CHAPTER ONE
INTRODUCTION
Sorghum (Sorghum bicolor L. Moench) belongs to the family Poaceae. Sorghum is the 5th most important cereal after rice, wheat, maize and barley in the world according to world sorghum production (WSP), 2017. It is grown on 40 million ha in 105 countries of Africa, Asia, Oceania and the Americas. Sorghum Production in 2017 was 63.7 million tons with the United States leading with 8.5 million metric tonnes and Nigeria is in the 2nd position with 6.5 million metric tonnes (WSP, 2017). Sorghum grows in a wide range of temperature, high altitudes, toxic soils and tolerate drought to some extent (Richard, 1968).
Sorghum, like many grains has different uses, including human consumption and animal feed. Globally, over half of all sorghum produced in the world is used for human consumption (Ogbaga et al., 2014). It is a major crop for many poor farmers, especially in Africa, Central America, and South Asia. Grain sorghum is used for flours, porridges and side dishes, malted and distilled beverages, and specialty foods such as popped grain. Sorghum is also considered to be a significant crop for animal feeds. A more recent use of sorghum is for ethanol production. New sweet sorghum varieties are being developed for bioenergy, the ethanol being attained from the lignocellulose-rich stalks after fermentation of the sweet sorghum juice (IEA, 2013).
Sweet sorghum is a water sipping, highly sustainable cropping option for producers in semi-arid regions with limited irrigation capacity or dry land producers with unpredictable rainfall. Compared to many other crops, sweet sorghum has high water and nutrient use efficiencies (Water requirement 8000 m3 as against 25,000 m3 for sugarcane) with a growing period of about 4 months as against 9-16 month for sugarcane and is considered environmentally sustainable (Sakellariou-Makrantonaki et al., 2007). Although research on alternative uses of sweet sorghum has been done(Taylor, 2006), it is still grown mainly for syrup, forage, and grain (Gnansounou et al., 2005). Sweet sorghum has the potential to produce up to 8000 Lha−1 ethanol:about twice the ethanol yield potential of maize, and 30% greater than the 6000 Lha−1 average obtained from Brazilian sugarcane (Luhnow et al., 2006). Determination of starch composition in sweet sorghum seed is also important because some sweet sorghum varieties may have potential as dual-purpose crops yielding both sugar-rich extractable juice and grain.
Sweet sorghum has traditionally been grown as a pure- line cultivar, but these cultivars produce very little seed and are too tall to harvest efficiently. The development of sweet sorghum hybrids, produced on grain-type females with high sugar concentrations is a practical way to overcome this limitation. (Audilakshmi et al., 2010).
Despite all the agronomic advantages of sweet sorghum as a bioenergy crop, little scientific effort has been directed in the past toward the elucidation of swee t sorghum traits relevant to biofuel production. There are many cultivars of sweet sorghum distributed throughout the world, providing a diverse genetic base from which to develop regionally specific, highly productive cultivars (Audilakshmi et al., 2010). Traits like plant height, stem diameter, green biomass, stem sugar content, and stem juice extractability are the major contributors for sweet sorghum‟s economic importance. However, these traits are quantitative and polygenic inheritance in nature and are complex to be manipulated directly in breeding procedure (Zou et al., 2012). Therefore, to successfully improve these complex traits, they need to be dissected into smaller morphological, physiological and yield components, which could be easily analyzed and evaluated (Makanda et al., 2009). However, information on the extent of variation in growth (plant height and stem diameter), physiology (chlorophyll content) and components of stem sugar (brix, juice yield and stem fresh weight) among sweet sorghum germplasm are limited. Furthermore, correlations between the traits are of great importance in selection process for successful breeding programs. The objectives of this research are:
- To determine heterosis for sugar content and grain yield in the cross of sweet and grain sorghum
- To determine the magnitude of heritability and mode of gene action controlling sugar content in sweet sorghum.
- To determine correlation between brix content and other agronomic traits in sweet sorghum parents and hybrids
