Genetics of induced dwarf mutants in pearl millet,Pennisetum americanum (L.)Leeke

Summary Inheritance pattern of seven dwarf mutants revealed each of them to be controlled by a single recessive gene. Tests for allelism indicated existence of two groups of dwarfs, group 1 comprising six mutants and group 2 a single dwarf. The dwarfs of group 1 were found to be allelic to D₂ of the dwarf types already known in this crop and the dwarf of group 2 was allelic to D₁ of these types.Botany Department, R.V.V.N. College, Dharanikota, India.     

The Attempted Transfer of Male Sterility from the Cornerstone Mutant of Tetraploid Wheat to Diploid Wheat

An attempt was made to transfer male-sterility, mslc, from the Cornerstone mutant of tetraploid wheat to diploid wheat. The N-banding technique revealed that chromosome 4 A of tetraploid wheat does not pair with chromosome 4 of diploid wheat in triploid F₁ hybrids: consequtntly the transfer of male-sterility gene(s) from tetraploid wheat to diploid was not successful. The culchiane induced ampliploids possessing AAAABB in mslc background were fully fertile indicating the complete compensation of mslc by the newly introduced A genome of T. monocaccum. The fertility compensating gene(S) presumably located on chromosome 4 of diploid wheat may be used to produce hybrid wheat by the XYZ system.     

Individual and combined effects of plant height reducing genes in periwinkle

Inheritance of an induced bushy mutant (EMS 24-5) of periwinkle (Catharanthus roseus) and its genetic relationship with an earlier reported dwarf mutant (NEU 6-15) was studied by crossing it with its parental variety, Nirmal and the dwarf mutant. The bushy mutant was found to be under the control of a monogenic recessive gene (by), which was inherited independently of the recessive gene (dw ₁ ) involved in the dwarf mutant. The double mutant (bydw ₁ ) recombinant, which was recovered from the F₂ generation of the cross (NEU 6-15) × (EMS 24-5), its parental mutants and variety, Nirmal were used for determining the individual and combined effects of plant height reducing genes dw ₁ and by. Individually, the recessive genes by and dw _1, reduced plant height by 27–30, 64–68%, respectively, while together they reduced plant height by 73–77%. The double mutant recombinant was found to be 63–68 and 25–29% shorter than its parental mutants (EMS 24-5) and (NEU 6-15), respectively. The effects of the recessive gene by on plant height were discernable only after the age of 4 months while those of dw ₁ and combined effects of dw ₁ and by became apparent one to 2 weeks after germination. The double mutant recombinant was found to have higher content of total alkaloids in the roots than parental mutants as well as the variety, Nirmal.     

Dwarfing and lethal genes in apple progenies

Summary Three dwarf types are described, early dwarf, determined by two recessive genes d ₁ and d ₃, in the double homozygous state, and an additional recessive gene d ₄ and crinkle dwarf and sturdy dwarf each also determined by a recessive gene.The gene l, for pale green lethal was found to be closely linked to the gene V _f , for scab resistance.There was evidence of a regrowth promoting gene, G, in some seedlings homozygous for d ₁ and d ₃.     

Transfer of new dwarfing genes from the weed species Avena fatua into cultivated oat A. byzantina

New sources of dwarfing genes were identified from accessions of Avena fatua in Japan and Korea. The dwarfing genes were transferred from backcrossed and self‐pollinated relatives to the cultivated oat ‘Kanota’. In the cultivated form, the dominant dwarfing gene Dw8 showed a relatively lower transmission rate than recessive, semi‐dominant and nondwarfing genes and was characterized by a distinct link with wild gene cluster. This was also supported by the high transmission rate of wild specific SSR alleles. Four dwarf inbred lines (L153, L169a, L169b and L812) were identified as involving a single recessive dwarfing gene(s). The recessive dwarfing genes that showed normal and stable transmission rates in BC₁F₃ were first reported in hexaploid oats. The L169 segregated two different recessive dwarf lines in BC₁, which were selected as semi‐ (L169a) and extreme‐ (L169b) dwarf lines. The L169a was a good genotype with a high grain yield. L288 is a semi‐dwarf line conditioned by a semi‐dominant dwarfing gene, with a unilateral panicle, large florets and good grain quality due to strong resistance to lodging. L342 had a short peduncle, making the panicle compact, and its phenotype was similar to the dwarfness controlled by Dw7, but the dwarfing genes were different.     

Inheritance of a gibberellin-responsive dwarf mutant in red clover

Summary Smooth-leaved, regular-flowering dwarf mutants were observed among the progeny of a cross between two normal red clover clones. This dwarf characteristic was controlled by one gene and is recessive to normal growth. The symbol dw₁ is proposed for this character. Dwarf plants responded to foliar application of gibberellic acid.     

四倍体小麦地方品种矮蓝麦矮秆性状的遗传分析

四倍体圆锥小麦(Triticum turgidum L.ssp.turgidum)地方品种矮蓝麦是我国重要的小麦矮秆基因资源,经鉴定其矮秆特性对外源赤霉酸敏感。2012年配制矮蓝麦与2个高秆圆锥小麦的正反交组合,2012—2013年在四川绵阳分别种植F1、F2代和F2:3家系,对株高的遗传分析表明,矮蓝麦的矮秆性状受1对隐性基因控制。利用BSA法构建高秆和矮秆池筛选多态性SSR标记,并对矮蓝麦/青稞麦F2分离群体进行连锁分析,将目标基因定位于7AS染色体上,与标记GWM471的遗传距离为2.5 c M。矮蓝麦与矮秆番麦正反交的F1和F2群体表现非常相似的株高变异特征,初步推测矮蓝麦的矮秆基因是Rht22;进一步用高通量SNP和DAr T标记对两品种进行全基因组扫描,发现二者的遗传相似性高达98.7%~99.3%。因此认为,历史上矮蓝麦和矮秆番麦可能是同一品种,是通过人为交流而传播到不同地方。矮蓝麦携带的矮秆基因在人工合成六倍体小麦遗传背景中降低株高能力中等或较弱,在育种中需要聚合其他矮秆基因而被利用。     

Inheritance of plant height and allelism tests of the dwarfing genes in Chinese barley

In order to find new dwarfing genes, the inheritance of plant height in 25 Chinese barley dwarf accessions was studied and allelism tests carried out, not only between the dwarfing genes found but also with the known dwarfing genes uz, br, sdw and denso. The results showed that out of the 25 dwarf accessions, 20 were due to monogenic recessiveness and four to digenic recessiveness. Only the short plant character in ‘1974E’ was controlled by a recessive together with a dominant dwarfing gene. In the present study, seven recessive and one dominant new dwarfing genes were identified. Five recessive genes were found in the monogenic mutants ‘91G318’, ‘91D27’ and ‘93‐597’ and in the Tibetan monogenic dwarf landraces ‘Jia Jiu’ and ‘BQK’, respectively. The other two recessives were found in the Tibetan digenic dwarf landraces ‘ZLL’ and ‘ZLLQK’, and the one dominant gene in the digenic mutant ‘1974E’.     

An induced brachytic mutant of chickpea and its possible use in ideotype breeding

Mutations were induced in chickpea (Cicer arietinum L.) cultivar ‘JG 315’ through treatment of seeds with ethyl methane sulphonate (EMS). One of the mutants, named JGM 1, had brachytic growth (compact growth), characterized by erect growth habit, thick and sturdy stem, short internodal and interleaflet distances and few tertiary and later order branches. It was isolated from M₂ derived from seeds treated with 0.6% EMS for 6 h. Segregation analyses in F₂ progenies of its crosses with normal chickpea genotypes (JG 315, ICC 4929, and ICC 10301) suggested that a single recessive gene controlled brachytic growth in JGM 1. This gene was not allelic to the br gene for brachytic growth in spontaneous brachytic mutant E100YM. Thus, the gene for brachytic growth in JGM 1 was designated br2 and the br gene of E100YM was redesignated br1. Efforts are being made to use JGM 1 in development of a plant type with short internodes and erect growth habit. Such plant type may resist excessive vegetative growth in high input (irrigation and fertility) conditions and accommodate more plants per unit area.     

An approach to DNA polymorphism screening in <Emphasis Type="Italic">SBEIIa</Emphasis> homeologous genes of polyploid wheat (<Emphasis Type="Italic">Triticum</Emphasis> L.)

The non-transgenic manipulation of starch properties in common wheat (Triticum aestivum L.) generally implies combining mutant alleles of the particular gene copies in all three subgenomes (A, B and D). The redundancy of the hexaploid wheat chromosome set substantially complicates the identification of recessive mutations and breeding. Nevertheless, naturally occurring or induced genetic polymorphism has already been successfully exploited for the production of waxy (GBSSI-deficient) and elevated amylose (SSIIa-deficient) wheats. However, in order to achieve the amylose content above 50% of wheat endosperm starch, it may be necessary to inactivate the starch branching enzyme (SBEIIa) isoforms, as the RNAi repression results and gene expression data strongly suggest. The identification of null SBEIIa alleles and their combination in a single genotype is therefore a promising approach to the production of non-transgenic high-amylose wheat; however, wheat SBEIIa polymorphism has not been characterized as of yet. In order to develop an approach to SBEIIa mutation screening, we sequenced the SBEIIa central region (exons 9–12) from the three subgenomes of common wheat cv. Chinese Spring and the A genome of diploid einkorn T. monococcum. The genome-specific primers were developed that amplify the exons downstream from intron 11 selectively from each homeologous gene. Using a single-stranded DNA conformation polymorphism (SSCP) approach, we screened 60 wheat cultivars, landraces, and rare species for naturally occurring SNPs in exons 12, 13 and 14 of the three SBEIIa homeologs. In total, 13 SNPs were discovered in the A and B wheat genomes. Two of these SNPs affect the amino acid sequences of SBEIIa isoforms and may change the enzyme functional properties. The presence of restriction site polymorphism at SNP positions enables their easy genotyping with CAPS assays. Our results indicate that the mining for naturally occurring sequence polymorphism in starch biosynthesis genes of wheat can be successfully performed at the DNA level, providing the starting point for a search for SBEIIa mutants at a larger scale.     

Inheritance of morphological traits of periwinkle mutants with modified contents and yields of leaf and root alkaloids

Periwinkle Catharanthus roseus is a medicinally important plant producing anticancer and antihypertension alkaloids. Two mutants, one dwarf and one semidwarf and both, with a high alkaloid content in the roots and one mutant with a wavy leaf margin and a high alkaloid content in its leaves were obtained after induced chemical mutagenesis with ethyl methane sulphonate and N-nitroso-N-ethylurea in the variety ‘Nirmal’, which is resistant to dieback disease. These mutants were evaluated in the M₃ and M₄ generations. The dwarf and semidwarf mutants differed from the parental variety for many morphological characters, while the mutant with the wavy leaf margin differed mainly in leaf size and leaf thickness. Although both dwarf and semidwarf mutants showed a significantly higher alkaloid content in their roots in both generations, only the semidwarf mutant gave a significantly higher (23%) root alkaloid yield than the parental variety. The mutant with the wavy leaf margin showed a significantly higher alkaloid content in the leaves in both the M₃ and M₄ generations and also had a significantly higher (21%) leaf alkaloid yield than the parental variety. All three mutants were found to be controlled by monogenic recessive genes; the genes for ‘dwarfness’ and ‘semidwarfness’ were allelic to each other, with the allele for semidwarfness being dominant over the allele for dwarfness. The gene for the wavy leaf margin was inherited independently of the genes for dwarfness and semidwarfness.     

The characteristics and stability of a range of Cox's Orange Pippin apple mutants showing different growth habits

Summary Seven hundred and fifty gamma-irradiated scions of Cox's Orange Pippin apple were grown to produce a V₁ generation and were then multiplied to produce a V₂ of 13 158 individual trees. 272 obvious vegetative mutants, mainly dwarf or compact types, were found in this population and classified according to growth habit. These were propagated to produce clones of the mutant types (V₃) and a study of these clonal mutants as compared with their original (V₂) characteristics showed that while the vast majority of the selected mutants produced dwarf or compact clones, no clear indication of final cropping performance could be drawn from the original phenotype of the selected V₂ mutants.The majority of mutants produced were not of commercial value, and the main reasons for the rejection of V₃ clones depended, in many cases, on the phenotype of the V₂ selection. Thus while all types of V₂ mutant produced approximately the same proportion of acceptable trees, the reason for the rejection of the V₃ clones varies with the V₂ phenotype. Therefore selection can be carried out at an early stage in a mutation breeding programme to reduce the proportion of certain unwanted types such as mericlinal chimaeras that otherwise are carried forward to yield trials. From the orchard trials of 82 mutant clones, 24 were short-listed for possible commercial introduction. All were derived from the less extreme mutant types.     

Agronomical performance and breeding value of selected strains of diploid wheat,Triticum monococcum

Summary Twenty-one germplasm accessions and breeding lines of einkorn wheat (Triticum monococcum ssp. monococcum and ssp. sinskajae) were grown at two sites in Italy and evaluated for various field and seed characteristics. Grain yields of germplasm accessions were relatively high (317–3238 kg/ha), but distinctly lower than those of four modern cultivars of tetraploid (T. turgidum ssp. durum) and hexaploid wheat (T. aestivum ssp. Aestivum) included in the experiments as controls. As expected, all Einkorns-including some substantially higher yielding crossbred lines (3415–4362 kg/ha)-were defective for one or more agronomically relevant features. However, a few of the accessions examined were found to contain, as a group, practically all the genes needed to breed monococcums having the main field attributes of a modern wheat cultivar: high yielding capacity, good threshability, large kernel size, earliness, short stature and adequate lodging resistance. Still higher yielding diploid wheats, more responsive to improved growing conditions and of better seed quality, could probably be obtained from crosses with wild monococcums bearing mostly two-seeded florets and with accessions producing less slender-shaped kernels. Some of the Einkorns examined were found to carry minor genes for easy threshing which might enhance the efficacy of the major gene for soft glumes carried by T. monococcum ssp. sinskajae, a partially free-threshing diploid wheat taxon. Seed protein percentage of monococcums was markedly higher than that of durum and bread wheat cultivars even in those cases where their grain yields surpassed those of the polyploid checks. The possibilities offered by diploid wheat in the exploitation of novel endosperm mutants and F₁ hybrid vigour, as well as in the fields of celiac disease, crop diversification and resistance to agro-biological stresses are discussed. Breeding priorities and strategies are also proposed.     

On the inheritance of the dwarf character in Polyantha × Rosa chinensis minima (Sims) Voss F1-populations

Summary The inheritance of the dwarf character was studied in F1-seedling populations arisen from crosses between diploid Polyantha cultivars and the diploid dwarf species R. chinensis minima (Sims) Voss. Dwarfness is controlled by a single dominant gene D. R. chinensis minima and its dwarf descendants are heterozygous for D, while polyanthas are homozygous for d. The origin of R. chinensis minima and its potential for breeding new pot roses are discussed.     

Inheritance of internode length,plant form,and annual habit in a cross of cabbage and broccoli (Brassica oleracea var. capitata L. and var. italica Plenck.)

Summary When an inbred line of cabbage, Brassica oleracea L. var. capitata L., was crossed with an inbred line of broccoli B. oleraceae var. italica, the F₁ progeny were vigorous late annuals. All F₁ × broccoli backcross plants and 92% of the 3260 F₂ plants were annuals, while 40% of the F₁ × cabbage backcross plants were biennials. Annual habit is thus dominant and controlled by more than a single gene. Number of days to bud appearance in annuals varied continuously, and was primarily additive in inheritance. F₁ data suggested partial dominance for lateness but this was not supported by the F₂. Internode length was also continuous in distribution and primarily additive in inheritance, but with some dominance for short internodes in the F₁. Cabbage head forming ability was recessive and multigenic, with 2% of the F₂ plants forming heads, of which none were of commercial type and about half bolted as annuals. There was a significant chi square association between biennial habit and tendency for cabbage head formation. Clasping habit of terminal leaves was recessive to open leaves, multigenic, and associated with both cabbage heading and biennial habit.Technical Paper 4836, Oregon Agricultural Experiment Station; from an M.S. thesis by the senior author.     

Characteristics and Inheritance of Seed-Ageing Induced Mutations in Lettuce (Lactuca sativa L.)

Mutations affecting qualitative traits were induced by seed ageing in lettuce. The mutant plants were isolated in the A₂ generation and included chlorophyll-deficient types (chlorotica, lutescens, chlorina-virescens, luteo and viridalbo maculate), and morphological variants (dwarf and narrow, thick and curly leaf types). The leaf mutants were found to be either partially or completely sterile. Segregation pattern of the mutants in A₃ generation showed that, except for the maculata types, all chlorophyll deficiencies and the dwarf mutant are controlled by single recessive nuclear genes. The genetic status of the leaf mutants was not clear, due to possible pleiotropic effect of the mutant genes in inducing gametophytic sterility. The maculata mutants exhibited sorting out of the normal and chlorophyll deficient regions during vegetative development and segregated for different degrees of chlorophyll deficiency in selfed progenies. The maculata mutants probably originated by plastome mutations induced by nuclear mutator genes.     

Genetic analysis of apical lethality in <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

Investigations were carried out to determine the nature and number of genes governing apical lethality (apical death) in a number of intervarietal crosses of wheat. Genetic analysis of data in segregating generations of the cross WR95/HW2041 and its reciprocal cross revealed that WR95 carries a recessive gene that leads to the death of certain individuals when combined with another recessive gene derived from HW2041. The phenomenon, which is denoted here as “apical lethality”, is controlled by two complementary recessive genes coming together from two different parents in certain F₂ individuals. The gene symbols apd ₁ in WR95 and apd ₂ in HW2041 are proposed for these genes of apical lethality, respectively. Uniculms observed in the F₂ generation are heterozygous (apd ₁ apd ₁ Apd ₂ apd ₂) and, therefore, the uniculmness trait does not breed true. Of the wheat genotypes tested, the gene apd ₂ was found to be present in CL983, CL1019, Lok-1, HW2041, HD2329, HW2011, WH147, HW2042, HW2047, WR196, WR544, WR798 and WR936, while the remaining genotypes, including some of the exotics such as Atila, carried both Apd ₁ and Apd ₂ in the homozygous condition.     

The effects on grain endosperm structure of an introgression from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch. into chromosome 5A of bread wheat

The endosperm structure of the wheat kernel determines its end-use quality. The known diversity in endosperm structure is related to the Pina-D1 and Pinb-D1 genes comprising the Ha locus on chromosome 5DS. We studied the effect of a gene introduced into bread wheat from the diploid relative, Aegilops speltoides, a putative donor of the B genome. Grain hardness and vitreousness were investigated in lines with homoeologous introgressions into chromosome 5A of spring wheat cultivar ‘Rodina’. One introgression changed the endosperm texture from hard to soft and had the same effect when transferred to other wheat genotypes. This indicated that its action was analogous to the dominant allele at the Ha locus. The temporary symbol Ha–Sp is given to the gene. Segregation for vitreousness in F₃ offspring from monosomic hybrids was also investigated. Genetic variability for endosperm structure in wheat may be extended by manipulating both hardness and vitreousness. Wheat germplasm with introgressions from wild relatives can increase the genetic variability of milling characteristics.     

Hybrid dwarfness in wheat

Hybrid dwarfness is the phenomenon that after crossing of normal genotypes dwarfs are obtained in the F₁ or not before the F₂-generation. The literature on hybrid dwarfness in wheat is critically discussed. A new hypothesis on its genetic basis is given, taking McMillan's (1937) as a starting point. Dwarfness is assumed to be determined by the additive interaction of three genes D ₁, D ₂ and D ₃, differing in dominance relations and in quantitative contribution to the dwarf phenotype.Three dwarf types are described. Type 1-dwarfs are dwarf during their whole life cycle and normally do not produce seeds. Type 2-dwarfs start as normal seedlings, become dwarfs while tillering and die dwarfs; some produce seeds, others do not. Type 3-dwarfs emerge as normal seedlings, become dwarfs during the tillering stage, but after some time they start to shoot and develop into nearly or even completely normal plants; in the F₂ the proportion of dwarfs decreases during the growing season. The occurrence and genetic basis of the three dwarf types is discussed.On the basis of their genotype 315 varieties and lines are divided into six genotypeclasses. Over 1000 intra- and inter-class crosses were made and F₁, F₂, F₃, and BC studied. Also some triple crosses and crosses with pure breeding dwarfs were investigated. In general the results obtained fit the hypothesis. Unstable ratios involving type 3-dwarfs are discussed separately.Linkage of the dwarf gene D ₂ and the necrosis gene Ne ₂ (both on chromosome 2B (XIII) was apparent from F₂-data and from results of a triple cross in which both forms of hybrid weakness occurred. Crossing-over between D ₂ and Ne ₂ is calculated to be 34%.Methods are outlined to use hybrid dwarfness in a wheat breeding programme. The possible incompleteness of the three-gene hypothesis and the variability of dwarfness are discussed and finally some suggestions are made for future research.     

Effect of alien 5R(5A) chromosome substitution on ear-emergence time and winter hardiness in wheat-rye substitution lines

Ear emergence time and response to vernalization were investigated in 12 alien substitution lines in which a pair of chromosomes 5A of recipient spring wheat cultivars was replaced by a pair of chromosomes 5R of Siberian spring rye ‘Onokhoiskaya’. The recipients were 12 spring cultivars of common wheat, each carrying different Vrn genes. Spring rye ‘Onokhoiskaya’ had the Sp1 (now called Vrn-R1) gene for spring growth habit located on chromosome 5R, but its expression was weaker. The Vrn-R1 gene had no effect on growth habit, ear emergence time and response to vernalization in wheat-rye substitution lines. Ears emerged significantly later in the 5R(5A) alien substitution lines than in the recipient wheat cultivars with the Vrn-A1/Vrn-B1/vrn-D1 or Vrn-A1/vrn-B1/Vrn-D1 genotypes. No difference in ear emergence time was found between most of the 5R(5A) alien substitution lines and the cultivars carrying the recessive vrn-A1 gene. The presence of the Vrn2a and Vrn2b alleles at the Vrn2 (now called Vrn-B1) locus located on wheat chromosome 5B was confirmed.The replacement of chromosome 5A by chromosome 5R in wheat cultivars ‘Rang’ and ‘Mironovskaya Krupnozernaya’, which carries the single dominant gene Vrn-A1, converted them to winter growth habit. In field studies near Novosibirsk the winter hardiness of 5R(5A) wheat–rye substitution lines of ‘Rang’ and ‘Mironovskaya Krupnozernaya’ was increased by 20–47% and 27–34%, respectively, over the recurrent parents.