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Cucurbitacins are a group of secondary metabolites produced by cucurbits including bottle gourd [Lagenaria siceraria (Molina) Standl.]. The role of cucurbitacins in plant responses to drought stress is not well-determined. The objective of this study was to investigate the response of bottle gourd to drought stress and to establish the relationship between cucurbitacins accumulation and drought tolerance. Leaf gas exchange, chlorophyll fluorescence and level of cucurbitacins production were investigated on 12 bottle-gourd landraces grown under drought-stressed (DS) and non-stressed (NS) conditions. Results showed that stomatal conductance (gs), transpiration (T) rate, net CO2 assimilation rate (A), the ratio of CO2 assimilation rate and intercellular CO2 concentration (Ci/Ca), intrinsic and instantaneous water-use efficiencies declined in landraces that were subjected to drought stress. Intercellular CO2 concentration, the ratio of intercellular and atmospheric CO2 concentration increased significantly in response to drought stress. The maximum quantum efficiency of photosystem II photochemistry (Fv’/Fm’), the effective quantum efficiency of photosystem II photochemistry, photochemical quenching (qP) and non-photochemical quenching (qN) were not affected by drought stress; whereas, electron transport rate, electron transport to oxygen molecules (ETR/A) and alternative electron sink (AES) declined. Cucurbitacin E and I were detected under NS and DS conditions in some of the tested bottle gourd landraces. Significant and positive correlations were observed between cucurbitacin I content with ETR/A and AES. The current study identified drought tolerant bottle gourd landraces namely: BG-48, BG-58, BG-70, BG-78 and BG-79 based of high values for gs, T, A, Fv’/Fm’ and qN under DS condition. These selections may be useful for drought tolerance breeding in bottle gourd or related cucurbits. There is a need for a further investigation whether cucurbitacin I accumulation may be involved in the regulation of the physiological processes evaluated in the present study.

The bottle gourd or calabash [Lagenaria siceraria (Mol.) Standl.] (2n = 2x = 22), also known as opo squash or long melon, is an important cucurbit crop worldwide. Commonly used as a vegetable, bottle gourd fruits have a peculiar umami taste that is important for their market value. To date, the umami chemical ingredients of bottle gourd fruits and their genetic determinants remain unidentified. In the current study, the relationship between umami flavor and free amino acid (FAA) contents was analyzed using a representative panel of twenty-eight accessions. Among the FAAs identified, free glutamate (Glu) was found to have the most significant association with umami taste, suggesting that free Glu is the main umami-conferring ingredient of bottle gourd. To further identify the genetic regions associated with umami taste, a genome-wide association study (GWAS) for free Glu content was conducted in a diversity panel consisting of 139 inbred lines, each sequenced with a restriction site-associated DNA sequencing (RAD-Seq) technology. Seventeen SNPs were identified as associated with free Glu content, each accounting for 7.5% to 15.1% of the phenotypic variation. The number of the favored alleles for each line varied from 0 to 13. Free Glu content exhibited a significant positive correlation with the number of the favored alleles. These results indicated that there is considerable genetic potential to develop new varieties with stronger umami taste through targeting more favored alleles of free Glu content. To our knowledge, this is the first GWAS study in bottle gourd. Our work reveals the genetic architecture of umami taste in the bottle gourd and will help facilitate molecular breeding of cultivars with improved flavor.

Bottle gourd [ Lagenaria siceraria (Molina) Standl.] belonging to the family Cucurbitaceae is an important crop widely grown for its fruits, seeds or succulent leaves. Sub-Saharan Africa (SSA) is believed to be the centre of genetic diversity of bottle gourd where it is commonly grown by smallholder farmers predominantly using unimproved and genetically diverse landrace varieties. Bottle gourd received limited research and development priority towards genetic improvement and cultivar deployment and conservation in SSA compared to the continental Asia and America. The genetic variation present among landraces in SSA is a useful raw material for bottle gourd improvement programmes in the region and globally. The objective of this review is to present the perspectives on the genetic diversity and genetic resources, population structure and breeding progress of bottle gourd. Further, the review discusses the potential of genomic resources for genetic analysis and genomic selection of bottle gourd to accelerate conventional breeding in enhancing productivity and systematic conservation of the crop.

Phenotypic and genotypic characterization of plant genetic resources is fundamental for breeding and strategic conservation. This study assessed the genetic diversity present in bottle gourd landraces using 10 fruit qualitative traits and 11 simple sequence repeat (SSR) markers. Thirty six South African bottle gourd landraces collected from various geographic locations were used for the study. Phenotypic diversity was estimated using Shannon-Weaver diversity indices, principal component and cluster analyses. Phenotypic diversity index was 0.98, showing high genetic diversity among bottle gourd landraces. Principal component analysis identified four PCs which contributed for 75.3% of the total phenotypic variation. Presence or absence of fruit neck, fruit shape, degree of neck bending and fruit neck length positively correlated with PC1, which accounted for 37.6% of the total variation. Primary fruit colour and fruit texture highly correlated with PC2 which accounted for 15.78% of the total variation. Number of alleles varied from 3 to 9 with a mean of 6 per SSR locus. Number of effective alleles ranged from 1.99 to 6.72 with a mean of 3.75. Expected heterozygosity values ranged from 0.5 to 0.87 with a mean of 0.71 with polymorphic information content varying from 0.5 to 0.85 and a mean of 0.7. Qualitative traits and SSR markers analyses had significant correlation ( r = 0.15, P = 0.02) in clustering the landraces. The present study revealed that fruit qualitative traits are useful attributes in bottle gourd breeding and genetic analysis.

The experiments were conducted to characterize eighteen Fusarium wilt resistant Citrullus accessions for their root parameters and to evaluate their performance as rootstocks for vigour, earliness, quality, yield and tolerance to sudden wilt disease of grafted watermelon in comparison with Cucurbita and Lagenaria rootstocks. Significant variations were observed among the rootstocks for all the root traits under study. The length and diameter of the rootstock hypocotyl were found to be an indicator of the robustness of the root system. A significant influence on vine length and earliness of the grafted crop was observed across different rootstocks. The grafts on Citrullus rootstocks could maintain the oblong fruit shape of the scion compared to those onto Cucurbita hybrid and Lagenaria rootstocks which yielded from flat-globe to spherical shaped fruits. A wide variation of TSS and carotenoid content was observed upon grafting while the pulp pH remained largely unaffected. An increase of average fruit weight by 82.37% and yield per plant by 112.15% in grafts onto RS-18 and RS-10 respectively were recorded. The grafts onto rootstocks viz., RS-10, RS-21 and RS-25 also exhibited reduced severity of sudden wilt; hence are of value in regions prone to both Fusarium wilt and sudden wilt diseases. Overall, the Citrullus accessions viz., RS-10, RS-11 and RS-18 were found to be promising in comparison to Cucurbita hybrids and Lagenaria rootstocks. Grafting onto resistant rootstocks can help in environment-friendly management of Fusarium and sudden wilt diseases in watermelon without compromising the yield and quality.

Bottle gourd [ Lagenaria siceraria (Mol.) Standl.] is an easy growing climber that has made great impact due to its medicinal importance. For estimating genetic diversity among accessions in breeding programs, SSR markers are an essential tool, but for the species that have meager number of these markers available, their development is a challenging aspect. In the present study a microsatellite-enriched library was constructed from the genotype ‘Pusa Santushti’. Sequencing of 100 putative SSR-positive clones from a total of 220 clones provided 44 SSR repeats and primer pairs could be designed for a total of 40 SSRs. Of these, 30 (75%) primer pairs yielded scorable amplicons and seven (17.5%) primers showed polymorphism among 40 bottle gourd accessions. The 20 polymorphic alleles from seven polymorphic markers were used for UPGMA dendrogram and population structure analysis; both revealed that five populations are present in the 40 accessions that did not group consistent with their geographical origins probably due to gene flow. The results of this study provide 30 novel SSR markers that would be valuable in agriculture via plant breeding, phylogenetic relationships, cultivar identification and linkage mapping in cultivated bottle gourd as well as related cucurbits species. Significantly, 49 partial genome sequences were also isolated that can be helpful in further gene based studies in this vegetable crop.

Production of seedless watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) using soft X-ray irradiated pollen has the advantage that this method can be used with diploid cultivars; however, pistillate flowers must be covered with a bag before flowering to prevent normal pollination by insects. Therefore, we attempted to prevent normal pollen penetration by pollinating pistillate watermelon flowers with intergeneric pollen before anthesis. In the course of conducting these studies, we found a new method to produce seedless watermelon by pollinating with bottle gourd (Lagenaria siceraria (Molina) Standl.) pollen. When the pollen of bottle gourd was used to pollinate pistillate watermelon flowers, the fruit set rate was 57.1%. On the other hand, the fruit set rate by pollinating with watermelon pollen was 65.0%. Although the fruit set rate using bottle gourd pollen was slightly lower than the fruit set rate obtained when watermelon pollen was used, this percentage was higher than expected. Preservation of pollen collected from staminate flowers of bottle gourd was difficult, and fruit did not set. In contrast, fruit developed when bottle gourd pollen from staminate flowers stored at 4 °C for 72 h was used to pollinate watermelon. All parthenocarpic fruits produced by pollination with bottle gourd pollen were deformed (triangular or oblong shaped). There was a significant difference in the ratio of fruit length to fruit width; however, fruit weight, rind thickness, flesh color and Brix in the parthenocarpic fruit were almost the same as control fruit. There were no normal seeds except for small, white empty seeds in the fruit obtained from pollinating with bottle gourd pollen. Bottle gourd pollen tubes did not reach the ovules of watermelon ovaries. Therefore, we concluded that parthenocarpy resulting from pollination with bottle gourd pollen was stimulative parthenocarpy, not pseudo parthenocarpy (pseudogamy).

To investigate the feasibility of using salt tolerant rootstock to increase fruit yield and quality of cucumber under NaCl stress, a greenhouse experiment was carried out to determine fruit yield, leaf relative water content, fruit quality, and mineral composition of cucumber plants (Cucumis sativus L. cv. Jinchun No. 2), either self-grafted or grafted onto the commercial salt tolerant rootstock Figleaf Gourd (Cucurbita ficifolia Bouche) and Chaofeng Kangshengwang (Lagenaria siceraria Standl). Plants were grown in a substrate culture (peat:vermiculite:perlite = 1:1:1, v/v) and irrigated with half-strength Hoagland solutions containing 0, 30, or 60 mM NaCl. The results showed that salinity significantly reduced fruit yield of cucumber owing to a decrease both in mean fruit weight and fruit number. Rootstock had no significant effect on leaf relative water content. Plants grafted onto Figleaf Gourd and Chaofeng Kangshengwang had higher fruit number, marketable and total fruit yield than those of self-grafted plants under 0, 30, and 60 mM NaCl, which could be attributed to, at least in part, the higher K+ but lower Na+ and/or Cl− contents in the leaves. Salinity improved fruit quality by increasing fruit dry matter, soluble sugar, and titratable acidity contents of all the plants, but had no significant effect on vitamin C content. In comparison to the self-grafted plants, plants grafted onto Figleaf Gourd and Chaofeng Kangshengwang had an overall improved fruit quality under NaCl stress owing to an increase in contents of soluble sugar, titratable acidity, and vitamin C, and a decrease in the percentage of non-marketable fruit and Na+ and/or Cl− contents of fruits in comparison to the self-grafted plants, mainly under 60 mM NaCl. Overall, it is suggested that the use of salt tolerant rootstock could provide a useful tool to improve fruit yield and quality of cucumber under NaCl stress.

Pending the release of new genetic material with satisfactory resistance, grafting techniques may represent a quick, though expensive method for controlling race 1,2 of Fusarium oxysporum f. sp. melonis in Italian growing regions of melon (Cucumis melo L.). We evaluated the potential of grafting for resistance to this pathogen in 13 commercial melon rootstocks and various Cucurbitaceae spp. and determined productivity and fruit quality characteristics of grafting on resistant rootstocks. Following inoculation, P360 and PGM 96-05 commercial rootstocks, as well as Benincasa hispida, Cucumis metuliferus, Cucumis ficifolius, Cucurbita maxima, Cucurbita moschata, and Lagenaria siceraria were resistant to the race 1,2 of Fusarium. Yield and quality attributes of scion cultivars (Supermarket and Proteo) grafted on P360 and PGM 96-05 rootstocks were not improved relative to ungrafted controls. Grafts onto B. hispida negatively influenced both yield and fruit quality, while C. metuliferus, and C. zeyheri had negative impacts on productivity and fruit quality, respectively. These results indicate that rootstock influences on disease resistance as well as productivity and quality of scion fruit are important in determining the potential utility of grafting applications.

A study on the effect of maleic hydrazide (MH) on vegetative growth, flowering and yield of bottle gourd (Lagenaria siceraria (Mol) Standl.) was conducted during the rainy and summer seasons of 1979 and 1980, respectively. MH at 150 mg l−1 stimulated the elongation of the main shoot, while MH at 50 mg l−1 induced more branches per plant. Staminate flowers appeared late and at the lowest node number in control plants, whereas MH at 150 mg l−1 had a profound effect on the earliest appearance of pistillate flowers at the lowest node number. Male: female ratio was lowered with MH at 50 mg l−1 and was most effective in producing the maximum number of fruits and fruit weight per plant and ultimately the yield. GA3, NAA and ethrel did not influence yield, while MH did.