Intersubspecific Hybrids Research Articles

Delimitation of the rice wide compatibility gene S5 n to a 40-kb DNA fragment

Wide compatibility varieties (WCVs) are a special class of rice (Oryza sativa L.) germplasm that produces hybrids with normal pollen and spikelet fertility when crossed with both indica and japonica subspecies. The wide compatibility gene S5 ( n ) has been used extensively in inter-subspecific hybrid breeding programs. We previously mapped the S5 locus to a 2.2-cM genomic region between RM253 and R2349 on chromosome 6, using a population of 356 F(1) plants derived from the three-way cross 02428/Nanjing11//Balilla. In this study, a chromosome walking strategy was employed to construct a physical map covering this genomic region using these two closest markers as the starting points. A physical map consisting of six overlapping BAC clones was formed, spanning a genomic region of 540-kb in length. By analyzing recombination events from a population of 8,000 F(1) plants derived from a three-way cross based on near isogenic lines of the S5 locus, the S5 locus was localized to a DNA fragment of 40-kb in length, flanked by two shotgun subclones, 7B1 and 15D2. Sequence analysis of this fragment predicted five open reading frames, encoding xyloglucan fucosyltransferases, dnak-type molecular chaperone BiP, a putative eukaryotic aspartyl protease, and a hypothetical protein. This result will be very useful in molecular cloning of the S5 ( n ) allele and marker-assisted transferring of the wide compatibility gene in rice breeding programs.

Delimiting a rice wide-compatibility gene S 5 n to a 50 kb region

Wide-compatibility (WC) is one of the most important traits in rice, which can overcome the fertility barrier in the indica/japonica hybrids, and hence to make it possible to utilize the higher yield potential of inter-subspecific hybrids. The S5n gene located on chromosome 6 has been previously reported to be responsible for the wide-compatibility in rice. Here we report the precise location of the S5n gene. In the first-pass mapping, the S5n gene was restricted within a 200 kb region by using a population of 242 isogenic lines in combination with high-density markers developed in the S5 region. In the fine mapping, the S5 region was further saturated with newly developed markers and more isogenic lines (549 in total) were investigated. Eventually, the S5n gene was mapped within a 50 kb region delimited by the left marker J13 and the right marker J17. One BAC clone screened from the BAC library of the WC rice variety 02428 covered the whole S5 region. Sequence analysis of the 50 kb region revealed two candidate genes, coding an aspartyl protease and a hypothetical protein. This result would greatly accelerate both cloning and marker-assisted selection of this important S5n gene.

Identification and confirmation of three neutral alleles conferring wide compatibility in inter-subspecific hybrids of rice (Oryza sativa L.) using near-isogenic lines

Wide-compatibility varieties (WCVs) are a special class of rice germplasm that is able to produce fertile hybrids when crossed to both indica and japonica subspecies. Previous studies determined 'Dular' and 02428 as two WCVs and identified a number of QTLs as having large effects on fertility of inter-subspecific hybrids. In this study, we developed five near-isogenic lines (NILs) for three of the QTLs, f5, f6 and S5, by backcrossing and marker-assisted selection, using "Dular" and 02428 as the donors and "Zhenshan 97" as the recipient. Three of the NILs each carried one introgressed allele, and two NILs each carried two introgressed alleles in combinations. The NILs were testcrossed to an indica tester "Nanjing 11" and a japonica tester "Balilla". The results showed that the f5 allele from "Dular"(f5-Du) is a neutral allele conferring wide compatibility, with a large effect on both pollen and spikelet fertility, and the f6 allele from "Dular" (f6-Du) is a neutral allele for spikelet fertility with smaller effect. The S5 allele from 02428 (S5-08) was confirmed to be a neutral allele for spikelet fertility. It is likely that f6 and S5 are the same locus as deduced by their genomic locations and effects. The results also showed that even in combination, two neutral alleles of different loci were not able to produce normal fertility hybrids in typical indica-japonica crosses. The implications of the findings in rice breeding programs are discussed.

Genetic dissection of embryo sac fertility, pollen fertility, and their contributions to spikelet fertility of intersubspecific hybrids in rice

The partial sterility of hybrids has been a major barrier for utilization of the strong heterosis expressed in hybrids between Oryza sativa ssp. indica and O. sativa ssp. japonica. Wide-compatibility varieties, comprising a special class of germplasm, are able to produce fertile hybrids when crossed to both indica and japonica varieties. However, all the work on wide compatibility and majority of studies on indica/japonica hybrid sterility reported so far were based only on spikelet fertility; thus, it is not known to what extent male and female gamete abortions influence hybrid sterility. In this study, we investigated pollen fertility, embryo sac fertility, and spikelet fertility in an F1 population of 202 true hybrid plants derived from a three-way cross ('02428'/'Nanjing 11'//'Balilla'). A partial regression analysis showed that the pollen and embryo sac fertility contributed almost equally to spikelet fertility. QTL analysis based on a linkage map of 191 polymorphic marker loci identified two QTLs for pollen fertility, one QTL for embryo sac fertility, and three QTLs for spikelet fertility. The S5 locus, previously identified as a locus for wide compatibility by spikelet fertility analysis, is a major locus for embryo sac fertility, and a QTL on chromosome 5 had a major effect on pollen fertility. These two loci coincided with the two major QTLs for spikelet fertility. The study also detected a QTL on chromosome 8, showing a large effect on spikelet fertility but no effect on either pollen or embryo sac fertility. Very little interaction among the QTLs was detected. The implications of the findings in rice breeding programs are discussed.

Variation in Anther Culture Response and Fertility of Backcrossed Hybrids between Indica and Japonica Rice (Oryza sativa)

This study was conducted to investigate the variations of fertility, callus induction and plant regeneration in backcrossed hybrids between a responsive japonica variety (Mankeumbyeo, recurrent parent) and a recalcitrant indica variety (Ranta Emas, donor parent) to anther culture. The mean spikelet fertility of inter-subspecific F1 and BC1F1 hybrids was 33.5% and 67.2%, and the spikelet fertility of BC1F1 among backcrossed hybrids showed the most extensive variation (a low of 4.5% to a high of 90.6%). The mean fertility and distribution range in BC5F1 hybrids were almost the same as that of the japonica recurrent parent (94.6%). The mean callus induction of F1 and BC1F1 hybrids was higher than that of donor parent, and the distribution range in BC1F1 hybrids varied from a low 0% to a high 18.7%. The mean callus induction and plant regeneration of BC4F1 hybrids was almost that of japonica recurrent parent, and there were no statistical differences between BC4F1 and BC5F1 hybrids. These results may help to accelerate the introgression of desirable traits from indica into japonica rice using anther culture of backcross hybrids as a breeding strategy.

Performance of intersubspecific alfalfa hybrids in sward versus space planted plots

Intersubspecific hybrids between Medicago sativa subsp. sativa and subsp. falcata show biomass yield heterosis in space planted plots. Relative biomass yield of alfalfa is known to differ in space planted versus sward plots, although the magnitude of the difference is variable. The objective of this study was to determine if and how much of the biomass yield heterosis observed in space planted alfalfa hybrids was retained in sward planted plots. Two falcata genotypes (WISFAL-6 and PI502453-1) and three elite sativa genotypes were crossed in a diallel mating design. Progeny were transplanted into space-planted plots and harvested three times per year or drilled into sward plots harvested four times per year. Hybrids of WISFAL-6 with the sativa genotypes produced as much first harvest biomass yield as intra-sativa hybrids in space-planted plots and more in sward plots. Yield in subsequent harvests was lower than intra-sativa hybrids in sward plots only. Hybrids of PI502453-1 with sativa were generally lower yielding than intra-sativa crosses. A moderate correlation was observed between biomass yield in space planted and sward plots. Heterosis expression in swards was lower than that in spaced planted nurseries for progeny of both falcata genotypes. The increased plant-to-plant competition in swards is the likely cause of the loss of heterosis.

Male and female gamete abortions, and reduced affinity between the uniting gametes as the causes for sterility in an indica/japonica hybrid in rice

Hybrid sterility frequently occurs in crosses between indica and japonica subspecies of Asian cultivated rice. In this study, we investigated the cytological processes involved in formation and development of male and female gametes as well as their interactions in fertilization, using an indica/japonica hybrid in comparison with an indica/indica hybrid. It was found that more than 50% of the microspores generated in the indica/japonica hybrid could not develop into functional pollen. The abortion rate of microspores in the indica/japonica hybrid was much higher than that in the indica/indica hybrid. Abortive embryo sacs made up roughly 70% of the embryo sacs examined in the indica/japonica hybrid, which was also much higher than that detected in the indica/indica hybrid. Moreover, the amount of pollen adherence on stigmas of the indica variety upon hand-pollination with pollen from the japonica variety was much lower than the indica/indica pollination, and the number of pollen adhered on the stigmas by natural self-pollination was much greater in the indica/indica hybrid than in the indica/japonica hybrid. The indica/japonica hybrid also encountered difficulties in pollen tube growth after pollination, and the fertilization rate of the indica/japonica hybrid was much lower than that of the indica/indica hybrid. These results clearly illustrate the complexity of the mechanisms underlying inter-subspecific hybrid sterility in rice involving both pre- and post-zygotic reproductive isolation mechanisms.

AFLP-based assessment of genetic diversity among nine alfalfa germplasms using bulk DNA templates.

Improving commercial utilization of perennial Medicago collections requires developing approaches that can rapidly and accurately characterize genetic diversity among large numbers of populations. This study evaluated the potential of using amplified fragment length polymorphism (AFLP) DNA markers, in combination with DNA bulking over multiple genotypes, as a strategy for high-throughput characterization of genetic distances (D) among alfalfa (Medicago sativa L.) accessions. Bulked DNA templates from 30 genotypes within each of nine well-recognized germplasms (African, Chilean, Flemish, Indian, Ladak, Medicago sativa subsp. falcata, Medicago sativa subsp. varia, Peruvian, and Turkistan) were evaluated using 34 primer combinations. A total of 3754 fragments were identified, of which 1541 were polymorphic. The number of polymorphic fragments detected per primer combination ranged from 20 to 85. Pairwise D estimates among the nine germplasms ranged from 0.52 to 1.46 with M. sativa subsp. falcata being the most genetically dissimilar. Unweighted pair-group method arithmetic average (UPGMA) analysis of the marker data produced two main clusters, (i) M. sativa subsp. sativa and M. sativa subsp. varia, and (ii) M. sativa subsp. falcata. Cluster-analysis results and D estimates among the Chilean, Peruvian, Flemish, and M. sativa subsp. varia germplasms supported the hypothesis that Peruvian was more similar to original Spanish introductions into Central and South America than Chilean. Hierarchical arrangement of the nine germplasms was supported by their respective geographic, subspecific, and intersubspecific hybrid origins. Subsets of as few as seven highly informative primer pairs were identified that produced comparable D estimates and similar heirarchical arrangements compared with the complete dataset. The results indicate that use of primer-pair subsets for AFLP analysis of bulk DNA templates could serve as a high-throughput system for accurately characterizing genetic diversity among large numbers of alfalfa populations.

分子系統分析に基づく国内飼育チンパンジーの亜種判定

One of the primary objectives in the captive management of chimpanzees is to preserve to the greatest extent possible the genetic diversity that still exists in wild gene pools. Furthermore, it is desirable to prevent the occurrence of intersubspecific hybrids. It is possible to sort chimpanzees into their three subspecies (Pan troglodytes verus, P. t. troglodytes, P. t. schweinfurthii) by investigating mitochondrial DNA sequences. Thus, in order to obtain the basic data necessary to establish a future-breeding protocol, we have decided to evaluate the subspecies of all captive chimpanzees living in Japan. At present, a total of 373 animals including 193 known captive-born, 152 known wild-born, and 28 known captive-born from foreign countries have been raised in Japan. Data on the location of capture of most of these apes is unknown. The 249 chimpanzee samples used in the present study were obtained from 43 zoos in Japan. DNA samples from 180 chimpanzees were extracted from follicle-shed hairs: 67 were from blood samples and 2 were from tissues. We used PCR amplification and direct sequencing of the mitochondrial D-loop region. We compared these sequences with chimpanzees of known geographic origin. Finally, the subspecies of 332 chimpanzees that belonged to 217 maternal lineages were identified. The findings clarified that 230 individuals (61.7%) were P. t. verus. Additionally, four chimpanzees were P. t. troglodytes and 15 were P. t. schweinfurthii. The present findings have also confirmed the existence of another previously unrecognized subspecies of chimpanzee in Nigeria (Pan troglodytes vellerosus). Four of the captive chimpanzees we examined are referable to this subspecies. Examination of the registration book of pedigree and DNA data indicated that 56 chimpanzees born in Japan were actually hybrids of these three subspecies. Molecular data must be carefully examined and reconciled in order to establish a viable breeding plan for chimpanzees in Japan.

Mapping QTLs for defective female gametophyte development in an inter-subspecific cross in Oryza sativa L.

The embryo-sac is an essential structure for angiosperm reproduction. The cytological and genetic characterization of embryo-sac sterility was examined in a cross between Oryza sativa ssp. indica cv. ZYQ8 and ssp. japonica cultivar, JX17. The arrest of embryo-sac development was manifested following meiosis in the F1 hybrid. When the megaspore carried the lethal genotype, the nucleus either failed to divide or divided only once, and the immature embryo-sac degenerated. Abortion of the embryo-sac in the indica-japonica hybrid background was not observed in their original parents, and an effect of cytoplasmic gene(s) on embryo-sac sterility in the reciprocal F1 hybrids was not detected. Using a rice molecular linkage map based on a doubled haploid (DH) population from the cross of ZYQ8 /JX17, we mapped quantitative trait loci (QTLs) for the defective development of the female gametophyte in backcross progenies from the DH lines. The result demonstrated that a polygenic system is involved in both megagametogenesis and postzygotic isolation in inter-subspecific hybrid rice.

Yield Potential Trends of Tropical Rice since the Release of IR8 and the Challenge of Increasing Rice Yield Potential

ABSTRACTSince the release of IR8 in 1966, 42 additional indica rice (Oryza sativa L.) cultivars developed by the International Rice Research Institute (IRRI) for the irrigated and favorable rainfed lowlands have been released in the Philippines. The maximum yield of IR8 has been reduced by about 2 Mg ha−1 during the past 30 yr. Empirical breeding for population improvement within the indica germplasm has resulted in the maintenance of rice yield potential in the tropics of about 10 Mg ha−1. To break the yield barrier, several approaches are being explored. These include development of a new plant type (NPT) with low tillering capacity and large panicles from tropical japonica germplasm and exploitation of heterosis through intervarietal and intersubspecific hybrids. Hybrid rice between indicas increased yield potential by about 9% under the tropical conditions. The higher yield potential of indica/indica hybrids compared with indica inbred cultivars was attributed to the greater biomass production rather than harvest index. New plant type breeding has not yet improved yield potential due to poor grain filling and low biomass production. Factors that cause poor grain filling and low biomass production of the NPT lines have been identified. Selecting parents with good grain filling traits, introduction of indica genes into NPT's tropical japonica background, and a refinement of the original NPT design are expected to improve the performance of the NPT lines. Further enhancement in yield potential may be possible from use of intersubspecific heterosis between indica and NPT lines.

Analysis of the Kit and Pdgfra genes in the patch-extended (Phe) mutation.

The patch (Ph) locus allele, patch-extended (Phe), has significantly less pigmentation than the original mutation and homozygotes have been known to survive to term. Analysing intersubspecific F1 hybrids, we were able to demonstrate that Phe is a deletional mutation encompassing the platelet-derived growth factor receptor alpha subunit (Pdgfra). The deletion does not appear to extend into the coding sequence of the Kit gene (a related tyrosine kinase receptor). However, we were able to demonstrate that, while the Kit gene is transcribed, it does not encode a functionally active receptor.

The extent of parental genotypic divergence determines maximal heterosis by increasing fertility in inter-subspecific hybrids of rice (Oryza sativa L.)

The magnitude of heterosis in F1 hybrids is related not only to the performance of parents per se but also to the genetic diversity between two parents. The extent of genotypic divergence between hybrid rice parents was investigated at the molecular level, using two subsets of rice materials: a subset of doubled haploid (DH) lines derived from an Indica × Japonica cross (Gui630/02428) and another subset of Indica or Japonica lines representative of a broad spectrum of the Asian cultivated rice gene pool, including landraces, primitive cultivars, historically important cultivars, modern elite cultivars, super rice and parents of superior hybrids. 57 entries deliberately selected from the 81-DH lines (in total) were testcrossed to two widely used rice lines in China, photoperiod-sensitive genic male sterile (PGMS) N422s and thermo-sensitive genic male sterile (TGMS) Peiai64s. Results of the two sets of test-cross F1 populations showed congruently that parental genotypic divergence has a relatively low impact on heterosis for the two yield components, i.e., panicle number and 1000-grain weight, but it has a great bearing on fertility parameters, i.e., filled grains per plant and seedset. Heterosis for grain yield in the two test-cross populations exhibited a sharp maximum when the proportion of Japonica alleles in the male parent was between 50 and 60%, so was the heterosis for fertility parameters correspondingly. Thus fertility parameters were the most sensitive and important factors which were influenced by the extent of parental genotypic divergence. Moreover, our results showed that parents with moderate extent of genotypic divergence played an important role in the use of inter-subspecific rice heterosis.

A genome-wide analysis of wide compatibility in rice and the precise location of the S5 locus in the molecular map

The discovery of wide-compatibility varieties (WCVs) that are able to produce normal fertility hybrids when crossed both to indica and japonica rice has enabled the fertility barrier between indica and japonica subspecies to be broken and provided the possibility of developing inter-subspecific hybrids in rice breeding programs. However, a considerable variation in the fertility level of hybrids from the same WCV crossed to different varieties has often been observed. One hypothesis for this variable fertility is that additional genes are involved in hybrid fertility besides the wide-compatibility gene (WCG). To assess such a possibility, we performed a genome-wide analysis by assaying a large population from a three-way cross ‘02428’/‘Nanjing 11’//‘Balilla’ using a total of 171 RFLP probes detecting 191 polymorphic loci distributed throughout the entire rice linkage map. Our analysis recovered 3 loci conferring significant effects on hybrid fertility. The major locus on chromosome 6 coincided in chromosomal location with the previously identified S 5 locus, and the 2 minor loci that mapped to chromosomes 2 and 12, respectively, were apparently distinct from all previously reported hybrid sterility genes. Interaction between the indica and japonica alleles at each of the loci caused a reduction in hybrid fertility. The joint effect of the 2 minor loci could lead to partial sterility even in the presence of the WCG. The location of the S 5 locus on the molecular marker linkage map was determined to be approximately 1.0 cM from the RFLP locus R2349. This tight linkage will be useful for marker-aided transfer of the WCG in hybrid rice breeding and for map-based cloning.

Molecularmarker diversity and hybrid sterility in indica-japonica rice crosses

The partial sterility of hybrids between the indica and japonica rice subspecies of Asian cultivated rice is a serious constraint for utilizing inter-subspecific heterosis in hybrid rice breeding. In this study, we have investigated the relationship between molecular-marker polymorphism and indica-japonica hybrid fertility using a diallel set involving 20 rice accessions including 9 indica and 11 japonica varieties. Spikelet fertility of the resulting 190 F1s and their parents was examined in a replicated field trial. Intra-subspecific hybrids showed much higher spikelet fertility than inter-subspecific hybrids except in crosses involving wide-compatibility varieties. The parents were surveyed for DNA polymorphism using 96 RFLP and ten SSR markers, which revealed extensive genetic differentiation between indica and japonica varieties. A large number of markers detected highly significant effects on hybrid fertility. The chromosomal locations for many of the positive markers coincided well with previously identified loci for hybrid sterility. The correlation between hybrid fertility and parental distance was low in both intra- and inter-subspecific crosses. The results suggest that the genetic basis of indica-japonica hybrid sterility is complex. It is the qualitative, rather than the quantitative, difference between the parents that determines the fertility of hybrids.

Use of androgenesis in intersubspecific hybrid rice breeding

AbstractSignificant differences of callus induction, green plant regeneration and culture efficiency were observed among restorer lines and their hybrids in rice. Average callus induction percentage of F1, hybrids was about twice that of their parents. Twenty doubled haploid (DH) lines that showed normal fertility with both indica and japonica CMS lines, were selected as widely compatible restorers (WCRs). TG8 derived from CPSLO17/Minghui 63 not only showed normal fertility to both indica and japonica test varieties and CMS lines, but also exhibited superior agronomic traits, in particular short plant, desired plant type, high tillerability, large panicles, good grain quality and resistance to rice blast disease. Strong heterosis for yield was observed in crosses between indica or japonica CMS lines and TG8. TG8 possessed a dominant, widely compatible gene (WCG) that was inherited from the variety CPSLO17. Results confirmed that the anther culture technique is a quick and effective way of developing widely compatible restorers in rice and that it is applicable to the direct use of intersubspecific heterosis with the three‐line method.

Evidence for Mutational Origin of Hybrid Sterility Genes in Rice(Oryza sativa L.).

Semi-sterile panicles found in inter-subspecific hybrids between Indica and Japonica rice are caused by partial abortion of gamete having S-5j on heterozygote S-5ilS-5j at the locus on chromosome 6, where a neutral allele S-5 is also identified and the genotype of S-5n /S-5i and S-5nIS-5j do not show hybrid sterility. Similar allelic in-teractions were also identified at some other loci including S-7. We report here two cases of mutant alleles at such hybrid sterility loci. First, the semi-sterility in hybrids be-tween Toyonishiki and an Indica tester IR 36 was found to be caused only by an allelic interaction of i IS-5j . When Miyukimochi, which is an irradiated mutant from Toyonishiki was tested, the semisterility in F1 hybrids between Miyukimochi and IR 36 was attributed to allelic interactions by both S-5i IS-5j and S-7iIS-7j . Toyonishiki was found to possess a neutral allele S-7n at S-7. Thus, the neutral allele S-7n in Toyonishiki was found to be mutated into S-7j by irradiation with 60Co. Second, an experimental line, 02428 was tested, which possesses the wide compatible allele,

Meiotic Stability of Intersubspecific Hybrids of Snake River × Thickspike Wheatgrasses

Based on genomic makeup and partial hybrid fertility, Snake River wheatgrass (proposed name Elymus lanceolatus ssp. wawawaiensis) has been recognized since 1986 as a subspecies of E. lanceolatus (Scribn. & J.G. Smith) Gould. Thus it is conspecific with thickspike wheatgrass [E. lanceolatus ssp. lanceolatus (Scribn. & J.G. Smith) Gould]. However, these two wheatgrasses display distinct morphological features, physiological traits, geographical distributions, and habitat preferences. Hybridization of the two subspecies generates valuable germplasm with considerable heterosis, but the hybrids are partially male sterile. Our objective was to determine the degree and nature of hybrid male sterility. Mean chromosome pairing (and pollen stainability) was 0.11 I + 13.90 II + 0.02 IV (84%) for ‘Secar’ Snake River wheatgrass and 0.10 I + 13.83 II + 0.01 III + 0.05 IV (78%) for ‘Bannock’ thickspike wheatgrass, the parents in the original cross, 0.60 I + 13.61 II + 0.01 III + 0.04 IV (55%) for three F1 hybrid populations, and 0.09 1 + 13.92 II + 0.01 III + 0.03 IV (80%) and 0.441 + 13.66 II + 0.01 Ill + 0.05 IV (64%) for backcross populations to Bannock thickspike wheatgrass and BBR‐syn Snake River wheatgrass, respectively. The low frequency of multivalents in the hybrids indicated that male sterility resulted from some degree of genetic incompatibility rather than a major chromosomal rearrangement. Because hybrid and backcross populations possessed reasonable levels of pollen stainability and chromosome abnormalities were absent, they should respond readily to selection for high pollen stainability.

Groundunt Ideotype: Its Agro-physiological Characteristics and Contribution of Subsp. fastigiata.

In groundnut (Arachis hypogaea L.), it is presumed that stem-system has no substantial mechanical role in supporting the pods. In order to assess whether a reduced partitioning of dry matter to stems (includes petioles) is associated with an increased seed yield, a 3-year field trial was conducted using 27 cultivars (cvs.). In this study, correlations between seed yield and major agro-physiological characteristics, including yield components and botanical groups of the cvs. were analyzed. It was concluded that seed yields above 3000 kg ha-1 in cvs., including Japanese Norin cvs., developed by inter-subspecific hybridization, were associated with high seed/stem ratio (2∼3), harvest index (30∼40%), by decrease of the number of branches and large seed size (above 70 g/100-seed weight). A further analysis indicated that these cvs. were early in flowering and maturation and erect in growth habit. Based on these results, a contribution of subsp. fastigiata to increase seed yield was noted and the characteristics of a groundnut ideotype were proposed.

BIOSYSTEMATICS OF THE GENUS IPS (COLEOPTERA: SCOLYTIDAE) IN NORTH AMERICA: REVIEW OF THE IPS CALLIGRAPHUS GROUP

AbstractThe recognition of four taxa within the calligraphus species group of the genus Ips DeGeer is supported by breeding experiments, karyology, morphology, ecology, and distributions. Ips calligraphus calligraphus (Germar) occurs in the eastern United States and adjacent parts of Canada. Ips c. ponderosae (Swaine) occurs in the range of Pinus ponderosa in the Black Hills, eastern Rocky Mountains, and in the northern Sierra Madre Oriental in Mexico. Ips c. interstitialis (Eichhoff) occurs in the Caribbean Archipelago but the homogeneity of populations on the islands of Hispaniola and Jamaica and the true type locality are uncertain. Ips apache Lanier infests various pines (excluding pinyon pines) at lower altitudes from southeastern Arizona through Mexico. Populations south of the Isthmus of Tehuantepec in Caribbean pines on the east coast of Central America are provisionally considered to be I. apache. Pairings of female I. calligraphus subspecies with male I. apache were infertile. Reciprocal pairing produced rare, sterile hybrids. Fertility of I. calligraphus subspecies was normal when I. c. calligraphus was the female but reduced when the female was either I. c. ponderosae or I. c. interstitialis. All members of the group had 15 pairs of autosomes plus a sex bivalent (2n = 32) that assumed a “parachute” configuration to give a male meiotic formula of 15 AA + Xyp. Second meiosis chromosomes of I. apache lack some of the heterochromatic arms present in I. calligraphus. Meiotic divisions of rare interspecific hybrids (I. apache ♀ × I. calligraphus s. lato ♂) had numerous autosomal rearrangements, a possible translocation, and oversized (probably tetraploid) spermatozoa. Meiosis was mostly normal in intersubspecific hybrids, but the presence of occasional anaphase bridges or nonmigrating chromosomes and alignment of pachytene homologs revealed inversions and other possible rearrangements. Univariate and multivariate analyses of pars stridens strial width, pronotal width, and male genitalia revealed significant differences among all four taxa.