Striga Resistance Research Articles

Application of fast technology for analysis (FTA)® for sampling and recovery of deoxyribonucleic acid (DNA) for molecular characterization of cowpea breeding lines for Striga resistance

Striga gesnerioides (Willd) Vatke is a significant constraint to cowpea production in the dry savannas of sub-Saharan Africa. Yield losses caused by S. gesnerioides in these regions are estimated in millions of tons annually and the prevalence of Striga soil infestation is steadily increasing. Conventional breeding efforts have developed some cowpea lines with Striga resistance as well as other important agronomic traits but it is time-consuming and difficult to pyramid favorable traits. The use of marker-assisted selection (MAS) makes it easier to select plant traits and reduce the time needed to develop new varieties. The potential of Fast Technology for Analysis (FTA) as an effective technology for sampling and retrieval of DNA from plant tissue and their subsequent molecular analysis was assessed in the laboratory. DNA was successfully recovered from the leaf tissues of cowpea pressed into the FTA ® Classic card and the DNA obtained from the FTA papers was found to be suitable for molecular analysis by PCR-based techniques. The marker efficiency of Sequence Characterized Amplified Region (SCAR) marker MahSe2 and C42B was 93% in detecting SG3 resistance. This study demonstrated that the application of MAS using FTA technology has the potential to put the breeding process on a fast track and increase the efficiency of breeding activities. Key word: Marker assisted selection, Striga gesnerioides , race, FTA ® PlantSaver Card, PCR, tissue prints, DNA.

Host-Parasite Interactions Throughout the Striga Life Cycle, and their Contributions to Striga Resistance

Field screening for resistance to Striga has been slow and difficult, with only modest success. Successful Striga parasitism is dependent upon a series of chemical signals produced by its host. Interruption of one or more of these signals results in failure to establish parasitism. We have embarked upon a programme a characterizing these signals, developing simple laboratory assays for them; identifying genotypes which are resistant because they produce abnormal levels of signals; elucidating the mode of inheritance to genotypes with high yield potential and broad adaptation. Focusing on the initial stage, the signal required for Striga seed germination, our collaborative research work in sorghum has resulted in the development of elite sorghum genotypes which combines Striga resistance with yield potential and good quality characteristics. These germplasm are currently under wide international testing in several African countries. We hope to follow this pattern for each host-dependent step in the development of Striga plants, then pyramid the resulting resistance genes into a single genotype which should exhibit durable, broad-based resistance.Keywords: Host-parasite interactions, Striga

An In Vitro Method for Identifying Postattachment Striga Resistance in Maize and Sorghum

Breeding for durable Striga resistance requires identification and stacking of multiple genetic barriers to parasitism in crops. This task would be greatly aided by having screening tools for identifying in parent sources and breeding populations resistance traits that function at various stages in the parasitic association. In this study, we describe a root observation system called the sand packed titer plate assay (SPTPA) used to study early postattachment development of Striga hermonthica (Del.) Benth. on two maize (Zea mays L.) and two sorghum [Sorghum bicolor (L.) Moench] inbred lines selected for field resistance and susceptibility to Striga. The resistant maize and sorghum lines had fewer Striga attachments and these showed delayed parasitic development, and higher mortality compared to those on susceptible cultivars. The SPTPA was useful in identifying specific resistance reactions to S. hermonthica in maize and sorghum and reflected results from field studies of these varieties. This assay would complement field testing during development of Striga‐resistant varieties.

Combining Ability of Early‐maturing White Maize Inbreds under Stress and Nonstress Environments

Maize (Zea mays L.) hybrids resistant to Striga hermonthica (Del) Benth and tolerant to drought are vital to the sustainability of productivity of the maize‐based farming systems of West and Central Africa (WCA). Thirty‐six diallel crosses derived from nine early maturing white maize inbreds were evaluated under drought, well‐watered, striga‐infested, and striga‐free conditions at five locations in Nigeria between 2007 and 2009. The objective was to examine the combining ability, performance and stability of the inbreds, and to identify the heterotic groups. Additive and nonadditive gene actions were important in the control of the inheritance of drought tolerance and striga resistance in the inbreds. General combining ability (GCA) mean squares of grain yield and other traits were larger than those of specific combining ability (SCA), indicating that additive gene action was more important in the inheritance of drought tolerance. The GCA mean squares for striga damage rating at 8 and 10 weeks after planting (WAP) were about six and five times greater than those of the SCA, indicating that additive gene action played a major role in the inheritance of the striga traits. The GGE biplot analysis revealed that TZEI 4 and TZEI 5 were the most promising inbreds in yield performance and stability across the test environments. Two heterotic groups were identified; [TZEI 7, TZEI 19, TZEI 2, TZEI 4] and [TZEI 5, TZEI 3]. Tester TZEI 3 was the closest to the ideal tester. Entry TZEI 7 had the highest GCA effects and TZEI 2 the lowest.

Cultivar evaluation and trait analysis of tropical early maturing maize under Striga-infested and Striga-free environments

Striga hermonthica is a major constraint to maize ( Zea mays L.) production in sub-Saharan Africa. The use of secondary traits that have high heritability and genetic correlation with grain yield can improve the precision with which Striga resistant genotypes are identified. Fifteen early cultivars were evaluated under Striga-infested and Striga-free conditions for 2 years at Mokwa and Abuja, Nigeria. The objective was to examine their performance based on multiple traits under stress and non-stress conditions and analyze the interrelationship among traits using genotype-by-trait (GT) biplot so as to assess the value of traits used in the base index for selection for Striga resistance and improved grain yield (YLD). TZE-W DT STR C 4 had the best performance based on multiple traits while TZE-W DT STR C 4, TZE-Y DT STR C 4, Multicob Early DT, and TZE-W DT STR QPM C 0 were the closest to the ideal cultivar when Striga infested. Ears per plant, Striga damage at 8 and 10 weeks after planting, and ear aspect (EASP) were the most reliable traits for selecting for resistant genotypes. Striga emergence count at 8 and 10 weeks after planting were not among the reliable traits identified for selection for improved grain yield and their inclusion in the base index needs to be further verified. EASP had high correlation with grain yield and was one of the most reliable traits for selection for increased grain yield under Striga infestation and should be included in the index.

English

  The genetic diversity and phylogenetic relationships among cowpea (Vigna unguiculata L. Walp) genotypes used in breeding for resistance to Striga gesnerioides in Burkina Faso have been evaluated using simple sequence repeat(SSR) molecular markers. Sixteen primer combinations were used to polymerase chain reaction (PCR) amplify SSRs from 16 different cowpea genotypes yielding a total of 96 (76.3%) polymorphic bands ranging in size from 220 to 1018 bp. High coefficients of genetic similarity were obtained among Striga resistant varieties. Very few (~22%) primer combinations showed polymorphic bands capable of discriminating Striga-resistant from susceptible cultivars. The 16 Burkinabe cowpea cultivars examined clustered into three main groups, two formed by resistant phenotypes (Group I: Gorom and Wango and Group II: B301, IT82D-849, HTR, KVX 745-11P, KVX 61-1 and IT84S-2049) and one by a combination of resistant and susceptible cultivars (Group III). These data will be helpful in designing streamlined breeding strategies for cowpea improvement for Burkina Faso and specifically for the introgression of the Striga resistance trait into local farmer acceptable types.   Key words: Cowpea, genetic diversity, germplasm, microsatellite, phylogenetic structure, simple sequence repeat.

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

ABSTRACTStriga hermonthica (Del.) Benth threatens maize (Zea mays L.) production in sub‐Saharan Africa. In an extra‐early population, S1 families derived from four cycles of recurrent selection for grain yield and Striga resistance were evaluated with and without Striga infestation at three locations in Nigeria for 2 yr to determine relative changes in genetic variances, heritabilities, and genetic correlations for yield and other traits. Under infestation, yield was not correlated with other traits at C0 but was significantly correlated with ears per plant (EPP), Striga damage, and emerged Striga plants in advanced cycles. Genetic correlations between yield and most traits were significant in C0 when Striga‐free but was reduced in advanced cycles. Genetic variances and heritabilities for yield and ear aspect increased in advanced cycles. Genetic variances decreased with selection for emerged Striga counts and EPP under infestation. A response to selection for improved yield, Striga emergence and EPP is expected in subsequent cycles. Low genetic variances and heritabilities for Striga damage and low predicted gain cycle−1 for all traits except numbers of emerged Striga plants suggest a need to introgress novel resistance genes into the population for faster progress from selection for increased yield.

An in vitro technique for studying specific Striga resistance mechanisms in sorghum.

Witchweed (Striga sp.) is a noxious parasitic weed of many cereals, that causesconsiderable crop damage in the semi-arid tropics. Although, a number of control measures have been suggested, breeding crops which are resistant to the attack is the most feasible and effective way of control. However, breeding efforts have been hampered by the lack of adequate laboratory techniques that uncover critical host-parasite interactions, that occur naturally beneath the soil. Germination stimulant production is the sole Striga resistance mechanism in sorghum [Sorghum bicolor (L) Moench] that has been extensively studied and exploited for breeding purposes. Other Striga resistance mechanisms have not been effectively characterized and used. The purpose of this study was to develop an in vitroscreening technique for evaluation of sorghum germplasm for specific Strigaresistance mechanisms. We hereby report the development of a reliable screening technique, the Extended Agar Gel Assay (EAGA). Using the technique, we screened seven sorghum genotypes with known reactions to Striga parasitsm, SRN39, Framida, IS9830, 555, N13, Dobbs, Serena , CK60B, Shanqui Red, IS-4225, and two wild sorghum accessions, P78, and P47121, and we were able to characterize specific host defense reactions (mechanisms). These reactions indicate the potential existence of at least four separate mechanisms of Strigaresistance in sorghum: 1) low production of Striga seed germination stimulants; 2) evidence of germination inhibitors; 3) low production of the signal required for haustoria initiation and 4) a hypersensitive response (characterized by a distinct necrotic area on the host root at the attachment site that discourage parasitic establishment. The development of this laboratory assay enabled us to identify and characterize distinct resistance mechanisms. These mechanisms can be exploited through conventional plant breeding programs. Additionally, the resistance genes can be pyramided into one background for more durable Strigaresistance. Key words: Witchweed, Striga resistance, host parasite interaction, germination, haustoria.

The Pattern of Grain Yield Response of Normal and Quality Protein Maize Cultivars in Stress and Nonstress Environments

Maize (Zea mays L.) cultivars combining high grain yield with elevated levels of lysine, tryptophan, and desirable endosperm modification, could reduce food insecurity and malnutrition in West and Central Africa (WCA). Sixteen early‐ and nine extra‐early‐maturing quality protein maize (QPM) and normal cultivars were evaluated under Striga hermonthica (Del.) Benth infestation and Striga‐free environments in Nigeria from 2006 to 2008 to identify stable and high yielding cultivars. The extra‐early normal maize cultivars 2000 Syn EE‐W STR and 99 TZEF‐Y STR, were similar in yield to the QPM versions under both research conditions. While TZEE‐Y Pop STR C4 was superior in grain yield to its QPM version only under Striga‐free conditions, TZEE‐W Pop STR C4 significantly outyielded the QPM version, under both test conditions and was superior in Striga resistance. In the early maturity group, TZE‐W DT STR C4 outyielded the QPM version by 21% under Striga infestation and by 10% when Striga‐free. In contrast, the QPM cultivar 98 Syn WEC STR QPM C0 outyielded the normal endosperm version by 31% when Striga‐infested. GGE‐biplot analysis demonstrated that two extra‐early and three early maturing cultivars had outstanding performance in both research environments. TZEE‐W Pop STR QPM C0 and EV DT‐W 99 STR QPM C0 were high‐yielding and stable when Striga‐infested while TZE‐Y Pop DT STR C4, TZE‐W Pop DT STR C4, and TZE‐Y Pop STR QPM C0 were superior when Striga‐free. The QPM cultivars with grain yield performance and Striga resistance comparable or superior to those of their normal endosperm versions have been developed in our program.

Participatory evaluation of integrated pest and soil fertility management options using ordered categorical data analysis

Maize is becoming the major food crop around Lake Victoria. Major constraints to its production are Striga, stem borer, and declining soil fertility. Innovative integrated technologies have been developed: the ‘push–pull’ system (intercropping with Desmodium and surrounded by Napier grass), soybean and Crotalaria rotations, and imidazolinone-resistant (IR) maize seed. In 12 demonstration trials in four villages in Siaya and Vihiga districts (Kenya) and two villages in Busia (Uganda) in 2003 and 2004, 504 farmers evaluated all cropping systems and a mono-cropped continuous maize, each cropped with IR or local maize, and supplemented or not with fertilizer, totaling 16 treatments. Farmers evaluated all treatments for yield, resistance to Striga and stem borer, improvement of soil fertility, and provided an overall evaluation score, using an ordered scale of 1 (very poor) to 5 (very good). Data were analyzed using ordinal regression, estimating log odds ratios. The results show significant preferences for all treatments over the control. Push–pull with IR and fertilizer had the highest log odds ratio (2.93), so the odds of farmers preferring this treatment are 18.7 times the odds that farmers prefer the control. The odds ratios for the other push–pull combinations were generally highest (9–15), followed by the rotation systems with Crotalaria (3.5–7.0), and soybeans, especially with IR maize and fertilizer (odds ratio of 5.7). In mono-cropping systems, IR maize was only appreciated in combination with fertilizer, and then only in 2004. Push–pull and Crotalaria were more appreciated in 2004 than in 2003. Farmers in Vihiga had a stronger preference for push–pull, and those in Busia for soybean rotations. Significant differences among farmers were observed, but the effects were small. Women appreciated push–pull more than men, while other technologies were gender-neutral. Older farmers were more likely to prefer push–pull and Crotalaria with fertilizer. Livestock ownership was not found to have an effect on technology preferences. Measured yield, stem borer and Striga infestation all had significant but small effects, although their inclusion did not eliminate the treatment effects, indicating that other factors are still important. OLS of the scores for different criteria on the overall score shows yield to be the most important criterion (coefficient of 0.40), followed by soil fertility enhancement (0.25) and Striga resistance (0.13). Labor saving (0.09) and stem borer resistance (0.03) are relatively minor criteria. This research shows that scoring and analysis with ordinal regression is a convenient way to solicit and analyze farmers’ preferences for new technologies, with wide applicability in farming systems and participatory research. Its application here shows that farmers like the new technologies, especially push–pull, but that there are substantial differences between years, sites and farmers. The use of this method can be very helpful to define and focus further research and formulate specific and targeted recommendations for agricultural extension.

Application of Hosaka and DJ Kim Whatmann paper protocols for rapid isolation of cowpea DNA

The traditional liquid nitrogen DNA extraction method is expensive and tedious. There is, therefore, the need for cheaper and faster methods of DNA extraction for efficient application of marker assisted selection (MAS) for breeding for striga resistance in cowpea to be able to handle large number of samples at a time. Two DNA extraction methods; Hosaka (2004) and DJ Kim Whatmann paper (unpublished) were tested on cowpea line IT06K-5-83 under different conditions. The results revealed that both methods with modifications can work with cowpea. However, Hosaka (2004) method seems to be more promising than the other method for DNA extraction in cowpea because it gives better and more consistent DNA band.

Exploiting rice–sorghum synteny for targeted development of EST-SSRs to enrich the sorghum genetic linkage map

The sequencing and detailed comparative functional analysis of genomes of a number of select botanical models open new doors into comparative genomics among the angiosperms, with potential benefits for improvement of many orphan crops that feed large populations. In this study, a set of simple sequence repeat (SSR) markers was developed by mining the expressed sequence tag (EST) database of sorghum. Among the SSR-containing sequences, only those sharing considerable homology with rice genomic sequences across the lengths of the 12 rice chromosomes were selected. Thus, 600 SSR-containing sorghum EST sequences (50 homologous sequences on each of the 12 rice chromosomes) were selected, with the intention of providing coverage for corresponding homologous regions of the sorghum genome. Primer pairs were designed and polymorphism detection ability was assessed using parental pairs of two existing sorghum mapping populations. About 28% of these new markers detected polymorphism in this 4-entry panel. A subset of 55 polymorphic EST-derived SSR markers were mapped onto the existing skeleton map of a recombinant inbred population derived from cross N13 x E 36-1, which is segregating for Striga resistance and the stay-green component of terminal drought tolerance. These new EST-derived SSR markers mapped across all 10 sorghum linkage groups, mostly to regions expected based on prior knowledge of rice-sorghum synteny. The ESTs from which these markers were derived were then mapped in silico onto the aligned sorghum genome sequence, and 88% of the best hits corresponded to linkage-based positions. This study demonstrates the utility of comparative genomic information in targeted development of markers to fill gaps in linkage maps of related crop species for which sufficient genomic tools are not available.

Improvement of Yield and other Traits of Extra‐Early Maize under Stress and Nonstress Environments

Striga, drought, and low soil fertility constrain maize (Zea mays L.) productivity in West and Central Africa (WCA). Two Striga‐resistant extra‐early populations, TZEE‐W Pop STR (white) and TZEE‐Y Pop STR (yellow) were improved by four cycles of S1 recurrent selection, and the products were evaluated in field trials in Nigeria from 2005 to 2007. The objective was to assess progress in improvements for grain yield, Striga resistance, and other traits when Striga‐free, Striga‐infested, and under low‐ and high‐N management. Under Striga infestation, yield gain from C0 to C4 was 136 kg ha−1 for the yellow population and 71 kg ha−1 cycle−1 for the white. The yield gain in advanced cycles of selection in the yellow population was associated with decreases in Striga emergence at 8 and 10 wk after planting (WAP) and Striga damage at 8 WAP, while that of the white was accompanied by increased days to silking (DS) and ears per plant (EPP) as well as a decrease in Striga emergence at 8 WAP. Under Striga‐free conditions, yield gain from C0 to C4 was 164 kg ha−1 cycle−1 for the white and 221 kg ha−1 cycle−1 for the yellow. The yield gain in advanced cycles of selection was more pronounced under high‐N (157 kg ha−1 cycle−1) than low‐N conditions (144 kg ha−1 cycle−1) in the yellow, and higher under low N than high‐N conditions in the white. Selection in the yellow was accompanied by increased days to anthesis (DA) and DS, plant and ear heights under low N and increased DS under high N. In the white, selection induced increased DA, ear height, and decreased anthesis–silking interval (ASI).

A major QTL for resistance of rice to the parasitic plant Striga hermonthica is not dependent on genetic background.

The use of Striga-resistant germplasm is likely to be a cost-effective control strategy for preventing loss of yield owing to Striga. Previously, the authors identified quantitative trait loci (QTL) for resistance in rice to Striga hermonthica (Del.) Benth. in backcross inbred lines (BILs) derived from a cross between two cultivars Nipponbare and Kasalath. It is essential to validate QTL in different environments and/or genetic backgrounds to develop molecular markers linked to resistance QTL for use in marker-assisted selection (MAS) programmes. This study aimed to establish whether a large-effect Kasalath-derived resistance QTL allele on chromosome 4 of rice also conferred resistance in a different mapping population derived from a cross between Koshihikari and Kasalath, and to identify any further Striga resistance QTL. Three Striga resistance QTL were detected in Koshihikari-Kasalath BILs, two of which were derived from the Kasalath allele and one from the Koshihkari allele. The largest QTL (Kasalath allele) explained 16% of the variation in the mapping population and was located on chromosome 4. Comparison between these data and those of the authors' previous analysis revealed that the confidence intervals of the chromosome-4 QTL in the Nipponbare-Kasalath cross and the Kasalath-Koshihikari cross overlapped between 6.5 Mbp and 8 Mbp on the physical rice genome assembly. This study has both verified and narrowed down the position of a Striga resistance QTL of major effect, and demonstrated that it may be a tractable target for MAS.

S1 Family Selection in Early‐Maturing Maize Populations in Striga‐Infested and Striga‐Free Environments

Striga and drought are major constraints to maize (Zea mays L.) production in the savannas of west and central Africa (WCA). A study was conducted in 2005 and 2006 in Nigeria to determine the level of resistance to Striga hermonthica for two early‐maturing maize populations, one white and one yellow, and to assess the progress made in improving each for grain yield and level of resistance after four cycles of S1 recurrent selection. Percentage yield gain per cycle of the yellow population when Striga infested was 13% with r2 = 82% and 5% with r2 = 97% in a Striga‐free environment. Corresponding values for the white population were 15% with r2 = 40% and 1% with r2 = 9% for the two Striga environments. For the two populations, therefore, realized gain in grain yield was higher under Striga‐infested than Striga‐free conditions. Yield gains in the advanced cycles of selection were accompanied by increased number of ears per plant in both populations. Striga damage at 10 wk after planting (WAP) and Striga emergence at 8 WAP decreased by about 5 and 4% cycle−1, respectively in the yellow population. For the white population, Striga damage decreased also by about 5 and 4% per cycle−1 at 8 and 10 WAP, respectively, while Striga emergence decreased by about 5% cycle−1 at 8 WAP. In conclusion, S1 recurrent selection was effective in improving grain yield and Striga resistance in the two early maize populations.

Breeding for Striga Resistance in Sorghum: Exploitation of an Intricate Host–Parasite Biology

ABSTRACTThe parasitic weed Striga Lour. has been one of the more intractable agricultural problems seriously limiting productivity of cereal and legume crops in sub‐Saharan Africa. The development of crop plants with resistance to Striga has been limited because of the complexity of interactions between host, parasite, and the physical environment. We formulated a novel approach based on developing and exploiting a thorough understanding of the biology of this intricate association. We employed this knowledge‐based approach to develop powerful selection assays, to conduct genetic analyses, and to characterize the range of mechanism involved in host plant resistance to Striga Information thus generated has been used to identify unique sources of resistance to Striga, introgress these genes into selected cultivars, and deploy sorghum [Sorghum bicolor (L.) Moench] cultivars with known sources of Striga resistance either independently or in tandem as genotypes with multiple mechanisms of resistance. High yielding sorghum cultivars with Striga resistance and evident grain quality characteristics have been developed and deployed in a number of African countries to be used as cultivars per se or as a central component of an integrated Striga management program.

Genetic Variability for Grain Yield and Its Components in an Early Tropical Yellow Maize Population Under Striga hermonthica Infestation

A major problem that usually confronts the breeder is ensuring that there is sufficient genetic variability in a population for the trait being improved because this determines the breeding schemes to use for improvement and whether or not sufficient progress could be made. Three hundred full-sib families from cycle 3 of the early maturing yellow endosperm maize (Zea mays L.) population, TZE-Y Pop DT STR, were evaluated under artificial Striga hermonthica infestation at Mokwa and Abuja, Nigeria in 2003. The objectives of this study were to investigate the type of gene action involved in the inheritance of S. hermonthica resistance in TZE-Y Pop DT STR C3, determine the extent of genetic variability available in the population after three cycles of S1 recurrent selection, and the phenotypic and genetic correlation coefficients among the traits used for selecting for resistance to S. hermonthica. Estimates of dominance variances were larger than additive genetic variances for grain yield, plant height, ear height, number of ears at harvest, and Striga damage rating at 8 weeks after planting (WAP). Even though h2 estimates were generally low for most traits (< 0.40), moderate-to-large additive genetic variances, and wide ranges were obtained in TZE-Y Pop DT STR C3 for most traits, suggesting that there was adequate genetic variation for improving Striga resistance and grain yield in the population. Highly significant phenotypic correlation coefficients were obtained between grain yield and ears per plant, plant height, ear height, days to anthesis and silking, anthesissilking interval, and Striga damage score at 10 WAP. Recurrent selection methods that capitalize on both additive and dominance variances would be effective for improving the population for Striga resistance and grain yield.

EVALUATION OF EXPERIMENTAL VARIETIES FROM RECURRENT SELECTION FOR STRIGA RESISTANCE IN TWO EXTRA-EARLY MAIZE POPULATIONS IN THE SAVANNAS OF WEST AND CENTRAL AFRICA

A breeding programme for resistance to Striga hermonthica in maize (Zea mays) was initiated in Côte d'Ivoire in 1994. Two extra-early populations, white (TZEE-W Pop STR) and yellow (TZEE-Y Pop STR), were formed from diallel crosses of the best adapted extra-early maturing maize germplasm in the West and Central African subregion. In an effort to improve the populations for Striga resistance, TZEE-W Pop was crossed to inbred 1368 STR (Tzi 3 STR), and TZEE-Y Pop to 9450 STR (Tzi 25 STR). The resulting F1 populations were carried through two backcross (BC) generations. S1 lines were developed from the BC2 and subjected to two cycles of random mating to generate TZEE-W Pop STR C0 and TZEE-Y Pop STR C0. These two populations were subjected to three cycles of S1 recurrent selection under artificial Striga infestation and several experimental varieties were extracted from the different cycles of the selection programme. The original populations (C0), improved populations, and experimental varieties were evaluated in two experiments under Striga-infested and Striga-free conditions. The primary objective was to determine the effectiveness of S1 recurrent selection in developing Striga-resistant extra-early maize varieties. Results of the performance tests showed that the populations were good sources of Striga-resistant varieties with high-yield potential under both Striga-infested and Striga-free conditions. The results have also confirmed the effectiveness of inbreeding, selection and hybridization, as well as the backcross breeding methods, as tools for the development of extra-early populations, synthetic varieties and inbred lines.

Agronomic Performance of Striga Resistant Early‐Maturing Maize Varieties and Inbred Lines in the Savannas of West and Central Africa

ABSTRACTThe potential maize (Zea mays L.) yield in the savannas of West and Central Africa (WCA) is constrained by Striga hermonthica (Del.) Benth. parasitism. Field trials at Ferkessedougou, Côte d'Ivoire; Abuja, Nigeria; and Mokwa, Nigeria, in 2002, and at Mokwa and Abuja in 2004, evaluated the performance of 11 early maturing maize varieties under artificial Striga infestation and Striga‐free conditions. Another trial at Mokwa and Abuja in 2004 evaluated 100 early maturing inbred lines under Striga infestation and Striga‐free conditions. The varieties differed significantly in grain yield under both conditions. Acr 94 TZE Comp 5‐W, Acr TZE Comp 5‐Y, and TZE‐W Pop × 1368 STR C1 were identified as promising varieties, based on grain yield, Striga damage ratings, and Striga emergence counts. The most promising variety, Acr 94 TZE Comp. 5‐W in terms of high grain yield, reduced Striga damage and low Striga emergence, outyielded the reference entry by 2% under Striga‐free conditions and 45% under Striga infestation. Ward cluster analysis of the varieties and inbred lines produced four major clusters each, under both Striga‐infested and Striga‐free conditions. In each case, the varieties and inbred lines assigned to each cluster under Striga infestation differed from those in the Striga‐free conditions. Several inbred lines with high grain yield, low Striga emergence and reduced Striga damage were identified as sources of Striga resistance for maize breeding programs in WCA.