Understanding the regulatory role of important growthhormonesin relation to parthenocarpy in cucumber (Cucumis sativus L.)
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Date
2022
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DIVISION OF VEGETABLE SCIENCE ICAR- INDIAN AGRICULTURAL RESEARCH INSTITUTENEW DELHI – 110012
Abstract
The 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
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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.