Interspecific hybridization among the three most economically important cultivated species of Cucurbita spp., Cucurbita pepo, C. moschata, and C. maxima can be made but not readily. By means of various pollination measures, different mating systems, and varying selection methods, nine advanced interspecific-bridge lines were developed, in which the crossing barrier among the species and the male sterility of the F1 and subsequent generations were overcome over a 12-year period from 1999 through 2011. Despite the considerable influence of parental cultigens and environmental factors on the incompatibility of interspecific crosses, the plant and population compatibility significantly increased when a backcross with a recurrent parent in the same species or a multiple-way cross with a parent in the different species was made. As the generations advanced, the percentage of fertile seeds (PFS) significantly increased in all the sib- and self-families. The four advanced interspecific-bridge lines out of nine not only have gained the normal crossability of interspecific hybridization, but also could eliminate the sexual obstacles of the subsequent generations. The results demonstrate that a two- or three-species bridge line with crossing compatibility can be created by two- or three-species recombination and continuous selection. More importantly, the breakthrough of the advanced interspecific-bridge lines could provide a powerful platform for breeders to transfer favorable traits freely among the species and create more valuable and unique types or varieties through a conventional breeding process.
Biosolids are valued as a source of plant nutrients, soil organic matter, and biologically active substances. This greenhouse study was designed to examine if application of biosolids can improve plant drought tolerance by affecting nitrogen (N) and hormone metabolism as well as root growth in kentucky bluegrass (Poa pratensis L.; KBG). The three treatments, which provided N rates equivalent to 75 mg plant-available N/kg soil, included: 1) biosolids at 1× agronomic (Ag) N rate (75 mg N/kg soil completely provided with biosolids); 2) biosolids at 0.5× Ag N rate (37.5 mg N/kg soil provided with biosolids and 37.5 mg N/kg soil provided with NH4NO3); and 3) control (75 mg N/kg soil completely provided with NH4NO3). The treated KBG was grown under either well-watered (90% container capacity) or drought stress (≈25% container capacity) conditions. Biosolids application improved turf quality and delayed leaf wilting under drought stress. The grass treated with biosolids at 1× N rate had higher leaf proline and amino acid content and greater nitrate reductase activity than the control under drought stress. Biosolids treatments also increased leaf and soil indole-3-acetic acid (IAA) content. Moreover, biosolids at 1× N rate increased root length density by 23% compared with the control under drought stress. The results of this study suggest that biosolids may enhance plant drought tolerance by improving N and hormone metabolism and root growth in KBG.
Plant growth and development are determined by complex exogenous and endogenous cues. A plant follows several temporally distinct developmental stages, including embryonic, vegetative, and reproductive. The vegetative stage, which is usually the longest stage, can be subdivided into juvenile and adult phases. The transition from the juvenile to the adult phase, also called the vegetative phase change, is characterized by anatomical, morphological, and physiological changes in the vegetative parts of the shoot. Recent studies in several systems have identified the genetic temporal mechanisms of this process, which is regulated by an endogenous age cue (i.e., microRNA156/157) and its targeted genes (i.e., Squamosa promoter binding protein-box transcription factors). This review summarizes the recent advances in the study of the underlying regulatory mechanisms of vegetative phase change. This review also describes the modes of miRNA action and the functions of their targeted genes in this highly conserved developmental process.
‘Fuyu’ perisimmon fruit were treated with 500 nL·L−1 1-methylcyclopropene (1-MCP) for 24 h at 20 °C and then stored at 4 °C for 45 days to investigate the effects of 1-MCP on chilling injury (CI) during storage at 4 °C. Persimmon fruit developed CI, manifested as rapid softening and external and internal browning. Injury symptoms were reduced by 1-MCP treatment. 1-MCP also delayed increases in respiration and ethylene production. Compared with control fruit, 1-MCP-treated fruit exhibited increased superoxide dismutase and catalase activities within the initial storage period and lower membrane permeability, malondialdehyde content, and peroxidase and polyphenol oxidase activities throughout the entire storage period. These results suggest that reduction of CI symptoms in persimmon fruit in response to 1-MCP treatment may be attributed to altered oxidative status.
Hybridization between species of the genus Juglans is common because of weak reproductive isolation mechanisms between closely related species with sympatric distributions. In this research, we investigated the possibility of naturally occurring interspecific hybrids between two species in the genus Juglans: persian walnut (Juglans regia) and chinese walnut (Juglans cathayensis). We used 12 pairs of microsatellite markers to analyze introgression between the two species. All amplified microsatellites were polymorphic in the two species. The result of Bayesian admixture analyses showed that introgression between the two species is rare; only three of nine individuals tentatively identified as hybrids, based on intermediate morphological characteristics, were defined as mixed genotypes. The other six putative hybrids and 156 morphologically pure individuals showed no sign of introgression.
Rosa laxa is widely distributed in the Xinjiang Uygur Autonomous Region of China and is highly adaptable and rich in variation. In this study, we investigated the morphology, habitats, and palynomorphology of R. laxa botanical varieties from Xinjiang, China. In addition to R. laxa var. laxa, there were three other botanical varieties of R. laxa growing in southern Xinjiang, including var. mollis, var. kaschgarica, and var. tomurensis. Together, these four botanical varieties exhibited morphological variation, mainly in the morphology of prickles and the glandular trichome and in flower color. The pollen grains of the R. laxa botanical varieties, all medium in size (21.77–48.39 μm), came in three shapes: perprolate, prolate, and subspheroidal. Their pollen exine sculptures were characterized by either a striate-perforation pattern or striate pattern, but perforation varied in terms of diameter and density and striae varied in depth and density. Palynomorphological assessment showed that three types of evolution, i.e., primitive, transitive, and evolved, were present among R. laxa botanical varieties, and pollen dimorphism was observed in the same botanical variety. Perprolate pollen with a dense striate pattern was the most evolved type. Based on morphological and palynomorphological investigations, var. tomurensis was considered to be the most evolved one among the studied botanical varieties.
The karyotypes of 21 herbaceous peony (Paeonia) cultivars were studied using root tip squashes revealing a wide variety of ploidy levels. There were three tetraploid (2n = 4x = 20), 11 triploid (2n = 3x = 15), and one diploid (2n = 2x = 10) cultivars in the hybrid group; five triploid (2n = 3x = 15) cultivars in the Itoh group; and one diploid (2n = 2x = 10) cultivar in the lactiflora group (LG). The asymmetry index (AI) ranged from 59.61% (‘Cytherea’) to 64.03% (‘Little Red Gem’). The karyotypes of all peony cultivars were 2A with 60% metacentric (m), 20% submetacentric (sm), and 20% subtelocentric (st) chromosomes. The karyotypic background of these 21 herbaceous peony cultivars is discussed in the context of the evolution of ploidy and the three cultivar groups. These results provide cytological information that would assist in a peony hybridization program.
Hydrangea macrophylla is the most popular species in the genus Hydrangea because of its large and brightly colored inflorescences. Since the early 1900s, numerous cultivars with showy flowers have been selected. Although many H. macrophylla cultivars have been developed, cold hardiness is still the major limitation to their outdoor use. Hydrangea arborescens is a small attractive shrub or subshrub native to northeastern parts of the United States, which is valued for its hardiness. Interspecific breeding of H. arborescens and H. macrophylla has been tried, but putative hybrid seedlings either died at an early stage or were not verified. We made successful hybridizations between H. macrophylla ‘Blue Diamond’ and H. arborescens ‘Annabelle’ and used in vitro ovary culture to produce viable plants. Hybrids were intermediate in appearance between parents, but variable in leaves, inflorescences, and flower color. The success of this hybridization was confirmed by six simple sequence repeat (SSR) genetic markers. The maternal chromosome number was 36, and the paternal number was 38. Chromosome counts of hybrids indicated that nearly half of them were aneuploids. Male fertility of progeny was evaluated by fluorescein diacetate staining of pollen. Twelve out of 14 hybrids (85.7%) had male fertility. We documented the first flowering progeny of H. macrophylla and H. arborescens, suggesting an effective beginning to a cold hardiness breeding program.
Big fruit size and nice red pigmentation combined with good flavor should be the major target for red-fleshed kiwifruit (Actinidia spp.) breeding programs. Genetic diversity and plant characteristics were evaluated on a set of kiwifruit accessions with predominantly red flesh to identify the superior individuals for further breeding or study of commercial application. The leading phenotypic characters varied widely among the accessions. Accession R reached average fruit weight ≈100 g, whereas it ranged from 43.15 to 84.71 g for the other accessions. Fruits of L and Q were flatter in shape than the others. The core volume accounted for fruit proportions ranging from 2.33% to 11.42%. ‘Chuhong’, ‘Honghua’, and K exhibited a round fruit apex, whereas most others showed a depressed apex. R, L, and Q had the highest a* values in the inner pericarp and also the most appealing visual coloration. Results revealed significantly higher soluble solid content (SSC), total sugar, and sugar/acid ratio in Q, R, and L. The 12 pairs of simple sequence repeat (SSR) markers were successfully used to characterize the genetic variability and confirm true-to-type identity for four accessions. However, the limited number of markers had no ability to discriminate among the other 11 accessions. Based on additional 28 SSRs, six of the indistinguishable accessions were confirmed to be genetically different, and three seemed to belong to the same clone vine. The results demonstrated that application of SSR data could improve the efficiency of identifying red-fleshed kiwifruit germplasm.