Genetic analysis of resistance to <Emphasis Type="Italic">soil-borne wheat mosaic virus</Emphasis> derived from <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Genetic Analysis of Resistance to Soil-Borne Wheat Mosaic Virus Derived from Aegilops tauschii. Euphytica. Soil-Borne Wheat Mosaic Virus (SBWMV), vectored by the soil inhabiting organism Polymyxa graminis, causes damage to wheat (Triticum aestivum) yields in most of the wheat growing regions of the world. In localized fields, the entire crop may be lost to the virus. Although many winter wheat cultivars contain resistance to SBWMV, the inheritance of resistance is poorly understood. A linkage analysis of a segregating recombinant inbred line population from the cross KS96WGRC40 × Wichita identified a gene of major effect conferring resistance to SBWMV in the germplasm KS96WGRC40. The SBWMV resistance gene within KS96WGRC40 was derived from accession TA2397 of Aegilops taushcii and is located on the long arm of chromosome 5D, flanked by microsatellite markers Xcfd10 and Xbarc144. The relationship of this locus with a previously identified QTL for SBWMV resistance and the Sbm1 gene conferring resistance to soil-borne cereal mosaic virus is not known, but suggests that a gene on 5DL conferring resistance to both viruses may be present in T. aestivum, as well as the D-genome donor Ae. tauschii.     

Genotypic variation for cellular thermotolerance in <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss., the D genome progenitor of wheat

Corn leaf aphids (Rhopalosiphum maidis Fitch) are found throughout the year on maize in Hawaii and occasionally cause yield loss. Sweet corn inbred Hi38-71 was observed to have high field resistance to aphids and was chosen for this genetic study. An artificial infestation technique was developed using hair-pin clip cages (2.2 cm diameter) which we devised and built. The cages were applied to field-grown plants into which three wingless viviparous adults were placed. Aphid populations were classified on a 1–10 rating scale after about 2 weeks based on digital images of the cages. Mean aphid coverage ratings were 2.97 for the resistant parent and 7.28 for the susceptible parent (representing >200 insects per cage). The F₁ hybrids showed similar susceptibility (6.72), showing resistance to be recessive in nature. Six generations of the cross between Hi38-71 and susceptible inbred Hi27 were artificially infested to provide a generation mean analysis of 360 treated plants over two growing seasons. A joint scaling test showed that the fit to a 3-parameter additive-dominance model satisfactorily explained the observed variability with no assumed linkage or epistasis. We conclude that resistance to corn leaf aphid in Hi38-71 is conferred by a single recessive gene labeled aph. These results concur with a previous study under uncontrolled natural infestation in a single environment. The hair-pin clip cage method was most effective in distinguishing resistant and susceptible genotypes under diverse natural growing conditions in Hawaii.     

Molecular tagging of a stripe rust resistance gene in <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important diseases of common wheat (Triticum aestivum L.). China has the largest stripe rust epidemic areas in the world and yield losses can be large. Aegilops tauschii Coss, the D-genome progenitor of common wheat, includes two subspecies, tauschii and strangulata (Eig) Tzvel. The ssp. strangulata accession AS2388 is highly resistant to the prevailing physiological races of PST in China, and possesses a single dominant gene for stripe rust resistance. In order to tag this gene, AS2388 was crossed with the highly susceptible ssp. tauschii accession AS87. The parents, F₂ plants, and F_2:3 families were tested at adult plant stage in field trials with six currently prevailing races. Simple sequence repeat (SSR) primers were used to identify molecular markers linked to the resistance gene. SSR markers Xwmc285 and Xwmc617 were linked to the resistance gene on chromosome arm 4DS flanking it at 1.7 and 34.6 cM, respectively. Based on the chromosomal location, this gene temporarily designated as YrAS2388 is probably novel. The resistance in Ae. tauschii AS2388 was partially expressed in two newly developed synthetic hexaploid backgrounds.     

Reduction of <Emphasis Type="Italic">Aegilops sharonensis</Emphasis> chromatin associated with resistance genes <Emphasis Type="Italic">Lr56</Emphasis> and <Emphasis Type="Italic">Yr38</Emphasis> in wheat

The Lr56/Yr38 translocation consists primarily of alien-derived chromatin with only the 6AL telomeric region being of wheat origin. To improve its utility in wheat breeding, an attempt was made to exchange excess Ae. sharonensis chromatin for wheat chromatin through homoeologous crossover in the absence of Ph1. Translocation heterozygotes that lacked Ph1 were test-crossed with Chinese Spring nullisomic 6A tetrasomic 6B and nullisomic 6A-tetrasomic 6D plants and the resistant (hemizygous 6A) progeny were analyzed with four microsatellite markers. Genetic mapping suggested general homoeology between wheat chromosome 6A and the translocation chromosomes, and showed that Lr56 was located near the long arm telomere. Thirty of the 53 recombinants had breakpoints between Lr56 and the most distal marker Xgwm427. These were characterized with additional markers. The data suggested that recombinants #39, 157 and 175 were wheat chromosomes 6A with small intercalary inserts of foreign chromatin containing Lr56 and Yr38, located distally on the long arms. These three recombinants are being incorporated into adapted germplasm. Attempts to identify the single shortest translocation and to develop appropriate markers are being continued.     

Resistance screening of <Emphasis Type="Italic">Coffea</Emphasis> spp. accessions for <Emphasis Type="Italic">Pratylenchus coffeae</Emphasis> and <Emphasis Type="Italic">Radopholus arabocoffeae</Emphasis> in Vietnam

Coffee varieties with resistance for the plant-parasitic nematodes Pratylenchus coffeae and Radopholus arabocoffeae are limited in Vietnam. A selection of imported varieties and high yield varieties of Arabica coffee in Vietnam were evaluated for resistance to both plant-parasitic nematode species in Northern Vietnam. The same experiments were carried out with hybrid arabica coffee, three selected clones of Coffea canephora and one clone of Coffea excelsa in the Western Highland of Vietnam. The screened coffee accessions from Ethiopia (KH1, KH13, KH20, KH21, KH29, and KH31) were susceptible and good host for P. coffeae. Also accessions 90P4 (Portugal) and Oro azteca (Mexico) had a reproduction factor Rf > 1. Pluma Hidalgo (Mexico), 90/6 (Vietnam), 90P3 (Portugal), 90P2 (Vietnam), Variedad (Mexico), 90T (Portugal), and Garnica (Mexico) were poor hosts (Rf < 1) but not tolerant to P. coffeae, expressed by a reduction of root weight compared to untreated control plants. Most of the coffee accessions tested in Northern Vietnam were intolerant to R. arabocoffeae, except 90T which showed no reduction of root weight, even at high initial nematode densities (4,000/pot). Good hosts for R. arabocoffeae were Variedad, KH1, KH21, KH29, KH20, KH31, and KH13 with Rf > 1. Pluma Hidalgo, 90/6, 90P3, 90P2, 90T, Oro azteca, and Garnica were poor hosts (Rf < 1). In the Western Highland experiment, all arabica coffee accessions were susceptible for P. coffeae with Rf ranging from 1.41 to 1.59. Tolerance to P. coffeae was found in C. liberica var. Dewevrei, Hong34 and Nhuantren. Coffea excelsa, Hong34, Nhuantren, and H1C19 were tolerant to R. arabocoffeae at the highest inoculation density (4,000 nematodes/pot). The most susceptible accessions were Nhuantren and K55. Resistance (Rf < 1) to R. arabocoffeae was found in C. liberica var. Dewevrei and Hong34. This article reports on the first screening for resistance and tolerance to P. coffeae and R. arabocoffeae in coffee accessions in Vietnam and shows promising results for enhanced coffee-breeding.     

Allelic variation for the rust resistance gene <Emphasis Type="Italic">Lr34</Emphasis>/<Emphasis Type="Italic">Yr18</Emphasis> in Canadian wheat cultivars

The wheat (Triticum aestivum L.) gene Lr34/Yr18 conditions resistance to leaf rust, stripe rust, and stem rust, along with other diseases such as powdery mildew. This makes it one of the most important genes in wheat. In Canada, Lr34 has provided effective leaf rust resistance since it was first incorporated into the cultivar Glenlea, registered in 1972. Recently, molecular markers were discovered that are either closely linked to this locus, or contained within the gene. Canadian wheat cultivars released from 1900 to 2007, breeding lines and related parental lines, were tested for sequence based markers caSNP12, caIND11, caIND10, caSNP4, microsatellite markers wms1220, cam11, csLVMS1, swm10, csLV34, and insertion site based polymorphism marker caISBP1. Thirty different molecular marker haplotypes were found among the 375 lines tested; 5 haplotypes had the resistance allele for Lr34, and 25 haplotypes had a susceptibility allele at this locus. The numbers of lines in each haplotype group varied from 1 to 140. The largest group was represented by the leaf rust susceptible cultivar “Thatcher” and many lines derived from “Thatcher”. The 5 haplotypes that had the resistance allele for Lr34 were identical for the markers tested within the coding region of the gene but differed in the linked markers wms1220, caISBP1, cam11, and csLV34. The presence of the resistance or susceptibility allele at the Lr34 locus was tracked through the ancestries of the Canadian wheat classes, revealing that the resistance allele was present in many cultivars released since the 1970s, but not generally in the older cultivars.     

Transformation of <Emphasis Type="Italic">Campanula</Emphasis> by wild type <Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis>

Compact growth is an important quality criterion in horticulture. Many Campanula species and cultivars exhibit elongated growth which is suppressed by chemical retardation and cultural practice during production to accommodate to the consumer’s desire. The production of compact plants via transformation with wild type Agrobacterium rhizogenes is an approach with great potential to produce plants that are non-GMO. Efficient transformation and regeneration procedures vary widely among both plant genera and species. Here we present a transformation protocol for Campanula. Hairy roots were produced on 26–90% of the petioles that were used for transformation of C. portenschlagiana (Cp), a C. takesimana × C. punctata hybrid (Chybr) and C. glomerata (Cg). Isolated hairy roots grew autonomously and vigorously without added hormones. The Cg hairy roots produced chlorophyll and generated plantlets in response to treatments with cytokinin (42 µM 2iP) and auxin (0.67 µM NAA). In contrast, regeneration attempts of transformed Cp and Chybr roots lead neither to the production of chlorophyll nor to the regeneration of shoots. Agropine A. rhizogenes strains integrate split T-DNA in T_L- and T_R-DNA fragments into the plant genome. In this study, regenerated plants of Cg did not contain T_R-DNA, indicating that a selective pressure against this T-DNA fragment may exist in Campanula.     

Development of microsatellite markers in cultivated and wild species of sections <Emphasis Type="Italic">Cepa</Emphasis> and <Emphasis Type="Italic">Phyllodolon</Emphasis> in <Emphasis Type="Italic">Allium</Emphasis>

The potential of microsatellite markers for use in genetic studies has been evaluated in Allium cultivated species (Allium cepa, A. fistulosum) and its allied species (A. altaicum, A. galanthum, A. roylei, A. vavilovii). A total of 77 polymerase chain reaction (PCR) primer pairs were employed, 76 of which amplified a single product or several products in either of the species. The 29 AMS primer pairs derived from A. cepa and 46 microsatellites primer pairs from A. fistulosum revealed a lot of polymorphic amplicons between seven Allium species. Some of the microsatellite markers were effective not only for identifying an intraspecific F₁ hybrid between shallot and bulb onion but also for applying to segregation analyses in its F₂ population. All of the microsatellite markers can be used for interspecific taxonomic analyses among two cultivated and four wild species of sections Cepa and Phyllodolon in Allium. Generally, our data support the results obtained from recently performed analyses using molecular and morphological markers. However, the phylogeny of A. roylei, a threatened species with several favorable genes, was still ambiguous due to its different positions in each dendrogram generated from the two primer sets originated from A. cepa and A. fistulosum.     

Resistance to late blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) in ten wild <Emphasis Type="Italic">Solanum</Emphasis> species

Nineteen accessions of the tuber-bearing species Solanum berthaultii, S. chacoense, S. leptophyes, S. microdontum, S. sparsipilum, S. sucrense, S. venturii, S. vernei and S. verrucosum were tested for their resistance to late blight in two years of field experiments. Plants were artifically inoculated with zoospores of race 1.2.3.4.5.7.10.11 and the development of the disease was followed. Resistance ratings, calculated as the areas under the disease progress curves (ADPC), demonstrated a high resistance in all accessions except in S. sparsipilum, S. leptophyes and their interspecific hybrid. Segregations suggest that major genes for resistance are present in S. sucrense and S. venturii, and may also play a role in S. verrucosum. It is not yet certain wether the resistance of the other accessions is comparable to the partial and durable resistance of S. tuberosum cultivars like Pimpernel, as inheritance and mechanism have yet to be established. However, segregations suggesting the presence of single major genes with complete dominance were not found in these other accessions. Tuber initiation in the field occurred in only one accession, S. tuberosum ssp. andigena, and maturity of the clones was not related to their resistance. In the other accessions maturity types could not be assessed, as the clones require short day conditions for tuber initiation.     

Expression of <Emphasis Type="Italic">Bruguiera gymnorhiza</Emphasis><Emphasis Type="Italic">BgARP1</Emphasis> enhances salt tolerance in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> plants

We have previously reported that expression of salt-responsive genes, including Bruguiera gymnorhiza ankyrin repeat protein 1 (BgARP1), enhances salt tolerance in both Agrobacterium tumefaciens and Arabidopsis. In this report, we further characterized BgARP1-expressing Arabidopsis to elucidate the role of BgARP1 in salt tolerance. BgARP1-expressing plants exhibited more vigorous growth than wild-type plants on MS plates containing 125–175 mM NaCl. Real-time PCR analysis showed enhanced induction of osmotin34 in the 2-week-old transformants under 125 mM NaCl. It was also showed that induction of typical salt-responsive genes, including RD29A, RD29B, and RD22, was blunted and delayed in the 4-week-old transformants during 24 h after 200 mM NaCl treatment. Ion content analysis showed that transgenic plants contained more K⁺, Ca²⁺, and NO₃ ⁻, and less NH₄ ⁺, than wild-type plants grown in 200 mM NaCl. Our results suggest that BgARP1-expressing plants may reduce salt stress by up-regulating osmotin34 gene expression and maintaining K⁺ homeostasis and regulating Ca²⁺ content. These results indicate that BgARP1 is functional on a heterogeneous background.     

Molecular mapping of <Emphasis Type="Italic">Pc68</Emphasis>, a crown rust resistance gene in <Emphasis Type="Italic">Avena</Emphasis><Emphasis Type="Italic">sativa</Emphasis>

Crown rust, which is caused by Puccinia coronata f. sp. avenae, P. Syd. & Syd., is the most destructive disease of cultivated oats (Avena sativa L.) throughout the world. Resistance to the disease that is based on a single gene is often short-lived because of the extremely great genetic diversity of P. coronata, which suggests that there is a need to develop oat cultivars with several resistance genes. This study aimed to identify amplified fragment length polymorphism AFLP markers that are linked to the major resistance gene, Pc68, and to amplify the F₆ genetic map from Pc68/5*Starter × UFRGS8. Seventy-eight markers with normal segregation were discovered and distributed in 12 linkage groups. The map covered 409.4 cM of the Avena sativa genome. Two AFLP markers were linked in repulsion to Pc68: U8PM22 and U8PM25, which flank the gene at 18.60 and 18.83 centiMorgans (cM), respectively. The marker U8PM25 is located in the linkage group 4_12 in the Kanota × Ogle reference oat population. These markers should be useful for transferring Pc68 to genotypes with good agronomic characteristics and for pyramiding crown rust resistance genes.     

<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.     

Use of artificially-induced freezing temperatures to identify freeze tolerance in above-ground buds of <Emphasis Type="Italic">Saccharum</Emphasis> and <Emphasis Type="Italic">Erianthus</Emphasis> accessions

Sugarcane is a crop which is primarily grown between 30°N and 30°S latitude in tropical environments. Small areas of production in sub-tropical regions exist, and there is an increasing desire to produce the crop in colder environments. Cold-tolerant sugarcane is important both to the sub-tropical sugarcane industries and potential biofuels producers who seek to use sugarcane as a feedstock. Selection for this trait under natural conditions is difficult in sugarcane growing regions because damaging freezes are sporadic. The objective of this study was to identify sugarcane accessions for use in introgression breeding which have above-ground buds that are tolerant to freezing conditions. Above-ground (stalk) buds of 63 Saccharum, and 4 Erianthus accessions were frozen for 6 days at ?7 °C, and germinated buds were counted three weeks post-treatment. Accessions which had more bud cold tolerance than the Louisiana commercial cultivar ‘L 97-128’ were MPTH97-213, SES114, Guangxi87-22 and SES234A. Heritability estimates for percent reduction in bud germination and height of the shoots following freeze treatment was 0.47 and 0.49, respectively. Identified clones will be used in future breeding efforts at the United States Department of Agriculture, Agricultural Research Service, Sugarcane Research Unit in Houma, LA, USA.     

Mapping of new resistance (<Emphasis Type="Italic">Vr2</Emphasis>, <Emphasis Type="Italic">Rm1</Emphasis>) and ornamental (<Emphasis Type="Italic">Di2</Emphasis>, <Emphasis Type="Italic">pl</Emphasis>) Mendelian trait loci in peach

Peach powdery mildew is one of the major diseases of the peach. Various sources of resistance to PPM have thus been identified, including the single dominant locus Vr2 carried by the peach rootstock ‘Pamirskij 5’. To map Vr2, a linkage map based on microsatellite markers was constructed from the F₂ progeny (WP²) derived from the cross ‘Weeping Flower Peach’ × ‘Pamirskij 5’. Self-pollinations of the parents were also performed. Under greenhouse conditions, all progenies were scored after artificial inoculations in two classes of reactions to PPM (resistant/susceptible). In addition to Vr2, WP² segregated for three other traits from ‘Weeping Flower Peach’: Rm1 for green peach aphid resistance, Di2 for double-flower and pl for weeping-growth habit. With their genomic locations unknown or underdocumented, all were phenotyped as Mendelian characters and mapped: Vr2 mapped at the top of LG8, at 3.3 cM, close to the CPSCT018 marker; Rm1 mapped at the bottom of LG1, at a position of 116.5 cM, cosegregating with the UDAp-467 marker and in the same region as Rm2 from ‘Rubira’^®; Di2 mapped at 28.8 cM on LG6, close to the MA027a marker; and pl mapped at 44.1 cM on LG3 between the MA039a and SSRLG3_16m46 markers. Furthermore, this study revealed, for the first time, a pseudo-linkage between two traits of the peach: Vr2 and the Gr locus, which controls the red/green color of foliage. The present work therefore constitutes a significant preliminary step for implementing marker-assisted selection for the four major traits targeted in this study.     

Screening of pepper accessions for resistance against two thrips species (<Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> and <Emphasis Type="Italic">Thrips parvispinus</Emphasis>)

Thrips are damaging pests in pepper worldwide. They can cause damage directly by feeding on leaves, fruits or flowers, and also indirectly by transferring viruses, especially tomato spotted wilt virus (TSWV). Although thrips are among the most damaging pests in pepper, until now there is no commercial variety with a useful level of resistance to thrips. This is at least partly due to the lack of knowledge on resistance levels in pepper germplasm of QTLs and/or genes for resistance, and of information about resistance mechanisms to thrips in pepper. This paper describes our research aimed at developing practical and reliable screening methods for thrips resistance in pepper and at identifying pepper accessions showing a strong resistance to thrips. Thirty-two pepper accessions from four species of pepper (Capsicum annuum, C. baccatum, C. chinense and C. frutescens) and two species of thrips (Frankliniella occidentalis and Thrips parvispinus) were used in this study. Our results indicate that the laboratory based leaf disc test and the detached leaf test can be used as reliable screening methods for thrips resistance in pepper. We observed a large variation for resistance to thrips in Capsicum that can be exploited in breeding programs.     

Characterization of genes <Emphasis Type="Italic">Rpp2</Emphasis>, <Emphasis Type="Italic">Rpp4</Emphasis>, and <Emphasis Type="Italic">Rpp5</Emphasis> for resistance to soybean rust

Asian rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease currently threatening soybean crops in Brazil. The development of resistant cultivars is a top priority. Genetic characterization of resistance genes is important for estimating the improvement when these genes are introduced into soybean plants and for planning breeding strategies against this disease. Here, we infected an F₂ population of 140 plants derived from a cross between ‘An-76’, a line carrying two resistance genes (Rpp2 and Rpp4), and ‘Kinoshita’, a cultivar carrying Rpp5, with a Brazilian rust population. We scored six characters of rust resistance (lesion color [LC], frequency of lesions having uredinia [%LU], number of uredinia per lesion [NoU], frequency of open uredinia [%OU], sporulation level [SL], and incubation period [IP]) to identify the genetic contributions of the three genes to these characters. Furthermore, we selected genotypes carrying these three loci in homozygosis by marker-assisted selection and evaluated their genetic effect in comparison with their ancestors, An-76, PI230970, PI459025, Kinoshita and BRS184. All three genes contributed to the phenotypes of these characters in F₂ population and when pyramided, they significantly contributed to increase the resistance in comparison to their ancestors. Rpp2, previously reported as being defeated by the same rust population, showed a large contribution to resistance, and its resistance allele seemed to be recessive. Rpp5 had the largest contribution among the three genes, especially to SL and NoU. Only Rpp5 showed a significant contribution to LC. No QTLs for IP were detected in the regions of the three genes. We consider that these genes could contribute differently to resistance to soybean rust, and that genetic background plays an important role in Rpp2 activity. All three loci together worked additively to increase resistance when they were pyramided in a single genotype indicating that the pyramiding strategy is one good breeding strategy to increase soybean rust resistance.     

Development of PCR-based markers for the identification of the <Emphasis Type="Italic">S</Emphasis>-<Emphasis Type="Italic">RNase</Emphasis> alleles in wild potato species

Sexual self-incompatibility in wild diploid potato species is controlled by a single multiallelic S-locus encoding a polymorphic stylar ribonuclease (S-RNase) that is responsible for the female function in pollen–pistil recognition. In this study, an approach using PCR-based markers were originally developed to amplify the S-RNase alleles in Solanum chacoense. Subsequently, to investigate their general applicability in Solanum, this molecular approach was successfully tested on S. spegazzinii and S. kurtzianum. Application of PCR-SSCP approach revealed potentially new S-RNase alleles in the three species, demonstrating for the first time the existence of S-RNase genetic variability within and between populations of wild diploid potato species. Species-specific SSCP markers that may be successfully used in gene flow studies was also detected in this investigation.     

Over-expression of <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">FT</Emphasis> gene reduces juvenile phase and induces early flowering in ornamental gentian plants

Ornamental gentian plants are perennial and have a juvenile period of over 1 year before flowering. We transformed gentian plants with a construct comprising the Arabidopsis FLOWERING LOCUS T (FT) gene (encoding a major component protein of the flowering hormone ‘florigen’) under the control of the rolC promoter from Agrobacterium rhizogenes, which is known to induce vascular-specific expression. The resultant rolCpro-FT transgenic gentian plants showed early flowering in vitro and the earliest line formed floral buds within 4 months after transformation. Regeneration experiments from leaf explants of these rolCpro-FT transgenic plants also confirmed the early flowering phenotype. After acclimatization, these transgenic plants showed normal floral development in a closed greenhouse. There is no effective method to induce early flowering by cultivation management in gentian, therefore these lines might be very useful as annual early season cultivars.     

Increased resistance to <Emphasis Type="Italic">Ustilago zeae</Emphasis> and <Emphasis Type="Italic">Fusarium verticilliodes</Emphasis> in maize inbred lines bred for <Emphasis Type="Italic">Fusarium graminearum</Emphasis> resistance

Preliminary field observations in our maize breeding nurseries indicated that breeding for improved resistance to gibberella ear rot (Fusarium graminearum) in maize may indirectly select for resistance to another ear disease, common smut (Ustilago zeae). To investigate this, we compared the disease severity ratings obtained on 189 maize inbreds, eight of which included our inbreds developed with selection for gibberella ear rot resistance after field inoculation and breeding for 8–10 years. No correlation was found between disease severities for the 189 inbreds but the eight gibberella-resistant lines were consistently more resistant to smut. To further examine this relationship and to determine if these eight inbreds would be useful for developing inbreds with either common smut or fusarium ear rot (F. verticilliodes) resistance, we conducted a Griffing’s diallel analysis on six inbreds of maize, four with high levels of gibberella ear rot resistance representing all of the pedigree groups in our eight gibberella lines, and two with very low levels. Our most gibberella ear rot resistant inbreds, CO433 and CO441, had the lowest disease ratings for all three diseases, the consistently largest general combining ability effects and several significant specific combining ability effects. It was concluded that some inbreds bred specifically for gibberella ear rot would also be useful in breeding for resistance to common smut and fusarium ear rot.