Development of a multiplex polymerase chain reaction for the simultaneous detection of microsporidians, nucleopolyhedrovirus, and densovirus infecting silkworms

We have developed a novel PCR-based assay for individual and simultaneous detection of three major pathogens (microsporidians, nucleopolyhedrovirus (NPV) and densovirus (DNV)) infecting the silkworm, Bombyx mori. Multiplex PCR, using three primer pairs, two of which were designed from the conserved regions of 16S small subunit ribosomal RNA gene of microsporidians, and polyhedrin gene of NPVs respectively, and a third primer pair designed from the internal sequences of B. mori DNVs (BmDNV), showed discrete and pathogen specific PCR products. The assay showed high specificity and sensitivity for the pathogenic DNA. Under optimized PCR conditions, the assay yielded a 794 bp DNA fragment from Nosema bombycis, 471 bp fragment from B. mori NPV (BmNPV) and 391 bp fragment from BmDNV. Further, this detection method was successfully applied to other silkworm species such as Antheraea mylitta and Samia cynthia ricini, in detecting same or similar pathogens infecting them. This method is a valuable supplement to the conventional microscopic diagnostic methods and can be used for the early detection of pathogens infecting silkworms. Furthermore it can assist research and extension centers for the safe supply of disease-free silkworms to farmers.     

The regulation of immune responses to multiple non-H-2 antigens on tumor cells: I. Differential responses of BALB/c F1 hybrids to the P815 mastocytoma in vivo

Factors influencing host resistance to the growth of a tumor bearing many mismatched minor histocompatibility antigens (MiHA) were studied. BALB/c (H-2^d) and several of its F₁ hybrids were injected intraperitoneally with DBA/2 (H-2^d) P815 tumor cells. Compared to BALB/c, which was moderately susceptible, F₁ hybrids of BALB/c with CBA, AKR, C3H.OH, and BIO H-2-congenic strains were highly susceptible, whereas hybrids of BALB/ c with A, A.SW, and BALB.B strains were quite resistant. Susceptibility was observed only with the intraperitoneally injected tumor, since both BALB/c and (CBA x BALB/c)F₁ were resistant to the same tumor injected subcutaneously, and survival times of DBA/2 skin grafts did not differ between susceptible and resistant strains. Susceptibility was in part a function of the number of MiHA incompatibilities between tumor and host although the specific loci involved could not be identified. For example, susceptible (CBA x BALB/c)F₁ hybrids probably shared certain MiHA with DBA/2 which BALB/c lacked, and which therefore subtracted from the net antigenic strength of the tumor in the hybrid, compared to its strength in BALB/ c. This interpretation was supported by in vitro studies which confirmed that the susceptible hybrids shared more MiHA with DBA/2, than did the resistant hybrids. Resistance was at least partially regulated by the host H-2 genotype, as shown by the observation that (BALB/ c x BALB.B)F₁ (H-2^d/b) mice were significantly more resistant than BALB/c. Segregation studies of the resistant (BALB/c x A)F₁ hybrids, indicated that in addition to H-2, a nonH-2 gene in the A background was operating to confer resistance. Thus the factors influencing susceptibility to the MiHA-incompatible tumor were: (i) site of injection; (ii) the combined strength of the disparate MiHA; (iii) the host H-2 genotype; and (iv) at least one host nonH-2 gene conferring increased responsiveness.     

Inheritance of Cry1Ac resistance and associated biological traits in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

The analysis of reciprocal genetic crosses between resistant Helicoverpa armigera strain (BH-R) (227.9-fold) with susceptible Vadodara (VA-S) strain showed dominance (h) of 0.65-0.89 and degree of dominance (D) of 0.299-0.782 suggesting Cry1Ac resistance as a semi-dominant trait. The D and h values of F₁ hybrids of female resistant parent were higher than female susceptible parent, showing maternally enhanced dominance of Cry1Ac resistance. The progeny of F₂ crosses, backcrosses of F₁ hybrid with resistant BH-R parent did not differ significantly in respect of mortality response with resistant parent except for backcross with female BH-R and male of F₁ (BH-R × VA-S) cross, suggesting dominant inheritance of Cry1Ac resistance. Evaluation of some biological attributes showed that larval and pupal periods of progenies of reciprocal F₁ crosses, backcrosses and F₂ crosses were either at par with resistant parent or lower than susceptible parent on treated diet (0.01 μg/g). The susceptible strain performed better in terms of pupation and adult formation than the resistant strain on untreated diet. In many backcrosses and F₂ crosses, Cry1Ac resistance favored emergence of more females than males on untreated diet. The normal larval period and the body weight (normal larval growth) were the dominant traits associated with susceptible strain as contrast to longer larval period and the lower body weight (slow growth) associated with resistance trait. Further, inheritance of larval period in F₂ and backcross progeny suggested existence of a major resistant gene or a set of tightly linked loci associated with Cry1Ac sensitivity.     

Integrated transcript and metabolite profiling reveals coordination between biomass size and nitrogen metabolism in Arabidopsis F1 hybrids

Heterosis refers to the improved agronomic performance of F₁ hybrids relative to their parents. Although this phenomenon is widely employed to increase biomass, yield, and stress tolerance of plants, the underlying molecular mechanisms remain unclear. To dissect the metabolic fluctuations derived from genomic and/or environmental differences contributing to the improved biomass of F₁ hybrids relative to their parents, we optimized the growth condition for Arabidopsis thaliana F₁ hybrids and their parents. Modest but statistically significant increase in the biomass of F₁ hybrids was observed. Plant samples grown under the optimized condition were also utilized for integrated omics analysis to capture specific changes in the F₁ hybrids. Metabolite profiling of F₁ hybrids and parent plants was performed using gas chromatography-mass spectrometry. Among the detected 237 metabolites, 2-oxoglutarate (2-OG) and malate levels were lower and the level of aspartate was higher in the F₁ hybrids than in each parent. In addition, microarray analysis revealed that there were 44 up-regulated and 12 down-regulated genes with more than 1.5-fold changes in expression levels in the F₁ hybrid compared to each parent. Gene ontology (GO) analyses indicated that genes up-regulated in the F₁ hybrids were largely related to organic nitrogen (N) process. Quantitative PCR verified that glutamine synthetase 2 (AtGLN2) was upregulated in the F₁ hybrids, while other genes encoding enzymes in the GS-GOGAT cycle showed no significant differences between the hybrid and parent lines. These results suggested the existence of metabolic regulation that coordinates biomass and N metabolism involving AtGLN2 in F₁ hybrids.     

Maternal and Reciprocal Effects on Seedling Characters in ARABIDOPSIS THALIANA (L.) Heynh

Five early growth characters were examined in six races of Arabidopsis thaliana (L.) Heynh, their reciprocal F₁ hybrids (1974) and F₁ by tester hybrids, using a seventh race as a paternal tester. Three of the five characters were also examined at two nutrient levels in reciprocal F₁ hybrids (1972) of all seven races. Analyses of F₁ and F₁ by tester hybrids revealed significant maternal effects in all characters examined in F₁ hybrids (1972) and in root length and plant weight of F₁ (1974) and F₁ by tester hybrids. Significant reciprocal effects were found for plant weight in F₁ by tester hybrids and for seed weight, percentage of germination and root length in F₁ (1974) and F₁ by tester hybrids. The presence of significant maternal and/or reciprocal components in both F₁ (1974) and F₁ by tester diallels suggests that differences in maternal cytoplasm rather than maternal genotype per se were responsible for much of the variation resulting from these non-direct genetic effects.     

Asymmetric introgression between Magnolia stellata and M. salicifolia at a site where the two species grow sympatrically

In order to understand the ongoing evolutionary relationships between species, it is important to elucidate patterns of natural hybridization. In the zone where two species are sympatrically distributed, we examined 274 individuals of Magnolia stellata, Magnolia salicifolia, and their putative hybrids by means of 16 nuclear and three chloroplast microsatellite markers. Hybrid classes of individuals were estimated by admixture analyses. Morphological traits were also investigated for 64 of the 274 individuals. Admixture analyses revealed that 66 of the 274 individuals were classified as hybrids, comprising 17 F₁ and 19 F₂ individuals, 27 backcrosses to M. salicifolia, and 3 individuals of unknown origin. Morphological data from the 64 individuals agreed well with their genetic admixture rates. Spatial locations of F₁ and F₂ hybrids at the study site were intermediate between the two purebred species, indicating that the site preferences of hybrids are intermediate. The occurrences of F₂ and backcross hybrids indicate that F₁ hybrids are fertile. The chloroplast DNA haplotypes of all F₁ hybrids corresponded to those detected in M. salicifolia, so that maternal parents of the F₁ hybrids were all M. salicifolia. Furthermore, no hybrid individuals derived from a backcross to M. stellata were detected. These results suggest that the direction of hybridization and the subsequent introgression have been quite asymmetric and that the introgression occurred from M. stellata into M. salicifolia.     

Hybridization and introgression between the exotic Siberian elm, Ulmus pumila, and the native Field elm, U. minor, in Italy

In response to the first Dutch elm disease (DED) pandemic, Siberian elm, Ulmus pumila, was planted to replace the native elm, U. minor, in Italy. The potential for hybridization between these two species is high and repeated hybridization could result in the genetic swamping of the native species and facilitate the evolution of invasiveness in the introduced species. We used genetic markers to examine the extent of hybridization between these two species and to determine the pattern of introgression. We quantified and compared the level of genetic diversity between the hybrids and the two parental species. Hybrids between U. pumila and U. minor were common. The pattern of introgression was not as strongly biased towards U. pumila as was previously observed for hybrids between U. rubra and U. pumila in the United States. The levels of heterozygosity were similar between U. minor and the hybrids and both groups had higher levels of heterozygosity relative to U. pumila. The programs Structure and NewHybrids indicated the presence of first- (F₁) and second- generation (F₂) hybrids and of backcrosses in the hybrid population. The presence of healthy DED resistant U. minor individuals combined with the self-compatibility of U. minor could help explain the presence of F₂ individuals in Italy. The presence of F₂ individuals, where most of the variability present in the hybrids will be released, could facilitate rapid evolution and the potential evolution of invasiveness of U. pumila in Italy.     

Morphological,chemical, and cytogenetic characters of F1 hybrids betweenParthenium argentatum (Guayule) andP. fruticosum var.fruticosum (Asteraceae) and their potential in rubber improvement

Interspecific hybrids betweenParthenium argentatum, the guayule rubber plant, andP. fruticosum var. fruticosum were evaluated for their potential rubber content and quality. Fifteen-mo-old field-grown plants ofP. fruticosum var.fruticosum measured four times more in height and spread than those ofP. argentatum, but contained less than 0.05% rubber of low mol wt.Parthenium argentatum showed 2% rubber content, with a mol wt of about one million. Resin contents varied little among parents or hybrids. The same age F₁ hybrids were intermediate in height and spread and had low rubber content, but showed presence of high mol wt rubber like the guayule parent. This indicates that high mol wt rubber is expressed over the low mol wt rubber in F₁ hybrids. Despite low rubber content but favorable biomass production, F₁ hybrids revealed irregular meiotic chromosome behavior and low pollen and seed germination. These results suggest that interspecific F₁ hybrids may be used in backcross programs to increase biomass and rubber content in guayule.     

Development and cultivation of F2 hybrid between Undariopsis peterseniana and Undaria pinnatifida for abalone feed and commercial mariculture in Korea

The kelp Undariopsis peterseniana (Kjellman) Miyabe et Okamura is warm water tolerant and consequently there is currently considerable interest in developing commercial cultivation techniques for this species in Korea. Undaria is an important species for both the abalone industry and for commercial seaweed mariculture. In an attempt to extend the culture period of Undaria we bred and cultured hybrid kelp that is a cross between free-living gametophytes of U. peterseniana and Undariopsis pinnatifida. The morphological characteristics of the F₁ hybrid sporophytes were intermediate between those of the parent plants having shallow pinnated blades and forming both sorus and sporophyll. A F₂ generation was produced by isolating zoospores from sorus and sporophyll separately from a F₁ hybrid thallus. Using free-living gametophyte seeding and standard on-growing techniques, F₀ (female U. pinnatifida and male U. peterseniana), F₁, and F₂ gametophytes were cultured from December 2011 to May 2013. The morphological differences between the F₁ and F₂ generations were assessed. The F₂ hybrids were found to have longer pinnate blades and narrower midribs than the F₁ hybrid and only formed sporophylls. Growth and morphology of F₂ hybrids originating from the sporophyll or sorus of the F₁ hybrids were not morphologically different from each other. Both of the F₂ hybrids exhibited late maturation, with the early stages of sporophylls appearing in April. This late maturation of F₂ hybrids is beneficial in the development of hybrid strains that extend the period of availability of Undaria for abalone feed and cultivation in Korea.     

Inheritance pattern and expression of resistance to phosphine in larval stage of Tribolium castaneum (Coleoptera: Tenebrionidae)

Resistance developed by Tribolium castaneum (Herbst), a major pest of stored grain and grain products, to phosphine is a serious concern. Treatment of phosphine is given to all the stages (egg, larva, pupa and adult) of insects simultaneously in the infected commodity. Effective resistance management tactics need a proper understanding of expression of resistance in relation to dosage in immature stages including larvae. So, this study was undertaken to understand the genetic basis of phosphine resistance in larval stage of T. castaneum by crossing the resistant and susceptible parents to obtain the F₁, F₂ and the back-cross progenies. The resistant parent had a resistance ratio of 37.75 when compared to the susceptible parent. The susceptibility levels of the reciprocal F₁ hybrids did not show any significant difference indicating autosomal mode of inheritance of resistance. Level of dominance for the reciprocal F₁ hybrids was estimated (-0.70 and ?0.68) which showed that the resistance is expressed as incompletely recessive in larval stage of T. castaneum. χ² analysis showed that the observed and expected mortalities differed significantly (P < 0.05) in most of the concentrations indicating that more than one gene is responsible for phosphine resistance. Two plateaus at ～ 40 % and ～ 90 % mortality levels for the back-cross progeny to the resistant parent further confirmed the involvement of two or more genes in imparting resistance to phosphine. Our results will aid in enhancing the knowledge on the development of resistance to phosphine in the field and thus facilitate in designing suitable resistance management tactics.     

Molecular Confirmation of Intraspecific Tomato (<Emphasis Type="Italic">Solanum lycopersicum)</Emphasis> Hybrids and Their Evaluation Against Late Blight and Cucumber Mosaic Virus

Tomato is one of the most consumed vegetables in the world. Diseases are the number one concern in the development of high-yield and disease-resistant tomato hybrids which is the foremost priority of breeders. Present study was conducted (1) to develop DNA-based markers for genetic confirmation of tomato F₁ hybrids, (2) to utilize sequenced characterized amplified region (SCAR) marker linked to the Ph-3 gene for Phytophthora infestans resistance in tomato and (3) to evaluate male and female parental genotypes and their F₁ hybrids against late blight (LB) and cucumber mosaic virus (CMV). For molecular studies, 58 previously reported markers including RAPDs (10), SCAR (01), EST-SSR (01) and SSR (46) were applied. The SCAR marker clearly differentiated the LB3 and LB4 from Roma and T-1359 and provided evidence for Ph-3 gene. The SCAR marker was able to confirm the Ph-3 gene in the hybrids Roma × LB4, Roma × LB3, Riogrande × LB2, Riogrande × LB3 and Roma × LB7. Out of several tested primers, SSR-22 proved useful for genetic confirmation of F₁ hybrid TMS1 × Money Maker (MM). For LB, tested hybrids/genotypes were ranked as susceptible to highly susceptible with different infection percentage (IP). However, the pace of symptom development was slower in hybrid Rio × LB2, 45% IP after 10 days of inoculation compared with 85% disease in one of the parent genotypes (Riogrande). None of the tested genotypes was found resistant; however, TMS1 responded as tolerant against CMV using mechanical inoculation. Under natural field conditions, TMS1 was found resistant while hybrids TMS1 × Naqeeb and TMS1 × MM were tolerant where as others were found to be susceptible. In conclusion, all tomato hybrids were genetically confirmed using DNA-based markers. SCAR marker was useful for marker-assisted confirmation of the Ph-3 gene in parental lines and hybrids; however, this gene was unable to provide protection against the local population of P. infestans.     

Production of Polyploids and Unreduced Gametes in Lilium auratum × L. henryi Hybrid

Intergenomic F₁ hybrids between L. auratum x L. henryi and their BC₁ progeny were investigated through genomic in situ hybridization technique (GISH) to determine their potential value in lily breeding. We confirmed that F₁ intergenomic hybrids possessed a set of chromosomes (x=12) from both parents and that flowers of the F₁ auratum × henryi hybrid showed an intermediate morphological phenotype. Pollen size, viability and germination ability were measured through microscopic observations. F₁ intergenomic hybrids produced a relevant frequency of 2n-gametes, which were successfully used to perform crosses with Oriental hybrids, resulting in the triploid Oriental Auratum Henryi (OAuH) hybrid. Twenty BC₁ plants were generated by crossing between four different Oriental hybrid cultivars and F₁ AuH hybrids using an in vitro embryo rescue technique, after which the genome constitution and chromosome composition were analyzed by GISH. All plants were triploid, showing 12 from female parents (diploid Oriental hybrid) and 24 from male parents (diploid F₁ AuH hybrid). Overall, 16 out of 20 BC₁ progeny possessed recombinant chromosomes with 1-5 crossover sites per plant. Cytological analysis of 20 BC₁ plants by GISH verified that the occurrence of 2n pollen formation in all F₁ AuH hybrids was derived from the FDR (first division restitution) mechanism, in which the genome composition of all BC₁ plants possess 12 Oriental + 12 L. auratum + 12 L. henryi chromosomes. Allotriploids derived from the AuH hybrid were used as female for crossing with the diploid Oriental hybrid cultivar ''Sorbonne'' and considerable numbers of plants (0-6.5 plants per ovary) were only obtained when female OAuH (BC₁) triploids were used. Taken together, the results of this study indicate that production and analysis of F₁ AuH hybrids and their progeny through sexual polyploidization can be useful for efficient creation of important horticultural traits.     

Apomixis in Taraxacum paludosum (section Palustria, Asteraceae): Recombinations of apomixis elements in inter-sectional crosses

Recent studies have shown independent control of apomixis elements (restitution/diplospory, parthenogenesis and autonomous endosperm) in Taraxacum sect. Ruderalia. We studied inheritance of apomixis elements in the section Palustria using the crosses between various sections used as mother plants and apomictic T. paludosum (sect. Palustria) as pollen donor. Non-apomictic plants prevailed in F₁ progeny, and a high incidence of sterility was observed. Triploid non-apomictic F₁ hybrids were backcrossed with diploids (sects. Ruderalia, Palustria) and tetraploids (sects. Palustria, Piesis), and produced various types of progeny. These F₁ hybrids were classified into three types depending on the occurrence of parthenogenesis along with restitution, and the occurrence of various progeny in particular crosses (i.e. within the same mother plant) was observed. The results indicate the independent genetic control of all apomixis elements in T. paludosum, and recombinations during a restitutional megasporogenesis in hybrids.     

Interspecific hybrids of Antheraea roylei and A. pernyi — a cytogenetic reassessment

Summary A rare case of interspecific hybridization between the Indian oak feeding silkworm Antheraea roylei (n=31) and Chinese oak feeding silkworm A. pernyi (n=49) yielding fertile and vigorous offspring is reported. The F₁ and the backcross (A. roylei X A. pernyi X A. pernyi male individuals of the above cross and the F₂₃ and F₃₂ male offspring derived from an earlier cross between another race of A. roylei (n=30) and A. pernyi (n=49) were cytogenetically analysed in order to study their chromosome dynamics. The F₁ hybrids showed 18 trivalents and 13 bivalents in the first meiotic prophase and metaphase. The backcross individuals possessed either 9 trivalents and 31 bivalents or 49 bivalents, in Metaphase I cells. The F₂₃ and F₃₂ individuals were karyotypically alike and exhibited 49 bivalents. The following conclusions were drawn from the above observations: (a) in spite of allopatry and karyotypic divergence in number, a high degree of homology exists between the chromosomal complements of the two species; (b) A. pernyi possibly evolved from A. roylei, during the course of which 18 chromosomes of the latter underwent fission to give rise to the 36 chromosomes of the former. This is demonstrated by trivalent formation and pairing affinities in F₁ hybrids; (c) selection has favoured the elimination of large A. roylei chromosomes which participated in trivalent formation in successive generations of inbred hybrids to establish a stable Karyotype like that of A. pernyi.     

Putative Thinopyrum intermedium-derived stripe rust resistance gene Yr50 maps on wheat chromosome arm 4BL

Stripe rust-resistant wheat introgression line CH223 was developed by crossing the resistant partial amphiploid TAI7047 derived from Thinopyrum intermedium with susceptible cultivars. The resistance is effective against all the existing Chinese stripe rust races, including the most widely virulent and predominant pathotypes CYR32 and CYR33. Cytological analyses using GISH detected no chromosomal segments from Th. intermedium. It was presumed that the segment was too small to be detected. Normal bivalent pairing at meiosis in CH223 and its hybrids confirmed its stability. Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from crosses of CH223 with susceptible lines indicated that resistance was controlled by a single dominant gene. The resistance gene was mapped using an F_2:3 population from Taichung 29/CH223. The gene was linked to five co-dominant genomic SSR markers, Xgwm540, Xbarc1096, Xwmc47, Xwmc310 and Xgpw7272, and flanked by Xbarc1096 and Xwmc47 at 8.0 and 7.2 cM, respectively. Using the Chinese Spring nulli-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome arm 4BL. As no permanently named stripe rust resistance genes had been assigned to chromosome 4BL, this new resistance gene is designated Yr50. The gene, together with the identified closely linked markers, could be used in marker-assisted selection to combine two or more resistance genes in a single genotype.     

Spawning and fertility of F<Subscript>1</Subscript> hybrids of the coral genus <Emphasis Type="Italic">Acropora</Emphasis> in the Indo-Pacific

The role of hybridization through multi-specific synchronous spawning in the evolution of reef-building corals has been discussed since the 1990s, particularly for the genus Acropora. However, F₁ hybrids have been reported as common in only one case in the Caribbean, with no evidence of mechanisms that would allow continuous reproduction of the hybrids. In this study, we report for the first time the fecundity of two F₁ hybrid colonies produced experimentally from two Indo-Pacific species, A. intermedia and A. florida. These F₁ hybrids spawned at the same time as the parental corals. Backcrossing and F₁ hybrid crossing were successful in both directions. Furthermore, more than 90% self-fertilization was achieved in an F₁ hybrid, although it was negligible in the parental corals. While it is possible that the F₁ hybrid was a chimera, these results suggest that some products of interspecific hybridization may persist as the offspring of self-fertilizing F₁ hybrids.     

CO(2) Exchange, Cytogenetics, and Leaf Anatomy of Hybrids between Photosynthetically Distinct Flaveria Species

Hybrids between the C₄-like species, Flaveria brownii, A. M. Powell and the C₃-C₄ intermediate species Flaveria linearis Lag., Flaveria floridana Johnston, and Flaveria oppositifolia (DC.) Rydb. exhibited bivalent chromosome pairing during meiosis and stainability of pollen was high, ranging from 51 to 95%. An F₂ population produced from an F. brownii × F. linearis F₁ hybrid, exhibited bivalent chromosome pairing and high pollen stainability indicating a high degree of fertility in the hybrid. Oxygen inhibition of apparent photosynthesis averaged 6.8% for F. brownii and 22.2% for the C₃-C₄ species (in two experiments), and F₁ hybrids exhibited inhibitions which were intermediate to their parents. Values of carbon dioxide compensation concentration determined at low irradiance were 4.0, 34.0, and 6.5 microliters per liter for F. brownii, F. linearis and their F₁ hybrid, respectively. The mean value at low irradiance for 33 F₁ plants was 6.8 microliters per liter, and individual values ranged only from 3.7 to 11.7 microliters per liter. Anatomical characteristics for the F₁ hybrid leaves were intermediate to those of the parents, and there was considerable variation among F₂ plants derived from F. brownii × F. linearis. In the F₂ population δ¹³C values ranged from −27‰ to −20‰. The expression of more C₄-like characteristics by the F₁ hybrids in this study and their apparent high fertility make them promising specimens for producing segregating populations for use in C₄ inheritance studies.     

Morphological characteristics and chromosome behaviour in F1, F2 and BC1 progenies between Chrysanthemum × morifolium and Ajania pacifica

The garden chrysanthemum (Chrysanthemum × morifolium) variety ??Aoyunhuoju?? (2n = 6x = 54) was crossed as female with Ajania pacifica (2n = 10x = 90) to produce intergeneric F1 hybrids, which were used both as the source of F₂ generation and as the parent for a first back-cross with ??Aoyunhuoju??. The morphology of all of the F₁ hybrids and hybrid derivatives was intermediate with respect to the two parents, although the BC₁ progenies resembled ??Aoyunhuoju?? more closely than any of the F₁ and F₂ progenies did. In the F₁ generation, the density of silvery hairs on the lower leaf surface and along the margin of the leaf was lower than in A. pacifica, while that in the BC1 generation, this trait was less prominent than in the F₁. The somatic chromosome number of the F₁, F₂ (with an exception of F₂-6 of a mainly 63) and BC1 generations was 2n = 8x = 72, 2n = 8x = 72 and 2n = 7x = 63 respectively, as expected. The hybrids and their derivatives retained a variable degree of fertility. There was a low frequency of meiotic chromosome pairing failure in all three hybrid generations, with most of the chromosomes involved as bivalents. Some BC₁ individuals show potential for commercialization thanks both to their flower shape and the inheritance of the silvery leaf trait from A. pacifica.     

Photosynthesis, Morphology, Leaf Anatomy, and Cytogenetics of Hybrids between C(3) and C(3)/C(4)Panicum Species

The Laxa group of the Panicum genus contains species which have CO₂ exchange and anatomical characteristics intermediate to C₃ and C₄ photosynthetic types (C₃/C₄), and also species characterized as C₃. Hybrids were made between two of the C₃/C₄ species and two C₃ species. Carbon dioxide exchange and morphological, leaf anatomical, and cytogenetic characteristics of F₁ hybrids between Panicum milioides Nees. ex Trin (C₃/C₄) and P. laxum Mez. (C₃), P. spathellosum Doell (C₃/C₄) and P. boliviense Hack. (C₃), and P. spathellosum and P. laxum were studied. There were no consistent differences in apparent photosynthesis, although two of the three hybrids had higher net CO₂ uptake than the C₃ parent. Values of inhibition of apparent photosynthesis by 21% O₂, CO₂ loss in the light, and CO₂ compensation concentration for the hybrids were between those of the parents. All three hybrids showed leaf anatomical traits, especially organelle quantities in the bundle sheath cells, between those of their respective parents. Linear regression of CO₂ compensation concentration on the percentage of mitochondria and chloroplasts in vascular bundle sheaths of the parents and hybrids gave correlation coefficients of −0.94. This suggests that the reduction in CO₂ loss in the C₃/C₄ species, and to a lesser degree in the F₁ hybrids, was due to development of organelles and perhaps a higher proportion of leaf photorespiration in bundle sheaths. The overall morphology of the hybrids was so different from the parents that they could be described as new taxonomic forms. The chromosomes in the hybrids were mainly unpaired or paired as bivalents indicating possible homology between some parental genomes.