SCREENING OF SOME CULTIVATED HYBRIDS OF MAIZE (Zea mays L

Two experiments were carried out at the Research Farm of the National Root Crops Research Institute, Kuru near Jos, during the 2007 and 2008 planting seasons, to study the productivity of seven (7) hybrid varieties of maize (Zea maysL.), namely SUWAN-1-Y, ‘Kenya Kitali’, ACR-9776-2, TZMSR-W, DMESR-Y, ACROSS-98 and TZPBSR-W. The experiments were laid out in a randomized complete block design (RCBD) with three replications. The results show that the germination rate was similar across the varieties in 2007; it was higher in the variety ACR-9776-2 (91.67%) than in the variety DMESR-Y (79.58%) in 2008. The highest mean number of days to mid-tasselling in 2007 (76.50) and 2008 (81.17) as well as the mid-silking in 2007(88.33) and 2008 (95.33) were observed in the variety ‘Kenya Kitali’. Similarly, the highest mean plant height in 2007 (2.07m) and 2008 (2.07 m) as well as the mean earwidth in 2007 (16.96 cm) were observed in the variety ‘Kenya Kitali’. The variety also had the highest one-thousand seed weight in 2007 (377.90 g) and 2008 (456.71 g). The variety ACR-9776-2 out-yielded the other varieties in the mean number of kernels per row in 2007 (21.79) and 2008 (29.60). The variety also had the highest shelling percentage in 2007 (88.77%) and 2008 (78.45%). The highest mean number of rows per ear was observed in the variety DMESR-Y in 2007 (15.97) and in the pooled data (14.47). In both years the varieties did not differ significantly in the mean ear-weight, although this was generally higher in 2007 than in 2008. The grain yield per plant was highest in the variety ACROSS-98 (139.93 g plant) in 2007 but in 2008 it was similar across the varieties. Total grain yield in 2007 was significantly higher in the variety ACROSS-98 (4.37 t ha ) than in the other varieties. Grain yield was similar across the varieties in 2008 and in the pooled results. Generally, grain yield and its components were higher in 2007 than in 2008. The study shows that growth, grain yield and yield components of maize vary with variety and environment and that the varieties ACROSS-98, ACR-9776-2, TZMSR-W and ‘Kenya Kitali’ have potentials for high productivity in the Jos-Plateau environment.


INTRODUCTION
Maize (Zea maysL.)is an important cereal crop of the world. It is used as human and animal food and as a raw material for the manufacture of hundreds of industrial products including corn starch, maltodextrins, corn syrup and products of fermentation and distillation industries.
It is grown from 58 o N to 40 o S, from below sea level to latitudes higher than 3,000 metres and in areas with 250mm to more than 5,000mm of rainfall per annum (Shaw 1988;Downswell et al., 1996). Most of the crop is grown in the warmer parts of the temperate regions and in the humid sub-tropical climate. The greatest production is in areas having the warmest isotherms from 21 o to 27 o C and a frost-free season of 120-to 180-day duration. The major maize-growing countries include the U.S.A., China, Mexico, Brazil, Argentina, India, Indonesia, the Philippines and Thailand (USDA, 1996). Worldwide, maize production continues to increase but at a slower rate than in the earlier years. The demand in 2020 is estimated to reach about 138 percent of the demand in 1995 (Rosegrant et al., 1995;USDA, 1996). Presently, the industrialized world uses more maize than the developing world, but forecasts indicate that by 2020 developing countries will demand more maize than the industrialized world (Duvick, 1998).
The projected increase will certainly not be large enough to satisfy the projected demand. Increasing emphasis must, therefore, be placed on significantly enhancing productivity per unit area, particularly in the maize growing countries in the developing world, where the average maize productivity is 2.4t ha -1 compared to 5.9t ha -1 in the developed world (CIMMYT, 1994). The grain yield of maize is the most important and complex trait. It is quantitatively inherited and its expression is influenced by several yield components, including number of ears, kernel rows, kernels per row, test weight and shelling percentage. The important physiological traits influencing grain yield include nutrient uptake, photosynthesis, translocation, sink-size, transpiration and respiration. Grain yield also depends on maturity duration, standability and resistance to abiotic stresses (Dhillon and Prassanna, 2001).
Cultivated varieties may be open-pollinated (OP) population or hybrid between inbred lines. Hybrid cultivars have the advantage of higher yield potential and uniformity. They are, therefore, preferred to openpollinated populations when there is sufficient heterosis. But the production of hybrid seed is costlier and complicated. For this reason and in order to meet the increasing demands as well as to maximize profit, there is a tendency for local seed-producing companies to compromise standards. Therein lies the need to continually screen cultivated varieties to ascertain their yield potentialities. The present study was, therefore, designed to screen seven (7) hybrids of maize for their productivity in the Jos-Plateau environment. , which was equivalent to 320g per plot. A basal application of N-fertilizer (urea) was supplied at the rate of 50kg ha -1 or 83.6g per plot at 65 DAP in 2007 and 70 DAP in 2008 in order to supplement the loss due to leakages caused by excessive rainfall.

MATERIALS AND METHODS
The plots were hoe-weeded twice at 32 DAP and89 DAP in both 2007 and2008. In between the two weedings, the plots were earthed up at 58 DAP in the two years to prevent lodging.

Germination Rate
This was computed as the ratio of the number of seeds that germinated ten days after sowing to the total number of seeds planted and multiplied by 100.

Mean Number of Days to Mid-Tasselling
This was recorded as the number of days from planting to when at least 50% of the total number of pants in each plot had tasseled.

Mean Number of Days to Mid-Silking
This was recorded as the number of days from planting to when at least 50% 0f the total number of plants in each plot had silked.

Plant Height at Harvest
Five (5) plants were sampled from each plot each of which was measured from the ground level to the flag leaf.

Mean Number of Ears per Plant
The total number of ears harvested from each plot was divided by the number of plant stands in the respective plots at harvest to obtain the mean number of ears per plant.

Mean Ear-Length
Five (5) ears were sampled from each plot, each of which was measured from the bottom to the top. The mean was used for the statistical analysis.

Mean Ear-Width
Each of the five (5) sampled ears was measured at the widest portion and the mean was used for the statistical analysis.

Mean Number of Rows per Ear
From each of the five (5) sampled ears, the number of rows was counted and divided by five to obtain the mean number of rows per ear.

Mean Number of Kernels per Row
From each of the five (5) sampled ears, the kernels of three rows were counted and recorded. The mean was used for the statistical analysis.

Mean Ear-Weight
After sun-drying the ears harvested in each plot for seven (7) days, five (5) of them were sampled and weighed. The weight obtained was divided by five (5) to give the mean ear-weight.

Shelling Percentage
Each of the five (5) ears sampled was weighed with the kernels. Thereafter, the ear was shelled and the kernels alone were weighed. Shelling percentage was computed as the ratio of the weight of the kernels to the weight of the kernels plus the cob and multiplied by 100 as follows: Shelling percentage % = b x 100 a where, a = weight of kernels + cob b = weight of kernels alone

One Thousand Seed Weight
From the whole grain-lot harvested from each plot, one thousand (1,000) seeds were taken and weighed.

Grain Yield per Plant
The grain shelled from five (5) cobs harvested from five (5) sampled plants in each plot was weighed and divided by five (5) to obtain the grain yield per plant.

Total Grain Yield
The cobs harvested from each plot were sundried, shelled and weighed. Total grain yield was computed at 12% moisture, which is the safe storage moisture level.

Data Analysis
Data collected from the two-year experiment were analysed separately and then pooled, using the one-way analysis of variance (ANOVA) test. Means were compared using the Duncan's new Multiple-Range Test (DMRT) (Steel and Torrie, 1960).

Germination Rate
The results of the germination rate for 2007 and 2008 planting seasons are presented in In the 2007 planting season, the varieties did not differ significantly in germination rate; in 2008, the variety ACR-9776-2 recorded a significantly higher germination rate (91.07%) than the variety DMESR-Y (79.58%).

Mean Number of Days to mid-Tasselling
In 2007, the mean number of days to midtasselling varied from 72.00 in the variety ACROSS-98 to 72.33, 73.00, 73.67, 75.00 and 76.50 days in the varieties TZMSR-W, SUWAN-1-Y, ACR-9776-2, TZPBSR-W and DMESR-Y, respectively. In 2008, the mean number of days to mid-tasselling was 80. 50, 81.17, 78.83, 82.67, 78.83, 79.33 and 77.67 in the varieties SUWAN-1-Y, 'Kenya Kitali', ACR-9776-2, TZMSR-W, DMESR-Y, ACROSS-98 and TZPBSR-W, respectively. The mean number of days to mid-tasselling in the variety 'Kenya Kitali' was higher than in the other varieties. In the year 2008, the number of days to midtasselling did not differ significantly amongst the varieties. The number of days to mid-tasselling was generally higher in 2008 than in 2007 (Table 1). Table 1 shows the results of the number of days to mid-silking in 2007 and 2008. The variety 'Kenya Kitali' had the highest number of days to mid-silking in 2007 (88.33). This was followed by the varieties TZPBSR-W (82.83 days), ACR-9776-2 (81.67 days), SUWAN-1-Y (78.00 days) and DMESR-Y (77.83 days). In 2008, the mean number of days to mid-silking varied from 83.33 in the variety SUWAN-1-Y to 95.33 in the variety 'Kenya Kitali'. Again the number of days to midsilking was generally higher in 2008 than in 2007.

Plant Height
The

Mean Number of Ears per Plant
The results of the mean number of ears per plant are shown in Table 2 Table 2  10.11 cm in ACR-9776-2. The mean ear-length was generally higher in 2007 than in 2008.

Mean Ear-Width
The results of the mean ear-width in the twoyear experiment are shown in Table 2. The highest mean ear-width in 2007 was observed in the variety 'Kenya Kitali' (16.96 cm) and was followed by the varieties SUWAN-1-Y (16.82 cm), ACROSS-98(16.17 cm), TZMSR-W (15.76 cm) and TZPBSR-W (15.61 cm). In 2008 the ear-width in the seven varieties studied were statistically similar, ranging from 14.71 cm in the variety TZMSR-W to 13.70 cm in the variety 'Kenya Kitali'. Again, ear length was generally higher in 2007 than in 2008.

Mean Number of Rows per Ear
The mean number of rows per ear was highest in the variety DMESR-Y (15.97) and lowest in the variety 'Kenya Kitali' (11.23) in 2007. The mean number of rows per ear did not differ significantly (p=0.05) amongst the other varieties. In the year 2008,the mean number of rows per ear was statistically similar across the varieties. Generally, the mean number of rows per ear was higher in 2007 than in 2008 in all the varieties except 'Kenya Kitali' (Table 3).

Grain Yield per plant
Results  Table 4 shows results of the total grain yield of seven varieties of maize in 2007 and 2008. In the year 2007, the highest total grain yield of 4.37 t ha -1 was observed in the variety ACROSS-98, followed closely by varieties TZMSR-W, SUWAN-1-Y, ACR-9776-2 and TZPBSR-W with total grain yields of 4.25, 3.96, 3.66 and 3.55 t ha -1 .The lowest total grain yield of 3.40 t ha -1 was observed in the variety DMESR-Y. In 2008 the total grain yield varied from 2.80 t ha -1 in the variety TZPBSR-W to 2.37, 2.25, 2.18, 2.14, 2.04 and 1.94 t ha -1 in the varieties ACR-9776-2, 'Kenya Kitali', TZMSR-W, SUWAN-1-Y, ACROSS-98 and DMESR-Y, respectively. The differences were, however, not significant. Across the varieties, the total grain yield was higher in 2007 than in 2008.

DISCUSSION AND CONCLUSION
The variety `Kenya Kitali' took a longer time to transit from the vegetative to the reproductive phase, an indication that it is late-maturing and that tasselling and silking are influenced by the genotype and environment. Breeding for maturity is important in maize improvement. Maturity traits include the number of days from planting to flowering, brown huskformation,kernel moisture at harvest and black layer formation (Dhillon and Prassanna, 2001). Days to silk is widely used as an index to maturity.The expression of these traits differs with season and location as they are affected by environmental factors.
The mean number of ears per plant, ear-length, ear-width and the mean number of rows per ear all varied with genotype and ear. Dhillon and Prassanna (2001) have identified number of ears, kernel rows, kernels per row, seed weight and shelling percentage as the major components of total grain yield in maize.
The variation in the grain yield per plant and in the total grain yield with variety and year shows that grain yield in maize is quantitatively inherited and that it is genotypically and environmentally influenced.

CONCLUSION
The results of this study indicate that growth, yield and yield components of maize vary with genotype and environment. The varieties ACROSS-98, ACR-9776-2, TZMSR-W and `Kenya kitali' showed promising potentials for high productivity in the Jos-Plateau environment.