**9. Final considerations and benefits for developing countries**

**7. The role of genotype in soybean transformation**

32 Transgenic Crops - Emerging Trends and Future Perspectives

[57] in *Cajanus cajan*, *Secale cereale* L., *Zea mays* L. and *Triticum aestivum*.

It has been more than two decades, since the introduction of genetically modified plants established through *in vitro Agrobacterium*-mediated transformation. In soybean, the first successful transformation was reported by Hinchee et al. [58], using cotyledonary explants with *Agrobacterium* pTiT37-SE harbouring pMON9749 for herbicide glyphosate tolerance. The success in this method depended upon several factors; which included tissue culture conditions, strains of *Agrobacterium* used and the selected host plant genotypes aimed at receiving the transgenes. To date, this technique has succeeded in the production of high yielding transgenic plants, particularly for corn, chickpea, rice, cowpea, as well as a few new soybean cultivars [59–62].

Genetic transformation is now considered the most economic and highly effective method of genetic engineering that has been reported so far. The method holds the potential and promise to efficiently regenerate transgenic plants, especially for recalcitrant legume crops. Legumes like soybeans are some of the most important pulse crops and a good source of high quality proteins and oils, required for human consumption, health benefits and industrial processing. However, the vegetative and reproductive stages of soybean continuously show high sensitivity

**8. Efficacy of soybean genetic manipulation**

Several studies including those of Zhang et al. [51], Yan et al. [47], Paz et al. [52] and Li et al. [49] have showed that genetic transformation in soybean is highly genotype specific. According to the results in **Tables 4** and **5**, cultivar TGx 1740-2F and TGx 1835-10E were highly recalcitrant. These cultivars showed consistent difficulties for callus and shoot proliferation under used culture conditions. Consecutively, the highest number of shoots were induced in soybean cv. Peking, LS 677 and LS 678. This was followed by cultivar Dundee and lastly, the two TGx varieties. These soybeans gave the same morphogenic trend when cultured for *in vitro* regeneration in the controls. The reports cited above support this study by concurring with the findings made in this study. The generation of reactive oxygen species upon *Agro*-infection of explants leading to oxidative browning and subsequent tissue browning was also more prevalent in Dundee, TGx 1740-2F and TGx 1835-10E genotypes. The intensity of explant tissue browning and necrosis is a key indicator of explant proliferative or totipotency potential. However, the continued testing of different types and concentrations of antioxidants such as DTT may minimise cell necrosis and improve the transformation frequencies in soybean. The ability of genotypes to resist the influence of modified culture conditions aimed at regenerating new plants have been widely reported. Thirty-eight cultivars of *Gossypium* showed high, moderated, low and non-somatic embryogenic response under different regime of plant growth regulators. The level of responses did not change and genotypic variation for embryogenesis was found to exist as indicated by Trolinder and Xhixian [53]. Relatively low breeding progress, high self-incompatibility and inbreeding depression may be some of the factors encouraging genotype specificity and recalcitrance in many crops. Evidence of these effects were reported by Gawali et al. [54], Targonska et al. [55], Nguyen et al. [56] and Wang et al.

The findings presented in this study clearly indicate that, the induction of transformed callus tissues and regeneration of transgenic plantlets through cotyledonary node method of soybean transformation in tissue culture still present serious challenges. The study further highlighted poor plant tissue culture reproducibility, less culture efficiency and genotype specificity as some of the major obstacles. The lack of a stably routine transformation protocol for genetic manipulation of soybean will encourage transformation rates to remain at less than 10% efficiency. The lower transformation rates affect distribution of better transgenic cultivars availability for farmers, encourage the continued losses in yields and the deterioration of soy-products quality. This has a direct negative impact on the growth and well-being of many human lives, animals and countries' economy. Soybean could be a driving force behind the development of many economies, particularly in Africa. Country's growth and stability, food security and other United Nation related strategic goals will be achieved, if there is full commercial exploitation of benefits offered by important agro-economic crops such as soybean.

Genetic transformation is a tool that could guarantee continuous productivity of crops even under severe climatic conditions. Floods, chilling and drought are major causes of yield losses in many regions, particularly in developing countries. Crops like soybean, are considered major rainy season pulses [63] and their growth is highly sensitive to waterdeficit stress. Introduction of soybean cultivars with improved traits will immensely benefit farmers, enhancing cropping intensity and increased profitability per unit land area as discussed by Agarwal et al. [63]. Soybean will continue to remain a major oilseed crop. Its potential use in industrial production of biodiesel, current pharmaceutical and nutritional uses still encourages improvement of modern and conventional breeding systems. The systems need to be improved in order to develop novel varieties that meet the current environmental challenges, raise yields to unprecedented levels and feed the world-wide increasing populations. Finally, the success in the development of new varieties will allow for the incorporation of soybeans in daily diet. In developing countries for example; South Africa, soybean is used mainly for the manufacturing of animal feeds and vegetable oil. Direct human consumption of soybean makes a very smaller portion of the population's diet as indicated by Dlamini et al. [64].
