T. K. Behera

Molecular diversity and its relationship with hybrid performance and heterosis in ash gourd [Benincasa hispida (Thunb.) Cogn.]

Summary Ash gourd or wax gourd [Benincasa hispida (Thunb.) Cogn.], belonging to the family Cucurbitaceae, is an underexploited vegetable in spite of having considerable economic and medicinal importance. Very little information is available on the genetic diversity and exploitation of heterosis in this crop. In the present study, nine inbred lines of ash gourd were crossed to produce all (72) possible F1 hybrids, including reciprocals, which were evaluated along with the nine parents for 13 growth- and yield-related traits and 14 quality traits, in a replicated field trial. A high level of heterosis was observed among the hybrids for most of the traits examined, including iron and zinc content. Significant reciprocal differences in heterosis were observed. The inbred lines were analysed using 130 RAPD primers, of which 26 were informative and amplified 163 DNA marker bands. A total of 47 polymorphic bands were obtained with a mean of 1.8 per primer which, in combination, discriminated all the inbreds from each other. Pair-wise genetic distance measurements ranged from 0.056 to 0.179, suggesting a narrow genetic base for the inbreds. Although the results indicated significant positive correlations of genetic distance with hybrid performance and heterosis, the magnitudes of the correlations were not high enough to be of predictive value.

Cytotaxonomical analysis of Momordica L. (Cucurbitaceae) species of Indian occurrence

Somatic chromosome number and detailed karyotype analysis were carried out in six Indian Momordica species viz. M. balsamina, M. charantia, M. cochinchinensis, M. dioica, M. sahyadrica and M. cymbalaria (syn. Luffa cymbalaria; a taxon of controversial taxonomic identity). The somatic chromosome number 2n = 22 was reconfirmed in monoecious species (M. balsamina and M. charantia). Out of four dioecious species, the chromosome number was reconfirmed in M. cochinchinensis (2n = 28), M. dioica (2n = 28) and M. subangulata subsp. renigera (2n = 56), while in M. sahyadrica (2n = 28) somatic chromosome number was reported for the first time. A new chromosome number of 2n = 18 was reported in M. cymbalaria against its previous reports of 2n = 16, 22. The karyotype analysis of all the species revealed significant numerical and structural variations of chromosomes. It was possible to distinguish chromosomes of M. cymbalaria from other Momordica species and also between monoecious and dioecious taxa of the genus. Morphology and crossability among the dioecious species was also studied. Evidence from morphology, crossability, pollen viability and chromosome synapsis suggests a segmental allopolyploid origin for M. subangulata subsp. renigera. The taxonomic status of the controversial taxon M. cymbalaria was also discussed using morphological, karyological and crossability data.

Molecular diversity and phenetic relationship of Momordica spp. of Indian occurrence

Twenty-one RAPD and twelve ISSR primers were used for assessment of genetic diversity and establishing phenetic relationships among 35 genotypes of six currently cultivated Indian Momordica species and five genotypes of two Luffa species. A total of 436 RAPD and 230 ISSR scorable fragments were produced of which 99.8% fragments showed polymorphism among the species and varieties of Momordica and Luffa. The level of polymorphism detected by the 33 random primers was higher among the species (99.8%) of Momordica than that estimated among the varieties (61.3%). The varieties belonging to dioecious Momordica species (75.6%) showed a higher level of polymorphism as compared to monoecious species (50.3%). A significant level (68.6%) of polymorphism however was detected by the two marker types among the Indian varieties of monoecious M. charantia species. A wider range of molecular diversity (16–95%) detected by both RAPD and ISSR markers reflected presence of high level of genetic variation among the species and Indian varieties of Momordica and Luffa. The level of inter-specific diversity was maximum (90%) between annual monoecious M. charantia and perennial dioecious M. cochinchinensis whereas the extent of intra-specific diversity was highest particularly in dioecious species (51%) as compared to monoecious species like M. charantia (38%). Wider divergence of the taxon of controversial identity, M. cymbalaria from the other Indian cultivated Momordica species and their evolutionary closeness with Luffa species was evident. The clustering pattern obtained among the 40 genotypes belonging to different Momordica and Luffa species corresponded well with their morphological, cytological and taxonomic classification, which was further supported by high boot-strap values and PCA analysis. Species and genotype-specific fragments detected by the random markers would be useful in introgression breeding for genetic improvement of Momordica cultivated in India. A smaller set of 28 informative random markers screened in this study could precisely differentiate the Momordica genotypes from each other and thus would be of use in many marker-based genotyping applications in Momordica.

SHORT HYPOCOTYL1 Encodes a SMARCA3-Like Chromatin Remodeling Factor Regulating Elongation.

SHORT HYPOCOTYL1 (SH1), a chromatin remodeler, regulates hypocotyl elongation in cucumber through modulating the UVR8-mediated UVB signaling pathway. In Arabidopsis (Arabidopsis thaliana), the UVR8-mediated signaling pathway is employed to attain UVB protection and acclimation to deal with low-dosage UVB (LDUVB)-induced stresses. Here, we identified SHORT HYPOCOTYL1 (SH1) in cucumber (Cucumis sativus), which regulates LDUVB-dependent hypocotyl elongation by modulating the UVR8 signaling pathway. We showed that hypocotyl elongation in cucumbers carrying the recessive sh1 allele was LDUVB insensitive and that Sh1 encoded a human SMARCA3-like chromatin remodeling factor. The allele frequency and distribution pattern at this locus among natural populations supported the wild cucumber origin of sh1 for local adaptation, which was under selection during domestication. The cultivated cucumber carries predominantly the Sh1 allele; the sh1 allele is nearly fixed in the semiwild Xishuangbanna cucumber, and the wild cucumber population is largely at Hardy-Weinberg equilibrium for the two alleles. The SH1 protein sequence was highly conserved among eukaryotic organisms, but its regulation of hypocotyl elongation in cucumber seems to be a novel function. While Sh1 expression was inhibited by LDUVB, its transcript abundance was highly correlated with hypocotyl elongation rate and the expression level of cell-elongation-related genes. Expression profiling of key regulators in the UVR8 signaling pathway revealed significant differential expression of CsHY5 between two near isogenic lines of Sh1. Sh1 and CsHY5 acted antagonistically at transcriptional level. A working model was proposed in which Sh1 regulates LDUVB-dependent hypocotyl elongation in cucumber through changing the chromatin states and thus the accessibility of CsHY5 in the UVR8 signaling pathway to promoters of LDUVB-responsive genes for hypocotyl elongation.

Response to phenotypic and marker-assisted selection for yield and quality component traits in cucumber (Cucumis sativus L.).

Two cucumber recombinant inbred lines (RILs) differing in plant habit were crossed and progeny self-pollinated to produce F3 individuals upon which phenotypic selection was practiced to identify a base population which in turn underwent either two cycles of MAS or random mating without selection (RAN). MAS and RAN were practiced to produce F4 and F5 progeny sets. RIL, crossing parents, and F3–F5 progeny sets were then evaluated under replicated field conditions for fruit yield and quality (L:D and E:T) to evaluate gain from selection (ΔG). The broad-sense heritability (h2B) over cycles (C) of selection ranged 0.22–0.45, 0.09–0.20, and 0.11–0.15 for yield, L:D, and E:T, respectively. Although one cycle of PHE selection followed by MAS was effective in conserving the performance of the traits examined during inbreeding, progeny performance during RAN fluctuated (F4–F5 generation; C2). Lack of ΔG during advanced generations (F4–F5) of MAS was likely due to allelic fixation and/or optimized epistatic complementation.

‘Pusa Santushti’: A New High-Yielding Bottle Gourd Variety

‘Pusa Santushti’ is a new, high-yielding bottle gourd [Lagenaria siceraria (mol.) Standl.] cultivar developed from a local landrace from Rishikesh, Uttaranchal, India. At the edible stage fruit are green with soft pubescence, pear shaped, ˜20 cm in length, and ˜12 cm in diameter. Fruit set at night temperature of 10–12°C or 35–40°C under field conditions. Individual fruit weight varies from 0.8 to 1.0 kg and first fruit matures ˜60 days after sowing. The cultivar Pusa Santushti performed better than the check (‘Pusa Naveen’) in six locations over 3 years. This cultivar recommended by the All India Coordinated Research Projects on Vegetable Crops for release.

Comparative transcriptome analysis of female and hermaphrodite flower buds in bitter gourd (Momordica charantia L.) by RNA sequencing

ABSTRACT Bitter gourd, Momordica charantia L., is an economically and nutraceutically important crop in the family Cucurbitaceae. The predominant sex-form of bitter gourd is monoecious, but a gynoecious form also exists which is controlled by a single recessive gene (gy-1). Whole transcriptome sequencing of female and hermaphrodite flower buds of bitter gourd was performed using Roche 454 parallel pyrosequencing technology. A total of 1,994,113 expressed sequence tags (ESTs) were generated, of which 834,476 and 1,159,637 ESTs were obtained from female and hermaphrodite flower buds of the gynoecious bitter gourd inbred line, DBGY-201, respectively. The unigenes were functionally annotated by comparing their sequences with various protein and functional domain databases and assigned gene ontology (GO) terms. A total of 477 annotated unigenes were found to be significantly differentially expressed between the female and hermaphrodite flower buds of DBGY-201, of which 237 were down-regulated and 59 were up-regulated in hermaphrodite flower buds. Differentially expressed ESTs between the two different flower types, as well as putative simple sequence repeat (SSR) markers are reported. These EST sequences will provide valuable information to increase our understanding of the molecular mechanisms of sex determination and represent a rich resource for future functional genomic analysis, marker development, and bitter gourd breeding.

Induction and Morphological Characterization of Hermaphrodite Flowers in a Gynoecious Line of Bitter Gourd by Silver Nitrate, Gibberellic Acid, and Silver Thiosulfate

Gynoecious sex form in bitter gourd (Momordica charantia L.) has importance in hybrid breeding, but lack of easy and economic techniques to maintain gynoecious lines limits its use. Sex modification with chemicals can be an option in this regard. Bitter gourd is a typical monoecious (both male and female flower in same plant at separate nodes) plant. The gynoecious line was isolated from its related wild form M. charantia var. muricata L. Effects of concentrations of silver nitrate (SN), gibberellic acid (GA3), and silver thiosulfate (STS) for induction of male flowers in the gynoecious variety DBGy-201 were determined. The STS at 3 and 6 mm induced staminal tissue in female flowers of gynoecious bitter gourd and GA3 at 2.9 and 4.3 mm induced increased vegetative growth and rudimentary stamen production without viable pollen. The SN at 1.2 and 1.5 mm had no effect. The highest percentage (57.63%) of altered sex form was in plants treated with STS at 6 mm. Stamens were observed in female flowers that matured between 7 and 15 days after treatment. Induced hermaphrodite flowers had ovaries, stigma, styles, stamens, anthers, calyx, corolla, and petioles that were double the size of normal female flowers. Silver nitrate applied at 6 mm was best for inducing hermaphrodite sex form in the gynoecious line of bitter gourd.

Estimating combining ability for yield and yield contributing traits in cucumber

A study was conducted on a 8 × 8 diallel set of cucumber excluding reciprocals to find out the extent of combining ability for yield and yield attributing characters. The magnitudes of variance due to general as well as specific combining ability were highly significant indicating the importance of both additive and non-additive gene action. Among parents, gynoecious line GBS-1(P1) showed maximum g.c.a effects in desirable direction for node number of first female flower, days to first female flower anthesis, days to fruit set from opening of first female flower, days to first fruit harvest, number of fruits per plant, and vine length. The parent P5 (Pusa Uday) exhibited highest positive g.c.a effect for fruit length, fruit diameter, average fruit weight and yield per plant. In order of merit the gynoecious hybrids P1 × P5 (GBS-1 × Pusa Uday) and P1 × P6 (GBS-1 × Punjab Naveen) followed by monoecious hybrid P3 × P5 (GS-4 × Pusa Uday), which exhibited highest s.c.a effects for number of characters including total fruit yield per plant. In case of yield and other yield contributing characters like node number of first female flower, days to first female flower anthesis, days to fruit set from opening of first female flower, days to first fruit harvest, number of fruits per plant and yield per plant where specific combining ability component of variance (s2s) is more than general combining ability component of variance (s2g), which indicated preponderance of non-additive gene action. Hence, an improvement programme based on heterosis breeding would be appropriate for improving different traits under study.

Genetics and molecular mapping of gynoecious (F) locus in cucumber (Cucumis sativus L.)

Gynoecious is an important economic trait of cucumber for determinant of earliness and yield, yet genetic mechanism is not well understood for this trait. The experiment was conducted using F₂ mapping population by crossing of PPC-2, a gynoecious and parthenocarpic line with Pusa Uday (monoecious and non-parthenocarpic cultivar). Out of 179 SSR markers screened, 39 markers differentiated the gynoecious and monoecious parents. However, only 17 markers were segregating with F₂ mapping population, those were used for genotyping and linkage map analysis and these markers were placed along with F locus on chromosome 6 covering a total distance of 100.4cM. The SSR markers, SSR13251 and UW020605 were found to be closely linked to gynoecious (F) locus at 1.0 and 4.5 cM, respectively. The segregation of F₂ population of PPC-2 × Pusa Uday and GPC-1 × Punjab Naveen and test crosses for sex type herein suggested that single dominant gene controlled the gynoecious sex expression in cucumber particularly in gynoecious genotypes PPC-2 and GPC-1. Therefore, the monogenic dominant nature of gynoecious sex identified in the present experiment and SSR markers closely linked to the F locus will be useful in marker-assisted backcross breeding for transfering gynoecious trait into horticulturally desirable varieties.