Present and Future Perspective of Soybean Cultivation as Important Crop in DRC

Abstract

Soya [Glycine max (L.) Merr.] is a relatively new vegetable in the Democratic Republic of Congo (DRC). It is one of the most important legumes in the Democratic Republic of Congo (DRC) and has an important role in its contribution to food and industry and from an agronomic point of view. Several activities have been carried out in favor of this crop since its introduction in the country until today. This document presents the activities and methods used in the DRC to genetically improve soybean cultivation.

1. Introduction

Soya [Glycine max (L.) Merr.] is a relatively new vegetable in the Democratic Republic of Congo (DRC). It is one of general staple crops for smallholders in sub-Saharan Africa that contribute to improvement of Africa’s nutrient-poor soils. It is one of the most important legumes in the Democratic Republic of Congo (DRC) and has an important role in its contribution to food and industry and from an agronomic point of view. Because of its protein content in the higher seeds of all other vegetables, soybeans are of great nutritional value [1, 2]. With an average national consumption of 0.28 Kg/inhabitant per year, soybeans rank fifth among the edible seed vegetables consumed in the DRC after groundnuts (12.57 Kg/inhabitant), the common bean (2.71 Kg/inhabitant), the pea (1.41 Kg/inhabitant), and the cowpea (1.08 Kg/inhabitant) (Nyabyenda, 2005; cited by [3, 4]). In the Democratic Republic of Congo, where income per capita is relatively low and animal protein is difficult to access, soya is one of the most important crops for human consumption [1, 2]. It is used effectively in programs to combat child malnutrition [5, 6, 7].

In the DRC, soya is usually grown in traditional production systems and is an important source of income for farm households. Its national production, mainly with farmers in 2019, was estimated at 25044 tons [8]. The areas sown for soybean cultivation in the DRC, estimated at 15000 hectares between 1995 and 1996, are ranked fourth among the areas of land used for vegetables after those of groundnuts (729,000 ha), beans (212,000 ha), and peas (95,000 ha) (FAO, 1997 cited by Nyabyenda, 2005; cited by [3, 4]). The soybean-producing provinces in the DRC vary depending on the period. From 2000 to 2004, it was the province of Katanga that produced the most with more than 40% of national production, followed by Bandundu and Equateur (SNSA, nd quoted by [7]). According to the National Agricultural Statistics Service (2012 and 2021), the provinces producing soybeans in the DRC during the period from 2000 to 2006 are Kasai Occidental (7376 tons/year), Bas-Congo (1588.3 tons/year), Equateur (1363 tonnes/year), and North Kivu (1141 tonnes/year). In 2019, Central Kongo, South Kivu, North Kivu, and South Ubangi were the largest soybean-producing provinces with 2552 tons, 1918 tons, 1907 tons, and 1405 tons of annual production, respectively [8].

Several activities, influenced by the varied uses of soybeans and the need for adaptability to different agroecological zones and cultural practices, have been carried out in favor of this crop since its introduction in the country until today. They have allowed growers to hold a large number of varied materials. Some work has contributed to the evaluation of the diversity of materials in the DRC gene pool as well as their improvement and the selection of genetically varied, productive, and adapted lines according to the environments across the country. However, there are no documents that bring together information that can provide breeders and decision-makers with elements to guide and develop soybean improvement strategies. This is why this document traces the activities and methods used in the DRC to genetically improve soybean cultivation. It provides key elements to breeders that will enable them to guide and develop successful soybean improvement strategies using existing materials under the conditions of the DRC.

1.1 History of the introduction of soya in DRC

The date of introduction of soybeans into tropical Africa, from its domestication in Northeast China around the 11th century BC, remains obscure. Nevertheless, its cultivation was reported in Tanzania in 1907 as well as in Malawi in 1909. But everything suggests that this plant was introduced during the 19th century by Chinese merchants, very active along the eastern coast of Africa (Auckland, 1970 cited IITA, 1982; cited by [9]). It was introduced in 1915 in DRC. Subsequently, research began with the introduction of new varieties, the creation of lines better adapted to various regions of the country [6, 10, 11], but cultivation was not a priority. Nowadays, soybeans are grown in different regions as multipurpose secondary food plants, forage plants, and green manure.

Extensive germplasm exchange has taken place around the world with international research centers such as IITA, INTSOY, CIAT, as well as AVRDC and has resulted in PNL holding up to 152 varieties of soybean in its collection [12]. In 1993, the lack of financial means and the looting of INERA’s infrastructures reduced the level of activities to be limited only to the maintenance of materials and collections. Currently, INERA has several varieties of soybeans, cowpeas, and beans in its centers, particularly in Mulungu, Gandajika, and Mvuazi, which have been developed by its researchers but which have not yet been disseminated among farmers [7].

2. Research work on soya in DRC

Soybean is ranked among the top priority crops for research in the DRC with regard to legumes in high altitude tropical regions (Nyabyenda, 2005; cited by [3, 4]). Until 1970, INERA only introduced and adapted varieties, as well as maintained collections of different species of grain legumes in its research centers. The new foreign varieties were tested in the stations, before being brought to the peasants for popularization among the indigenous populations. The creation of the National Leguminosae Program (PNL) in 1983 allowed the intensification of multidisciplinary research on grain legumes in the DRC, with specific activities for this sub-sector (varietal selection, production systems, pathology, entomology, etc.). It has enabled the development of certain varieties of soybeans [7].

In addition to breeding work, research is also being done on disease control methods and postharvest and feeding technologies. Studies on cultivation techniques mainly concern sowing systems, sowing dates, fertilization, and associations of soybeans with other crops. Significant research is also being done on soybean inoculation and nodulation, identification and selection of effective Rhizobium strains, inoculum production, and its popularization (Nyabyenda, 2005; cited by [3, 4]).

To solve the problems related to the low chemical fertility of the sandy soils of the Kinshasa hinterland and to increase the productivity of tropical soils, Kasongo et al. [13] realized that the application of Kanzi phosphate and pink dolomite from Kimpese soil significantly stimulates the uptake of Ca, Mg, P, and K and significantly increases nodulation, dry matter, and seed yield of soybeans. Post-cultivation soil analysis reveals that amended soils contain, in some cases, nutrients (Ca, Mg, N, and P) that can produce long-term beneficial residual effects. In addition, the significant increase in pH generates a substantial increase in CEC with complete neutralization of aluminum phytotoxicity.

3. Morpho-agronomic characterization of accessions from the DRC genetic pool

With the support of the Canadian International Development Agency (CIDA), studies have been carried out on the molecular and morphological characterization of soybeans from the Democratic Republic of Congo gene pool in order to obtain knowledge on the behavior of soybeans and of its variability and promote efficient use and rational conservation of biodiversity. Indeed, the knowledge of the genetic variation and the description of the accessions available in the collection are of great necessity. They make it possible to identify those that are productive and that can be adapted according to the different agroecological zones and allow the choice of materials to be used and strategies to be adopted in the improvement program. Knowledge of the genetic variation also helps to understand changing relationships between accessions, improve germplasm sampling, and increase conservation efficiency [14]. Gene pool material represents a reservoir of genetic resources for soybean genetic improvement. The same is true of materials held by farmers that can be integrated into a regional genetic improvement program [15, 16].

Phenotypic identification based on morphological description is a fundamentally important step for the rational management of collections and knowledge of genetic diversity. It is a simple and quick way to estimate the genetic variation likely to be used in the improvement of cultivated species (Smith and Smith, 1992 cited by [17]).

Some results obtained by Mudibu et al. [3, 4] and Mudibu et al. [18] relating to the morpho-agronomic characterization of soybeans from the DRC gene pool are presented in Tables 1 and 2. Field experiments were conducted over 2 years (2008 to 2010) at two sites in Gandajika. They were also conducted over two agricultural seasons (November 2015 to February 2016 and March 2016 to June 2016) at two sites (commune of N’sele and the agricultural site of Kinkole). The plot at each site was plowed and ridged at spacing of 0.75×0.5 m. Gross plot size was 5 m long and 1.5 m wide. Two seeds were sown at every 10 cm to a depth of about 2 cm. The experiment was a completely randomized block design with three replicates. The trials were conducted with no fertilizer or pesticide applications. They provide data on the variability of this species. Indeed, the cultivation and improvement of soybeans require a good knowledge of the accessions available in the collection and the selection of those that are productive and adapted to the environment where they are to be cultivated.

Accessions	Observed and measured parameters
	Number of pods/plant	Weight of seeds/ha,	Height of plants cm	Collar diameter mm	Number of leaves per plant	Number of days to flower	Leaflet shape	Pod color	Seed color
AFYA	102,0	2.449,6	40,7	8,3	35,5	48,5	lanceolate	light brown	pink beige
AFYA Kiyaka	31,0	904,0	33,5	6,8	32,0	52,8	rhomboid-lanceolate	light beige	light beige
BOTULA 1	64,0	1.741,3	36,5	7,0	20,8	38,0	rhomboid-lanceolate	caramel	light beige
BOTULA 2	57,0	1.149,7	41,2	6,1	32,0	38,0	rhomboid-lanceolate	pink beige	brown
BWAMANDA	84,0	1.739,7	42,7	10,1	38,5	48,5	lanceolate	light brown	light beige
DAVIS	35,0	1.147,0	16,7	6,8	19,5	35,5	lanceolate	pink beige	curry
IMPERIAL	91,0	2.137,2	46,2	8,9	43,7	48,5	rhomboid-lanceolate	light beige	curry
KAMBULUKU	67,0	1.765,3	32,0	6,4	23,0	47,5	lanceolate	ochre yellow	pink beige
KENSOYA I	33,0	1.128,7	14,8	4,4	14,7	35,5	rhomboid	havana	light beige
KENSOYA II	49,0	1.708,7	31,0	7,1	21,2	33,8	oval	havana	light beige
KITOKO	75,0	2.036,0	37,2	8,9	33,7	51,0	rhomboid-lanceolate	light beige	light beige
MELOC	45,0	1.319,3	36,0	11,1	38,2	52,0	rhomboid-lanceolate	light beige	pink beige
NAMSOI 4 M	72,0	1.930,3	40,0	7,4	21,7	48,5	lanceolate	pink beige	curry
NI	69,0	1.541,2	39,2	7,9	29,3	47,8	lanceolate	light beige	light beige
N05	54,0	2.324,7	43,5	9,7	29,5	38,0	rhomboid-lanceolate	light brown	curry
ORIBI	80,0	2.898,0	15,8	6,0	17,7	38,0	oval	light beige	light beige
PKO6	36,0	1.196,0	19,0	5,6	20,7	35,5	oval	ochre yellow	curry
SAPRO	31,0	1.343,2	23,8	6,6	16,3	35,2	rhomboid-lanceolate	light beige	curry
SB4	65,0	2.054,2	21,2	7,5	28,0	37,0	rhomboid	ochre yellow	curry
SB19	59,0	1.545,5	35,5	7,0	28,5	41,3	rhomboid-lanceolate	light beige	light beige
SB24	33,0	1.233,8	16,3	7,2	18,0	37,0	oval	caramel	pink beige
SENASEM	89,0	2.389,7	34,5	7,1	31,8	50,0	rhomboid-lanceolate	light beige	light beige
TGM 1196	68,0	1.900,3	52,3	9,2	26,8	46,5	lanceolate	caramel	curry
TGX 814-26D	74,0	2.594,3	31,3	8,6	30,8	48,5	rhomboid-lanceolate	light brown	light beige
TGX 814-49D	84,0	1.776,8	36,8	6,8	34,7	46,5	rhomboid-lanceolate	light beige	curry
TGX 888-49F	68,0	1.390,7	34,2	6,3	21,0	49,7	lanceolate	light beige	light beige
TGX 1485-1D	40,0	1.153,7	19,8	5,9	17,7	37,0	rhomboid-lanceolate	light beige	light beige
TGX 1485-1D LUB	57,0	1.319,8	45,3	7,9	41,5	38,0	rhomboid-lanceolate	light beige	light beige
TGX 1740-7F	74,0	1.004,2	49,2	6,4	28,7	40,0	lanceolate	light beige	curry
TGX 1879-9F	36,0	1.095,2	35,5	8,0	28,5	47,5	rhomboid-lanceolate	light beige	light beige
TGX 1879–13E	79,0	1.732,2	35,7	8,9	44,2	49,0	oval	ochre yellow	light beige
TGX 1879-9E	97,0	2.060,0	31,2	9,2	21,2	49,0	lanceolate	ochre yellow	light beige
TGX1880-3E	60,0	1.770,3	24,2	8,1	34,3	37,0	lanceolate	light beige	light beige
TGX1888-29F	104,0	2.641,2	23,0	5,3	23,5	50,0	rhomboid-lanceolate	light beige	light beige
TGX 1895-33F	86,0	1.989,8	43,2	7,9	27,2	50,0	lanceolate	creamy pink	light beige
TGX 1895-49F	67,0	1.933,3	32,2	7,0	25,2	51,0	lanceolate	light beige	pink beige
TGX 1904-2F	54,0	1.278,3	16,2	4,8	16,3	37,0	rhomboid	havana	light beige
TGX 1908-6F	105,0	2.854,5	41,2	7,8	31,2	49,0	lanceolate	light beige	light beige
VUANGI	65,0	1.528,2	38,2	7,0	35,3	48,5	lanceolate	pink beige	light beige
ZAIRE 196	59,0	650,0	30,8	6,3	16,0	53,0	rhomboid	caramel	light beige
Lsd (p ≥ 0.05)	4,7	90,4	2,1	0,5	1,6	0,3

Table 1.

Number of pods/plant, weight of seeds/ha, height of plants, collar diameter, number of leaves per plant, number of days to flower, leaflet shape, pod color, and seed color in the soybean trials installed in Gandajika.

Accession	Plant Height	Number of branches per plant	Stem diameter	Number of pods per plant	Number of seeds per plant	Weight of 100 seeds	Grain yield per hectare
AFYA KIYAKA	36,2	4,3	4,6	42,3	98,3	12,2	5905,5
BOTULA I	38,9	2,9	5,1	28,3	54,6	15,2	2974,4
BOTULA II	48,6	4,1	4,2	53,5	91,2	8,2	1845,2
DAVIS	39,8	3,3	3,4	51,3	91,6	11,5	5668,4
KAMBULUKU	35,4	4,6	10,1	53,0	99,3	14,9	7094,4
KEN SOYAII	28,8	3,5	4,3	44,8	82,6	11,5	2909,4
KITOKO	32,8	3,0	3,7	27,3	44,3	11,9	5983,3
MELOC	48,0	4,0	4,8	62,8	112,8	12,9	1174,4
N°5	52,7	4,0	6,9	52,6	85,6	19,3	9549,9
NAMSOI4m	61,3	2,5	7,1	31,7	62,9	16,4	259,7
NI	34,9	3,6	5,6	52,2	95,9	11,1	366,5
ORIBI	24,9	3,0	5,1	45,6	50,3	14,3	4422,2
PKO6	29,6	2,6	5,5	38,6	77,4	12,4	355,3
SAPRO	32,3	4,0	5,6	34,4	67,4	14,3	3221,3
SB19	35,6	3,5	4,0	53,6	98,9	11,5	541,8
SB 24	46,8	5,3	6,6	86,6	154,3	11,6	5855,5
TGM 1196	48,1	2,7	5,6	30,8	57,6	15,3	3684,2
TGX BWAMANDA	35,4	3,6	8,4	65,4	110,7	11,0	282,6
TGX 1485-1D	29,8	2,6	2,9	20,5	45,2	12,8	2739,7
TGX1485-1DLub	38,6	4,2	5,5	61,8	112,8	12,5	3120,1
TGX1740-7F	41,8	4,1	5,5	49,1	94,5	13,2	3087,8
TGX 1879-9F	41,5	3,8	5,3	61,9	111,1	13,1	3269,6
TGX1879-13E	42,3	4,0	6,3	46,5	108,3	10,3	530,7
TGX 1895-33F	38,7	4,3	5,9	55,3	118,3	10,3	4938,8
TGX 1904-2F	27,3	3,3	3,1	34,3	65,6	12,9	5616,6
TGX1906-6F	41,0	4,3	5,7	58,0	125,7	14,5	2915,0
TGX 814-26D	32,8	4,3	4,1	69,6	129,0	11,8	5710,9
TGX814-49D	36,2	4,7	4,4	55,1	99,8	12,6	3015,6
TGX888-29F	32,6	4,2	3,7	50,5	86,2	11,9	3008,3
TGX888-49F	38	3,6	4,9	50,2	94,0	11,5	2721,4
TGX KOLOFUMA	50,5	6,3	10,4	92,7	158,6	12,4	6146,1
LSD	2,65	0,70	0,96	9,22	8,25	0,99	586,25
CV (%)	4,19	0,70	10,92	11,21	5,43	4,77

Table 2.

Plant height, stem diameter, number of branches per plant, number of pods per plant, number of seeds per plant, weight of 100 seeds, and grain yield per hectare in soybean accession on soybean trials installed in the outskirts of Kinshasa by Mudibu et al. [18].

Source: Mudibu et al. [18].

On reading the results given in Table 1, it appears that the average values of the number of pods/plant, weight of seeds/ha, height of the plants, diameter at the collar, number of leaves per plant, and number of days for the flowering vary, respectively, from 31 to 105 pods/plant, 650 to 2898 Kg of seeds/ha, 14.8 to 52.3 m, 4.4 to 11.1 mm, and 14.7 to 44.2 leaves per plant.

This evaluation is important for breeding programs, but particular soybean varieties are adapted to specific agroecological regions, and phenotypes are highly influenced by environmental factors (Li and Nelson, 2001; cited by [3, 4]). The analysis of morphological variability and agronomic characteristics of soybean accessions showed the presence of a high level of variability within the gene pool of Congo. The data indicate that 39.5% of the studied accessions of the soybean collection in DR-Congo had lanceolate leaves, 36.7% rhomboid-lanceolate leaves, 13.2% oval leaves, and 10.5% rhomboid leaves. At the level of the organs of production, 47.4% of accessions have light beige pods, 10.5% light brown pods, 10.5% caramel pods, 10.5% ocher yellow pods, 7, 9% beige pink pods, 7.9% tan pods, and 5.2% cream pink pods. About 61% of accessions had light beige-colored seeds, 26% curry, and 13% beige pink. All the quantitative characters measured showed differences between the accessions used. The heights of the accessions are between 14.8 and 52.3 cm of the accessions studied; 75% did not reach 40 cm in height. Plant height at maturity is an important characteristic in soybean germplasm and cultivar evaluation. Most current commercial soybean cultivars are less than 1 m tall. Within the USDA soybean collection, the plant height varied from 0, 2 to 3 m (Chen, 2002; cited by [3, 4]). Grain yield is one of the most important selection criteria used by breeders; it is controlled by many genes and is strongly affected by environmental conditions.

The mean values of plant height, stem diameter, number of branches per plant, number of pods per plant, number of seeds per plant, weight of 100 seeds, and grain yield per hectare are presented in Table 2.

Height of the plants at flowering indicates that the NAMSOI4m (61,3 cm) accessions have a higher height than the other accessions. The lowest height was observed in ORIBI (24,9 cm). The highest stem diameter at collar was found in the TGX KOLOFUMA (10,4 mm), and the lowest was observed in TGX 1485-1D (2,9 mm). The number of ramifications per plant at maturity show that the TGX KOLOFUMA (6,3) has a higher number of branches than the other accessions. The results indicate that TGX KOLOFUMA (92,7 pods per plant) has a higher number of pods per plant than the other accessions. TGX 1485-1D (20,5 pods per plant) produced fewer pods. The average number of seeds per plant indicates that the accessions TGX KOLOFUMA (158,7 seeds per plant) produced more seeds per plant and KITOKO (44,3 seeds per plant) produced fewer seeds per plant. Weight of 100 seeds varied from 8,2 g for BOTULA II to 19,3 g for N°5.

There were significant differences among the mean grain yield of accessions. The highest yield was obtained with the cultivated plants of Accession No 5 (9550 Kg/ha), followed by KAMBULUKU (7094,4 Kg/ha). The accessions SB19 (541,9 kg/ha), TGX1879–13 E (530,8 Kg/ha), NI (366,6 Kg/ha), PKO6 (355,3 Kg/ha), TGX BWAMANDA (282,7 Kg/ha), and NAMSOI4m (259,7 Kg/ha) are the least productive accessions.

The results obtained highlight the heterogeneity that exists among the accessions. The grain yield obtained from these trials varied from 259,7 to 9549,9 Kg/ha. The yields obtained by Mudibu et al. [3, 4] with the same accessions in the agroecological conditions of Gandajika in the DRC are generally low. Accessions with the lowest yields are probably the least adapted genotypes of the agroecological conditions on the periphery of Kinshasa. The differential response of varieties to different environments has been reported by several authors.

4. Work on the selection

The selection methods applied to soybean, which is an autogamous plant, aim to create purified lines, with high yields, resistance to the main diseases and existing enemies in a well-defined ecology, non-dehiscent pods, and so on [15]. They include, among others, the choice of starting material, the combination of desired characteristics, the selection of desired genotypes, the continuation of breeding work toward a new cultivar, and the maintenance and propagation of the new variety [19].

Even if other priorities have gradually emerged, the primary objective of the various breeding programs is still to obtain varieties with high productivity. Indeed, all over the world, the purpose of selection was to develop improved cultivars with a high and stable seed yield, resistance to the main diseases and pests, tolerance to the toxicity of Aluminum, resistance to lodging, pod indehiscence, generalized nodulation, seeds with improved longevity, acceptable colors, and good oil and protein content.

4.1 Obtaining lines by crossing and selection

Soybean selection and genetic improvement efforts in the DRC have focused on mass selection of segregating populations and on varietal selection [5]. Selection criteria based on adaptability, resistance to major diseases, efficiency, and other yield components were used as evaluation parameters; these from observation nurseries to multi-local trials, regional trials, and real-world trials [20]. Other objectives such as combining the “large grain” character with the “good conservation of germination power” character of local selections were also pursued in Yangambi [5].

In several countries of Central and Eastern Africa, varietal selection is based on material introduced from IITA or INTSOY and aims to identify varieties that are highly productive and acceptable to users and varieties with short vegetative cycle and disease resistance. Intensive germplasm exchanges have taken place around the world with international research centers such as IITA, INTSOY, CIAT, as well as AVRDC and have enabled the National Leguminosae Program (PNL) to hold up to 152 varieties of soybeans. In his collection [12]. In 1993, the lack of financial means and the looting of INERA’s infrastructures reduced the level of activities to be limited only to the maintenance of materials and collections. INERA has in its centers, notably that of Mulungu Gandajika, and Mvuazi, several varieties of soybeans that are not yet distributed in rural areas [7].

It was toward the end of the 1970s that soybean cultivation was greatly promoted thanks to the legume project (Project 064) that the government had set up at the Mulungu station, with the financial support of USAID. It has allowed the introduction of several dozen varieties of soybeans into the country. The breeding program conducted by IITA from the 1980s aimed to combine the yield potential of cultivars with natural nodulation ability. This program produced a series of excellent multipurpose cultivars combining a leafy habit with satisfactory seed type and high yield potential. We begin the selection that consisted, in this case, in the creation of better and better adapted lines. Some research stations did not do this work; the best varieties were all imported.

The effort to disseminate soybean cultivation in the DRC already existed, especially in the context of the fight against malnutrition, especially among children in mainly missionary hospitals and Development Centers [5]. To introduce soybean cultivation in a region, it was first necessary to import a complete collection of foreign varieties [21], after which the best acclimatized and the most promising were chosen.

In Yangambi, the pronounced shortening of the duration of vegetation of all foreign varieties, followed by a correlative reduction in yield, led breeders to lengthen the vegetative cycle [21]. We resorted to hybridizations with in particular the Sj10 (local), DAVIS, and EQUADOR (American) varieties to combine the “large grain” character with the “good conservation of germination power” character. Hybridizations have also been used to exploit the tolerance of local breeds to bacterial blight, lodging, and dehiscence [22].

Several varieties of soybeans have been selected and proposed for dissemination by the PNL [20] in the low-altitude regions of the DRC. These include UFV – 1, TGx814-26D, TGx849 – 294D, and IAC 73-5115. In the INERA collection [5], there were 60 varieties but with the loss of 4 varieties (S38, Bc/1/66, TAINUNG no4 and TUNIA). During this year, INERA received three new varieties from IRAT France (ISRA 22-72, ISRA 26-72, and ISRA 44A – 73). The varieties released during the 1980s to 1990s are: SJ 127, SJ 61/1, VEF 1, TGX 573-2090, TGX849 – 249D, Siatsa, SAM 86, Herno, Patience, TGX814-26 D, IAC-6, and ICAL 106 [3, 4].

In Kasese, for industrial crops, two varieties were used: Jupiter and TGm 294-4-b; in other regions, S17 and S14 hybrids created in Yangambi or black Otootan were grown. In Katanga, the SJ 1 variety was often used as a cover crop [11]. Some of these soybean varieties have been replaced by those currently released: AFYA, TGX814-26D, KITOKO, Siatsa, TGX573 – 209D, and VUANGI [23].

In Gandajika (Province of Kasai Oriental), one of the major soybean research centers that hosted the National Leguminosae Program (PNL), soybean has been cultivated since colonial times and is a food appreciated mainly by children who consume it in the form of dumplings in the sauce nicknamed “Mabulu”. The varieties used by PNL report yields varying between 1146 and 2500 kg/ha, slight dehiscence, good nodulation but associated with high lodging following heavy rains and pod weight [20]. The varieties distributed at the time, in particular AFYA, TGX 814-26 D and TGX 1906-6 F, were subject to attacks by several enemies (diseases especially of the bacteriosis type, pests, and weeds), which induce significant losses. They have been abandoned by the farmers because of the low level of yields and their instability. Pests and weeds that affect yields are Ootheca mutabilis and Alectra vogelii species, respectively.

In Mulungu, soya has been adopted by the population and has become part of their eating habits. This made it possible to solve the problem of malnutrition in the region and to constitute a collection of 152 accessions thanks to the financial support of USAID within the framework of the RAV project. The international trials (SPOT3712 trials, ASET trial, MUSHWESHWE, and Idjwi Island) consisted of evaluating the adaptability of INTSOY varieties to DRC conditions and evaluating their performance compared to local varieties. Soybean research has also contributed to the increase in soybean production and consumption. Extension is done to some extent through faith-based organizations and through the Anti-BWAKI committee in the mountainous Kivu region.

Research results at MULUNGU have made it possible to refine existing varieties and increase germplasm with the collaboration of international research institutes (IITA, INTSOY, etc.). Varieties adaptable to ecoclimatic conditions have been identified: IR09, IMPERIAL, TOKOY VERT, JUPITER, and so forth. Farmers’ farming techniques have also been improved with the installation of demonstration fields. The research methods showed certain weaknesses in Mulungu because of the fact that:

• The research methods were not standardized (test protocol, analysis and observation methods, etc.)

• The research themes did not respond to the specific problems encountered in the field by the farmer

• The tests were repeated but were not defined in time or space; hence, the conclusions were not in accordance with the truth.

• The work was more oriented toward international trials while neglecting national trials that solve specific local problems.

At the INERA KONDO station, research activities on soybeans consisted of varietal trials and the renewal of materials in the collection. The varieties kept in collection for seed production are G17, SJ127.

In M’vuazi, research consisted of the introduction, study of adaptation of new cultivars, and maintenance of the collection. The best varieties were propagated. These are UFV1, AGS66, DUOGROP, and so on.

The main problems encountered in this INERA station are related to the number of researchers and technicians. The level of scientific training of the staff was low. To remedy this, on the one hand, we had to resort to experts from high-level bilateral projects who should supervise and train INERA staff in the field. On the other hand, materials and logistics have been reinforced thanks to funding from the Common Market, UNDP, and IITA. The varieties introduced were V50 (originating from Nigeria), Sj70, and DEBMAR43 (originating from the USA) with yields ranging from 600 to 950 Kg/ha on average. Research has made it possible to identify and popularize the most productive cultivars.

4.2 Obtaining lines by radiation-induced mutations

The General Commission for Atomic Energy (CGEA) mainly has two tools (reactor and Cesium irradiator) that allow it to use radio-mutagenesis to obtain new varieties (mutants) bearing sought-after characteristics (plant architecture, disease resistance, early or late maturity, high yield, oil or protein composition, etc.). Radio-mutagenesis has extended the genetic variability of soybean cultivars in the DRC. Indeed, nuclear techniques, in particular treatment with ionizing radiation, have enabled the DRC, through the CGEA, to provide the Ministry of Agriculture with soybean lines with high levels of lysine and histidine [24, 25].

Radiation-induced mutations are an additional method that supports conventional crop improvement. After formulating the objectives of the mutational plant breeding program, the production of new cultivars begins with the choice of starting materials, which is the most important decision in a plant breeding program [19]. The best available and well-adapted material is selected from high-yielding cultivars. Breeding aims to develop improved cultivars with high and stable seed yield; resistance to the main fungal, bacterial and viral diseases, and pests; resistance to lodging, pod indehiscence, and generalized nodulation; and seeds with improved longevity, acceptable colors, and good oil and protein content. Only one character can be changed per mutation.

We start by subjecting soybeans to mutagenic treatments. Preliminary experiments are carried out in order to determine the optimal dose, that is to say the dose at which a maximum number of mutations is induced. For economic reasons, the first experiments are limited to M1 observations with a few hundred objects per dose and cultivar. There is also recourse in the literature to experiments that have succeeded with similar objectives. The results of mutagenic treatments are estimated with the M1 and M2 generations. A general idea of the efficacy of a mutagenic treatment (number of mutations per unit dose) can be obtained from the frequency of easily detectable mutational changes such as changes in chlorophyll or certain morphological characters within M2 populations. Based on these results, the main experiment is launched with the same starting material under identical conditions with the best processing method. In practice, decisions about “more appropriate” mutagenic treatments are often based on extrapolation from various effects of these treatments using parameters that can already be observed in M1, such as reduction in germination, seedling height, seed survival, and appearance of chlorophyll defects in M1. Mutagenic treatments can have a detrimental impact on a wide range of characteristics of the plant material (M1) treated.

Improvements can be identified and confirmed with varying degrees of difficulty depending on the character by statistical methods. Furthermore, the value of quantitative traits is variable and influenced by the interaction between genotype and environmental factors. Mutation selection methods for qualitative and quantitative traits differ. The recessive characters are mono-genetically controlled; their selection can start in M2; the selection of mutants for the quantitative characters must be postponed at least until M3 and continue in the following generations. Most mutants often show reduced vitality, possibly due to pleiotropic effects of mutated genes or due to additional mutations in their genome (Brock, 1965 and Brock and Micke, 1979 cited by [19]).

The complete breeding program can take 6–8 generations. The multi-local test phase often comes later due to a lack of financial and logistical means. For example, the lines obtained by CGEA researchers before the year 2000 (BOTULA I and BOTULA II) were submitted to multi-local tests in 2008. The application for plant breeders’ rights took a long time. The crucial step in a plant breeding and breeding program is the propagation and maintenance of these new cultivars. Often after mutagenic treatment, several million genes present in the plant change. The breeder, in some cases, can direct improvement for a small number of traits by eliminating plants that do not carry the desired traits.

Research by Mudibu [9] determined the effects of different doses of gamma irradiation of seeds on different morpho-agronomic traits and identified mutants with high seed yield potential. Indeed, the seeds of the TGX814-49D, Kitoko, and Vuangi varieties were irradiated in the LISA 1 CONSERVATOME brand irradiator with a Cesium-137 source at the Regional Center for Nuclear Studies in Kinshasa (CRENK) at doses of 200, 400, 600, and 800 Grays of gamma rays. The results obtained showed that in general, the treatment of seeds with gamma rays at doses of 0.2 KGy and 0.4 KGy led to a significant reduction in most of the morphological characters (number of leaves, plant height, collar diameter, etc.) on M1 plants.

On the other hand, in the M2 plants, there is no significant difference in the plants resulting from the seeds irradiated at the dose of 0.2 KGy with the control plants with regard to the size of the plants and other morphological characters for the three varieties studied. Treatment at a dose of 0.4 KGy of M2 induced a significant reduction in plant height, number of leaves/plant, and leaflet width. No significant difference was observed for the number of days for flowering of 50% of the plants in the two generations, M1 and M2, for the different treatments.

The results in relation to the weight of seeds per hectare obtained by the varieties used on the two sites during 2 years of experimentation for M1 and M2 are respectively presented in Tables 3 and 4.

Accessions	Doses d’irradiation (KGy)	Weight of seeds/ha Kg/ha)
		Sites et années				Moyenne
		INERA année1	INERA année2	MPIANA année 1	MPIANA année 2
KITOKO	0	1.831,8 ± 139,5	2.873,1 ± 150,0	1.937,2 ± 149,7	1.981,9 ± 108,8	2.156 ± 137
	0.2	972,2 ± 51,4	1.496,6 ± 114,1	1.201 ± 123,9	1.158,2 ± 58,6	1.207 ± 87
	0.4	965,6 ± 97,8	1.065,2 ± 101,1	1.133,6 ± 92,6	599,6 ± 28,5	941 ± 80
	Moyenne	1.256,5	1.811,6	1.423,9	1.246,5	1.434,6
VUANGI	0	1.640,6 ± 171,3	1.948,4 ± 196,3	1.237,6 ± 124,4	1213,4 ± 160,0	1.510 ± 163
	0.2	1.066,2 ± 177,1	1.582,4 ± 189,2	865,2 ± 108,5	826,2 ± 49,2	1.085 ± 131
	0.4	517,4 ± 93,2	798,2 ± 82,1	204 ± 27,5	176,4 ± 69,2	424 ± 68
	Moyenne	1.074,73	1.443	768,9	738,6	1.006,3
TGX 814-49D	0	1.695,6 ± 216,8	2.061,2 ± 205,6	1.741,6 ± 169,1	1.413,6 ± 84,5	1.728 ± 169
	0.2	852,8 ± 107,9	1.181,4 ± 120,6	873,3 ± 104,0	720,5 ± 63,5	907 ± 99
	0.4	239,24 ± 55,3	439,6 ± 61,5	579,2 ± 74,4	225,96 ± 12,8	371 ± 51
	Moyenne	929,213	1.227,4	1.064,7	786,687	1.002
LSD		120,4	126,3	89,4	104,9	110,2

Table 3.

Weight of seeds/ha of M1 plants from irradiated seeds.

Accessions	Doses d’Irradiation (KGy)	Weight of seeds/ha (Kg/ha)
		Sites		Moyenne
		INERA	MPIANA
KITOKO	0	3.051,4 ± 248,1	2.034,6 ± 109,9	2.543 ± 179
	0.2	2.356,8 ± 104,8	1.481,2 ± 137,2	1.919 ± 121
	0.4	2.427,1 ± 165,4	1.984,9 ± 106,6	2.206 ± 136
	Moyenne	2611,7	1.833,567	2.222
VUANGI	0	1.861,0 ± 167,6	1.165,0 ± 102,4	1.513 ± 135
	0.2	2.269 ± 241,8	1.285,0 ± 120,2	1.777 ± 181
	0.4	1.955,6 ± 119,4	1.452,4 ± 156,6	1.704 ± 138
	Moyenne	2028,5	1.300,8	1.664.9
TGX 814-49D	0	1.985,6 ± 143,8	1.752,4 ± 135,0	1.869 ± 139.4
	0.2	2.562,4 ± 200,4	1.587,6 ± 165,8	2.075 ± 183.1
	0.4	2.161,4 ± 155,9	1.480,6 ± 136,7	1.821 ± 146.3
	Moyenne	2.236,47	1.606,87	1.921.8
LSD		190,2	95,1	145

Table 4.

Weight of seeds/ha of M2 plants from irradiated seeds.

In the M1 generation, irradiation at all doses used significantly reduced seed yield compared to the control (plants from nonirradiated seeds) for all three varieties evaluated. In the M2 generation, in general, gamma irradiation significantly increased seed yield. The greatest increase in pod production was observed in the variety TGX 814-49D where a mutant plant progeny of seeds irradiated at the rate of 0.2 KGy produced 464 pods in the M2 generation compared to 64 pods per plant for the control treatment (Figures 1 and 2).

Figure 1.

Mutant plant with 464 pods progeny of seed irradiated at the rate of 0,2 KGy in M2 generation.

Figure 2.

Plant control with 64 pods.

This study clearly demonstrates that it is possible to improve seed yield and other agro-morphological characteristics of soybeans by using radiation-induced mutations.

5. Conclusion

Our objective is to bring together information that can provide breeders and decision-makers with elements to guide and develop soybean improvement strategies. This document provides key elements to breeders that will enable them to guide and develop successful soybean improvement strategies using existing materials under the conditions of the DRC. It has demonstrated that several activities, in particular, the exchange of materials between growers, the introduction of new materials and the tests of adaptability to different agroecological zones, and the obtaining of lines by crossing and by radiation-induced mutations, have made it possible the genetic pool of the DRC to hold a large number of varied materials. Soybean is usually grown in traditional production systems. The soybean producing provinces in the DRC vary depending on the period. There are results of work on the assessment of the diversity of materials in the DRC gene pool. Indeed, soybean accessions from the DRC gene pool were characterized using morpho-agronomic parameters and molecular analyses [3, 4]. The agronomic performances of genotypes from irradiated soybeans were evaluated. The use of seed treatments with ionizing radiation has made it possible to induce genetic variability and increase diversity within cultivated soybean varieties and germplasm capable of supporting a breeding program.

The use of ionizing radiation treatment of seeds has made it possible to induce genetic variability and increase diversity within cultivated soybean varieties and germplasm. The results of this research indicate that irradiation would be an adequate tool to increase the level of genetic variation in soybeans to support a breeding program. Other work has made it possible to improve and select lines that are genetically varied, productive, and adapted to environments across the country.

In perspective, it will be necessary to:

• Use intensive introductions and radiation-induced mutations to expand genetic variability and

• Establish collections of local materials scattered throughout the country