Dr. Anilabha Das MunshiNEHA KUMARI MANDALT-108732024-04-032024-04-032022https://krishikosh.egranth.ac.in/handle/1/5810208104The current study, titled “Understanding the regulatory role of important growth hormones in relation to parthenocarpy in cucumber” was carried out at the ICAR-Indian Agricultural Research Institute, New Delhi during 2021-22. The experiments were carried out at Division of Vegetable Science in collaboration with Division of Plant Physiology and Division of Agricultural Chemicals, ICAR-IARI, New Delhi. In cucumber, parthenocarpic seedless genotypes are widely grown under protected condition throughout the world. Parthenocarpy is the process by which fruits develop in a flower that has without fertilization and it literally translates to "virgin fruit". Seedless cucumbers are gaining popularity day by day and their cultivation fetches more income per unit area to the farmers. It is well known that phytohormones play a crucial role in the negative and positive signalling processes that occur during pollination and fertilisation and are essential for the growth and development of fruit and seeds. The present study was conducted using three cucumber genotypes namely, Pusa Parthenocarpic Cucumber-6 (PPC-6: slicing type gynoecious parthenocarpic), Pusa Pickling Cucumber-8 (DG-8: processing type gynoecious parthenocarpic) and Improved Pusa Uday (IMPU-1: Gynoecious non-parthenocarpic developed through MABC of F locus). Effects of exogenous application of auxin (AUX), gibberellin (GA) and cytokinin (CKs) was studied in the genotype, IMPU-1. Besides, endogenous concentration of important growth hormones and expression of the important genes related to the metabolic pathways of auxins, gibberellins and cytokinin were studied in the three genotypes at different developmental stages. It was observed that exogenous application of phytohormones, particularly AUX, GA, CKs and their combined application resulted in parthenocarpic fruit set and their development into seedless fruit without fertilization in the non-parthenocarpic genotype, IMPU-1. The percentage of fruit set in the genotype, IMPU-1 was as high as the fruit set percentage of parthenocarpic genotypes, PPC-6 and DG-8 through exogenous application. Among various treatments of growth regulators, the combination of AUX and CK had shown the best results followed by individual application of AUX and CK. During the quantification of different endogenous hormones from different cucumber genotypes, it was seen that IAA concentration was highest on 4, 8 and 6 DAA in PPC-6, DG-8 and IMPU-1, respectively. Whereas highest concentration of GA3 was recorded in the genotype, PPC-6 in all the developmental stages. In the case of CKs like trans-zeatin & dihydro-zeatin, mixed responses were seen across the Page 117 | Abstract (English) parthenocarpic and non-parthenocarpic genotypes. But in most of the cases, the concentration of CKs were higher in parthenocarpic genotypes as compared to the non-parthenocarpic. The expression of different genes related to the pathway of AUX, CKs and GA biosynthesis were checked through RT-PCR. The genes like LOG, CYP735A, IPT and CsRR were strongly expressed in the case of parthenocarpic genotypes, whereas lower expression was observed in the non-parthenocarpic one. The CKX gene family showed mixed responses among the parthenocarpic and non-parthenocarpic genotypes. All the genes related to the auxin biosynthesis pathway were upregulated in the case of parthenocarpic genotypes and downregulated in case of non-parthenocarpic genotype, IMPU-1. GA3ox & GA2ox genes, which help in producing various active forms of gibberellin, were shown to have high expression in parthenocarpic pickling cucumber DG-8 in almost all cases. The findings of the present study provide insight about the role and cross-talk among important phytohormones in determining parthenocarpy in cucumber.EnglishThesis