Marker based enrichment of provitamin A content in two tropical maize synthetics

Most of the maize (Zea mays L.) varieties in developing countries have low content of micronutrients including vitamin A. As a result, people who are largely dependent on cereal-based diets suffer from health challenges due to micronutrient deficiencies. Marker assisted recurrent selection (MARS), which increases the frequency of favorable alleles with advances in selection cycle, could be used to enhance the provitamin A (PVA) content of maize. This study was carried out to determine changes in levels of PVA carotenoids and genetic diversity in two maize synthetics that were subjected to two cycles of MARS. The two populations, known as HGA and HGB, and their advanced selection cycles (C1 and C2) were evaluated at Ibadan in Nigeria. Selection increased the concentrations of β-carotene, PVA and total carotenoids across cycles in HGA, while in HGB only α-carotene increased with advances in selection cycle. β-cryptoxanthine increased at C1 but decreased at C2 in HGB. The levels of β-carotene, PVA, and total carotenoids increased by 40%, 30% and 36% respectively, in HGA after two cycles of selection. α-carotene and β-cryptoxanthine content improved by 20% and 5%, respectively after two cycles of selection in HGB. MARS caused changes in genetic diversity over selection cycles. Number of effective alleles and observed heterozygosity decreased with selection cycles, while expected heterozygosity increased at C1 and decreased at C2 in HGA. In HGB, number of effective alleles, observed and expected heterozygosity increased at C1 and decreased at C2. In both populations, fixation index increased after two cycle of selections. The greatest part of the genetic variability resides within the population accounting for 86% of the total genetic variance. In general, MARS effectively improved PVA carotenoid content. However, genetic diversity in the two synthetics declined after two cycles of selection.

Increasing selection gain and accuracy of harvest prediction models in Jatropha through genome-wide selection

Genome-wide selection (GWS) has been becoming an essential tool in the genetic breeding of long-life species, as it increases the gain per time unit. This study had a hypothesis that GWS is a tool that can decrease the breeding cycle in Jatropha. Our objective was to compare GWS with phenotypic selection in terms of accuracy and efficiency over three harvests. Models were developed throughout the harvests to evaluate their applicability in predicting genetic values in later harvests. For this purpose, 386 individuals of the breeding population obtained from crossings between 42 parents were evaluated. The population was evaluated in random block design, with six replicates over three harvests. The genetic effects of markers were predicted in the population using 811 SNP's markers with call rate = 95% and minor allele frequency (MAF) > 4%. GWS enables gains of 108 to 346% over the phenotypic selection, with a 50% reduction in the selection cycle. This technique has potential for the Jatropha breeding since it allows the accurate obtaining of GEBV and higher efficiency compared to the phenotypic selection by reducing the time necessary to complete the selection cycle. In order to apply GWS in the first harvests, a large number of individuals in the breeding population are needed. In the case of few individuals in the population, it is recommended to perform a larger number of harvests.

Recurrent selection for resistance to Thrips tabaci in a tropical onion population

Recurrent selection for resistance to onion Thrips tabaci has not been well studied by breeding programmes. Onion thrips is a pest of major concern and is controlled by insecticide spraying, raising production costs and potentially damaging the environment. This study aimed to estimate onion bulb yield genetic gain through six cycles in the ‘BRS Alfa São Francisco’ developed by recurrent selection for T. tabaci resistance. Experiments were carried out in a randomised block design, with three replications, in two locations. The degree of infestation in plants was evaluated five times after transplanting, as well as plant architecture traits and bulb yield. The latest selection cycle presented bulb commercial yield of 32.1 t.ha-1, while the base population ‘Alfa Tropical’ and IPA 10 check cultivar 15.9 and 14.0 t.ha-1, respectively (p<0.01). The broad sense heritability values ranged from 0.65 to 0.74 for bulb yield. The mean genetic gain was 1.0 t.ha-1 or 6% per selection cycle, indicating the efficiency of the method to increase the frequency of favourable alleles for thrips resistance and the possibility of onion cultivation in the total absence of insecticide applications to control this pest, or a reduction in their number

Reduced Iris Yellow Spot Symptoms through Selection within Onion Breeding Lines

Iris yellow spot (IYS) disease in onion (Allium cepa L.) is caused by onion thrips (Thrips tabaci L.) vectored Iris yellow spot virus (IYSV). The absence of cultivars that are resistant/tolerant to thrips and/or IYS is a challenge for onion bulb and seed production worldwide. To measure selection progress for reduced/delayed IYS symptom expression in onion breeding lines after two selection cycles, selections were performed in 2011 on previously evaluated lines that exhibited a reduced symptom expression after one selection cycle. Selected plants from each line were massed in a cage and the resulted progenies were evaluated in 2013 and 2014 along with their original populations and a susceptible check—’Rumba’. In some comparisons, the selection progress for delayed/reduced IYS symptom expression was observed for some breeding lines. Plants of most selected breeding lines exhibited less disease expression than plants of ‘Rumba’. For some selections, a low disease severity was observed even with a relatively high number of thrips per plant. These results suggest that further improvement might be achievable with additional cycles of selection.

Recurrent Selection with Glufosinate at Low Rates Reduces the Susceptibility of a Lolium perenne ssp. multiflorum Population to Glufosinate

Repeated applications of herbicides at the labelled rates have often resulted in the selection and evolution of herbicide-resistant weeds capable of surviving the labelled and higher rates in subsequent generations. However, the evolutionary outcomes of recurrent herbicide selection at low rates are far less understood. In this study of a herbicide-susceptible population of Lolium perenne ssp. multiflorum, we assessed the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and cross-resistance to herbicides with other modes of action. Reduced susceptibility to glufosinate was detected in progeny in comparison with the parental population following three rounds of selection at low glufosinate rates. Differences were mainly observed at the 0.5X, 0.75X, and 1X rates. Comparing the parental susceptible population and progeny from the second and third selection cycle, the percentage of surviving plants increased to values of LD50 (1.31 and 1.16, respectively) and LD90 (1.36 and 1.26, respectively). When treated with three alternative herbicides (glyphosate, paraquat, and sethoxydim), no plants of either the parental or successive progeny populations survived treatment with 0.75X or higher rates of these herbicides. The results of this study provide clear evidence that reduced susceptibility to glufosinate can evolve in weed populations following repeated applications of glufosinate at low herbicide rates. However, the magnitude of increases in resistance levels over three generations of recurrent low-rate glufosinate selection observed is relatively low compared with higher levels of resistance observed in response to low-rate selection with other herbicides (three fold and more).

Recurrent selection with glufosinate at low rates reduces the susceptibility of a Lolium perenne ssp. multiflorum population to glufosinate

ABSTRACTRepeated applications of herbicides at the labelled rates have often resulted in the selection and evolution of herbicide-resistant weeds capable of surviving the labelled and higher rates in subsequent generations. However, the evolutionary outcomes of recurrent herbicide selection at low rates are far less understood. In this study of an herbicide-susceptible population of Lolium perenne ssp. multiflorum, we assessed the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and cross-resistance to herbicides with other modes of action. Reduced susceptibility to glufosinate was detected in progeny in comparison with the parental population following three rounds of selection at low glufosinate rates. Differences were mainly observed at the 0.5X, 0.75X, and 1X rates. Comparing the parental susceptible population and progeny from the second and third selection cycle, the percentage of surviving plants increased to values of LD50 (1.31 and 1.16, respectively) and LD90 (1.36 and 1.26, respectively). When treated with three alternative herbicides (glyphosate, paraquat, and sethoxydim), no plants of either the parental or successive progeny populations survived treatment with 0.75X or higher rates of these herbicides. The results of this study provide clear evidence that reduced susceptibility to glufosinate can evolve in weed populations following repeated applications of glufosinate at low herbicide rates. However, the magnitude of increases in resistance levels over three generations of recurrent low-rate glufosinate selection observed is relatively low compared with higher levels of resistance observed in response to low-rate selection with other herbicides (three fold and more).

Comparing Efficiencies of Two Selection Approaches for Improving Fusarium Basal Rot Resistance in Short-Day Onion after a Single Cycle of Selection

The development of Fusarium Basal Rot (FBR)-resistant onion cultivars through field and seedling screening approaches faces tremendous challenges due to non-uniform distribution of the disease pathogen and possible multiple mechanisms of host–plant resistance. This study compared the efficiencies of these two methods for increasing FBR resistance of short-day onion after a single selection cycle. Asymptomatic plants or bulbs of seven onion cultivars were selected using a seedling screen performed in a growth chamber or a field screening of mature bulbs. Original and selected populations were evaluated for their responses to FBR stress thereafter employing the same two methods used for screening. The field screening of mature bulbs was found unreliable in both selection and evaluation, likely due to a non-random distribution of the FBR pathogen and variable environmental factors present in the field. The seedling screening successfully increased FBR resistance in the selected cultivar populations revealed by a seedling evaluation. From the results, it is recommended to use a consistent method for both screening and evaluation to make the most selection progress.

Efficiency of the backcrossing method in dihaploid maize breeding

The doubled haploid (DH) lines, obtained by doubling the haploid genome, are now widely used in breeding many crops, since they allow to transfer gene variants to the homozygous state in a short time. However, the advantages of doubled haploids are not fully utilized in maize breeding. The present work is devoted to the evaluation of the backcrossing method efficiency and to further development of the original schemes of creating highly productive homozygous maize lines on the basis of DH lines originating from an interline F1 hybrid. Rf7 and Ku123 maize lines were used as the initial material. The breeding cycle consisted of producing haploid plants in the selected genotype (matroclinic haploidy using an inducer), subsequent chromosome doubling (colchicine‑induced or spontaneous), followed by multiplication of the doubled haploids for obtaining a new set of DH lines. In the first cycle, the DH lines were obtained from the F1 hybrid (Rf7 × Ku123), while in the subsequent cycles they were obtained from the genotypes obtained by crossing a DH line selected from the previous cycle with F1, P1 or P2. Three cycles of selection for productivity were performed, and in 2017 the DH lines obtained in all cycles were simultaneously tested in the field. The breeding progress was estimated by the increase in the first ear productivity compared to the best parent Rf7 (103.9 g per plant in 2017). The first selection cycle resulted in 43 DH lines obtained on the basis of the F1 hybrid. Productivity of the best line rk‑5 amounted to 112.5 g per plant. Three lines (rk‑6, rk‑5 and rk‑22) selected for the next cycle were further crossed with F1 or with the parental line Rf7. The second selection cycle yielded three series containing 41, 49 and 16 lines, while productivity of the best genotypes was 121.2, 117.0 и 107.1 g per plant, respectively. The third cycle included populations of 24 and 8 lines obtained through backcrosses with Rf7 and Ku123 lines, respectively. The best genotypes in these series had productivity of 135.6 and 97.7 g per plant. As a result of selection, the obtained rk‑433 line had a productivity 30.5% higher than that of the best parent Rf7. The progress averaged 10.2% per cycle. In maize breeding using doubled haploids it is promising to use backcrosses of the selected DH lines with the initial material or with F1. Thanks to such an approach, a noticeable progress can be reached with a small number of cycles including from 20 to 50 DH lines.

First Report of Recurrent Genomic Selection with Real Data in Popcorn and Genetic Gain Increases

Recurrent Selection increases the frequencies of favorable alleles for economically important traits, which in the case of popcorn are popping expansion and grain yield. However, is time-consuming, since each selection cycle consists of three stages: progeny development and evaluation, and recombination of the best families. With the Recurrent Genomic Selection use, the time required for each selection cycle can be shortened, as it allows the evaluation and recombination phases to be performed simultaneously, reducing the time needed to complete one selection cycle to only one growing season. In this respect, the objective of this study was to determine the selection accuracy and genetic gains for different selection strategies: PhEN = estimates based exclusively on the phenotypic data of 98 plants; PhEN + GEN = estimates based exclusively on the phenotypic and genotypic data of 98 plants; and GEN = estimates based exclusively on SNP marker genotyping. The following traits were evaluated: 100-grain weight, ear height, grain yield, popping expansion, plant height, and popcorn volume. Field trials were carried out with 98 S1 progenies, at two locations, in an incomplete block design with three replications. The parents of these progenies were genotyped with a panel of ~ 21K SNPs. From the results based on the predictions by strategy GEN, at different selection intensities, the average annual genetic gain for the different traits was 29.1% and 25.2% higher than that by the strategies PhEN and GEN + PhEN for 98 selection candidates; 148.3% and 140.9% higher for 500; and 187.9% and 179.4% higher for 1,000 selection candidates, respectively. Therefore, recurrent genomic selection may result in a high genetic gain, provided that: i) phenotyping is accurate; ii) selection intensity is explored by genotyping several plants, increasing the number of selection candidates, and iii) genomic selection is used for early selection in recurrent selection.