Recurrent Selection Procedures Research Articles

Pamukta (Gossypium hirsutum L.) Nep ve Lif Kalite Özellikleri Üzerine Modifiye Tekrarlamalı Seleksiyonun Etkisi

The aim of this research was to evaluate the efficiency of the recurrent selection method for increasing ginning out-turn, optimizing fiber characters and neppiness in cotton breeding. This study started with the creation of 24 F1 combinations at Nazilli Cotton Research Institute in 2013. According to recurrent selection method, plants of 45 populations were evaluated for the first cycle of the recurrent selection procedure such that the F1: C1S0 was evaluated in 2017, the F2: C1S1 in 2018 and the F3: C1S2 in 2019. The fiber nep number and size decreased with each filial generation (from F1 to F3). Generally, high heritability coupled with genetic advance was estimated for ginning out-turn, fiber characters and neppiness. The results of inbreeding depression values indicated that ginning out-turn and fiber length in the population increased while the fibers became coarser under stable fiber strength. In addition, inbreeding depression for nep and SCN (Seed Coat Neps) number were higher than that of nep and SCN size. Our results showed that the recurrent selection method can be successfully applied in a cotton breeding program.

Genetic analysis of low-n traits in maize (Zea mays L) using triple test cross

Low-N maize variety is developed for its ability to tolerate low nitrogen soil environment. This experiment was conducted to study the genetic implication of Low-N maize variety for grain yield and related traits under low nitrogen soil conditions triple test cross analysis. Inbred lines used for the study were generated from twelve low nitrogen tolerance open pollinated maize varieties after six generations of selfing. Two inbred lines along with their F1 were used as testers for ten inbred lines in a triple test cross pattern to generate 30 crosses. The 30 crosses, their parents and the testers to State University, Ado-Ekiti during 2017 planting season. The experimental design was a Randomized Complete Block Design (RCBD). Data were collected on plant height, ear height, days to 50% anthesis, days to 50% silking, incidence of curvularia leaf spot, blight, plant aspect, ear aspect, ear rot, stay green, cob per plant, ear weight, grain moisture content and grain yield. All data were subjected to analysis of variance and complete genetic estimates. Additive and dominants were significant (P < 0.05) for all traits; however, epitasis estimates were not significant for all the traits tested. The degree of dominance component indicated partial dominance for all the traits. Correlation coefficients for days to 50% anthesis and 50% silking, plant height, ear height, number of cobs per plant and grain yield were positive and significant (P < 0.05). Since both additive and dominance gene actions were important for low-N traits, the use of reciprocal recurrent selection procedure can be adopted in incorporating the trait into elite maize varieties.

BREEDING FOR DROUGHT TOLERANCE IN MAIZE

This study carried-out in four successive summer seasons (2015 to 2018) at the experimental farm of the faculty of agriculture, Menoufia University, in Shebin El-Kom, Egypt. In 2015 season, S1 recurrent selection procedure was provied (Tep#5 and Gemmeiza yellow), where 200 S0 plants from each population were selfed to produce S1 progenies. In 2016 season, kernels of 100 S1 lines that selected from each two populations were separately sown for evaluation under two water regimes, i.e normal irrigation (NI) and drought stress conditions (DS). In 2017 season, the highest 10% of S1 progenies (10 S1 progenies of first Population (Tep#5) and 10 % S1 progenies of second Population (GMY) were planted for randomly mated by bulking pollen from the S1 plants. kernels harvested, four blends of seeds were obtained (Tep#5-NI, Tep#5-DS, GMY-NI and GMY-DS). In 2018 summer season, for each population the original cycle (C0) and the improved cycle (C1) were evaluated under normal irrigation (NI) and drought stress (DS). The results could be summarized as follows: Evaluate of 100 S1 progenies (Tep#5 and Gemmeiza yellow) for drought tolerance. Analysis of variance showed significant differences among the genotypes (S1 progenies) for all studied traits under both normal and drought stress conditions for two populations. A significant average reduction of 59.88% and 61.93% in grain yield/plot of the 100 S1’s for Tep#5 and Gemmeiza yellow respectively, due to drought stress. The superiority of the selected 10 S1’s over the 100 S1’s in grain yield was higher under drought stress than under normal conditions. Evaluation of the effectiveness of S1 recurrent selection of the two cycles for Tep#5 and Gemmeiza yellow populations under normal and drought conditions. One cycle of S1 recurrent selection using water-stress as a selection environment caused a significant actual improvement of grain yield of the newely developed populations (Tep#5-DS and GMY-DS) over its original populations (Tep#5 and GMY) of 15.47 and 12.78% under water stress condition. The improved populations Tep#5-NI and GMY-NI developed by using normal irrigation as a selection environment showed significant actual improvements in grain yield under normal irrigation (12.46 and 9.06%) environment. Both water stressed and non-stressed selection environments were efficient in improving grain yield under target environments. The two improved populations showed significant superiority in grain yield/fed over origin population under normal and drought stress conditions.

Genetic Dissection of Low-N Traits using Triple Test Cross Analysis in Maize (Zea mays L.)

Low-N maize is bred for its ability to tolerate low soil nitrogen (N) by growing and producing grain that compares appreciably to conventional varieties. This experiment was conducted to study the genetic effects of grain yield and other agronomic traits in Low-N maize using triple test cross analysis. Twelve low-N open pollinated maize varieties were converted to the inbred line after six generations of selfing and used for the experiment. Two inbred lines along with their F1 were used as testers for ten inbred lines in a triple test cross pattern to generate 30 crosses and along with their parents and testers to make a total of 43 entries which were evaluated at the Teaching and Research Farms of Ekiti State University, Ado-Ekiti during in 2017. The design was a Randomized Complete Block Design (RCBD). Data was collected on plant height, ear height, days to 50% anthesis, days to 50% silking, the incidence of Curvularia leaf spot, blight, plant aspect, ear aspect, ear rot, stay green, cob per plant, ear weight, grain moisture content and grain yield. All data was subjected to analysis of variance and complete genetic estimates made. Additive and dominants were significant (P0.05) for all traits, however, epitasis estimates were not significant for all the traits. The degree of dominance component indicated partial dominance for all the traits. Correlation coefficients for days to 50% anthesis and 50% silking, plant height, ear height, number of cob per plant and grain yield were positive and significant (P0.05). Since both additive and dominance gene actions were important for low-N traits, the use of reciprocal recurrent selection procedure can be adopted in incorporating the trait into elite maize varieties.

Performance and grain yield stability of maize populations developed using marker-assisted recurrent selection and pedigree selection procedures.

A marker-assisted recurrent selection (MARS) program was undertaken in sub-Saharan Africa to improve grain yield under drought-stress in 10 biparental tropical maize populations. The objectives of the present study were to evaluate the performance of C1S2-derived hybrids obtained after three MARS cycles (one cycle of recombination (C1), followed by two generations of selfing (S2), and to study yield stability under both drought-stress (DS) and well-watered (WW) conditions. For each of the 10 populations, we evaluated hybrids developed by crossing 47–74 C1S2 lines advanced through MARS, the best five S5 lines developed through pedigree selection, and the founder parents with a single-cross tester from a complementary heterotic group. The hybrids and five commercial checks were evaluated in Kenya under 1–3 DS and 3–5 WW conditions with two replications. Combined across DS locations, the top 10 C1S2-derived hybrids from each of the 10 biparental populations produced 0.5–46.3 and 11.1–55.1 % higher mean grain yields than hybrids developed using pedigree selection and the commercial checks, respectively. Across WW locations, the best 10 hybrids derived from C1S2 of each population produced 3.4–13.3 and 7.9–36.5 % higher grain yields than hybrids derived using conventional pedigree breeding and the commercial checks, respectively. Mean days to anthesis of the best 10 C1S2 hybrids were comparable to those of hybrids developed using the pedigree method, the founder parents and the commercial checks, with a maximum difference of 3.5 days among the different groups. However, plant height was significantly (P < 0.01) different in most pairwise comparisons. Our results showed the superiority of MARS over pedigree selection for improving diverse tropical maize populations as sources of improved lines for stress-prone environments and thus MARS can be effectively integrated into mainstream maize breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1007/s10681-015-1590-1) contains supplementary material, which is available to authorized users.

Resistance of maize to the maize weevil: III. Grain weight loss assessment and implications for breeding

The maize weevil (Sitophilus zeamais) is a significant pest of stored maize grain in tropical and subtropical regions worldwide. As a further step towards finding maize genotypes with acceptable levels of resistance to the maize weevil, 53 experimental maize hybrids that were generated in a North Carolina design II mating scheme, were evaluated for grain weight loss due to maize weevil damage under ambient temperature and humidity (ATH) conditions, in the on-station stock room at Harare, Zimbabwe. The study indicated that genotypic variation for grain weevil resistance was large (19%–57%) after five months of infestation by the maize weevils. A few F2 populations with potential for use as sources of breeding new varieties for maize weevil resistance were identified. They displayed consistency of high performance (better than the standard control varieties) and showed a lower rate of grain weight loss due to the maize weevils over the five months in the stock room. The male and female GCA and SCA effects were highly significant (P ≤ 0.01) for maize weevil resistance, especially at two months after infestation, indicating that resistance was controlled by genes with both additive and non-additive effects, respectively. Further, the distribution of grain weight loss data for the hybrids was continuous and almost normal at the four intervals of data collection, clearly supporting that resistance was partial and possibly conditioned by minor genes with cumulative effects. Therefore, resistance could probably be improved by selection among the promising F2 populations identified in this study. Although resistance was partial, a plot of grain weight loss of hybrids from the different categories demonstrated the advantage to farmers for growing a resistant variety (low percentage loss over time) compared to the susceptible ones that incurred significant grain weight losses. However, grain weight loss data were not significantly correlated with yield (r = 0.14; P > 0.05), suggesting that the traits are not mutually exclusive. Therefore, breeding for maize weevil resistance in these populations would not necessarily compromise grain yield. Our results demonstrate that there is potential in developing maize varieties with acceptable levels of maize weevil resistance through recurrent selection procedures which exploit both GCA and SCA effects with sustainable impact on food security and the environment.

Combining ability and genetic components for pod and seed traits in cowpea lines

The identification of suitable parental genotypes potentially generating superior lines with traits contributing to the overall yield of cowpea is an important step in the development of improved varieties. Eight parents and their 28 hybrids obtained through diallel crossing design were evaluated in a randomized complete block design with three replications. Highly significant differences among the parents and their hybrids for different traits were observed. General combining ability (GCA) mean squares were larger than the specific combining ability mean squares for all the traits analysed. The ratio h 2 /H 2 revealed different number of genes controlling the traits, pointing out their polygenic inherited control. The estimated low narrow sense heritability recorded in this study indicated that recurrent selection procedure could be effective to improve the analysed traits in the genotypes included in this study. Kananado with large, positive and significant GCA effects was identified as the parent with desirable genes for the genetic improvement of the considered yield component in cowpea. In addition, IT03K-316-1 x Cowpea-2 and IT99K-316-2 x Kananado seemed to be the best hybrids for number of pods/plant and 100-seed weight, respectively.

Inheritance and general combining ability studies of detached pod, leaf disc and natural field resistance to Phytophthora palmivora and Phytophthora megakarya in cacao (Theobroma cacao L.)

Black pod is a major disease of cocoa. Knowledge of the inheritance of resistance to black pod would be important in devising strategies to breed resistant varieties. The mode of inheritance of resistance to black pod disease was investigated using leaf disc, detached pod tests and natural field observation in a 6 × 4 factorial and 6 × 6 diallel mating designs analyzed using North Carolina design-II approach and Griffing’s method II model I approach, respectively. The dominant component was smaller than the additive component for pod lesion size, leaf disc scores and natural field infection. Both general combining ability and specific combining ability (SCA) effects influenced the inheritance of pod lesion number and leaf disc scores suggesting that both additive and non-additive (dominance or epistatic) effects influence the inheritance of resistance to black pod disease. However, SCA effect was not significant for pod lesion size and natural field infection suggesting the importance of additive genes in the inheritance of these traits. The higher heritability of leaf disc scores, pod lesion numbers and pod lesion sizes than the heritability of natural field infection which was almost zero, shows the influence of environment on natural field infection and suggests that ranking of resistance of cocoa genotypes need to be done under controlled environmental conditions to observe true resistance levels. Good general combiners, in combination with each other, did not necessarily yield good specific combinations suggesting that parents’ performance cannot be used for selecting superior progenies. The non-significance of reciprocal effects indicates absence of maternal effects or cytoplasmic inheritance in resistance to black pod disease. Recurrent selection procedures and inter-crossing aimed at general combining ability would be more suitable for improvement of black pod disease resistance. Cocoa genotypes with good combining ability for resistance to black pod disease such as T60/887, Pa 150, Sca 6, and Pa7/808, identified in this study could be important parents to form base population for such recurrent selection procedures.

Selection and breeding experiments at the haploid level in maize (Zea mays L.)

Selection at the haploid level allows increasing the efficiency of recurrent selection procedures. After four cycles of a recurrent selection approach involving haploid plants, grain yield of a synthetic population, SPC4, was at the same level as that of current commercial hybrids. The SPC4 population had a good performance in comparison with 27 synthetic populations obtained from Iowa State University. Transgressive segregation for plant height and ear length was revealed at the haploid level in two single crosses. It was demonstrated that the utilization of haploid plants to identify, create and improve elite breeding material might be very efficient. Key words: Zea mays, haploids, recurrent selection, synthetic populations, hybrids, transgressive segregation.

Genetic analysis of resistance to common smut in maize (Zea mays L.) using triple test cross

Understanding of gene action for resistance to maize common smut is essential for maize breeding programs, therefore, triple test cross analysis was employed to assess gene action controlling resistance to common smut in maize. Parental inbred lines and their progenies were evaluated using randomized complete block design with three replications in Karaj Field Station, Seed and Plant Improvement Institute, in 2007 and 2008 cropping seasons. Epistasis was observed for resistance to maize common smut. Partitioning of the total epistasis revealed that [i] type (additive × additive) and [I+J] types (additive × dominance and dominance × dominance) were highly significant. Additive (L1i+L2i) and dominance (L1i – L2i) effects for resistance to maize common smut were also significant, over two growing seasons. Dominance ratio (H/D) 1/2 indicated that resistance to maize common smut was controlled by dominance effect. However, the direction of dominance (rs,d) for this character in two growing seasons was not-significant which implies that dominant alleles were distributed in parents, therefore they did not express any directional dominance for this attribute. Since F′ was positive, therefore, dominant alleles increased disease severity of maize common smut. Cytoplasmic effects were also important for resistance to maize common smut. Combined analysis of variance showed that the effect of year and genotype × year interaction were highly significant. Generally, the additive, dominance and epistatic components were important in resistance to maize common smut. It is concluded that Genetic analysis of Resistance to Common Smut in Maize (Zea mays L.) using triple test cross recurrent selection procedure may be efficient in breeding for resistant to maize common smut, since it exploits additive and non-additive components of genetic variation for improvement resistance to maize common smut. Key words: Zea mays, triple test cross, common smut, gene action.

Performance of maize single-crosses developed from populations improved by a modified reciprocal recurrent selection

Maize (Zea mays L.) elite inbred lines developed from pedigree programs tend to be genetically related. Therefore, it is necessary to incorporate unrelated inbreds to those programs to allow the continued release of outstanding single-crosses. The objectives of this research were to compare the usefulness of a modified reciprocal recurrent selection procedure (MRRS) to improve populations to be used as sources of elite inbreds and outstanding single-crosses to integrate pedigree programs, and to investigate the effects of selection on the relative contribution of general (GCA) and specific combining (SCA) abilities to the single-crosses variation. Eight and six S3 lines from populations IG-3-C1 and IG-4-C1, respectively, selected from the first cycle of the MRRS program were crossed in a partial-diallel mating design, and the 48 experimental and five commercial single-crosses were evaluated in six environments. Grain yield mean of the experimental single-crosses (9.57 t ha¹) did not differ from the commercial single-crosses (9.86 t ha¹), and ten of the 48 experimental single-crosses could be released as cultivars because they compared favorably to the currently used single-crosses. Thus, one cycle of the MRRS procedure improved efficiently the populations allowing the development of outstanding single-cross, but additional cycles of selection should be carried out since none of the experimental single-crosses outperformed the highest yielding commercial single-cross. The relative contribution of the GCA over SCA may have been affected by the MRRS, since the SCA was more important than GCA for some of the traits assessed.

Comparison of predicted responses to three types of recurrent selection procedures for the improvement of a maize (Zea mays L.) population

A maize population was subjected to three different selection procedures to determine the best method for its improvement in a study conducted at Ibadan, Nigeria. Considerable genetic variability existed within the population for effective selection for each of the traits considered, using any of the procedures namely full-sib, half-sib and S1 family selection. Heritability estimates were from moderate to large for most traits. Direct selection for grain yield is expected to result in favourable increases in other traits except that the selected materials will flower earlier. Since increases in plant height due to selection for grain yield is undesirable, it was concluded that the best selection method for yield improvement that will increase height, the least would be full-sib family selection. Key words: Recurrent selection, predicted responses, maize.

Optimization of DH-line based recurrent selection procedures in maize under a restricted annual loss of genetic variance

Doubled haploid (DH) lines are increasingly being used in commercial hybrid maize (Zea mays L.) breeding. They allow for various quantitative genetic and logistic advantages provided that they are implemented in efficient and optimally allocated breeding procedures. In the present study, a new software was applied to optimize two recurrent selection (RS) schemes for hybrid maize breeding based on DH lines under a restricted annual budget and an upper limit for the relative annual loss of genetic variance. This software maximizes the expected gain from selection in general combining ability by means of quantitative genetic model calculations. Optimization results are compared for one, two, and three stages of testcross selection under different assumptions regarding the evaluation of lines per se and the annual budget. Results show that the optimum allocation of technical and budget resources to the individual steps of an RS program and the efficiency of alternative RS procedures are decisively determined by the number of selection stages. Under standard assumptions, one-stage selection was superior to two- and three-stage selection. Thus, shortening the length of an RS scheme considerably increases its efficiency. By intercrossing a reduced number of selected lines for starting a new RS cycle, the short-term response to selection may be increased, but the population size and, thus, the selection limits in the long run are diminished. Therefore, fair comparisons of alternative RS procedures require to define the intended time span for maximizing the genetic gain from RS and to restrict the relative annual loss of genetic variance accordingly.

Responses to selection and changes in combining ability after three cycles of a modified reciprocal recurrent selection in maize

This research reports responses to selection and changes in general (GCA) and specific (SCA) combining abilities after three cycles of a modified reciprocal recurrent selection procedure (MRRS) in EPB-4 and EPB-5 maize populations. In the MRRS procedure a cycle can be completed in 1 or 2 years depending on the availability of winter breeding nurseries. The original and the three selection cycles of the two populations per se (eight entries) and the partial diallel developed from the crosses between them (16 entries) were evaluated in six environments. Realized response to selection on the population cross was 7.25% cycle−1 for grain yield, −13.63% cycle−1 for plant lodging, and 11.93% cyle−1 for prolificacy, whereas plant and ear heights remained unchanged. GCA estimates increased with selection cycles for both populations for grain yield and prolificacy, and decreased for plant lodging, indicating that the frequency of favorable alleles with additive effects for these traits increased with the MRRS cycles in both populations. SCA estimates increased for grain yield and prolificacy indicating that the frequency of favorable complementary alleles at loci with non-additive effects in the reciprocal populations increased with the MRRS cycles. For grain yield, SCA effects increased more than GCA effects with selection cycles, indicating that MRRS exploited more the non-additive effects than the additive effects for the improvement of this trait. The overall results showed that the MRRS procedure was highly effective in improving the population cross, exploiting both GCA and SCA effects.

Genetic parameters for hydrocyanic acid content in forage sorghum (Sorghum bicolor L. Moench)

Six lines (IS 1003, IS 3504, IS 3541, IS 6354, CO 27 and CO 28) and four testers (IS 0030, AKSS 5, GSSV 1 and TNS 52) were crossed in line x tester design to produce 24 hybrid combinations. These hybrids along with their ten parents were grown in a randomized block design with three replications. The samples for estimation of hydrocyanic acid content were taken 32 days after sowing. The analysis of variance indicated significant differences for HCN content in all the genotypes. It also clearly shown that, the specific combining ability (SCA) variance for HCN content was higher than general combining ability (GCA) variance indicating the trait is controlled by non additive gene action. The parents IS 3541, CO 27 and IS 0030 were found to be the best ones based on GCA effects and the hybrids IS 1003 x TNS 52, IS 6354 x IS 0030 and IS 3541 x TNS 52 were found to have maximum negative SCA effects for HCN content. Heterosis breeding, recurrent selection and other population improvement procedures were suggested for getting varieties with reduced HCN contents.

Heritability of Terbacil Herbicide Tolerance in Strawberry

A partial diallel design was used to investigate the inheritance of tolerance to terbacil herbicide in cultivated strawberry, Fragaria ×ananassa Duch. Two tolerant cultivars, `Honeoye' and `Earliglow', two moderately tolerant cultivars, `Lester' and `Allstar', and two susceptible cultivars, `Red Chief' and `Guardian' were used as parents to create populations that segregated for tolerance to the herbicide. Tolerance rankings of the populations closely coincided with expected rankings based on the published tolerance levels of parental cultivars. `Honeoye' and `Earliglow' derived populations had the highest average tolerance ratings, while `Guardian' derived populations had the lowest tolerance ratings. Heritability was estimated at h2 = 0.50, indicating that significant progress in increasing the tolerance of new cultivars to terbacil can be achieved through traditional recurrent selection procedures. General and specific combining abilities suggest that the tolerant cultivars in this study may be fixed in their tolerance and that increased mean tolerance will be most apparent in progenies combining tolerant and susceptible cultivars. As such, a broader pool of germplasm may be needed to develop cultivars that are more tolerant than those in this study. Chemical names: terbacil (3-tert-butyl-5-chloro-6-methyluracil)

Selection in Setaria sphacelata for winter survival

Choice of warm‐season grasses for use in North Florida, United States, is limited because of the cold winters, which are characterised by both radiation frosts and freezes. With the objectives of increasing the adaptation of the forage Setaria sphacelata to these conditions, a breeding programme was undertaken at the University of Florida from 1997 to 2000. A recurrent selection procedure was used for three cycles to select for winter survival and early spring growth after frost and freezes in Gainesville (29.6°N latitude) and for one cycle in Quincy (31 °N latitude). Heritability estimates for the first two cycles in Gainesville and the cycle in Quincy ranged from 0.35 to 0.50 on a family basis. Predicted gains ranged from 10.4 to 17.4% in winter survival over the preceding cycle. These populations were compared in Gainesville to the original population and to cultivars ‘Solander’ and ‘Splenda’ in two experiments, one wide‐ and one close‐spacing. Results showed that selection for winter survival in Gainesville reduced canopy height in the second and third cycles and the reproductive height in the third cycle. Leaf dry matter yield was decreased in the first and second cycles and leaf percentage in the first cycle. These effects were reversed in the remaining cycles. Selection did not have a consistent effect on the width of leaves, length or number of inflorescences, or on total and stem dry matter yields. However, selection for winter survival in Quincy increased canopy height and the number of inflorescences. Selection for winter survival after frosts and freezes in Gainesville was successful because all cycles of selection had a higher survival rate after the winter of 1999–2000 than the original population. This winter, which killed many of the Setaria plants, was effective in providing additional screening for winter survival after frosts and freezes. Further research with this species for Florida conditions appears warranted.

Genetic Analysis of Quantitative Traits in Synthetic Population 316P02 of Maize (Zea mays L.)

The choice of recurrent selection procedure depends mostly on the genetic constitution of populations undergoing selection. We studied components of genetic variance of grain yield, ear length, 1000-kernel weight, ear row number, kernel depth, 10-kernel length and height of ear of the medium late synthetic maize population 316P02. This population includes Lancaster Surecrop germplasm (about 70%) and exotic germplasm (30%). It should be an important source of new maize inbred lines. Except for ear row number, most of the total genetic variability of the other traits was determined by additive gene action. We estimated negative value of variance due to dominance deviations for kernel depth. The average degree of dominance was at the level of superdominance except for kernel depth and 10-kernel length. Grain yield and 1000-kernel weight had higher values of narrow sense heritability (hn2=0,56, h"2=0,5) than expected. Ear row number(h"2=0,45) had lower. In the case of kernel depth, we couldn't been able to

Diallel analysis of sooty stripe resistance in sorghum

Sooty stripe [Ramulispora sorghi (Ellis and Everhart) Olive and Lefebre] is a widespread foliar disease of sorghum [Sorghum bicolor (L.) Moench] in West Africa, responsible for grain yield losses up to 46%. We studied the inheritance of sooty stripe resistance in a 9 × 9 sorghum F2-population diallel grown together with parent lines and checks in1996 under natural disease pressure at two locations in Mali. The percentage of infected leaf area was determined twice over a two-week interval during the season. At the second evaluation, the mean sooty stripe severity amounted to 13% infected leaf area at Samanko and 12% at Cinzana. The frequency distribution of the entries was approximately normal for the mean disease severity, averaged across assessment dates and locations, pointing to the involvement of multiple genes. With the data combined across the two locations, genetic differences among lines and among F2 populations were highly significant. Genotype × location interaction variances were also significant but much smaller than the genetic variances. Broad-sense heritability estimates were 0.92 for lines and 0.94 for the F2 populations, for the mean percentage infected leaf area across the two assessment dates. General combining ability effects (GCA) determined most of the differences among the F2 populations. Specific combining ability effects (SCA), and the interactions of GCA or SCA with locations were also significant but less important. Line performance per se was highly correlated with GCA. Because of the high heritability and predominance of additive effects, prospects are good for the genetic improvement of resistance to sooty stripe in sorghum in Mali, using simple pedigree or recurrent selection procedures.

Random Amplified Polymorphic DNA-Based Evaluation of Diversity in the Hierarchical, Open-Ended Population Enrichment Maize Breeding System

Commercial maize germplasm has a narrow genetic base. The hierarchical, open-ended population enrichment (HOPE) maize (Zea mays L.) breeding system was created with the dual purpose of developing useful inbred lines and of diversifying the maize breeding germplasm. The objective of this study was to estimate the genetic diversity in the HOPE populations at initiation and after 15 yr of operation. The HOPE system has two heterotic population sets (A and B). Each set has a hierarchical structure and consists of four open-ended populations: elite (E), high (H), intermediate (I), and low (L). New germplasm is added to the system, and high-performing entries from a lower level can be advanced to the next higher level. Increasingly stringent recurrent selection procedures are employed at each higher level of the hierarchy. Twelve random amplified polymorphic DNA (RAPD) primers were used to analyze 19 plants from the initial and last cycle of selection for each of the four levels of the two population sets. The greatest polymorphism (65.9%) was observed for the last selection cycle of the L level of the B set, while the last selection cycle of the E level of the A set was the least polymorphic (39.2%). Intrapopulation diversity was the greatest for the L level, and the smallest for the E level. Diversity appeared to be enhanced due to introgressions and advancements of material in the hierarchy. Principal component (PC) analysis indicated that the populations of the lower levels were more similar to one another than were the two E populations. All polymorphisms present in commercial check hybrids were also observed in the HOPE populations, while 32 of the observed 91 bands were polymorphic in the HOPE system and monomorphic in the hybrids. This study indicates that HOPE populations offer variability not present in commercial material and supports the HOPE system as a source of nontraditional germplasm for maize breeding programs.