Volume 1 Number 2 2007

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CONTENTS AND ABSTRACTS

Jutta Schulze (Germany) Improvements in Cereal Tissue Culture by Thidiazuron: A Review (pp 64-79)

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Invited Review: This article reviews research to establish highly regenerative cell and tissue culture systems in cereals and grasses as a prerequisite for crop improvement using biotechnological methods. The strategies were described in the historical framework of investigations in this field and then new approaches were discussed focussing on the considerable recent progress made using the cotton defoliant thidiazuron (TDZ) for enhancement of morphogenic competence in the Poaceae during the last 15 years. In 1982, TDZ was first described to have cytokinin-like activity and subsequently, numerous studies have characterized this compound as a powerful plant growth regulator for dicots with special emphasis on recalcitrant leguminous and woody species. However, TDZ was evaluated for cereal tissue culture with a remarkable delay. The results summarized clearly showed that TDZ can significantly improve morphogenic response from callus derived from a wide range of explants concerning frequency of shoot formation, number of shoots per explant and the time needed for shoot induction compared to other cytokinins. Moreover, TDZ has been used effectively for establishment of shoot meristematic cultures from model and agronomically important cultivars using shoot apices, shoot meristematic segments as well as nodes and pronounced differences were obtained regarding shortening of the time frame especially for barley and wheat. Besides that, high frequency plant regeneration with long-term retention of morphogenecity in a relatively genotype-independent manner was observed. Nevertheless, in a few cases problems associated with the use of TDZ were noted. The data summarized imply that TDZ is also a potent growth regulator for cereals which (i) further minimizes the recalcitrant nature of the Poaceae and which (ii) extends the application of transformation protocols to elite genotypes and to more readily available explants.

Maria Alexandra Jorge (Ethiopia), Marjatta Eilittä (USA), Fiona Janice Proud (Ethiopia), Barbara V. Maasdorp (Zimbabwe), Hanna Beksissa (Ethiopia), Ashok K. Sarial (India), Jean Hanson (Ethiopia) Mucuna Species: Recent Advances in Application of Biotechnology (pp 80-94)

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Invited Review: Biotechnology techniques have been widely used for legumes - important crops with excellent nutritional characteristics and soil improvement qualities. Limited work has been carried out with underutilized legume crops such as velvet bean (Mucuna spp.), which have great potential for multiple uses. In recent decades, there has been increased interest in the potential of Mucuna spp. as a cover crop and green manure for tropical and subtropical regions. Mucuna is also used as a minor food crop in many countries and interest in it as livestock feed - a common use for it in the early 1900s in the USA and elsewhere - is growing. Other minor uses exist, such as roasting the seeds as a coffee substitute. More importantly, L-dopa, extracted from Mucuna bean seeds and plants, is used for symptomatic relief of Parkinson’s disease. Despite these numerous qualities, some constraints have limited its adoption. Biotechnology techniques can provide a window of opportunity for new or expanding products of Mucuna. Earlier biotechnology work with Mucuna was mostly related to its medicinal uses and focused on the mechanism of L-dopa production. More recently, biotechnology has also been applied to identify the major virus diseases affecting Mucuna, to develop new diagnostic methods for early virus indexing of in vitro plants and to clean virus diseases using meristem and thermotherapy techniques, as well as to study genetic diversity through the use of molecular tools. There are still niches to be explored such as the numerous phytochemical qualities of Mucuna that can be used to benefit human and animal nutrition and health as well as the environment through use of these compounds in natural weed and pest control management.

Ariel R. Vicente, Gabriel O. Sozzi (Argentina) Ripening and Postharvest Storage of ‘Soft Fruits’ (pp 95-103)

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Invited Review: The terms ‘soft fruit’ have been used to refer to different commodities including strawberries, blueberries and several species of the genus Rubus. Most work in ‘soft fruit’ ripening regulation has been done on strawberry. Auxin has been shown to be a repressor of several ripening-associated genes which led to hypothesize that reduction in auxin levels in the receptacle could activate those genes. Despite that, some evidence suggest that that is only part of the story and that other factors are also involved in the regulation of ‘soft fruits’ ripening process. Softening is one of the most dramatic changes observed in ‘soft fruit’ ripening. Early reports on strawberry stated that the average molecular size of hemicelluloses greatly declines during ripening. In contrast, later work showed that pectin size is reduced while only slight depolymerization occurs in hemicellulosic polymers. Pectin metabolism has recently shown to be a major modification accompanying softening in species of the genus Rubus. Contrarywise, a reduction in glucan content and downshifts in hemicellulose molecular size are the main changes observed in blueberry. Extension of ‘soft fruit’ postharvest life has been an ongoing challenge. Strategies to reduce ‘soft fruit’ losses include selection of firmer genotypes and optimum postharvest handling procedures. A single postharvest technique is unlikely to fully control postharvest losses but new tools such as UV radiation, heat treatments or chitosan coatings may be added to the overall management plan (cooling conditions, modified atmospheres) to further delay softening and prevent decay losses. Biotechnology may be useful to address some of the concerns about bramble quality attributes (e.g. increased fruit firmness, improved flavor) and engineered resistance may be a sustainable method to control Botrytis cinerea.

Guang-jae Lee, Bo-goo Kang, Tae-il Kim, Tae-jung Kim, Jin-han Kim (Korea) Tomato Hydroponics in Korea (pp 104-109)

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Invited Mini-Review: Hydroponics is ideal for improving tomato quality, increasing yields, and escaping insects and/or disease. From a view point of these advantages, a tomato hydroponic system is highly recommended. Fertilizer application dosage and methods affect plant growth, yield and tomato quality. Potassium accelerates lycopene accumulation, and selenium increases fruit firmness. Chlorine and silicon increase soluble solid contents. Tomatoes contain various food functional substances such as lycopene, β-carotene, ascorbic acid, tocopherol, etc. The kinds of salts and their concentration in nutrient solution affect fruit texture, the amount of minerals, lycopene, and food functionality. Food functionality of tomatoes is well known to consumers, having antioxidants that prevent cancer and heart disease. In this chapter we review the benefits of hydroponics on tomato quality, with a focus on Korea.

K.P. Baiyeri, S.C. Aba (Nigeria) A Review of Protocols for Macropropagation in Musa Species (pp 110-115)

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Invited Mini-Review: Bananas and plantains (Musa spp.) are the most important tropical fruit crops. They are staple food in most part of the humid tropics and important source of rural income for the smallholders who produce them in compound farms. A common limiting factor to large-scale production of Musa crops and expansion of existing plantations is the difficulty in obtaining planting materials. This is due to poor suckering ability accentuated by the strong hormone-mediated apical dominance exerted by the main plant. Rapid production of propagating materials could be achieved through various vegetative multiplication techniques, including micro-propagation, but micro-propagation is not an option for the traditional small-scale farmers in the humid tropics. Therefore, several macropropagation techniques have been developed, such as field decapitation, excised bud, and the detached corm techniques. These techniques are relatively simple and require minimum investment to set up, and plantlets obtained thereof, have the uniformity of tissue-culture plantlets. However, rootless explants obtained through macropropagation have lower survival rate during the acclimatization and stabilization stages in the nursery compared to tissue-culture plantlets. Several organic nursery substrates have been developed for optimum performance of Musa explants in the nursery. Musa plantlets require a warm, humid, and translucent nursery environment to allow the plantlets stabilize and escape desiccation. These conditions can be met by raising plantlets under green polyethylene chamber or under palm frond shade as commonly practiced in tropical sub-Saharan Africa . Above all, nursery substrates must be composted for at least eight weeks before use, and rooted explants should be preferred during nursery planting. Other valuable options discussed include nutrient, moisture and shade management.

V. Phani Deepthi (India), Luke Simon (UK/India), P. Narayanaswamy (India) Identification of Elite Somaclonal Variants from Tissue Cultured Grand Naine Banana (Musa spp. AAA) Types Using RAPDs (pp 116-120)

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Original Research Paper: In vitro propagation of Grand Naine banana (Musa sp. ‘AAA’) is gaining importance in the banana industry. However, the occurrence of somaclonal variants is at present limiting the use of tissue cultures plants in spite of several advantages. Hence a brief study was carried to characterize the somaclonal variants of tissue-cultured Grand Naine from the farmers’ fields around Bangalore, India. Eleven positive variants were characterised based on their morphological and yield characters. To confirm the variants at the DNA level, Random Amplified Polymorphic DNA (RAPD) analysis was conducted to identify differences in the banding patterns. Forty three primers were used for the analysis of which OPF-09 differentiated the variants and the normal Grand Naine bananas. A band size of 320 bp was produced in all the normal samples but was absent in the variants tested. In the present study RAPD markers proved to effectively and precisely confirm the variants identified using molecular characters. Of the eleven superior variants analysed, variants GNV-04, GNV-08 and GNV-10 showed positive phenotypic characters which could be used in developmental programmes of Grand Naine banana.

Julieta Andrea Silva de Almeida, Valéria Cristina Barbosa Carmazini, Luis Carlos da Silva Ramos (Brazil) Indirect Effect of Agar Concentration on the Embryogenic Response of Coffea canephora (pp 121-125)

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Original Research Paper: Coffea leaf explants can present curvature of their edges after inoculation on solid culture medium, decreasing contact with the medium and leading to a less efficient embryogenic process. In the present study greater contact was shown between cv. ‘Robusta’ explants and the culture medium surface when an agar concentration of 3 g L^-1 was used instead of 6 g L^-1, a concentration widely used for the majority of species inoculated in vitro. In addition, the treatment with 3 g of agar also resulted in greater efficiency of direct somatic embryogenesis of this species, verified by an increase in the number of sides of the explants showing the formation of embryogenic structures, and also from their size and the number of embryos formed. Thus the reduction in agar concentration allowed for greater physical contact between the edge of the explants and the surface of the culture medium, and also favoured the efficiency of somatic embryogenesis in leaf explants of C. canephora cv. ‘Robusta 2264 Mar’.

A. Manoj Kumar, Kalpana N. Reddy (India) Biological Control Agent in Bell Pepper Infected by Powdery Mildew (Leveillula taurica) (Lev.) Arn.: A Biochemical Study (pp 126-130)

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Original Research Paper: Biological control agents and botanicals are increasingly being used as alternative strategies to chemicals in the control of plant diseases. The effect of some of the biological control agents and botanicals viz., Trichoderma viride, T. harizianum and Pseudomonas fluorescens IIHR⁺3, emulsified neem (Azadirachta indica) oil and NSKE (neem seed kernel extract) as foliar spray in powdery mildew infected bell pepper, grown in a polyhouse were compared with fungicides such as dinocap^® and Contaf^® in treated and untreated - positive control (healthy) and negative control (diseased) - plants. Estimation of biochemical changes associated with all the above treatments was assessed. Our data show that T. viride recorded maximum levels of 1.23, 0.92, 6.75 mg g^-1 at 35 DAT and 1.0, 0.71, 8.1 mg g^-1 at 50 DAT in total phenolics, ortho-dihydroxy phenolics and total soluble sugar, respectively. The next best treatment was T. harizianum. Similarly, the maximum amount of chlorophyll a, b, and total chlorophylls was observed in T. viride- and T. harizianum-treated plants. Overall total phenolics and ortho-dihydroxy phenolics decreased at 50 DAT more than at 35 DAT suggesting that foliar spray of biological control agents, botanicals and fungicides could control powdery mildew disease after one or two sprays which resulted in low levels of pathogen load and ultimately lower levels of defense-related biochemical components. Interestingly, during this study we found increased levels of biochemical constituents at 50 DAT in T. viride and T. harizianum even though powdery mildew was less than 5%. These fungal biological control agents may have played a vital role in enhancing the defense related biochemical components.