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. 2023 Nov 3:14:1284070.
doi: 10.3389/fpls.2023.1284070. eCollection 2023.

Genetic enhancement of okra [ Abelmoschus esculentus (L.) Moench] germplasm through wide hybridization

A Suma  1 , K Joseph John  1 , Kangila Venkataramana Bhat  2 , Madhavan Latha  1 , Chakkamadathil Jayasundaran Lakshmi  1 , Mottaiyan Pitchaimuthu  3 , V A M Nissar  1 , Polavakkalipalayam Palanisamy Thirumalaisamy  1 , Chitra Devi Pandey  2 , Sushil Pandey  2 , Ashok Kumar  2 , Raj Kumar Gautam  2 , Gyanendra Pratap Singh  2
Affiliations

Genetic enhancement of okra [ Abelmoschus esculentus (L.) Moench] germplasm through wide hybridization

A Suma et al. Front Plant Sci. .

Abstract

Introduction: The introgression of genetic material from one species to another through wide hybridization and repeated back-crossing, plays an important role in genetic modification and enriching the cultivated gene-pool with novel genetic variations. Okra (Abelmoschus esculentus [(L.) Moench)] is a popular vegetable crop with high dietary fibre and protein, rich in essential amino acids, lysine and tryptophan. The wild Abelmoschus genepool has many desirable traits like ornamental value, short internodal length, more number of productive branches, extended bearing, perennation tendency, reduced fruit length (more consumer preferred trait), high mucilage content (medicinal value), abiotic stress tolerances such as drought, high temperature and biotic stress resistances such as okra Yellow Vein Mosaic Virus (YVMV) and Enation Leaf Curl Virus (ELCV) diseases. The repeated use of elite breeding lines led to narrowing of the genetic base of the okra crop, one of the major factors attributed to breakdown of resistance/ tolerance to biotic stresses. YVMV and ELCV are the two major diseases, causing significant yield loss in okra. Hence, wide hybridization was attempted to transfer tolerance genes from wild species to the cultivated genepool to widen the genetic base.

Material and methods: The screening of germplasm of wild Abelmoschus species at hotspots led to the identification of tolerant species (Abelmoschus pungens var. mizoramensis, A. enbeepeegeearensis, A. caillei, A. tetraphyllus and A. angulosus var. grandiflorus), which were further used in a wide-hybridization programme to generate interspecific hybrids with the cultivated okra. Presence of pre- and post-zygotic barriers to interspecific geneflow, differences in ploidy levels and genotype specific variations in chromosome numbers led to varying degrees of sterility in F1 plants of interspecific crosses. This was overcome by doubling the chromosome number of interspecific hybrids by applying Colchicine at the seedling stage. The 113 cross derivatives generated comprising amphidiploids in the F1 generation (30), F3 (14), one each in F2 and F4 generations, back cross generation in BC1F2 (03), BC1F3 (25), and BC2F3 (02), crosses between amphidiploids (27), multi-cross combinations (07) and inter-specific cross (between A. sagittifolius × A. moschatus subsp. moschatus) selfed derivatives at F8 generation (03) were characterized in the present study. Besides they were advanced through selfing and backcrossing.

Results and discussion: The amphidiploids were found to possess many desirable genes with a considerable magnitude of linkage drag. Majority of the wide cross derivatives had an intermediate fruit morphology and dominance of wild characters viz., hispid fruits, stem, leaves, tough fruit fibre, vigorous perennial growth habit and prolonged flowering and fruiting. The fruit morphology of three BC progenies exhibited a high morphological resemblance to the cultivated okra, confirming successful transfer of useful genes to the cultivated okra genepool. The detailed morphological characteristics of the various combinations of Abelmoschus amphidiploids and the genetic enhancement of the genepool achieved in this process is reported here.

Keywords: amphidiploids; colchicine; crop wild relatives; morphological characterization; polyploidization; pre-breeding.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
(A) Colchicine treatment using cotton swab method on interspecific hybrid seedlings. Inset: close-up photograph of colchicine treatment. (B) Colchicine un-treated and treated seedlings. (C) Bulging at the colchicine-treated site.
Figure 2
Figure 2
Flowchart of wide hybridization, Abelmoschus amphidiploid development, and generation advancement.
Figure 3
Figure 3
Timeline showing the wide hybridization program in okra.
Figure 4
Figure 4
Variability in fruits of various amphidiploid derivatives.
Figure 5
Figure 5
(A) Reddish coloration on stems and petioles. (B) Clustered flower buds in C1Pusamizo derivatives. (C) Hispid fruits.
Figure 6
Figure 6
Fruit variability in selfed derivatives of F2, F3, and F4 generation. (A) Reddish fruits of AM-8. (B) Short fruit of AM-23. (C) Soft and spongy fruit of AM-3. (D) Fruit of C2/Ruchi/tetra1 with intermediate fruit length. (E) General variability in fruits of selfed derivatives.
Figure 7
Figure 7
(A) Fruit of C3/50/mizo34 × Parbhani Kranti. (B) Segregation in stem color in C3/50/mizo34 × Salkeerthi. (C) Medium-long fruits of C3/50/mizo1 × IC31398A. (D) Velvety fruits of C3/50/mizo34 × IC22232. (E) Tall growth habit of C3/106/mizo6 × Hissar Unnat. (F-1, F-2) Fruits of C3/106/mizo6 × Kashi Vibhuti and C3/106/mizo6 × Hissar Unnat with low trichome density. (G-1, G-2) Short fruits of B16 × Arka Anamika and B13 × Arka Anamika.
Figure 8
Figure 8
(A) Fruit. (B) Flower bud with epicalyx. (C) Flower base of C3/50/mizo1 × A.esculentus cv. Kashi Lalima. (D) Kashi Lalima.
Figure 9
Figure 9
Backcrossed derivatives with cultivated okra morphology (A) Ruchi × AM-6. (B) Ruchi × AM-24. (C) Arka Anamika × AMPK-1.
Figure 10
Figure 10
Increase in fruit length in derivatives of cross between amphidiploids (A) B-15 × AM-25, (B) AM-25 × CR-1, (C) B-13 × AM-24, and (D) B-16 × AM-24.
Figure 11
Figure 11
(A) Slender epicalyx. (B) Bright yellow flower. (C) Oblong fruit of AM-19.
See this image and copyright information in PMC

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