Palmer amaranth (Amaranthus palmeri S. Watson), a dioecious wind-pollinated plant, is one of the most troublesome crop weeds in the United States and is spreading northward. The prodigious production of seed contributes to establishment of populations and spread across the landscape. Sexual reproduction via outcrossing is likely the primary mode of seed production for this dioecious plant. However, A. palmeri may also be capable of autonomous asexual seed production (apomixis), which could be beneficial during colonization. We conducted two studies of female isolation from pollen to investigate the propensity for autonomous seed production in 19 populations across eastern North America. In the first, we observed low-frequency seed production on many isolated females. Using flow cytometry of seed samples (FCSS) we primarily found patterns of ploidy consistent with sexual reproduction; no significant differences in ploidy between seeds produced on isolated females (putative apomicts) and non-isolated females (putatively sexual) were detected. We also investigated patterns of DNA content and found no evidence in 153 samples for polyploidy, which is often observed in apomictic species. The second female isolation trial utilized sex-specific molecular markers to identify and remove males before flowering, and we observed zero seed production. Overall, we did not detect evidence in support of apomixis in these populations of A. palmeri, suggesting that apomixis is unlikely to have played a role in the northward advance of this species in eastern North America. We also investigated whether there is variation between females and males in size and secondary reproductive traits. We found evidence for sexual dimorphism in three of six traits investigated: females are taller at senescence and produce longer secondary branches and more axillary flowers than males. Differences in cost of reproduction and strategies for pollen release versus pollen capture are likely factors shaping the evolution of sexual dimorphism in this wind-pollinated dioecious plant.

The endosperm is the storage tissue of seeds and is an important source of nutrients for humans and animals. In the previous work, the gene expression was characterized at 3 and 24 h after pollination (AP). The results suggested that eATP would act as a signalling molecule at the beginning of endosperm development and that sucrose metabolism could be related to EBN insensitivity. In addition, differentially expressed transcripts derived fragments (DETDFs) were related to the failure of fusion of the polar nuclei and the accumulation of storage products in seeds of Arabidopsis thaliana. The objective of the present study was to identify genes related to endosperm development in apomictic and sexual ovaries of Paspalum notatum 48 h AP, a stage at which development is prior to post-zygotic collapse. The cDNA-AFLP analysis was carried out to analyse different crosses and DETDFs categorized according to their function. The main cellular functions at 48 h AP were metabolism and signal transduction. Fourteen out of 39 DETDFs with relevant functional information were found in crosses for which normal endosperm development was expected. Three DETDFs were found in crosses where viable and unviable seeds were predicted and presented similarity with a casein kinase II (CK2), an enzyme that governs the accumulation of storage proteins in seeds of A. thaliana and Zea mays. The results obtained at 3, 24 and 48 h AP suggest that CK2 is involved in early endosperm development in P. notatum.

Endosperm tissue that nourishes the embryo during seed development, upon maturity, nourishes the global population with special reference to cereal crops like maize, wheat and rice. In about 70% of the angiosperms, endosperm genome content is ‘3n’ with 2:1 (maternal:paternal) contribution, as a result of the second fertilization event. However, angiosperms evolution also documents diversity in endosperm genome content from ‘2n’ to ‘15n’, in scale with the corresponding maternal genome dosage variability (‘1n’ to ‘14n’), whereas paternal contribution is invariable. In apomicts, due to lack of fertilization, or pseudogamy (fertilization of the central cell for endosperm formation), endosperm genome dosage (m:p) has been reported to range between 1:1 and 8:3. Exceptionally, the central cell with one unreduced nucleus and fused with a reduced sperm cell, with 2:1 normal genome dosage, has been reported in Panicum. Altered genome dosage levels are reportedly correlative with eccentricities among maternal and paternal contribution to seed resource allocation. Besides endosperm ploidy variability between species of angiosperms, the present review gives an overview of the ploidy variability in endosperm cells within a seed, up to ‘690n’. In addition to genome-scale variability in the endosperm, some taxa of angiosperms exhibit chlorophyllous endosperms and some chlorophyllous embryos. Also, endosperm cell number during seed development is reported to have a strong association with grain weight at maturity. Genes underlying these traits of variability are unknown, and the present review underscores the variability and highlights the potential of the single-cell sequencing techniques towards understanding the genetic mechanisms associated with these variable traits.

A new biotype of common cocklebur, called multiple-seeded cocklebur (MSC), was found in Bell County, TX, in 1994. MSC has up to 25 seeds per bur, usually producing up to nine seedlings, whereas normal common cocklebur (NCC) has two seeds per bur which usually produce only one seedling. MSC burs are large, round, covered with hairy spines or prickles, and flattened on one end, with each seed terminated by a beak. Leaf morphology differs among the biotypes, and stems of MSC are straighter and smoother than NCC. Apomixis occurred with MSC but not with NCC. Both biotypes have potential dormancy with germination occurring in the second growing season. MSC produces increased numbers of seedlings which increases the difficulty in controlling common cocklebur.

Croftonweed has established itself as a pernicious weed in China. Experiments were conducted to test for anemophily, self-pollination, hand crossing, and apomixis. Additionally, pollen viability, seed set, and seed viability were investigated. Pollen cultured in vitro with the use of 14 culture media did not germinate, nor did self- or cross-pollen germinate on the stigma, and no pollen tubes were seen in the style. Young embryos developed into globular- or heart-shaped embryos before the opening of the captimulum, although neither meiosis to form an embryo sac nor fertilization occurred. Furthermore, seeds developed normally after closed flowers were emasculated and bagged. The plump seed ratio (plump seeds/total seeds) from apomixis (emasculation and bagged treatment) was high (41 ± 17.0%), and plump seed germination ratio exceeded 50%. These results provided additional evidence for the previous conclusion that croftonweed reproduces by apomixis. Apomixis, high seed production, and high seed germination may explain why this weed spreads so rapidly.

Dandelion is a cosmopolitan weed of economic and environmental significance because of its negative effects on crop yield and the large amount of herbicides used for its control in agricultural, residential, and recreational areas in North America. Asexual dandelion plants, which are apomictic and produce genetically identical seeds, provide a great experimental model for biological studies, such as examination of its reproductive responses to global environmental changes. In a growth chamber experiment, we investigated how elevated CO2 affected reproduction and seed dispersal properties in dandelion. Dandelion plants were grown at ambient (370 µmol mol−1) or elevated (730 µmol mol−1) CO2 until reproductive maturity. Results showed that dandelion plants examined in our study produced 83% more inflorescences and 32% more achenes, i.e., single-seed fruits, per plant at elevated than at ambient CO2. Seeds from elevated CO2-grown plants were significantly heavier and had a higher germination percentage, leading to larger seedlings and earlier establishment in the subsequent generation. Furthermore, achenes from plants grown at elevated CO2 had characteristics, such as higher stalks at seed maturity, longer beaks, and larger pappi, which would increase the distance of seed dispersal by wind. In addition to these elevated CO2-induced changes in reproductive properties, dandelion has a number of inherent characteristics, e.g., high competitiveness and adaptations to disturbance, that would increase its vegetative and reproductive success in a higher CO2 environment. Consequently, dandelion can potentially become more widespread and noxious as atmospheric CO2 continues to rise because of human activities.

Although apomixis is the most common form of parthenogenesis in diplodiploid arthropods, it is uncommon in the haplodiploid insect order Hymenoptera. We found a new type of spontaneous apomixis in the Hymenoptera, completely lacking meiosis and the expulsion of polar bodies in egg maturation division, on the thelytokous strain of a parasitoid wasp Meteorus pulchricornis (Wesmael) (Braconidae, Euphorinae) on pest lepidopteran larvae Spodoptera litura (Fabricius) (Noctuidae). The absence of the meiotic process was consistent with a non-segregation pattern in the offspring of heterozygous females, and no positive evidence was obtained for the induction of thelytoky by any bacterial symbionts. We discuss the conditions that enable the occurrence of such rare cases of apomictic thelytoky in the Hymenoptera, suggesting the significance of fixed heterosis caused by hybridization or polyploidization, symbiosis with bacterial agents, and occasional sex. Our finding will encourage further genetic studies on parasitoid wasps to use asexual lines more wisely for biological control.

Introduction. Shanxi province is one of the main walnut production areas in the North of China. The cultivated species mainly belong to a Chinese walnut tree population, named ‘Mian Hetao’ (Juglans regia L.), which reproduces from seedlings. Although the walnut apomixis characteristics were discovered very early and have an important breeding value, this variety has not yet been reported as an important breeding resource. Cultivar origin. ‘Qinquan 1’ is a new cultivar of walnut tree (Juglans regia L.), selected in 1982 from walnut seedling resources in the department of Shanxi, in the North of China. This cultivar is characterized by apomixis, the ratio of which can reach 24.7%. After more than 20 years of selection and many local experiments, its characteristics were given and the cultivar was certificated in March 2007. Cultivar characteristics. Characteristics of ‘Qinquan 1’ fruits, trees, development stages, production and the apomixis rate are given. Main cultural techniques. Many characteristics of this new cultivar are suitable for its growth in the middle or south Loess Highlands (China), where the annual average temperature is 9~13 °C and rainfall is above 450 mm. The cultivar is also cultivable in the North of China where the soil and climate conditions resemble those of the original area. Other recommendations are given for improving the ‘Qinquan 1’ tree growth.

The Dilatata group of Paspalum is a polyploid complex native to the grasslands of temperate South America. A pentaploid apomictic biotype of P. dilatatum is a widely recognized forage grass; however, the complex includes apomictic tetra- and hexaploids along with sexual allotetraploids (P. urvillei, P. dasypleurum, P. dilatatum ssp. flavescens, and biotypes Virasoro and Vacaria of P. dilatatum) which are suspected to be hybrids between different combinations of biotypes. Fifteen primer pairs for nuclear microsatellite loci were developed from a (CA)n-enriched genomic library. A single, low stutter, robust two-step PCR profile was used for all the primer pairs. Twelve primer pairs were analysed for their variability and transferability among all the sexual biotypes of the Dilatata group and the common apomictic pentaploid. Six primer pairs amplified more than one locus, and sequence and segregation evidence suggest that the additional bands correspond to homeologous loci. No close linkage was found among the 16 loci amplified in the tetraploids. One variable chloroplast microsatellite is also reported. All loci were successfully amplified from most members of the Dilatata group and variability was recorded for all the biotypes analysed. The set of loci reported here provide highly variable markers for intra-biotypic population studies, biotype-specific markers for the analysis of hybrid apomicts and a biotype-specific chloroplast marker.

The literature from 1794 to the present on the infrageneric classification of Hieracium L. sensu stricto is analysed. The 38 informal groups recognized in Flora Europaea by Sell & West (1976) are considered as sections, and the correct name for each at that rank is listed, with basionym and synonymy. The 38 names include three new combinations and four new sections.