Dwarf Trait Research Articles

Using achievements of fruit crop genetics and breeding: a contribution from the Michurinsk Department of the Vavilov Society of Geneticists and Breeders

The Michurinsk Department of the Vavilov Society of Geneticists and Breeding Scientists (VOGiS) was formed in 1966 after the constituent congress of VOGiS and nowadays includes 54 members. The scientists are engaged in 4 scientific institutions affiliated with FASO of Russia. The paper presents investigations of the individual genetics of leading fruit crops (pear, cherry, apple), identified genes, regularities of inheriting resistance to low temperatures, the most harmful diseases and several characters responsible for fruit quality. Some genes were identified for the first time. These are genes regulating Coccomyces hiemalis Higg. resistance (A), retarded growth habit in cherry (O2), astringency (Ta) and juiciness (Su) of fruit in pear. On the base of hybridological analysis and DNA marking, genotypes were identified. These genotypes carry target alleles of the following genes: columnar growth habit (Co) in apple, dwarf trait (PcDw) in pear, retardant growth (O2) in cherry. It was found that the markers C18470-25831, Mdo.chr 10.12, Co04R12 do not always show robust results for screening of young apple seedlings with columnar growth habit (Co) because they are identified as non-columnar forms. The primer pairs of 29f1 и jwi1r are the most robust ones for identification of columnar genotypes. These primers amplify specific PCR product of 586 bp (5’CR). On the basis of molecular-genetic analysis of apple initial forms and hybrid seedlings, there were identified targeted alleles of monogenic scab resistance genes including dominant homozygous genotype (Rvi6Rvi6) and also alleles of genes involved in the control of the biosynthesis of ethylene (Md-ACS1 and Md-ACO1) and expansin (Md-Exp7) controlling fruit long shelf life and pulp firmness.

An RNA-Seq analysis of the pear (Pyrus communis L.) transcriptome, with a focus on genes associated with dwarf

Dwarfing rootstocks, such as that of the Chinese pear variety ‘Zhongai 1’, are an important resource in modern fruit production. An RNA-Seq analysis of ‘Zhongai 1’ and its progenitor non-dwarfing variety ‘Jinxiang’ revealed a set of 234 genes which were differentially transcribed in the two varieties. Among the differentially transcribed gene set were some potential candidates for the dwarf trait: one encoded a gibberellin 3-beta-dioxygenase, four encoded auxin-associated proteins, one encoded LRR receptor-like serine/threonine-protein kinase, four encoded cytochrome P450s, two encoded enzymes involved in abscisic acid synthesis, three were ethylene-responsive transcription factors, six were moisture status related proteins, two were NAC and four WRKY transcription factors. The assessment of transcript abundance derived by the RNA-Seq analysis was validated using quantitative real time PCR for ten of the differentially transcribed genes. The transcript levels of these genes in other dwarf and non-dwarf varieties were also analyzed by the qPCR, but no completely consistent regularity was found. The concentration of some phytohormones (GA3, IAA and ABA) was also determined, the results accorded with the transcript levels of some related genes in some varieties, but did not accord in all the survey varieties.

Screening of molecular markers linked to dwarf trait in crape myrtle by bulked segregant analysis.

Plant height is one of the most important traits of plant architecture as it modulates both economic and ornamental values. Crape myrtle (Lagerstroemia indica L.) is a popular ornamental woody plant because of its long-lasting mid-summer bloom, rich colors, and diversified plant architecture. These traits also make it an ideal model of woody species for genetic analysis of many ornamental traits. To understand the inheritance of plant height and screen for genes modulating plant height in Lagerstroemia, segregation of the plant height trait was analyzed using the F1 population of L. fauriei (standard) x L. indica 'Pocomoke' (dwarf) with 96 seedlings, while dwarf genes were screened using the bulked segregant analysis method, combined with 28 amplified fragment length polymorphism primers and 41 simple sequence repeat primers. The results showed that the dwarf trait of crape myrtle was controlled by a major gene and modified by minor genes. An amplified fragment length polymorphism marker, M53E39-92, which was 23.33 cM from the loci controlling the dwarf trait, was screened. These results provide basic information for marker-assisted selection in Lagerstromia and cloning of dwarf genes in future studies.

Differential proteomic analysis of dwarf characteristics in cucumber (Cucumis sativus Linn.) stems

Dwarfism was one of the mo st important agronomic traits in cucumber breeding. The current study was conducted to identify dwarf-related proteins using two-dimensional electrophoresis. Twenty-two differentially expressed protein spots were detected between dwarf and vine genotypes while 20 of them were successfully identified by MALDI-TOF/TOF MS. Out of 20 identified proteins in dwarf genotype, 14 were up-regulated and six were down-regulated. The classification of differential proteins showed that the identified proteins were functionally involved in photosynthesis, energy metabolism, cytoskeletal functions, transduction and signal regulation, detoxification and redox regulation. Five differentially regulated proteins were analyzed using the technique quantitative real-time PCR (qRT-PCR). The results showed that four proteins, including histone deacetylase, the EIN2-like protein, chlorophyll A/B binding protein, and ubiquitin-conjugating enzyme Spm2 (E2) were up-regulated and one F-box family protein was down-regulated in the dwarf genotype. Further western blot analysis revealed that only E2 protein was detected in the dwarf genotype, indicating its important role in the cucumber dwarf trait.

Expression of gibberellin 2-oxidase 4 from Arabidopsis under the control of a senescence-associated promoter results in a dominant semi-dwarf plant with normal flowering

Gibberellin (GA), a plant hormone, is involved in many aspects of plant growth and development both in vegetative and reproductive phases. GA2-oxidase plays a key role in the GA catabolic pathway to reduce bioactive GAs. We produced transgenic Arabidopsis plants expressing GA2-oxidase 4 (AtGA2ox4) under the control of a senescenceassociated promoter (SEN1). As we hypothesized, transgenic plants (SEN1::AtGA2ox4) exhibited a dominant semi-dwarf phenotype with a decrease of bioactive GAs (e.g., GA4 and GA1) up to two-fold compared to control plants. Application of bioactive GA3 resulted in increased shoot length, indicating that the GA signaling pathway functions normally in the SEN1::AtGA2ox4 plants. Expressions of other members of GA2-oxidase family, such as AtGA2ox1, AtGA2ox3, AtGA2ox6, and AtGA2ox8, were decreased slightly in the flower and silique tissues while GA biosynthetic genes (e.g., AtGA20ox1, AtGA20ox2 and AtGA3ox1) were not significantly changed in the SEN::AtGA2ox4 plants. Using proteome profiling (2-D PAGE followed by MALDI-TOF/MS), we identified 29 protein spots that were increased in the SEN1::AtGA2ox4 plants, but were decreased to wild-type levels by GA3 treatment. The majority were found to be involved in photosynthesis and carbon/energy metabolism. Unlike the previous constitutive over-expression of GA2-oxidases, which frequently led to floral deformity and/or loss of fertility, the SEN1::AtGA2ox4 plants retained normal floral morphology and seed production. Accordingly, the expressions of FT and CO genes remained unchanged in the SEN1::AtGA2ox4 plants. Taken together, our results suggest that the dominant dwarf trait carried by SEN1::AtGA2ox4 plants can be used as an efficient dwarfing tool in plant biotechnological applications.

Characterization and molecular mapping of a dwarf mutant in wheat

A spontaneous dwarf mutant of wheat was found in an F5 generation line derived from a cross between Huamai No. 9 and Een No. 1 in 1998; it was named Huaai 01. We characterized the genetic pattern of Huaai 01 and mapped the gene controlling the dwarf trait. This dwarf mutant was found insensitive to exogenous gibberellic acid treatment, based on the length of the first leaf and the coleoptile at the seedling stage, suggesting that it plays a crucial role in the gibberellin response pathway. Genetic analysis revealed that a single gene that is partially recessive controls the dwarf phenotype in Huaai 01. We named the dwarfing gene Rht-B2. Simple sequence repeats (SSR) were examined as identifying markers linked to the Rht-B2 gene in an F2 population. We screened 904 pairs of primers and identified 5 SSR markers linked to the Rht-B2 gene. Two markers, barc1096 and xgwm495, were located on the flanking region of the Rht-B2 gene at genetic distances of 2.9 and 3.3 cM, respectively. Based on published SSR linkage data for wheat, the Rht-B2 gene was mapped to the long arm of chromosome 4B. This identification and characterization of the Rht-B2 dwarfing gene will facilitate its utilization in wheat breeding.

Genome-Wide Association Study Identifies Candidate Genes That Affect Plant Height in Chinese Elite Maize (Zea mays L.) Inbred Lines

BackgroundThe harvest index for many crops can be improved through introduction of dwarf stature to increase lodging resistance, combined with early maturity. The inbred line Shen5003 has been widely used in maize breeding in China as a key donor line for the dwarf trait. Also, one major quantitative trait locus (QTL) controlling plant height has been identified in bin 5.05–5.06, across several maize bi-parental populations. With the progress of publicly available maize genome sequence, the objective of this work was to identify the candidate genes that affect plant height among Chinese maize inbred lines with genome wide association studies (GWAS).Methods and FindingsA total of 284 maize inbred lines were genotyped using over 55,000 evenly spaced SNPs, from which a set of 41,101 SNPs were filtered with stringent quality control for further data analysis. With the population structure controlled in a mixed linear model (MLM) implemented with the software TASSEL, we carried out a genome-wide association study (GWAS) for plant height. A total of 204 SNPs (P≤0.0001) and 105 genomic loci harboring coding regions were identified. Four loci containing genes associated with gibberellin (GA), auxin, and epigenetic pathways may be involved in natural variation that led to a dwarf phenotype in elite maize inbred lines. Among them, a favorable allele for dwarfing on chromosome 5 (SNP PZE-105115518) was also identified in six Shen5003 derivatives.ConclusionsThe fact that a large number of previously identified dwarf genes are missing from our study highlights the discovery of the consistently significant association of the gene harboring the SNP PZE-105115518 with plant height (P = 8.91e-10) and its confirmation in the Shen5003 introgression lines. Results from this study suggest that, in the maize breeding schema in China, specific alleles were selected, that have played important roles in maize production.

The Genetically Unstable Dwarf Locus in Azuki Bean (Vigna angularis (Willd.) Ohwi & Ohashi)

We characterized a spontaneous dwarf mutant showing extremely short internodes and dark green leaves originating from azuki bean (Vigna angularis (Willd.) Ohwi & Ohashi) cultivar "Erimo-shouzu." F(1) plants of 3 cross combinations between the dwarf mutant and several representative wild-type plants, Erimo-shouzu, V. angularis accession Acc2265 and wild relative V. riukiuensis accession Acc2482, supported the dwarf genotype being recessive. In a total of 3328 F(2) progeny of these 3 crosses, 65 dwarfs (2.0%) and 5 chimeric dwarfs (0.2%) segregated and the remainder were wild-type plants (97.8%). In F(3) progeny derived from self-pollinated dwarf F(2) plants, we observed wild type (54.3%), dwarf (39.1%), and chimeric dwarf (6.5%) plants. Two types of chimeric plants were observed: dwarf branches on the axils of wild-type plant stems and wild-type branches on the axils of dwarf stems. In 21 dwarf F(2) plants, the dwarf trait cosegregated with simple sequence repeat marker CEDG154 on chromosome 4. Conversely, homozygote F(2) plants at this chromosomal segment from the dwarf mutant frequently (>90%) expressed the wild-type phenotype. We concluded that the dwarf phenotype is mitotically and meiotically inheritable and controlled by a single genetically unstable locus, designated Azuki Dwarf1 (AD1), which converts between 2 phenotypic states bidirectionally.

Morphological characters, inheritance and response to exogenous hormones of a cotton super‐dwarf mutant of Gossypium hirsutum

With 2 figures and 4 tables AbstractA novel super‐dwarf mutant, named AS98, was discovered from an interspecific hybrid in 1998. Compared to the normal line LHF10W99, plant height and internode length were significantly shorter in AS98, but it had only slightly (3–5%) fewer internodes. Therefore, the shorter plant height was the result of shorter internodal length. AS98 was crossed with LHF10W99, and the F1, F2, BC1, and BC2 populations were used for genetic analysis of the dwarf trait. The results showed that the trait was controlled by a single incomplete‐dominant gene. Exogenous application of gibberellin acid (GA3), brassinosteroid and indol acetic acid showed a significant response to GA3, which could restore plant height in AS98. The results thus provide a basis for utilizing the dwarf trait in breeding and studying the biosynthesis of GA or signal transduction in cotton.

Genetic Mapping of PcDw Determining Pear Dwarf Trait

European pear (Pyrus communis) ‘Aihuali’ carrying the dwarf character originating from ‘Nain Vert’ was crossed with ‘Chili’ (Pyrus bretschneideri). A total of 352 F1 progenies was produced to investigate the inheritance of the dwarf trait, and 111 of these were used to develop molecular markers. Chi-square analysis showed that the character fitted a 1:1 ratio indicative of a single dominant gene, which we have named PcDw. Using a bulked segregant analysis approach with 500 random amplified polymorphic DNA (RAPD) and 51 simple sequence repeat (SSR) markers from pear (Pyrus pyrifolia and P. communis) and apple (Malus ×domestica), four markers were identified as cosegregating with the dwarf character. Two of these were fragments produced by the S1212 and S1172 RAPD primers, and the other two were the pear SSR markers KA14 and TsuENH022. The RAPD markers were converted into sequence-characterized amplified regions (SCARs) and designated S1212-SCAR318 and S1172-SCAR930 and, with the SSR markers KA14 and TsuENH022, were positioned 5.9, 9.5, 8.2, and 0.9 cM from the PcDw gene, respectively. Mapping of the KA14 and TsuENH022 markers enabled the location of the PcDw gene on LG 16 of the pear genetic linkage map.

Simultaneous Expression of Spinacia oleracea Chloroplast Choline Monooxygenase (CMO) and Betaine Aldehyde Dehydrogenase (BADH) Genes Contribute to Dwarfism in Transgenic Lolium perenne

Choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH) catalyze the first and second steps in the biosynthesis of glycine betaine in betaine-accumulating plants. Over-expression of the Spinacia oleracea chloroplast choline monooxygenase (SoCMO) and betaine aldehyde dehydrogenase (SoBADH) genes has not been reported in Lolium perenne. In this investigation, the SoCMO and SoBADH genes have been used to generate transgenic L. perenne plants via particle bombardment. Transgenic plants have been confirmed with PCR, Southern blot, and Northern blot analyses. Enhanced salt stress tolerance has been observed from SoBADH–SoCMO transgenic L. perenne plants. The dwarf phenotype was first observed 3 months after transgenic plants were established in soil and was to be stably inherited. Height of transgenic plants was decreased by 63% compared to the control. Measurement of endogenous GAs content demonstrated that the content of endogenous GA1 was decreased by 75.2%, and the content of endogenous GA4, GA12, GA19, and GA53 of transgenic plants was increased by 200%, 221%, 105%, and 108%, respectively, compared to the control plants. Dwarf trait of SoBADH–SoCMO transgenic L. perenne plants can be recovered by application of exogenous GAs. These results demonstrated that simultaneous expression of the SoCMO and SoBADH genes enhanced salt stress tolerance and induced dwarfism in transgenic L. perenne. Dwarfism induced by expression of the SoCMO and SoBADH genes was associated with synthesis of endogenous GAs and it could be recovered by application of exogenous GAs. This is the first report on dwarfism induced by expression of the SoCMO and SoBADH genes in a species in turfgrass.

Activation of gibberellin 2-oxidase 6 decreases active gibberellin levels and creates a dominant semi-dwarf phenotype in rice (Oryza sativa L.)

Gibberellin (GA) 2-oxidase plays a key role in the GA catabolic pathway through 2beta-hydroxylation. In the present study, we isolated a CaMV 35S-enhancer activation tagged mutant, H032. This mutant exhibited a dominant dwarf and GA-deficient phenotype, with a final stature that was less than half of its wild-type counterpart. The endogenous bioactive GAs are markedly decreased in the H032 mutant, and application of bioactive GAs (GA(3) or GA(4)) can reverse the dwarf phenotype. The integrated T-DNA was detected 12.8 kb upstream of the OsGA2ox6 in the H032 genome by TAIL-PCR. An increased level of OsGA2ox6 mRNA was detected at a high level in the H032 mutant, which might be due to the enhancer role of the CaMV 35S promoter. RNAi and ectopic expression analysis of OsGA2ox6 indicated that the dwarf trait and the decreased levels of bioactive GAs in the H032 mutant were a result of the up-regulation of the OsGA2ox6 gene. BLASTP analysis revealed that OsGA2ox6 belongs to the class III of GA 2-oxidases, which is a novel type of GA2ox that uses C20-GAs (GA(12) and/or GA(53)) as the substrates. Interestingly, we found that a GA biosynthesis inhibitor, paclobutrazol, positively regulated the OsGA2ox6 gene. Unlike the over-expression of OsGA2ox1, which led to a high rate of seed abortion, the H032 mutant retained normal flowering and seed production. These results indicate that OsGA2ox6 mainly affects plant stature, and the dominant dwarf trait of the H032 mutant can be used as an efficient dwarf resource in rice breeding.

Mechanisms for miniature dwarf characteristics of Mi-cro-Tom tomato and its application in plant functional genomics studies

Micro-Tom is a miniature dwarf tomato, which can grow at a high density, has a short life cycle, and can be transformed efficiently. As a result, it became a new model plant for functional genomics study. The origin and biological characteristics of Micro-Tom were summarized. Recent advances in the mechanisms involved in the miniature dwarf trait, as well as the application of Micro-Tom in plant functional genomics study and the improved genetic transformation systems were reviewed.

RAPD and SSR Polymorphisms in Mutant Lines of Transgenic Wheat Mediated by Low Energy Ion Beam

Two types of markers-random amplified polymorphic DNA (RAPD) andsimple sequence repeat DNA (SSR)-have been used to characterizethe genetic diversity among nine mutant lines of transgenic wheatintermediated by low energy ion beam and their four receptorcultivars. The objectives of this study were to analyze RAPD-basedand SSR-based genetic variance among transgenic wheat lines and withtheir receptors, and to find specific genetic markers of specialtraits of transgenic wheat lines. 170 RAPD primers were amplified to733 fragments in all the experimental materials. There were 121polymorphic fragments out of the 733 fragments with a ratio ofpolymorphic fragments of 16.5%. 29 SSR primer pairs were amplifiedto 83 fragments in all the experiment materials. There were 57polymorphic fragments out of the 83 fragments with a ratio ofpolymorphic fragments of 68.7%. The dendrograms were prepared basedon a genetic distance matrix using the UPGMA (Unweighted Pair-groupMethod with Arithmetic averaging) algorithm, which corresponded wellto the results of the wheat pedigree analysis and separated the 13genotypes into four groups. Association analysis between RAPD andSSR markers with the special traits of transgenic wheat mutant linesdiscovered that three RAPD markers, s1, opt-16, and f14, weresignificantly associated with the muticate trait, while three SSRmarkers, Rht8 (Xgwm261), Rht-B1b, and Rht-D1b, highly associatedwith the dwarf trait. These markers will be useful formarker-assistant breeding and can be used as candidate markers forfurther gene mapping and cloning.

Identification and characterisation of a gibberellin-related dwarf mutant in pumpkin (Cucurbita moschata)

Summary‘Non-vine I’ is a dwarf variety of pumpkin (Cucurbita moschata) with short vines, while ‘Yellow wolf’ is a normal variety with long vines. The phenotypes of ‘Non-vine I’ and ‘Yellow wolf’ pumpkin were compared, and changes in the length of the vine in ‘Non-vine I’ were observed after treatment with gibberellin A3 (GA3), naphthylacetic acid (NAA) or brassinolide (BL). Cell sizes in the internode in ‘Non-vine I’ were then observed and compared after application of 0.6 mM GA3 or water (control). The results obtained showed that: (1) the morphological characteristics of ‘Non-vine I’ plants were similar to normal pumpkins except for the vine trait; (2) ‘Non-vine I’ plants were sensitive to exogenous GA3 which significantly promoted the elongation of vines and petioles, but did not respond to exogenous auxin (NAA) or brassinolide (BL); (3) internode cells of ‘Non-vine I’ plants were shorter than those of normal pumpkins, and GA3 promoted internode cell elongation in ‘Non-vine I’ plants. We propose that ‘Non-vine I’ is a GA-related mutant, and the dwarf trait results from the failure of normal internode cell elongation.

Inheritance and potentials of a mutated dwarfing gene ndf1 in Brassica napus

AbstractA dwarf mutant ‘NDF‐1′, approximately 70 cm high, was derived from a 200‐cm high doubled haploid (DH) line ‘3529’ (Brassica napus), seeds of which were jointly treated with chemical inducers and bombardment of fast neutron. The leaves of the ‘NDF‐1’ mutant were wrinkled and thicker compared with the wild‐type control. The mutant had much lower values than its original parents for all agronomic traits, except for its seed weight. A genetic analysis revealed that dwarfism is under the control of a major gene (designated as ndf1) with a mainly additive effect and non‐significant dominance effect. Because of the high level of resistance to lodging, breeding programmes for double low dwarf oilseed rape and heterosis utilization were initiated. Some new dwarf strains with improved agronomic performance were developed. The hybrid of the cross between the tall parent and the dwarf line showed increased harvest index and significantly higher seed yield than the tall parent or the control variety ‘Zhongyou 821’ and presented an estimated heterosis vigour rate as high as 12.5–25.8%. The dwarf trait will be a promising marker for a simple, economic and efficient way to control the purity of F1 hybrid varieties in hybrid production of B. napus.

Horticultural characterization of Angelonia salicariifolia plants transformed with wild-type strains of Agrobacterium rhizogenes.

Genetic transformation was carried out with wild-type strains of Agrobacterium rhizogenes for introducing a dwarf trait into the Scrophulariaceous ornamental plant, angelonia (Angelonia salicariifolia). Leaf segments of two angelonia genotypes (Ang.1 and Ang.2) were co-cultivated with mikimopine-type strains of A. rhizogenes. Adventitious roots that showed vigorous growth and increased lateral branching when cultured on half-strength Murashige and Skoog's (MS) basal salts medium lacking plant growth regulators (PGRs) after co-cultivation were selected as putatively transformed lines. All of these selected lines produced mikimopine. Adventitious shoots were efficiently induced from putatively transformed root segments on half-strength MS basal salts medium containing 1 mg l(-1) benzyladenine (BA) under continuous illumination (24-h photoperiod), and the shoots easily rooted following their transfer to half-strength MS basal salts medium lacking PGRs. The transgenic nature of regenerated plants was confirmed by Southern hybridization. Transformed plants frequently died during their acclimatization, and acclimatized plants of eight transformed lines grew very slowly for 1-5 months after transplantation to the greenhouse. Plants of two transformed lines of Ang.2 flowered 4-6 months after transplantation. These transformed plants exhibited phenotypic alterations such as dwarfness and smaller leaves. There were no apparent alterations observed in the number, shape, and size of the flowers. Pollen fertility of the transformed plants was 60-80% based on aceto-carmine staining. These results indicate the possibility of applying A. rhizogenes-mediated transformation for introducing a dwarf trait into angelonia.

Construction of a genetic map and location of quantitative trait loci for dwarf trait in maize by RFLP markers

Using F2 population derived from the cross of tall inbred 7922 by dwarf inbred 5003, an RFLP linkage map of maize has been constructed, on which 85 markers are distributed among 10 linkage groups and span maize genome about 1827.8 cM with an average distance (24.4 cM) between markers. 106 F2:3 lines of the population were grown in a 10 × 11 simple rectangular lattice design of one-raw plots with two replications and evaluated for plant height (PH). With interval mapping procedure, 5 QTLs controlling plant height have been identified and their genetic effects and gene action determined. 2 major QTLs with opposite effect have been discovered. One for increasing plant height isph1 which is located at chromosome 2 and accounts for 51.8% of the total phenotypic variation; the other for decreasing plant height isph3 which is located at chromosome 5 and accounts for 38.6% of the total phenotypic variation. The chromosomal location ofph3 might be the same as or close to the position ofbv1, a dwarf mutant of maize.

Inheritance of Pod Type, Stem Color, and Dwarf Growth Habit in Medicago polymorpha

Identification of marker traits in annual Medicago species (medics) would assist plant breeders in cultivar development. The objective of this research was to determine the inheritance of pod type, stem color, and dwarf growth habit in Medicago polymorpha L., a diploid species. Progeny from each of three crosses were evaluated in the F1, F2, and F3 generations. Results indicate that pod type was controlled by a single gene with a dominant allele for spiny pods. We propose the gene symbol Sp1 for the pod type trait. Stem color also was controlled by a single gene, with a dominant allele for red stems. We propose Rs1 as the gene symbol for this trait. The dwarf trait was not present in the parents or the F1 generation, but was observed in the F2 generation of one of the crosses. Dwarf plants had much shorter stems, internodes, and leaf petioles than normal plants, and they also had smaller, puckered leaves. The trait appeared to be controlled by two genes with partial recessive epistasis. We propose the gene symbols Dwl and Dw2 for this trait. Results indicated that the genes for pod type and stem color segregated independently and were not linked.

Random amplified polymorphic DNA (RAPD) detection of dwarf off-types in micropropagated Cavendish (Musa spp. AAA) bananas

A RAPD marker specific to the dwarf off-type (hereafter known as dwarf) from micropropagation of Cavendish banana (Musa spp. AAA) cultivars New Guinea Cavendish and Williams was identified following an analysis of 57 normal (true-to-type) and 59 dwarf plants generated from several different micropropagation events. Sixty-six random decamer primers were used in the initial screen, of which 19 (28.8%) revealed polymorphisms between normal and dwarf plants. Primer OPJ-04 (5'-CCGAACACGG-3') was found to amplify an approx. 1.5 kb band which was consistently present in all normal but absent in all dwarf plants of both cultivars. Reliable detection of dwarf plants was achieved using this marker, providing the only available means ofin vitro detection of dwarfs. The use of this marker could facilitate early detection and elimination of dwarfs from batches of micropropagated bananas, and may be a useful tool in determining what factors in the tissue culture process lead to this off type production.Other micropropagation-induced RAPD polymorphisms were observed but were not associated with the dwarf trait.