Field trials were conducted at Samaru and Bagauda, Nigeria for a two year period (1997 and 1998 rainy seasons) to evaluate the use of cotton trap-crop cultivars in mixture with maize varieties for the management of Striga hermonthica. The treatments were made up of five maize varieties in mixture with two cotton cultivars and sole maize as control. The experimental design was split-plot with maize varieties in main plot and cotton trap-crop cultivars in sub-plots, replicated three times. Results at Samaru and Bagauda in 1997 and 1998 showed that the Striga tolerant open-pollinated (OP) maize variety Acr.93 TZL comp.1-W and TZL Comp.1C3 and commercial hybrids, Oba supper I and 99022-13 had significantly fewer Striga shoots and incidence and produced higher grain yields than the susceptible checks. In 1997 and 1998, at Samaru, maize intercropped with SAMCOT 10 and 9 reduced Striga infestation and produced 19% and 12% higher grain yields, respectively than sole maize crop. However, at Bagauda sole maize and intercropped maize with the two cotton varieties did not differ in Striga infestation and incidence. Only in 1997 that sole maize produced significantly higher grain yield than the intercrop. In conclusion, improved maize productivity could be achieved through the use of Striga tolerant varieties and inter-cropping with promising cotton trap-crop cultivars for the management of striga. However, it is suggested that a broader multi-location testing of this management strategy be carried out in order to further validate its wider application.

KEYWORD:Trap-crop, Intercropping, Maize, Striga Control

Introduction

The major obstacles to maize production in the West and central African savannas are nitrogen deficiency and Striga hermonthica parasitism (Berner and Kling, 1995). Striga which is endermic in the African savannas can cause serious devastation to maize especially on the fields of resource-poor farmers. Even under good management conditions about 79% reduction in yield was observed in susceptible hybrid maize (Lagoke et al., 1997). The value of total annual crop loss due to Striga in Africa has been estimated at 7 billion US Dollars (M'Boob, 1986).

Traditional African cropping systems which have included prolonged fallow and rotation were common management practices that have been used in the past to improve soil fertility and kept the infestation of Striga spp. at tolerable levels. However, increasing human population has resulted in intensive land use and a shift away from traditional cropping systems, which in turn has resulted in the depletion of soil fertility and decrease in Striga control (Berner et al., 1996). A number of improved tolerant maize varieties have been developed by IITA. However, for effective management of Striga an integration of various control methods in a technological package is mandatory and highly expedient (Lagoke et al., 1997). Intercropping of maize with non-host crops have been reported to increase the efficiency of land use through improved soil productivity and reduction of striga hermonthica soil seed bank caused by the stimulation of suicidal germination of Striga seeds by non-host cultivars (Lagoke et al., 1997). The spreading vegetation of non-host crops (trap crops) also smoother emerging Striga plants (Venon, 1995; Kureh et al., 2000). Varieties of cotton with very high Striga seed germination potential have been identified (Lagoke et al., 1997). The objective of the study was to ameliorate yield loss due to Striga soil seed bank and seed production through the use of cotton trap-crop in mixture with maize.

Materials and Methods

Field trials were conducted on Striga sick fields during the 1997 and 1998 wet seasons at Samaru in the Northern Guinea Savanna (NGS) and Bagauda in the Sudan Savanna (SS) to evaluate the use of non-host crop (Trap-crop) cultivars in mixture with maize varieties for the management of Striga hermonthica in maize. The treatments were made up of five maize varieties including three tolerant maize varieties, a susceptible check and a recommended variety for the location in mixture with two cotton cultivars and sole maize as control. The experimental design was split-plot, with maize varieties in main plot and trap-crop cultivars in sub-plots. The treatments were replicated three times.

The fields were ploughed, harrowed and ridged at 75cm width. The fields were further inoculated with about 3,000 germinable Striga seeds per hill at about 50cm apart. Maize seeds were planted on the inoculated spots one week later. Intercropped cotton was planted between maize hills on the same day. Spot application of fertilizer was carried out at the rate of 100kg N/ha, 50kg P₂O₅/ha and 50kg K₂O/ha to maize using 20-10-10 compound fertilizer and Urea. The nitrogen fertilizer was split-applied at 3 and 6 weeks after sowing (WAS). The intercropped cotton received a basal application of 20kg N/ha and 50 P₂O₅/ha using urea and single super phosphate. At Samaru, Gramazone at 2.5 a.i kg/ha was applied after planting to control established weeds. At both locations, hoe weeding was carried out at 3 and 5 WAS followed by careful hand-pulling of other annual weeds at 7WAS. The plot sizes were 22.5m² and 18.0m² at Samaru and Bagauda, respectively in 1997 but in 1998, the plot sizes were 15m² and 9m² at Samaru and Bagauda, respectively.

Data were collected on Striga incidence (crop plants infested), level of infestation (Striga shoot count), yield and yield attributes of maize. The data collected were subjected to analysis of variance using the General Linear Model procedure (GLM SAS package (SAS 1999) and means were compared using the standard error of the means.

Results

Maize varieties differed significantly in their reaction to Striga and subsequent performance at the two locations. In 1997, at Samaru, in the Northern Guinea savanna, the tolerant open-pollinated (OP) maize variety Acr.93 TZL comp.1-W had fewer Striga shoots and incidence and produced 33% higher grain yield than the susceptible check TZESRW. The grain yield of Acr.93 TZL comp.1-W was comparable with other maize varieties tested (Table 1). The OP variety TZBP-SR-W also produced 51% higher maize grain yield than TZESRW, inspite of support for high Striga emergence. Maize intercropped with cotton variety, SAMCOT 9 significantly supported fewer Striga shoots than sole maize. Maize intercropped with SAMCOT 10 is comparable to both sole maize and maize intercropped with SAMCOT 9 in the number of emerged Striga shoots. There was no yield difference between the intercrop and the sole maize.

At Bagauda in the drier savanna with poor soil fertility, the OP maize variety, Acr.93 TZL comp.1-W also had fewer Striga shoots and incidence and produced 54% higher grain yield than the susceptible hybrid, 8338-1 (Table 2). Maize hybrids Oba super 1 and 9022-13 also produced higher maize grain yield than the susceptible variety inspite of support for moderate Striga infestation and incidence. Sole maize and intercropping maize with the two cotton varieties did not differ in Striga infestation and incidence. However, sole maize produced 26.1% and 26.5% higher grain yield than intercropping maize with SAMCOT 9 and SAMCOT 10, respectively.

At Samaru in 1998, the commercial hybrid maize, Oba supper I, had significantly fewer Striga shoots and incidence and produced 28% higher grain yields than the susceptible hybrid, 8338-1 (Table 3). Although all the other varieties supported fewer Striga shoots and incidence, 9022-13 and TZL comp.1C4 also produced 51% and 36% higher grain yields than the susceptible hybrid. The recommended maize variety TZBP-SR-W actually produced significantly lower yield than the three Striga tolerant varieties evaluated in the trial. Maize intercropped with cotton cv. SAMCOT 10, significantly reduced Striga infestation on maize compared with cotton cv. SAMCOT 9 and resulted in significantly higher cob yield than the sole maize crop. Maize intercropped with SAMCOT 10 and 9 produced 19% and 12% higher grain yields, respectively than sole maize crop.

At Bagauda, maize variety Mega white supported more Striga shoots than 9021-18, TZL comp.1C3 and 8338-1 (Table 4). In spite of low plant count observed with 9022-13, the variety and 9021-18 produced significantly higher cob and grain yields than the other three varieties, 8338-1, TZL comp.1C3 and Mega white. Mega white was obviously susceptible as reflected in support for high Striga shoot emergence and production of low grain yield.

Discussion

The open-polliated maize variety Acr.93 TZL comp.1-W and the tolerant hybrids 9022-13 and oba super I exhibited tolerance to Striga hermonthica and adapatbility to Northern Guinea savanna and Sudan savanna agroecological zones through the production of acceptable grain yield in spite of support for low to moderate Striga emergence in the two years of evaluation. This confirmed the stability of the varieties in their reaction to Striga over years and across locations in the northern Guinea savanna and Sudan savanna agroecologies as earlier reported by Lagoke et al. (1997). TZL comp.1C4 as well as TZBP-SR-W also exhibited tolerance to Striga hermonthica and adaptability to Northern Guinea savanna and Sudan savanna, respectively through the production of high grain yields than the susceptible checks 8338-1 and Mega white in the respective locations. Apparently, these varieties exhibited high tolerance, moderate resistance and adaptability to Northern Guinea savanna and Sudan savanna agro-ecologies, respectively. Ejeta et al. (1991) had indicated that genotype x environment interaction largely influence the reaction of varieties to Striga. The low yield of 8338-1 despite lower Striga emergence confirmed the susceptibility of the variety to Striga and that the low emergence could be attributed to underground competition among high population of Striga.

The performance of the OP varieties relative to the hybrid 8338-1 is a highly encouraging development in the effort to explore host-plant resistance or tolerance as a component for Striga integrated pest management (IPM). Farmers are more likely to be able to adopt and manage the OP's in the Striga control packages than the hybrids (Kim, 1991). Once the skill is acquired, farmers can produce their seeds for use in subsequent years rather than relying on seed companies (Kim, 1994; Berner et al., 1996; Lagoke et al., 1996).

In all the trials, adequate fertilizer was applied to the varieties. The performance of the varieties is therefore a product of trap-cropping effect, agronomic potentials, tolerance to Striga and the environment as earlier suggested by Ejeta et al. (1991) and Lagoke et al. (1997). Adetimirin and Kim (1995) reported that more effective reduction in yield loss and Striga infestation can be achieved through the application of adequate fertilizers on Striga tolerant hybrids.

Inter-cropping maize with cotton cv. SAMCOT 10 depressed Striga shoot emergence and caused higher maize grain production at Bagauda and cob yield at Samaru, respectively in 1998. Both these non-host crop cultivars exhibited potential for use as trap-crops for Striga management. Earlier reports indicated that intercropping maize with non-host crop cultivars increased the efficiency of land use through reduction of Striga hermonthica soil seed bank caused by the stimulation of suicidal germination of Striga seeds by non hosts (Lagoke, et al., 1997). Traditional African cropping systems which included rotation and inter-cropping were common management practices in the past that improved soil fertility, kept Striga infestation at tolerable levels and increased seed yields and crop values (Berner and Kling, 1995).

Emerged Striga plants in the intercrop were etiolated in growth and died earlier than the Striga that emerged on the sole crop probably as a result of the smoothering effects of the trap-crops. This finding confirmed earlier reports by Vernon (1995) and Kureh, et al. (2000) who found that the spreading vegetation of the non-host crops (trap-crops) also smother emerging Striga plants.

Acknowledgement

The authors are grateful to West and Central Africa Maize Research Network (WECAMAN) for financial assistance and Director of the Institute for Agricultural Research, Samaru for permission to publish the paper. The technical assistance of Mr. S. Yaro, Mal. B. Mohammed and A. Mohammed are very much appreciated.