The potential of local cultivars in sorghum improvement in Mali
A. TOURE, K. TRAORE^1, A. BENGALY^2, J.F. SCHEURING^3, D. T. ROSENOW^4 and L.W. ROONEY^5
IER, CRRA-Sotuba BP 438 Bamako, Mali, West Africa
(Received 12 June, 1997; accepted 22 October, 1997)
Over 1300 accessions of sorghum were collected in several regions of Mali. Cultivars were evaluated for photoperiod sensitivity, maturity, genetic traits, yield, agronomic desirability, and food quality. Three major races of sorghum exist in the country: guinea, durra and caudatum. The race guinea represents about 70% of the germplasm in the country and is divided into 2 important groups: Keninke (54%) and Kende (16%). Durra sorghums are the second most important race and represents 17% of Malian sorghums. Different sources of resistance to different abiotic and biotic constraints have been identified. Series of decortication trials were performed to test the effect of kernel texture and shape on yields of decorticated grain. Milling yields of local guineas were consistently above 70%, while experimentals varied from 35% to 68%. Photoperiod sensitive sorghums tend to decrease their seed number by 34 to 58% per panicle for 15 to 30 days of delay in planting. White-seeded, tan-plant guinea-type breeding lines have been developed from the direct cross of guinea with Zerazera, Malisor 84-7 and Sureno. Progenies showed a loose panicle and a large number of seeds per panicle. N'tenimissa, a new tan plant straw glume colour progeny, possesses excellent guinea traits and yield potential and could be useful in processing. Significant information on key characteristics of guineas has been used successfully in breeding to develop new cultivars with improved agronomic and food processing properties.
Key Words: Guinea, improvement, milling properties, tan-plant sorghum quality
Plus de 1300 accessions de sorgho ont ete collectes dans plusieurs regions du Mali. Les cultivars ont ete evalues pour la sensibilite a la photoperiode, le cycle, les caracteristiques genetiques, le rendement grain, les caraceristiques agronomiques et organoleptiques. Trois dominantes races de sorgho existent dans le pays: guinea, durra et caudatum. La race guinea represente 70% du germplasme Malien et est dividee en 2 groupes: Keninke (54%) et Kende (16%). Les sorghos durra constituent la seconde importante race et representent 17% des sorghos du Mali. Des sources de resistance aux differentes contraintes biotiques et abiotiques ont ete identifiees. Des tests de decortication ont ete realises pour apprecier l'effect de la texture et la forme de grain sur le rendement grain au decorticage. Les rendements au decorticage des sorghos guinea etaient superieurs a 70% et ceux des varietes experimentales varient entre 35% et 68%. Les sorghos sensibles a la photoperiode tendent de reduire leur nombre de grains par panicule de l'ordre de 34%a 58% suite a un retard de semis de 15 a 30 jours. Des lignees a plante-tan et a grain blanc ont ete developpees a partir des croisements de guinea avec Zerazera, Malisor 84-7 et Sureno. Les descendances ont un grand nombre de grains par panicule et une forme paniculaire leche. N'tenimissa, une nouvelle plante tan, a glume paille, possede des traits guinea et un rendement eleve. Des informations importantes sur des caracteristiques majeures des guineas ont ete utilisees en selection avec succes pour le developpement de nouveaux cultivars avec des proprietes agronomiques et de moulage ameliorees.
Mots Cles: Guinea, amelioration, proprietes de moulage, qualite plante-tan
Sorghum (Sorghum bicolor [L.] Moench) ranks fifth in world food grain production following wheat, rice, maize, and barley. Sorghum is the traditional cereal crop for millions of people in West Africa where it represents about 37% of the total food grain production in the region. In 1996 for example, total sorghum grain production was 10,544,000 tons harvested on 11,678,000 ha. About 90% of that production was accounted for by Nigeria, Burkina Faso, Mali, and Niger (FAO, 1997). In 1996 Mali produced 710,275 tons on 851,006 ha with an average grain yield of 834 kg ha^-1. Many of the traditionally grown cultivars are photoperiod sensitive. These sorghums flower at the end of the rainy season; the grains mature under dry conditions. They are well known for their grain quality, good weathering, pest resistance, and storage qualities. However, the yield capacity of most local cultivars is relatively low though they are very stable producers.
Mould and head bugs (Eurystylus marginatus) in the rainy season cause physical, chemical and structural changes in sorghum that significantly affect the food and nutritional quality of sorghum. Sorghum grain quality is reduced significantly by the staining due to grain mould and head bugs damage. Factors affecting milling properties, food quality, and nutritional value affect critically other efforts to improve sorghum in most of the countries.
Plant colour in local cultivars is red or purple and glume color is mainly black or red. In spite of their good adaptation, local cultivars produce poor grain quality in very wet seasons due to the migration of anthocyan pigments into the grain. Grain is discoloured because of plant and glume colour. Efforts to improve grain yield and other agronomic traits are lost if the grain is not acceptable to consumers. Breeding sorghum with acceptable traditional and industrial properties will more likely give rise to sorghum products that can be marketed successfully.
The early experimental progenies showed poor grain quality (low yield of decorticated grain, black specks, poor flour colour) which has been a major problem in development of new products with value added. The resulting to (traditional food) had unacceptable texture, colour, and keeping properties. One of the advantages of the new released varieties over the local cultivars is early maturity and grain yield. However, head bugs and moulds affect the grain quality of the new cultivars significantly and prevented them from being widely used. Significant information on major characteristics of local cultivars has been used successfully in breeding for improved agronomic and organoleptic properties. The local germplasm for the most part have remained under utilised by the breeders because of its photosensitivity.
The objectives of this study were to characterise the local cultivars and to document that they can be used to produce improved cultivars with high yields, agronomic and superior grain quality for the harsh environment of Mali and West Africa.
MATERIALS AND METHODS
Over 1300 accessions of sorghum were collected in the different regions of Mali (from the North-guinea zone to the Sahel zone) during germplasm missions organised and carried out by ORSTOM, IBPGR and IER in 1978, 1982, 1989 and 1990. Each of the germplasm collections was evaluated systematically in the main sorghum stations (Sotuba 12 degrees 39', Cinzana 13 degrees 17', Same 14 degrees 26', Longorola 12 degrees 21', Bema, 15 degrees 02' and Baramandougou 13 degrees 35'). Each entry was planted in a 2 replicated trial with 3 planting dates at each location and 15 days between planting dates. Each plot consisted of four rows, 0.75 m apart and 5 m long. Cultivars were evaluated for photoperiod sensitivity, maturity, yield, agronomic desirability and food quality. Photoperiod sensivity was estimated by comparing days to 50% anthesis from the 3 planting dates at each location.
Selected elite local guineas, CSM 388, Tiemarifing and Bimbiri Soumale were crossed to particular selected varieties Zerazera, Malisor 84-7, Sureno etc. to obtain white-seeded, tan-plant guinea lines. Selections were made in F2, F3 and F4 progenies grown at Sotuba, Cinzana, Longorola, Bema and Samanko. Selected F4 progenies were identified for advance in the off season to be entered as F6s in a two replicate preliminary yield trial. Selected lines in the preliminary yield trial were placed in an advanced yield trial. A randomised complete block design with 4 replications was used to compare parents and progenies for grain yield, number of seeds per panicle, 1000 seed weight, days to 50% flowering and plant height. The plot size was five rows of 5 m long spaced 0.75 m apart. Seeds were sown in hills 0.50 m apart and thinned to two plants per hill. A bulk of the pedigree, Bimbiri Soumale*87CZ-Zerazera (N'tenimissa), was planted in farm trials in 1995 in the medium maturity zone (Cinzana and Bamako).
N'tenimissa, white-seeded, tan-plant guinea-type breeding line was compared to N'darila, Dususuma, 89-SK-F4-192-2PL (all Caudatum) and a local guinea for milling properties. Data based on mean of four observations on grain grown at Yrimadio in 1996. Measurements were taken on 1000 seed weight in grams (g) on a 1000-seed sample; Decortication yields for 3 and 5 minutes performed on samples of 20 g using TADD ( Tandential Abrasive Deluller Device). Decortication yields are measured as the percentage of dehulled grain weight over total non dehulled grain weight (75% or higher = good and 40% or lower = poor). Grain vitrosity was recorded on a 1-5 scale (1 = vitreous, 5 = soft). To consistency was based on a 1-5 scale (1 = consistent, 5 = soft). To colour on a 1-5 scale (1= good, 5 = poor), and Plant colour was classified as tan , purple or red.
RESULTS AND DISCUSSION
Three major sorghum races exist in Mali: guinea, durra and caudatum (Toure, 1979). The guinea sorghums represent about 70% of sorghum races in Malian sorghums; they predominate throughout the Savannah region. It is divided into 2 important groups: Keninke (Guineense gambicum, 54%) and Kende (Guineense margeritiferum, 16%). The height, maturity, and grain yield of some improved guinea sorghums are shown in Table 1.
The durra sorghums are the second most important race and represents 17% of Malian germplasm. The durra are constituted only of Gadiaba and are grown mainly throughout the Sahel. The race caudatum accounts for less than 1% of Malian germplasm; it is randomly distributed in the country. The remaining 13% of Malian germplasm, is comprised of intermediate types of sorghum. Local germplasm collected in Mopti and Kayes regions do not have any Gadiaba*Keninke intermediate types of sorghum. However, germplasm collected in the lake regions (Mopti, Tombouctou) accounts for most of intermediate types of Gadiaba*Keninke which are mainly comprised of Saba and Hombo.
The evaluation of the germplasm provides information on each cultivar and permits prediction of different phenotypes of progenies in crosses (pericarp colour, presence of testa, glume colour, plant colour, coleoptile colour, awn etc.). Three major groups of photoperiod sensitivity were identified: photoperiod insensitive, photoperiod sensitive and intermediate photoperiod sensitive sorghums (Toure, 1980). The study also showed three sorghum maturity groups. The early cultivars are those with less than 65 days from planting to 50% flowering. The late cultivars flower 90 days after planting. The medium sorghums flower 65 to 90 days after planting. Keninke is the group containing the most photoperiod sensitive and late sorghums compared to Kende and Gadiaba.
Local cultivars showed resistance to different abiotic and biotic constraints. Screening in charcoal pits during the hot off-season at Cinzana indicated that local cultivars showed more resistance to drought and heat at seedling stage (CSM 205). Many cultivars (Seguetana) showed good tolerance to Striga hermonthica during evaluation in large field nurseries at several locations. Sorghum panicle-feeding bugs and grain moulds are the major constraint to the use of improved high yielding non-guinea type sorghum in Mali. The insects suck the grain which is attacked by moulds resulting in a soft, discoloured endosperm, rendering it unfit for food products (INTSORMIL, 1995). Malisor 84-7, an improved cultivar, has good tolerance to head bugs which can be genetically transferred to its progeny. The local guinea sorghums have good resistance to the panicle feeding bugs and grain moulds. Inheritance of head bugs resistance is quantitative and primarily recessive (INTSORMIL, 1995).
The long glumes show some head bugs resistance. Studies indicated the importance of grain filling rates in head bugs resistance. There is some direct evidence that the glumes play a role in the protection and filling of the sorghum grain. Generally, there is a reduction of grain weight when the glumes of cultivars are cut after fertilisation (Traore, 1982). Cultivars were evaluated for B/R fertility restorer reaction on A1 cytoplasm. The distribution of fertility restorers (R-lines) among sorghum race groups in Mali is presented in Table 2. The distribution of the B-lines throughout the country did not show any obvious distribution pattern (Toure and Scheuring, 1982).
Significant information on key traits of local cultivars has been used successfully in breeding for improved agronomic and organoleptic properties. For leaf disease, it is very important to distinguish between complete immunity and adequate tolerance. In guinea sorghums, lower leaves are readily attacked by an array of leaf diseases, but the top leaves, especially the top three, are practically free of all leaf disease symptoms.
Most of the traditionally grown cultivars are photoperiod sensitive. These sorghums have been selected to flower at the end of the rainy season, so that the grains mature under dry conditions. The guineas are able to produce vitreous grain under post anthesis drought stress while under identical conditions, exotic varieties fail to adequately fill the grain after flowering. Photoperiod- sensitive improved sorghums are our target. These sorghums like local guineenses will be adapted to diverse areas of cropping. The good adaptation of guineenses is due mainly to daylength-sensitivity. These local cultivars are well adapted to climatic stresses and fit the growing season well. However, photoperiod sensitive sorghums tend to decrease their seed number by 34 to 58% per panicle for 15 to 30 days of delay in planting. Guinea sorghums seem to maintain a relative low yield under adverse conditions by reducing the number of seeds per panicle and seed size (Toure et al., 1996).
Plant colour in local cultivars is red or purple and glume colour is mainly black or red. In spite of their good adaptation, local cultivars produce poor grain quality in very wet seasons due to the migration of anthocyan pigments into the grain. Grain is discoloured because of plant and glume colour. The grains available in local market are always mixed with a high percentage of discoloured grain which lowers their quality for use in value added processing. The quality of sorghum in Mali can be significantly improved by the development of white-seeded, tan, photoperiod sensitive cultivars with straw glume colour, which can be processed into acceptable food products that can be marketed successfully.
Mould and head bugs in the rainy season cause physical, chemical and structural changes in sorghum that significantly affect also the food and nutritional quality of sorghum. They cause staining and significantly reduce the milling value of the grain. The development of tan photoperiod sensitive cultivar with loose panicle, straw glume colour, and head bug resistance will help to avoid the mould-head bugs problem. Tan sorghum with improved grain quality with better processes will generate acceptable end -use- products that can be competitive with imported grain.
Decortication trials were performed on samples to test the effect of kernel texture and shape on milling yields. Grain of local guineas gave consistently 70% or more yields, while experimental progenies varied from 35% to 68% (Scheuring et al., 1982). The caudatum, "turtle back" shape grains had consistently lower yields than oval or rounded kernels with similar textures. The lower rates were caused by breakage of the kernel near the germ end. The extended decortication time required to remove all the pericarp on the belly surface of the caudatum kernel reduces the yield. The women doing the decortication complained about the difficulty to remove the caudatum pericarp compared to local guinea kernels. The kernel weight of local guinea sorghum varied between 20 and 24g per 1000 kernels. Many improved and exotic had less than 20g per 1000 kernels weights, which is the lower end of local guineense.
One of the major constraints is breeding for tan photoperiod sensitive sorghums that will help to get good quality and value -added processing of improved cultivars and which can be used by large industrial and small scale processor. These tan plant sorghums are much lighter in colour than the local guineas when there is high humidity during maturation, however, should have some photosensitivity to mature during the end of the rainy season. More than twenty years experience with photoinsensitive white tan sorghum cultivars has demonstrated that they are destroyed by moulds and head bugs or the grain is stained, soft and cannot be dehulled effectively. Avoidance of grain moulds is an essential characteristic required for sorghum.
White-seeded, tan-plant guinea-type breeding lines have been developed from the direct cross of guinea with Zerazera, Malisor 84-7 and Sureno. Progenies showed a loose panicle and a large number of seeds per panicle. They also had long glumes and vitreous grain. Inadequate seed number was one of the drawbacks of some of our earlier experimental progenies like 83-SB-474; which had excellent traits except for seed number per panicle.
N'tenimissa (Bimbiri soumale*Zerazera), a new tan plant straw glume colour sorghum, possesses excellent guinea traits and yield potential (Table 3). It has a white endosperm and a thin pericarp. N'tenimissa could be useful in processing because it has a white, tan plant that has some pothoperiod sensivity which means it matures near the end of the rainy season. These white, tan plant sorghum lines produce excellent flour which can be used for bread and biscuits. They also demonstrate their properties in food systems (Table 4). The new tan plant, guinea-type breeding materials provide an opportunity to develop new food and industrial products which could enhance demand and stabilise prices. These value -added sorghum cultivars are the basis for identity -preserved production for use in processing into value added products.
This study suggests that potential exists for improving yields through use of local cultivars. Some realised gains are probably due to the diversity existing among the guineas and the fact that most of the improved varieties currently used are derived from crosses between introduced materials. These materials thus present a very useful source of variability for improvement of future varieties for Mali.
Great potential exists for improving yields and other consumer preferred traits through the use of local cultivars. Different sources of resistance to different abiotic and biotic constraints have been identified. A significant amount of information about key characteristics of the local cultivars has been used successfully as breeding selection criteria. White-seeded, tan-plant guinea-type breeding lines have been developed from the direct cross of guinea with improved or introduced cultivars. These findings suggest that exploitation of the local landraces can lead to cultivars with quite significant improvements that will be productive in Mali and perhaps other areas of West Africa.
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Copyright 1998, African Crop Science Society
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