Effect of cultural methods on Striga (Striga hermonthica (Del.)) Benth management and yield of cereals in the Savanna Zone of Nigeria: a review

Data were obtained from the research done in the Guinea Savanna (Zaria 11°11′N; 070 38′E) and Sudan Savanna (Maiduguri ?11°51′N; 13°15′E) regions of Nigeria, respectively on different cultural methods of Striga control and management. In the Guinea Savanna, trials on the effects of nitrogen on the response of resistant and susceptible upland rice varieties to Striga hermonthica infestation and the effect of resistant and susceptible varieties of maize and crop rotation on Striga infestation was carried out, while the effect of inter-cropping trap crop (Bambaranut) with resistant sorghum varieties on S. hermonthica was studied in the Sudan Savanna Zone of Nigeria. In the Guinea Savanna, it was observed that a combination of upland rice variety, Faro 40 and an application of 90 kg N/ha in the wet season and WAB 56-50 upland rice variety and 120 kg N/ha in the dry season, respectively reduced Striga infestation and produced maximum grain yield. Also, the growing of resistant variety of maize (Across 97ITZ comp. I-W) after 1 or 2 years' rotation with cowpea or soybean was observed not only to be effective in Striga control, but resulted in higher grain yield of maize. In the Sudan Savanna, the use of resistant varieties of sorghum, 1CSV1002 and 1CSV1007 intercropped with bambaranut significantly reduced Striga infestation, but the grain yield of the resistant varieties was low. From these studies, Faro 40 with 90 kg N/ha application rate and WAB56–50 with 120 kg N/ha were suitable for the management of Striga and for higher grain yield of upland rice in both wet and dry seasons, respectively, while Across 97ITZ comp. I-W, resistant maize variety and 1 or 2 years rotation with cowpea or soybean were also the best for the management of S. hermonthica and for higher maize yield in the Guinea Savanna zone. Further research needs to be carried out in the Sudan Savanna to select a high yielding resistant variety of sorghum which when intercropped with bambaranut will not only control Striga infestation but will also give high grain yield.     

Diversity of Rice yellow mottle virus in Benin and Togo and Screening for Resistant Accessions

Surveys were conducted in rice fields in Benin, Cote d'Ivoire, Mali, Nigeria, Togo and Niger to assess the importance of Rice yellow mottle virus (RYMV). Diseased leaf samples were collected. In Togo, surveys were made mainly in the southern part of the country, and in Benin, all areas where rice is grown were covered. Leaf samples were serologically confirmed by ACP ELISA as bearing RYMV, propagated and all conserved. One hundred and forty‐eight (148) Beninese and 27 Togolese strains were serotyped. They were also phenotyped on three susceptible accessions including IR 64, four resistant lines with known alleles on RYMV 1 gene namely TOG 5681 (rymv 1‐3), TOG 5672 (rymv 1‐4 and RYMV 2), TOG 5674 (rymv 1.5) and Gigante (rymv 1‐2). RYMV spots with 9–100% incidences were identified. Serotyping by triple antibody sandwich (TAS) ELISA indicated that two main groups S1 and S2 coexisted in Benin with S1 being prevalent. In Togo, 26 strains were S1 and only one was S2. Phenotyping of the 148 Beninese and 27 Togolese indicated that they all attacked the three susceptible accessions, while TOG 5681 (rymv 1‐3), TOG 5672 (rymv 1‐4 and RYMV 2), TOG 5674 (rymv 1‐5) and Gigante (rymv 1‐2) remained symptomless. The use of the genes/alleles above in these countries against the disease is discussed. Three representative Beninese strains were selected to screen 48 accessions for disease resistance. Nine accessions were as susceptible as IR 64 to all strains while six (NERICA 9, NERICA 12, NERICA 13, TOG 7291, WAB56‐50, CG 14 and Moroberekan) were very resistant. Susceptibility of the six ARICA and resistance of some NERICA lines could be explained by the fact that one or both parental lines were, respectively, susceptible or resistant to the strains.     

Classification of cowpea cultivars for field resistance to the legume pod borer, Muruca testulalis in Nigeria using cluster analysis

Cluster analysis was used to classify cowpea cultivars developed for resistance to M. testulalis in Nigeria based on data collected on four damage parameters. The cultivars were grouped into classes for each of two locations under two protection regimes. Differences were observed in the groupings for the two locations while one cultivar, MR×6–84F was found to have wide adaptability in the presence or absence of M. testulalis infestation. This is particularly useful for the selection of breeding materials in cultivar improvement for specific or general ecological zones.     

Molecular marker-based genetic diversity assessment of Striga-resistant maize inbred lines

Striga-resistant maize inbred lines are of interest to maize breeding programs in the savannas of Africa where the parasitic weed is endemic and causes severe yield losses in tropical maize. Assessment of the genetic diversity of such inbred lines is useful for their systematic and efficient use in a breeding program. Diversity analysis of 41 Striga-resistant maize inbred lines was conducted using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers to examine the genetic relationships among these lines and to determine the level of genetic diversity that exists within and between their source populations. The two marker systems generated 262 and 101 polymorphic fragments, respectively. Genetic similarity (GS) values among all possible pairs of inbred lines varied from 0.45 to 0.95, with a mean of 0.61±0.002 for AFLPs, and from 0.21 to 0.92, with a mean of 0.48±0.003, for SSRs. The inbred lines from each source population exhibited a broad range of GS values with the two types of markers. Both AFLPs and SSRs revealed similar levels of within population genetic variation for all source populations. Cluster and principal component analysis of GS estimates with the two markers revealed clear differentiation of the Striga-resistant inbred lines into groups according to their source populations. There was clear separation between early- and late-maturing Striga-resistant inbred lines. Considering the paucity of germplasm with good levels of resistance to Striga in maize, the broad genetic diversity detected within and among source populations demonstrates the genetic potential that exists to improve maize for resistance to Striga.     

Fusarium oxysporum and post-emergence herbicide for the control of the parasitic plant Striga hermonthica in maize

Two trials were conducted to evaluate the efficacy of a granular mycoherbicide formulation based on Fusarium oxysporum and post-emergence herbicide for the control of the parasitic plant, Striga hermonthica in the Nigerian Savanna. Four fungal treatments were used: F. oxysporum followed by 2,4-D, F. oxysporum followed by supplementary hoe weeding, F. oxysporum followed by Triclopyr and a control (No F. oxysporum but hoe-weeded). The experiments were laid out in a split plot design with three replications in the two locations. The two varieties (Across 97 TZL and farmer's local variety) formed the main plot treatments, while the Striga fungal treatments formed the sub-plot treatments. At the Lafia location, the emergence of Striga was delayed by 7 days (46 days) as compared to the Makurdi location, which germinated earlier 39 days after sowing. Maize variety Across 97 TZL similarly delayed the time to Striga emergence when compared to the farmer's local variety. However, the different Striga control methods did not have any significant effect on the time of Striga emergence. Generally, number of maize plants infected with Striga was highest with the farmer's local variety throughout the period of observation, while in the Striga control treatments, hoe-weeded check recorded the highest; the minimum was obtained with plots treated with F. oxysporum followed by postemergence application of Triclopyr at the rate of 0.36 kg a.i./ha at 6 weeks after sowing. Highest maize grain yields were obtained at Lafia with Across 97 TZL and plots treated with F. oxysporum followed by either post-emergence 2,4-D or Triclopyr at 0.36 kg a.i./ha each. The results demonstrate the high potentiality of using F. oxysporum as a spot application at planting followed by post-emergence herbicide (2,4-D or Triclopyr) application at 6 weeks after sowing for the control of the parasitic plant S. hermonthica in the Nigerian Savanna.     

Parasitism of grain legumes by Alectra species (Scrophulariaceae)

In glasshouse pot experiments in the United Kingdom, the host preference of nine seed samples of Alectra vogelii from Eastern, Western and Southern Africa and of two samples of A. picta from Cameroon and Ethiopia, to cultivars of cowpea, groundnut, bambara and mung bean, was assessed. A susceptible cowpea cultivar, Blackeye, and four cultivars of groundnut were attacked by all samples of both parasitic species regardless of whether the host of origin was cowpea, groundnut or bambara. Five “strains” of A. vogelii were distinguished using two criteria: their ability to parasitise bambara and/or mung bean and their ability to parasitise cowpea B301 and bambara TVU 870. The latter proved in an associated experiment to be resistant to collections of the parasite from some locations. Strain 1, including populations from Mali, Nigeria and Cameroon, attacked all groundnuts, cowpea cultivar Blackeye, but not cowpea line B301, mung bean or bambara. Strain 2, from Botswana, differed in attacking B301 and mung bean. Three other strains were identified which attacked susceptible lines of all four legume species. Strain 3 from Kenya failed to attack either cowpea B301 or bambara TVU 870, strain 4 from Malawi attacked cowpea B301, but not bambara TVU 870, while strain 5 from Northern Transvaal, South Africa, attacked bambara TVU 870, but not cowpea B301. Cowpea B359 was resistant to A. vogelii samples from all locations and also to A. picta, which has a similar host preference to strain 1 populations of A. vogelii from West Africa. Two out of 13 groundnut lines tested showed low susceptibility to A. vogelii from Cameroon suggesting there is scope for selecting resistance in this crop also.     

Molecular tagging and validation of microsatellite markers linked to the low germination stimulant gene (<Emphasis Type="Italic">lgs</Emphasis>) for <Emphasis Type="Italic">Striga</Emphasis> resistance in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Striga is a devastating parasitic weed in Africa and parts of Asia. Low Striga germination stimulant activity, a well-known resistance mechanism in sorghum, is controlled by a single recessive gene (lgs). Molecular markers linked to the lgs gene can accelerate development of Striga-resistant cultivars. Using a high density linkage map constructed with 367 markers (DArT and SSRs) and an in vitro assay for germination stimulant activity towards Striga asiatica in 354 recombinant inbred lines derived from SRN39 (low stimulant) × Shanqui Red (high stimulant), we precisely tagged and mapped the lgs gene on SBI-05 between two tightly linked microsatellite markers SB3344 and SB3352 at a distance of 0.5 and 1.5 cM, respectively. The fine-mapped lgs region was delimited to a 5.8 cM interval with the closest three markers SB3344, SB3346 and SB3343 positioned at 0.5, 0.7 and 0.9 cM, respectively. We validated tightly linked markers in a set of 23 diverse sorghum accessions, most of which were known to be Striga resistant, by genotyping and phenotyping for germination stimulant activity towards both S. asiatica and S. hermonthica. The markers co-segregated with Striga germination stimulant activity in 21 of the 23 tested lines. The lgs locus similarly affected germination stimulant activity for both Striga species. The identified markers would be useful in marker-assisted selection for introgressing this trait into susceptible sorghum cultivars. Examination of the sorghum genome sequence and comparative analysis with the rice genome suggests some candidate genes in the fine-mapped region (400 kb) that may affect strigolactone biosynthesis or exudation. This work should form a foundation for map-based cloning of the lgs gene and aid in elucidation of an exact mechanism for resistance based on low Striga germination stimulant activity.     

Evaluation of some Iranian wheat elite lines’ reaction to Septoria tritici leaf blotch

Septoria tritici blotch is an important wheat disease in many areas of the world including Iran’s warm, humid regions. In this study, reaction of 79 lines from elite regional wheat yield trials of the Cereal Research Department from four climate zones was evaluated to S. tritici leaf blotch in adult plant stage under an artificial field inoculation in Khuzestan province in the south of Iran for two years (2008–2009 and 2009–2010). Nurseries were artificially inoculated by spreading infected plant debris (from last growing season). Taking notes was performed with a modified Saari and Prescott method in 00–99 double-digit scale. Wheat lines were classified in groups of immune (00), highly resistant (11–14), resistant (15–34), moderately resistant (35–44), moderately susceptible (45–64), susceptible (65–84) and highly susceptible (85–99). Result showed that from 79 lines, 37 lines had susceptible reaction; 2 lines had moderately susceptible; and 40 lines showed immune.     

Stem borer's species composition,abundance and infestation on maize and millet in Maiduguri,Nigeria

The species composition, abundance and plant infestation of stem borers attacking maize and millet were investigated in farmers' fields during the cropping season of 2010 and 2011 in Maiduguri, Nigeria. Stem borers were collected via destructive sampling. In total, three stem borer species (Busseola fusca, Sesamia calamistis and Coniesta ignefusalis) were found, of which S. calamistis (64%) and C. ignefusalis (72%), respectively, were predominant on maize and millet. Across both years, whereas mean plant infestation ranged from 4.8% on millet to 20.8% on maize, mean stem borer abundance ranged from 1.6 individuals on millet to 13.8 individuals on maize. Mean total plant infestation and stem borer abundance varied with different years and both were significantly higher during the 2010 than 2011 cropping season. In spite of the generally low stem borer abundance per farmers' field, plant infestation particularly on maize plants seems to be moderate during different years.     

Herbivore-induced resistance in different groundnut germplasm lines to Asian armyworm, Spodoptera litura (Fab.) (Lepidoptera: Noctuidae)

Three groundnut germplasm lines, ICGV86699 (resistant), NCAC 343 (resistant) and TMV 2 (susceptible), were examined for Spodoptera litura (Fab.) resistance. Biochemical parameters such as oxidative enzyme activities, peroxidase (POD) and polyphenol oxidase (PPO), other defensive components such as total phenols, hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and protein contents were evaluated in these germplasm lines after 24, 48, 72 and 96 h following S. litura infestation to characterize the mechanism of resistance. Enzyme activities and total phenols, H₂O₂, MDA and protein contents were increased following infestation; however, significance varied at different time intervals and among germplasm lines depending upon the induced level of resistance. The three germplasm lines differed in resistance mechanisms to S. litura and the resistance may be partly due to higher enzyme activities, and other components studied. Among the three germplasms tested, ICGV86699 showed greater elevation in POD and PPO activities and in phenolic and H₂O₂ contents at different time intervals as compared to NCAC 343 and TMV 2.     

High Genetic Variability of Schistosoma haematobium in Mali and Nigeria

Schistosoma haematobium is one of the most prevalent parasitic flatworms, infecting over 112 million people in Africa. However, little is known about the genetic diversity of natural S. haematobium populations from the human host because of the inaccessible location of adult worms in the host. We used 4 microsatellite loci to genotype individually pooled S. haematobium eggs directly from each patient sampled at 4 endemic locations in Africa. We found that the average allele number of individuals from Mali was significantly higher than that from Nigeria. In addition, no significant difference in allelic composition was detected among the populations within Nigeria; however, the allelic composition was significantly different between Mali and Nigeria populations. This study demonstrated a high level of genetic variability of S. haematobium in the populations from Mali and Nigeria, the 2 major African endemic countries, suggesting that geographical population differentiation may occur in the regions.     

Sorghum root length density and the potential for avoiding striga parasitism

Striga hermonthica is a serious root parasite of sorghum in the semiarid tropics. Successful parasitism is dependent on interactions of Striga seeds and host roots. Several sorghum cultivars have been found which resist parasitism. The basis of resistance is not well known. One possible method for reducing the chances of parasitism is by restricted host root development. This research was conducted to evaluate this hypothesis in sorghum known to possess resistance to parasitism by Striga.Root length density of 21-day-old pot-grown resistant cultivars, Framida, N-13, IS-9830, Tetron and P-967083, were compared to that of the susceptible check, Dabar, using the line intercept method of measuring root length. There was no significant difference between resistant cultivars and the susceptible cultivar Dabar. The RLD of resistant P-967083 however was significantly less than Framida, another resistant cultivar.The RLD of Dabar was compared to that of Framida and P-967083 in USA and Niger field trials. Root length density was determined on soil cores taken at flowering with a Giddings Soil Sampler. Each core was divided into 10-cm fractions for estimating RLD by the line intercept method. In the USA Dabar had significantly greater RLD than the two resistant cultivars in the upper 10-cm portion of the soil profile, but only significantly greater than P-967083 in the 10–20-cm portion. Significant differences in RLD between susceptible and resistant cultivars were not found at depths between 20–60 cm. In field trials in Niger, RLD of Dabar was significantly greater than either resistant cultivar in the (0 to 30 cm) portion of the soil core. These results suggest that part of the Striga resistance of P-967083 and perhaps Framida may be a result of avoiding interactions between parasitic seeds and host roots.     

Interaction between Rhynchosporium secalis and Pyrenophora teres in the Field and Identification of Genotypes with Double Resistance in a Doubled-haploid Barley Population

Net blotch [Pyrenophora teres (Died.) Drechsl.] and scald [Rhynchosporium secalis (Oudem.) J.J. Davis] are the two most important foliar diseases of barley (Hordeum vulgare L.) in Tunisia. The use of cultivars with double resistance is the most effective method in controlling both diseases. A doubled‐haploid barley population derived from Tunisian cultivars was evaluated to both net blotch and scald during two growing seasons in the field. Mass disease index (MDI), area under the disease progress curve (AUDPC) and apparent infection type (r) were used to assess disease reaction. MDI of net blotch and scald reached up to 65% and 90% respectively. Least significant difference (LSD) test and comparison of the reaction of the doubled haploid (DH) lines to the overall population mean value were efficient in identifying lines with double resistance to both diseases. From the 59 DH lines screened, lines 21, 33, 37, 46 and 47 showed the best level of adult plant resistance to both diseases and may be used in a breeding program for diseases resistance. Interactions between R. secalis and P. teres were investigated at the level of the whole plant under variable epidemic conditions. Under low epidemic conditions, net blotch and scald developments were usually independent, but positively associated for tolerant lines for both diseases. Under high epidemic conditions, competition effects were obtained for susceptible and resistant genotypes. This competition seems to be an exploitation competition that is associated with decreasing resource availability as it occurs only with high levels of infestation or/and when susceptible lines are infected. This study demonstrates the variability of net blotch and scald interaction with epiphytotic conditions and group of resistance.     

Genotypic variation in susceptibility of honey bees (Apis mellifera) to infestation by tracheal mites (Acarapis woodi)

Two-way selection for lines of honey bees (Apis mellifera L.) susceptible and resistant to infestation by tracheal mites (Acarapis woodi Rennie) was conducted for two generations. Individuals of the susceptible line were 1.4 and 2.4 times more likely to become infested by female mites after the first and second generations, respectively. These results demonstrate that genotypic variability exsts within North American populations and that selection for resistance is feasible. The mechanisms of resistance are unknown.     

A USA–Africa collaborative strategy for identifying, characterizing, and developing maize germplasm with resistance to aflatoxin contamination

Aflatoxin contamination of maize by Aspergillus flavus poses serious potential economic losses in the US and health hazards to humans, particularly in West Africa. The Southern Regional Research Center of the United States Department of Agriculture, Agricultural Research Service (USDA-ARS-SRRC) and the International Institute of Tropical Agriculture (IITA) initiated a collaborative breeding project to develop maize germplasm with resistance to aflatoxin accumulation. Resistant genotypes from the US and selected inbred lines from IITA were used to generate backcrosses with 75% US germplasm and F₁ crosses with 50% IITA and 50% US germplasm. A total of 65 S₄ lines were developed from the backcross populations and 144 S₄ lines were derived from the F₁ crosses. These lines were separated into groups and screened in SRRC laboratory using a kernel-screening assay. Significant differences in aflatoxin production were detected among the lines within each group. Several promising S₄ lines with aflatoxin values significantly lower than their respective US resistant recurrent parent or their elite tropical inbred parent were selected for resistance-confirmation tests. We found pairs of S₄ lines with 75–94% common genetic backgrounds differing significantly in aflatoxin accumulation. These pairs of lines are currently being used for proteome analysis to identify resistance-associated proteins and the corresponding genes underlying resistance to aflatoxin accumulation. Following confirmation tests in the laboratory, lines with consistently low aflatoxin levels will be inoculated with A. flavus in the field in Nigeria to identify lines resistant to strains specific to both US and West Africa. Maize inbred lines with desirable agronomic traits and low levels of aflatoxin in the field would be released as sources of genes for resistance to aflatoxin production.     

Abundance of 24-methylenecholesterol in traditional African rice as an indicator of resistance to the African rice gall midge, Orseolia oryzivora Harris & Gagné

Rice production is of great importance to food security in Nigeria. The African rice gall midge (AfRGM), Orseolia oryzivora Harris & Gagné, is a major pest of lowland rice in Nigeria and many other Africa countries. Current management efforts are directed at integrating host plant resistance with biological agents. The type and abundance of some phytochemicals are known to affect resistance in host plants, so in this study we measured rice culm hardness, rice culm stickiness and the type and quantity of phytosterols in rice cultivars, and investigated the effects of these factors on resistance to the AfRGM. The study was conducted at 24 ± 2°C, 60 ± 5% relative humidity, and a 12 h light : 12 h dark photoperiod. Three rice cultivars were studied: one Oryza glaberimma cultivar, Tog 7442 (resistant), and two O. sativa cultivars, Cisadane (tolerant) and ITA 306 (susceptible). We found no significant differences in culm hardness and stickiness among the cultivars tested. Using gas chromatography (flame ionization detection) analysis, we identified four major phytosterols: campesterol, 24‐methylenecholesterol, stigmasterol and β‐sitosterol. 24‐Methylenecholesterol was the most abundant sterol in the resistant O. glaberimma cultivar (79.20 μg), whereas β‐sitosterol was most abundant in the two susceptible O. sativa cultivars (Cisadane, 71.27 μg; ITA 306, 66.37 μg). The comparatively high concentration of 24‐methylenecholesterol in this cultivar of O. glaberimma may be an indicator of resistance to AfRGM.     

A time-course study of early establishment stages of parasitic angiosperm Striga asiatica on susceptible sorghum roots

A time-course study of the early establishment stages of Striga asiatica was carried out on a susceptible sorghum hybrid, CSH 1, using polyethylene bags and whole-root clearing and staining techniques. Preconditioned Striga seeds were applied to different aged segments of primary root but the results did not differ for these different aged segments. Most of the Striga seeds (63%) germinated within 24 h of inoculation on the host roots. The attachment of Striga radicles to host root was rapid and it occurred between 36 and 48 h after inoculation. Only 9% of the germinated Striga seeds attached to the host root but 65% of these attachments successfully penetrated through the epidermis and entered the host cortex within 72 h. Penetration through the cortical cells was difficult; only 17% of attachments were able to reach the endodermis. Penetration took from 12 to 43 h after the first appearance of haustorial cells in the cortex; a total of 84 to 120 h after inoculation on the host root. Penetration through the endodermis and establishment on the host stele was relatively easier, as most of the haustoria reaching the endodermis were able to establish on the host stele. But this is a slow process taking a minimum of 24 h, and a maximum of 60 h after first contact of haustorial cells with the endodermis. The minimum time taken from inoculation of ungerminated Striga seed on the host root to establishment is about 108 h. The results are discussed in relation to published reports on other parasitic species such as Agalinis purpurea.     

Sources of resistance to Exserohilum turcicum (Pass.) and Puccinia polysora (Underw.) incitant of Turcicum leaf blight and polysora rust of maize

A study was carried out to identify the sources of resistance to Turcicum leaf blight (TLB) and polysora rust in maize. Sixty indigenous and exotic inbred lines were evaluated under artificial epiphytotic conditions at two identified hot spot locations, Almora and Nagenahalli. After two years continuous screening, a total of 20 inbred lines were identified as a sources of resistance at both the locations for TLB, whereas 10 inbred lines were identified resistant against Polysora rust at Nagenahalli. A clear cut variation in virulence pattern in case of E. turcicum was observed. Some of the inbred inbred lines, i.e CM 138, CM 212, IML 235, NAI 135, showed resistant reaction in both the locations in the year 2005, whereas they acted as susceptible in 2006 at both locations. It was also observed that the Nagenahalli isolate of E. turcicum was more virulent than the Almora isolate.     

Stem borer infestation of cereal crops in Jere,the Sudan-Sahelian savanna region of Nigeria

Field data collected during the rainy season of two years, 2010 and 2011, were used to determine the per cent plant infestation and stem borer abundance on cultivated cereal crops grown by farmers' in Jere or the Sudan-Sahelian savanna ecological region of Nigeria. Stem borers were recovered using destructive sampling. Mean total per cent plant infestation and stem borer abundance per farmers' field were significantly higher on millet (40% and 25 individuals, respectively) and sorghum (30% and 21 individuals, respectively) than on maize (19% and 13 individuals, respectively). Of the five stem borer species found in this study, Coniesta ignefusalis (Lepidoptera: Pyralidae) (3.5)/Chilo sp. nr. aleniellus (Lepidoptera: Crambidae) (2), Busseola fusca (Lepidoptera: Noctuidae) (3.1)/Sesamia calamistis (Lepidoptera: Noctuidae) (2.4) and S. calamistis (2.9), with significantly higher number of individuals per plant, tended to be more important pests on millet, sorghum and maize crops, respectively. Although, mean total per cent plant infestation and abundance of stem borers in this study were generally moderate, further studies on the effects of different types of cereals intercropping (locally practiced) on stem borer infestation and abundance should ascertain the true importance of these pest species in the Sudan-Sahelian savanna ecological region of Nigeria.     

A Comparative Study of the Haustorial Development of Striga asiatica (L.) Kuntze on Sorghum Cultivars

Ten sorghum cultivars were studied for their mode of Strigaparasitization, and the factors conferring resistance in resistantcultivars most of the Striga haustona failed to penetrate beyondthe endodermis, whereas in susceptible cultivars the haustonapenetrated the endodermis and became established Resistant cultivars showed marked endodermal and pencyclic thickeningand the deposition of silica in their endodermal cells, whichwere lacking in the susceptible cultivars Extra thickening inpencyclic cells as a response to the entrance of haustonum wasobserved in cultivars N-13 and IS-4202 Ten cultivars studied showed differential haustorial reactionsThese reactions included extra thickening in the pericycle inresponse to haustonal infestation, haustonal collapse, tylosts-likeocclusions in the xylem vessels, and the deposition of dark-stainingmaterials in the cortex Although no definite conclusion couldbe drawn regarding the relationship between the degree of mechanicaltissue development and field resistance, there was evidencethat some field-resistant cultivars have strong mechanical tissuesThere could, however, be other factors governing resistanceto Striga in the field Striga asiatica, sorghum, haustorium, anatomy, endodermis, pot test, host resistance mechanism, parasitization, susceptibility