Reciprocal recurrent selection for obtaining water-deficit tolerant maize progeny

ABSTRACT: In view of the need to increase genetic variability to obtain materials with a significant capacity to drought tolerance, this study conducted a cycle of a reciprocal recurrent selection of full-sib families of maize. To this end, 64 full-sib families of maize were evaluated in two environments according to their morpho-agronomic data in a randomized block design with two replicates. It were analyzed of Male flowering (MF); Female flowering (FF); Flowering interval (IF); days for flowering (DF); Plant height (PH); Ear height (EH); number of plants at the Stand (NPS); Number of broken plant (NBrP); Number of bedded plants (NBeP); Strawing (St); Ear length (EL); Ear diameter (ED); Ear number (EN); Prolificacy (Pr); Number of diseased ears (NDE); Number of ears attacked by pests (NEP); Ear weight (EW); Yield (YIE) and Total Chlorophyll Index (TCI). The analysis of variance was performed by the F test at 5% significance level, and also the evaluation of genetic parameters. Regarding morpho-agronomic data, the analysis of variance and the analysis of genetic parameters showed that there was no interaction genotype x environment with regard to the genetic variability among the families under study. Lastly, the final selection of the superior genotypes was made on the basis of the ranking of the 40 most productive families, from which, combined with the molecular data, the 30 most productive, most drought-tolerant, and most genetically diverse ones were selected to compose the next cycle of recurrent maize selection aiming water-stress tolerance.

Designing the best breeding strategy for Coffea canephora: Genetic evaluation of pure and hybrid individuals aiming to select for productivity and disease resistance traits

Breeding programs of the species Coffea canephora rely heavily on the significant genetic variability between and within its two varietal groups (conilon and robusta). The use of hybrid families and individuals has been less common. The objectives of this study were to evaluate parents and families from the populations of conilon, robusta, and its hybrids and to define the best breeding and selection strategies for productivity and disease resistance traits. As such, 71 conilon clones, 56 robusta clones, and 20 hybrid families were evaluated over several years for the following traits: vegetative vigor, incidence of rust and cercosporiosis, fruit ripening time, fruit size, plant height, canopy diameter, and yield per plant. Components of variance and genetic parameters were estimated via residual maximum likelihood (REML) and genotypic values were predicted via best linear unbiased prediction (BLUP). Genetic variability among parents (clones) and hybrid families was detected for most of the evaluated traits. The Mulamba-Rank index suggests potential gains up to 17% for the genotypic aggregate of traits in the hybrid population. An intrapopulation recurrent selection within the hybrid population would be the best breeding strategy because the genetic variability, narrow and broad senses heritabilities and selective accuracies for important traits were maximized in the crossed population. Besides, such strategy is simple, low cost and quicker than the concurrent reciprocal recurrent selection in the two parental populations, and this maximizes the genetic gain for unit of time.

GENE ACTION AND COMBINING ABILITY STUDY IN SESAME

The study of gene action and combining ability have been conducted in 28 F1 cross combinations along with eight parents in 8x8 half-diallel scheme following Griffing’s Approach for 14 morphoeconomic traits including seed yield and oil content in sesame. The general combining ability (GCA) and specific combining ability (SCA) component of variation were significant for parents and crosses respectively for all characters except internode length for GCA indicating role of both additive and nonadditive gene action. However, higher proportion of SCA variance (?2 sca) than GCA variance (?2 gca) revealed preponderance of non-additive gene action for all characters except capsule length and capsule width under study. Further, variance due to dominance played a significant role than additive variance in all traits except capsule width and 100-seed weight. Nirmala is considered as the best general combiner owing to its higher estimate of gca effects for yield per plant, for days to maturity, plant height, branches per plant, capsules per plant, seeds per capsule, capsule length and 100-seed weight. Among cross combinations; Rama × GT-10, AT-382 × Krishna, AT-382 × Nirmala, Krishna × Nirmala, Krishna × Uma, Nirmala × Prachi and Prachi × Uma showed significantly higher sca effect for seed yield per plant in the desired direction indicating their merit for recovery of transgressive segregants for higher productivity following reciprocal recurrent selection.

Combining Ability and Heterosis of Algerian Saharan Maize Populations (Zea mays L.) for Tolerance to No-Nitrogen Fertilization and Drought

Drought and low nitrogen are major stresses for maize (Zea mays L.), and maize populations from the Sahara Desert are potential sources of stress tolerance. The objectives were to assess the tolerance and varietal and heterosis effects of Algerian populations under no-nitrogen fertilization and water stress. A diallel among six Algerian maize population was evaluated under drought (300 mm irrigation) vs. control (600 mm) and no-nitrogen fertilization vs. 120 kh ha−1 N fertilization. Genotypes showed significant differences and genetic effects for water- and nitrogen-stress tolerance. We propose a reciprocal recurrent selection to take advantage of additive and non-additive effects, using AOR and IGS, since they showed good performance in optimum and stress conditions, for improving yield heterosis for AOR × IGS. Negative effects are not expected on plant height, anthesis–silking interval or early vigor. These populations and BAH could be sources of inbred lines tolerant to drought and no-nitrogen fertilization. There was no relationship between origin and genetic group and stress tolerance per se or as parents of tolerant crosses. These populations and crosses could be used as base material among Algerian populations, for breeding programs focusing on tolerance to water or nitrogen stress.

Selection gains for the palm oil production from progenies of American oil palm with oil palm

The objective of this work was to estimate the genetic parameters, correlations, and selection gains for the oil production of interspecific hybrids progenies between American oil palm, of ‘Manicoré’ origin, and oil palm, of ‘La Mé’ origin. Thirty-nine progenies were evaluated from the sixth to the ninth year after planting, for the productivity of fresh fruit bunches (PROD_FFB), oil content in the bunch (OCB), and palm oil productivity (PROD_OP). The genetic parameters and gains from direct (GDS) and indirect (GIS) selection were estimated for PROD_OP. High values of heritability for the CVg/CVe ratio indicated favorable conditions for the selection. With the selection of 20% of the progenies (selection in both sexes), the following estimates were obtained: 11.15% GDS for PROD_OP, 9.1% GIS for OCB, and 8.1% GIS for PROD_FFB. The PROD_OP of the progenies was of 6,175, 6,057, and 5,995 kg ha-1 per year with GDS and GIS for OCB and PROD_FFB, respectively. The restricted selection of the LM2T male genitor offspring resulted in 5.1% estimated GSD and in a mean of 5,800 kg ha-1 per year for PROD_OP. Selection gains for PROD_OP can be achieved immediately through the selection restricted to oil palm male genitors, and, in the medium and long term, through the interspecific reciprocal recurrent selection between American oil palm and oil palm populations.

Number of progenies and repetitions for reciprocal full-sib recurrent selection programs in maize

ABSTRACT For a reciprocal recurrent selection (RRS) program to succeed, it is essential to maintain genetic variability throughout the selection cycles and to obtain accurate estimates of genetic parameters, which in turn are directly related to the number of progenies and repetitions evaluated. This study evaluates the potential of maize progenies of the sixth cycle of RRS and proposes, using simulation methods, the ideal combination of the number of progenies and repetitions to employ in reciprocal full-sib recurrent selection. A total of 163 full-sib progenies were evaluated in a randomized block design with six repetitions. Based on the yield data, analysis of variance was carried out, and different scenarios were simulated using the Monte Carlo chain method. These scenarios varied in the number of repetitions (two, four, and six) and progenies (30 to 163). The contrast between progenies and controls was significant, revealing the potential of the progenies of the sixth cycle of RRS. The high magnitude of the selective accuracy (0.77) was reflected in high estimates of heritability, which allowed for efficient phenotypic selection, obtaining selection gains of 14.07%. From the estimates of phenotypic and genotypic variance, heritability, accuracy, and standard error, it was found that a repetition number above two results in drastic changes in the estimates of these parameters; however, with the use of 130 progenies, these estimates tend to stabilize, implying that a high number of progenies does not interfere decisively in the quality of most parameters, except for the limits of maximum and minimum variation.

Response of Forty (40) High-Producing Cacao Genotypes to Cacao Swollen Shoot Disease

Aims: Cocoa swollen shoot is a dreaded viral disease that is prevalent in the producing areas of West Africa. In Côte d'Ivoire, it undermines the sustainability of cocoa farming. Integrated pest management based on the use of disease-resistant or disease-tolerant plant material remains a sustainable solution. Place and Duration of Study: Integrated Pest Management Unit against Cocoa swollen shoot, Experimental greenhouse of Bouaflé, National Centre for Agronomic Research (CNRA). Methodology: Forty elite genotypes of cocoa trees selected from different populations in the Reciprocal Recurrent Selection program of Cocoa in Côte d'Ivoire were evaluated against strain D of Cacao Swollen Shoot Virus (CSSV). Five seedlings of each genotype were infected by patch grafting and observed for 5 months. Study Design: Plants are placed in a greenhouse in a completely random arrangement, with five repetitions. Results: Three cocoa genotypes (C77, C87 and C96) were free of disease symptoms and eight genotypes (C77, C87, C96, C3, C12, C26, C53 and C98) had the lowest infection scores. The disease significantly affected plant development and growth. Conclusion: Some genotypes selected within the Reciprocal Recurrent Selection program are promising for breeding against CSSV disease. These eight genotypes will be tested in a field environment to confirm their tolerance.

Genetic Gains to Grain Yield of Maize Varieties for Small Farmers in Brazil

The demand for expanding the genetic base in working collections of older maize breeding programs points to the need to pool efforts and reaffirm methodologies for conserving genetic variability that can still be accessed in maize populations. The objective of the work was to select full sib maize progenies and to estimate genetic gains in the first cycle of reciprocal recurrent selection for common maize intended for cultivation in a region characterized by family farm, in Brazil. We evaluated 120 full sib families of maize from crossbreeding between individuals of the Cimmyt and Piranão varieties. Competition trials were conducted at two experimental stations in the state of Espírito Santo, Brazil. A randomized block design was adopted with 2 repetitions, arranged in sets. Different selection indexes were tested in order to enhance gains in productivity and prolificacy. The selection of 40 superior families made it possible to estimate a gain of 0.77 Mg ha-1 in grain productivity for producers in the region. With these results, we discussed the importance of work to improve maize populations for small producers to motivate the conservation of the genetic variability of tropical maize germplasm. Thus, from the results obtained in this study, we show the possibility of investing in technologies aimed at small producers in order to motive the conservation of genetic resources, food sovereignty of producers and, consequently, world security, given the importance of this culture for human feed.

Genetics of resistance to Fusarium stalk rot caused by Fusarium verticilloides in maize (Zea mays L.)

Fusarium stalk rot disease (FSR), incited by Fusarium verticilloides, is becoming an important biotic production constraint in many major maize growing areas causing substantial yield losses. The present investigation was conducted to understand the genetics of resistance to FSR through six generation means and variances, as a first step in addressing the problem. Five crosses were developed by crossing four FSR susceptible inbreds (VL1043, VL108867, VL121096 and VL1218) with two resistant inbreds (CM202 and CM212). Six generations of the five crosses (VL1043 × CM212, VL108867 × CM202, VL121096 × CM212, VL1218 × CM202 and VL1218 × CM212) were evaluated through artificial disease inoculation during post rainy season of 2018 and summer, 2019. The scaling tests and joint scaling tests indicated the inadequacy of additive-dominance model and showed the presence of epistatic gene effects in all the five crosses for FSR resistance. The study further revealed the importance of additive, dominance and additive × additive gene effects in the expression of FSR. The magnitude and direction of the additive genetic effects [a], dominance genetic effects [d], magnitudes of additive genetic variance (2A) and dominance genetic variance (2D) varied with the genetic background of the crosses over seasons. Duplicate gene interaction was evident in the inheritance of FSR resistance. Both, additive and non-additive components were found important thus reciprocal recurrent selection would be more effective in obtaining FSR resistant maize inbred lines.

Genetic progress in maize from advanced cycles of reciprocal recurrent selection through REML/BLUP

Breeding methods such as reciprocal recurrent selection (RRS) is very important alternative to breeders. This strategy, besides allowing continuous genetic progress, helps maintaining the genetic variability of populations. The aim of the present study was to estimate genetic parameters, as well as to predict selection gains in advanced cycles of reciprocal recurrent selection of maize progenies through mixed models. Two selection cycles were considered. We evaluated 196 and 169 progenies in the 15 and 16 cycles, respectively. The yield potential of the progenies was evaluated from the following characteristics: grain yield, number of ears, weight of ears and weight of 100 seeds. The estimate of variance components and the prediction of genetic values were based on the REML/BLUP method. Overall, the genetic parameters were increased in the 16th cycle estimates compared to the previous cycle. It is worth highlighting that heritability coefficient for the grain yield was (0.81) in the 16th cycle, since it resulted in 21% of selection gain. Results showed that, even after sixteen recurrent selection cycles, the populations under selection have high potential for satisfactory genetic gains.