The immature fruits of L. acutangula (ridge gourd) and L. cylindica (sponge gourd) are edible and are consumed as fresh slices, in soups, or cooked. The leaves in Africa are also used as a leafy vegetable and the seeds are employed in soup and sauce preparations. Loofa sponge is used primarily for bathing and as pot scrubbers, filters, packing material, as well as for crafts. The application of biotechnology for Luffa gourd improvement is given below.

Tissue Culture

Matsumoto et al. (1987) reported a procedure for the successful isolation and culture of protoplasts from suspension culture of L. cylindrica. Initially, seeds of cultivar Futo were surface sterilized, germinated in Murashige-Skoog (MS) agar medium to produce seedlings. Then calli were induced from these seedlings by placing 2 to 3 week-old dissected cotyledon pieces onto MS agar media supplemented with 2,4-D and kinetin. Cells were then collected by centrifugation for use in protoplast isolation. The growth phase of the callus culture strongly influences the yield and viability of protoplasts. The highest protoplast yield was obtained 6 days after isolation, where approximately 90% of the cells were viable. Protoplast plating efficiency was maximized in media containing 0.5 mgl^-1 kinetin. The first cell division after transfer occurred in 5-7 days, and after 10 days 35% protoplasts had divided at least once. Cell clusters were formed in about the first one-third of the protoplasts that divided, which subsequently developed into visible colonies. Ito et al. (1991) produced hybrid cell lines between L. cylindrica (2n = 2x = 26) and Gynostemma pentaphyllum needed (2n = 6x = 66; Jiaogulan plant) by protoplast fusion. Hybridity was confirmed by karotype and isozyme analyses, where putative hybrid cell lines were 2n > 158 and possessed parental homodimeric isoenzymes of glucose-6-phosphate isomerase.

In gourd, male sterile parental stocks can be maintained through tissue culture. For instance, Pradeepkumar et al. (2007, 2010) identified a male sterile line in ridge gourd possessing rudimentary male flowers in racemes, and shrunken, small, and sterile microspores. Male sterile plants were maintained by culturing the shoot tips and nodal portions. It was found that the most abundant seedling establishment and shoot length growth of these explants (60%) occurred after 45 days in MS media supplemented with 1.5 mg Indole acetic acid (IAA) + 2.0 mg benzyladeninelitre^-1. In vitro-derived shoots were best rooted on half-strength MS medium containing 1.0 mg Indole butyric acid (IBA) and 200 mg charcoallitre-1. Thereafter, half-strength MS medium without hormone suppliments was used to stimulate roots during plant hardening (i.e. exposure to natural environment just before planting).

Genetic Diversity Analysis

Genetic diversity assessments of Bangladesh landraces of ridge gourd have been performed using RAPD markers (Hoque and Rabbani, 2009), where the similarity among landraces was found to be relatively high [e.g., average gene diversity value = 0.278; Shannon's Information Index (SII) = 0.415]. Likewise, Pandey et al. (2007) employed SDS-PAGE analysis of seed proteins for the biochemical characterization of 48 Indian sponge gourd genotypes. Tolentino et al. (1997) also employed SDS-PAGE electrophoresis of seed proteins to determine genetic diversity and taxonomic relationships among Luffa species. The similarity indices among the L. cylindrica (ridge gourd) and L. acutangula (smooth gourd) accessions examined were 80% and 71%, respectively, indicating that substantial genetic affinities exist between these species. This earlier assertion, however, was not supported by the morphological and RAPD-based genotype analyses of LiLin et al. (2007), which revealed that the genetic similarity between these species were relatively small (e.g., similarity coeffient = 0.17). Similarly, the allozymic and morphological diversity analysis of L. acutangula and L. aegyptiaca cultigens (e.g., landraces and cultivars) from diverse geographical regions performed by Marr et al. (2005) revealed that these species share fixation for different alleles at nine loci and are reproductively isolated. JunHiu and ChangPing (2008) employed morphological and RAPD markers to study genetic diversity in Luffa. They detected considerable RAPD-based variation (i.e., 86% polymorphism; Shannon's similarity index = 0.33) among the 26 Luffa accessions examinated. These results, however, did not mirror those obtained by morphological evaluation, which indicated that they were similar.

Evolution and Genetic Mechanisms

Three species of Luffa, L. acutangula, L. cylindrica, and L. hermaphrodita, possess similar patterns of reassociation kinetics in homologus DNA, indicating considerable similarities in genome organization (Pasha and Sen, 1995). Luffa acutangula, however, possessed relatively high (29%; Cot value = 10-3 -10-1) and moderate (23%; Cot value >10-1 -102) degree of repeated sequences, and L. cylindrica exhibited a relatively high number of unique sequences (50%), as well as, a high (30%) and moderate (20%) numbers of repeated sequences.

Munshi et al. (2012) recently developed a sponge gourd line, ‘DSG-6’, that is highly resistant to Tomato Leaf Curl New Delhi Virus (ToLCNDV). Subsequently, Saha et al. (2013) amplified the nucleotide-binding site (NBS) domain of the putative resistance gene candidates (RGCs) from DSG-6. Sixteen non-redundant RGCs sequences with un-interrupted open reading frames (ORFs) and high amino acid sequence homologies (60â€"98%) to various nucleotide-binding site leucine-rich repeat (NBS-LRR) proteins were identified using comparative sequence analysis with the GenBank database. Of these, six and ten sponge gourd, RGCs were associated with the Toll Interleukin Receptor (TIR) and non-TIR group of NBS-LRR genes, respectively. The sponge groud RGCs consist of the relatively conserved NB-ARC [homologous region shared with APAF-1 (apoptotic protease-activating factor-1), R proteins and CED-4 (Caenorhabditis elegans death-4 protein)] domain from the P-loop nucleoside triphosphatase (NTPase) family with its characteristic P-loop, Kinase-2, RNBS-A, Kinase-3A, and GLPL motifs. The comparative analysis of expression profiles of sponge gourd RGCs in asymptomatic and symptomatic leaf tissues of field identified ToLCNDV resistant and susceptible genotypes indicating that the expression of the RGCLc28 motif in resistant genotypes were consistent. The differentially expressed RGCLc28 motif of DSG-6 has a strong association with a resistance gene for leaf curl and mosaic disease in sponge gourd, and, thus, may serve as important genomic resource for candidate gene discovery in Luffa in the future.

A novel circulating loop bioreactor operating with a cell immobilized L. cylindrica sponge-based substrate has been used for the bio-conversion of raw cassava starch to ethanol (Roble et al., 2003). Loofa sponge has also been used as a medium for the culture of human hepatocyte cell lines (Chen et al., 2003). Similarly, L. cylindrica has been shown to be a high performance solid substrate for biofilm aggregating microorganisms that are effective in the metabolization of organic and inorganic compounds, particularly those responsible for nitrification (Tavares et al., 2008). Luffa sponge is a good support matrix for retention of microbial cells and plant cell immobilization because of its high degree of porosity, high specific pore volume, stable physical properties, biodegradability, non-toxicity, and low cost (Liu et al., 1998).

References

Chen, J.P., S.C. Yu, B.R. Hsu, S.H. Fu, and H.S. Liu. 2003. Loofa sponge as a scaffold for the culture of human hepatocyte cell line. Biotechnol. Prog. 19:522-527.

Hoque, S., and M.G. Rabbani. 2009. Assessment of genetic relationship among landraces of Bangladeshi ridge gourd (Luffa acutangula Roxb.) using RAPD markers. J. Sci. Res. 1(3):615-623.

Ito, M., H. Morimoto, S. Matsumoto, K. Oosumi, and H. Konishi. 1991. Hybrid cell lines produced by protoplast fusion between Luffa cylindrica Roem. and Gymnostemma pentaphyllum Makino. Jpn. J. Breed. 41(2):325-329.

JunHui, X., and X. ChangPing. 2008. Analysis of genetic diversity in luffa via morphological and RAPD markers. China Vegetables 10:21-25.

LiLin, H., L. ManWai, H. ChiHsiung, L. TzongShyan, and Y. WenJu. 2007. Genetic diversity among the lines and cultivars of Luffa species. J. Taiwan Soc. Hortic. Sci. 53(1):99-110.

Liu, Y.K., M. Seki, H. Tanaka, and S. Furusaki. 1998. Characteristics of loofa (Luffa cylindrica) sponge as a carrier for plant cell immobilization. J. Ferment. Bioeng. 85(4):416-421.

Marr, K.L., N.K. Bhattarai, and M.X. Yong. 2005. Allozymic, morphological and phonological diversity in cultivated Luffa acutangula (Cucurbitaceae) from China, Laos and Nepal and allozyme divergence between L. acutangula and L. aegyptiaca. Economic Bot. 59(2):154-165.

Matsumoto, S., M. Ito, H. Konishi, and I. Takebe. 1987. Isolation and culture of protoplasts from Luffa cylindrica suspension cultures. Plant Tiss. Cult. Lett. 4(1):35-37.

Munshi, A.D., S. Islam, R. Kumar, B. Mandal, T.K. Behera, and A.K. Sureja. 2012. DSG-6 (IC0588956; INGR12013), a sponge gourd (Luffa cylindrica) germplasm highly resistant to Tomato Leaf Curl New Delhi Virus. Indian J. Plant Genet. Resour. 25(3):321-322.

Pandey, R., D.K. Singh, and M. Upadhyay. 2007. Biochemical characterization of germplasm of sponge gourd (Luffa cylindrica Roem.). Veg Sci. 34(2):185-186.

Pasha, M.K., and S.P. Sen. 1995. Molecular analysis of cucurbitaceae genome: reassociation kinetic classes and its evolutionary significance. Biochem. Systematics Ecol. 23(4):399-406.

Pradeepkumar, T., R. Sujatha, B.T. Krishnaprasad, and I. Johnkutty. 2007. New source of male sterility in ridge gourd (Luffa acutangula (L.) Roxb.) and its maintenance through in vitro culture. Cucurbit Genet. Coop. 30:60-63.

Pradeepkumar, T., V.C. Hegde, R. Sujatha, and T.E. George. 2010. Characterization and maintenance of novel source of male sterility in ridge gourd Luffa acutangula (L.) Roxb. Curr. Sci. 99(10):1326-1327.

Roble, N.D., J.C. Ogbonna, and H. Tanaka. 2003. A novel circulating loop bio-reactor with cells immobilized in loofa (Luffa cylindrica) sponge for the bioconversion of raw cassava starch to ethanol. Appl. Microbiol. Biotechnol. 60(6): 671-678.

Saha, D., R.S. Rana, A.K. Sureja, M. Verma, L. Arya, and A.D. Munshi. 2013. Cloning and characterization of NBS-LRR encoding resistance gene candidates from Tomato Leaf Curl New Delhi Virus resistant genotype of Luffa cylindrica Roem. Physiol. Mol. Plant Pathol. 81:107-117.

Tavares, J., N.H. Israel, O. Rui, S.L. Wilton, and D.L. Valderi. 2008. Nitrification in a submerged attached growth bioreactor using Luffa cylindrica as solid substrate. Afr. J. Biotechnol. 7(15):2702-2706.

Tolentino, M.I.S., R.P. Laude, and A.C. dela Vina. 1997. Genetic diversity analysis of Luffa species based on seed protein profile using SDS-PAGE. Philippine J. Crop Sci. 22(3):141-146.




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Working as a Senior Scientist at ICAR-Indian Agricultural Research Institute, Pusa, New Delhi