Agronomic Performance of Single Crosses of Maize in Kiambu and Embu Counties of Kenya

Aims: This study was conducted to determine the agronomic performance of respective maize single crosses in different environments in varying soil and climatic zones in Kenya. Methodology: The trials were conducted at experimental stations of Kenya Agricultural and Livestock Research Organization (KALRO), Muguga South and KALRO Embu in Kiambu and Embu counties of Kenya respectively. The germplasm used in this study were 36 single crosses among 18 inbred lines of maize. The experiment was laid out in a 6 x 6 lattice randomized complete block design (RCBD) with two replications. Agronomic performance was measured by collecting and analyzing data on plant height, ear height, disease scores of maize streak virus and gray leaf spot and grain yield. Data was subjected to analysis of variance (ANOVA) using Genstat 12 program for individual single crosses. Mean separation was done using Tukey’s comparison method at 5% significance level. Results: The best performing crosses in Muguga were also the best in Embu on grain yield production with exception of cross MUL 516 x MUL508 which had a mean grain yield of 11.9 t/ha in Muguga but produced 2.7 t/ha in Embu which was attributed to other factors other than genetic makeup. Variation in yield showed a diverse genetic background of genotypes studied under these conditions. The grain yield ranged between 1.01 t/ha (MUL533 x MUL513) to 11.9 t/ha (MUL 516 x MUL 508) both in Muguga). The best performing cross for grain yield in Muguga was MUL 516 x MUL 508) while in Embu the best performing cross for grain yield was MUL541 x POPA. Data on disease scores where natural infestation was visually scored showed that majority of the crosses had a score of one confirming their near immunity status. Conclusions: For grain yield improvement crosses MUL508 x MUL688, POPA x MUL14, MUL513 x MUL114 and MUL513 x CN244 can further be evaluated and eventually released to farmers as they indicated promising relationship with yield potential compared to other crosses. Further research on agronomic performance of the crosses can be done not only in the research sites but also in other regions of Kenya.


INTRODUCTION
Maize (Zea mays L.) is the world's most widely grown cereal and it is the primary staple food for majority of population in many developing countries [1]. It is a major source of food in Sub-Saharan Africa and it is grown by both small and large scale farmers [2]. Maize is an important source of carbohydrate, protein, iron, vitamin B, minerals, livestock fodder and it is used in industries for starch and oil extraction [3]. In Kenya maize production is divided into six agroecological zones based on elevation and climate. These regions include: the lowland tropics comprising of the coastal strip and adjoining inland area, the dry mid attitude, the dry transitional zones in the South East, the highlands tropics, the moist transitional zone to the East and West of the highland tropics, the moist mid altitude zone around Lake Victoria [4]. The moist transitional zones are the most important maize production zones followed by the highland tropics. Maize yield variability is extremely high in Sub-Saharan Africa (SSA) than other regions of the world, as maize production is primarily rain fed. Between 2005 and 2008, for example the average maize yield in SSA was estimated at 1.4 t/ha which is very low as compared to 2.5 to 3.9 in developing countries [5]. Between 2003 and 2005 the World Food Program spent USS1.5 billion to alleviate food shortage due to drought and food failure in SSA alone [6]. With maize occupying such central position in Kenya's diet and farm production activities, it's imperative that ways and means of improving maize productivity be sought [7]. One way of increasing maize production is by identifying maize varieties that perform well in different agro-climatic zones of Kenya. The main objective of this study was to evaluate performance of single cross hybrids in varying climatic and soil conditions of Kenya.

Study Area
The experiment was undertaken in KALRO Muguga and KALRO Embu in Kiambu and Embu counties respectively as shown in Fig. 1.

Planting Materials and Field Management
The experiment was laid out in a 6 x 6 lattice randomized complete block design (RBCD) with two replications. The plots were ploughed before the onset of rains and harrowed to produce a medium tilth for maize. The plots consisted of 3 rows of 11 hills each at a spacing of 75 cm inter row and 25 cm between hills. Planting at Muguga was done on 10/4/2012 and in Embu on 14/4/2012 at the onset of the long rains. A compound fertilizer di-ammonium phosphate (DAP) was applied at the recommended rate of 80 kg P 2 O 5 per hectare during planting time. Two seeds were planted per hill but later thinned to leave one plant per hill. The plot area measured 5.55 m 2 (0.75 m x 3 rows) x (0.3 x 11 plants) and had a population of 33 plants, giving a total population of 53333 plants per ha -1 . Hand weeding was done twice during the growth period; first two weeks after emergence and the second weeding four weeks after the first weeding. Top dressing was done using nitrogenous fertilizer, Calcium Ammonium Nitrate (CAN 21%N) at the rate of 80 kg N per hectare after thinning the plants. Maize stalk borer (Busseola fusca) was controlled using Bulldock ® (Beta-cyfluthrin) applied on the funnel of each plant at the rate of 6 kg per ha -1 . Harvesting was done on 9/10/2012 at KALRO Muguga and 10/10/2012 at KALRO Embu.
The germplasm used in this study were 18 inbred lines and their respective single crosses derived from KALRO Muguga. The entries were used both as the maternal parents in one cross as well the paternal parents in the reciprocal cross (Table 1).

Data Collection
Data was collected during growth period and after attainment of physiological maturity. Data was recorded on 12 randomly picked plants from each row. The pre harvest data included measurement of plant height, ear height and visually scoring for gray leaf spot (GLS) and maize streak virus (MSV). The post-harvest data collected was grain yield per hectare.

Fig. 1. Study sites of KALRO Muguga and KALRO Embu
Arrows designate the two study areas Source: [8]

Data Analyses
Data collected was subjected to analysis of variance (ANOVA) using Genstat 12 software. Mean separation was done using Tukey's comparison method at 5% significance level. The data from the two environments, KALRO Muguga and KALRO Embu was analyzed separately. Agronomic performance was analyzed by determining coefficient of variation (CV) for plant height, ear height, maize streak virus and gray leaf spot and grain yield (GY). Genotypes with low CV, low disease scores and high grain yield (GY) were considered most desirable.

Mean Performance of Crosses on Different Morphological Traits in KALRO Embu
The analysis of variance (ANOVA), showing the mean squares of plant height (PH), ear height (EH), disease scores of maize streak virus (MSV) disease, gray leaf spot (GLS), and grain yield (GY) for Embu are shown in Table 2. The crosses showed a highly significant difference (p=.001) for plant height and ear height. They also showed a significant difference (p=.05) on grain yield.
The data (

Mean Performance of Crosses in KALRO Muguga
The analysis of variance (ANOVA) for plant height, ear height, disease scores for MSV and GLS and grain yield for Muguga are shown in Table 4. The crosses showed significant (p=.05) difference for plant height, ear height and GLS, while there was no significant difference on MSV and grain yield on the crosses in Muguga (Table 4).
Data on the mean plant height in Muguga ranged between 148±4.00 cm for MUL 533 x MUL 513 (entry 30) to 278±3.00 cm for POPA x MUL541 (entry 23) ( Table 5). The cross which had the lowest mean plant height MUL533 x MUL 513 (entry 30) also had the lowest mean grain yield of 1.01±0.4742 t/ha, the cross also had low mean ear height (45±6 cm) and a GLS score of 3.25±0.25 (Table 5). Cross MUL516 x MUL508 (entry 2) had a mean plant height of 178±1.5 cm, mean ear height of 55±2 cm and the highest grain yield of 11.9±10.84 t/ha ( Table 5). The second best cross in grain yield was POPA x MUL541 (entry 23) which had grain yield of 10.08±0.83 t/ha; this test cross also had the second highest mean ear height of 123±1.00 cm ( Table 5). Cross POPA x MUL 141(entry 19) had the highest mean ear height of 125±2.5 cm and was the third best in mean grain yield of 8.65±0.33 t/ha. Crosses CN244 x MUL508 (entry 12) and POPA x MUL511 (entry 13) had equal mean plant heights but different mean ear heights and different mean grain yields (Table 5).    The height of the main ear is a very important characteristic for breeding maize, the higher it is the more ears can develop from the nodes below, however if it is too high the weight of the ear may bend the stalk or even break it. Although low ear height is unfavorable for yield and makes harvesting difficult, it does protect the stalk from excessive weight [9]. The study revealed that crosses from inbred line POPA had the highest plant height, ear height and also the highest grain yield in Embu (  Table 5). The contrast was observed with entry 30 (MUL 533 X MUL 513) having plant height of (119±4.0 cm) in Embu which was the lowest and also recorded the lowest grain yield of (1.675±0.47 t/h) ( Table 4). The possible reason for the observed differences among the crosses on yield and yield components was variation in genetic makeup. Different hybrids have also been evaluated for morphological and agronomic traits, showing significant variation [11].
Grain yield being a complex trait is influenced by various environmental factors including biotic and abiotic factors. There is also interplay of various morphological characteristics that influence final yield. The best performing crosses in Muguga were also the best in Embu on grain yield production with exception of cross MUL 516 x MUL508 which had a mean grain yield of 11.9 t/ha in Muguga but produced 2.7 t/ha in Embu which was attributed to other factors other than genetic makeup. Variation in yield showed a diverse genetic background of genotypes studied under these conditions. The grain yield ranged between 1.01t/ha entry 30 (MUL533 x MUL513) to 11.9 t/ha entry 2 (MUL 516 x MUL 508) both in Muguga ( Table 5). The best cross for grain yield in Muguga was MUL 516 x MUL 508 (entry 2) (

CONCLUSION
In Embu inbred line POPA produced the best grain yields when crossed with MUL541 and MUL521. Its high grain yield was also witnessed in Muguga where on average its performance was superior to other inbred lines. Cross MUL 516 x MUL 508 had the highest overall mean grain yield (11.9 t/ha) but had a GLS score of 3 compared to the second best in mean grain yield POPA x MUL541 10.1t/ha. These findings showed that POPAX MUL541 though a good yielding cross was affected by GLS disease though at a late stage when the ears had already developed. Crosses with high plant height had higher mean grain yield than those with low plant height, while crosses with low ear height had low mean grain yield and vice versa. In order to develop promising genotypes, it is essential to know the different traits particularly those associated with grain yield which is the ultimate objective in any breeding program.
The present findings are useful to breeders in selecting the potential parental materials for maize improvement programs in mid altitude agro-ecological zones in Kenya. For grain yield improvement crosses MUL508 x MUL688, POPA x MUL141, MUL513 x MUL114 and MUL513 x CN244 can further be evaluated and eventually released to farmers as they indicated promising relationship with yield potential compared to other crosses. Inbred line MUL 513 can further be evaluated for grain yield improvement with all the other inbred lines which had high grain yields. Inbred lines MUL 508, POP A and MUL513 can be used in improving other genotypes on disease resistant trait. There is also need for further study of the inbred lines used in this study for stability and adaptability in other counties of Kenya.