Striga Infestation Research Articles

Effect of imazapyr treated maize on Striga infestation and time of intercropping cowpea in Samaru, Nigeria

Two field experiments were conducted at the research farm of Institute for Agricultural Research (IAR) Samaru, Zaria during the 2011 cropping season, with the aim of determining the effect of imazapyr treated maize on Striga infestation and time of intercropping cowpea in Samaru, northern guinea savannah of Nigeria. There were two sets of experiments: the first experiment consisted of Six (6) hybrids (AS1128-1, AS1128-2, AS1128-3, AS1128-4, AS1128-6 and AS1128-8) of imazapyr resistant (IR) maize seeds treated with imazapyr chemical and intercropped with cowpea at 2, 4 and 6 weeks after sowing (WAS) of maize. The second experiment consisted of the same Six (6) hybrids of IR maize seeds but untreated and also intercropped with cowpea at 2, 4 and 6 WAS of maize. The experiments were laid out in a split plot design with time of intercropping cowpea as main plot and hybrid maize varieties as sub plot, and replicated three times. The cowpea variety used for the trial was IT97K-499-35. Among the treated IR-maize hybrids, only AS1128-1, AS1128-2, AS1128-3 and AS1128-4 germinated while for the untreated, all the six hybrids germinated. The grain yields per hectare of all the treated maize hybrids did not significantly differed whereas grain yields per hectare of the untreated maize hybrids AS1128-1, AS1128-2, AS1128-3 and AS1128-4 were significantly higher than the hybrid AS1128-8. The treated IR maize hybrids exerted 100% control of Striga while the untreated supported Striga emergence. There was no visible damage symptoms observed on the cowpea intercropped with treated maize at all times of intercropping. It is therefore concluded that the IR-maize hybrids ASII28-1, ASII28-2, ASII28-3 and ASII28-4 should be used in the treated forms for the control of Striga. Moreover, the intercropping of cowpea with imazapyr treated maize can be carried out starting from 2 WAS of maize.Key words: Intercropping, imazapyr resistant maize (IR-maize), cowpea, Striga.

Consistency of performance of early-maturing maize cultivars in Striga-infested and Striga-free environments

Badu-Apraku, B., Yallou, C., Oyekunle, M., Akinwale, R., Aweke, G. and Kamara, A. 2015. Consistency of performance of early-maturing maize cultivars in Striga-infested and Striga-free environments. Can. J. Plant Sci. 95: 1073–1084. Despite the immense potential of maize (Zea mays L.) in savannas of West and Central Africa (WCA), production and productivity is constrained by Striga hermonthica parasitism. Sixteen early-maturing cultivars were evaluated at two locations in Nigeria and three locations in the Republic of Benin from 2007 to 2009 to assess the grain yield, stability and the consistency of the rankings of the cultivars under Striga-infested and Striga-free environments. The combined analysis of variance showed significant (P<0.01) cultivar and cultivar×environment interactions for grain yield and other traits under Striga-infested and Striga-free environments. The test of concordance was significant (P<0.001) for grain yield (W=0.68), number of emerged Striga plants (W=0.74) and Striga damage (W=0.56) under Striga infestation, indicating stability of resistance in the cultivars developed from diverse sources under artificial S. hermonthica infestation across environments. There was high consistency of the rankings of the cultivars for grain yield and other Striga-resistance traits under Striga-infested and Striga-free environments in Benin and Nigeria. The additive main effects and multiplicative interaction (AMMI) biplot analysis for grain yield revealed POOL15SR/ACR94TZECOMP5-W/ACR94TZECOMP5-W and 2004 TZE-Y Pop DT STR C4 as the most stable cultivars with above-average mean grain yield in Striga-infested environments and they can be combined with other crop management options to control the parasite in the Striga endemic environments. Cultivars TZE Comp 5-W C7F2 and TZE Comp5-Y C6 S6 (Set B) had less Striga damage and number of emerged Striga plants across test environments. These cultivars could therefore serve as unique sources of favorable alleles for improving Striga resistance in maize in different production environments and farming systems.

Climate-adapted companion cropping increases agricultural productivity in East Africa

Production of cereals, the main staple and cash crops for millions of farmers in sub-Saharan Africa (SSA) is severely constrained by parasitic striga weed Striga hermonthica, stemborers and poor soil fertility. A companion cropping system known as ‘push–pull’ overcomes these constraints while providing additional soil fertility and forage grass benefits to smallholder farmers. To ensure the technology's long-term sustainability in view of the current and further potential aridification as a consequence of climate change, drought-tolerant crops, Brachiaria cv mulato (border crop) and greenleaf desmodium (intercrop), have been identified and incorporated into a ‘climate-adapted push–pull’. The aims of the current study were to evaluate effectiveness of the new system (i) in integrated control of striga and stemborer pests and (ii) in improving maize grain yields, and to evaluate farmers’ perceptions of the technology to assess potential for further adoption. 395 farmers who had adopted the technology in drier areas of Kenya, Uganda and Tanzania were randomly selected for the study. Each farmer had a set of two plots, a climate-adapted push–pull and a maize monocrop. Seasonal data were collected in each plot on the number of emerged striga plants, percentage of maize plants damaged by stemborers, plant height and grain yields. Similarly, farmers’ perceptions of the benefits of the technology were assessed using a semi-structured questionnaire. There were highly significant reductions in striga and stemborer damage to maize plants in the climate-adapted push–pull compared to the maize monocrop plots: striga levels were 18 times lower and stemborer levels were 6 times lower. Similarly, maize plant height and grain yields were significantly higher. Mean yields were 2.5 times higher in companion planting plots. Farmers rated the climate-adapted push–pull significantly superior in reducing striga infestation and stemborer damage rates, and in improving soil fertility and maize grain yields. These results demonstrate that the technology is effective in controlling both weeds and pests with concomitant yield increases under farmers’ conditions. It thus provides an opportunity to improve food security, stimulate economic growth, and alleviate poverty in the region while making agriculture more resilient to climate change.

Marker-assisted introgression improves Striga resistance in an Eritrean Farmer-Preferred Sorghum Variety

The parasitic weed Striga hermonthica hampers the production of sorghum, the most important cereal crop in Eritrea. This weed has a complex mode of infestation that adapts to many hosts and environments, complicating conventional breeding for resistance, which is the only form of crop improvement available to Eritrean breeders, but has failed. This study aimed at improving resistance against this parasite by transferring 5 Striga resistant Quantitative Trait Loci (QTLs) from resistance donor N13 to Striga susceptible Farmer-Preferred Sorghum Variety (FPSV) Hugurtay from Eritrea. The method involved backcrossing using marker-assisted selection (MAS) and evaluation of the best introgressed lines for Striga resistance in artificially infested fields. Foreground selection was performed with up to 11 polymorphic simple sequence repeat (SSR) markers linked to Striga resistance QTLs, while background selection was conducted in the BC3F2 generation with 27 polymorphic unlinked SSR markers to identify the best recovery of the recurrent parent (RP) genetic background. Out of 84 BC3F3 lines, L2P3-B, L1P5-A and L2P5P35 performed best with respect to both grain yield and reduced Striga infestation. These lines were more resistant to Striga than Hugurtay, but less resistant than N13. The three lines yielded twice as much as N13, with Area Under Striga Number Progression Curve (AUSNPC) values on average 18% higher than that of N13 and 38% lower than that of Hugurtay. This suggests that the introgressed QTLs conferred significant Striga resistance and yield advantage to these BC3F3 backcross progenies under Striga pressure. These lines have good potential for future release and demonstrate that when MAS is available to conventional breeders, even in countries with no genotyping facilities, it is a useful tool for enhancement, expediency and precision in crop improvement.

English

Evaluation of 15 F1 hybrids and six parents obtained from partial diallel crosses was carried out during 2011 rainy season at Institute of Agricultural Research (IAR) Samaru, Zaria Striga infested field and Striga free field (2 environments). Interrelationships of grain yield and its components under Striga infestation revealed that character ear height had positive and highly significant phenotypic correlation with grain yield (rph = 0.55)**. While the remaining six characters recorded no significant correlation with grain yield. Similarly, Striga related parameters with Striga affected traits indicated high and highly significant positive correlation between Striga count one with Striga count two (rg= 0.79, rph = 0.92 and re  = 0.96)** and Striga rating (rg = 0.84, rph = 0.71 and re = 0.77)** and also had highly significant positive genotypic correlation with number of leaves per plant (rg = 0.79**) Striga count two exihibited high and highly significant positive phenotypic and environmental correlation with the traits Striga rating (rph = 0.78**and re = 0.71**) and number of leaves per plant (rph = 0.64** and re = 0.55**). While Striga rating recorded highly significant positive genotypic correlation (rg = 0.89**) coefficient rph = 0.78** and rph= 0.97** respectively. At Striga free environment grain yield was positively significantly correlated with 1000 grain weight (rph = 0.43* and re = 0.45*), highly significantly positively correlated at genotypic level (rg= 0.69)**, phenotypic level (rph = 0.52)* and environmental level (re = 0.43)* with number of leaves per plant. Furthermore, plant height with grain yield recorded highly significant positive correlation genotypically, phenotypically and environmentally with the following coefficients (rg = 0.86, rph= 0.67 and re = 0.58)**, and likewise ear height and grain yield revealed significantly positive correlation with the following coefficients rg = 0.45*, rph = 0.48* and re = 0.49*. Thus characters such as ear height, plant height, number of leaves per plant and 1000 grain weight should be taken into cognizance when selecting high yielding genotypes. Hybrids TZEEI 11 x TZEEI 3, TZEEI 11 x TZEEI 7 are outstanding in performance, especially grain yield and TZEEI 11 is good for hybrid formation.   Key words: correlation, Striga parameters, grain yield and Striga affected traits.

Striga species distribution and infestation in cereal food crops of northern Côte d’Ivoire

Most cereal food crops in Côte d'Ivoire are infested by Striga species. In this study the distribution, abundance and degree of infestation of Striga species were determined. Infested areas under cereal crops were estimated. Data was collected through extensive and intensive surveys and field visits. According to the updated map of Striga infestation, infested areas covered all the north of the country between latitudes 8°47.17' N to 10°38.84' N and longitudes 2°47.68' W to 7°55.20' W. The infested zone covered 3,191,850 hectares of farmland. 71.8% of the villages located in the region were infested by Striga species. The hypothesis of an extension of Striga infestations according to a north-south gradient was confirmed. Infestations began in the Sudan Savannah zone and have now reached half of the sub-Sudanian Savannah zone. Striga hermonthica, with a frequency of 97.1%, was the most abundant species under cereal crops, followed by Striga aspera (2.0%) and Striga asiatica (0.9%). Striga gesnerioides was not recorded on cowpea. Mutants of S. hermonthica and S. aspera with white flowers were identified. Red-flowered morphotypes of S. asiatica were found parasitizing upland rice. S. hermonthica is a major threat to cereal crop production in northern Côte d'Ivoire where it severely infested 57.2% (268,250 ha) of lands under maize (108,160 ha), millet (38,300 ha), sorghum (30,360 ha) and upland rice (91,430 ha). The infestation rates under millet, maize, sorghum and upland rice were 65.9%, 56.5%, 51.0% and 40.5%, respectively. Striga has today become a major national threat to the production of these cereals as well as to food security in endemic areas.

Screening Sorghum for Resistance to Striga Hermonthica (Del.) Benth

The root hemiparasitic weed Striga hermonthica is a serious constraint to grain production of economically important cereals in sub-Saharan Africa. Six cultivars of sorghum Abu sabien, were tested for resistance and tolerance to this root hemi-parasite by applying one of two levels of Striga infestation (2 and 4 mg/pot). Results indicated that Striga emergence infesting on roots of all cultivars, indicating that none exhibited a true resistance mechanism. However, cultivar, V6 sustained the lowest Striga emergence and no significant decrease in host biomass. Cultivar V3 exhibited the highest in height and biomass on infection indicating the operation of a tolerance mechanism. Under high infestation, one promising variety namely V6 constantly recorded low number of parasite plants and lowest Striga growth. Sorghum V3 sustained the highest plant growth although it has high Striga infestation. Mature plant resistance was also expressed by delay of parasite emergence and inhibition of its development, low reduction in sorghum growth and production (dry matter) in comparison with susceptible cultivars. Adoption of an integrated approach encompassing high yielding Striga resistant and/or tolerant cultivars may provide a cheap and easy to apply method for Striga control under low-input farming systems.

Maize-Soybean Intercropping System: Effects on <i>Striga</i> Control, Grain Yields and Economic Productivity at Tarka, Benue State, Nigeria

On-Farm trials were conducted from July to November during the 2009 and 2010 cropping seasons, at Tarka, Benue State, Nigeria to evaluate the effects of intercropping maize and soybean on striga control, grain yields and economic productivity. The treatments consisted of sole maize, sole soybean and the intercrop of maize and soybean, replicated three times in a randomized complete block design. The results obtained showed that intercropping maize and soybean significantly (P ≤ 0.05) reduced striga shoot count by 55.9 % and 56.1 % respectively, in 2009 and 2010 compared to that produced on pure maize plots. Number of affected maize plants, lodging score of maize and infestation rate were lower for intercropping than for sole maize plots. The severity level was also recorded lower for intercropping compared to that recorded for pure maize stands, where severity level is in the range of high to very high. Though, soybean yield was reduced by intercropping, however, soybean and maize intercropping system increased maize grain yield, total intercrop yield, land equivalent coefficient greater than 0.25, land equivalent ratio values greater than one (LER > 1), higher total intercrop values and monetary equivalent ratio greater than 1.00, indicating yield and economic advantages. The implication of study showed that intercropping maize and soybean can be adopted by farmers as an efficient cropping system strategy to reduce striga infestation, increase maize yield and give greater economic productivity.

Maize-Soybean Intercropping System: Effects on <i>Striga</i> Control, Grain Yields and Economic Productivity at Tarka, Benue State, Nigeria

On-Farm trials were conducted from July to November during the 2009 and 2010 cropping seasons, at Tarka, Benue State, Nigeria to evaluate the effects of intercropping maize and soybean on striga control, grain yields and economic productivity. The treatments consisted of sole maize, sole soybean and the intercrop of maize and soybean, replicated three times in a randomized complete block design. The results obtained showed that intercropping maize and soybean significantly (P ≤ 0.05) reduced striga shoot count by 55.9 % and 56.1 % respectively, in 2009 and 2010 compared to that produced on pure maize plots. Number of affected maize plants, lodging score of maize and infestation rate were lower for intercropping than for sole maize plots. The severity level was also recorded lower for intercropping compared to that recorded for pure maize stands, where severity level is in the range of high to very high. Though, soybean yield was reduced by intercropping, however, soybean and maize intercropping system increased maize grain yield, total intercrop yield, land equivalent coefficient greater than 0.25, land equivalent ratio values greater than one (LER > 1), higher total intercrop values and monetary equivalent ratio greater than 1.00, indicating yield and economic advantages. The implication of study showed that intercropping maize and soybean can be adopted by farmers as an efficient cropping system strategy to reduce striga infestation, increase maize yield and give greater economic productivity.

Combining ability of maize (Zea mays) inbred lines resistant to Striga hermonthica (Del.) Benth evaluated under artificial Striga infestation

The parasitic weed Striga affects maize on an estimated 20 million ha in Africa, making it a major cause of maize yield reduction from near world average of 4.2 t/ha few decades ago to the present 1.5 t/ha. The objectives of this study were to examine the combining ability of 20 inbred lines and identify single crosses which can be used to develop other hybrids resistant to Striga hermonthica (Del.) Benth. Fourteen female lines were mated using North Carolina Design II with all six males. The resulting 84 F1s along with six commercial checks were evaluated in four separate trials for two rainy seasons during 2010. The trials were conducted on station under both artificial Striga infestation and Striga free environments using standard procedures at the Kibos and Alupe sites, both in the Kenya’s Lake Victoria Basin. Data were recorded on Striga counts, Striga damage rating (SDR), grain yield and other agronomic traits. General combining ability (GCA) and specific combining ability (SCA) effects were computed using SAS. The new F1 hybrids outperformed the commercial checks in grain yield and reaction to Striga. Single crosses JI-30-3/TESTR 151, JI-30-18/TESTR 151, CML206//56/44-6-3-7-1/TESTR 149 and JI-30-18/TESTR 156 gave the highest yield while single cross JI10-28-#/TESTR 136 gave the lowest yield. The ratio of GCA: SCA mean squares exhibited a predominance of additive gene effects in the inheritance of Striga resistance traits as opposed to dominance gene effects. Inbred lines with good GCA for yield and Striga resistance traits were identified as TESTR 151, TESTR 156 and OSU231//56/44-6-4-17-3. The high GCA inbred lines and the superior single crosses will provide a basis for future use perse and also development of three-way and double cross hybrids to be grown in Striga prone areas of the Lake Victoria Basin in eastern Africa. Key words: Maize, Striga hermonthica, general combining ability (GCA), specific combining ability (SCA), host plant resistance, sub-Saharan Africa.

Assessment of level, extent and factors influencing Striga infestation of cereals and cowpea in a Sudan Savanna ecology of northern Nigeria

Infestation of cereals and cowpeas by Striga species constitute a major constraint to increased crop productivity in the savannas of northern Nigeria. Field surveys were undertaken in Jigawa State, Nigeria in 2012 to assess (i) the level and extent of Strgia infestation of cereal and cowpea fields (ii) the severity of Striga attack on crops and (iii) to determine the factors associated with Striga infestation of crop fields. The study was conducted in 48 communities. Eight farmer's fields were sampled in each community along two intersecting transects. Striga hermonthica incidence ranged from 58 to 100% in sorghum fields and from 0 to 100% in millet fields. In sorghum and millet fields, number of emerged Striga plants ranged from 4750 to 431,500 and 0 to 251,750plantsha−1 respectively. For cowpea, S. gesnerioides population ranged from 1625 to 105,375plantsha−1. The severity of Striga attack on sorghum was devastating in all the communities studied. Except in a few cases, all cowpea plants in fields surveyed in most communities were attacked by S. gesnerioides. Field infestation was largely related to poor soil fertility. Stepwise multiple regression identified latitude, pH, available P, Cu and exchangeable K as potentially most important in explaining observed variations in S. hermonthica infestation in sorghum fields. For millet fields, soil pH, available P, Zn and latitude accounted for most of the variations in Striga population whereas latitude, total N, organic C, exchangeable Ca, ECEC, pH, available Mn and Cu accounted for most of the observed variations in S. gesnerioides population in cowpea fields. Our study showed that Striga is a major problem in Jigawa State with almost all the cowpea, sorghum and millet fields infested with the parasite. Improved soil fertility management technologies and Striga-resistant crop varieties are needed to address the menace of Striga in the State.

Efficiency of secondary traits in selecting for improved grain yield in extra‐early maize under Striga‐infested and Striga‐free environments

AbstractA base index involving Striga damage, number of emerged Striga plants and ears per plant is used for selecting for maize (Zea mays L.) grain yield under Striga infestation. There are contradictory reports on the reliability of number of emerged Striga plants for selecting for Striga resistance. The objective of this study was to confirm reliability of the secondary traits for selecting for improved grain yield under Striga infestation. Ten Striga‐resistant extra‐early cultivars were evaluated for 3 years under artificial Striga‐infested and Striga‐free environments in Nigeria. Analysis of variance combined across years and locations showed significant mean squares for genotype, year, location and their interactions for most traits. Sequential path analysis identified ear aspect as the only trait with significant direct effect on yield under artificial Striga infestation, while GGE biplot confirmed ear aspect, ears per plant and Striga damage as the most reliable traits. Ear aspect should be included in the base index for selecting for improved grain yield of extra‐early maize under Striga infestation, while the number of emerged Striga plants should be excluded.

Cumulative effects and economic benefits of intercropping maize with food legumes on Striga hermonthica infestation

The parasitic weed Striga hermonthica, commonly known as striga, is a major biotic constraint to maize production in sub-Saharan Africa (SSA) where it causes serious food insecurity and poverty in smallholder farming communities. We previously discovered an effective control method for it involving intercropping cereals with fodder legumes in the genus Desmodium, commonly known as desmodium. The objectives of the current study were to evaluate cumulative effects of intercropping maize with the commonly grown food legumes on striga infestation, and to establish any economic benefits of the same. Treatments comprised maize plots planted in monocrop stands or intercropped with five different food legume species or desmodium. Intercropping maize with desmodium gave the most consistent and significant suppression of striga. Out of the food legume intercrops, only crotalaria, groundnut and greengram intercrops had significantly lower striga counts and only in some of the cropping seasons. Grain yields were consistently and significantly higher with desmodium intercrop, although they were also increased with food legume intercrops compared to maize monocrop, thus confirming superiority of intercropping with legumes over maize monocrop. Although production costs in terms of total labor and variable costs were significantly higher for the intercrops than for the maize monocrop, total revenue and net benefits were significantly higher in the former, especially for desmodium. The desmodium intercrop gave the highest economic benefits followed by crotalaria and greengram intercrops. These results confirmed the effectiveness of desmodium in suppressing striga and improving yields and economic returns to smallholder farmers. They also showed that it is profitable to invest in food legume intercrop systems, especially the crotalaria and greengram systems, and indicate that intensifying maize cropping systems through integration of these food legumes in combination with other approaches can contribute to an integrated management of striga and provide a more sustainable and profitable productive system to smallholder farmers.

English

  Trials were carried out using five composite maize varieties in a Striga lutea (Lour) endemic soil of Temidire-Eruwa, Oyo State, Nigeria, in 2004 and 2005. The composite maize varieties were tested under varied fertilizer types, nitrogen (N) concentrations and artificial striga infestation. The objective was to test these striga resistant maize varieties for yield and agronomic performance under the above conditions. The result showed that, variety and year of evaluation differed significantly (P<0.01) for almost all agronomic characters such as plant stand, days to anthesis (silking and tasselling), plant and ear heights as well as root and stalk lodging resistance at both 100 and 200 kgN/ha. Variety x year interaction were also significantly different (P<0.01) for all agronomic characters except root lodging and husk tip cover. Fertilizer type differed only for days to silking, plant height and plant aspect, while year x nitrogen source and variety x nitrogen source was highly significant (P<0.01) for field weight. Plant stands were generally better in 2004 than 2005 for all varieties except Acr 97syn-W and DMR-LSR-W. The composite maize varieties were able to tolerate high N-concentration except DMR-LSR-Y which do not utilize excess nitrogen above 100 kgN/ha. Use of striga resistant maize varieties concomitantly with nitrogen fertilizer is recommended for farmers in S. lutea endemic ecology, for higher grain yield.   Key words: Composite maize, fertilizer type, nitrogen (N) concentrations, striga resistance, yield.

Effects of Organic and Microbial Fertilizers on Striga Hermonthica in Maize

A pot experiment was conducted at the Environment and Natural Resources Research Institute, NCR, Sudan to investigate the effect of organic (Elkhairat (T) and Elkhasseb (X)) and microbial (Azospirillin (A) and Phosphobacterin (B)) bio-fertilizers and their combinations on S. hermonthica growth and development in Maize. Results showed that all treatments reduced emergence of the parasite, except inoculation with A which enhanced Striga emergence compared to control. Treating maize plants with Striga, irrespective to treatments reduced maize height as compared with free maize. Plants fertilized with T sustained the highest plant growth at 4 weeks after sowing (WAS). It increased maize height by 79% as compared to infested control. At 6 WAS fertilization with X, B+T and A+B+T were significantly increased plant heights as compared to infested control. Leaf number was affected due to Striga infestation. At 6 WAS, all treatments significantly increased leaf numbers except B, A+B and X as compared to infested control. While at 10 WAS, results showed that only A+B+T was significantly increased leaf numbers compared to infested control. Averaged across all fertilization treatments, maize plants infested with Striga had smaller leaf areas than did uninfected plants. At 6 and 10 WAS, X sustained the highest leaf area index compared to all other treatments. Maize treated with X and A+B+T sustained the highest shoot dry weight as compared to infested control . Maize fertilized with X, A+T and A+X showed the highest root dry weight as compared to infested control.

English

  Maize is one of the most important food crops in Ghana even though its production has not reached self sufficiency levels. Drought and striga infestation are among the most important production constraints of maize in Ghana. Promising high yielding, drought and striga tolerant maize varieties are being evaluated by CSIR and IITA in participatory on-farm trials and demonstrations. These varieties however need to meet farmers’ varietal preferences in order for them to adopt. This study therefore sought to assess farmers’ preference for the different drought tolerant maize varieties, and determine factors that influence their choices. Kendall’s coefficient of concordance was used to test the level of agreement between farmers on their preferences. The ordered logistic regression was used to estimate the determinants of farmer’s preference using cross-sectional observations from 120 maize farmers in the Transitional and Savannah zones of Ghana. Results indicate that maize varieties that are early maturing (2.38) and drought tolerant (2.45) were most preferred by farmers. Area under maize cultivation, fertilizer usage and family size are the factors that were found to influence farmers’ preference for improved maize varieties. These factors should therefore be considered in varietal promotion.   Key words: Drought tolerant, farmers’ preferences, determinant, savannah and transition zones of Ghana, ordered logit.

Genetic gains from selection for high grain yield and Striga resistance in early maturing maize cultivars of three breeding periods under Striga-infested and Striga-free environments

Maize is the most important staple cereal crop in sub-Saharan Africa (SSA) and has great potential to rectify the food insecurity in the sub-region. A study was conducted at four locations two each in Nigeria and Benin in 2010 and 2011 to determine the rate of genetic improvement in the grain yield of 50 maize cultivars developed during three breeding periods, 1988–2000 (period 1), 2001–2006 (period 2) and 2007–2010 (period 2) under Striga-infested and Striga-free conditions. Under Striga infestation, mean grain yield ranged from 2537kgha−1 for the period 1 cultivars to 3122kgha−1 for period 3 cultivars with a corresponding annual genetic gain of 1.93%. When Striga-free, grain yield ranged from 3646kgha−1 for the period 1 cultivars to 4227kgha−1 for the period 2 cultivars with an annual genetic gain of 1.0%. The average annual rate of increase in grain yield was 41kgha−1 when Striga-infested and 34kgha−1 when Striga-free. The annual genetic gain in grain yield was 0.86% for period 1 cultivars, 2.07% for period 2 cultivars, and 2.11% for period 3 cultivars under Striga infestation. The increase in grain yield under Striga infestation was associated with significant decrease in Striga damage and the number of emerged Striga plants at 8 and 10 weeks after planting (WAP), an improvement in ear aspect, lodging resistance, plant height, and increase in the number of ears per plant (EPP) from the period 1 to the period 3 cultivars. For the emerged Striga plants, the annual genetic gains of −0.63% for 8WAP and −0.57% for 10WAP were obtained from the period 1 to the period 2 cultivars. The increase in genetic gains was 0.70% for EPP and −0.65% for ear aspect. The increase in grain yield from period 1 to period 3 cultivars when Striga-free was associated with increased days to anthesis, increased plant and ear heights, improvement in ear aspect, and husk cover and increased EPP. Cultivars 28, 14, 29, and 26 were the most outstanding across Striga-infested environments. Substantial progress has been made in breeding for high yielding, Striga resistant/tolerant cultivars during the past three decades.

EVALUATION OF STRIGA-RESISTANT EARLY MAIZE HYBRIDS AND TEST LOCATIONS UNDER STRIGA-INFESTED AND STRIGA-FREE ENVIRONMENTS

Emergence of several seed companies in the West Africa sub-region during the last decade has necessitated intensified efforts towards hybrid development and extensive testing. The objectives of the present study were to evaluate selected Striga-resistant maize (Zea mays L.) hybrids for grain yield and stability of performance based on multiple traits. Thirty Striga-resistant single–cross maize hybrids plus two checks were evaluated under artificial Striga infestation and Striga-free conditions at 2 locations in Nigeria in 2008 and 2009. The two test locations possessed high discriminating ability. More promising genotypes were identified under Striga infestation based on multiple traits than based on yield per se, suggesting that grain yield alone is not a precise predictor of Striga resistance. Based on both biplot analyses, TZEI12 x TZEI25 was identified as the most outstanding in performance under both research conditions. Furthermore, TZEI11 x TZEI127 and TZEI80 x TZEI2B were identified as the most outstanding under Striga-infested conditions and TZEI60 x TZEI87 under Striga-free conditions by the two biplot methods. The hybrids with outstanding performance should undergo extensive multilocational testing and promotion for adoption for commercial production. Key Words : GGE biplot, multiple traits, Zea mays

Constraints to On-Farm Maize (Zea mays L.) Seed Production in Western Kenya: Plant Growth and Yield

Studies have shown that that about 85% of maize farmers in Western Kenya plant local varieties with about 80% using own farm-saved seeds. The production system is characterized by late harvesting, heavy striga infestation, use of local varieties, and low-soil fertility. The objective of this study was to test an on-farm seed production system which would help improve yield and quality of farm saved seeds. The trials were set up in a factorial design fitted as random complete block design. There were 3 factors each at 2 levels: time of harvest, variety choice, and fertilizer application. Fertilizer application led to an 88% increase in yield, 54% increase in number of seeds per cob, and 14% increase in 100-seed weight. Fertilizer application also led to an increase in seed vigour and viability. Yield differences between the 2 varieties were not significant. The correlation between 100-seed weight and seed vigour was significant showing that heavy seeds were more vigourous. Nitrogen application was therefore recommended for increasing yields and for producing vigourous seeds but should be done with caution to avoid lodging as witnessed. This study also noted that farmers are rational and their decisions are usually based on strong economic considerations.

Relative changes in genetic variability and correlations in an early-maturing maize population during recurrent selection

Four cycles of S(1) family recurrent selection to improve grain yield and resistance to Striga hermonthica have been completed in TZE-Y Pop STR C(0.) In order to determine whether or not to continue with the recurrent scheme, it was desirable to evaluate the amount of residual genetic variance and associated parameters in the population. The objective of this study was to characterize the relative changes in the levels of the genetic variances, heritability estimates and genetic correlation coefficients, and to predict future gains from selection for grain yield, Striga resistance and other agronomic traits. Fifty S(1) families, derived from each cycle, were evaluated under Striga-infested and Striga-free conditions at Mokwa, Ikenne and Abuja, Nigeria, in 2005 and 2007. Under Striga infestation, genetic variances for grain yield, days to anthesis, plant height and Striga damage generally increased in the advanced cycles of selection. In contrast, the genetic variances for days to silk, anthesis-silking interval, ears per plant, ear aspect and number of emerged Striga plants decreased with selection. The advanced cycles of selection significantly out-yielded the original cycle in both research environments. Heritabilities for grain yield, Striga damage and number of emerged Striga plants were significantly greater than zero. The realized gains from selection for grain yield under Striga infestation (52kgha(-1)cycle(-1)) and Striga-free conditions (130kgha(-1)cycle(-1)) were remarkably lower than the predicted gains (350 and 250kgha(-1)cycle(-1), respectively). Adequate genetic variability exists in cycle 4 of the scheme to ensure future gains from selection.