Evaluation of yellow rust resistance in backcross populations of wheat

Aim: To screen wheat populations derived from cross DBW17 × WH1105 for loci imparting yellow rust resistance and selection of plants using polymorphic SSRs. Methodology: The study for yellow rust resistance was carried out on two populations, i.e., BC1F2 and BC2F2. Stress was provided by planting infector rows between the blocks and by artificial inoculation using a mixture of races 46S102, 47S103 and 78S84 of stripe rust pathogen. DNA isolated from young leaves was checked for the presence of yellow rust resistance genes using gene specific primers. Results: Fifteen primers were found to be polymorphic among parents DBW17 and WH1105. Fifteen polymorphic SSR markers were dispersed over the wheat genome (AABBDD), with allele range 2-5. These polymorphic SSR markers were used to produce molecular diversity among progeny lines. Cluster analysis of parents and both the populations, showed that two parents were diverse genetically and in both backcrosses progeny lines resembled their respective recurrent parent. Single marker analysis using data revealed that primers on nine chromosomes were associated with grain yield per plant, other yield attributes and yellow rust resistance in both populations. Interpretation: This study showed that a linked marker like Xgwm582 could be a promising tool for breeding wheat with enhanced tolerance to yellow rust resistance. However, growth rates and biomass production provide reliable criteria for assessing the degree of yellow rust resistance and the ability of a plant to withstand it.

Characterization and inheritance of dicamba resistance in a multiple-resistant waterhemp (Amaranthus tuberculatus) population from Illinois

Waterhemp (Amaranthus tuberculatus (Moq.) Sauer) is one of the most troublesome agronomic weeds in the midwestern US. The rapid evolution and selection of herbicide-resistance traits in A. tuberculatus is a major challenge in managing this species. An A. tuberculatus population, designated CHR, was identified in 2012 in Champaign County, IL, and previously characterized as resistant to herbicides from six site-of-action groups: 2,4-D (Group 4), acetolactate synthase inhibitors (Group 2), protoporphyrinogen oxidase inhibitors (Group 14), 4-hydroxyphenylpyruvate dioxygenase inhibitors (Group 27), photosystem II inhibitors (Group 5), and very long chain fatty acid synthesis inhibitors (Group 15). Recently, ineffective control of CHR was observed in the field after dicamba application. Therefore, this research was initiated to confirm dicamba resistance, quantify the resistance level and investigate its inheritance in CHR. Multiple field trials were conducted at the CHR location to confirm poor control with dicamba and compare dicamba treatments with other herbicides. Greenhouse trials were conducted to quantify the resistance level in CHR and confirm genetic inheritance of the resistance. In field trials, dicamba did not provide more than 65% control, while glyphosate and glufosinate provided at least 90% control. Multiple accessions were generated from controlled crosses and evaluated in greenhouse trials. Greenhouse dicamba dose-response experiments indicated a resistance level of 5 to 10-fold relative to sensitive parental line. Dose-response experiments using F1 lines indicated that dicamba resistance was an incompletely dominant trait. Segregation analysis with F2 and backcross populations indicated that dicamba resistance had moderate heritability and was potentially a multigenic trait. Although dicamba resistance was predominantly inherited as a nuclear treat, minor maternal inheritance was not completely ruled out. To our knowledge, CHR is one of the first cases of dicamba resistance in A. tuberculatus. Further studies will focus on elucidating the genes involved in dicamba resistance.

Identification and Validation of QTLs for Macronutrient Contents in Brown and Milled Rice Using Two Backcross Populations between Oryza sativa and O. rufipogon

Mineral malnutrition as a prevalent public health issue can be alleviated by increasing the intake of dietary minerals from major staple crops, such as rice. Identification of the gene responsible for mineral contents in rice would help breed cultivars enriched with minerals through marker-assisted selection. Two segregating populations of backcross inbred lines (BIL) were employed to map quantitative trait loci (QTLs) for macronutrient contents in brown and milled rice, BC1F5, and BC2F4:5 derived from an interspecific cross of Xieqingzao B (Oryza sativa) and Dongxiang wild rice (O. rufipogon). Phenotyping the populations was conducted in multiple locations and years, and up to 169 DNA markers were used for the genotyping. A total of 17 QTLs for P, K, Na, Ca, and Mg contents in brown and milled rice distributed on eight regions were identified in the BC1F5 population, which is explained to range from 5.98% to 56.80% of phenotypic variances. Two regions controlling qCa1.1 and qCa4.1 were validated, and seven new QTLs for Ca and Mg contents were identified in the BC2F4:5 population. 18 of 24 QTLs were clustered across seven chromosomal regions, indicating that different mineral accumulation might be involved in common regulatory pathways. Of 24 QTLs identified in two populations, 16 having favorable alleles were derived from O. rufipogon and 10 were novel. These results will not only help understand the molecular mechanism of macronutrient accumulation in rice but also provide candidate QTLs for further gene cloning and grain nutrient improvement through QTL pyramiding.

Does fruiting habit traits affect green fruit yield and its component traits in chilli (Capsicum annuum L.)?

In chilli, farmer preferences for fruiting habit traits, namely fruit orientation (pendant erect) and fruits node−1 (solitary cluster), vary from region to region. For increased acceptability by farmers/consumers, cultivars should be bred with preferred fruiting habit traits in high green fruit yielding background. An investigation was carried out to study the influence of fruiting habit traits on green fruit yield and its component traits during the 2016 and 2017 rainy seasons. The F2, backcross populations and near-isogenic lines (NILs) derived from crosses involving parents differing for single or both the fruiting habit traits were grouped into fruiting habit classes (single and cluster fruiting; and clustered erect, clustered pendant, single erect and single pendant). Significance of differences in fruit yield and its component traits between/among different fruiting habit trait classes were examined using ‘t’/‘F’ tests. The significance of ‘t’/‘F’ tests was regarded as pieces of evidence for considerable effects of fruiting habit traits on fruit yield and its component traits. While results-based on F2 and backcross generations indicated a lack of effects, those based on NILs indicated significant effects of fruiting habit traits on fruit yield and its component traits. The plants bearing pendant fruits (irrespective of whether they are clustered or single) produced a large number of heavier and longer fruits than those bearing erect fruits. The results are discussed about the strategies to develop high yielding cultivars with farmer preferred fruiting habit traits.

Heterosis for egg production in native by exotic by inbred chicken crosses

Inbred lines generated from the native and exotic chickens were compared with their F1 and backcross populations for a range of short term egg production traits. The experimental birds were brooded for 8 weeks and raised on a deep litter pens from 8 to 40 weeks of age. Age at first eggs were longer in the crossbred groups and the delay was mostly caused by the dominant genes from the exotic parents. Highly significant (P>0.01) heterosis were obtained by the crossbred groups in hen day rate and total egg mass respectively. The heterosis observed in the crossbred groups for egg weight was low and mostly non significant. the backcross groups recorded residual heterosis in egg production traits ( hen day rate, total egg mass and egg weight) and the magnitude was higher in the exotic than the native backcrosses. The results further indicate that the egg production performance of the crossbred groups were mostly influenced by maternal, sex linked, dominance and epistatic gene effects. It was suggested that the egg production potential of the native chicken could be improved further by cross mating-selected native and exotic backcross groups. This should be followed by crisscrossing.

Genetic architecture of a body color cline in Drosophila americana

Phenotypic variation within a species is often structured geographically in clines. In Drosophila americana, a longitudinal cline for body color exists within North America that appears to be due to local adaptation. The tan and ebony genes have been hypothesized to contribute to this cline, with alleles of both genes that lighten body color found in D. americana. These alleles are similar in sequence and function to the allele fixed in D. americana’s more lightly pigmented sister species, Drosophila novamexicana. To test this hypothesis, we examined the frequency and geographic distribution of D. novamexicana-like alleles of tan and ebony in D. americana. Among alleles from over 100 strains of D. americana isolated from 21 geographic locations, we failed to identify additional alleles of tan or ebony with as much sequence similarity to D. novamexicana as the alleles previously described. However, using genetic analysis of 51 D. americana strains derived from 20 geographic locations, we identified one new allele of ebony and one new allele of tan segregating in D. americana that are functionally equivalent to the D. novamexicana allele. An additional 5 alleles of tan also showed marginal evidence of functional similarity. Given the rarity of these alleles, however, we conclude that they are unlikely to be driving the pigmentation cline. Indeed, phenotypic distributions of the 51 backcross populations analyzed indicate a more complex genetic architecture, with diversity in the number and effects of loci altering pigmentation observed both within and among populations of D. americana. This genetic heterogeneity poses a challenge to association studies and genomic scans for clinal variation, but might be common in natural populations.

Identification of blast resistance QTLs based on two advanced backcross populations in rice

Background: Rice blast is an economically important and mutable disease of rice. Using host resistance gene to breed resistant varieties has been proven to be the most effective and economical method to control rice blast and new resistance genes or quantitative trait loci (QTLs) are then needed. Results: In this study, we constructed two advanced backcross population to mapping blast resistance QTLs. CR071 and QingGuAi were as the donor parent to establish two BC 3 F 1 and derived BC 3 F 2 backcross populations in the Jin23B background. By challenging the two populations with natural infection in 2011 and 2012, 16 and 13 blast resistance QTLs were identified in Jin23B/CR071 and Jin23B/QingGuAi population, respectively. Among Jin23B/CR071 population, 3 major and 13 minor QTLs have explained the phenotypic variation from 3.50% to 34.08% during six observation times. And, among Jin23B/QingGuAi population, 2 major and 11 minor QTLs have explained the phenotypic variation from 2.42% to 28.95% during six observation times. Conclusions: Sixteen and thirteen blast resistance QTLs were identified in Jin23B/CR071 and Jin23B/QingGuAi population, respectively. QTL effect analyses suggested that major and minor QTLs interaction is the genetic basis for durable blast resistance in rice variety CR071 and QingGuAi.