Estimation of genetic diversity among 34 genotypes in the genus <Emphasis Type="Italic">Cajanus</Emphasis> with contrasting host response to the pod borer and its allied pests

The genetic divergence among 34 genotypes belonging to 12 species of genus Cajanus were carried out using plant pest interaction and DNA marker analysis. Principal component analysis based on average percentage of pod damage caused by pod borer, plume moth, and blue butterfly in the field conditions, and growth of their larva and pupa on an artificial diet in vitro dispersed these genotypes into four coordinates evincing high genetic divergence as expected. DNA marker analysis using 11 pairs of SSR and nine ISSR primers showed higher polymorphism at the species level, and these primers exhibited variation with regard to average band informativeness, resolving power, and PIC value. No single primer was able to distinguish between all the 34 genotypes of Cajanus but nine species specific amplified fragments were generated by five ISSR primers. The pairwise Jaccard’s similarity coefficient and Nei’s genetic distance values revealed a higher level of inter-specific genetic variation in the genus Cajanus. The clustering of genotypes based on Jaccard’s similarity coefficient vis-a-vis Nei’s genetic distance agreed with the sectional classification of the genus Cajanus. Seven cultivars of C. cajan and the genotypes of their wild progenitor C. cajanifolius remained in one cluster, whereas accessions of C. platycarpus and C. scarabaeoides were out grouped. The rest of the genotypes belonging to nine species of Cajanus formed another cluster. The principal coordinate analysis also supported this clustering pattern. Moreover, these findings have good many implications for future breeding endeavors aimed at the introgression of pod borer resistance alleles.     

Genetic transformation of pigeonpea (<Emphasis Type="Italic">Cajanus cajan</Emphasis> L.) and screening transgenic progenies based on lateral root inhibition

Production of transgenic pigeonpea is becoming increasingly important, but the methods currently employed in production and subsequent screening still requires improvement. Here, we describe Agrobacterium-mediated genetic transformation of pigeonpea with reporter uidA (gus) gene and selectable marker, neomycin phospho-transferase (nptII) gene. Histochemical assay demonstrate localization of gus activity in cells and transformed plants. Overall, a transformation frequency of 0.33% was achieved using the protocol. Grafting of in vitro-regenerated healthy shoots indicates higher survival percent (72.6%), when stock and scion are of the same variety. Seeds harvested from primary transgenic plants can be screened based on lateral root inhibition strategy. Approximately 87% of the screened T₁ plants were found to be PCR positive. In conclusion, in vitro grafting of transgenic pigeonpea shoots leads to better plant establishment and screening based on lateral root inhibition leads to quick identification of positive segregants.     

<Emphasis Type="Italic">Rf4</Emphasis> has minor effects on the fertility restoration of wild abortive-type cytoplasmic male sterile <Emphasis Type="Italic">japonica</Emphasis> (<Emphasis Type="Italic">Oryza sativa</Emphasis>) lines

Wild abortive (WA)-type cytoplasmic male sterility (CMS) has been exclusively used for breeding three-line hybrid indica rice, but it has not been applied for generating japonica hybrids because of the difficulties related to breeding japonica restorer lines. Determining whether the major restorer-of-fertility (Rf) gene used for indica hybrids can efficiently restore the fertility of WA-type japonica CMS lines may be useful for breeding WA-type japonica restorer lines. In this study, japonica restorer lines for Chinsurah Boro II (BT)-type CMS exhibited varying abilities to restore the fertility of ‘WA-LiuqianxinA’, which is a WA-type japonica CMS line. Additionally, Rf genes for WA-type CMS were identified in the BT-type japonica restorers. Meanwhile, ‘C9083’, which is a BT-type japonica restorer, exhibited a limited ability to restore the fertility of WA-type japonica CMS lines, and a genetic analysis revealed that the fertility restoration was controlled by one locus. The Rf gene was mapped to an approximately 370-kb physical region and was identified as Rf4. Furthermore, Rf gene dosage effects and the temperature influenced the fertility restoration of WA-type japonica CMS lines. This study is the first to confirm that Rf4 has only minor effects on the fertility restoration of WA-type japonica CMS lines. These results may be relevant for the development of WA-type japonica hybrids.     

Identification of genetic sources with attenuated <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>-induced symptoms in <Emphasis Type="Italic">Solanum</Emphasis> (section <Emphasis Type="Italic">Lycopersicon</Emphasis>) germplasm

The whitefly-transmitted Tomato chlorosis virus (ToCV) (genus Crinivirus) is associated with yield and quality losses in field and greenhouse-grown tomatoes (Solanum lycopersicum) in South America. Therefore, the search for sources of ToCV resistance/tolerance is a major breeding priority for this region. A germplasm of 33 Solanum (Lycopersicon) accessions (comprising cultivated and wild species) was evaluated for ToCV reaction in multi-year assays conducted under natural and experimental whitefly vector exposure in Uruguay and Brazil. Reaction to ToCV was assessed employing a symptom severity scale and systemic virus infection was evaluated via RT-PCR and/or molecular hybridization assays. A subgroup of accessions was also evaluated for whitefly reaction in two free-choice bioassays carried out in Uruguay (with Trialeurodes vaporariorum) and Brazil (with Bemisia tabaci Middle-East-Asia-Minor1—MEAM1?=?biotype B). The most stable sources of ToCV tolerance were identified in Solanum habrochaites PI 127827 (mild symptoms and low viral titers) and S. lycopersicum ‘LT05’ (mild symptoms but with high viral titers). These two accessions were efficiently colonized by both whitefly species, thus excluding the potential involvement of vector-resistance mechanisms. Other promising breeding sources were Solanum peruvianum (sensu lato) ‘CGO 6711’ (mild symptoms and low virus titers), Solanum chilense LA1967 (mild symptoms, but with high levels of B. tabaci MEAM1 oviposition) and Solanum pennellii LA0716 (intermediate symptoms and low level of B. tabaci MEAM1 oviposition). Additional studies are necessary to elucidate the genetic basis of the tolerance/resistance identified in this set of Solanum (Lycopersicon) accessions.     

Stability of <Emphasis Type="Italic">Solanum aethiopicum</Emphasis> Shum accessions under varied water deficit stress levels and identification of pertinent breeding traits for resistance to water shortage

Drought is a major constraint to productivity of Solanum aethiopicum ‘Shum’ group due to loss in market and nutrient value of stressed plants. This study evaluated S. aethiopicum Shum group accessions to identify genotypes (G) that excel across moisture deficit stress levels (WLs). A split-plot arrangement composed of four WLs and twenty accessions of S. aethiopicum as main plot and sub-plot factors, respectively, was implemented in a screenhouse, and repeated for two experiments. In each experiment, there was a highly significant effect of at least two WLs on mean performance among at least two accessions for most of the traits at p < 0.05. Further, very highly significant WL × G interactions were obtained for leaf relative water content (LRWC), leaves per plant (LPP) and plant height (PH), and non-significant for leaf blade length and leaf blade width. The order of priority as breeding traits for stability superiority across WLs was suggested as LRWC > PH > LPP. Consequently, based on LRWC, the most superiorly stable accessions were identified as accession 160 followed by accessions 145, 137, 108P and 184G while the least stable ones were identified as accessions 163G, 141, 163 and 108. The broad sense heritability (H ²) for each of the three recommended traits for drought resistance breeding was above 0.9 thus supportive for a good response to selection. Drought stress negatively affected the performance of S. aethiopicum Shum group but the exhibited variation allowed for selection of superiorly stable genotypes.     

Resistance to <Emphasis Type="Italic">Cucumber green mottle mosaic virus</Emphasis> in <Emphasis Type="Italic">Cucumis sativus</Emphasis>

Cucumber green mottle mosaic virus (CGMMV) is a severe threat for cucumber production worldwide. At present, there are no cultivars available in the market which show an effective resistance or tolerance to CGMMV infection, only wild Cucumis species were reported as resistant. Germplasm accessions of Cucumis sativus, as well as C. anguria and C. metuliferus, were mechanically infected with the European and Asian strains of CGMMV and screened for resistance, by scoring symptom severity, and conventional RT-PCR. The viral loads of both CGMMV strains were determined in a selected number of genotypes using quantitative RT-PCR. Severe symptoms were found following inoculation in C. metuliferus and in 44 C. sativus accessions, including C. sativus var. hardwickii. Ten C. sativus accessions, including C. sativus var. sikkimensis, showed intermediate symptoms and only 2 C. sativus accessions showed mild symptoms. C. anguria was resistant to both strains of CGMMV because no symptoms were expressed and the virus was not detected in systemic leaves. High amounts of virus were found in plants showing severe symptoms, whereas low viral amounts found in those with mild symptoms. In addition, the viral amounts detected in plants which showed intermediate symptoms at 23 and 33 dpi, were significantly higher in plants inoculated with the Asian CGMMV strain than those with the European strain. This difference was statistically significant. Also, the amounts of virus detected over time in plants did not change significantly. Finally, the two newly identified partially resistant C. sativus accessions may well be candidates for breeding programs and reduce the losses produced by CGMMV with resistant commercial cultivars.     

Antixenosis and antibiosis mechanisms of resistance to pod borer, <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> in wild relatives of chickpea, <Emphasis Type="Italic">Cicer arietinum</Emphasis>

The noctuid pod borer, Helicoverpa armigera is one of the most damaging pests of chickpea, Cicer arietinum. The levels of resistance to H. armigera in the cultivated chickpea are low to moderate, but the wild relatives of chickpea have exhibited high levels of resistance to this pest. To develop insect-resistant cultivars with durable resistance, it is important to understand the contribution of different components of resistance, and therefore, we studied antixenosis and antibiosis mechanisms of resistance to H. armigera in a diverse array of wild relatives of chickpea. The genotypes IG 70012, PI 599046, IG 70022, PI 599066, IG 70006, IG 70018 (C. bijugum), ICC 506EB, ICCL 86111 (cultivated chickpea), IG 72933, IG 72953 (C. reticulatum), IG 69979 (C. cuneatum) and IG 599076 (C. chrossanicum) exhibited non preference for oviposition by the females of H. armigera under multi-choice, dual-choice and no-choice cage conditions. Based on detached leaf assay, the genotypes IG 70012, IG 70022, IG 70018, IG 70006, PI 599046, PI 599066 (C. bijugum), IG 69979 (C. cuneatum), PI 568217, PI 599077 (C. judaicum) and ICCW 17148 (C. microphyllum) suffered significantly lower leaf damage, and lower larval weights indicating high levels of antibiosis than on the cultivated chickpea. Glandular and non-glandular trichomes showed negative correlation with oviposition, while the glandular trichomes showed a significant and negative correlation with leaf damage rating. Density of non-glandular trichomes was negatively correlated with larval survival. High performance liquid chromatography (HPLC) fingerprints of leaf surface exudates showed a negative correlation of oxalic acid with oviposition, but positive correlation with malic acid. Both oxalic acid and malic acid showed a significant negative correlation with larval survival. The wild relatives exhibiting low preference for oviposition and high levels of antibiosis can be used as sources of resistance to increase the levels and diversify the basis of resistance to H. armigera in cultivated chickpea.     

Phenotypic variation in root architecture traits and their relationship with eco-geographical and agronomic features in a core collection of tetraploid wheat landraces (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L.)

To obtain varieties with root systems adapted to marginal environments it is necessary to search for new genotypes in genetically diverse materials, such as landraces that are more likely to carry novel alleles for different root features. A core collection of ‘durum’ wheat, including three subspecies (dicoccon, turgidum and durum) from contrasting eco-geographical zones, was evaluated for root traits and shoot weight at the seminal root stage. Distinctive rooting phenotypes were characterized within each subspecies, mainly in subsp. durum. Contrasting rooting types, including large roots with shallow distributions, and others with high root numbers were identified. Correlations with climatic traits showed that root shape is more relevant in adaptation to eco-geographical zones in subsp. dicoccon, whereas in subsp. turgidum and durum, which come from warmer and drier areas, both size and shape of roots could have adaptive roles. Root traits with the largest positive effects on certain yield components under limited water conditions included root diameter in subsp. dicoccon, root size in turgidum, and root number in durum. Additionally, shoot weight at the seedling stage had important effects in subsp. turgidum and durum. Twenty-eight marker–trait associations (MTAs) previously identified in this collection for agronomic or quality traits were associated with seminal root traits. Some markers were associated with only one root trait, but others were associated with up to six traits. These MTAs and the genetic variability characterized for root traits in this collection can be exploited in further work to improve drought tolerance and resource capture in wheat.     

Identification of quantitative trait loci associated with drought tolerance traits in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under PEG and field drought stress

Two recombinant inbred line F₁₀ rice populations (IAPAR-9/Akihikari and IAPAR-9/Liaoyan241) were used to identify quantitative trait loci (QTLs) for ten drought tolerance traits at the budding and early seedling stage under polyethylene glycol-induced drought stress, and two traits of leaf rolling index (LRI) and leaf withering degree (LWD) under field drought stress. The results showed that the drought-tolerance capacity of IAPAR-9 was stronger than that of Akihikari and Liaoyan241. Thirty-four QTLs for 12 drought tolerance traits were detected, and among them, in the IAPAR-9/Akihikari population, qLRI9-1 and qLRI10-1 for LRI were repeatedly detected in RM3600-RM553 on chromosome 9 and in RM6100-RM3773 on chromosome 10, respectively, at two times points of July 31 and August 13 in 2014. The two QTLs are stable against the environmental impact, and qLRI9-1 and qLRI10-1 explained 6.77–13.66% and 5.01–8.32% of the phenotypic variance, respectively, at the two times points. qLWD9-2 for LWD in the IAPAR-9/Liaoyan241 population contributed 8.73% of variation was detected in the same marker interval with the qLRI9-1, and qLRI1-1 for LRI and qLWD1-1 for LWD were located in the same marker interval RM11054-RM5646 on chromosome 1, which contributed 18.82 and 5.78% of phenotype variation respectively. qGV3 for germination vigor and qRGV3 for relative germination vigor at the budding stage were detected in the same marker interval RM426-RM570 on chromosome 3, which explained 14.98 and 16.30% of the observed phenotypic variation respectively, representing major QTLs. The above-mentioned stable or major QTLs regions could be useful for molecular marker assisted selection breeding, fine mapping, and cloning.     

Effects of genotype and environment on seed quality traits variability in interspecific cross-derived <Emphasis Type="Italic">Brassica</Emphasis> lines

Genotype (G), environment [i.e. year (Y) and location (L)] and their interaction (GYL) play an important role in the final expression of quality attributes. A multi-environment trial in selected interspecific cross-derived Brassica lines was conducted to evaluate the magnitude of G, Y, L and GYL effects on seed quality traits of Brassica genotypes under three locations in Poland, during the 2011–2013 cropping season. The oil, protein, fiber (Acid Detergent Fiber and Neutral Detergent Fiber) as well as glucosinolate contents was determined by near-infrared reflectance spectroscopy (NIRS) and significant differences were observed between tested Brassica genotypes and across harvesting years and growing locations. Generally, all tested hybrid lines displayed wider genetic variability for studied quality traits than control genotypes. Analysis of variance indicated that the main effects of genotypes, years and locations as well as all interactions were significant for all traits of study (except year?×?location interaction for glucosinolates). However, location had the most significant effect on oil, protein and fiber content while genotype had significant impact on glucosinolates content in Brassica seeds. Moreover, the individual lines having combination of desirable traits were also identified from F₅ to F₇ generations of tested hybrids.     

Further QTL mapping for yield component traits using introgression lines in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under drought field environments

To better understand the underlying mechanisms of agronomic traits related to drought resistance and discover candidate genes or chromosome segments for drought-tolerant rice breeding, a fundamental introgression population, BC₃, derived from the backcross of local upland rice cv. Haogelao (donor parent) and super yield lowland rice cv. Shennong265 (recurrent parent) had been constructed before 2006. Previous quantitative trait locus (QTL) mapping results using 180 and 94 BC₃F_6,7 rice introgression lines (ILs) with 187 and 130 simple sequence repeat (SSR) markers for agronomy and physiology traits under drought in the field have been reported in 2009 and 2012, respectively. In this report, we conducted further QTL mapping for grain yield component traits under water-stressed (WS) and well-watered (WW) field conditions during 3 years (2012, 2013 and 2014). We used 62 SSR markers, 41 of which were newly screened, and 492 BC₄F_2,4 core lines derived from the fourth backcross between D123, an elite drought-tolerant IL (BC₃F₇), and Shennong265. Under WS conditions, a total of 19 QTLs were detected, all of which were associated with the new SSRs. Each QTL was only identified in 1 year and one site except for qPL-12-1 and qPL-5, which additively increased panicle length under drought stress. qPL-12-1 was detected in 2013 between new marker RM1337 and old marker RM3455 (34.39 cM) and was a major QTL with high reliability and 15.36% phenotypic variance. qPL-5 was a minor QTL detected in 2013 and 2014 between new marker RM5693 and old marker RM3476. Two QTLs for plant height (qPHL-3-1 and qPHP-12) were detected under both WS and WW conditions in 1 year and one site. qPHL-3-1, a major QTL from Shennong265 for decreasing plant height of leaf located on chromosome 3 between two new markers, explained 22.57% of phenotypic variation with high reliability under WS conditions. On the contrary, qPHP-12 was a minor QTL for increasing plant height of panicle from Haogelao on chromosome 12. Except for these two QTLs, all other 17 QTLs mapped under WS conditions were not mapped under WW conditions; thus, they were all related to drought tolerance. Thirteen QTLs mapped from Haogelao under WS conditions showed improved drought tolerance. However, a major QTL for delayed heading date from Shennong265, qDHD-12, enhanced drought tolerance, was located on chromosome 12 between new marker RM1337 and old marker RM3455 (11.11 cM), explained 21.84% of phenotypic variance and showed a negative additive effect (shortening delay days under WS compared with WW). Importantly, chromosome 12 was enriched with seven QTLs, five of which, including major qDHD-12, congregated near new marker RM1337. In addition, four of the seven QTLs improved drought resistance and were located between RM1337 and RM3455, including three minor QTLs from Haogelao for thousand kernel weight, tiller number and panicle length, respectively, and the major QTL qDHD-12 from Shennong265. These results strongly suggested that the newly screened RM1337 marker may be used for marker-assisted selection (MAS) in drought-tolerant rice breeding and that there is a pleiotropic gene or cluster of genes linked to drought tolerance. Another major QTL (qTKW-1-2) for increasing thousand kernel weight from Haogelao was also identified under WW conditions. These results are helpful for MAS in rice breeding and drought-resistant gene cloning.     

Genotyping by sequencing of rice interspecific backcross inbred lines identifies QTLs for grain weight and grain length

Grain weight and grain length are the most stable components of rice yield and important indicators of consumer preference. Considering the potentials of wild rice and to enhance the rice yields to meet the increasing demands, 185 Backcross Inbred Lines (BILs) in the background of O. sativa ssp. indica cv. PR114, including 63 rufi-BILs derived from O. rufipogon IRGC104433 and 122 glumae-BILs from O. glumaepatula IRGC104387 were evaluated for mapping QTLs for yield and yield component traits using Genotyping by Sequencing (GBS). Phenotypic evaluation of BILs in three seasons spanning two locations revealed significant differences compared with recurrent parent. BILs which did not show significant differences for any trait under investigation, or similar based on pedigree, were excluded from GBS. Some glumae-BILs had to be excluded from mapping QTLs due to less sequence information. A custom designed approach for GBS data analysis identified 3322 informative SNPs in 55 rufi-BILs and 3437 informative SNPs in 79 glumae-BILs. QTL mapping identified one QTL for thousand grain weight (qtgw5.1), two for grain width (qgw5.1, qgw5.2) and one for grain length (qgl7.1) in rufi-BILs. In the glumae-BILs, three QTL for thousand grain weight (qtgw2.1, qtgw3.1, qtgw6.1) and two for grain length (qgl3.1, qgl7.1) were identified. Most of the grain weight and width QTL showed positive additive effect contributed by wild species allele, whereas the grain length QTL showed positive additive effect contributed by recurrent parent allele. Based on their physical position, none of the QTLs were found similar to previously cloned QTLs. QTLs for grain traits identified from low yielding wild relatives of rice reveals their significance in improving further the rice yields and widen the genetic base of cultivated rice.     

Marker assisted selection (MAS) for developing powdery mildew resistant pea cultivars

In this contribution we review the state of the art for genetic resistance to powdery mildew, caused by Erysiphe pisi, in pea (Pisum sativum L.) and potential use of marker-assisted selection (MAS) for developing disease resistant cultivars. Powdery mildew is important in many production regions worldwide and reduces yield and crop quality when present in epidemic proportions. Although genetic resistance to powdery mildew is available (er1 and er2) and has been durable since its characterization in 1969, recently a new dominant gene (Er3) has been reported in Pisum fulvum, a wild relative of pea that is different from previously reported er1 and er2. The efficacy of these genes may be at risk from the point of view of new pathotypes and pathogens. Erysiphe trifolii has been reported that was not previously known as a pathogen of pea powdery mildew. A continued search for new and diverse resistant sources remains a priority in pea breeding and special emphasis should be paid to selection of resistance that will prolong durability of existing resistance genes. Marker assisted selection is a new emerging approach for target breeding that has been intensively employed especially in cereals and has recently got popularity among legume breeders. With the advancement of genomic research, especially related to quantitative traits loci, the MAS is potentially anticipated future technique for routine plant breeding that is scarce in legumes at present. In pea, various DNA markers have been reported linked to er1, er2 and Er3 at varying distances in different mapping populations that are currently being used in breeding programs. Currently MAS of single gene is the most powerful approach and successes have been witnessed. If single marker is not close enough to the gene of interest then two flanking markers are considerably utilized to improve the correct identification that is being successfully employed in MAS for powdery mildew resistance in pea.     

Identification of QTLs controlling low-temperature germinability and cold tolerance at the seedling stage in rice (<Emphasis Type="Italic">Oryza Sativa</Emphasis> L.)

Both low-temperature germinability (LTG) and cold tolerance at the seedling stage (CTS) are important traits for rice. In this study, a rice population of recombinant inbred lines (RILs), derived from the backcross population of a cross between Dongnong422 and Kongyu131, was developed to detect quantitative trait loci (QTL) affecting LTG and CTS by using seed of different storage times. Correlation analysis indicated that there was no significant relationship between LTG and CTS, suggesting that cold tolerance might be genetic differences for LTG and CTS. In total, Twelve and twenty-three major QTLs were detected for LTG and CTS, respectively, which could explain greater than 10% of the phenotypical variation. Eight (qCG12-1, qGI12-1, qGV9-1, qMLIT12-1, qPV6-1, qMDG12-1, qLDWcold10-1, qLFWcold10-1) significant QTLs were mapped for different storage time, it concluded that such QTLs were not affected by environment (storage time) and were closely related QTLs to cold tolerance. One or more QTLs were identified for each trait with some of these QTLs co-locating, qMLIT7-1, qCG7-1, and qGI7-1 for LTG, qLFWcold10-1, and qLDWcold10-1 for CTS with contributions over 15% were mapped common marker interval, respectively, co-location of QTLs for different traits can be an indication that a locus has pleiotropic effects on multiple traits due to a common mechanistic basis. Two lines, RIL128 and RIL73, might be valuable to improve the LTG and CTS through a combination of crosses. The identified QTLs might be applicable to improve the rice cold tolerance by the marker-assisted selection approach.     

Expression of the <Emphasis Type="Italic">Ga1-s</Emphasis> gametophyte factor in <Emphasis Type="Italic">shrunken2</Emphasis> sweet corn

Outcrossing is an important problem in specialty maize (Zea mays L.) that can be prevented by using gametophyte factors, such as Ga1-s, which preserve maize plants from pollen contamination. Our objective was to check if the gametophyte factor Ga1-s can protect sweet corn homozygous for sh2 in an efficient and stable way. We combined Ga1-s and sh2 by crossing two popcorn and three sweet corn inbred lines, respectively, in a North Carolina Design II, followed by an ear-to-row breeding program with selection for sh2 phenotype and absence of outcrossing. The released inbred lines homozygous for Ga1-s and sh2 were used for obtaining five hybrids that were evaluated for outcrossing and agronomic performance. Our results show that the gametophyte factor Ga1-s effectively protects the sh2 plants and that this effect was stable across environments. However, the agronomic performance of these inbred lines must be improved. Popcorn donors and sweet corn receptors of Ga1-s were unevenly represented in the released Ga1-s / sh2 inbred lines, suggesting that the viability of sh2 is affected by the genotypes involved. Therefore, breeders should pay attention to the choice of donors of Ga1-s that favors the viability of sh2.     

Analysis of population structure and genetic diversity reveals gene flow and geographic patterns in cultivated rice (<Emphasis Type="Italic">O. sativa</Emphasis> and <Emphasis Type="Italic">O. glaberrima</Emphasis>) in West Africa

To fully exploit the diversity in African rice germplasm and to broaden the gene pool reliable information on the population genetic diversity and phenotypic characteristics is a prerequisite. In this paper, the population structure and genetic diversity of 42 cultivated African rice (Oryza spp.) accessions originating from West Africa (Benin, Mali and Nigeria, Liberia etc.) were investigated using 20 simple sequence repeats (SSR) and 77 amplified fragment length polymorphisms (AFLP). Additionally, field trials were set up to gain insight into phenotypic characteristics that differentiate the genetic populations among rice accessions. The analysis revealed considerably high polymorphisms for SSR markers (PIC mean?=?0.78) in the germplasm studied. A significant association was found between AFLP markers and geographic origin of rice accessions (R?=?0.72). Germplasm structure showed that Oryza sativa accessions were not totally isolated from Oryza glaberrima accessions. The results allowed identification of five O. glaberrima accessions which grouped together with O. sativa accessions, sharing common alleles of 18 loci out of the 20 SSR markers analyzed. Population structure analysis revealed existence of a gene flow between O. sativa and O. glaberrima rice accessions which can be used to combine several interesting traits in breeding programs. Further studies are needed to clarify the contributions of this gene flow to valuable traits such as abiotic and biotic stresses including disease resistance.     

Selection of pea genotypes with partial resistance to <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> across a wide range of temperatures and periods of high relative humidity

Partial resistance to Sclerotinia sclerotiorum based on stem lesion advancement was assessed for nine wild pea genotypes from five geographic origins and two cultivated genotypes, when peas were inoculated and incubated at all combinations of five temperatures (15.6, 18.3, 21.1, 23.9, 29.4°C) and four period(s) of high relative humidity (PHRH; 12, 24, 48, 72 h). PHRH of 12 and 24 h should not be used when screening plants for resistance to S. sclerotiorum regardless of the incubation temperature, since stem lesions are rarely (2.7%) visible at 12 h and there were no significant differences (P ≤ 0.05) in lesion lengths among and within genotypes at all temperatures assessed after 24 h. However, PHRH of 48 and 72 h are recommended for use to assess partial resistance since significant differences in stem lesion length among the genotypes were observed and characterized for these periods. Genotypes with cool (15.6 and 18.3°C) versus warm (23.9 and 29.4°C) temperature partial resistance to S. sclerotiorum were identified, and genotypes PI 240515 and PI 169603 appear to have the best cool and warm temperature partial resistance, respectively, among the genotypes assessed. A temperature of 21.1°C was the optimal temperature favouring lesion advancement for the majority of the genotypes evaluated. PI 169603 demonstrated the best partial resistance to S. sclerotiorum across the widest temperature and PHRH ranges and is recommended to plant breeders as the best single genotype to develop future cultivars with improved partial resistance to S. sclerotiorum based on stem lesion advancement.     

Functional markers delimiting a <Emphasis Type="Italic">Medicago</Emphasis> orthologue of pea symbiotic gene <Emphasis Type="Italic">NOD3</Emphasis>

Symbiotic gene mutated in the pea (Pisum sativum L.) line RisfixC is a determinant of the number of symbiotic root nodules. In parallel to a sharp increase in nodule number, its mutational inactivation brings about the insensitivity of nodulation to the ambient nitrate level (Nts trait). Using the established localization to the SYM2-NOD3 region of the pea linkage group I, functional PCR markers were developed for the orthologous region on the chromosome 5 of the model species Medicago truncatula. Owing to the conservation of the binding regions of the designed primers, pea orthologues were successfully amplified with 60% of the primer pairs tested. When applied to a mapping pea population from the cross of the line RisfixC x Afghanistan L1268 (sym2), the new markers allowed to localize the supernodulation mutation within 2.5 cM confidence interval in the pea genome. The placement of the functional markers on the M. truncatula chromosome 5 confined the orthologous gene location to eight overlapping BACs spanning approximately 710 kbp (positions 37,755,678–38,467,472). The narrowed list of the annotated Medicago genes in combination with the published data on their symbiotic and nitrate regulation can be used for the candidate gene identification, together with the requirements imposed by the known function in nodule number initiation and nitrate sensing. In addition, the new markers are applicable for tracking the RisfixC allele in breeding programmes aimed at the improvement of symbiotic performance.     

Diploid and tetraploid progenitors of wheat are valuable sources of resistance to the root lesion nematode <Emphasis Type="Italic">Pratylenchus</Emphasis><Emphasis Type="Italic">thornei</Emphasis>

The root lesion nematode Pratylenchus thornei is widely distributed in Australian wheat (Triticum aestivum) producing regions and can reduce yield by more than 50%, costing the industry AU$50 M/year. Genetic resistance is the most effective form of management but no commercial cultivars are resistant (R) and the best parental lines are only moderately R. The wild relatives of wheat have evolved in P. thornei-infested soil for millennia and may have superior levels of resistance that can be transferred to commercial wheats. To evaluate this hypothesis, a collection of 251 accessions of wheat and related species was tested for resistance to P. thornei under controlled conditions in glasshouse pot experiments over two consecutive years. Diploid accessions were more R than tetraploid accessions which proved more R than hexaploid accessions. Of the diploid accessions, 11 (52%) Aegilops speltoides (S-[B]-genome), 10 (43%) Triticum monococcum (A ^m -genome) and 5 (24%) Triticum urartu (A ^u -genome) accessions were R. One tetraploid accession (Triticum dicoccoides) was R. This establishes for the first time that P. thornei resistance is located on the A-genome and confirms resistance on the B-genome. Since previous research has shown that the moderate levels of P. thornei resistance in hexaploid wheat are dose-dependent, additive and located on the B and D-genomes, it would seem efficient to target A-genome resistance for introduction to hexaploid lines through direct crossing, using durum wheat as a bridging species and/or through the development of amphiploids. This would allow resistances from each genome to be combined to generate a higher level of resistance than is currently available in hexaploid wheat.