Keywords

Sorghum; Genetic resources; Morphological variability; Intercropping

Introduction

In Sahelian countries such as Niger, Mali, Senegal and Burkina Faso, cereals serve as the primary source of food [1]. Sorghum bicolor is a frequently grown cereal crop used for human consumption. In Burkina Faso, sorghum is the second most important cereal crop after maize [2]. The prevalence of sorghum in the Sahel can be partly attributed to its varietal diversity, flexibility, multiple uses, and adaptability to low rainfall, marginal soils and high temperatures [3,4].

Grain sorghum is the primary crop in Burkina Faso, used in many local foods [2]. Apart from regular grain sorghum, there are three other types of sorghum: Sweet grain sorghum, which is consumed at soft dough stage, sweet sorghum, used as sugar cane, and dye sorghum, produced for artisanal purposes. These types of sorghum are important for ensuring people's food self-sufficiency [5,6], particularly in areas with low rainfall. These Sorghums are often produced in the same cultivation areas, which could lead to gene flow between them. According to [7], gene flow can produce new genotypes that are not often adapted to farming conditions. Previous studies highlighted the management methods and genetic diversity of grain sorghum [3,8] between different types of Sorghum based on agromorphological [9,10] and molecular characterization [11,12]. To date, the impact of coevolution of different types of sorghum on the organisation of sorghum diversity is still partially described in Burkina Faso. Describing the level of morphological variability of the different types of sorghum cultivated in intercropping conditions could help understanding the impact of faming system on sorghum genetic resources. Such knowledge is useful to build up a strategy of conservation and improvement of each type of Sorghum.

The aim of this research was to describe the morphological variability of the types of sorghum. The purpose was to establish their morphological similarities or dissimilarities based on qualitative traits for better management of these types of Sorghum.

Materials and Methods

Plant material

Plant material consisted of 130 accessions of Sorghum. Ninetyseven accessions were collected in farmers’ fields in two agroclimatic areas of Burkina Faso: 67 from the North Sudanian area and 30 from the Sub-Sahelian area. The whole zone of germplasm collection covered five (05) provinces and seven (07) villages (Table 1). Five accessions including two grain sorghum, two sweet grain sorghum and one sweet sorghum were collected from Joseph KI-ZERBO University gene bank. Twenty height accessions (ten grain sorghum and eighteen sweet sorghum) were collected from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Mali.

Table 1: Origin of the accessions of different types of Sorghum.

Experimental site

The agromorphological characterization was carried out from July 2021 to November 2021 at the Institute of Rural Development's experimental station in Gampèla, located at about 20 kilometers from Ouagadougou (1°21’ W longitude and 12°24’ N latitude). The experimental plot had a mostly sandy-loam texture. A total of 977 mm of rainfall was recorded in 45 days during the experimental period.

Experimental design and data collection

The experimental design was an incomplete Fisher block with three replications on a total area of 1484.72 m² (53.6 m × 27.7 m). Each block was subdivided into two sub-blocks and each subblocks consisted of 68 lines. Each replication consisted of 132 lines including two border lines. The line was 3.2 m long with 0.8 m spacing between lines and 0.4 m between holes. The distances between replications and sub-blocks were respectively 2 m and 1.5 m. The plot was plowed with a tractor prior to planting. Two weeks after sowing, 100 kg/ha of NPK (14-23-14) was applied to the plot. Urea was applied at a rate of 50 kg/ha during the swelling stage of the panicle. Data were collected throughout the entire plant growth cycle. Twenty-four qualitative traits were recorded (Table 2).

Table 2: List of qualitative traits.

Data analysis

The variants of qualitative traits for each type were summarized using Excel 2016 spreadsheet. Phenotypic frequency distributions of the traits were calculated for each sorghum type by village using SPSS 15.0 for Windows. To determine the morphological proximity and specific traits of each type of sorghum, a Multiple Component Analysis (MCA) was carried out based on the most variable qualitative traits. This analysis was carried out using RStudio 4.1.3 software.

Results

Variation in qualitative traits related to stem and leaf

The qualitative traits related to stem and leaf (Figure 1) varied depending on the Sorghum type and surveyed villages (Tables 3a and 3b). All the types of sorghum (grain sorghum, sweet grain sorghum and dyer sorghum) from the village of Sogué had erect port, red leaf spots, aerial tillers and no succulent stems. The discriminant traits were: Seedling Colour (SC), Midrib Colour (MC), Leaf Sheath Colour (LSCO) and Pith Colour (SPC). Grain sorghum and dyer sorghum had light red and light green seedlings, while the seedlings of sweet grain sorghum were dark red. In addition, grain sorghum and sweet grain sorghum had white midrib, green leaf sheaths and white pith, while dyer sorghum midrib had red midrib and reddish pith and leaf sheath. The Sorghum types from Sogué were not different from the sorghum types from Joseph KI-ZERBO University gene bank for the stem status and the presence or absence of aerial tillers. In addition, grain sorghum and sweet grain sorghum from Sogué were similar to those from the Joseph KI-ZERBO University gene bank for midrib colour, leaf sheath colour and stem succulence. Grain sorghum from Sogué was also similar to grain sorghum from the Joseph KI-ZERBO University gene bank in seedling colour and pith colour. On the other hand, the dyer sorghum from Sogué was different from the grain sorghum, sweet grain sorghum and sweet sorghum from the Joseph KI-ZERBO University gene bank. Comparison of the sorghum types from Sogué with grain sorghum and sweet sorghum from Mali revealed a similarity in stem status and the presence or absence of aerial tillers. For the other traits, these Sorghums were different.

Figure 1: Variation in midrib colour, leaf spot colour, leaf sheath and pith colour.

Table 3a: Variation in qualitative traits related to vegetative development (SC, MSS, BTS, LSC).

Table 3b: Variation in qualitative traits related to vegetative development (MC, LSCO, SPC, AT, SUC).

The two types of Sorghum (grain sorghum and sweet grain sorghum) from the village of Zambanega had erect port and no succulent stem. In addition, these types of Sorghum had red leaf spots, white midrib, red leaf sheaths and white pith and did not develop aerial tillers. Sweet grain sorghum had usually light green seedlings (80%), while grain sorghum had various colours of seedlings: Light red (38.8%), dark red (7.7%) and light green (53.5%). Grain sorghum and sweet grain sorghum from Zambanega were similar to those from Joseph KI-ZERBO University gene bank in stem status and succulence. These sorghum types had an erect stem and no succulent stem. For the other traits, these types of sorghum were different. Grain sorghum and sweet grain sorghum from Zambanéga were different from grain sorghum and sweet sorghum from Mali for the traits related to stem and leaf excepted for stem status.

The types of sorghum (grain sorghum, sweet grain sorghum and dyer sorghum) from the village of Nakomtenga had erect stem, red leaf spots, and white midrib. These types of sorghum did not develop aerial tillers and the stem was not succulent. In addition, grain sorghum and sweet grain sorghum had mainly white pith. Furthermore, both grain sorghum and sweet sorghum had mainly white pith. Dyer sorghum differed from the other sorghum in its dark red seedlings and reddish pith, while grain sorghum included accessions with succulent stem (6.2%). Grain sorghum, sweet grain sorghum and dyer sorghum from Nakomtenga were similar to those from Joseph KI-ZERBO University gene bank in stem status, midrib colour and stem succulence. A difference was therefore observed for the other traits. Dyer sorghum from Nakomtenga was also similar to grain sorghum from Mali in absence or presence of aerial tillers and succulent stem. For the other traits, this sorghum was different.

There is only a minor difference between grain sorghum and dyer sorghum from the village of Lado. These types of sorghum had light red and light green seedlings, erect stem, greenish leaf sheaths, white midrib, reddish pith, and succulent stem but did not develop the aerial tillers. Dyer sorghum differed from grain sorghum by the absence of yellow leaf spots. The grain sorghum and dyer sorghum from Lado were also similar to grain sorghum, sweet grain sorghum and sweet sorghum from Joseph KI-ZERBO University gene bank in the stem status, midrib colour, leaf sheath colour and presence or absence of aerial tillers. Grain sorghum and dyer sorghum from Lado were different from grain sorghum and sweet sorghum from Mali for all traits except for leaf sheath colour.

Both types of Sorghum (grain sorghum and sweet grain sorghum) from the village of Loango had erect stem, red leaf spots, green sheaths, white midrib and no aerial tillers. Grain sorghum differed from sweet grain sorghum by its light red seedlings, lack of reddish pith and the presence of succulent stem. The grain sorghum and sweet grain sorghum from Loango were similar to grain sorghum, sweet grain sorghum and sweet sorghum from the Joseph KI-ZERBO University gene bank for the stem status, midrib colour, leaf sheath colour and the presence or absence of aerial tillers. Comparison of grain sorghum and sweet grain sorghum from Loango with grain sorghum and sweet sorghum from Mali showed a difference in all the traits except for leaf sheath colour.

The sorghum from the village of Korsimoro (grain sorghum, sweet sorghum and sweet grain sorghum) had mostly erect stem, with aerial tillers, reddish leaf spots, greenish leaf sheaths and white pith. Grain sorghum and sweet grain sorghum had white midribs, not succulent stem, and mostly green seedlings. Sweet sorghum had mostly (88.9%) light red seedlings, green midrib and succulent stem. The grain sorghum, sweet grain sorghum and sweet sorghum from Korsimoro were not different from those from Joseph KI-ZERBO University gene bank for stem status. In addition, the grain sorghum and sweet grain sorghum from Korsimoro were also similar to those from the Joseph KI-ZERBO University gene bank in the midrib colour and the absence or presence of succulent stem. These types of sorghum were also different from those from Mali in all the traits.

The grain sorghum, sweet sorghum and sweet grain sorghum from the village of Fulnakambogo had erect stem, aerial tillers, reddish leaf spots, green midrb, greenish leaf sheaths and white pith. For the other traits, variability was observed between these types of sorghum. Sweet sorghum had usually light-red seedlings (75.5%), green midribs (25%) and succulent stem. Sweet grain sorghum and grain sorghum had mostly light green seedlings and not succulent stem. Grain sorghum and sweet grain sorghum from Fulnakambogo were similar to those from Joseph KI-ZERBO University gene bank in stem status, midrib colour and stem succulence. Grain sorghum, sweet sorghum and sweet grain sorghum from Fulnakambogo were different from types of sorghum from Mali in all the traits.

Variation in traits related to panicle and glume

A high variation was observed in the panicle and glume relatedtraits (Figure 2). From the village of Sogué, there was no difference between sorghum type for the type Exertion (EXE) and Peduncle Shape (PS) (Tables 4a and 4b). All the types of sorghum had positive exertion and erect peduncle. There was also no difference between grain sorghum and sweet grain sorghum in panicle type and glume appearance. These types of sorghum had loose panicle, and glume that were hairy (50%) or hairless (50%). Dyer sorghum, had compact panicle and hairless glume. However, the types of sorghum different in the aristation, grain coverage and glume colour.

Figure 2: Variation in panicle size according to Sorghum type.

Table 4a: Variation in qualitative traits related panicles and glumes (EXE, PS, PT, ARI).

Table 4b: Variation in qualitative traits related panicles and glumes (GC, GA, GCO).

All the types of sorghum from Sogué were similar to grain sorghum, sweet grain sorghum and sweet sorghum from Joseph KI-ZERBO University gene bank in peduncle shape (erect peduncle). In addition, sweet grain sorghum from Sogué were not different from sweet grain sorghum from Joseph KI-ZERBO University gene bank for the type of exertion and aristation. All the accessions had positive exertion and no aristation. For the other traits, these types of sorghum were different. The different types of sorghum from Sogué different from grain sorghum and sweet sorghum from Mali in all qualitative traits.

The Sorghum types (grain sorghum and sweet grain sorghum) from the village of Zambanega, had erect peduncle and positive exertion. The majority (at least 84.6%) of this sorghum had loose panicles. These two types of sorghum different in all the other traits. Grain sorghum had various glume colour, including straw (7.7%), black (61.5%), light brown (7.7%) and dark brown (23.1%). The majority had hairless glume and grain covered at 25%. All the accession developed aristation. But sweet grain sorghum had no aristation, hairy glumes, straw glume (80%) and grain coverage at 50%. Grain sorghum and sweet grain sorghum from Zambanega were similar to grain sorghum, sweet grain sorghum and sweet sorghum from Joseph KI-ZERBO University gene bank in peduncle shape. These types of sorghum had erect peduncle. In addition, sweet grain sorghum from Zambanega was similar to sweet grain sorghum from Joseph KI-ZERBO University gene bank in the type of exertion, the type of panicle and aristation. These accessions had positive exertion, erect peduncles and no aristation. However, these accessions different in the other traits. The types of sorghum from Zambanega different from Mali sorghum types in all the traits except for peduncle shape.

There was no different between grain sorghum, sweet grain sorghum and dyer sorghum from Nakomtenga for the type of exertion and peduncle shape. All the accessions had positive exertion and erect peduncle. However, the types of sorghum different in all the other traits. Grain sorghum and sweet sorghum had loose panicle, black and hairless glumes with aristation. The majority of grain sorghum (62.5%) had covered grains at 25%, while sweet grain sorghum, produced covered grain at 50% (70%). Dyer sorghum had compact panicles with red (50%) or dark brown (50%) glumes that were hairless with grain covered at 50%. Grain sorghum, sweet grain sorghum and dyer sorghum from Nakomtenga were different from grain sorghum, sweet grain sorghum and sweet sorghum from Joseph KI-ZERBO University gene bank for the traits, except for the peduncle shape. However, dyer sorghum from Nakomtenga and sweet sorghum from Joseph KI-ZERBO University were similar in the type of exertion, aristation and glumes appearance. The accessions had positive exertion, hairless glumes and no aerial tillers. The types of sorghum from Nakomtenga were different from grain sorghum and sweet stem sorghum from Mali in all the traits, except the peduncle shape.

Grain sorghum and dyer sorghum from Lado were similar in the peduncle shape, type of exertion, aristation and glume colour. The accessions of these sorghum had erect peduncle, positive exertion, aristation, and mostly black glume. For the other traits, these sorghums were different. Grain sorghum had loose panicle, hairless glumes that covered 25% of the grain. Dyer sorghum had mostly loose panicle (68.7%), hairless glumes (66.7%) and covered grain at 50% (66.7%). Grain sorghum and the dyer sorghum from Lado were not different from those from Joseph KI-ZERBO University gene bank and those from Mali for peduncle shape. Therefore, differences were observed in the other traits.

There was no difference between grain sorghum and sweet grain sorghum from Loango in the peduncle shape, type of exertion, panicle type and covered grains. Both types of sorghum had erect peduncles, positive exertion, loose panicles, and covered grains on 25%. For other characters, these sorghums are different. Most grain sorghum have the presence of aristation (80%), hairless (75%) glume and light-brown (75%) glumes. Sweet grain sorghum had mostly absence of aristation (76.7%), hairy (69.7%), and darkbrown (66.7%) glumes. Grain sorghum and sweet grain sorghum from Loango were not different from grain sorghum, sweet grain sorghum and sweet sorghum from Joseph KI-ZERBO University gene bank for peduncle shape. However, these sorghums were different for the other traits. The same observation was made with accessions from Mali.

Grain sorghum, sweet grain sorghum and sweet sorghum from Korsimoro were not different in the type of exertion. These types of sorghum had positive exertion. Grain sorghum and sweet grain sorghum had also erect peduncle and loose panicle, while sweet sorghum had erect peduncle (77.8%), or curved peduncle (22.2%) and variable panicle shape: Loose (33.4%), semi-compact (22.2%) and compact (44.4%). Grain sorghum had aristation, black or light brown glumes that were hairless and covered 25% of grain. Sweet grain sorghum had no aristation, mostly hairless, straw or light brown glumes. For sweet grain sorghum, the glume was hairless, and black with variable grain coverage: 25%, 50%, 75%, or completely covered without aristation. For the peduncle shape, grain sorghum, sweet grain sorghum and sweet sorghum from Korsimoro were not different from those collected from Joseph KI-ZERBO University gene bank. In addition, sweet grain sorghum from Korsimoro was similar to those from Joseph KIZERBO University gene bank for panicle type, aristation and type of exertion. The accessions had positive exertion, loose panicle and no aristation. However, these sorghums differed in the other traits. The types of sorghum from Korsimoro were different from grain sorghum and sweet sorghum from Mali in the traits except peduncle shape.

Grain sorghum and sweet grain sorghum from Fulnakambogo were not different in the type of exertion and the type of panicle. Both types of sorghum had positive exertion and loose panicle. For the other traits, these types of sorghum were different. Grain sorghum had aristation (87.5%), hairy glumes (75%) with variable colour: Black (37.5%), light brown (25%) or dark brown (37.5%) and grain covered at 25% (62.5%). Sweet grain sorghum had usually no aristation (66.7%), hairless glumes (66.2%) with variable colour: Straw (37.3%), black (32.4%) or red (34.3%) and covered grains at 50%. Sweet sorghum had compact panicles, no aristation, glume mostly black (75%), hairy (75%) and covered grains at 50%. These types of sorghum from Fulnakambogo different from the accessions collected from Mali and Joseph KIZERBO University gene bank in the traits except for the peduncle shape.

Variation of qualitative traits related to grain

The comparative analysis of different types of sorghum revealed a variation in most grain-related traits (Tables 5a and 5b). Nevertheless, some similar traits were found among the different types of Sorghum. Grain sorghum, sweet grain sorghum and dyer sorghum from Sogué were not different in the dry grain flavour. All the types of Sorghum produced grains that were not sweet in the dry stage. Grain sorghum and dyer sorghum had elliptical grains that were not sweet in the fresh stage. In addition, dyer sorghum and sweet grain sorghum had no rotation, while grain sorghum had a low grain rotation. For the other traits, a high variation was observed. Grain sorghum had grains that were mostly easy to ginning (69.5%), white (50%) or light red (50%) in colour and with variable endosperm texture: Mainly vitreous (50%), mainly floury (26.4%) and floury (23.6%) in the dry stage. On the other hand, sweet grain sorghum had grains that were easy to ginning, asymmetrical, light red and 50% floury (33.6%) or floury (66.4%) in the dry stage. Dyer sorghum had grains that were difficult to ginning, dark red and mostly floury (66.7%) in the dry stage. Grain sorghum, sweet grain sorghum and dyer sorghum from Sogué were similar to Joseph KI-ZERBO University gene bank grain sorghum, sweet grain sorghum and sweet sorghum in dry grain flavour. These sorghums had grains that were not sweet in the dry stage. In addition, the sweet grain sorghum from Sogué was similar to sweet grain sorghum from Joseph KI-ZERBO University gene bank in the type of ginning, grain shape and fresh grain flavour. The accessions had dissymmetrical grains that were easy to ginning and no sweet in fresh stage. However, the differences were observed in the other traits. A comparison of grain sorghum, sweet grain sorghum and dyer sorghum from Sogué with grain sorghum and sweet sorghum from Mali revealed a similarity in dry grain flavour. A similarity was only observed between grain sorghum from Sogué and those from Mali in grain shape, fresh and dry grain flavour.

Table 5a: Results of qualitative traits variation related grain (TG, GS, GRC).

Table 5b: Results of qualitative traits variation related grain (FGF, DGF, GRO, VIT).

Grain sorghum and sweet grain sorghum from Zambanega were not different in the traits except the dry grain flavour. Both types of sorghum had grains that were not sweet in the dry stage. Grain sorghum had grains that were mainly easy to graining (61.5%), low rotation (76.9%), elliptical (92.3%), not sweet in fresh stage and variable colour: White (46.2%), light red (7.7%), dark red (38.5%) or yellow (7.7%). Grain sorghum had also a variable endosperm texture: Mainly vitreous (38.5%), 50% floury (15.4%), mainly floury (23.1%) and floury (23.0%). Sweet grain sorghum had asymmetrical grains that were easy to ginning. The grains were light red (80%) or dark red (20%) and taste sweet when fresh. The accessions had a high (60%) or no (40%) rotation and mainly floury (20%) or floury (80%) endosperm texture. Grain sorghum and sweet grain sorghum from Zambanega were different from grain sorghum, sweet grain sorghum and sweet sorghum in Joseph KI-ZERBO University gene bank in the traits except the dry grain flavour. Similar variation was observed between sorghum form Zambanega and the accessions collected in Mali.

Most traits of Sorghum types (grain sorghum and dyer sorghum) from Lado did not show differences. Both types of sorghum had elliptical grains that were easy to ginning, no sweet grain in fresh or dry stage, and mostly low rotation. However, there were differences in the other traits. Grain sorghum had variable grain colours: White (50%), light red (25%), and dark red (25%). This type of sorghum had variable endosperm texture: Mainly vitreous (55.6%), 50% floury (19.4%), and mainly floury (25%). Dyer sorghum had a floury endosperm texture and dark red (66.7%) or red (33%) colour. Grain sorghum and dyer sorghum from Lado were different from grain sorghum, sweet grain sorghum and sweet sorghum from Joseph KI-ZERBO University gene bank in the traits, except for dry grain flavour. Grain Sorghum and dyer sorghum from Lado were similar to grain sorghum and sweet sorghum from Mali in the fresh and dry grain flavour. However, these sorghums were different in the other traits.

Grain sorghum and sweet grain sorghum from Loango were not different in the type of ginning and grain flavour. Both sorghum types produced grains that were mostly easy to ginning and no sweet in the fresh and dry stage. Grain sorghum, produced elliptical grains that had various colour: White (50%), dark red (25%), and grey (25%). Grain rotation was observed for most of the accessions (80.5%) and the endosperm texture was vitreous (20%), mainly vitreous (30%), mainly floury (25.6%), or floury (24.4%). Sweet grain sorghum produced grains that were asymmetrical shape, light red (66.7%) or grey (33.3%) colour, mostly low rotation and variable endosperm texture: Mainly vitreous (30.3%), 50% vitreous (36.4%) and floury (33.3%). The types from Loango different from sorghum collected in Joseph KI-ZERBO University gene bank and in Mali in the traits, except for dry grain flavour.

There was no difference between grain sorghum, sweet grain sorghum and dyer sorghum from Nakomtenga for the dry grain flavour. All the types of sorghum produced grains that were mostly easy to ginning and no sweet in fresh or dry stage. Grain sorghum and sweet grain sorghum were similar in grain shape, grain colour, and grain rotation. Both had elliptical grains, dark red colour and low rotation. For the other traits, these sorghums were different. Grain sorghum had mainly vitreous (18.8%), 50% vitreous (25%), mainly floury (25%) and floury (31.2%), while sweet grain sorghum had mainly floury (90%) endosperm texture. On the other hand, dyer sorghum grains were asymmetrical shape, dark red, mostly floury (70%) without rotation. The types of Sorghum from Nakomtenga different from Sorghum collected from Joseph KI-ZERBO University gene bank and Mali in traits, except for dry grain flavour.

Grain sorghum, sweet grain sorghum and sweet sorghum from Fulnakambogo had mainly no sweet grains in the fresh and dry stage. In addition, grain sorghum and sweet grain sorghum had grains that were mostly easy to ginning and have a high rotation. There were differences in the other traits. Grain sorghum had grains that were elliptical shapes and variable grain colour: White (50%), light red (37.5%), dark red (12.5%). It also had variable endosperm texture: Mainly vitreous (25%), 50% vitreous (25%), mainly floury (12.5%) and floury (37.5%). On the other hand, sweet grain sorghum had grains that were mainly asymmetrical shape (66.7%), light red (30.3%) or dark red (69.7%) and floury (76.7%). In sweet sorghum, most accessions were difficult to ginning and had asymmetrical shape, low rotation, floury grain and variable grain colour: White with black spots (50%), white (25%) and yellow (25%). Grain sorghum, sweet grain sorghum and sweet sorghum from Fulnakambogo were different from the sorghum from Mali and Joseph KI-ZERBO University gene bank in the traits, except for the flavour of the fresh and dry grain.

Grain sorghum and sweet sorghum from Korsimoro produced no sweet grains in fresh or dry stage. In addition, grain sorghum and sweet grain sorghum had grains that were easy to ginning. There were differences between the two types of sorghum in the other traits. Grain sorghum produced elliptical shape, white grain, low rotation and mainly vitreous (75%) endosperm. On the other hand, sweet grain sorghum, had grains that were asymmetrical, light red, sweet when fresh, mostly no sweet when dried (60%) and floury. Sweet sorghum had grains that were mostly difficult to ginning (88.9%), asymmetrical shape (66.7%), no rotation (88.9%) and variable grain colour: White spotted black (22.2%), white (11.1%), red (33.6%) and yellow (33.1%). It has also variable endosperm texture: mainly vitreous (11.1%), 50% vitreous (22.2%), mainly floury (22.2% and floury (44.4%). Comparison of grain sorghum from Korsimoro with those from Joseph KI-ZERBO University gene bank revealed a similarity for grain colour and grain flavour. These sorghums had white grains that were not sweet in fresh or dry stage. In addition, the sweet sorghum from Korsimoro and the sweet sorghum from Joseph KI-ZERBO University gene bank were similar in fresh and dry grain flavour. However, differences were observed in the other traits. Except the grain flavour, sorghum types from Korsimoro were different from those collected in Mali (Figure 3).

Figure 3: Variation in grain colour according to Sorghum type.

Botanical races of types of sorghum

A total of Four (04) botanical races (Guinea, bicolor, caudatum and dura) and Three (03) intermediate races (caudatum-bicolor, Guinea-bicolor and Guinea caudatum) were identified according to sorghum type and village (Figure 4). The results showed that most grain sorghum belonged to the Guinea race. Sweet sorghum and dyer sorghum belonged to the caudatum race, while sweet grain sorghum consisted of various races.

Figure 4:Distribution of botanical race frequency according to Sorghum type and villages. Note: ( ): Guinea; ( ): Caudatum; ( ): Guinea- Caudatum; ( ): Guinea-bicolor; ( ): Bicolor; ( ): Dura.

Grain sorghum and sweet grain sorghum from Lado, belonged mainly to the Guinea race. The majority of grain sorghum and sweet grain sorghum from Nakomtenga belonged to the Guinea race, while dyer sorghum belong to the caudatum race. Grain sorghum, sweet grain sorghum and dyer sorghum from Sogué included many botanical races. Half of the grain sorghum and sweet grain sorghum belonged to the Guinea race, while all the dyer sorghum accessions belonged to the caudatum race. The other part of grain sorghum was intermediate between the Guinea and bicolor races but sweet grain sorghum belonged to the caudatum race. The majority of grain sorghum from Zambanega belonged to the Guinea race, while the sweet grain sorghum belonged to the Guinea-caudatum race. There was a racial difference between the sorghum types from Fulnakambogo. All the grain sorghum accessions belonged to the Guinea race. The majority of sweet grain sorghum was intermediate between the Guinea race and the caudatum race, while the sweet sorghum accessions belonged to the caudatum race. The majority of sweet grain sorghum and sweet sorghum from Korsimoro belonged to the bicolor race. On the other hand, all grain sorghum accessions belonged to the Guinea race. Most of the grain sorghum from Loango belonged to the Guinea race, while the sweet grain sorghum consisted of variable botanical race: 33.34% Guinea, 33.33% caudatum and 33.33% caudatum-bicolor.

Except sweet grain sorghum accessions from Zambanega, the other accessions are different from Joseph KI-ZERBO University gene bank accessions. For the accessions from Mali, a racial diversity was observed. The majority of grain sorghum belonged to the Guinea race while, sweet sorghum belonged to the caudatum race. Comparative analysis revealed difference between the sorghum types collected in each village and those from Mali.

Morphological variability of sorghum types based on agroclimatic zones

For sorghum types from North Sudanian area, Multiple Component Analysis (MCA) of qualitative traits showed three groups (Figure 5) of traits association corresponding to different types of Sorghum. Seven traits were discriminant: Midrib Colour (MC), Leaf Sheath Colour (LSCO), Pith Colour (SPC), Panicle Type (PT), Grain Shape (GS), Grain Colour (GRC) and the Flavour of Fresh Grain (FGF). Grain sorghum had a greenish leaf sheath, white pith, white midrib, loose panicle, elliptical grain shape and no sweet grain in the fresh stage. Dye sorghum, on the other hand, had a reddish leaf sheath and pith, a reddish midrib and a compact panicle. Sweet grain sorghum, had light red grains, asymmetrical shape and sweet grains in the fresh stage.

Figure 5: Phenotypical proximity of Sorghum types in the North Sudan area.

The sorghum types from sub-Sahelian area, differed in Midrib Colour (MC), Panicle Type (PT), Grain Shape (GS), Grain Colour (GRC), Glume Colour (GC), Endosperm Texture (VIT), Succulence (SUS) and Ginning Type (TG). Three groups (Figure 6) of traits association according to the three types of Sorghum were observed. Grain sorghum had a white midrib, a loose panicle and light brown glumes, elliptical grains that were white, easy to ginning, vitreous and no sweet stem. Sweet sorghum, on the other hand, had a green midrib, a compact panicle, yellow grains that were difficult to ginning, black glume and a sweet stem. Sweet grain sorghum had light red grains that were floury and easy to ginning, asymmetrical grain shape and straw glumes colour.

Figure 6: Phenotypical proximity of Sorghum types in the Sub-Sahelian area.

Discussion

Comparative analysis of the variability of different types of sorghum revealed a morphological similarity in traits related to stem, leaf and panicle. Most of these types of sorghum had erect stem, red leaf spots, positive exertion, erect peduncle, absence of aerial tillers and no sweet grains in the dry stage. Similar findings were reported by [9,10], who observed monomorphism in several qualitative traits within sorghum genetic resources. This morphological proximity could be explained by gene flow between the Sorghum types. Despite its preferentially self-pollinated mode of reproduction, Sorghum has an outcrossing rate ranging from 5 to over 40%, with an average of 6 when grown in the field [13-15] which could promote gene flow between sorghum types. In addition, sorghum types are grown in nearby fields or in same fields [16], which would have favored cross-fertilization between sorghum types. This study showed that grain sorghum and sweet grain sorghum were very similar compared to sweet sorghum dyer sorghum, as reported by [9,12]. This could be explained by the fact that most of the grain sorghum and sweet grain sorghum have loose panicles and belong to the Guinea or intermediate Guinea-caudatum race. On the other hand, most of the sweet sorghum and dyer sorghum have compact and semicompact panicles. According to [13], loose panicles, such as those of local Guinea races favored cross-pollination, while very compact panicles, such as those generally found in local Durra races, hinder cross-pollination. Previous studies also shown that the rate of allogamy can be significant in cultivated sorghum, ranging from 5% to 7% in the Durra races [17] and 10% to 30% in the Guinea races [18].

The results also showed that the proximity between sorghum types varied from one village to another. Sorghum types from Zambanega, Nakomtenga, Lado and Loango, were much similar than those from other villages. This similarity between different types of sorghum from the same village revealed probably that farming practices have an impact on the genetic diversity of cultivated sorghum and should be taken into account in Sorghum improvement programmes in Burkina Faso. Genetic similarities were often higher between Sorghum types in the same village than between populations of the same types collected in different villages. This result is fully in agreement with those of [19] who found higher genetic similarities between local races sampled in the same village than between populations of the same local race collected in different villages. These results could be explained by the fact that these sorghum types are collected in the same areas or in nearby fields which allowed cross-fertilisation. According to [20], the proximity of individuals of different Sorghum varieties in the same plots or at the edges of plots in the agro-systems of Burkina Faso, Mali and Niger promotes intervarietal gene flow. These gene flow is the cause of several genetic introgression phenomena [7,21], which could lead to phenotypic changes within sorghum types or a change from one type to another. In millet, gene flow between domestic millet and wild millet lead to the formation of plants with an intermediate phenotype with lower yield potential in farming environments [22]. The appearance of intermediate races, intermediate vitrosity and no sweet grains in fresh stage in sweet grain sorghum, green leaf sheaths and white pith in dye sorghum suggest greater gene flow between these Sorghum types. These results confirmed farmers reported during the collection of accessions. These farmers reported changes from one type of Sorghum to another, decreasing of yield potential, changes in grain and stem succulence and changes in grain colour within the same type. The consequences of these changes could be the extinction of minor sorghum types (sweet grain sorghum and dyer sorghum), which are nevertheless useful for the local populations through the consumption of fresh grains and the sale of panicles during the lean season [16,6], and the use of dyer sorghum in dyeing [23]. According to [24], gene flow can lead to the disappearance of rare species.

The results of the multiple correspondence analysis showed high proximity between sweet grain sorghum and grain sorghum than sweet sorghum and dyer sorghum. This result confirms a possibility of more intense gene flow between grain sorghum and sweet grain sorghum. The consequences of these gene flows could be a homogenisation of allele frequencies [25], leading to a possible decrease in sorghum genetic diversity in Burkina Faso. The high different observed between sorghum collected and accessions from Joseph KI-ZERBO University and Mali gene banks showed that cropping practices have a significant impact on the organization of the genetic diversity of sorghum cultivated in Burkina Faso. Similar results were observed by [26] in Benin on sorghum cultivated by the Lokpa.

Conclusion

Comparative analysis based on qualitative traits revealed a significant morphological proximity between Sorghum types when grown in the same cultivation areas. These results showed that sweet grain sorghum and grain sorghum are very similar than sweet sorghum and dyer sorghum in the same village and in the same agro-climatic area. However, as morphological markers are influenced by environmental factors, it would be interesting to investigate the proximity of these types of sorghum based on molecular markers.

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