CREA Journals (Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria)
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Genetic diversity among maize inbred lines selected for the mid- altitudes and highlands of Rwanda
Get PDFUnderstanding the genetic diversity and relationships among breeding materials is fundamentally considerable for any crop improvement program. This study was carried out to apply specific single nucleotide polymorphism (SNP) markers to determine the amount of genetic diversity prevailing among maize inbred lines selected for the mid-altitudes and highlands of Rwanda and classify the inbred lines according to their relationships for an effective hybrid breeding program. Seventy one maize inbred lines from different sources were genotyped with ninety two SNP markers. The unweighted pair group method with arithmetic mean (UPGMA) revealed that there was a random allocation of the inbred lines into different clusters and they were allocated into 2 major clusters regardless their origin. The highest (0.375) polymorphic information content (PIC) observed was exhibited by 3 markers; PZA00543_12, PZA00878_2, and PZA01735_1; while the lowest PIC value was revealed by the marker PZA01755_1 (0.1224).The PIC value (0.30) revealed in this study may confirm the potential for these SNP markers to discriminate between inbred lines from diverse origins and their usefulness for diversity analysis of maize inbred lines under this study. Genetic clustering information acquired from the current study would be suitable information not only for maize hybrid program establishment in Rwanda, but also for other collaborative tropical maize breeding programs. This might guide towards suitable heterotic patterns and groups as well as the combining ability of the inbred lines involved in this study
Response of a maize composite to selfed progeny recurrent selection for earliness and yield traits
Get PDFPopulation improvement through recurrent selection is a traditional breeding method that has been used in maize for over 60 years. Objectives of the research were to: a) evaluate effect of selfed progeny recurrent selection on earliness and yield traits, b) compare responses of cycle-1 (S1-line) and cycle-2 (S2-line) populations, and c) determine better strategy for improvement of maize source population «PSEV3». The experiments were carried out in partially balanced lattice square design with two replications. In cycle-1 and cycle-2 populations, the differ- ences were highly significant for all studied traits. Selfing in both cycles of selection, resulted increase in days to tasseling while reduction in population means for yield traits. In selected progenies, an increase was seen in mean values of yield traits; however, not in days to tasseling and grain moisture in both cycles of selection. Moderate to high heritability values were observed for almost all the traits in both cycles. Selection differential values were positive and high for grain yield, ear height, prolificacy, ear length, and 100-grain weight in cycle-1 and cycle-2. However, negative values of selection differential were seen for days to tasseling and grain moisture in cycle-1 and
2 populations. The expected responses for days to tasseling and grain moisture were negative in first and second selection cycles. Comparatively, larger and positive responses were noted in cycle-2 than cycle-1 for grain yield and its components. Selfed progeny recurrent selection method was found more effective in improving the maize source population «PSEV3” for earliness and yield traits
Genetic architecture of lodging resistance revealed by genome- wide association study in maize (Zea mays L)
Get PDFLodging is one of key factors influencing biomass yield, restricting planting density and reducing mechanical harvesting productivity in maize. Targeted cultivating lodging resistance varieties with screened lines is an eco- nomical and effective approach to improve ability of maize lodging resistance. To accomplish this objective, we performed phenotypic assessment of seven lodging-related traits in a diverse maize population consisting of 290 inbred lines and conducted a genome-wide association study with 201 SSR markers to detected marker-trait as- sociations. Seven lodging-related traits all showed broad phenotypic variations. Through evaluation of stalk push- ing resistance in the field for two years, a number of 32 inbred lines featured with strong lodging resistance were selected out. Correlation analysis indicated that stalk pushing resistance had a significantly positive correlation with third internode diameter and fourth internode diameter and a significantly negative correlation with ear height. Furthermore, a total of 27 and 13 significant associations for lodging-related traits were identified in year 2012 and
2013, respectively. Interestingly, three associations on chromosome 4, 5, and 6 were discovered in both years. Thus, this study provides useful information for understanding genetic architecture of lodging resistance in maize and will benefit maize marker-assistant breeding program with improving lodging resistance
Combining ability for grain yield and resistance to maize streak virus in maize
Get PDFCombining ability effects for grain yield, yield-related traits and resistance to maize streak virus (MSV) were determined using 10 parents, 45 single crosses and five standard hybrid checks. Genotypes were evaluated at three locations (Ngaramtoni, Inyala, and Igomelo) over two seasons (2012/13 and 2013/14) using a 6 x 10 simple lattice design with two replications. Data were collected for days-to-50% silking (DSL), days-to-50% anthesis (DA), reaction to MSV disease, plant height (PHT), ear height (EHT), number of ears per plant (EPT), husk cover of cobs (HSC) and grain yield (YLD). General combining ability (GCA) and specific combining ability (SCA) effects were significant (P < 0.05) for all traits except DA and DSL. Parental line TL2012-42 was the best general combiner for YLD, while the parents TL2012-41, TL2012-1 and TL2012-42 were the best combiners for maize streak virus resistance, with negative GCA effects of -10.9%, -10.8% and -10.7%, respectively. The highest SCA effect for grain yield (4.80) was detected in the hybrid TL2012-7/TL2012-38. Crosses such as TL2012-38/TL2012-55 and TL2012-25/TL2012-26 had negative SCA effects for their MSV reaction. The above parental lines and hybrids can be recommended for direct production, or breeding to enhance grain yield and MSV resistance in maize varieties for Tanzania
Genotype by environment interaction effects on grain yield of highland maize (Zea mays L) hybrids
Get PDFMaize varieties adapted to highland environments are generally scarce in East and Central Africa (ECA) since most breeding efforts have focused on mid-altitude maize. As a result, farmers in the highlands of Uganda mainly grow varieties that are bred for the mid-altitude zones. Since these maize varieties are not adapted to highland conditions, their productivity in this region rarely exceeds 2 t ha-1. This study was aimed at determining the effect of genotype by environment interactions (GEI) on the grain yield of highland maize hybrids. The study was conducted
in three highland locations of Uganda in the maize growing season of March to October 2015. Thirty-six F
hybrids and two checks were arranged in a 2 x18 (0, 1) alpha lattice design with two replications. Hybrid by location interaction had highly significant differences (P ≤ 0.001) and explained 46.2% of phenotypic variance. Genotype by environment interactions (GEI), thus, had a strong effect on grain yield. Analyses revealed two maize mega- environments, with AMH701-9/AMH703-22 hybrid emerging the best genotype in Kachwekano and Kalengyere (6.69 t ha-1 and 14.30 t ha-1), and AMH701-9/AMH701-20 hybrid being the best in Buginyanya (14.39 t ha-1). Efforts to breed for high yielding maize cultivars for the highland areas of Uganda should therefore focus more on specific adaptation than broad adaptation
Can elite maize landraces help to improve forage yield and quality? A genetic analysis
Get PDFBroadening the genetic base of maize breeding program is a significant concern for plant breeders, since it restricts the magnitude of genetic gain. Identification of promissory exotic elite maize (Zea mays L) germplasm would be useful to increase the genetic variation within typically used heterotic groups and to improve the forage yield and quality. This study is aimed to assess the genetic potential of a group of elite maize landraces to improve forage yield and quality related traits and to broaden the genetic base of three temperate heterotic groups. Mean values and landrace general combining ability effects (GCA ) revealed that some landraces could be considered as a valuable genetic resource to broaden the current genetic base through introgression of forage yield and quality favorable alleles. When stover and ear dry matter yield were considered, ARZM17035 was the best landrace since it produced the best performing landrace × inbred line crosses that also were stable across environments. Additionally, this landrace showed high GCA . Considering quality traits, ARZM07134 was the most promising source of favorable alleles. The use of B73 as tester in a recurrent selection scheme would be the most efficient strategy, since both mentioned landraces crossed to B73, showed the highest yield and quality values. Additionally, evaluated traits were mainly controlled by additive effects, so it is expected to obtain a positive response by selection
Effectiveness of the R1-navajo embryo marker on sorting haploids in tropical maize germplasm
Get PDFModern maize breeding is currently based on Doubled Haploids (DH) technology. In following the steps to produce inbred lines by DH, sorting the haploids are the most important of them. Haploid inducers usually carry the R1 gene, responsible of purple pigmentation on seeds. Navajo is a typical phenotyping from this gene and leads to purple coloration on endosperm and embryo of the diploids but any pigmentation on haploid kernels. Aimed to analyze the effectiveness of R1-nj on sorting true haploids over tropical sources, two different experiments were conducted. In the first experiment, kernels analyzed came from the following induction cross (L47 x IL47), (P9 x IP9), (2B707 x IL47), and (2B707 x IP9) in which IL47 and IP9 were the tropical haploid inducers. In the second experiment, KHI (Krasnodar Haploid Inducer) was the haploid inducer and three commercial were adopting as sources. Putative haploids were sorted by R1-nj expression and the haploid level was checked by chromosome counting our phenotyping at the flowering stage. Overall, very low true haploid discovery rates were observed.
2B707 was the most reliable source in displaying true haploids. The ratio of this effectiveness among the two ex- periments to R1-nj marker ranged from 8.80 to 30.2%. These results can be explained by the presence of inhibitory genes on the tropical sources. Additionally, at the flowering stage, haploids plants had data of spontaneous doubling collected and summarized. Recovery on the female organs seems to be higher than male. Haploids from the IAC125 source exhibited best fully spontaneous doubling among the sources analyzed
Systematic analysis of leucine-rich repeat disease resistance genes in maize
Get PDFLeucine-rich repeat disease resistance (LRRDR) genes are important for defending plants from a range of pathogens. However, little information has been reported on the systematic analysis of LRRDR genes in maize. In this study, 235 LRRDR genes were identified in the complete genome sequence of maize (Zea mays cv. B73), classified as six different structural types, and then characterized based on conserved protein motifs, chromo- somal locations and gene duplications. Subsequent phylogenetic comparisons indicated that ~20 pairs of maize LRRDR proteins possessed high similarities to LRRDR proteins with known functions. Analyses of the physical locations and duplications of LRRDR genes indicated that gene duplication events involving LRRDR genes were high in maize and 84% occurred between chromosomes, which may ensure the functional performance and en- hancement of maize LRRDR genes. Meanwhile, the functions and expression patterns of the LRRDR genes were associated with their conserved protein secondary structures, suggesting that different conserved domains might distinguish their biological functions. Transcripts of 13 genes were regulated by two or more fungal pathogens, respectively, indicating that one LRRDR gene might mediate resistance to multiple fungal pathogens, suggest- ing that the signal networks of the maize-fungal pathogen interactions were partially crossed. Additionally, we screened five candidate LRRDR genes for ear rot resistance. The results reported in this study contribute to an improved understanding of the LRRDR gene family in maize
Can elite maize landraces help to improve forage yield and quality? A genetic analysis
Get PDFBroadening the genetic base of maize breeding program is a significant concern for plant breeders, since it restricts the magnitude of genetic gain. Identification of promissory exotic elite maize (Zea mays L) germplasm would be useful to increase the genetic variation within typically used heterotic groups and to improve the forage yield and quality. This study is aimed to assess the genetic potential of a group of elite maize landraces to improve forage yield and quality related traits and to broaden the genetic base of three temperate heterotic groups. Mean values and landrace general combining ability effects (GCA ) revealed that some landraces could be considered as a valuable genetic resource to broaden the current genetic base through introgression of forage yield and quality favorable alleles. When stover and ear dry matter yield were considered, ARZM17035 was the best landrace since it produced the best performing landrace × inbred line crosses that also were stable across environments. Addi- tionally, this landrace showed high GCA . Considering quality traits, ARZM07134 was the most promising source of favorable alleles. The use of B73 as tester in a recurrent selection scheme would be the most efficient strategy, since both mentioned landraces crossed to B73, showed the highest yield and quality values. Additionally, evalu- ated traits were mainly controlled by additive effects, so it is expected to obtain a positive response by selectio
Effect of saline stress on the physiology and growth of maize hybrids and their related inbred lines
Get PDFSalinity is one major abiotic stress that restrict plant growth and crop productivity. In maize (Zea mays L), salt stress causes significant yield loss each year. However, indices of maize response to salt stress are not completely explored and a desired method for maize salt tolerance evaluation is still not established. A Chinese leading maize variety Jingke968 showed various resistance to environmental factors, including salt stress. To compare its salt tolerance to other superior maize varieties, we examined the physiological and growth responses of three important maize hybrids and their related inbred lines under the control and salt stress conditions. By compar- ing the physiological parameters under control and salt treatment, we demonstrated that different salt tolerance mechanisms may be involved in different genotypes, such as the elevation of superoxide dismutase activity and/ or proline content. With Principal Component Analysis of all the growth indicators in both germination and seedling stages, along with the germination rate, superoxide dismutase activity, proline content, malondialdehyde content, relative electrolyte leakage, we were able to show that salt resistance levels of hybrids and their related inbred lines were Jingke968 > Zhengdan958 > X1132 and X1132M > Jing724 > Chang7-2 > Zheng58 > X1132F, respectively, which was consistent with the saline field observation. Our results not only contribute to a better understanding of salt stress response in three important hybrids and their related inbred lines, but also this evaluation system might be applied for an accurate assessment of salt resistance in other germplasms and breeding material