Hazelnut floral phenology in southern Ontario

Hazelnut (Corylus avellana) is a monoecious, dichogamous plant species that flowers in winter and early spring. In traditional hazelnut growing regions, hazelnut cultivars generally express protandry where the male flowers bloom before the female flowers. Nut set requires that compatible pollen be shed when the stigmas of the main cultivar are receptive. In this study, the floral phenology and date of leaf budbreak of five selections and 19 hazelnut cultivars from Europe and North America were observed over four years in southern Ontario, and results were compared with cumulative growing degree days. In the continental climate of southern Ontario, most cultivars showed protogyny. Flowering dates varied over the years with pollination occurring in a period of 2 - 3 weeks in early spring. These cultivars were classified into early, mid, and late blooming types. A growing degree day model was a better tool than average daily temperatures to predict the flowering dates of catkins and female flowers. Averaged over years, most of the cultivars in this study have a female bloom that is likely too early for the pollen shed by most of the other cultivars. This would likely impact yields in a commercial orchard. However, ‘Jefferson’, ‘Gene’, and ‘Epsilon’ have late females that are receptive when other cultivars are shedding pollen.

Evaluation of the possibility of obtaining viable seeds from the cross-breeding Hippeastrum × chmielii Chm. with selected cultivars of Hippeastrum hybridum Hort.

Hippeastrum sp. is a popular cut flower and a popular potted plant, currently occupying the 11th position among cut flowers sold on the Dutch flower auctions. Hippeastrum × chmielii was bred by Henryk Chmiel at the Warsaw University of Life Sciences (WULS), Poland. The aim of this study was designed to test the ability of two clones of H. × chmielii to reproduce generatively by pollinating by three cultivars of Hippeastrum hybridum – ‘Gervase’, ‘Rio Negro’ and ‘Royal Velvet’. Pollen viability was tested by germination on the medium and by acetocarmine staining. The receptiveness of the stigmas and ovules of H. × chmielii and thus their ability to possibly accept compatible pollen were checked by staining with red alizarin. The viability of pollen grains of tested cultivars was estimated at 66.4–83.0% and their high ability to develop pollen tube was found. It was determined that the embryos of both H. × chmielii clones were fully receptive. A total of 72 crossings were performed in 6 combinations. Seeds collected about 1 month after pollination were germinated immediately after harvest either on moist tissue paper on Petri dishes or in jars with distilled water. After 28 days the percentage of germinated seeds ranged between 48.3% and 77.9%, for different crosses. In the case of seeds obtained from crossing H. × chmielii clone 18 × H. hybridum ‘Gervase’ a higher average percentage of germinated seeds was obtained in jars while no differences were noted between the germination methods in other cases.

Role of Bumblebees (Hymenoptera: Apidae) in Pollination of High Land Ecosystems: A Review

Bumblebees are one among the anthophilous form and play a significant role in the pollination of major agricultural crops like medicinal, aromatic, ornamental and various other horticultural plants. They are abundant and mostly confined to flowers present in the temperate, alpine and arctic climates of the northern continents. The bumblebees are considered as most important pollinators and are mainly responsible for the conservation of high altitude vegetation germplasm where other insect pollinators are very much limited. They are more successful pollinators and can visit large number of flowers per minute than other bees and are perfect for picking up and transferring appreciable amount of compatible pollen to flowers and thus perform buzz pollination. It is quite evident that the population of bumblebee is gradually declining throughout the globe for the last 7 decades due to agricultural intensification, habitat loss, deforestation, overgrazing, pesticide poisoning and climate change. The present paper addresses this issue on the basis of literature survey.

Programmed Cell Death in Stigmatic Papilla Cells Is Associated With Senescence-Induced Self-Incompatibility Breakdown in Chinese Cabbage and Radish

Self-incompatibility (SI) is a genetic mechanism flowering plants adopted to reject self-pollen and promote outcrossing. In the Brassicaceae family plants, the stigma tissue plays a key role in self-pollen recognition and rejection. We reported earlier in Chinese cabbage (Brassica rapa) that stigma tissue showed upregulated ethylene responses and programmed cell death (PCD) upon compatible pollination, but not in SI responses. Here, we show that SI is significantly compromised or completely lost in senescent flowers and young flowers of senescent plants. Senescence upregulates senescence-associated genes in B. rapa. Suppressing their expression in young stigmas by antisense oligodeoxyribonucleotide abolishes compatible pollination-triggered PCD and inhibits the growth of compatible pollen tubes. Furthermore, ethylene biosynthesis genes and response genes are upregulated in senescent stigmas, and increasing the level of ethylene or inhibiting its response increases or decreases the expression of senescence-associated genes, respectively. Our results show that senescence causes PCD in stigmatic papilla cells and is associated with the breakdown of SI in Chinese cabbage and in radish.

Two subgroups of receptor-like kinases promote early compatible pollen responses in the Arabidopsis thaliana pistil

In flowering plants, cell–cell communication between the compatible pollen grain/growing pollen tube and the pistil is an essential component for successful sexual reproduction. In Arabidopsis thaliana, the later stages of this dialogue are mediated by several peptide ligands and receptors that guide pollen tubes to the ovules for the release of sperm cells. Despite a detailed understanding of these processes, a key gap remains regarding the nature of the regulators that function at the earlier stages which are essential steps leading to fertilization. Here, we report on new functions for A. thaliana Receptor-Like Kinase (RLK) genes belonging to the LRR-II and LRR-VIII-2 RLK subgroups in the female reproductive tract to regulate compatible pollen hydration and the early stages of pollen tube growth. Mutant pistils for the A. thaliana RKF1 gene cluster were observed to support reduced wild-type pollen hydration and, when combined with the SERK1 and SERK3/BAK1 mutations, reduced pollen tube travel distances occurred. As these mutant pistils displayed a wild-type morphology, we propose that the observed altered compatible pollen responses result from an impaired pollen–pistil dialogue at these early stages.

Pollination Compatibility and Xenia in Camellia oleifera

Camellia oleifera, a major woody oil plant, has a low oil yield because of self-incompatibility. For commercial oil production, compatible pollen and optimal cross-pollination combinations are required. To evaluate the effects of pollination compatibility and pollen source on oil yield and quality, four C. oleifera cultivars—Huashuo (HS), Huajin (HJ), Huaxin (HX), and Xianglin XLC15 (XL)—were subjected to self-, cross-, and natural pollination. Pollen compatibility, oil yield, and quality indices were analyzed. There were no significant differences in pollen germination and tube growth between self- and cross-pollination. Following self-pollination, fertilization was unsuccessful, resulting in severe ovule dysplasia; cross-pollination decreased the ovule abortion rate. Pollen source significantly affected the fruit set, fruit traits, seed traits, and fatty acid content, implying xenia in C. oleifera. In cross-pollinated plants, HX pollen produced more seeds, and HJ pollen increased linoleic acid content relative to naturally pollinated plants. For the XL and HS combinations, linolenic acid contents were significantly higher than other pollination combinations. However, oleic acid content was not significantly affected by pollen source, in any of the cultivars. Cultivar HX was, therefore, the most effective pollen donor, and HS × HX was the optimal cross-pollination combination for improving oil yield and sustainability.

Two groups of Arabidopsis receptor kinases preferentially regulate the growth of intraspecies pollen tubes in the female reproductive tract

SummaryIn flowering plants, continuous cell-cell communication between the compatible male pollen grain/growing pollen tube and the female pistil is required for successful sexual reproduction. In Arabidopsis thaliana, the later stages of this dialogue are mediated by several peptide ligands and receptor kinases that guide pollen tubes to the ovules for the release of sperm cells. Despite a detailed understanding of these processes, a key gap remains on the nature of the regulators that function at the earlier stages. Here, we report on two groups of A. thaliana receptor kinases, the LRR-VIII-2 RK subclass and the SERKs, that function in the female reproductive tract to regulate the compatible pollen grains and early pollen tube growth, both essential steps for the downstream processes leading to fertilization. Multiple A. thaliana LRR-VIII-2 RK and SERK knockout mutant combinations were created, and several phenotypes were observed such as reduced wild-type pollen hydration and reduced pollen tube travel distances. As these mutant pistils displayed a wild-type morphology, the observed altered responses of the wild-type pollen are proposed to result from the loss of these receptor kinases leading to an impaired pollen-pistil dialogue at these early stages. Furthermore, using pollen from related Brassicaceae species, we also discovered that these receptor kinases are required in the female reproductive tract to establish a reproductive barrier to interspecies pollen. Thus, we propose that the LRR-VIII-2 RKs and the SERKs play a dual role in the preferential selection and promotion of intraspecies pollen over interspecies pollen.