Sciences Papers and Journal Articles

Aggregation and Competitive Exclusion: Explaining the Coexistence of Human Papillomavirus Types and the Effectiveness of Limited Vaccine Conferred Cross-Immunity

Edward K. Waters — Tue, 27 Nov 2012 16:42:25 PST

Human Papillomavirus (HPV) types are sexually transmitted infections that cause a number of human cancers. According to the competitive exclusion principle in ecology, HPV types that have lower transmission probabilities and shorter durations of infection should be outcompeted by more virulent types. This, however, is not the case, as numerous HPV types co-exist, some which are less transmissible and more easily cleared than others. This paper examines whether this exception to the competitive exclusion principle can be explained by the aggregation of infection with HPV types, which results in patchy spatial distributions of infection, and what implications this has for the effect of vaccination on multiple HPV types. A deterministic transmission model is presented that models the patchy distribution of infected individuals using Lloyd’s mean crowding. It is first shown that higher aggregation can result in a reduced capacity for onward transmission and reduce the required efficacy of vaccination. It is shown that greater patchiness in the distribution of lower prevalence HPV types permits co-existence. This affirms the hypothesis that the aggregation of HPV types provides an explanation for the violation of the competitive exclusion principle. Greater aggregation of lower prevalence types has important implications where type-specific HPV vaccines also offer cross-protection against non-target types. It is demonstrated that the degree of cross-protection can be less than the degree of vaccine protection conferred against directly targeted types and still result in the elimination of non-target types when these non-target types are patchily distributed.

Estimating Global Arthropod Species Richness: Refining Probabilistic Models Using Probability Bounds Analysis

Andrew J. Hamilton et al. — Sun, 02 Sep 2012 18:20:35 PDT

A key challenge in the estimation of tropical arthropod species richness is the appropriate management of the large uncertainties associated with any model. Such uncertainties had largely been ignored until recently, when we attempted to account for uncertainty associated with model variables, using Monte Carlo analysis. This model is restricted by various assumptions. Here we use a technique known as probability bounds analysis to assess the influence of assumptions about (i) distributional form and (ii) dependencies between variables, and to construct probability bounds around the original model prediction distribution. The original Monte Carlo model yielded a median estimate of 6.1 million species, with a 90% confidence interval of [3.6, 11.4]. Here we found that the probability bounds (p-bounds) surrounding this cumulative distribution were very broad, owing to uncertainties in distributional form and dependencies between variables. Replacing the implicit assumption of pure statistical independence between variables in the model with no dependency assumptions resulted in lower and upper p-bounds at 0.5 cumulative probability (i.e., at the median estimate) of 2.9–12.7 million. From here, replacing probability distributions with probability boxes, which represent classes of distributions, led to even wider bounds (2.4–20.0 million at 0.5 cumulative probability). Even the 100th percentile of the uppermost bound produced (i.e., the absolutely most conservative scenario) did not encompass the well-known hyper estimate of 30 million species of tropical arthropods. This supports the lower estimates made by several authors over the last two decades.

Implications of reef ecosystem change for the stability and maintenance of coral reef islands

Chris T. Perry et al. — Tue, 27 Dec 2011 19:38:01 PST

Coral reef islands are among the most vulnerable environments on Earth to climate change because they are low lying and largely constructed from unconsolidated sediments that can be readily reworked by waves and currents. These sediments derive entirely from surrounding coral reef and reef flat environments and are thus highly sensitive to ecological transitions that may modify reef community composition and productivity. How such modifications – driven by anthropogenic disturbances and on-going and projected climatic and environmental change – will impact reef island sediment supply and geomorphic stability remains a critical but poorly resolved question. Here, we review the unique ecological–geomorphological linkages that underpin this question and, using different scenarios of environmental change for which reef sediment production responses can be projected, explore the likely resilience of different island types. In general, sand-dominated islands are likely to be less resilient than those dominated by rubble grade material. However, because different islands typically have different dominant sediment constituents (usually either coral, benthic foraminifera or Halimeda) and because these respond differently to individual ecological disturbances, island resilience is likely to be highly variable. Islands composed of coral sands are likely to undergo major morphological change under most near-future ecological change scenarios, while those dominated by Halimeda may be more resilient. Islands composed predominantly of benthic foraminifera (a common state through the Pacific region) are likely to exhibit varying degrees of resilience depending upon the precise combination of ecological disturbances faced. The study demonstrates the critical need for further research bridging the ecological–geomorphological divide to understand: (1) sediment production responses to different ecological and environmental change scenarios; and (2) dependant landform vulnerability.

The potential of herbaceous native Australian legumes as grain crops: a review

Lindsay W. Bell et al. — Tue, 27 Dec 2011 17:37:52 PST

Many agricultural systems around the world are challenged by declining soil resources, a dry climate and increases in input costs. The cultivation of plants that are better adapted than current crop species to nutrient poor soils, a dry climate and low-input agricultural systems would aid the continued profitability and environmental sustainability of agricultural systems. This paper examines herbaceous native Australian legumes for their capacity to be developed as grain crops adapted to dry environments. The 14 genera that contain herbaceous species are Canavalia, Crotalaria, Cullen, Desmodium, Glycine, Glycyrrhiza, Hardenbergia, Indigofera, Kennedia, Lotus, Rhynchosia, Swainsona, Trigonella and Vigna. A number of these genera (e.g., Glycine, Crotalaria, Trigonella and Vigna) include already cultivated exotic grain legumes. Species were evaluated based on the extent to which their natural distribution corresponded to arid and semi-arid climatic regions, as well as the existing information on traits related to harvestability (uniformity of ripening, propensity to retain pod, pod shattering and growth habit), grain qualities (seed size, chemistry, color and the absence of toxins) and fecundity. Published data on seed yield were rare, and for many other traits information was limited. The Australian species of Vigna, Canavalia and Desmodium mainly have tropical distributions and were considered poorly suited for semi-arid temperate cropping systems. Of the remaining genera Glycyrrhiza and Crotalaria species showed many suitable traits, including an erect growth habit, a low propensity to shatter, flowers and fruits borne at the end of branches and moderate to large seeds (5 and 38 mg, respectively). The species for which sufficient information was available that were considered highest priority for further investigation were Glycine canescens, Cullen tenax, Swainsona canescens, Swainsona colutoides, Trigonella suavissima, Kennedia prorepens, Glycyrrhiza acanthocarpa, Crotalaria cunninghamii and Rhynchosia minima.

Albinism does not correlate with biparental inheritance of plastid DNA in interspecific hybrids in Cicer species

Maya Kumari et al. — Tue, 27 Dec 2011 17:12:32 PST

Cultivated chickpea (Cicer arietinum) was crossed with its wild relatives from the genus Cicer to transfer favorable genes from the wider gene pool into the cultivar. Post-hybridization barriers led to yellowing and subsequent senescence from as early as 5 days after fertilization, however, the ovules of hybrid embryos could be rescued in vitro. Hybrids were classified as green, partially green or albino. The hybrid status of regenerated plantlets in vitro was confirmed by amplification of nuclear DNA markers. To check whether chloroplast development correlated with plastid DNA inheritance in these crosses, primers were designed using conserved plastid gene sequences from wild and cultivated species. All three possible plastid inheritance patterns were observed: paternal, maternal and biparental. This is the first report of biparental inheritance of plastid DNA in Cicer. No correlation was observed between parental origin of the plastid genome and degree of albinism, indicating that chloroplast development in hybrid genotypes was mostly influenced by nuclear factors.

Poorly formed chloroplasts are barriers to successful interspecific hybridization in chickpea following in vitro embryo rescue

Heather J. Clarke et al. — Sun, 20 Nov 2011 18:10:52 PST

Albinism is viewed as a major experimental bottleneck during wide hybridization in several species; the phenomenon is also widely reported in androgenesis and doubled haploid cultures. In this study, when chickpea (Cicer arietinum) was crossed with distant wild relatives, C. judaicum and C. pinnatifidum, the only hybrid embryos that survived were those rescued using in vitro techniques. Fourteen to 21-day-old embryos were incubated in ML6 medium with 90 g l⁻¹ sucrose, 1 mg l⁻¹ zeatin and 0.25 mg l⁻¹ indole acetic acid. Germinating embryos were dissected from the ovule and transferred to fresh medium without growth regulators. Later, shoots were micropropagated on solid MS medium, supplemented with B5 vitamins, 30 g l⁻¹ sucrose, 0.1 mg l⁻¹ 6-benzyladenine and 0.01 mg l⁻¹ naphthaleneacetic acid. Although some post-hybridization barriers were overcome by rescue in vitro, regenerated hybrid plantlets failed to thrive in culture and few survived transfer to soil. Here we report findings from characterization of this valuable breeding material, as a step towards a better understanding of albinism in chickpea wide hybrids and other plant tissue cultures. Following proliferation, hybrids were phenotyped as green, pale green and albino. Genotype affected pod set, regeneration and albinism. Plastid ultrastructure studies using transmission electron microscopy revealed that thylakoid membranes were well-formed in green hybrids but not in albinos. Spectrophotometric analysis of chlorophyll a, chlorophyll b and total carotenoids revealed that chlorophyll content was three to fourfold lower in albino compared to green hybrids; moreover green hybrids had two to threefold lower total chlorophyll content than in vitro-grown plantlets of their parents. In contrast, carotenoids were higher in some albino phenotypes and lower in others; however overall differences in carotenoids were less marked between all genotypes compared to chlorophyll pigments. Genetic variability between different wide crosses provides an opportunity to select certain chickpea parents and wild species which give rise to more frequent green hybrid regenerants. In future, only these hybrids will be maintained and multiplied for transfer to the glasshouse in our program.

Growth, yield and seed composition of native Australian legumes with potential as grain crops

Lindsay W. Bell et al. — Mon, 14 Nov 2011 22:26:59 PST

BACKGROUND: Many Australian native legumes grow in arid and nutrient-poor environments. Yet few Australian herbaceous legumes have been investigated for domestication potential. This study compared growth and reproductive traits, grain yield and seed composition of 17 native Australian legumes with three commercial grain legumes.

RESULTS: Seed yields of seven native legumes were greater than 40% of Cicer arietnum, with highest seed yields and harvest indices in Glycine sp. (14.4 g per plant, 0.54 g g⁻¹) and Lotus cruentus (10.2 g per plant, 0.65 g g⁻¹). Five native species flowered earlier than field pea (Pisum sativa) (109 days), though many were slower to flower and set seed. Largest seeds were found in Glycine canescens (17 mg), with seed of other native species 14 times smaller than commercial cultivars. Seed composition of many native legumes was similar to commercial cultivars (200–330 g protein kg⁻¹ dry weight (DW), 130–430 g dietary fibre kg⁻¹ DW). Two Cullen species had high fat content (greater than 110 g kg⁻¹ DW) and Trigonella sauvissima had the highest crude protein content (370 g kg⁻¹ DW).

CONCLUSION: The seed composition and reproductive traits of some wild native Australian legumes suggest they could offer potential as grain crops for soils and environments where the current grain legumes are uneconomic. Further evaluation of genetic diversity, especially for seed size, overall productivity, and reproductive development is needed.

The enigma of 3400 years BP coastal oolites in tropical northwest Western Australia… why then, why there?

Paul Hearty et al. — Mon, 31 Oct 2011 00:17:32 PDT

Oolites crop out along the northwestern coast of Western Australia at Port Smith, about 80 km SW of Broome. An oolitic coastal ridge truncated by marine erosion exposes subtidal, intertidal, and supratidal (aeolian) facies. The deposits are firmly indurated and composed of about 75% tangentially and moderately thickly layered, aragonitic ooid grains with over 90% quartz nuclei.

Global sea-level fluctuations during the Last Interglaciation (MIS 5e)

Paul J. Hearty et al. — Sun, 30 Oct 2011 23:48:25 PDT

The geomorphology and morphostratigraphy of numerous worldwide sites reveal the relative movements of sea level during the peak of the Last Interglaciation (Marine Isotope Stage (MIS) 5e, assumed average duration between 130±2 and 119±2 ka). Because sea level was higher than present, deposits are emergent, exposed, and widespread on many stable coastlines. Correlation with MIS 5e is facilitated by similar morphostratigraphic relationships, a low degree of diagenesis, uranium–thorium (U/Th) ages, and a global set of amino-acid racemization (AAR) data. This study integrates information from a large number of sites from tectonically stable areas including Bermuda, Bahamas, and Western Australia, and some that have experienced minor uplift (∼2.5 m/100 ka), including selected sites from the Mediterranean and Hawaii. Significant fluctuations during the highstand are evident at many MIS 5e sites, revealed from morphological, stratigraphic, and sedimentological evidence. Rounded and flat-topped curves derived only from reef tracts are incomplete and not representative of the entire interglacial story. Despite predictions of much different sea-level histories in Bermuda, the Bahamas, and Western Australia due to glacio- and hydro-isostatic effects, the rocks from these sites reveal a nearly identical record during the Last Interglaciation.

High-precision U-series measurements of more than 500,000 year old fossil corals

Morten B. Andersen et al. — Sun, 30 Oct 2011 23:26:12 PDT

Robust, independent age constraints on the absolute timing of climate events based on the U-series dating of fossil coral are sparse before the last glacial cycle. Using multiple-collector inductively coupled plasma mass spectrometry with multiple-Faraday protocols, we are able to date ∼ 600 ka samples with an uncertainty of better than ± 15 ka (2σ), representing a three-fold improvement in precision compared with previous techniques. Using these methods, we report U-series measurements for a suite of > 500 thousand year old (ka) corals from Henderson Island, an emergent atoll in the south-central Pacific Ocean. The fossil corals show extraordinarily little diagenetic alteration for their age and the best-preserved sample yields a U-series age of 600 ± 15 ka (2σ), which overlaps with the timing of the warm Marine Isotope Stage (MIS) 15 interglacial. The open-system model of Villemant and Feuillet [Villemant B. and Feuillet N. (2003) Dating open systems by the ²³⁸U–²³⁴U–²³⁰Th method: application to Quaternary reef terraces. Earth and Planetary Science Letters 210(1–2), 105–118.] and the linear regression (or open-system isochron) is clearly limited for such old samples. However, the open-system model developed by Thompson et al. [Thompson W.G., Spiegelman M.W., Goldstein S.L., and Speed R.C. (2003) An open-system model for U-series age determinations of fossil corals. Earth and Planetary Science Letters 210(1–2), 365–381.] appears to reliably correct for open-system effects in roughly half of the corals, giving a MIS 15 origin for these. Thus the data provide evidence that the systematic addition of ²³⁰Th and ²³⁴U through α-recoil is a dominant open-system process occurring in the Henderson Island fossil reef system. Several coral samples yield significantly older Thompson et al. open-system ages between 650 and 750 ka. The uncertainty on these ages (typically ± 30 kyrs) is too great for precise assignment but most data overlap with the MIS 17 interglacial. The reliability of these ages is currently unclear. It is shown that separate aliquots of the same coral can yield different Thompson model ages. Therefore, there appear to be additional diagenetic mechanisms that create further anomalous excursions in the U-series systematics, limiting the reliability of the Thompson et al. open-system model.

U-series evidence for widespread reef development in Shark Bay during the last interglacial

Michael J. O'Leary et al. — Sun, 30 Oct 2011 22:55:29 PDT

Field observations and U-series ages reveal that Shark Bay, Western Australia (WA) has been inundated by the sea on at least three occasions during the Late Pleistocene/Holocene, resulting in a succession of marine deposits around the Bay. The exact age of these deposits has until now been problematic due to a lack of reliable and accurate age data. This study reports 16 new U-series coral dates from emergent reef deposits around Shark Bay, and point to an extended period of coral reef development during the peak of the last interglacial, marine isotope stage (MIS) 5e. This is attributed to enhancement of marine circulation within the reaches and basins, a result of higher sea levels and an absence of major sill and bank structures. Stromatolites are absent from the geological record within Shark Bay until the late Holocene, suggesting that sea levels and marine sedimentary processes that have operated during the present sea-level highstand are unique to this period. There is little direct evidence of fossil reef development occurring during interglacials of the middle/late Pleistocene (MIS 9/11).

Geomorphic evidence of major sea-level fluctuations during marine isotope substage-5e, Cape Cuvier, Western Australia

M J. O'Leary et al. — Sun, 30 Oct 2011 22:34:28 PDT

A detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at Cape Cuvier, Western Australia, reveals two morphologically distinct units. A lower, well-developed accretional reef terrace between 3 and 5.5 m above MLWS (mean low-water springs; hereafter denoted as “+”) represents an extended interval of stable sea level. An upper erosional terrace and incipient coralgal rim between + 8.5 to 10.5 m represents a brief sea-level stillstand at this higher elevation. These features suggest the lower and upper terraces developed during discrete sea-level events. In an attempt to better define the timing of emplacement of each marine unit, 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with U-series dating. Unfortunately, all coral samples exhibited elevated δ²³⁴U_initial values, suggesting that pervasive uptake of ²³⁴U-enriched uranium and ²³⁰Th thorium had occurred. Despite the shortcomings of absolute dating, a succession of events can be resolved though morphostratigraphic relationships. Comparison of the facies relationships, coral growth, and morphostratigraphic features between the lower and upper terraces indicates that an early to mid MIS 5e stillstand at + 3 to 5 m was followed by a late rise to + 8.5 to 10.5 m. This agrees with an emerging global view of MIS 5e sea-level history derived from stable carbonate platforms, rejecting the hypothesis that these higher sea-level benchmarks are an artefact of localized tectonic processes.

Geographical patterns of genetic variation in the world collections of wild annual Cicer characterized by amplified fragment length polymorphisms

F Shan et al. — Sun, 23 Oct 2011 23:54:46 PDT

Cicer reticulatum, C. echinospermum, C. bijugum, C. judaicum, C. pinnatifidum, C. cuneatum and C. yamashitae are wild annual Cicer species and potential donors of valuable traits to improve chickpea (C. arietinum). As part of a large project to characterize and evaluate wild annual Cicer collections held in the world gene banks, AFLP markers were used to study genetic variation in these species. The main aim of this study was to characterize geographical patterns of genetic variation in wild annual Cicer germplasm. Phylogenetic analysis of 146 wild annual Cicer accessions (including two accessions in the perennial C. anatolicum and six cultivars of chickpea) revealed four distinct groups corresponding well to primary, secondary and tertiary gene pools of chickpea. Some possible misidentified or mislabelled accessions were identified, and ILWC 242 is proposed as a hybrid between C. reticulatum and C. echinospermum. The extent of genetic diversity varied considerably and was unbalanced between species with greatest genetic diversity found in C. judaicum. For the first time geographic patterns of genetic variation in C. reticulatum, C. echinospermum, C. bijugum, C. judaicum and C. pinnatifidum were established using AFLP markers. Based on the current collections the maximum genetic diversity of C. reticulatum, C. echinospermum, C. bijugum and C. pinnatifidum was found in southeastern Turkey, while Palestine was the centre of maximum genetic variation for C. judaicum. This information provides a solid basis for the design of future collections and in situ conservation programs for wild annual Cicer.

Toward Doubled Haploid Production in the Fabaceae: Progress, Constraints, and Opportunities

J S. Croser et al. — Sun, 23 Oct 2011 23:33:49 PDT

The Fabaceae species have a major role to play in sustainable farming systems, but they have lagged behind other families in respect to the development of doubled haploid protocols for plant improvement. Currently, no plant improvement program uses doubled haploids on a routine basis for any member of the Fabaceae. There has recently been renewed interest in haploid research as the usefulness of doubled haploid material in molecular mapping has become clear. This review provides a comprehensive account of the current information regarding the development of haploid protocols in the Fabaceae. In the Fabaceae crop species there have been isolated reports of haploid plant induction in the phaseoloid clade; soybean, cowpea and pigeonpea, as well as promising progress towards haploidy in peanut and winged bean. As yet there have been no reports of haploid plant production in the galegoid clade, but early stage haploid embryogenesis has been achieved in chickpea, field pea, and lupin. Success in the production of haploid plants has also been reported within the pasture genera Lotus, Medicago, and Trifolium and the arboreal genera Cassia, Peltophorum, and Albizzia. A review of the literature has enabled us to identify some general similarities between the protocols developed for haploid plant induction across the various legumes. These are the culture of intact anthers; use of a cold pretreatment to induce sporophytic development; targeting of microspores at the uninucleate stage of development; and use of MS (Murashige and Skoog, 1962) based nutrient medium with plant growth regulators to encourage continued division following induction. These protocol commonalities will assist researchers to identify approaches suited to their target Fabaceae species. The paucity of research funding for haploid research in most Fabaceae species has highlighted the need for strong collaborative linkages between institutions and researchers.

Successful stem cutting propagation of chickpea, its wild relatives and their interspecific hybrids

N Danehloueipour et al. — Sun, 23 Oct 2011 23:06:06 PDT

A successful stem cutting method was developed to propagate chickpea (Cicer arietinum L.), its crossable wild annual relatives (C. reticulatum Ladiz. and C. echinospermum P.H. Davis) and their interspecific hybrids. The effect of plant growth regulator powder (0.5 mg/g indole butyric acid and 0.5 mg/g naphthalene acetic acid), honey, combined honey + plant growth regulator powder, different growth stages of the donor plant, and rooting substrates on rooting rate, root number, root length, and survival rate were investigated. The highest propagation success rate was achieved when cuttings were taken at the pre-flowering stage, treated with plant growth regulator powder and grown in a sand + potting mix substrate. The rooting rate ranged from 87.5 to 100% for chickpea, C. reticulatum and C. echinospermum, and interspecific hybrids. All of the accessions examined in the study were successfully propagated with the new method. This study provides a simple and efficient technique for vegetative propagation of Cicer species which will be useful for the multiplication of seed, production of clones for disease screening or for the development of mapping populations.

Chickpea molecular breeding: New tools and concepts

Teresa Millan et al. — Sun, 23 Oct 2011 22:49:10 PDT

Chickpea is a cool season grain legume of exceptionally high nutritive value and most versatile food use. It is mostly grown under rain fed conditions in arid and semi-arid areas around the world. Despite growing demand and high yield potential, chickpea yield is unstable and productivity is stagnant at unacceptably low levels. Major yield increases could be achieved by development and use of cultivars that resist/tolerate abiotic and biotic stresses. In recent years the wide use of early maturing cultivars that escape drought stress led to significant increases in chickpea productivity. In the Mediterranean region, yield could be increased by shifting the sowing date from spring to winter. However, this is hampered by the sensitivity of the crop to low temperatures and the fungal pathogen Ascochyta rabiei. Drought, pod borer (Helicoverpa spp.) and the fungus Fusarium oxysporum additionally reduce harvests there and in other parts of the world. Tolerance to rising salinity will be a future advantage in many regions. Therefore, chickpea breeding focuses on increasing yield by pyramiding genes for resistance/tolerance to the fungi, to pod borer, salinity, cold and drought into elite germplasm. Progress in breeding necessitates a better understanding of the genetics underlying these traits. Marker-assisted selection (MAS) would allow a better targeting of the desired genes. Genetic mapping in chickpea, for a long time hampered by the little variability in chickpea’s genome, is today facilitated by highly polymorphic, co-dominant microsatellite-based markers. Their application for the genetic mapping of traits led to inter-laboratory comparable maps. This paper reviews the current situation of chickpea genome mapping, tagging of genes for ascochyta blight, fusarium wilt resistance and other traits, and requirements for MAS. Conventional breeding strategies to tolerate/avoid drought and chilling effects at flowering time, essential for changing from spring to winter sowing, are described. Recent approaches and future prospects for functional genomics of chickpea are discussed.

Embryo rescue and plant regeneration in vitro of selfed chickpea (Cicer arietinum L.) and its wild annual relatives

H J. Clarke et al. — Sun, 23 Oct 2011 22:20:47 PDT

The main constraint to the transfer of desired traits into cultivated chickpea from wild Cicer relatives is the presence of post-zygotic barriers which result in abortion of the immature embryo following interspecific hybridisation. Rescue of hybrid embryos in vitro and regeneration of hybrid plantlets could allow chickpea breeders to transfer desirable traits from wild relatives of chickpea. The development of embryo rescue techniques using selfed chickpea and selfed wild relatives is being used as a first step to protocols for wide hybrids. Optical microscopy studies of embryogenesis, in both selfs and hybrids, identified deleterious changes in the fertilised hybrid seed as early as 2–4 days after pollination in some crosses. These observations suggest that the appropriate time to rescue chickpea × C. bijugum hybrids is at the early globular stage of embryogenesis (2–7 days old), which requires the development of a complex tissue culture medium. In contrast hybrids between chickpea × C. pinnatifidum abort later (up to 15–20 days old) at the heart-shaped or torpedo stages, and are easier to rescue in vitro. Genotype also plays a significant role in the ability of immature selfed ovules to germinate in vitro. In this paper we report on the optimisation of␣protocols for rescueing immature embryos using selfed chickpea and its wild relatives in ovule, and subsequently to regenerate plantlets.

Identification of duplicates and fingerprinting of primary and secondary wild annual Cicer gene pools using AFLP markers

F Shan et al. — Sun, 23 Oct 2011 21:58:56 PDT

Wild annual Cicer gene pools contain valuable germplasm for chickpea improvement programs. Previous research showed that duplication might exist in accessions collected from these gene pools, which would hinder chickpea breeding and related research. AFLP (amplified fragment length polymorphism) markers were used to fingerprint the world collections of the primary and secondary gene pools including C. reticulatum Lad., C. bijugum K.H. Rech., C. judaicum Boiss. and C. pinnatifidum Jaub. et Sp. Duplicates were detected in a total of 24 accessions in both the gene pools, highlighting the necessity to fingerprint the germplasm. Genotypic difference was detected as gene pool specific, species specific and accession specific AFLP markers. These were developed into fingerprinting keys for accession identification between and within species and gene pools. Use of AFLP markers to detect duplicates and to identify accessions is a reliable method which will assist in the characterisation and use of wild annual Cicer germplasm in chickpea improvement programs. We recommend the procedure presented in this paper as a standard approach for the precise genetic identification and characterisation of future world collections of wild Cicer, to keep germplasm integrity and to benefit chickpea breeding and related research programs.

Diallel analyses reveal the genetic control of resistance to ascochyta blight in diverse chickpea and wild Cicer species

N Danehloueipour et al. — Sun, 23 Oct 2011 21:37:17 PDT

Ascochyta blight is a major fungal disease affecting chickpea production worldwide. The genetics of ascochyta blight resistance was studied in five 5 × 5 half-diallel cross sets involving seven genotypes of chickpea (ICC 3996, Almaz, Lasseter, Kaniva, 24B-Isoline, IG 9337 and Kimberley Large), three accessions of Cicer reticulatum (ILWC 118, ILWC 139 and ILWC 184) and one accession of C. echinospermum (ILWC 181) under field conditions. Both F₁ and F₂ generations were used in the diallel analysis. The disease was rated in the field using a 1–9 scale. Almaz, ICC 3996 and ILWC 118 were the most resistant (rated 3–4) and all other genotypes were susceptible (rated 6–9) to ascochyta blight. Estimates of genetic parameters, following Hayman’s method, showed significant additive and dominant gene actions. The analysis also revealed the involvement of both major and minor genes. Susceptibility was dominant over resistance to ascochyta blight. The recessive alleles were concentrated in the two resistant chickpea parents ICC 3996 and Almaz, and one C. reticulatum genotype ILWC 118. The wild Cicer accessions may have different major or minor resistant genes compared to the cultivated chickpea. High narrow-sense heritability (ranging from 82% to 86% for F₁ generations, and 43% to 63% for F₂ generations) indicates that additive gene effects were more important than non-additive gene effects in the inheritance of the trait and greater genetic gain can be achieved in the breeding of resistant chickpea cultivars by using carefully selected parental genotypes.

Leaf type is not associated with ascochyta blight disease in chickpea (Cicer arietinum L.)

Nader Danehloueipour et al. — Sun, 23 Oct 2011 21:15:36 PDT

The three major leaf types in chickpea are normal compound leaf, simple leaf and multipinnate. Simple leaf types are less commonly cultivated worldwide and are often reputed to be susceptible to ascochyta blight disease, whereas other leaf types range from resistant to susceptible. This study determined the association between host plant resistance to ascochyta blight and different leaf types in segregating populations derived from crosses between disease resistant and susceptible chickpea genotypes. In addition, the inheritance of disease resistance and leaf type was investigated in intraspecific progeny derived from crosses between two resistant genotypes with normal leaf type (ICC 3996 and Almaz), one susceptible simple leaf type (Kimberley Large) and one susceptible multipinnate leaf type (24 B-Isoline). Our results showed that, in these segregating populations, susceptibility to ascochyta blight was not linked to multipinnate or simple leaf types; resistance to ascochyta blight depended more on genetic background than leaf shape; leaf type was controlled by two genes with a dihybrid supplementary gene action; normal leaf type was dominant over other leaf types; and inheritance of ascochyta blight resistance was controlled by two major genes, one dominant and one recessive. Since there was no linkage between ascochyta blight susceptibility and leaf type, breeding various leaf types with ascochyta blight resistance is a clear possibility. These results have significant implications for chickpea improvement, as most current extra large seeded kabuli varieties have a simple leaf type.