A rapid, simple and efficient protocol for direct in vitro multiple shoot induction and plantlet recovery was achieved from shoot tip explants of Bambara groundnut [Vigna subterranea (L.) Verdc.]. Shoot tips, were isolated from in vitro-grown seedlings and cultured on Murashige and Skoog basal medium (MS) containing Gamborg’ vitamins (B5) and supplemented with different concentrations of the plant growth regulators Thidiazuron (TDZ), N6-benzylaminopurine (BAP), Kinetin (KIN) and Adenine sulfate (ADS). TDZ 0.45 μM was found to be best for shoot multiplication with a mean of 11shoots per explant. Among the carbon sources tested, the best response in terms of mean number of shoots per explant was obtained with sucrose (11). The mean number of shoots per explant induced among the studied landraces of Bambara groundnut varied from 9 to 13. Individual shoots, aseptically excised, produced normal roots within 2 weeks on the basal MS medium supplemented with Indole Butyric Acid (IBA) or Naphthalene acetic acid (NAA). The highest number of roots per shoot and the longest roots were obtained on MS medium with 2 mg/L IBA. Rooted plantlets were successfully hardened under greenhouse conditions and subsequently established in the field conditions, with a recorded survival rate of 70 and 80 %, respectively. The transferred plants in the field were morphologically normal and fertile. This protocol can be efficiently used for mass propagation, germplasm preservation and probably also for gene transfer of Vigna subterranea (L.).

In vitro shoot tip multiplication of bambara groundnut [ Vigna subterranea (L.) Verdc.]

Yard-long bean [Vigna unguiculata ssp. sesquipedalis (L.) Verdc], belonging to family Fabaceae, is a distinctive subspecies of cowpea [Vigna unguiculata (L.) Walp.], characterized by its climbing growth habit and long draping pods. It is cultivated for its tender pods relished as vegetable, a good source of vitamin A and C, protein, fiber, and other minerals. South East Asia is considered as the center of diversity of this crop. It is cultivated as a sole crop as well as an integral part of intercropping and sequential cropping systems. Lack of improved varieties, inadequate extension services, poor market price, and incidence of pests and diseases are some of the constraints to yard-long bean production. The primary breeding objective is to increase the pod yield per hectare by increasing the number of pods per plant and to improve other attributes namely earliness, determinate and less viny growth habit, photo-insensitivity, resistance/tolerance to biotic stresses, terminal drought tolerance, and wide adaptation to different agroclimatic conditions. With the advent of molecular markers, detailed scanning of yard-long bean genome led to the refined mapping of various agronomic traits to the respective linkage groups. A recent study reported a 632.8 Mb genome assembly (549.81 Mb non-N size) based on the whole-genome shotgun sequencing strategy wherein a total of 42,609 protein-coding genes as well as 3579 nonprotein-coding genes were reported. Detailed studies on the molecular physiology of abiotic stress tolerance will potentially identify the key genes or proteins that can provide a more simple and efficient strategy to improve the breeding process for the development of tolerant lines.

Yard-long bean

Vigna unguiculata (L.) Walp. ssp. sesquipedalis (L.) Verdc. is commonly known as asparagus bean, Chinese long bean, long-podded cowpea, pea bean, snake bean or yardlong bean, and is an underexploited crop with rich nutritional value. Yardlong bean has evolved and was domesticated from cowpea but differs phenotypically as a result of divergent selection. This crop has its origin in Southeast Asia and its habitat in Asia, Europe, Oceania and North America. It is a warm season crop and besides being a food source, it is used as an ornamental plant and for fodder. Ample germplasm diversity exists in this crop. Major commercial varieties were developed by pure line selection. At present, other breeding methods and principles have limited scope. The presence of genetic diversity in this crop needs to be studied with molecular tools. DNA marker analysis with RAPDs, SSRs and SNPs has begun in yardlong bean. However, genomic studies need to be further developed for the construction of high-density genetic maps and application of modern biotechnology tools. This chapter is an overview of yardlong bean origin, evolution and domestication, general cultivation practices, germplasm biodiversity, characterization, conservation strategies, world and Indian gene banks, biotic and abiotic stress tolerance and crop improvement strategies including conventional breeding, biotechnology, tissue culture and micropropagation.

Genetic Improvement of Yardlong Bean (Vigna unguiculata (L.) Walp. ssp. sesquipedalis (L.) Verdc.)

An in vitro propagation protocol has been established for yardlong bean (Vigna unguiculata ssp. sesquipedalis L. Walp. Verdc.) using shoot tip, nodal and leaf segment explants of the superior plant type obtained from crossing of two selected parental lines. Explants were cultured on MS medium supplemented with different concentrations and combinations of BAP, Kn and Zeatin and NAA, IAA, IBA. The highest percentage (86) of shoot regeneration with maximum shoots per culture (12 ± 0.43) was obtained from nodal explants on MS medium supplemented with 0.5 mg/l BAP and 0.2 mg/l NAA. Addition of 10% coconut water and 75 mg/l urea to the medium enhanced shoot multiplication and elongation, respectively. Rooting of the regenerated shoots was optimum on half-strength MS enriched with 3.0 mg/l IBA. Regenerated plantlets were successfully acclimatized. After acclimation, plantlets were transplanted in the experimental field where the survival rate was 80%. Yardlong bean (Vigna unguiculata ssp. sesquipedalis L. Walp. Verdc., Fabaceae) is a popular legume vegetable of Bangladesh which contributes substantially to vegetables supply and constitutes an important source of proteins in daily diet. Considering the nutritional values and public demand, the cultivation of this vegetable crop is being emphasized throughout the country. The major threats of yardlong bean cultivation are insects, mites and nematodes as well as viral, bacterial and fungal attacks. Micropropagation of a superior disease free yardlong bean variety or development of a disease resistant variety can solve this problem. Two selected parental lines of yardlong bean were crossed (Kashem king × Hazari’s Lal Borboti). A superior F1 was obtained and hence a suitable in vitro micropropgation was developed in order to maintain the characteristics of this superior F1 in the next progenies. Shoot tips, nodal segments and young leaves were collected from improved F1 of V. unguiculata ssp. sesquipedalis grown in the experimental field, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka and were used as explants in micropropagation. These plant materials were washed thoroughly with running tap water for 25 minutes. Surface sterilization was done by rinsing the plant materials with 0.1% HgCl2 for six minutes followed by washing repeatedly (7 - 8 times) with autoclaved distilled water. All these procedures were performed under aseptic conditions in a laminar air flow cabinet. Before implanting on to the culture media they were cut into appropriate sizes (approx. 1.0 - 1.5 cm in length) for explants. MS medium was used for regeneration of complete plantlets through in vitro culture. Explants were cultured on MS supplemented with different concentrations of BAP, Kn, zeatin and NAA, IBA, IAA either singly or in combination for shoot regeneration. Media supplements such as coconut water (CW) and urea were added to the medium for the determination of their effects on shoot multiplication and elongation, respectively. The pH of the

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Micropropagation of yardlong bean (vigna unguiculata (l.) walsp. ssp. sesquipedalis l. verdc.) through in vitro culture