Nature and type of gene action governing resistance to Helminthosporium turcicum leaf blight in maize (Zea mays L.)

Six generations, consisting of three resistant parents, three susceptible parents, their 15 possible F₁ crosses, 15 F₂'s, 15 BC₁'s (F₁ x resistant female parent) and 15 BC₂'s (F₁ x susceptible male parent) were analysed following Hayman (Heredity 12: 371–390, 1958) to evaluate the nature and type of gene action governing resistance to H. turcicum. The results showed that all types of gene effects, viz., additive, dominance and epistasis (i.e., additive x additive, additive x dominance and dominance x dominance) were operating in one cross or the other in controlling resistance. However, it was additive gene action and dominance x dominance type of epistasis with duplicate nature that were important in controlling resistance in most crosses. Depending upon the final objectives, one of the breeding methods, viz., recurrent selection, heterosis breeding, back-cross method or full-sib selection (bi-parental mating) may be followed.     

Inheritance and allelism tests of Raiden soybean for resistance to soybean mosaic virus

The gene symbol Rsv2 was previously assigned to the gene in the soybean [Glycine max (L.) Merr.] line OX670 for resistance to soybean mosaic virus (SMV). The Rsv2 gene was reported to be derived from the Raiden soybean (PI 360844) and to be independent of Rsv1. Accumulated data from our genetic experiments were in disagreement with this conclusion. In this study, Raiden and L88-8431, a Williams BC5 isoline with SMV resistance derived from Raiden, were crossed with two SMV-susceptible cultivars to investigate the mode of inheritance of SMV resistance in Raiden. They were also crossed with five resistant cultivars to examine the allelomorphic relationships of the Raiden gene with other reported genes at the Rsv1 locus. F1 plants, F2 populations, and F2-derived F3 (F2:3) lines were tested with SMV strains G1 or G7 in the greenhouse or in the field. The individual plant reactions were classified as resistant (R, symptomless), necrotic (N, systemic necrosis), or susceptible (S, mosaic). The F2 populations from R x S crosses segregated in a ratio of 3 (R + N):1 S and the F2:3 lines from Lee 68 (S) x Raiden (R) exhibited a segregation pattern of 1 (all R):2 segregating:1 (all S). The F2 populations and F2:3 progenies from all R x R crosses did not show any segregation for susceptibility. These results demonstrate that the resistance to SMV in Raiden and L88-8431 is controlled by a single dominant gene and the gene is allelic to Rsv1. The heterozygous plants from R x S and R x N crosses exhibited systemic necrosis when inoculated with SMV G7, indicating a partial dominance nature of the resistance gene. Raiden and L88-8431 are both resistant to SMV G1-G4 and G7, but necrotic to G5, G6, and G7A. Since the resistance gene in Raiden is clearly an allele at the Rsv1 locus and it exhibits a unique reaction to the SMV strain groups, assignment of a new gene symbol, Rsv1-r, to replace Rsv2 would seem appropriate. Further research is ongoing to investigate the possible existence of the Rsv2 locus in OX670 and its relatives.     

Inheritance of time to flowering in chickpea in a short-season temperate environment

Time to flowering is central in determining the adaptation and productivity of chickpea in short-season temperate environments. We studied the genetic control of this trait in three crosses, 272-2 x CDC Anna, 298T-9 x CDC Anna, and 298T-9 x CDC Frontier. From each cross, 180 F2 plants and parents were evaluated for time to flowering under greenhouse conditions. In summer 2004, multiple generations including P1, F1, P2, F2, and F2:3 (also called MG5) were evaluated for time to flowering under field conditions. The data on time to flowering in the F(2) populations were continuous in distribution but deviated from normal distribution. The F2:3 families derived from this showed a bimodal distribution for time to flowering, a typical case of major-gene inheritance model with duplicate recessive epistasis. A joint segregation analysis of MG5 also revealed that time to flowering in chickpea was controlled by two major genes along with other polygenes. Late flowering was dominant over early flowering for both major genes with digenic interaction between them, mainly an additive x additive type. This information can be used to formulate the most efficient breeding strategy for improvement of time to flowering in chickpea in short-season temperate environments.     

Gene action for adult-plant resistance to powdery mildew in wheat.

Gene action for adult-plant resistance to powdery mildew was studied using generation mean analyses of parents and of F1, F2, and backcross populations derived from a diallel cross of one susceptible and three adult-plant resistant wheat cultivars. Joint scaling tests showed that an additive-dominance model was sufficient to explain the variability in the expression of adult-plant resistance in one cross, while digenic epistasis was involved in the other five crosses. Additive gene effects were predominant; however, dominance was significant in four crosses, additive x additive interaction was significant in three crosses, additive x dominance interaction was significant in three crosses, and dominance x dominance interaction was significant in one cross. Therefore, selection for adult-plant resistance would likely be most effective in advanced generations derived from crosses among the adult-plant resistant cultivars Redcoat, Houser, and Massey.     

Inheritance and fine mapping of fertility restoration for cytoplasmic male sterility in Gossypium hirsutum L

Genetics of CMS fertility restoration was presented through the analysis of classic genetics and molecular markers. Based on F(2) segregation of the crosses between CMS and the restoring lines, the testcrosses and F(1) x F(1) populations, together with RAPD and SSR mapping, one dominant gene was identified to control the CMS fertility restoration in cotton. The strategy of genotype representation analysis (GRA) was put forward to screen the markers linked with the Rf(1) locus. Using 1,025 random decamer primers and 282 pairs of SSR primers, two RAPD and three SSR markers were identified to be closely linked to the Rf(1) gene. Among the five markers, three were co-dominantly inherited. Additionally, based on the analysis of monosomic and telesomic lines with one SSR maker, the Rf(1) locus could be located on the long arm of chromosome 4. The molecular markers available here are helpful in the development of the elite restoring lines in cotton by marker-assisted selection.     

Molecular mapping of two loci that confer resistance to Asian rust in soybean

Asian soybean rust (ASR) is caused by the fungal pathogen Phakopsora pachyrhizi Sydow & Sydow. It was first identified in Brazil in 2001 and quickly infected soybean areas in several countries in South America. Primary efforts to combat this disease must involve the development of resistant cultivars. Four distinct genes that confer resistance against ASR have been reported: Rpp1, Rpp2, Rpp3, and Rpp4. However, no cultivar carrying any of those resistance loci has been released. The main objective of this study was to genetically map Rpp2 and Rpp4 resistance genes. Two F(2:3) populations, derived from the crosses between the resistant lines PI 230970 (Rpp2), PI 459025 (Rpp4) and the susceptible cultivar BRS 184, were used in this study. The mapping populations and parental lines were inoculated with a field isolate of P. pachyrhizi and evaluated for lesion type as resistant (RB lesions) or susceptible (TAN lesions). The mapping populations were screened with SSR markers, using the bulk segregant analysis (BSA) to expedite the identification of linked markers. Both resistance genes showed an expected segregation ratio for a dominant trait. This study allowed mapping Rpp2 and Rpp4 loci on the linkage groups J and G, respectively. The associated markers will be of great value on marker assisted selection for this trait.     

Inheritance of resistance to Phomopsis seed decay in PI 360841 soybean

Phomopsis longicolla Hobbs is the primary cause of Phomopsis seed decay (PSD) in soybean. Infection may result in moldy seed and poor germination. The objective of this study was to conduct inheritance studies to characterize resistance to PSD in plant introduction (PI) 360481. Crosses were made between PI 360841 and 2 PSD-susceptible genotypes, Agripro (AP) 350 and PI 91113, to determine the number of genes for resistance. Additionally, crosses were made between PI 360841 and Phomopsis resistant parents MO/PSD-0259 and PI 80837 to test the allelism of the resistance genes. Seed infection assays were done using seed from parent plants and F(2) populations. Chi-square analysis of the resistant x susceptible F(2) data fit to a 9R:7S model for 2 complementary dominant genes conferring PSD resistance in PI 360841. Segregation for reaction in the F(2) of MO/PSD-0259 x PI 360841 exhibited a good fit to a 57R:7S model for 2 complementary dominant genes from PI 360841 and a different dominant gene from MO/PSD-0259. There was no apparent segregation in the F(2) population from PI 360841 x PI 80837 except for one suspicious susceptible plant, suggesting one of the genes in PI 360841 is the same gene in PI 80837 for PSD resistance.     

Inheritance of resistance to flumethrin in the Mexican Aldama strain of the cattle tick Boophilus microplus (Acari: Ixodidae)

The objective of this study was to evaluate the inheritance mode of resistance to flumethrin in the Mexican Aldama Boophilus microplus strain. Two Mexican strains were used, the Chiapas susceptible (SS), and the Aldama flumethrin-resistant from Tamaulipas. Six steers weighing ca. 250 kg were randomly assigned for each of six crosses: the susceptible (SS), resistant (RR), and the F1 (RS, SR) reciprocal crosses and F2 (RS x RS and SR x SR). The reciprocal crosses were made to evaluate maternal and sex linkage effects. Bioassays tested resistant and susceptible larvae along with their hybrid F1 and F2 progeny against a series of concentrations of flumethrin (0, 0.0075, 0.00150, 0.00300, 0.00600 and 0.01200 microg/g). To test the single-gene hypothesis of resistance, a nonparametric line-cross test proposed by Collins was used. The bioassay data were subjected to probit analysis and the resistance factor and effective dominance obtained. Results of this study indicated that inheritance for flumethrin resistance in the Aldama strain was autosomal and controlled for more than one gene. The F1 and F2 larvae had similar lower resistant factor (RF 2.8-4.5) while the resistant Aldama strain was 21-fold higher (RF 81.8) than the mean of the F1 and F2. The extent of flumethrin resistance in the Aldama B. microplus strain depended upon the concentration of the pesticide used. Resistance was almost dominant at the lowest dose while almost completely recessive at the highest dose. Maternal effects were shown for egg-mass. These results shown here indicate more than one gene basis of flumethrin resistance in B. microplus ticks are present. Therefore it is necessary to locate and understand the major loci for elucidate the mechanism of resistance and improve the ability to track and delay the evolution of resistance.     

Fitness costs and maternal effects associated with resistance to transgenic cotton in the pink bollworm (Lepidoptera: Gelechiidae).

Transgenic cotton producing a Bacillus thuringiensis (Bt) toxin is widely used for controlling the pink bollworm, Perctinophora gossypiella (Saunders). We compared performance of pink bollworm strains resistant to Bt cotton with performance of their susceptible counterparts on non-Bt cotton. We found fitness costs that reduced survival on non-Bt cotton by an average of 51.5% in two resistant strains relative to the susceptible strains. The survival cost was recessive in one set of crosses between a resistant strain and the susceptible strain from which it was derived. However, crosses involving an unrelated resistant and susceptible strain indicated that the survival cost could be dominant. Development time on non-Bt cotton did not differ between the two related resistant and susceptible strains. A slight recessive cost affecting development time was suggested by comparison of the unrelated resistant and susceptible strains. Maternal effects transmitted by parents that had eaten Bt-treated artificial diet as larvae had negative effects on embryogenesis, adult fertility, or both, and reduced the ability of neonates to enter cotton bolls. These results provide further evidence that fitness costs associated with the evolution of resistance to Bt cotton are substantial in the pink bollworm.     

Inheritance of apospory in bahiagrass,Paspalum notatum

Previous studies on the inheritance of aposporous apomixis in bahiagrass showed a wide range of segregation ratios in crosses involving sexual and aposporous apomictic plants. The F1 progenies were classified through a visual progeny test carried out on few F2 plants. The number of sexual F1s highly exceeded the apomictics leading to the conclusion that apomixis was controlled by a few recessive genes. The present study examines the inheritance of apospory in bahiagrass. A sexual plant was self-pollinated and crossed with an aposporous apomictic plant as pollen donor. Backcross and F2 progenies were obtained in several combinations. All self-pollinated sexual plants or sexual x sexual crosses produced progenies free of apospory. All crosses involving a sexual and an apomictic plant produced approximately three times more apospory-free plants than plants with apospory. Bahiagrass is of autotetraploid origin and hence is expected to display tetrasomic inheritance. The most widely accepted genetic model for inheritance of apospory in tropical grasses is a single dominant gene with tetrasomic inheritance. In the present experiments none of the apospory-free F1s segregated for the apospory trait indicating that it is most likely a dominant character. However, the observed results fit better a modified model: tetrasomic inheritance of a single dominant gene with pleiotropic effect and incomplete penetrance. The excess of apospory-free plants in the F1 progeny could be ascribed to some distortion in the segregation pattern due to a pleiotropic lethal effect of the dominant A allele with incomplete penetrance. Alternatively, partial lethality of factors linked to aposporous gene may account for segregation distortion against apospory.     

Maternal effects and generation mean analysis of seed-oil content in cotton (Gossypium hirsutum L.)

Summary The nature of gene action and of maternal influence governing cottonseed oil attributes were determined with four lines, two each with high and low seed-oil percentage. For this purpose, P1, P2, F0, F1, F2 and alternative sets of BC1 and BC2 generations were analysed in six cross-combinations and their reciprocals. Marginal extents of heterosis for seed-oil percentage were noticeable in F1, with inbreeding depression in F2. Data from reciprocal backcrosses provided evidence in favour of maternal rather than cytoplasmic effects of seed-oil development. Relatively higher extents of heterosis, sizeable inbreeding depression and reciprocally unequal F2 averages were characteristic of the seed index trait, which often showed a reversal of effects from F1 to F2. Reverse reciprocal backcrosses exhibited some differences, including greater resemblance between the types, (A/B)A and (B/A)A, in addition to variable dose effects in seed index. Thus, the differences between F1 seed index values were not due to cytoplasmic influence. Positive heterotic effects for seed-oil index, especially among the backcrosses, ranged between 16.08% and 47.29% over midparent averages. Genetic component estimates from analysis of similar sets of crosses differing only in reciprocal backcrosses, and also from sets of reciprocal crosses between any two parental combinations, were inconsistent. Scaling tests detected presence of epistasis within and between a majority of cross-combinations. Despite reciprocal differences, additive gene effects for seed-oil percentage were significant in 7 out of 24 crosses, representing high x low, low x high and low x low seed-oil parents. Those were, however, accompanied by significant dominance effects of higher order. In crosses involving low seed-oil percentage parents SA1060 and SA229, all six components were detected significant, with opposite effects of dominance and dominance x dominance epistatic components. Significant additive components were also detected for seed index and seed-oil index in 7 and 5 out of 24 crosses, respectively. In the inheritance of seed index and seed-oil index, dominance effects were more important. Epistatic components of additive x additive, and to a lesser extent, those of dominant x dominant were found significant.     

Genetics of Burley and Flue-Cured Tobacco Resistance to Globodera tabacum tabacum

Genotypes of burley (cultivars B-21 and B-49), flue-cured (line VA-81 and cultivar PD-4), and Connecticut broadleaf (cultivar C9) tobacco (Nicotiana tabacum) resistant (R) or susceptible (S) to the tobacco cyst nematode Globodera tabacum tabacum were crossed. F1 progeny of burley and susceptible broadleaf were selfed and backcrossed to produce additional progeny for evaluation of resistance in greenhouse experiments. Plants without adult female nematodes visible (×10 magnification) on the root surface 6 weeks after inoculation were classified as resistant, whereas those plants in which one or more females were evident were classified as susceptible. Segregation ratios for progeny of resistant and susceptible plants were not different from 3:1 and 1:1 for F2 (F1 × F1) and BC1 (F1 × S) lines, respectively, indicating that resistance in burley to G. t. tabacum is conferred by a single, dominant gene. Segregation ratios for resistance in crosses between nematode-resistant burley and flue-cured tobacco (F1 and F2 progeny) and between burley-flue-cured hybrids and broadleaf BC1 (F1 × S) and BC2 (BC1 × S) progeny were consistent with the assumption that resistance to G. t. tabacum in burley and flue-cured tobacco is conferred by the same or closely linked single, dominant gene(s).     

小粒野生稻导入系对稻飞虱的抗性鉴定与分析

稻飞虱是水稻生产最严重的害虫之一。野生稻拥有丰富的抗虫基因资源,导入系是鉴定和利用野生稻有利基因的有效途径。本研究通过对371份小粒野生稻导入系进行抗褐飞虱和白背飞虱接虫鉴定,分别筛选出了11份抗、72份中抗褐飞虱的材料和7份抗、45份中抗白背飞虱的材料,其中有5份材料兼抗褐飞虱和白背飞虱,这是从小粒野生稻中鉴定出抗白背飞虱材料的首次报道。通过对2份抗性导入系材料与感虫亲本杂交构建的F1和F2群体的抗虫鉴定和分析表明:K41对褐飞虱和白背飞虱的抗性受2对显性抗虫基因通过互补作用所控制;P114对褐飞虱和白背飞虱的抗性都是由1对主效的隐性基因控制。这些结果必将有利于小粒野生稻抗稻飞虱的基因定位和育种利用。     

Dominant Gene cplsr1 Corresponding to Premature Leaf Senescence Resistance in Cotton (Gossypium hirsutum L.)

Cotton (Gossypium hirsutum L.) premature leaf senescence-resistant inbred XLZ33 and senescencesusceptible inbred lines XLZ13 were selected and crossed to produce F1,F1-reciprocal,F2 and BC1 generations...     

Qualitative inheritance of water-stress induced apical sterility in wheat (Triticum aestivum)

Grain number per unit area is an effective component of grain yield in bread wheat. Water-stress induced apical sterility (tip sterility) reduces the number of grains and, consequently, the grain yield in semi-arid regions with a shortage of available water during the pre-anthesis period. Crosses between apical sterile and apical fertile varieties and selection lines were made and F1, BC1, and F2 populations were subjected to moderate water-stress to study the inheritance of this character. The F2 and BC1 plants were qualitatively categorised into two phenotypes and tested for monohybrid and dihybrid segregation hypotheses. All the spikes of F1 plants obtained from crosses between apical fertile and apical sterile varieties were fully fertile indicating apical fertility is dominant to apical sterility. The F2 segregation Results from crosses between apical fertile lines and Y82187 suggested two complementary dominant genes segregating independently were involved in tolerance to water-stress induced apical sterility. In other words, two dominant genes determine apical fertility in these crosses and if one of these loci is homozygous, recessive waterstress will induce apical sterility. One F2 population segregated for both apical sterility and vernalisation response. Semi-winter plants had more sterile spikelets and the result of chi-square test confirmed monhybrid segregation for vernalisation response.     

Discovery of second gene for solid dark green versus light green rind pattern in watermelon

The watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus) has high variability for fruit size, shape, rind pattern, and flesh color. This study was designed to measure the qualitative inheritance of rind phenotypes (solid dark green vs. light green). For each of the 2 families, "Mountain Hoosier" × "Minilee" and "Early Arizona" × "Minilee," 6 generations (P(a)S(1), P(b)S(1), F(1), F(2), BC(1)P(a), BC(1)P(b)) were developed. Each family was tested in summer 2008 in 3 environments in North Carolina. Phenotypic data were analyzed with the χ(2) method to test the segregation of Mendelian genes. Deviations from the expected segregation ratios based on hypothesized single dominant gene for solid dark green versus light green rind pattern were recorded, raising questions on the inheritance of this trait. Inheritance of solid dark green rind versus light (gray) rind showed duplicate dominant epistasis. Duplicate dominant epistasis gives rise to a 15:1 ratio (solid dark green:light rind pattern) in F(2) generation. When both the loci are homozygous recessive, we observe light rind pattern. The g-1 and g-2 genes were identified to control light green rind when in homozygous recessive form.     

Inheritance of diflubenzuron resistance and monooxygenase activities in a laboratory-selected strain of Lucilia cuprina (Diptera: Calliphoridae).

Inheritance of the high-level diflubenzuron resistance shown by a laboratory-selected strain of Lucilia cuprina (Wiedemann) was examined in matings with a susceptible reference strain. Progeny of reciprocal crosses between resistant females and susceptible males showed higher LC50 values than the alternate reciprocal cross, indicating some maternal influence on inheritance of resistance. Resistance was inherited in a codominant (S male x R female) or incompletely recessive (R male x S female) manner. Monooxygenase activities (aldrin epoxidation) of the F1 generations were also intermediate between the levels shown by the parental lines, however, inheritance of enzyme activities showed greater degrees of dominance than for resistance levels. There was also some maternal influence on inheritance of monooxygenase activities. Backcrosses of F1 generations to both susceptible and resistant parents did not fit the expected patterns for a major sex-linked resistance locus, indicating that the maternal influence on resistance inheritance was not associated with sex-linkage of a major resistance gene. The backcross data also failed to fit the model for a single major autosomal gene, suggesting that the resistance in the diflubenzuron-selected strain is polygenic, involving mechanisms additional to monooxygenases.     

Fitness of Cry1A-resistant and -susceptible Helicoverpa armigera (Lepidoptera: Noctuidae) on transgenic cotton with reduced levels of Cry1Ac

The performance of Helicoverpa armigera (Hübner) on 15-wk-old cotton plants was compared for a susceptible strain, a near-isogenic laboratory-selected strain, and F1 progeny of the two strains. Glasshouse experiments were conducted to test the three insect types on conventional plants and transgenic plants that produced the Bacillus thuringiensis (Bt) toxin Cry1Ac. At the time of testing (15 wk), the Cry1Ac concentration in cotton leaves was 75% lower than at 4 wk. On these plants, < 10% of susceptible larvae reached the fifth instar, and none survived to pupation. In contrast, survival to adulthood on Cry1Ac cotton was 62% for resistant larvae and 39% for F1 larvae. These results show that inheritance of resistance to 15-wk-old Cry1Ac cotton is partially dominant, in contrast to results previously obtained on 4-wk-old Cry1Ac cotton. Growth and survival of resistant insects were similar on Cry1Ac cotton and on non-Bt cotton, but F1 insects developed more slowly on Cry1Ac cotton than on non-Bt cotton. Survival was lower and development was slower for resistant larvae than for susceptible and F1 larvae on non-Bt cotton. These results show recessive fitness costs are associated with resistance to Cry1Ac.     

Trypanosoma congolense: Genetic control of resistance to infection in mice

Primary isolates of Trypanosoma congolense show a range of virulence in NMRI mice. Stabiliates derived from an isolate (Dinderesso/ 80/CRTA/3) which showed moderate virulence in most NMRI mice (moderate parasitemia and survival) were used in inbred mice. C57B1/6 were resistant with low parasitemia and survival. Parasitemias were higher in males than females. BALB/c were the most sensitive of the strains tested and died with fulminating parasitemia. Inheritance of resistance, defined as low parasitemia, was studied using these two strains. Male F1 showed high parasitemia; the backcrosses of F1 to the resistant parent had a ratio of one susceptible to one resistant product; the product of F1 to susceptible parent were all susceptible; and the F2 crosses showed a ratio of three susceptible to one resistant product. The results obtained with female F1, backcrosses, and F2 mice showed similar segregation to that found using males, but the range of parasitemia was always 1–2 log₁₀ lower, except for the F1 backcrossed to BALB/c, where female and male parasitemia were undistinguishable. The segregation ratios were identical whether resistant females were crossed with sensitive males or vice-versa. The results obtained are compatible with resistance being a recessive trait controlled by a single autosomal gene (or gene cluster). In addition, sex-associated factors appear to confer higher resistance in females.     

Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F(1) , F (2) , BC (1) Pr, and BC (1) Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn (Ko1) , Pn (Ko2) and Pn (Kr1) , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn (Bz1) , Pn (Bz2) and Pn (Kr2) , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance.