Abstract Background Identification of QTL with large phenotypic effects conserved across genetic backgrounds and environments is one of the prerequisites for crop improvement using marker assisted selection MAS. The objectives of this study were to identify meta-QTL mQTL for grain yield GY and anthesis silking interval ASI across 18 bi-parental maize populations evaluated in the same conditions across managed water stressed and well watered environments. Mean phenotypic variance explained by each mQTL varied from 1. Each physical interval of the mQTL consisted of 5 to candidate genes.
JRA1 5: This study aimed at combining both earliness and short ASI in one maize genotype. F2 progenies arising from crosses between these two types of germplasm were generated and tested under drought stress conditions. The results showed that ASI and earliness can be combined and selected for in the same maize genetic background.
Introduction Drought stress affects maize productivity most, when it Drought has had adverse effects on yields in most of the occurs during the two weeks of the flowering period .
It is farming regions around the world . According to , maize during flowering and pollination, when there is a high demand hybrids worldwide will only make an impact and result into for water to ensure grain filling [6,7]. However, variable field ASI period is an indicator of poor tolerance to drought stress.
Richards  reported that stress and tolerance. According to  recurrent se- measuring grain yield only . Flowering in maize is a crucial lection for low ASI, small tassels and delayed senescence trait in breeding for drought tolerance.
When maize flowers resulted in increased partitioning to early ear growth and high under drought, there is the delay in silking and the period grain yields. Genotypes that gave high grain yields under se- vere drought stress levels had a short ASI and were late ma- Journal of Renewable Agriculture 85 turing whereas those that matured early had a long ASI and scribed by .
Drought stress was imposed by irrigating at lower grain yields. Indeed even after eight cycles of recurrent an interval of 4 days for three hours, right from germination selection, grain yield under severe drought stress levels was stage up to 14 days before anthesis male flowering when highly positively correlated with a short ASI.
Subsequent water was withdrawn.
Leaf-rolling during flowering was scored as a [11,12]. The data were col- tion criterion. The objective of this study was an attempt to lected in the middle two rows per plot from a mean of ten combine early maturity and a short ASI in the same genotype plants randomly selected  for the following agronomic in order to enhance the drought tolerance of maize genotypes traits; anthesis and silking dates, ears per plant, kernel and subsequently increase grain yields of this important staple weight and grain yield.
ASI was calculated as the difference between the recorded anthesis and 2. M aterial and Methods silking dates . Leaf senescence was assessed four times 2. This was done Eleven genotypes which included four CIMMYT inbred lines through visual estimation of the whole plot and the proportion and KARI composites and synthetics were evaluated under of green leaves versus senescent dried leaves was scored on a drought stress environment.
Kiboko is at Longitude of The soils at Kiboko Research Farm are ferric fluvisols, 2. Hybridization to generate F 1 and F 2 populations which are mainly sandy clay type with a top soil pH of 7. Each plot consisted of four the University of Nairobi. Since, the CIMMYT inbred lines rows of maize spaced 75cm apart with an intra-row spacing of were late maturing compared to the female lines, they were 25cm.
The mating design used during crossing was the North [13,14].
According to the methods used by  and  one Carolina Design II where each male was crossed to each can be able to induce drought stress and select for drought female to generate a total of 12 F1 populations. There- were three weeks old. The F1 seed was planted and selfed to fore in this trial, the overhead irrigation was applied as de- obtain the F2 segregating populations.
The data were sub- 86 Kahiu Ngugi et al.: Phenotypic correla- time of planting and matured at days while those that tions were calculated to determine the relationships among flowered at more than 58 days from planting were regarded as the agronomic and physiological traits.
F ield Evaluation of F 2 Populations shown here below. The data collected was the genotypes except that of KDV5. The CML lines had the entered in the excel application and the days to anthesis were shortest ASI as compared to the rest of the genotypes Table used to select for early and mid-maturing genotypes in the 1.
The early maturing genotypes were T able 1. The CML genotype had the highest grain T able 2. Means for days to anthesis and days to silking for yield overall. Genotypes, KDV 2 and CML had signifi- different maize genotypes grown in long-rains season at cant higher yields than the rest.
Early maturing genotypes 90 80 70 Frequencies of genotypes 60 50 40 30 20 10 0 -2 -1 0 1 2 3 4 5 6 7 8 10 Anthesis to silking interval F ig 1. The early-maturing genotypes with an caping phenomenon. A negative ASI in this case signaled the occur- ured Table 3.When maize (Zea mays L.) is stressed at flowering because of deficits of water, light, nutrients, and sometimes by long photoperiods and lack of thermal adaptation, ear growth slows in relation to tassel growth and the anthesis-silking interval (ASI) increases.
The Anthesis to Silking Interval (ASI) is highly correlated to grain yields under drought stress as shown by experiments conducted at CIMMYT, Mexico. This study aimed at combining both earliness and short ASI in one maize genotype. When maize flowers resulted in increased partitioning to early ear growth and high under drought, there is the delay in silking and the period grain yields.
between male and female flowering increases giving rise to Drought affects maize production in most parts of Kenya anthesis silking interval (ASI). Summary of the 68 meta QTL (mQTL) for grain yield and anthesis-silking interval detected across 18 maize populations The number of mQTL identified on each chromosome varied from 4 on chromosome 10 to 9 on chromosome 1, with an average of mQTL per chromosome.
Abstract Stress caused by early weed competition is known to delay the rate of maize development which may result in a decrease in kernel number. Kernel number in maize is correlated negatively with the length of the anthesis-silking interval (ASI).
A short ASI has been identified as an easily measured, visual trait which may identify enhanced drought tolerance in maize. Maize, the most important stable crop in Kenya is affected by drought stress mostly at flowering stages causing delay in silk emergence.
The Anthesis to Silking Interval (ASI) is highly correlated.