**1. Introduction**

Sorghum (*Sorghum bicolor*) was originated in Africa; however, it is of high agricultural and economic importance in México. It is a multipurpose crop, since it serves as food, fiber and fuel. In addition, it can be grown in a wide range of agroecosystems, especially those of fragile conditions. It is also known as the "camel" of the crops, since to complete a productive cycle it requires less amount of water compared to other cereals of agricultural relevance. It has a remarkable ability to produce under low water availability regimes, as well as in other adverse abiotic conditions. Regarding the global production, it occupies the fifth place among the grains of economic importance [1]. Every year, sorghum production has been stabilized in 60 million tons in a producing area of 44 million hectares. México has

the third place worldwide with 4.5 million tons produced in 2018 [2]. From this, 62% corresponds to grain production, while 38% to forage.

Sweet sorghum is a natural variant of the common grain sorghum, with high content of sugars in the stem. It is frequently regarded as a "smart crop", since it can produce food as well as fuel. Currently, there are no records of commercial production of sweet sorghum in México, since it is a crop of recent introduction in the country. The first appearance of this crop in México was in the INIFAP Campo Experimental Río Bravo in the year of 2006, with the varieties Dale, Topper 76–6, Theis and M-81E [3]. Since then, the INIFAP genetic improvement program for sorghum, has searched for varieties which can adapt to the arid and semi-arid regions of the northeast or the country. These conditions are met by the variety RB Cañero, which has been tested in different environments, where it has shown a remarkable development and a high potential to produce bioethanol sugars [4].

Despite sweet sorghum is still a new crop in Mexico, the productive potential and the area of exploitation are highly promising. In 2010, INIFAP estimated the area available in México for sweet sorghum production, being the northeast region suitable with more than 4.38 million hectares [3]. The latter, pictures México as a country with great expectative of self-sufficiency in the generation of its own biofuel. The use of biofuels, being a cleaner and more efficient way of producing energy, would help to reduce pollution and greenhouse gases, which destabilize climate [5]. Pursuing this goal, biotechnology is an effective tool to develop methods which can optimize the bioethanol production from sweet sorghum. This review presents some of the biotechnological advances, as well as the current state of the genetic and molecular studies in sorghum, related to new routes to achieve an efficient generation of biofuels from this crop. This knowledge makes clear the necessity for effort and economic investment on this field, to reach self-sufficiency in the generation of energy sources in the country.

#### **2. Sorghum as a research model**

Sorghum possesses a small genome, which makes it attractive as a model organism for studies focused on understanding the structure, function and evolution of the cereals' genome. Sorghum is a tropical crop with a typical C4 photosynthesis, which uses a complex specialized biochemical and morphological system for carbon assimilation when it is exposed to elevated temperatures. This is a unique feature among the species of the same family it belongs to.

Like in other crops, sorghum is compared to other Poaceae of agricultural relevance such as maize (*Zea mays*), rice (*Oryza sativa*), sugar cane (*Saccharum officinarum*) or wheat (*Triticum aestivum*). Sorghum has ten diploid chromosomes and has a low degree of genetic duplication, which if compared to maize, makes it an outstanding model to develop functional genomics studies. On the other hand, maize developed a duplication of its entire genome since its evolutionary divergence from sorghum, changing the chromosome number from n = 5 to n = 10, being one of the sub genomes very similar to sorghum than to any other cereal [6]. However, evidence shown in NCBI database indicate that homologous genes between these species vary mainly in gene size and protein coding [7]. In the case of rice, it possesses a bigger genome than sorghum and also more genetic duplication. However, some comparisons prove that between sorghum and rice homologous gene exist, but with differences that could be attributed to the particularities of each species. Some reports indicate that sorghum and maize split from a common ancestor 12 million years ago [6], whereas the rice lineage is about 42 million years old compared to these two crops [7]. Lastly, sugar cage, possibly the most important sugar

**115**

**Table 1.**

*A General Overview of Sweet Sorghum Genomics DOI: http://dx.doi.org/10.5772/intechopen.98539*

genomic duplications [9].

and domestication [14**–**16].

them [17].

is available in several databases [10].

producing crop worldwide, could have share ancestors with sorghum approximately 5 million years ago [8], since they conserve similar genes [9], and even it is viable to generate offspring from intergeneric crosses. Sugar cane contains at least two

Sorghum represents an excellent model for research, since linkage mapping methodologies have been successfully implemented on it and possesses a wide mating system by self-pollination, which tends to preserve the association relationships for longer time periods compared to the self-pollination of cereals like maize, which facilitates the development of pure lines. Also, its genome sequence

**3. Differences between sweet sorghum and grain sorghum**

Sweet sorghum plant produces sugars which can be directly fermented, together with its ability to produce high biomass volumes under adverse conditions, this crop is consider ideal for the generation of bioethanol of first and second generation. Also, its cultivation is suitable for marginal lands, avoiding competence for land with other food crops [11**–**13]. However, the genetics underlying these traits have been barely studied. The genetic differences between sweet and grain sorghum consist on a series of variations in the sequence and alterations of the genetic structure. The variations at sequence level are usually identified by single-nucleotide polymorphisms (SNPs), association sequences, genetic diversity

*S. bicolor* has three subspecies: arundinaceum, bicolor y drummondii. All the feasible varieties belong to bicolor, which is divided into 5 races: bicolor, caudatum, durra, guinea y kafir. Sweet sorghum differs phenotypically from grain sorghum in several aspects: juicy stem rich in sugars, higher plant length, higher biomass production and less amount of grains in the spike [11]. These differences cannot be only explained by the genetic variation among these two varieties, which suggest DNA methylation and other epigenetic mechanisms are key factors to describe

Phenotypic Height (cm) 97.6 230–281

Spike (dry weight, g) (g plant−1)

Roots (dry weight, g) (g plant−1)

Stem (dry weight, g) (g plant−1)

divergence

*Ekefre* et al*., [22]. Genotypic differences data obtained from Jiang* et al*., [17].*

Line Keller (sweet) Protein functional

*Main differences between grain and sweet sorghum.*

Genotypic SNPs 85,041(14,782 genes) Line BTx623 (grain) Indels 16,781 (7,977 genes) vs. SVs 1,847 (2,071 genes)

*Grain sorghum data obtained from Assefa* et al., *[20] and Wang* et al., *[21]. Sweet sorghum data obtained from* 

**Trait Grain sorghum Sweet Sorghum**

24.2 60–80

15.1 68–88

27 164

563(SNP), 287(Indels), 69 (SV)

Biomass (g plant−1) 67 605–1096

*A General Overview of Sweet Sorghum Genomics DOI: http://dx.doi.org/10.5772/intechopen.98539*

*Biotechnological Applications of Biomass*

the third place worldwide with 4.5 million tons produced in 2018 [2]. From this,

Sweet sorghum is a natural variant of the common grain sorghum, with high content of sugars in the stem. It is frequently regarded as a "smart crop", since it can produce food as well as fuel. Currently, there are no records of commercial production of sweet sorghum in México, since it is a crop of recent introduction in the country. The first appearance of this crop in México was in the INIFAP Campo Experimental Río Bravo in the year of 2006, with the varieties Dale, Topper 76–6, Theis and M-81E [3]. Since then, the INIFAP genetic improvement program for sorghum, has searched for varieties which can adapt to the arid and semi-arid regions of the northeast or the country. These conditions are met by the variety RB Cañero, which has been tested in different environments, where it has shown a remarkable development and a high potential to produce bioethanol sugars [4]. Despite sweet sorghum is still a new crop in Mexico, the productive potential and the area of exploitation are highly promising. In 2010, INIFAP estimated the area available in México for sweet sorghum production, being the northeast region suitable with more than 4.38 million hectares [3]. The latter, pictures México as a country with great expectative of self-sufficiency in the generation of its own biofuel. The use of biofuels, being a cleaner and more efficient way of producing energy, would help to reduce pollution and greenhouse gases, which destabilize climate [5]. Pursuing this goal, biotechnology is an effective tool to develop methods which can optimize the bioethanol production from sweet sorghum. This review presents some of the biotechnological advances, as well as the current state of the genetic and molecular studies in sorghum, related to new routes to achieve an efficient generation of biofuels from this crop. This knowledge makes clear the necessity for effort and economic investment on this field, to reach self-sufficiency

Sorghum possesses a small genome, which makes it attractive as a model organism for studies focused on understanding the structure, function and evolution of the cereals' genome. Sorghum is a tropical crop with a typical C4 photosynthesis, which uses a complex specialized biochemical and morphological system for carbon assimilation when it is exposed to elevated temperatures. This is a unique feature among the

Like in other crops, sorghum is compared to other Poaceae of agricultural relevance such as maize (*Zea mays*), rice (*Oryza sativa*), sugar cane (*Saccharum officinarum*) or wheat (*Triticum aestivum*). Sorghum has ten diploid chromosomes and has a low degree of genetic duplication, which if compared to maize, makes it an outstanding model to develop functional genomics studies. On the other hand, maize developed a duplication of its entire genome since its evolutionary divergence from sorghum, changing the chromosome number from n = 5 to n = 10, being one of the sub genomes very similar to sorghum than to any other cereal [6]. However, evidence shown in NCBI database indicate that homologous genes between these species vary mainly in gene size and protein coding [7]. In the case of rice, it possesses a bigger genome than sorghum and also more genetic duplication. However, some comparisons prove that between sorghum and rice homologous gene exist, but with differences that could be attributed to the particularities of each species. Some reports indicate that sorghum and maize split from a common ancestor 12 million years ago [6], whereas the rice lineage is about 42 million years old compared to these two crops [7]. Lastly, sugar cage, possibly the most important sugar

62% corresponds to grain production, while 38% to forage.

in the generation of energy sources in the country.

**2. Sorghum as a research model**

species of the same family it belongs to.

**114**

producing crop worldwide, could have share ancestors with sorghum approximately 5 million years ago [8], since they conserve similar genes [9], and even it is viable to generate offspring from intergeneric crosses. Sugar cane contains at least two genomic duplications [9].

Sorghum represents an excellent model for research, since linkage mapping methodologies have been successfully implemented on it and possesses a wide mating system by self-pollination, which tends to preserve the association relationships for longer time periods compared to the self-pollination of cereals like maize, which facilitates the development of pure lines. Also, its genome sequence is available in several databases [10].
