluctuation in the expression of these genes. The results suggested that autumn apical flowering in rabbiteye blueberries was positively correlated with the transcription of VcFT but negatively correlated with the expression of VcCEN and VcCOL5.

The rabbiteye blueberry (Vaccinium virgatum Aiton) is a promising new fruit crop in the subtropical lowland. However, mid-day temporary wilting of young shoot tips often occurs in the high summer heat and strong irradiance, warranting breeding for heat tolerance. Differences in leaf color among rabbiteye blueberry genotypes are visually distinguishable. To test the hypothesis that leaf color can be a morpho-physiological index for early screening in heat tolerance breeding with lighter leaf color preferred, leaf color of selected 'Blueshower' open-pollinated siblings was quantified using CIE L*a*b* color space. Diurnal leaf to air temperature differences (Delta Tleaf-air), chlorophyll content (Chl), mid-day gas exchange parameters and water use efficiency (WUE) were measured. The collected data were correlated with L*a*b* information. In hot sunny days, the genotypes with dark leaf color or low L* absorbed heat quicker than those with light leaf color or high L*, resulting in greater Delta Tleaf-air in the morning hours. The differences in Delta Tleaf-air were similar among the genotypes after mid-day, likely due to the negative correlation between L* and transpiration (E) that facilitates heat dissipation. Maximum leaf net CO2 assimilation (A(n)) was recorded at leaf temperature around 35 degrees C in all genotypes and was positivly corrected with b*. a* was positively correlated with leaf Chl content but not with any gas exchange parameters, suggesting that the effect of Chl content on A(n) was overpowered by the effect of leaf lightness derived from cuticular wax layers on leaf surface. Although increasing L* reduced E and thus improved WUE, the genotype with the highest L* value had the lowest mid-day stomatal conductance and intercellular CO2 concentration, resulting in a significantly low A(n) than that in the genotypes with moderate L *. We concluded that leaf lightness is a feasible index for heat tolerance breeding. For hot and arid climates, genotypes with high L* are recommended for their outstanding WUE but in the expense of A. For the hot humid subtropical climate, genotypes with moderate L* and high b* will be better candidates for their high A(n) in well-watered conditions.

In nature conditions, mutualization of ericaceous plant (Ericaceae) roots with mycorrhizal fungi or other soil symbiotic fungi improves efficiency on nutrient uptake and tolerance to heavy metal stress. Effects of ericoid mycorrhizal fungi (EMF) or dark septate endophyte (DSE) colonization have been evaluated in highbush blueberry ( Vaccinium corymbosum ) but remained unclear in rabbiteye blueberry ( V. virgatum Ait.). In this study, callused cuttings of ‘NTU-104’ rabbiteye blueberry were grown in substrate containing either sterilized (SP) or unsterilized (UP) nature Finnish peat moss as a fungal inoculum. Vegetative growth, fungal colonization frequency ( Cf ) and intensity ( Ci ), substrate pH and electrical conductivity (EC), and plant nutritional elements were assessed. Sterilization did not completely exclude fungi resources in the peat moss and colonization of EMF and DSE was found in both SP and UP substrate types. Regardless, UP treatment resulted in greater total Cf (69.3%) and Ci (9.91%) than those of SP (41.49% and 6.17%, respectively). In either substrate type, both Cf and Ci of DSE were greater than those of EMF. Plants in UP treatment produced more shoots (2.33), number of leaves (76.33), greater total leaf area (494.18 cm 2 ), and shoot length (121.78 cm) than in SP substrate (1.67, 24.17, 116.13 cm 2 , and 30.22 cm, respectively). Fresh weights of roots, shoots, and leaves in UP plants were significantly greater (7.57, 9.64, and 15.25 g, respectively) than in SP plants (1.29, 2.62, and 3.08 g, respectively). Dry weights of roots, shoots, and leaves in UP plants were also significantly greater (4.34, 2.37, and 4.51 g, respectively) than in SP plants (0.67, 0.47, and 0.90 g, respectively). Concentrations of phosphorous and magnesium in roots and potassium in shoots were increased in UP plants while other nutritional elements remained consistent. Contents of all nutritional elements were increased in UP plants due to greater dry weight. After the establishment of the transplants, pH and EC of both substrate types were in the optimal range for blueberries but significant lower pH while higher EC were measured in UP substrate. The results indicated that using nature Finnish peat moss as a symbiotic fungi inoculum was capable of establishing symbiotic fungal colonization and promoting rooting and vegetative growth in rabbiteye blueberry cuttings.

Introduction - Wax apple (Syzygium samarangense Merr. & Perry) is an economically important fruit crop in tropical Asia. The developmental changes of wax apple fruit, calcium (Ca) accumulation and allocation, and xylem functionality within the fruit were assessed in this study. Materials and methods - Fruits were sampled at eight developmental stages and subjected to analyses for quality associated properties. Functionality of xylem inside fruit was evaluated with a methyl blue dye-infusion approach and the spatial distribution of Ca in mature fruit was assessed. Results and discussion - The growth of a wax apple fruit expressed a typical single sigmoidal curve against time. The breaker stage or the beginning of skin coloration signaled the onset of maturation process as indicated by a rapid increase in total soluble solids and skin anthocyanin content, and a simultaneous decrease in titra table acidity. Xylem remained fully functioning through the whole fruit before the breaker stage. However, a sharp functional decline in xylem toward the distal end of the fruit was observed after the breaker stage. Total Ca content continued to increase but overall Ca concentration reduced after the breaker stage. At harvest, a mature fruit expressed a high to low Ca conc. gradient from the proximal to the distal end. Conclusion - The low Ca cone. in the flesh near the distal end could be attributed to the loss of xylem function after the breaker stage. Therefore, early and efficient Ca uptake is essential for maintaining high Ca cone. in the distal end where corky calyx end disorder, a speculative Ca deficiency symptom of wax apple fruit, may occur.

To accelerate the mulberry breeding program and examine the genome size and ploidy levels of 27 mulberry accessions of promising lines in Taiwan, nuclei suspensions were prepared from unfolded young leaves and analyzed by a flow cytometer. The genome size of each accession was estimated by referring to the standard genome size of chicken erythrocyte nuclei (CEN, 2.5 pg). Our results indicated that 25 among 27 investigated accessions in M. bombycis, M. alba, M. latifolia, M. australis, M. formosnensis, and M. atropurpurea are diploids with genome sizes ranging from 0.61 to 0.71 pg. 'Elongated mulberry No. 1' (M. laevigata) with a genome size of 1.06 pg is a triploid. Two populations were identified in the accession '67C001' (M. australis Poir.) with a genome size of either 0.63 pg or 0.98 pg. Due to their similarity in appearance, we suspected that they are probably from the same origin, thus warranting further investigations. Several important vegetative characters of diploids and triploids have been estimated, including leaf length, leaf width, petiole length, petiole width, leaf thickness, and internode length, to document their correlation using the unpaired t-test. Subsequently, the statistical relationship between diploid and triploid species on some of these important characters, including leaf width, petiole width and internode length, was determined through binary regression analysis. We suggested that the internode length could provide a beneficial index to distinguish individuals with different ploidy levels in the field. Results of this study provide useful information to clarify the taxonomy of Morus and improve breeding programs aiming to advance horticulture and sericulture.

Wax apple (Syzygium samarangense Merr. & Perry) has been a popular fruit crop in Taiwan because of its refreshing taste and attractive appearance. Pingtung County, accounting for 78% of the total planting area, is the major cultivation area. Regardless of the stable domestic and export market demand, the production area in Taiwan has decreased by almost 30% in the past decade, mainly due to labor shortage, high technical threshold, and production risk. Nevertheless, the cultivation area in central Taiwan has been increasing in recent years, especially in Nantou, Chiayi, and Yunlin Counties. The expansion of production regions facilitates year-round supply of wax apple fruits. By choosing suitable cultivars and forcing techniques in combination with adequate geographical and environmental conditions, a continuous supply chain for premium fruit has been established. Between October and December, market demand is fulfilled by fruits from Liukuei District in Kaohsiung City. Fruits from Pintung area satisfied the winter/spring market, from November to May. The cool temperatures in high altitude areas (600-1000 m a.s.I.) of Chiayi and Nantou favor the production of high quality fruits for niche markets from June to September. In addition, quality fruits of cultivars with consistent good fruit coloring and low cracking rates can be produced, from March to May, in Pingtung and, between June and September, in central Taiwan. Innovative production technologies and progressive breeding programs further ensure the sustainability of year-round wax apple production in Taiwan.

In the subtropical lowland of Taiwan with a warm winter climate, most rabbiteye blueberry cultivars (Vaccinium ashei) are semi-deciduous, and their leaves remain green through the winter. We investigated whether fertigation with nitrogen (N) and phosphorus (P) during the dormant season had any subsequent effects on vegetative growth and flowering of rabbiteye blueberry in this region. Potted 3-year-old ‘Blueshower’ plants were fertigated weekly from November 2012 to March 2013 with combinations of 100, 200, or 400 mg·L-1 N and 200 or 400 mg·L-1 P. Plants fertigated without N and P served as the control. Fertigation with any N and P treatment during the dormant season significantly increased photosynthesis (Pn) of overwintered leaves relative to the control, but had no effect on Pn of the new leaves. N at 100 mg·L-1 increased the total chlorophyll content in overwintered leaves more than two-fold compared to the control; total chlorophyll content in overwintered leaves increased with N rate, but was not affected by P rate. Dormant-season N and P fertigation advanced vegetative budburst. However, new shoot growth was negatively affected by dormant-season P fertigation. The number of flowers increased with N rate. We concluded that in the subtropical lowland with a warm winter climate, dormant-season fertigations, especially to supply N, can improve flowering and canopy development in the following spring.

Improving berry skin coloration is one of the major challenges in the tropical and subtropical viticulture. In this paper we aimed to document the effects of girdling at veraison on berry coloration and quality in grapevines on different rootstocks and we assessed the seasonal variations of girdling effects in the subtropical double cropping system. In the first experiment, girdling at veraison was tested in 'Kyoho' on 5C rootstocks. In the second experiment, own-rooted 'Kyoho', 5C or 1202C rootstocks were compared. Vines were trained to a horizontal overhead trellis with a single trunk and two short arms. One arm of each vine was girdled at veraison and the other arm served as the control. Girdling at veraison significantly improved skin color of berries from own-rooted vines or 5C rootstocks in the summer cropping cycle but was less effective in the winter cropping cycle. Girdling improved total soluble solids in own-rooted vines in the summer cropping cycle and in vines on 1202C in the winter cropping cycle. Girdling made in the winter cropping cycle did not completely heal until post-bloom in the following spring and reduced length of the fruiting shoot, number of leaves per shoot, and length of inflorescences of the next summer cropping cycle. We concluded that girdling at veraison is a good practice to improve berry color and quality for the summer cropping cycle but is not recommended for the winter cropping cycle.

Strawberry (Fragaria x ananassa Duch.) plants continuously produce flowers and berries in subtropical winter conditions and berry size declines in late harvest windows. Fruit or flower thinning has been applied on many fruit crops to improve fruit size or fruit quality. We hypothesized that positive effects of thinning are also appreciable in annual plasticulture strawberry production. Field grown 'Toyonoka' strawberry plants were unthinned (CK) or hand thinned to remove 1) primary flowers, 2) quaternary and younger flowers, or 3) quinary and younger flowers, upon bloom. Leaf area, fruit growth, yield, and total soluble solids (TSS) were measured. Reducing berry number by flower thinning treatments had little effect on leaf area development and plant growth. Growth and final size of tertiary berries of the second and the third harvest windows were improved by removing primary flowers. Number of unmarketable berries was also reduced by thinning treatments. However, TSS and total marketable yield were not improved by flower thinning. Considering the intensive input of labor and time for flower thinning, we conclude that flower thinning is not economical in Chinese Taipei's strawberry production.

The double cropping system has been commercially adopted in subtropical viticulture regions. However, very limited information about rootstock and seasonal effects on berry quality traits are available for this unique production system. Developing ‘Kyoho’ berries from own-rooted vines and from vines on 5C and 1202C rootstocks were periodically sampled from veraison until harvest in two consecutive cropping cycles to document the potential seasonal influence on rootstock effects. Anthocyanin concentration in berry skin, total soluble solids content (TSS), and titratable acidity (TA) were analyzed. In both cropping cycles, own-rooted vines produced berries with the highest anthocyanin concentration while vines on 1202C produced berries with the lowest anthocyanin concentration among the three scion/rootstocks. Anthocyanin concentrations were not differentiated by the differential climate pattern between the summer and the winter cropping cycles. Berries of own-rooted ‘Kyoho’ and ‘Kyoho’/5C vines accumulated satisfactory and equal amount of TSS in both cropping cycles. 1202C rootstocks did not affect berry TSS in the summer cropping cycle but reduced TSS in the winter cropping cycle. Significant rootstock and seasonal effects on berry TA were detected. Own-rooted vines produced berries with the lowest TA while vines on 1202C produced berries with the highest TA among the three scion/rootstock combinations. TA of berries from the winter cropping cycle was significantly higher than that from the summer cropping cycle especially in ‘Kyoho’/1202C. Relationships between anthocyanins and TSS of developing berries after veraison properly fitted into a sigmoidal function regardless of rootstocks and cropping cycles. However, the duration of the initial lag phase, the onset and the trend of both quality triats in the increasing phase, and the presence and degree of the final lag phase in the relationship were all modulated by rootstocks and by seasonal variations.

Although many new tomato cultivars with various degrees of heat-tolerance have been released, year-round tomato production in subtropical lowlands is still challenged by summer heat and an increasing risk from salinity stress. Little information about the simultaneous effects of heat and salinity on growth and fruiting in tomatoes is available. It was hypothesized that cultivars which perform better in high temperatures are also more tolerant to salinity stress. Two highly heat-tolerant cultivars, ‘Tainan ASVEG No. 19’ (TA19) and ‘Taiwan Seed ASVEG No. 22’ (TSA22), and one moderately heat-tolerant cultivar, ‘Hualien ASVEG No. 21’ (HA21), were grown under high temperature conditions and were irrigated with a 0, 50, 150, or 200 mM NaCl solution for 20 days. Vegetative growth, fruiting behavior, and fruit quality were monitored. Number of leaves, leaf area, shoot fresh and dry weights, and root fresh weight were generally decreased with increasing level of salinity stress, but root dry weight was not affected, resulting in an increase in root to shoot ratio in all three cultivars. Yield was also decreased by salinity treatments in all three cultivars due to reduced number of flowers, fruit set, and fruit size. The highly heat-tolerant ‘TA19’ had the lowest vegetative growth and the highest yield under the high temperature condition, but the yield was strongly suppressed by the short-term mild salinity treatment. On the other hand, vegetative growth was little affected and the degree of yield reduction was less intense with the short-term mild salinity treatment in the moderately heat-tolerant ‘HA21’. The result indicated that effects of heat stress and salinity stress are not additive and differential responses to salinity under high temperatures exist among cultivars with various degrees of heat-tolerance.

For rapid and mass-propagation of rabbiteye blueberry (”Vaccinium ashei”) plants, a protocol for tissue culture was required. The objectives of this study were 1) to investigate the optimal tissue culture condition for rapid proliferation of rabbiteye blueberry plants, and 2) to establish standard operating procedure of tissue culture for rabbiteye blueberry. ”In vitro” derived leaf explants of 'Blueshower', 'Woodard' and 'Tifblue' rabbiteye blueberry were used as plant materials to identify the optimal medium for tissue culture and ”ex vitro” rooting. The results showed that segments from the middle section of a leaf from regenerated axillary shoots were suitable for culture in the medium containing 2.3 μM TDZ. After incubation in the dark for one month and then in the light for another one month, the number of adventitious buds per explant was 15.89 in 'Blueshower', 2.5 in 'Woodard', and 0.17 in 'Tifblue'. The bud clumps of 'Blueshower' were transferred to medium containing 4 μM zeatin and cultured for 1 month. On average, a bud clump generated 2.25 shoots longer than 1 cm. The regenerated shoots were used for ex vitro rooting test. The shoots were dipped in 2000 ppm IBA and inserted in moist rooting mixture of 3 peat moss and 2 perlite (by volume), 80%-90% shoot cuttings rooted after 40 days.

Production of strawberry (”Fragaria” × ”ananassa” Duch.) using plastic tunnel system is popular in northern Taiwan due to the rainy winter conditions. Although the plastic tunnel system provides shelter for strawberry leaves and fruits from the raining damage, it unavoidably reduces irradiation for energy source of photosynthesis. The negative effect of shading on whole-plant photosynthesis and growth has yet to be documented in strawberries. During winter and spring in Taipei area, the PE plastic tunnel system caused 30% declination of light intensity and led to 30% reduction of whole canopy photosynthesis rate in container-grown 'Toyonoka' strawberries. Consequently, total leaf area decreased by 35% and dry weight by 60% in the late production season in strawberry plants grown in the plastic tunnel, as compared to field-grown plants. The vegetative growth and whole canopy photosynthesis of strawberry plants in the tunnel was severely suppressed by the shading effect from the plastic tunnel. The consequences on yield and fruit quality in commercial strawberry production should be further evaluated.

•Vegetative traits and chilling requirements were used to classify Morus spp. into 3 major taxonomic groups in Taiwan.•A new unbiased key to Morus spp. with variable sex expression patterns was established based on 9 representative traits.•M. atropurpurea in Taiwan might have evolved independently from related species in other areas.•An indigenous species, M. formosensis, may be derived from M. australis.

Removing runners and old leaves are two major routine and labor consuming tasks in winter strawberry ( Fragaria × {ptananassa} Duch.) production in subtropics. However, the potential negative effects of defoliation has not been evaluated. We studied the effects of partial defoliation and runner removal on plant growth, leaf photosynthesis (P n ), and yield in field-grown or potted strawberry plants (‘Toyonoka’). The treatments were consisted of partial defoliation by removing leaves older than 45 days (PD), removing all runners (DR), PD + DR, and the control (CK). Treatments were applied weekly from mid-November until early March. DR promoted yield and number of fruits for the first harvest cycle but not for the second harvest cycle. Multiple linear regressions indicated that leaf area had greater overall effects on runnering and fruit traits than the existence of runners. The leaf P n was not responsive to DR but a transient increase in P n was consistently detected on the remaining leaf after each PD treatment. The compensatory increase in P n was only detectable within 1 days after each PD treatment, indicating that the actual compensation for partial loss of functioning leaf area may be negligible. Crown dry weight was less affected by canopy manipulation than growth and dry weight of roots. Our results indicated that yield of strawberry in Taiwan’s subtropical climate can be improved by removing runners while maintaining a greater leaf area with less severe defoliation.