Hand Pollination Research Articles

Use of timelapse photography to determine flower opening time and pattern in banana (Musa spp.) for efficient hand pollination

Sterility and low seed set in bananas is the main challenge to their conventional genetic improvement. The first step to seed set in a banana breeding program depends on pollination at the right time to ensure effective fertilization. This study aimed at determining bract opening time (BOT) to enhance efficient pollination and seed set in bananas. A Nikon D810 digital camera was set-up to take pictures of growing banana inflorescences at five-minute intervals and time-lapse movies were developed at a speed of 30 frames per second to allow real-time monitoring of BOT. Genotypes studied included wild banana (1), Mchare (2), Matooke (4), Matooke hybrid (1), and plantain (1). Events of bract opening initiated by bract lift for female flowers (P < 0.01) started at 16:32 h and at 18:54 h for male flowers. Start of bract rolling was at 18:51 h among female flowers (P < 0.001) and 20:48 h for male flowers. Bracts ended rolling at 02:33 h and 01:16 h for female and flowers respectively (P < 0.05). Total time of bract opening (from lift to end of rolling) for female flowers was significantly longer than that of male flowers (P < 0.001). On average, the number of bracts subtending female flowers opening increased from one on the first day, to between one and four on the fourth day. The number regressed to one bract on day eight before start of opening of bracts subtending male flowers. There was a longer opening interval between bracts subtending female and male flowers constituting spatial and temporal separation. Bract rolling increased from partial to complete rolling from proximal to the distal end of the inflorescence among female flower. On the other hand, bracts subtending male flowers completely rolled. Differences in BOT of genotypes with the same reference time of assessment may be partly responsible for variable fertility. Hand pollination time between 07:00 and 10:00 h is slightly late thus an early feasible time should be tried.

An easy-to-manage two-entrance honey bee hive system for greenhouse pollination that improves fruit production

An alternative two-entrance hive system demonstrated here is less taxing for the bee colonies. Bees are directed to forage inside the greenhouse when the crop is in flower, and only have access to the outside after anthesis. Consequently, there are no bees in the greenhouse in the afternoon, facilitating crop management. This system allows the farmer to control bee access to the crop without the need for a smoker or protective equipment. Using this system, we compared pollination by honey bees (Apis mellifera) to hand pollination of zucchini squash (Cucurbita pepo) in greenhouses, during two crop seasons. Data included number of flower visits by the bees, fruit production, and the time and consequent labor costs needed to control bee flight direction versus the costs of hand pollination. In the greenhouses with bees, each female flower received a mean of more than 40 bee visits. When eight or more bees visited a flower, the fruits were significantly heavier than with manual pollination (313 versus 232 g, respectively). Total production was increased 41% with bee pollination. Using bee pollination increased profit over 12%, taking into account hive rental and labor costs for hand pollination versus manipulating the hive entrances.

High fruit setting rate without male participation: A case study of obligate apomixis in Rhomboda tokioi (Orchidaceae)

Seed production is the key factor for maintaining plant population renewal and development. Because of pollination limitations and other factors, orchids, especially rewardless ones, generally have low fruit set rates. In Rhomboda tokioi, however, the natural fruit setting rate is very high, more than 90%. Common reasons for such a high natural fruit setting rate include high pollinator efficiency, autonomous selfing, seed formation through apomixis and so on. To test these possibilities, we carried out field observations, morphological examinations, and breeding system experiments. The results showed no migration of pollinia into or out of flowers and suggested that the structure of the floral organs hinder autonomous selfing. Interestingly, the fruit setting rate of this orchid was still higher than 90% when the gynostemium was removed prior to flowering. Additionally, after hand pollination, the pollen tube stopped growing at a late stage and could not enter the ovule, indicating the seeds were produced by obligate apomixis. Morphological experiments showed that a megasporocyte first forms a chain tetrad and then develops into a mature embryo sac, while the embryo of the offspring developed from unfertilized egg cells. More interestingly, the offspring had the same number of chromosomes as the female parent. According to the existing theory of apomixis, we can infer that the reproductive model of R. tokioi is Allium-type apomixis.

Pollination and Plant Reproductive Success of Two Ploidy Levels in Red Clover (Trifolium pratense L.)

Plant reproduction in red clover requires cross-fertilization via insect pollination. However, the influences of visitation rate and timing on maximizing ovule utilization are yet to be determined. We aimed to study the influences of visitation rate, flowering stage, and self-incompatibility on reproductive success. We applied hand and honey bee pollination in the study of eight red clover cultivars with two ploidy levels released between 1964 and 2001. In hand pollination, increasing the visitation rates (from 10 to 80 pollinated florets per flower head) increased the seed number per flower head but reduced the seed number per pollinated floret. Different flowering stages (early, middle, and full flowering) did not influence the seed number per pollinated floret significantly. There was a marked difference in reproductive success depending on the ploidy level, with 0.52 seeds per pollinated floret in diploid and 0.16 in tetraploid cultivars. During the cultivar release history, seed number per pollinated floret seemed to decrease in diploid cultivars, whereas it increased in tetraploids. In honey bee pollination, diploid cultivars had more two-seeded florets than tetraploids. Different visitation rates and the stochastic nature of pollen transfer resulted in difficulties when the plant reproductive success between hand and bee pollination was compared. A maximum of 0.27 seeds per pollinated floret were produced in hand pollination compared to the 0.34 in honey bee pollination. In spite of this, hand pollination provided a valuable method for studying the pollination biology and reproduction of red clover. Future studies may employ hand pollination to unravel further aspects of the low reproductive success with the future perspective of improving seed number per pollinated floret in tetraploid red clover.

Floral biology and pollen grain presentation in “Arbequina” olive (Olea europaea L.) cultivar under non-traditional crop climatic conditions

ABSTRACT Olea europaea L. (Oleaceae), a traditional oil crop of Mediterranean basin, has been expanded considerably in the last decades to other regions of the world. “Arbequina” is one of the most widely planted cultivars due to its good agronomic and technological attributes, but interannual variability in thermal and rainfall regimes affects its regular fruit production in countries of the Southern Hemisphere, including Uruguay. To better understand the floral mechanisms that regulate fruit set in Southern Hemisphere climatic conditions, our work addresses the “Arbequina” flower functionality and pollen grains presentation along flower life span. In this andromonoecious species, the fruitful perfect flower morphs were evaluated by means of determining functional parameters such as stigmatic receptivity and pollen grain viability in each floral phenological stage, and pollen grain adhesion and pollen tube growth rate in hand pollination treatments. This flower morph did not show functional limitations under Uruguayan climatic conditions for the year in which the study was carried out, but a breeding system expressed by two different functional phases was detected. The first pistillate functional phase, where the stigma is receptive but no pollen release occurs, tends to avoid self-pollination and promotes crosspollination in the same flower. Then, a second perfectly functional phase follows, where the stigma remains receptive and the anthers release their pollen grains. In a self-incompatible olive cultivar such as “Arbequina”, this pollen grain presentation further stresses the importance of combining inter-compatible olive cultivars with synchronized flowering in orchard design, as a first step to ensure fruit set.

Self-incompatibility of raspberry cultivars assessed by SSR markers

Self-incompatibility in European red raspberry (Rubus idaeus L.) is less studied compared to other horticulturally relevant rosaceous crops, although cultivars of this species show differences in self-fertility. In this study, we genotyped progenies of 16 open pollinated raspberry cultivars with SSR markers to determine their natural propensity for self- and cross-fertilization. In further experiments, we genotyped progenies of selected cultivars from a topcross environment and studied seed set after hand pollination. A wide spectrum of cross-fertilized progeny ratio was discovered among the cultivars ranging from 5% of 'Dorman Red' progeny to 100% of 'Rumla' progeny derived by cross-fertilization. This was consistent with results obtained by hand pollination, where a significantly higher number of seed was produced in self-pollinated fruit of 'Dorman Red' and cross-pollinated fruit of 'Rumla'. The difference was particularly large in 'Rumla'; its self-pollinated fruit developed 10.95 drupelets per fruit on average, almost seven times less than its cross-pollinated fruit. The cultivar 'Rumla' showed 100% cross-fertilized progeny in a topcross environment as well, in contrast to the cultivars 'Lucana' and 'Preußen', which both had no cross-fertilized progeny. The results of this study show that there are differences in fertilization behavior between raspberry cultivars. Such information on the fertilization behavior of selected cultivars is useful in planning for cultivar selection in protected growing, where pollination is of special consideration.

Reproductive strategies in the rare and endangered Killickia grandiflora (Lamiaceae) – implications for its urgent conservation

Populations of rare and restricted species are commonly challenged due to risks associated with reduced genetic diversity, environmental variation, and demographic stochasticity. Killickia grandiflora (Lamiaceae) is one of three Killickia species endemic to the Drakensberg Mountain Centre in KwaZulu-Natal, South Africa. Its confirmed distribution is restricted to a firebreak between two catchments in the Cathedral Peak region of the Ukhahlamba Drakensberg Transfrontier Park, where it is threatened by habitat transformation. In this study, we aimed to understand factors that promote or inhibit gene flow within this highly restricted K. grandiflora population, to estimate inbreeding, and to assess its status as a potentially threatened species. Exclusion and hand pollination trials indicate that K. grandiflora cannot autonomously self-pollinate and is dependent on pollinators for outcrossing. Germination trials and tetrazolium staining suggest that the seeds may have dormancy breaking requirements or are inviable. Inbreeding and genetic diversity analyses show that the K. grandiflora population nonetheless maintains a high level of genetic diversity, likely through outcrossing, despite the small population size and apparent poor reproductive success. We recommend that the IUCN conservation status of K. grandiflora be changed from Vulnerable to ‘Critically Endangered’ based on observed reductions in population size, limited extent of occurrence, small number of mature individuals, and threats by woody competitors. We strongly recommend that the known population(s) be monitored and the habitat patches be conserved regardless of size and maintained through regular burning to enable the species’ survival and conservation. Ex situ propagation and reintroduction to its historical habitat should be explored as additional conservation measures for this species.

Blocked pollen release prevents fruit formation in the halophyte Elaeagnus angustifolia in non-saline habitats

Anther development affects the reproduction of flowering plants. Halophyte Elaeagnus angustifolia can bear fruits when grown in saline soils. However, no fruits are born in non-saline soils. The possible reasons and differences in E. angustifolia under two growing conditions were elucidated. We examined features including pollen viability and germination, in situ pollen germination after natural and hand pollination, anthers after pollen release, and the transcriptome in anthers. No significant difference was observed in pollen viability or stigma receptivity in E. angustifolia in non-saline vs. saline habitats. However, no pollen tubes were present in styles, and pollen grains were abundant in E. angustifolia anthers under non-saline conditions. Notably, many pollen tubes formed in styles of E. angustifolia after hand pollination in the non-saline habitat. The differentially expressed genes in anthers from saline vs. non-saline habitats were mainly related to phytohormone, cell wall secondary thickening, transcription factors and ion transport. E. angustifolia fail to form fruits in non-saline habitats due to poor anther pollen release. The induction and coordinated upregulation of genes related to anther cell wall formation and JA biosynthesis likely contribute to anther dehiscence in E. angustifolia in saline habitats, whereas anther dehiscence is blocked in plants grown in non-saline habitats.

Direct and insect‐mediated effects of pathogens on plant growth and fitness

Abstract Plants are attacked by a large diversity of pathogens. These pathogens can affect plant growth and fitness directly but also indirectly by inducing changes in the host plant that affect interactions with beneficial and antagonistic insects. Yet, we lack insights into the relative importance of direct and indirect effects of pathogens on their host plants, and how these effects differ among pathogen species. In this study, we examined four fungal pathogens on the wood anemone Anemone nemorosa. We used field observations to record the impacts of each pathogen species on plant growth and fitness throughout the season, and experimental hand pollination and insect feeding trials to assess whether fitness impacts were mediated by pathogen‐induced changes in plant–pollinator and plant–herbivore interactions. Three out of four pathogens negatively affected plant size, and pathogens differed strongly in their effect on plant architecture. Infected plants had lower fitness, but this effect was not mediated by pollinators or herbivores. Even so, two out of four pathogens reduced herbivory on anemones in the field, and we found negative effects of pathogen infection on herbivore preference and performance in feeding trials. Synthesis. Our results are of broader significance in two main respects. First, we demonstrated that pathogens negatively affected plant growth and fitness, and that the magnitude of these effects varied among pathogen species, suggesting that pathogens constitute important selective agents that differ in strength. Second, direct effects on plant fitness were more important than effects mediated by beneficial and antagonistic insects. In addition, although we did not detect insect‐mediated effects on plant fitness, the negative effects of some pathogens on herbivore preference and performance indicate that pathogen communities influence the distribution and abundance of herbivores.

Different pollination approaches to compare the seed set of diploid and tetraploid red clover Trifolium pratense L.

In red clover seed production, low seed yield is limiting the commercial exploitation of tetraploid red clover. To explore if pollination is the limiting factor for the seed yield in tetraploid red clover, we investigated pollinator behaviour and plant reproductive success in diploid (2x) cultivar ‘Rajah' and tetraploid (4x) cultivar ‘Amos' using honey bee and hand pollination approaches. We measured the seed set at the flower head level with the increasing visitation rate of honey bees (one bee, two bees and open pollination) and pollen diversity (one and two pollen donors) of hand pollination. We found no difference in honey bee pollination behaviour (visitation rate) between the diploid and tetraploid red clover. Surprisingly, the seed set in two bees was significantly lower than that of one bee in ‘Rajah'. We suggest that honey bees prefer to visit already tripped florets or to visit fewer florets due to scent marks left by the previous honey bees. In open pollination, seed number per flower head in ‘Amos' (on average 11) was half of ‘Rajah' (on average 20). Seed set in ‘Amos' was lower than 50% of ‘Rajah' in honey bee (one bee treatment) and hand pollination (one and two pollen donors treatments). There were no differences in stigma receptivity whereas pollen viability in ‘Amos' was lower than ‘Rajah' after the peak pollen viability was reached (six days after the onset of flowering). We suggest that the fertility problems such as low pollen viability may be the reason for the low seed set in tetraploid red clover. This conclusion should be verified by investigating other fertility traits during the ovary, embryo and seed development with a broader range of diploid and tetraploid cultivars.

Pulsating Air Pollinator for Greenhouse Cultivation

Greenhouses has been accepted worldwide for round the year cultivation of quality produce. Greenhouse provides a desired climatic condition for crops but, at the same time, has obstacles for natural pollination. A pollinator was designed on the principle of pulsating air jet for pollination. The pollinator was developed with 3D printed three pulsation units with a provision for varied air pulsation frequency and angular movement to cover the complete flower bed. This can be easily moved by an operator in the greenhouse alleys. The developed pollinator was compared with hand pollination and pollination by a blower in tomato crops. The effects of Airflow rates, Pulsation frequencies of air and Exposure times on pollination efficiency and yield were studied. Experiments were performed in tomato plants cultivated in greenhouse. The highest pollination efficiency (83.66%) was achieved at 1.99 m 3 /min airflow rate, 23.50 Hz pulsation frequency and exposure time of 19.40 seconds; Average yield of 19.52 kg was observed at 1.99 m 3 /min of airflow rate, 22.25 Hz of pulsation frequency and exposure time of 15.78 seconds in flowers of 5 m length sections. The yield was also higher with developed pollinator compared to pollination by a blower (36.6%) and controlled plot (95.7%).

No Tradeoff in Fiber Quality with Increased Cotton Yield Due to Outcross Pollination

The societal and economic benefits of ecosystem services are both immense and multi-faceted. To holistically quantify the contribution of pollinators to agriculture requires measuring multiple indices of crop production beyond crop yield. Here, we conduct a field-based hand pollination experiment to measure the effects of self and outcross pollen on fiber yield and quality in conventionally managed cotton crops. First, we determine how different pollination treatments affect specific indices of fiber yield and fiber quality, including fiber length and fineness. Second, we investigate the suggested tradeoff between fiber yield and quality. We find that flowers receiving outcross pollen produce larger, heavier bolls than either self-crossed or non-crossed flowers. However, contrary to expectation, flowers of different treatments are indistinguishable in terms of fiber quality. Overall, we find that pollination treatment has no discernable effect on either fiber length or fiber fineness. Understanding the contribution of ecosystem services across multiple axes provides growers with information concerning potential tradeoffs or synergies, and offers insight into management decisions.

Pollination of &lt;i&gt;Nypa fruticans&lt;/i&gt; (Wurmb.) in a South Florida botanic garden

When plants are removed from their native habitat, reproduction can be compromised if pollinators are absent, especially when plant-pollinator interactions are species-specific and the plant is self-incompatible. To avoid these pitfalls, botanic gardens often use hand pollination to ensure reproductive success of their living collections, an important aspect of ex-situ conservation. The nipa palm, Nypa fruticans, presents an interesting case study of pollination in a botanic garden and a plant’s ability to successfully reproduce outside its native range without assisted pollination. Nypa fruticans has been growing at Montgomery Botanical Center (MBC) in South Florida since 1984, but for years required hand pollination to produce viable fruit. A recent shift from hand pollination to unassisted pollination suggests that this palm has found an alternative to fertilize its flowers. We investigate possible pollinators and new opportunities for pollination outside the palm’s native range. Rather than the insects typically associated with N. fruticans pollination in its native range in Southeast Asia (i.e., flies and beetles), ants, specifically Paratrechina longicornis, were overwhelmingly the most abundant visitors to nipa palm inflorescences at MBC and likely represent an important pollinator or facilitator of pollination at the garden. Pollination research at botanic gardens complements in-situ field studies and provides important insights into the flexibility of pollination systems to achieve reproductive success outside a plant’s native range.

Effects of pollination techniques and harvesting stage on the physico-chemical characteristics of jackfruit

Pollination techniques could affect fruit size, whereas optimal maturity stage during harvest could affect postharvest life and the eating quality of fruit. Therefore, the right pollination technique and timing to harvest fruit is an important factor in reducing postharvest losses. The objective of this study was to determine the physico-chemical changes of jackfruit harvested at four different maturity stages and produced from natural and assisted pollination. This study was conducted at a jackfruit commercial farm in Bukit Beruntung, Selangor, Malaysisa. For assisted pollination, the selected female inflorescences were covered with bags before anthesis. Hand pollination was performed by gently rubbing mature male inflorescences over the surface of receptive female inflorescences. For natural pollination, female inflorescences were left to develop into syncarps by themselves. Syncarps at the age of 12, 13, 14 and 15 weeks after anthesis (WAA) were used in this study. For each maturity stage, four syncarps were harvested and allowed to ripen naturally at 27±2 °C and 70−80% relative humidity until a sweet aroma was detected. Physico-chemical characteristics such as colour, firmness, pH, titratable acidity, β-carotene, lycopene content, sugars, organic acid content and antioxidant activity were evaluated. In this study, the pollination technique did not affect the eating quality of jackfruit flesh. However, the physico-chemical quality of jackfruit flesh was affected by ripening level and WAA. The initial stages of syncarp maturity, the L*, C* and ho values, remained unaffected. However, the L*, C* and ho decreased significantly from 14 WAA onwards when the syncarp rind turned fully yellow. This indicated that the rind and bulb colour became lighter and less intense with a green colour changing to yellow during ripening. Rind and flesh firmness decreased as ripening progressed due to cell wall modification and starch hydrolysis when ripening occurred. The β-carotene content of fleshy syncarps harvested at 14 and 15 WAA was higher than those harvested at 12 and 13 WAA. Sugar content such as glucose, fructose and sucrose increased as syncarps ripened. Total phenolic, flavonoid and antioxidant content were higher after syncarps ripened compared to before ripening. The ripe edible parts of jackfruit contain high levels of antioxidant and thereby signify the nutritional value of jackfruit for human health. In conclusion, harvesting stages affect the nutritional quality of jackfruit cv. Tekam Yellow, and it is recommended that the optimal harvesting stage of jackfruit is 14 WAA for local markets and 12 WAA for long-distance markets.

Seed Set Patterns in East African Highland Cooking Bananas Show Asymmetric Distribution in Bunches and Fruits

Low female fertility in bananas is the biggest hurdle for banana breeding. The aim of this study was to determine seed set patterns in East African Highland Cooking bananas (EAHBs) to inform future decisions on a more targeted approach of increasing seed set and subsequently banana-breeding efficiency. Matooke (AAA) and Mchare (AA) bananas are genetically distinct but belong to the same genetic complex, referred to as EAHBs. Seed set patterns in “Enzirabahima” (AAA), “Mshale” (AA), and “Nshonowa” (AA), all with residual fertility, were examined after hand pollination with a highly male fertile wild banana “Calcutta 4” (AA). Seed set in “Enzirabahima” is predominant in distal hands. Mchare cultivars have a slightly more even distribution of seeds in their hands compared to “Enzirabahima”. There is a gradual increase in seed set from proximal to distal hands with a slight drop in the last hand. This pattern is more definite in “Enzirabahima” and “Mshale”, while “Nshonowa” has a somewhat inconsistent pattern. There is also a drop in seed set per 100 fruits per hand from small to larger bunches. However, larger bunches have a higher pollination success compared to smaller bunches. They therefore set more seed on 100 fruits per hand and per bunch basis, if bunches without seed are accounted for. Pollination success rate increases from smaller to larger bunches of EAHBs. Seed set is biased toward the distal third part of fruits of examined EAHBs, as well as tetraploid Matooke hybrid “401K-1” (AAAA), and improved diploid “Zebrina” GF (AA) that were used for comparison. In comparison, in the highly female fertile “Calcutta 4”, seed set is along the entire length of the fruit. Seed set bias in the distal hands and distal end of fruits suggests a systematic mechanism rather than a random occurrence. It is expected that this information will provide a foundation for increased crossbreeding efficiency in bananas.

Unlikely transmission of Cowpea aphid-borne mosaic virus by hand pollination of passionflower

Passion fruit plants are self-incompatible and fruiting is exclusively dependent on cross-pollination, which in nature is performed by carpenter (mamangava) bees, especially Xylocopa spp. (family Apidae). To ensure satisfactory productivity, daily manual pollination is a common practice among passionflower growers. Therefore, we studied whether manual pollination mechanically transmits the cowpea aphid-borne mosaic virus (CABMV), the causal agent of the passion fruit woodiness disease. None of the eight healthy passion fruit plants manually pollinated with pollen from CABMV field-infected plants were infected, as confirmed by PTA-ELISA and RT-PCR. Healthy passion fruit plants mechanically inoculated with extracts of pollen collected from flowers of CABMV field-infected plants were not infected. CABMV was only detected by RT-PCR in groups of three anthers, and in pollen from groups of 20 anthers collected from flowers of infected passion fruit plants. RT-qPCR conducted with different amounts of pollen grains and anthers indicated extremely low virus titers. In addition to low virus titers, transmission failure may be associated with an absence of virus particles outside the pollen grains and/or absence of enough wounding produced on the stigmas by the fingertips. The improbability of CABMV transmission via pollen during manual pollination showed that this widely used cultural practice is a negligible factor in the epidemiology of passion fruit woodiness disease.

Landscape complexity benefits bumble bee visitation in faba bean (Vicia faba minor L.) but crop productivity is not pollinator-dependent

Faba bean (Vicia faba minor L.) is partially dependent on insects for pollination, but the degree of pollinator-dependency and whether crop productivity is limited by insufficient insect pollination remain unknown. We monitored insect pollinators and their foraging behaviors (i. e., legitimate flower visitation, nectar robbing and extra-floral nectary visitation) in a total of 20 faba bean fields of a single cultivar (Tiffany) 2018–2019. Focal fields were situated along a gradient of landscape complexity. In each field, a pollination experiment was established, where plants were either bagged to exclude pollination by insects or remained open for pollinator visits. In addition, all flowers on half of the bagged and open-pollinated plants were pollinated by hand to measure the degree of pollen limitation. We found that bumble bee abundance was higher, and legitimate flower visitor abundance tended to be higher, in complex landscapes with more semi-natural habitat, indicating that the faba bean pollination potential is higher in complex landscapes. The pollination experiment showed that the number of beans per pod was lower in bagged plants compared with other treatments in one of the years, but the lower number of beans per pod was compensated for by a higher individual bean weight, such that there was no pollinator-dependency or effect of hand pollination on total bean mass per plant. We conclude that to be able to characterize the value of insect pollination services in faba bean we need an improved understanding of how pollinator-dependency varies across modern cultivars, and how environmental conditions can increase or, as in our case, cancel this pollinator-dependency.

The utility of ISSRs for the identification of interspecific hybrids between pearl millet (Pennisetum glaucum [L.] R.Br.) × napier grass (Pennisetum purpureum Schumach)

AbstractInterspecific hybrids between pearl millet (Pennisetum glaucum) and napier grass (Pennisetum purpureum) give rise to perennial fodder crops characterized by high biomass, broad clumps and good palatability. These hybrids are triploid and developed by hand pollination of napier grass pollen on pearl millet panicles. The progeny shows a high percentage of pearl millet genotype due to self-pollination in the female parent. Identification of hybrids at a young stage based on morphological characters is difficult. DNA-based molecular markers have high discriminating power and were used to assess genetic differences between hybrids and their parents. Genetic diversity was studied in 18 pearl millet × napier grass hybrids along with their parents and two released national checks using inter simple sequence repeat (ISSR) markers. Eight ISSR primers gave rise to 125 bands, of which 120 bands were polymorphic. Polymorphic information content and ISSR primer index ranged from 0.40 to 0.49 and 8.88 to 11.14, respectively. The hybrids showed the presence of unique bands, besides those shared with male and female parents. Female (pearl millet) parents formed a separate group in the dendrogram constructed based on ISSR polymorphism. The male (napier grass) parents formed a separate group along with hybrids, indicating a higher similarity of hybrids with the male parents. Principal component analysis and STRUCTURE analyses showed a similar grouping. The close resemblance of hybrids to the male parents confirmed their interspecific origin. The study revealed that ISSR marker analysis could be a quick and reliable method to identify interspecific hybrids at an early stage of growth.

Recipient and donor characteristics govern the hierarchical structure of heterospecific pollen competition networks

Abstract Pollinator sharing can have negative consequences for plant fitness via competition for visits as well as with the arrival of heterospecific pollen. Plant traits and relatedness of donor and recipient species have been suggested to drive the observed variation in plant fitness effects of both processes, but how they shape the structure of interspecific pollen competition networks has been overlooked at the community level. To understand the importance of reproductive traits and relatedness to the impact of heterospecific pollen, we conducted a controlled glasshouse experiment with an artificial co‐flowering community. We performed 2,200 hand pollination crosses by experimentally transferring conspecific pollen alone or with 50% and 100% foreign pollen among 10 species belonging to three different plant families. Relative to conspecific pollen alone, there was a significant reduction in seed set with 50% heterospecific pollen for 67% of the crosses. This effect is driven largely by recipient traits and the interaction between recipient and donor traits under specific circumstances of trait matching. In general, species with shorter styles, smaller stigmas and lower pollen:ovule ratios were more impacted by heterospecific pollen. These traits and their differences among species led to a hierarchical (or transitive) structure of pollen competition with clear winners and losers. However, phylogenetic distance among recipient and donor species did not explain the effects. Synthesis. Our study shows that specific traits and trait combinations between donor and recipient species are important in determining seed production outcomes with heterospecific pollen receipt. Moreover, the differences in traits between species lead to a competitive structure with clear ‘winners’ or ‘losers’ species. The results of this study highlight the importance of specific traits in understanding the position of the competitive hierarchy of the species and the mechanisms underlying heterospecific pollen impacts upon plant reproductive success.

Reproductive character displacement and potential underlying drivers in a species-rich and florally diverse lineage of tropical angiosperms (Ruellia; Acanthaceae).

Reproductive character displacement is a pattern whereby sympatric lineages diverge more in reproductive character morphology than allopatric lineages. This pattern has been observed in many plant species, but comparably few have sought to disentangle underlying mechanisms. Here, in a diverse lineage of Neotropical plants (Ruellia; Acanthaceae), we present evidence of reproductive character displacement in a macroevolutionary framework (i.e., among species) and document mechanistic underpinnings. In a series of interspecific hand pollinations in a controlled glasshouse environment, we found that crosses between species that differed more in overall flower size, particularly in style length, were significantly less likely to produce viable seeds. Further, species pairs that failed to set seed were more likely to have sympatric distributions in nature. Competition for pollinators and reinforcement to avoid costly interspecific mating could both result in these patterns and are not mutually exclusive processes. Our results add to growing evidence that reproductive character displacement contributes to exceptional floral diversity of angiosperms.