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Striga hermonthica (Del.) Benth parasitism, low soil N, and nutritional deficiencies of normal‐endosperm maize (Zea mays L.) threaten maize yield and exacerbate nutritional problems in sub‐Sahara Africa (SSA). This study was conducted (a) to evaluate genetic variation among extra‐early maturing maize hybrids with provitamin A and quality protein characteristics, (b) to investigate gene action governing the inheritance of Striga resistance, grain yield, low N tolerance, and other measured traits under low‐N, high‐N, and Striga‐infested environments, and (c) to identify hybrids with high yield and stability across environments. One hundred and fifty hybrids developed using North Carolina Design II were evaluated with six checks under low‐N, high‐N, and Striga‐infested environments in Nigeria. Mean squares for hybrids were highly significant (P

A desirable tester that elicits greater genetic difference in Striga resistance among test crosses in a breeding program has not been reported. Therefore, this study was conducted to characterize 30 Striga resistant yellow endosperm maize inbred lines and three testers with varying resistance levels to Striga using DArTseq SNP markers and agronomic traits to identify a suitable tester for resistance hybrid breeding. Marker-based and agronomic trait-based genetic distances were estimated for yellow endosperm maize inbred lines and testers with varying resistance levels to Striga. The Marker-based cluster analysis separated the Striga resistant lines and testers into two distinct groups. Although the susceptible tester (T3) was the most distantly related to the 30 Striga resistant inbred lines, it exhibited a narrower range in genetic distance estimates and poor agronomic performance under Striga infestation in crosses with the resistant lines. In contrast, the resistant tester (T2) showed a broader range in genetic distance estimates in pairs with the 30 resistant lines. Also, it formed many high yielding hybrids with desirable traits under parasite pressure. Furthermore, the most significant positive association between agronomic trait-based and marker-based distance estimates (r = 0.389, P = 0.01) was observed when T2 has paired with the Striga resistant maize inbred lines. It thus appears that T2 may be used as a suitable tester to determine the breeding value of lines in hybrid maize resistance breeding programs. T2 was the most suitable tester, with a tolerant tester (T1) as an alternative tester to characterize the combining ability of Striga resistant maize inbred lines. This result can also encourage other breeders to investigate testers relative discriminating ability with varying levels of resistance in hybrid breeding for resistance to diseases, pests, and other parasitic plants.

The choice of an appropriate tester is important for success in resistance hybrid breeding programs. Limited information is available on the most suitable testers that allow the selection of yellow endosperm maize inbred lines with good combining ability for resistance to witchweed (Striga hermonthica) and superior agronomic performance in hybrids targeted to areas infested with the parasite. Testcrosses of 30 Striga-resistant yellow endosperm maize inbred lines with three testers having varying levels of resistance to S. hermonthica were evaluated at Abuja and Mokwa in Nigeria under Striga-infested and non-infested conditions in 2018 and 2019. The lines &times, tester interaction was significant for grain yield under Striga infestation, indicating that the performance lines in testcrosses varied with the testers. The respective average general combining ability effect of lines and testers was 1.5 and 32.4 times greater than the corresponding specific combining ability effects under infestation, showing the greater importance of additive gene action controlling the performance of testcrosses under Striga infestation. The different testers exhibited a different capacity to discriminate among the test lines with the susceptible tester being the least effective. Most of the criteria used to determine the best tester favored the selection of the tolerant and resistant testers as promising candidates to identify superior Striga-resistant yellow endosperm inbred lines for the hybridization and development of resistant hybrids. The results of this study demonstrated that testers with a high frequency of desirable alleles were superior to the tester with a low frequency of favorable alleles in hybrid breeding programs for resistance to S. hermonthica.

SUMMARYMaize (Zea maysL.), a major staple food crop in West and Central Africa (WCA), is adapted to all agro-ecologies in the sub-region. Its production in the sub-region is greatly constrained by infestation ofStriga hermonthica(Del.) Benth. The performance and stability of the extra-early maturing hybrids, which are particularly adapted to areas with short growing seasons, were assessed underStriga-infested andStriga-free conditions. A total of 120 extra-early hybrids and an open-pollinated variety (OPV) 2008 Syn EE-Y DT STR used as a control were evaluated at two locations each underStriga-infested (Mokwa and Abuja) andStriga-free (Ikenne and Mokwa) conditions in 2010/11. TheStriga-resistant hybrids were characterized by higher grain yield, shorter anthesis–silking interval (ASI), better ear aspect, higher numbers of ears per plant (EPP), lowerStrigadamage rating, and lower number of emergedStrigaplants at 8 and 10 weeks after planting (WAP) compared with the susceptible inbreds. UnderStrigainfestation, mean grain yield ranged from 0·71 to 3·18 t/ha and 1·19 to 3·94 t/ha underStriga-free conditions. The highest yielding hybrid, TZEEI 83×TZEEI 79, out-yielded the OPV control by 157% underStrigainfestation. The hybrids TZEEI 83×TZEEI 79 and TZEEI 67×TZEEI 63 were the highest yielding under bothStriga-infested andStriga-free conditions. The genotype main effect plus genotype×environment interaction (GGE) biplot analysis identified TZEEI 88×TZEEI 79 and TZEEI 81×TZEEI 95 as the ideal hybrids across research environments. Twenty-three pairs of simple sequence repeat (SSR) markers were used to assess the genetic diversity among the inbred lines. The correlations between the SSR-based genetic distance (GD) estimates of parental lines and the means observed in F1hybrid underStrigainfestation and optimum growing conditions were not significant for grain yield and other traits except ASI under optimum conditions. Grain yield of inbreds was not significantly correlated with that of F1hybrids. However, a significant correlation existed between F1hybrid grain yield and heterosis underStrigainfestation (r=0·72,PStrigaendemic areas in WCA.

Maize (Zea mays) is a staple food crop in sub-Saharan Africa, but its production is threatened by Striga hermonthica (Del.) Benth. Transfer of resistance genes from wild relatives may increase resistance to S. hermonthica in tropical maize. The objective of this study was to determine the combining ability of resistance to S. hermonthica among lines containing Zea diploperennis and tropical germplasm. Forty-five diallel crosses of 10 inbred lines were evaluated in an alpha-lattice design with and without artificial Striga infestation at two locations each in the Republic of Benin and Nigeria for 3 years. Results of analyses showed that only general combining ability (GCA) mean square was significant (P = 0.01) for number of emerged Striga plants (NESPP), while both GCA and specific combining ability (SCA) mean squares were significant for host damage score (HDS) and grain yield under Striga infestation. The ratio of GCA to SCA mean squares for the three traits varied from 3.5 to 57.5. Although GCA x environment interaction was significant for the three traits, two inbred lines containing Z. diploperennis (ZD 551) and tropical (TZL TC 87) germplasm had negative and significant GCA effects for NESPP and HDS and positive GCA effects for grain yield under Striga infestation in the two countries. Correlation between NESPP and HDS was strong and significant (r = 0.87, P = 0.01). Our results highlight the importance of harnessing useful genes from wild relatives to improve resistance to S. hermonthica in adapted maize germplasm.

The incidence of the parasitic weeds, Striga spp. in the savanna and the mid-altitude ecology of Africa is on the increase. Eight inbred lines of maize developed for the mid-altitude ecology and a susceptible check (TZi 10) were evaluated in Mokwa, Nigeria for two seasons to determine their performance under Striga hermonthica, the most widespread species of Striga in Africa. The experiment was a split-plot with three replications; infestation treatments (Striga-infested and non-infested) and maize inbreds constituted the main and sub-plots, respectively. There were no significant differences among the inbred lines for number of underground attachments of Striga seedlings to maize roots. However, differences in number of emerged Striga plants were significant (P < 0.01). Damage scores at 10 WAP and reductions in height and biomass at 12 WAP varied significantly (P < 0.01) among the maize lines tested. Damage score was significantly related to the severity of height and biomass reduction by Striga (r = 0.70 − 0.73). Differences in response of the lines to Striga manifested fully after silking. Thus, resistance was expressed at adult plant stage. Damage scores and number of emerged Striga plants were lower (P < 0.05) for TZMi 102, TZMi 302 and TZMi 306 than the susceptible check. These lines demonstrated potential as sources of resistance to Striga. Genetic variation for resistance to S. hermonthica is therefore present among the mid-altitude inbreds tested.

A split-plot experiment was conducted in 1992 and 1993 at Mokwa in the southern Guinea savanna zone of Nigeria to determine the responses of maize yield components to infestation by parasitic weed Striga hermonthica (Del.) Benth. and identify the most important yield components under Striga parasitism. Infestation treatments (infested v. non-infested) and hybrids [9022-13 (highly tolerant), 8644-31 (moderately tolerant), 8321-21 (moderately susceptible) and 8338-1 (highly susceptible)] were the main and subplots, respectively.Striga significantly reduced grain yield and all the yield components considered. Pre-flowering stress due to Striga parasitism was higher than post-flowering stress and resulted in higher reduction for ears per plant (44%) than reductions for other yield components (12–29%). The numbers of yield components for which the hybrids exhibited the highest percentage reduction increased with the degree of susceptibility to Striga. Thus, 8338-1, the highly susceptible hybrid, suffered more severe reductions in a larger number of yield components than the other hybrids. Number of ears per plant was a major yield component and accounted for an overwhelming proportion (R2 = 0·95) of the variation in grain yield under Striga. Reductions in maize grain yield and its components were more severe under the moisture stress that occurred in 1992.

Twelve maize genotypes with different degrees of resistance were evaluated in plots inoculated with seeds of the phytoparasite Striga hermonthica (Del.) Benth. and in Striga-free (control) plots for three seasons between 1991 and 1993. Resistant genotypes, although showing similar levels of underground infection as susceptible 9 weeks after maize planting (WAP), had significantly fewer emerged parasitic plants and sustained lower damage. Host damage was not determined by the severity of infection. Percent height and dry matter reductions increased from 3 to 6 WAP for resistant and susceptible genotypes. While percent height and dry matter reductions for resistant genotypes declined at 9 and 12 WAP, susceptible genotypes either maintained or increased their levels of damage. Correlation between the severity of height and dry matter reductions at the vegetative (3 and 6 WAP) and reproductive (9 and 12 WAP) stages of maize growth were not significant, indicating that damage at early stages of growth cannot be used to predict mature plant response. Maize damage score (1–9) at 8 WAP, a non destructive and composite shoot indicator of host performance under Striga infestation, was significantly correlated (r = 0.88, r = 0.82; p < 0.01) to the level of shoot reduction at mature plant stages. Emerged Striga count at 8 WAP was significantly correlated (r = 0.98, p < 0.01) to the count at 10 WAP, the time when parasite emergence was highest. Under high and uniform infestation, mature plant resistance can be detected at 8 WAP, the onset of flowering in maize.

A parasitic plant, Striga hermonthica (Del.) Berth.,infests millions of hectares of arable land in sub-Saharan Africa, and it threatens production of major cereal crops including maize (Zea mays L). Erratic natural infestation is considered a major constraint to assess host plant resistance to the parasite. The objective of this study was to evaluate the effects of different S. hermonthica seed inoculum rates on a tolerant and a susceptible maize genotype. Individual maize plants of the tolerant (8322-13) and the susceptible maize hybrid (8338-1) were inoculated with six rates of germinable Striga seeds: 750, 1500, 2250, 3000, 3750, and 4500. Uninfested plots served as the control. The experiment was conducted at two locations, Mokwa (two seasons) and Abuja (one season), in Nigeria. Increasing Striga inoculum level increased Striga emergence and the amount of damage to the host plant, plant height, and grain yield of the host crop. The tolerant hybrid showed less host plant damage (P < 0.01) and that fewer S. hermonthica plants emerged (P < 0.05) than the susceptible hybrid. Among the four traits studied, host plant damage score was most correlated with grain yield (r = -0.65**). Average grain yield of the tolerant hybrid, 8322-13, was 97% higher than that of the susceptible hybrid, 8338-1, across the six inoculum rates. The tolerant hybrid produced similar grain yields under all levels of the inoculum; the yield reductions ranged from 27% (2250 seeds) to 35% (4500 seeds), while the yield reduction of the susceptible hybrid ranged from 43% (750 seeds) to 74% (3750 seeds). Based on the results of this study, we conclude that host plant tolerance is the key element for stabilizing crop yield under S. hermonthica infestation.

A phytoparasite, Striga hennonthica (Del.) Benth., infests millions of hectares of cultivated fields of cereal crops in sub-Saharan Africa. Yield losses are often 70 but can be as high as 100% and farmers often abandon infested fields and move to new areas. The objectives of this study were to investigate the effects of nitrogen on S. hennonthica infestation and the subsequent grain yield and agronomic traits of tolerant and susceptible maize hybrids (Zea mays L.). Two tolerant and two susceptible hybrids were grown under six levels of N (0-150 kg ha -1 ), with and without Striga seed infestation. The trials were conducted for 3 yr at Mokwa, Nigeria. Each plant was infested with approximately 3000 germinable Striga seeds, and the density of Striga that emerged, Striga damage on the host plant, plant height, stalk lodging, and grain yield were measured. Striga infestation (emergence and host damage), maize grain yield, and plant height were significantly affected by N rates. Two tolerant hybrids showed significantly lower Striga emergence and host plant damage symptoms than the susceptible hybrids (P < 0.001). Interactions between infested and uninfested plots and hybrid (tolerant vs. susceptible) for grain yields and stalk lodging were significant (P < 0.001). Striga infestation reduced grain yields of two susceptible hybrids by 49%, and of two tolerant hybrids by 24%. The two tolerant hybrids produced on average 87% greater grain yields than the two susceptible hybrids under low N rates (0-60 kg ha -1 ) and 51% greater yields under high N (90-150 kg ha -1 ). Among the plant traits measured, Striga damage score had the highest correlation with grain yield (r = -0.60**).

Purple witchweed [Striga hermonthica (Del.) Benth.], here called just striga, parasitizes cereal crops in the savanna zone of sub-Saharan Africa. The objectives of this study were to investigate the expressions of a tolerant and a susceptible cultivar of maize (Zea mays L.) to striga as affected by timing (0, 2, 4, and 6 wk after maize planting) and rates (60 and 120 kg N ha -1 ) of N application under striga infestation. The experiment was designed as a split-split plot with four replications. Timing of N application and N rates significantly affected striga emergence, host-plant damage scores, agronomic traits, and grain yield. Nitrogen rate x application time interaction was highly significant for striga emergence. Time of N application was more important than N rate in suppressing striga emergence and host-plant damage. Nitrogen application at 2 wk after planting and 120 kg N ha -1 gave the best result in terms of maize performance and reduction of striga emergence. Host-plant damage symptoms were more useful in differentiating response of host genotypes to striga than striga emergence values. The tolerant cultivar (hybrid 8322-13) produced 188% higher grain yield than the susceptible cultivar (hybrid 8338-1) across all treatments. Grain yield of the tolerant cultivar at 60 kg N ha -1 was 88% higher than that of the susceptible cultivar at 120 kg N ha -1 . The tolerant cultivar produced an average 157% more ears at 60 kg N ha -1 and 51% more ears at 120 kg N ha -1 than the susceptible cultivar. Among all the factors studied, the most important component for striga management was genetic tolerance, the ability of a host plant to withstand the parasite.

Seeds of the obligate parasite Striga hermonthica , germinate in response to stimulants in the root exudate of maize and other host crops. Under laboratory conditions, conditioning (defined as treatment with moisture) of Striga seeds for one to three weeks before exposure to germination stimulant is required for optimum germination. The objective of this study was to determine if maize performance and Striga emergence, both indices of resistance, were influenced by the interval between Striga seed infestation and maize planting, under high parasite inoculum (3000–6000 germinable seeds) as practiced in maize resistance breeding field nurseries. Four conditioning treatments were investigated: maize planted immediately after Striga seed infestation, and maize planted after one, two and three weeks after infestation. Experimental design was randomized complete block with four replications. Differences among the four conditioning treatments were not significant for maize damage score, height, stalk lodging, number of ears harvested, grain yield and number of emerged Striga plants. Thus, maize planted on the same day as Striga infestation showed similar response as maize planted one to three weeks after infestation. Using high seed inoculum, maize can be planted immediately after Striga infestation in maize breeding nurseries. Combining Striga seed infestation and maize planting into a single field operation is convenient and reduces cost of screening.

[EN] The acceptable leve! of inclusion of unthreshed inflorescence or seedheads of mature grain amaranth plants (GASH) as feed ingredient of concentrate diets of rabbits was examined. Four diets were formulated with GASH inclusion levels of O (control), 10, 20 and 30%, respectively, by partially replacing the levels of oil cakes in the diets. These were fed to rabbits in an eight-week long feeding trial (8 rabbits/treatment) and a digestibility trials (4 rabbits per treatment). The initial weight of the 7-8 week old rabbits was 710 g (adult weight of this population is 1 .8 to 2.4 kg). The proximate composition (g/kg DM) of GASH was : 151 crude protein ; 43 crude fibre ; 572 nitrogen free extrae!. lntake and weight gain were reduced with diets containing 20 and 30% GASH but values of the control diet, which were highest, were not significantly higher than those of the 10% GASH diet (daily intake 44 and 37.4 g DM, and weight gain 10.0 and 8.2 g for O and 10 % GASH). Feed efficiency was similar for the 4 diets : 0.22 weight gain/g DM feed intake. Dry matter and nutrient digestibility and feed conversion efficiency of the GASH diets were generally high with minar differences among the diets. Haematological parameters and serum metabolites were generally better with the 1 O and 20% GASH diets than with the control diet but poorer with the 30% GASH diet. Higher white blood cell counts were recorded in the GASH diets than the control. Thus, unthreshed mature grain amaranth seedhead can be used as a componen! of the concentrate feeds of rabbits, up to 10% dietary level, to partially replace expensive oil cakes in the diets., [FR] Cette étude a pour but de déterminer le niveau optima! d'inclusion dans un aliment concentré pour lapins, des sommités florales mares mais non battues d'amarante a grain (GASH), c'est a dire de !'ensemble brut de la partie portan! les graines. Quatre aliments ont été formulés comme suit: addition de GASH a 0% (témoin), 10%, 20% et 30% respectivement, par remplacement partiel des tourteaux (palmiste principalement). Ces aliments ont été distribués aux lapins dans un essai de croissance ayant duré 8 semaines (8 lapins par lot) et dans un essai de digestibilité (4 lapins par lot). Les lapins ílgés de 7-8 semaines en début d'essai avaient un poids initial de 71 Og (poids adulte dans cette population : 1,8 a 2,4 kg). La composition approximative du GASH (g/kg MS) était: protéines brutes 151 ; cellulose brute 43 ; extractif non azoté 572. La consommation alimentaire et le gain de poids ont été réduits avec les aliments contenant 20 et 30 % GASH ; mais les valeurs pour l'aliment témoin, nettement plus élevées, ne sont pas significativement différentes de celles obtenues avec 10 % de GASH (consommation journaliére 44 et 37,4g MS et gain de poids 10,0 et 8,2g/j. pour O et 1 O % de GASH). L'efficacité alimentaire a été identique pour les 4 aliments : gain de poids 0,22/g MS ingérée. La digestibilité de la matiére séche et des différents nutriments et l'efficacité alimentaire des aliments contenant du GASH étaient élevés. Les meilleurs résultats par rapport a l'aliment témoin ont été obtenus avec les aliments contenant 10 et 20 % de GASH, les plus mauvais concernant l'aliment avec 30 % de GASH. Par rapport au lot témoin, une quantité plus élevée de globules blancs a été trouvée dans le sang des lapins des lots recevant du GASH. En conclusion, les inflorescences non battues, portan! des graines matures d'amarante a grain peuvent étre utilisées a hauteur de 1 o % dans les aliments concentrés pour lapin, pour remplacer partiellement les tourteaux de graines oléagineuses.