Cross-pollination Rate Research Articles

Unveiling elevated spontaneous mutation rates in Phyllostachys edulis (Moso Bamboo) through whole genome sequencing (WGS) and investigating the impact of atmospheric and room temperature plasma (ARTP) induced mutagenesis

Moso bamboo, recognized for its wide distribution and economic importance, encounters challenges in varietal enhancement owing to its protracted sexual reproduction cycle. This study employed whole-genome resequencing to identify spontaneous mutations in Moso bamboo and investigated mutagenesis using atmospheric and room temperature plasma (ARTP). Through the sequencing results, we identified a population of flowering bamboo as an asexual breeding line. Notably, the flowering Moso bamboo population, exclusively derived from asexual reproduction, exhibited a high spontaneous mutation rate (4.54 × 10−4 to 1.15 × 10−3/bp) during sexual reproduction, considering parental and cross-pollination effects. Genetic disparities between the offspring and parents exhibited a bimodal distribution, indicating a substantial cross-pollination rate. ARTP mutagenesis increased structural variations in offspring, whereas changes in SNPs and INDELs were less pronounced. Sanger sequencing validated the gene subset, providing a foundation for the investigation of spontaneous mutation rates via whole-genome sequencing. These insights, particularly from mutagenized offspring sequencing, can contribute to Moso bamboo breeding strategies.

High cross-pollination rate of Greek oregano (O. vulgare ssp. hirtum) with Common oregano (O. vulgare ssp. vulgare) under open field conditions as revealed by microsatellite marker analysis

We studied the mode of pollination in Greek oregano (Origanum vulgare ssp. hirtum) under both controlled and open pollination conditions. When grown indoors without the presence of insects, Greek oregano plants did not develop any seeds, indicating a low level of spontaneous self-pollination. Applying manual self-pollination under the same conditions resulted in only 16 seeds, of which only five were able to germinate. At the same time, a clonally propagated Greek oregano plant of the same genotype produced a rich set of over 300 seeds in open field conditions when the flowers were visited by insects in an area where no other Origanum species were observed. Analysis with SSR markers showed that over 70% of the seeds likely resulted from self-pollination, indicating that insect-mediated pollination is essential for the seed development. We further analyzed the cross-pollination of Greek oregano with Common oregano (O. vulgare ssp. vulgare) in open field conditions where the two subspecies were grown in close proximity. Applying SSR markers, we analyzed 83 plants obtained from seeds of three vegetatively propagated Greek oregano mother plants. Surprisingly, the results showed that all analyzed seedlings resulted from cross-pollination of Greek oregano with Common oregano, indicating that cross-pollination between the two subspecies can completely take over the self-pollination or cross-pollination between the Greek oregano plants. The possible impact of the observed high cross-pollination rate on the genetic origin of seeds of selected Greek oregano lines and varieties, as well as on the genetic diversity and structure of natural populations, is discussed.

Viabilitas Serbuk Sari dan Keberhasilan Persilangan antara Durian Montong dan Sitokong pada Tiga Waktu Berbeda

The success of durian pollination in nature is very low (<5%) due to high self-incompatibility in durian flowers. Artificial cross-pollination is an alternative method that can be used to increase the successful pollination of durian. So, information on the pollen viability of the durian flower and the time of artificial cross-pollination accurate and effective is required. This research aimed to examine the pollen viability of the durian varieties of Montong and Sitokong varieties at three different times and to determine the success rate of artificial cross-pollination between both varieties at three different times. This research was carried out at the Morpoyan Seed Center and the Genetic and Breeding Laboratory of the Faculty of Agriculture, UIN Suska Riau. Pollen viability testing used the staining method. Artificial cross-pollination between the Montong durian and the Sitokong durian was carried out reciprocally at three different times (11.00–13.00, 15.00–17.00, and 19.00–21.00). The total number of flowers crossed was 300. The results of this study showed that the percentage of pollen viability of Montong durian at 11.00–13.00, 15.00–17.00, and 19.00–21.00 was 94.91, 97.67, and 97.23%, respectively. While the pollen viability of Sitokong durian was 93.33% at 11.00–13.00, 94.45% at 15.00–17.00, and 94.76% at 19.00–21.00. The successful rate of crosses of durian Montong (♀) x Sitokong (♂) at 11.00–13.00, 15.00–17.00, and 19.00–21.00, respectively were 46, 26, and 34%, while the percentage of success of durian Sitokong crosses (♀) x Montong (♂) is 48% at 11.00–13.00, 54% at 15.00–17.00, and 22% at 19.00–21.00. Successful artificial cross-pollination between Montong and Sitokong durian or vice versa was higher at 11.00–13.00 compared to other times. The results of this study can be utilized to formulate the timing of artificial cross-pollination of durian in the future.

Bumblebees (Bombus terrestris) Improve 'Hass' Avocado (Persea americana) Pollination.

Pollination is limiting for avocado production. We examined whether adding bumblebees (BBs; ca. 10 hives/ha) to conventional honeybees (HB; 5 hives/ha) would improve ‘Hass’ avocado pollination and yields. A preliminary trial (2017/18) in an avocado orchard with four consecutive rows of ‘Hass’ followed by one row of ‘Ettinger’ serving as a pollenizer (20% ‘Ettinger’) showed a considerable increase in ‘Hass’ yield in rows adjacent to (up to 80 m from) the BB hives vs. distant rows (=controls). In 2018/19, the trials were extended to three additional orchards. A significant yield increase was obtained in the BB hive-adjacent trees compared to BB hive-distant ones. Similar results were obtained in 2019/20, in experiments conducted throughout the country. The SNP analysis, to determine the parents of ‘Hass’ fruit at varying distances from the BB hives, showed no differences in the cross-pollination rate (‘Hass’ × ‘Ettinger’). However, pollination rates and the number of germinating pollen grains per stigma decreased with distance from the hives, and correlated to the negative gradient in yield. Taken together, our data suggest that adding BB hives to ‘Hass’ avocado orchards, at ca. 10 hives/ha resulting in 0.5–1.0 BB visits/tree per min, increases pollination and, accordingly, total yield.

Effectiveness of different sampling schemes in predicting adventitious genetically modified maize content in a smallholder farming system

ABSTRACT When genetically modified (GM) maize is planted in an open field, it may cross-pollinate with the nearby non-GM maize under certain airflow conditions. Suitable sampling methods are crucial for tracing adventitious GM content. By using field data and bootstrap simulation, we evaluated the performance of common sampling schemes to determine the adventitious GM content in small maize fields in Taiwan. A pollen dispersal model that considered the effect of field borders, which are common in Asian agricultural landscapes, was used to predict the cross-pollination (CP) rate. For the 2009–1 field data, the six-transect (Tsix), JM method for low expected flow (JM[L]), JM method for high expected flow (JM[H]), and V-shaped transect (TV) methods performed comparably to simple random sampling (SRS). Tsix, TV, JM(L), and JM(H) required only 13% or less of the sample size required by SRS. After the simulation and verification of the 2009–2 and 2010–1 field data, we concluded that Tsix, TV, JM(L), and systematic random sampling methods performed equally as well as SRS in CP rate predictions. Our findings can serve as a reference for monitoring the pollen dispersal tendencies of maize in countries with smallholder farming systems.

Participatory Plant Breeding and the Evolution of Landraces: A Case Study in the Organic Farms of the Collserola Natural Park

Although consumers appreciate the genetic diversity among tomato landraces, traditional varieties have been displaced from commercial agriculture. Their cultivation through organic farming in natural parks can contribute to their resurgence. With this aim, we developed a participatory plant breeding (PPB) program in Collserola Natural Park (Barcelona, Spain) to promote the conservation of the Mando landrace and to obtain new varieties adapted to local organic farms. Taking advantage of the natural genetic variation from the variety’s high cross-pollination rate, farmers developed five experimental inbreeds that were tested in a multi-locality trial in 2018. As a result of the PPB program, cultivation of the original landrace increased from 80 plants in 2011 to more than 2000 plants in 2018, which protected the variety from genetic erosion. Locality was the factor that contributed mostly to agronomic traits (e.g., yield (66% of the phenotypic variance)), while the genotype contributed more to the quality traits (except for soluble solids (37%) and dry matter (38%)). Farmer evaluations were highly correlated with the phenotypic traits recorded by researchers (Pearson coefficient ranging from 0.63–0.83), and led to the same final varietal selection. The superior inbred selected (3.9) is now being cultivated in the area of study. This paper discusses the efficiency of PPB in guiding the evolution of landraces.

Modeling and estimation of pollen-mediated gene flow at the landscape scale

Abstract Undesired pollen-mediated gene flow (PMGF) in large-scale agriculture has received considerable attention for their ability to affect biological invasions. However, it has been not yet sufficiently understood how landscape structure and large-scale anthropogenic dispersal influence the gene spreading process. To explore the possible gene flow from crop species to wild relatives, we performed a literature review in ecosystem PMGF research for four major transgenic crops (maize, rice, wheat, oilseed rape). We found that whether pollen flow results induce a high cross-pollination rate mainly depends on the types of genetically modified (GM) species and cropping practice. Interestingly, the increase in the plot size of a pollen donor can lead to the increase in PMGF under ideal field conditions. However, while in a much larger landscape, it rapidly drops due to the exponential decrease in pollen density and the relatively low out-crossing rates. In large-scale field surveys, seeds of those plants with dormancy capability amplify the occurrence of transgene invasion and can remain alive in the seedbank for several years. Furthermore, in comparison with the distance-based methods, more and more spatio-temporal simulation models have proposed that a higher up-scaling percentage of GM crops is acceptable in a coexistence area of GM and non-GM crops. This highlights that the fate of (trans)genes should be emphasized in designing coexistence approaches. These results carry implications for gene dispersal management and indicate areas for future work, such as how to incorporate the response functions of different pollination factors into simulating models.

Mating system and pollen dispersal in Dipteryx alata Vogel (Leguminosae): comparing in situ and ex situ conditions

Dipteryx alata is a Neotropical tree widely distributed throughout the Brazilian Cerrado biome and is popularly known as baru. In this study, we evaluated the mating system of D. alata and compared pollen dispersal patterns between the in situ and ex situ conditions. For this, we used 515 genotypes of adults, juveniles, and progeny from a natural population (in situ) in Orizona-GO, Brazil. In addition, we used 488 genotypes of adults and progeny from a germplasm collection (ex situ) located at the Federal University of Goias. Both locations are situated in central Brazil. The genetic diversity, cross-pollination rates, and pollen dispersal distance under both conditions were estimated. Genetic diversity and polymorphism differed between the in situ and ex situ conditions. The average number of alleles found in situ (5.2) and ex situ (6.2) showed that the germplasm collection stores greater genetic diversity than the in situ condition. Cross-pollination detected among mother trees under both the in situ and ex situ conditions were high (tm = 0.815 and tm = 0.934, respectively), indicating that the species has a mixed reproductive system that was predominantly allogamous. The difference between tm and ts indicated that the in situ condition shows greater biparental inbreeding. Our results showed that, across generations, the ex situ condition preserved a larger number of alleles, confirming that the D. alata germplasm collection plays a role in conserving genetic diversity. The presence of self-fertilization suggests self-compatibility. Paternity correlation and the dispersal distance of the pollen donors were higher in the in situ condition, a maximum distance of 2.9 km of pollen flow. This can be explained by the number of pollinators and tree spatial distribution.

Three-dimensional numerical simulations of windbreak effects on pollen dispersal and cross-pollination

Based on the atmospheric turbulence diffusion model, a three-dimensional numerical model was applied for predicting the cross-pollination rate distribution in leeward area of windbreaks by considering actual weather observation data, daily fluctuation parameter of pollen release rate, pollen life during flowering period, etc. Several cases of cross-pollination effect of windbreak distributions in the field were simulated. It is demonstrated that windbreak nets and windbreaks plant or forest are effective in suppressing pollen dispersal and cross-pollination. By simulating pollen diffusion under actual weather conditions using this model, it is possible to evaluate the effect of cross-pollination by the windbreak facilities and give advises of how to set windbreaks for suppressing crossing.

Assessment of natural cross-pollination levels in chili pepper (Capsicum annuum L.)

Inconsistency of the current information on the natural cross-pollination (NCP) stimulated this research to update the natural cross-pollination rates of chili pepper. The objective of this study were to determine the level of natural cross pollination and the various factors that influence of the NCP in chili pepper. The experiment used four genotypes of chili peppers, “IPBC2, IPBC5, IPBC120” (green hypocotyl) and IPBC20 (purple hypocotyl). The experiment utilized the dominance of purple hypocotyl colors over green hypocotyl colors to determine NCP. The experimental field consisted of three blocks of trial. Each blocks was planted by purple hypocotyl genotype in the central plot and green hypocotyl genotypes in the surrounding four plots. Seeds were harvested from each plant and were examined for the levels of NCP in the next generation. The result showed that there were the differences on percentages of NCP on different chili pepper genotypes. The results also showed that the levels of NCP in chili pepper could be associated with by stigma exertion length and the level of successful artificial cross-pollination.

EFFECTS OF POLLEN CONTAMINATION AND KERNEL WEIGHT ON KERNEL STRUCTURE OF MAIZE IN OPEN AND SELF POLLINATION TREATMENTS

In small plot experiments conducted in maize, the mostly used pollination methodsare open and self-pollination treatments. Comparative studies using thesetreatments are abundant in scientific literature; however studies on the effect ofcross pollination and kernel weight on kernel biochemical properties in differenttreatments are limited. In this study, we conducted a comparative experiment toinvestigate the effect of pollen contamination and mean kernel weight on kernelbiochemical composition of ten different maize genotypes by using two differentpollination methods.Open and self-pollination treatments were applied aspollination methods. Eight different traits; kernel weight, cross pollination rate,protein, oil, carbohydrate, oleic acid linoleic acid and carotenoid content weremeasured. Regression analyses were performed to understand the effects of crosspollination and mean kernel weight on biochemical constituents of maize kernel indifferent treatments. Results showed that the major biochemical traits, such asprotein, oil and carbohydrate content were significantly affected by pollencontamination but minor traits were not. When data were combined (n=60) theeffect of pollen contamination in different treatments was not clearly understood.When data (n=30) of each treatment were separately analyzed, it was found thatcross pollination rate had significant effect on the most of biochemical constituentsin open pollination. Overall, results suggested that pollen contamination had aneffect on major biochemical traits in maize and hand pollination could be used forpreventing of unwanted effect of pollen contamination in small plot experiments.However, it should be considered that the effects of hand pollination on kernelweight affect the some biochemical traits in maize.

Seed germination and seedling allogamy in Rosmarinus officinalis: the costs of inbreeding.

Self-pollination by geitonogamy is likely in self-compatible plants that simultaneously expose a large number of flowers to pollinators. However, progeny of these plants is often highly allogamous. Although mechanisms to increase cross-pollination have been identified and studied, their relative importance has rarely been addressed simultaneously in plant populations. We used Rosmarinus officinalis to explore factors that influence the probability of self-fertilisation due to geitonogamy or that purge its consequences, focusing on their effects on seed germination and allogamy rate. We experimentally tested the effect of geitonogamy on the proportion of filled seeds and how it influences germination rate. During two field seasons, we studied how life history and flowering traits of individuals influence seed germination and allogamy rates of their progeny in wild populations at the extremes of the altitudinal range. The traits considered were plant size, population density, duration of the flowering season, number of open flowers, flowering synchrony among individuals within populations and proportion of male-sterile flowers. We found that most seeds obtained experimentally from self-pollination were apparently healthy but empty, and that the proportion of filled seeds drove the differences in germination rate between self- and cross-pollination experiments. Plants from wild populations consistently had low germination rate and high rate of allogamy, as determined with microsatellites. Germination rate related positively to the length of the flowering season, flowering synchrony and the ratio of male-sterile flowers, whereas the rate of allogamous seedlings was positively related only to the ratio of male-sterile flowers. Rosemary plants purge most of the inbreeding caused by its pollination system by aborting the seeds. This study showed that the rates of seed germination and allogamy of the seedlings depend on a complex combination of factors that vary in space and time. Male sterility of flowers, length of the flowering season and flowering synchrony of individuals within populations all favour high rates of cross-pollination, therefore increasing germination and allogamy rates. Flowering traits appear to be highly plastic and respond to local and seasonal conditions.

Research Article Estimate of natural cross-pollination rate of Capsicum annuum using a codominant molecular marker associated with fruit pungency

The production of seeds with high genetic quality requires accurate estimates of the natural cross-pollination rate in cultivated Capsicum species. This is important in order to establish the most suitable isolation distance among fields of distinct genotypes, to minimize the risk of genetic contamination and to ensure that the agronomic and horticultural traits of an elite breeding material are preserved in a given seed lot. Cross-pollination studies in C. annuum are practically non-existent under Brazilian conditions. The objective of the present study was to estimate the natural rate of C. annuum cross-pollination in seed production fields established in the highland area of Central Brazil (“Cerrado”). A molecular marker (CA-Pun1), which allows the identification of cross-fertilization between C. annuum accessions with pungent and sweet fruits, was employed to identify hybrid seeds. This marker detects functional and non-functional alleles of an acyl-transferase (Pun1) gene, responsible to produce capsaicin (pungency) in placental tissue of C. annuum fruits. Seedlings of cultivar ‘Magali R’ (sweet fruits) were planted in the field at incremental distances from cultivar ‘BRS Garca’ (pungent fruits). Progenies obtained from ‘Magali R’ plants were genotyped with marker CA-Pun1. Approximately 10.8% of the fruits displayed at least one seed originated from cross-pollination. The overall natural cross-pollination rate in C. annuum was estimated at 1.2%, according to the percentage of hybrid seeds detected by molecular analysis. No significant differences were detected in the rate of cross-pollination among plants for distances of up to 7.2 m.

Genetic and physical mapping of anther extrusion in elite European winter wheat.

The production and cultivation of hybrid wheat is a possible strategy to close the yield gap in wheat. Efficient hybrid wheat seed production largely depends on high rates of cross-pollination which can be ensured through high anther extrusion (AE) by male parental lines. Here, we report the AE capacity and elucidate its genetics in 514 elite European winter wheat varieties via genome-wide association studies (GWAS). We observed a wide range of variation among genotypes and a high heritability (0.80) for AE. The whole panel was genotyped with the 35k Affymetrix and 90k iSELECT single nucleotide polymorphism (SNP) arrays plus Ppd-D1, Rht-B1 and Rht-D1 candidate markers. GWAS revealed 51 marker-trait associations (MTAs) on chromosomes 1A, 1B, 2A, 4D and 5B, with Rht-D1 (4D) being the most significant marker. Division of whole panel according to the Rht-D1 genotype resulted in 212 and 294 varieties harboring Rht-D1a and Rht-D1b allele, respectively. The presence of Rht-D1a compared to Rht-D1b (mutant) allele had a large phenotypic influence on AE resulting in its ~17% increase. GWAS performed on the sub-panels detected novel MTAs on chromosomes 2D, 3B and 6A with increased phenotypic variance imparted by individual markers. Our study shows that AE is a highly quantitative trait and wild type Rht-D1a allele greatly improves AE. Moreover, demarcating the quantitative trait loci regions based on intra-chromosomal linkage disequilibrium revealed AE’s candidate genes/genomic regions. Understanding the genetics of AE in elite European wheat and utilizing the linked markers in breeding programs can help to enhance cross-pollination for better exploitation of heterosis.

Hybrid-breeding of medicinally used valerian ( Valeriana officinalis L. s.l.). A possible concept developing new varieties?

The aim of this work was to develop and verify a new concept for breeding new hybrid-varieties of valerian without a male sterility system. For this the cross-pollination rate and the performance of inbreeded plants must be determined.

Pollen-Mediated Movement of Herbicide Resistance Genes in Lolium rigidum

The transfer of herbicide resistance genes by pollen is a major concern in cross-pollinated species such as annual ryegrass (Lolium rigidum). A two-year study was conducted in the greenhouse, under favorable conditions for pollination, to generate information on potential maximum cross-pollination. This maximum cross-pollination rate was 56.1%. A three-year field trial was also conducted to study the cross-pollination rates in terms of distance and orientation to an herbicide-resistant pollen source. Under field conditions, cross-pollination rates varied from 5.5% to 11.6% in plants adjacent to the pollen source and decreased with increasing distances (1.5 to 8.9% at 15 m distance and up to 4.1% at 25 m in the downwind direction). Environmental conditions influenced the cross-pollination both under greenhouse and field conditions. Data were fit to an exponential decay model to predict gene flow at increasing distances. This model predicted an average gene flow of 7.1% when the pollen donor and recipient plants were at 0 m distance from each other. Pollen-mediated gene flow declined by 50% at 16.7 m from the pollen source, yet under downwind conditions gene flow of 5.2% was predicted at 25 m, the farthest distance studied. Knowledge of cross-pollination rates will be useful for assessing the spread of herbicide resistance genes in L. rigidum and in developing appropriate strategies for its mitigation.

Herança genética da resistência de capim-amargoso ao glyphosate

A herança genética da resistência ao glyphosate em capim-amargoso (Digitaria insularis) pode ajudar a entender sua disseminação, porém a mesma não foi previamente caracterizada. Estas informações são essenciais para o entendimento da evolução de resistência à herbicidas na agricultura e o fluxo gênico entre plantas resistentes e suscetíveis. Portanto, o objetivo desta pesquisa foi investigar a herdabilidade dos genes de resistência entre os biótipos resistente e suscetível ao glyphosate, através da determinação da suscetibilidade dos biótipos na progênie F1. Para isso foi comparada a suscetibilidade da geração F1 dos biótipos resistente (MG) e suscetível (S), que permaneceram isolados ou induzidos à polinização cruzada através do acondicionamento de panículas em sacos de polinização. O grau de suscetibilidade ao glyphosate foi medido através de curvas de dose-resposta da progênie F1. A geração F1 de plantas oriunda de um possível cruzamento entre os biótipos demonstrou o mesmo padrão de suscetibilidade ao glyphosate que a progênie oriunda da planta mãe. Comparando as médias dos biótipos resistentes com os suscetíveis ao glyphosate foi calculado um fator de resistência de 4,01. Conclui-se que não há a transferência de genes de resistência após indução ao cruzamento entre biótipos, sendo necessários mais estudos para determinar se isso ocorreu devido à espécie ser exclusivamente autógama ou se a resistência é poligênica, não seguindo o modelo de hereditariedade monogênica. Desta forma, a dispersão da resistência do capim-amargoso pode ser atribuída à disseminação de suas sementes, e não à transferência gênica entre biótipos pela polinização cruzada entre plantas, pois o trabalho evidência fecundação cruzada em taxas imperceptíveis pelo estudo.

Response to low-dose herbicide selection in self-pollinated Avena fatua.

When applied at the correct plant stage and dose, herbicides are highly toxic to plants. At reduced, low herbicide doses (below the recommended dose) plants can survive and display continuous and quantitative variation in dose-survival responses. Recurrent (directional) selection studies can reveal whether such a phenotypic variation in plant survival response to low herbicide dose is heritable and leads to herbicide resistance. In a common experimental garden study, we have subjected a susceptible population of self-pollinated hexaploid Avena fatua to low-dose recurrent selection with the ACCase-inhibiting herbicide diclofop-methyl for three consecutive generations. Significant differences in response to low-dose diclofop-methyl selection were observed between the selected progenies and parent plants, with a twofold diclofop-methyl resistance and cross-resistance to ALS-inhibiting herbicides. Thus, the capacity of self-pollinated A. fatua to respond to low-dose herbicide selection is marginal, and it is much lower than in cross-pollinated L. rigidum. Lolium rigidum in the same experiment evolved 40-fold diclofop-methyl resistance by progressive enrichment of quantitative resistance-endowing traits. Cross-pollination rate, genetic variation and ploidy levels are identified as possible drivers affecting the contrasting capacity of Avena versus Lolium plants to respond to herbicide selection and the subsequent likelihood of resistance evolution at low herbicide dose usage.

Pollen viability, stigma receptivity and fruiting characteristics of botanical origin of Jinxianlian

The viability and life span of pollen were evaluated by TTC (2,3,5-triphenyl tetrazlium chloride) and the peroxidase solution, the stigma receptivity were estimated by benzidine-H2O2 method and the fruiting characteristics were investigated. The results showed that (1) Anoectochilus roxburghii and A. formosanus appeared the same up-and-down trend of the pollen viability, increased and then decreased. The storage temperature and storage time had significant impact on the pollen viability. With the extension of storage time, the pollen activity decreased. 4 degrees C refrigerator storage may be extended the pollen vitality. (2) The stigma had receptivity in 1st day and reached the highest level in the 4th day after blooming. A. roxburghii lost receptivity in the 8th day while A. formosanus lost receptivity in the 10th day after blooming. (3) The different pollination had significant impact on seed setting rate. The seed setting rate of artificial cross-pollination was higher than that of the artificial self-pollination. Collecting pollen in the 3rd day and carrying out artificial cross-pollination in the 4th day after blooming can significantly improve seed setting rate. The results provided technical assurance for A. roxburghii and A. formosanus breeding of new varieties and seed breeding.

Patterns of nectar and pollen presentation influence the attractiveness of four raspberry and blackberry cultivars to pollinators

SummaryFloral rewards such as nectar and pollen have a major influence on successful pollination and fruit-set, even in selffertile Rubus sp. (Rosaceae), which include most cultivated raspberries and blackberries. A 2-year study was designed to examine the diurnal dynamics of nectar secretion and pollen shedding in the raspberry cultivars ‘Autumn Bliss’ and ‘Malling Exploit’, and in the blackberry cultivars ‘Arapaho’ and ‘Hull’, in order to establish the effect of these traits on floral attractiveness to various insect visitors. The volume of nectar secreted per flower was measured using calibrated capillaries, and the concentrations of sugars in the nectar were measured using a hand-held refractometer. The four Rubus cultivars differed in their patterns of nectar and pollen presentation. Volumes of nectar and concentrations of sugars were influenced by year, cultivar, age of the flower, and time of sampling. The four cultivars exhibited different patterns of nectar secretion over the 2 years. In year-1, an early morning peak in nectar volume was followed by a rapid decline, while the concentrations of sugars increased during the day. In year-2, both the volume of nectar and the concentrations of sugars increased from the morning to the afternoon. The patterns of pollen presentation were similar in both years of study. Anther dehiscence took only 3 - 8 h per flower in the poorest nectar producer, ‘Arapaho’; while, in cultivars with higher nectar yields, pollen shedding lasted for 6 - 10 h. Pollen-shedding flowers secreted significantly higher volumes of nectar, with significantly lower concentrations of sugars, compared to pre-pollen-shedding flowers in year-1. The concentrations of sugars in the nectar were higher in both raspberry cultivars than in the blackberry cultivars, but both blackberry cultivars were as attractive to bees due to their more appealing nectar sugar composition. Bees were more attracted to flowers of cultivars which simultaneously offered ample nectar and some pollen (i.e., ‘Autumn Bliss’, ‘Malling Exploit’, and ‘Hull’) than to flowers with a rapid rate of pollen shedding, but a low nectar yield (i.e., ‘Arapaho’). Higher rates of bee-mediated cross-pollination may provide economically important increases in fruit yields and better quality fruit.