A leaf rust resistance gene, different from Lr34, associated with leaf tip necrosis in wheat

The gene Lr34 has contributed to durable resistance to leaf rust caused by Puccinia triticina in wheat worldwide. The closely associated leaf tip necrosis is generally used as the gene's marker. Lr34 has been postulated in many Indian bread wheat cultivars including ‘C 306’, based on the associated leaf tip necrosis and a few other field and glasshouse observations. The present study showed monogenic control of adult‐plant resistance in ‘C 306’ to leaf rust pathotype 77‐5 (121R63‐1). The F₂ segregation in the crosses between ‘C 306’ and the two known carriers of Lr34, ‘Line 897’ and ‘Jupateco 73’‘R’ fitted a digenic ratio. The F₃ families derived from the susceptible F₂ segregants were true breeding for susceptibility, proving the absence of Lr34 in ‘C 306’. The cross between ‘Line 897’ and ‘Jupateco 73’‘R’ did not segregate for susceptibility. Resistance in the cross ‘Agra Local’ (susceptible) × ‘C 306’ was associated with leaf tip necrosis, showing that the leaf rust resistance gene in ‘C 306’ was associated with leaf tip necrosis, but was different from Lr34. This gene is being temporarily designated as Lr‘C 306’. Hence, leaf tip necrosis cannot be considered as an exclusive marker for selecting Lr34 in wheat improvement.     

Intergeneric crosses for the transfer of resistance to the beet cyst nematode from Raphanus sativus to Brassica napus

Summary The possibilities to transfer important traits and in particular resistance to the beet cyst nematode (Heterodera schachtii, abbrev. BCN) from Raphanus sativus to Brassica napus were investigated. For these studies B. napus, R. sativus, the bridging hybrid ×Brassicoraphanus (Raparadish) as well as offspring of the cross ×Brassicoraphanus (Raparadish) ×B. napus were used. Reciprocal crosses between B. napus and R. sativus were unsuccessful, also with the use of embryo rescue. Crosses between ×Brassicoraphanus as female parent and B. napus resulted in a large number of F₁ hybrids, whereas the reciprocal cross yielded mainly matromorphic plants. BC₁, BC₂ and BC₃ plants were obtained from backcrosses with B. napus, which was used as the male parent. F₁ hybrids and BC plants showed a large variation for morphology and male and female fertility. Cuttings of some F₁ and BC₁ plants, obtained from crosses involving resistant plants of ×Brassicoraphanus, were found to possess a level of resistance similar to that of the resistant parent. These results and indications for meiotic pairing between chromosomes of genome R with those of the genomes A and/or C suggest that introgression of the BCN-resistance of Raphanus into B. napus may be achieved.     

Heterosis in crisphead lettuce (Lactuca sativa L.) hybrids

Summary Six of 16 F₁ hybrids from diverse crosses of crisphead lettuce with butterhead, cos or other crispheads significantly outyielded their respective better parent. Four were crosses between crisphead and cos parents, one was a butterhead × crisphead cross and one, a winter crisphead × winter crisphead cross. This latter hybrid plus one other also proved heterotic in a subsequent trial of ten crosses involving five winter crisphead parents, with yield excesses over better parent of 16 and 19%. It appeared significant that the heterotic crosses were given by parents of dissimilar origin. Trials of F₂ segregants from one of these heterotic hybrids enabled predictions to be made for 10.2 to 24.1% yield increases over better parent by the retention and clonal multiplication of the 10% highest yielding selections. Heterosis demonstrated in these trials may constitute the first reported cases in lettuce.     

Inheritance of the virgata pattern of partly colored seed coats in ‘Early Giant’ common bean

The inheritance of the virgata pattern of partly colored seed coats found in common bean (Phaseolus vulgaris L.) Early Giant (EG) was studied by a series of test crosses with line 5-593 and genetic stocks developed by backcrossing selected genes into the recurrent parent 5-593, a Florida dry bean breeding line with a self-colored, black seed coat with genotype T Z Bip P [C r] J G B V Rk. Analysis of the F₂ from the cross EG × 5-593 led to the hypothesis that the virgata pattern of EG has genotype t z bip^vgt, where vgt stands for virgata. The test cross EG × t z virgarcus BC₃ 5-593 confirmed the hypothesis that EG carries t z from data recorded in F₁, F₂, and 27 F₃ progenies from randomly selected F₂ plants. The F₃ segregation was also consistent with the hypothesis that a single recessive gene converts virgarcus into virgata. The test cross EG × t z bip bipunctata BC₃ 5-593 failed to show genetic complementation in F₁ progeny, and the F₂ segregated 3:1 for the parental phenotypes virgata and bipunctata, respectively. Including previously published data, all possible crosses were made among bipunctata, virgata, and virgarcus parents, supporting a multiple allelic series at Bip. We propose the gene symbol bip^vgt for the new allele at Bip, where the allelic series has the order of gene dominance Bip > bip^vgt > bip. Based on test crosses, the complete seed-coat color and pattern genotype of EG is tz bip^vgt P [C r] J G B v^lae rk^d.     

Major gene control of tolerance of bread wheat (Triticum aestivum L.) to high concentrations of soil boron

Summary The genetic control of tolerance of wheat to high concentrations of soil boron was studied for five genotypes. Each genotype represented one of five categories of response to high levels of boron, ranging from very sensitive to tolerant. Tolerance to boron was expressed as a partially dominant character, although the response of an F₁ hybrid, relative to the parents, varied with the level of boron applied. The F₁ hybrids responded similarly to the more tolerant parent at low B treatments and intermediate to the parents at higher treatments. Ratios consistent with monogenic segregation were observed for the F₂ and F₃ generations for the combinations (WI^*MMC) × Kenya Farmer, Warigal × (WI^*MMC) and Halberd × Warigal. The three genes, Bo1, Bo2 and Bo3, while transgressive segregation between two tolerant genotypes, G61450 and Halberd, suggested a fourth locus controlling tolerance to boron.     

Hybrid necrosis as a problem for the wheat breeder

Hybrid necrosis is the premature gradual death of leaves and leaf sheaths in certain wheat hybrids. It is based on two complementary genes Ne ₁ and Ne ₂. Hitherto 89 Ne ₁-carriers and 207 Ne ₂-carriers from many countries are known (table 1 and 2). This corresponds with more than 18,000 different necrotic cross combinations.The degree of necrosis in the F₁'s varies greatly, due to multiple allelism of Ne ₁ and Ne ₂. Nine necrosis grades are described in table 3. Grades 6–8 are called severe necrosis (no seed is produced), 3–6 moderate necrosis (premature seed), 0–3 weak necrosis (normal seed). Most severely necrotic F₁'s could be brought to seed production by raising them under extra favourable conditions in a small growth-chamber. Growing moderately necrotic F₁'s in pots outside, at a high fertility level of the soil, resulted in a striking increase of the seed production.On the basis of the above mentioned data and results some practical advice is given to the breeders about the handling of necrotic crosses. In addition some ways to preclude hybrid necrosis are indicated, though the wheat breeder is advised against a systematic avoiding of necrosis because many combinations of excellent varieties then remain untried.     

The transfer of triazine resistance from Brassica napus L. to B. oleracea L. III. First backcross to parental species

Summary Atrazine resistant Brassica napus × B. oleracea F₁ hybrids were backcrossed to both parental species. The backcrosses to B. napus produced seeds in both directions but results were much better when the F₁ hybrid was the pollen parent. Backcrosses to B. oleracea failed completely but BC₁s were rescued by embryo culture both from a tetraploid hybrid (2n = 4x = 37; A₁C₁CC) and sesquidiploid hybrids (2n = 3x = 8; A₁C₁C). Progeny of crosses between the tetraploid hybrid and B. oleracea had between 25 and 28 chromosomes. That of crosses between the sesquidiploid hybrid and B. oleracea had between 21 and 27. A few plants that had chromosome counts outside the expected range may have originated from either diploid parthenogenesis, unreduced gametes or spontaneous chromosome doubling during in vitro culture. Pollen stainability of the BC₁s ranged from 0% to 91.5%. All the BC₁s to B. oleracea were resistant to atrazine.     

Heterosis in Primary Hexaploid Triticale with Heterozygous Wheat or Rye Genome*)

Twelve primary hexaploid triticale (X Triticosecale Wittmack), synthesized from, three lines of tetraploid wheat (Triticum durum L., T. turgidum L.) and four inbred lines of rye (Secale cereale L.), were used to produce 18 crosses with homozygous wheat and heterozygous rye genome and 12 crosses with heterozygous wheat and homozygous rye genome. Parents and crosses of triticale, wheat, and rye were tested for two years (rye for one year only) in two-replicate block designs with 1 m²-plots. Data were assessed for plant height, grain yield and for yield-related traits. Performance of triticale crosses was considerably lower than that of the wheat and rye crosses. The amount of heterosis varied greatly between years. Positive and mainly significant heterosis was revealed in triticale generations F₁ and F₂. The average values were closer to those in wheat than to those in rye. For most characters a high level of heterosis was retained in tnucalt1 generation F₂. Heterozygosity of the wheat and rye genome both contributed to heterosis in triticale. However, gene action of the rye genome strongly depended on the homozygous wheat background: one wheat line almost completely suppressed and another greatly stimulated the heterotic effect of the rye genome. In the later case, the amount of heterosis was related to that in rye per se. Information from hybrid rye breeding may therefore be used when establishing gene pools for hybrid breeding in triticale.     

Inheritance of downy mildew resistance in Indian cauliflower (group III)

Summary Inheritance of downy mildew (Peronospora parasitica) resistance in three resistant x susceptible crosses, one susceptible x susceptible and one resistant x resistant cross were studied in Indian cauliflower (Group III) over the two years (1990 and 1991). No significant difference was observed between the years for various estimates and hence pooled data are presented. Downy mildew resistance in crosses cc×HR 5-4 and 3-5-1-1×244 (R×S) is governed by single dominant gene PPA3 but in cross cc×244 (R×S), recessive epistasis was observed. The resistance level was not improved in both the cc×3-5-1-1 (R×R) and 244×267-6-9 (S×S) crosses. Exploitation of downy mildew resistance from cc and 3-5-1-1 in F₁ hybrid is explained in detail.     

Inheritance of the mosaic and necroses reactions induced by bean severe mosaic comoviruses in Phaseolus vulgaris L.

The inheritance of the localized necrosis, apical necrosis, and mosaic reactions induced by bean severe mosaic comoviruses in common bean (Phaseolus vulgaris L.), was studied in crosses of Great Northern 123 × Pitouco, Great Northern 123 × Iguaçu and Pitouco X Iguaçu. Great Northern 123 reacts with mild mosaic, Iguaçu with localized necrosis, and Pitouco with apical necrosis to bean severe mosaic comoviruses. The analysis of the F₁ and F₂ generations indicated that localized necrosis was dominant over mild mosaic, and apical necrosis was dominant over the localized necrosis and the mild mosaic. An independently inherited single dominant gene controlled the expression of localized and apical necrosis in cultivars Iguaçu and Pitouco, respectively. The dominant gene for apical necrosis (Anv) found in Pitouco, was epistatic over the dominant gene (Lnv) conditioning localized necrosis in Iguaçu, as suggested by the F₂ of Pitouco × Iguaçu, that yielded a ratio of 12 apical necrosis: 3 localized necrosis:1 mild mosaic. The genotypes of Pitouco, Iguaçu and Great Northern 123 are: Anv Anv lnv lnv, anv anv Lnv Lnv, and anv anv lnv lnv, respectively.     

Inheritance of resistance to cucumber green mottle mosaic virus in muskmelon (Cucumis melo L.)

Summary Studies on inheritance of resistance to CGMMV showed that resistance was governed by polygenes with recessive nature. Out of 15 crosses studied, 10 were found to be interacting. All the interacting crosses (except one Phoot x Harela) showed duplicate type of epistasis. Kachri x Phoot (R × R type) cross exhibited heterosis in F₁ and transgressive segregation in F₂ for resistance. Studies pointed out the need to exploit this F₁ further to develop a new breeding line with higher level of resistance than both the parents.     

Productivity of F hybrids of botanical varieties ofBrassica oleracea L.

Summary F₁ hybrids were obtained by making pair-crosses between nine botanical varieties ofBrassica oleracea. Although non-inbred parents were used, their yield was surpassed by all F₁ hybrids. The highest yields were shown by the crosses marrow-stem kale × sprouting broccoli and marrow-stem kale × cauliflower while the highest consumable yield (assessed by feeding plants to sheep) was that of F₁ hybrids marrow-stem kale × cauliflower and wild cabbage × cauliflower. A scheme for the production of F₁ hybrid seed is suggested, based upon an adaptation ofThompson's (1964) Triple-cross technique.     

Segregation for heading date and stem enlargement in kohlrabi x broccoli crosses

Summary F₁ and F₂ progenies from crosses of an early broccoli (Brassica oleracea var. italica L.) line with kohlrabi (B. oleracea var. gongyloides) indicated that days to flower bud maturity in annual segregates is quantitative and additive in inheritance. It appeared that the biennial kohlrabi parent strongly contributed genetic factors for late maturity. F₁ plants of both crosses, 98% of F₂ plants from early broccoli × kohlrabi, and 81% of the F₂ plants from late broccoli × kohlrabi were annual in 1980. In 1986, 96% of early broccoli × kohlrabi F₂ and 87% of late broccoli × kohlrabi F₂ plants were annual. Kohlrabi stem enlargement showed a continuous range of expression in the F₂ with some dominance of broccoli type. Few F₂ plants were close to the kohlrabi parent in degree of stem enlargement.     

Distribution and allelic expressivity of genes for hybrid necrosis in some elite winter and spring wheat ecotypes

The distribution and allelic expressivity of hybrid necrosis genes (Ne ₁ and Ne ₂) were studied in 21 winter (mostly exotic) and 43 spring type elite wheat genotypes, by crossing them with two known testers, C 306 (Ne ₁-carrier) and HD 2380 (Ne ₂-carrier).Ne ₁ gene was present in one north-west Himalayan winter wheat landrace, Shoure Local, but absent in the other winter as well as spring wheats. Ne ₂ gene was prevalent to a much lower extent in the exotic winter wheat germplasm (31.57%) as compared to the recently developed Indian and Mexican spring wheat semidwarfs (69.80%). This may suggest that breeders have tried to preclude hybrid necrosis by selecting for non-carrier genotypes in the development of exotic winter wheats in contrast to the situation in spring wheats. Based on the degree of expression of hybrid necrosis genes in the F₁ hybrids, the carrier genotypes were characterized with respect to the allelic strength of the hybrid necrosis genes. The 27 non-carrier genotypes of the two ecotypes identified in the present study have a greater potential use in future hybridization programmes so as to overcome the problem of hybrid necrosis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of diploid and tetraploid potato families derived from Solanum phureja x dihaploid S. tuberosum hybrids and their vegetatively doubled counterparts

Summary To determine whether in potatoes the tetraploid level is preferable to the diploid level, especially regarding tuber yield, four diploid (2n=2×=24) Solanum phureja x dihaploid S. tuberosum hybrid parents and their vegetatively doubled, tetraploid (2n=4×=48) counterparts were intermated, which resulted in two F₁ hybrid families at both levels of ploidy. The parents and clones of the F₁ families and their offspring were used in crosses in such a way that in addition Sib₁, Sib₂, F₁×Sib₁, BC₁ and Sib₁×Sib₁ families were produced. Of the first clonal generation of the 12 2 x families and their 12 counterpart 4 x families two tubers per clone were planted in three replications in a field experiment at Sturgeon Bay in 1969; of the parents six tubers were planted in each replication. Data were recorded on 16 characters, including plant height at four different times.The ANOVA's showed significant clone effects within each family for all characters. Computed from all family means as well as from the family means per ploidy level, differences due to family were also significant for all characters except one.As at the 2 x level and at the 4 x level of ploidy the mean phenotypic correlations between characters were of similar magnitude, it is concluded that they are independent of ploidy level.With the exception of eye depth, the mean coefficient of variation was greater at the 2 x than at the 4 x level of ploidy, indicating the greatest response to selection for those characters at the 2 x level. From the differences in family means between the 4 x and the 2 x level of ploidy it was apparent that the 4 x families generally had significantly taller plants, later maturity, fewer tubers, higher mean tuber weight, more tuber yield and more dry matter yield than their counterpart 2 x families. In contrast, the 4 x parents had on the average shorter plants, lower mean tuber weight, much lower tuber yield and lower dry matter yield than their 2 x counterparts.The phenotypic correlation and Spearman's rank correlation between the family means of the 2 x and the 4 x level of ploidy were positive for almost all characters and significant for nearly half of them.From the results it is concluded that 1. in potatoes the 4 x level of ploidy is preferable to the 2 x level, and 2. the performance of 4 x families is predictable from the performance of their counterpart 2 x families.Based on results mentioned in the literature and on the present results, a continued use of S. tuberosum dihaploids in potato breeding needs to be dissuaded.     

Interspecific crosses in the genus Lycopersicum

The use of a tetraploid tomato as a pistillate parent in the crosses with Lycopersicum peruvianum and Lycopersicum glandulosum, instead of a diploid tomato, increases about 80 times the set of hybrid seed and thus gives a broader basis for the breeding work. The results seem to indicate that in the crosses on a diploid level, only unreduced eggcells of the tomato fertilized by haploid pollen of the above wild species, develop into normal seeds, and give rise to sesquidiploid F₁ progeny.     

Individual reaction of <Emphasis Type="Italic">Capsicum</Emphasis> F<Subscript>2</Subscript> hybrid genotypes in anther cultures

The present study evaluated the individual plants reaction of F₂ hybrid generation of C. annuum: ATZ1 × PO and ATZ1 × CDT as well as two interspecific hybrids: C. frutescens × C. annuum ATM1 and C. frutescens × C. chinense on androgenesis conditions in in vitro anther cultures. The experiment was carried out following a modified method of Dumas de Vaulx et al. (Agronomie 1:859–864, 1981). There were demonstrated clear differences in the effectiveness of androgenesis both between the pepper hybrid forms as well as among individual plants of all the genotypes tested. The highest effectiveness of androgenic embryos development was observed for the cultivated form of C. annuum: (ATZ1 × PO)F₂. Anthers of most of the plants of this hybrid produced embryos at the level higher than 5%, while in anther cultures of the second C. annuum hybrid (ATZ1 × CDT)F₂ almost 3-fold fewer embryos and plants were produced. Anthers isolated from flower buds of interspecific hybrids formed much lower number of embryos. A positive reaction was recorded for five hybrid plants of (C. frutescens × C. annuum ATM1)F₂, while in case of (C. frutescens × C. chinense)F₂ androgenic embryos were obtained from anthers of two plants. Only in the case of a one of these plants did the effectiveness of androgenesis exceed 5%. The ploidy level of the regenerants was determined by flow cytometry. Among the regenerants there were observed both haploid forms and the plants with the diploid number of chromosomes.     

Predicting transgressive segregants in early generation using single seed descent method-derived <Emphasis Type="Italic">micro-macrosperma</Emphasis> genepool of lentil (<Emphasis Type="Italic">Lens culinaris</Emphasis> Medikus)

In a self-fertilised crop like lentil, the identification of transgressive segregants for economically important trait such as seed yield is an important aspect of any practical breeding programme. The prediction of expected transgressive segregants in F₁ generation obtained as a ratio of additive genic effect [d] and additive variance (D) i.e. [d]/√D was studied in 28 crosses of lentil generated in a diallel fashion involving four parents each of macrosperma (exotic) and microsperma (Indian) types, respectively, resulting in three hybridization groups. The seed material advanced to F₂, F₃ and F₄ generations through single seed descent method was evaluated to determine the observed transgressive segregants for seed yield/plant. The observed frequency of crosses showing more than 20% transgressive segregants in F₂ to F₄ generations were exhibited in 9(32%) crosses, of which 7(77%) crosses were of macrosperma × microsperma type. Genotypes Precoz and HPL-5 of the exotic group (macrosperma) produced maximum number of transgressive segregants with the genotypes L-259, L-4145 and PL-406 of the Indian origin (microsperma). Goodness of fit (non-significant χ² value) in F₂ generation was observed for 19(68%) crosses of the total genepool, out of which 9(56%) crosses each in F₃ and F₄ generation belonged to the macrosperma × microsperma group, depicting it as the gene pool of paramount importance to obtain maximum transgressive segregants, therefore establishing the efficacy of the method used.     

Inheritance of insensitivity to culture filtrate of Pyrenophora tritici-repentis, race 2, in wheat (Triticum aestivum L.)

Tan spot of wheat is caused by the fungus Pyrenophora tritici‐repentis. On susceptible hosts, P. tritici‐repentis induces two phenotypically distinct symptoms, tan necrosis and chlorosis. This fungus produces several toxins that induce tan necrosis and chlorosis symptoms in susceptible cultivars. The objectives of this study were to determine the inheritance of insensitivity to necrosis‐inducing culture filtrate of P. tritici‐repentis, race 2, and to establish the relationship between the host reaction to culture filtrate and spore inoculation with respect to the necrosis component. The F₁, F₂, and BC₁F₁ plants and F_2:8 lines of five crosses involving resistant wheat genotypes ‘Erik’, ‘Red Chief’, and line 86ISMN 2137 with susceptible cultivars ‘Glenlea’ and ‘Kenyon’ were studied. Plants were spore‐inoculated at the two‐leaf stage. Four days later, the newly emerged uninoculated third leaf was infiltrated with a culture filtrate of isolate Ptr 92–164 (race 2). Reactions to the spore inoculation and the culture filtrate were recorded 8 days after spore inoculation. The segregation observed in the F₂ and BC₁F₁ generations and the F_2:8 lines of all crosses indicated that a single recessive gene controlled insensitivity to necrosis caused by culture filtrate. This gene also controlled resistance to necrosis induced by spore inoculation.     

Hybrid seed production using nutritional mutants

Summary This paper describes a method of obtaining pure stands of F₁ hybrids even if selfing occurs, e.g. the male-sterility is imperfect. The procedure is based on the use of recessive nutritional (auxotrophic) gene(s). The F₁ hybrids of the auxotroph × prototroph crosses are phenotypically and physiologically normal. The self-or sib-pollinated auxotrophic parental line(s) produce lethal offspring in the absence of the required nutrient.In crosses involving functional male-sterile maternal lines and thiamine-dependent male tomato lines (or reciprocals), the described scheme works as predicted. This scheme is now being employed in the production of hybrid tomato. Although some problems were experienced during the preliminary work with barley mutants the overall results are promising.The hybrid-production scheme has various advantages: (I) it is applicable in normally selfing species, too. (II) the two parental lines can be blended in hybrid crossing blocks, thereby increasing cross pollination, (III) it involves a genetically determined built-in system for selective elimination of the plants of unwanted constitution, and the scheme can therefore be used with imcomplete male- or self-sterile lines, too.