Cytogenetics and Consequences of Polyploidization on Different Biotic-Abiotic Stress Tolerance and the Potential Mechanisms Involved

Abstract

The application of polyploidy in sustainable agriculture has already brought much appreciation among researchers. Polyploidy may occur naturally or can be induced in the laboratory using chemical or gaseous agents and results in complete chromosome nondisjunction. This comprehensive review described the potential of polyploidization on plants, especially its role in crop improvement for enhanced production and host-plant resistance development against pests and diseases. An in-depth investigation on techniques used in the induction of polyploidy, cytogenetic evaluation methods of different ploidy levels, application, and current research trends is also presented. Ongoing research has mainly aimed to bring the recurrence in polyploidy, which is usually detected by flow cytometry, chromosome counting, and cytogenetic techniques such as fluorescent in situ hybridization (FISH) and genomic in situ hybridization (GISH). Polyploidy can bring about positive consequences in the growth and yield attributes of crops, making them more tolerant to abiotic and biotic stresses. However, the unexpected change in chromosome set and lack of knowledge on the mechanism of stress alleviation is hindering the application of polyploidy on a large scale. Moreover, a lack of cost-benefit analysis and knowledge gaps on the socio-economic implication are predominant. Further research on polyploidy coupling with modern genomic technologies will help to bring real-world market prospects in the era of changing climate. This review on polyploidy provides a solid foundation to do next-generation research on crop improvement.

Keywords: cytogenetics; fluorescent in situ hybridization; genomic in situ hybridization; polyploidy; stress.

Figure 1

Mechanism of in vivo polyploidization; (a). Seeds soaking (6–24) hours with colchicine (0.01–0.2)%, (b). Colchicine treatment (10–20 µL) 10 days in the young leaves, (c). Leaves binding with clips for maximum chemical attachment, (d). Flow cytometry analysis for ploidy level assessment, (e). Ploidy level assessment by a histogram, (f). Hibiscus ploidy assessment using chromosome number; and 5S rDNA (green) and 18 rDNA (red) signals.

Figure 2

Histograms show the flow cytometry analysis of comparative changes in ploidy levels in watermelon. (a) Diploid (2n = 2x = 24), (b) tetraploid (2n = 4x = 48), and (c) octaploid (2n = 8x = 96). Red arrows indicate ploidy levels of diploid, tetraploid and octaploid.

Figure 3

Working steps for fluorescent and genomic in situ hybridization were used for the cytogenetic study of horticultural modified crops. Different methods, such as nick translation, random primed labeling, and PCR, are used to label the probe during marker labeling. Various methods, such as autoclaving, shearing the DNA with a tiny needle in a syringe, or sonicating, are used to prepare to block DNA. Chromosome slide preparation is the selection of well-spread chromosomes prepared from a young root tip using an enzyme mixture at 37 °C. Slide pretreatment is the enzymatic digestion of the chromosomes in order to unmask the DNA prior to hybridization. Hybridization involves the attachment of blocking and probe/genomic markers with chromosomes to identify the specific loci/origin of the genome of the respective chromosome. During detection, attachment of the designed antibody against the target marker along with blocking buffer to detect the specific fluorochrome.

Figure 4

In situ hybridization of diploid (2n = 2x = 24) Lilium. (a). FISH analysis of intraspecific F1 using 5S and 45S ribosomal DNA; (b). GISH analysis of interspecific (L. longiflorum × L. hansonii) F1 using genomic DNA; and (c). FISH and GISH combined analysis of interspecific (L. longiflorum × L. Oriental hybrid) F₁ using 5S, 45S rDNA, and genomic DNA.

Figure 5

Leaf morphology and stomata size of watermelon induced by oryzalin. (a). diploid leaf, (b). tetraploid leaf, (c). stomata of diploid, and (d). stomata of a tetraploid leaf, respectively. Scale bar= 10 μm [17].

Figure 6

Can insects identify different ploidy level plants? According to Segraves and Anneberg [185], insects forage more on predominant cytotypes in a natural habitat where different ploidy plants coexist ((a); where we imagine that small plants are predominant here, insect will forage more on small plants rather than flowers of bigger plants, i.e., irrespective of ploidy level). Contrarily, insects forage equally in a common garden where mixed cytotypes are grown ((b); imagine there are different ploidy levels flower in the common garden. Insects generally fail to detect different ploidy levels; thus, they forage equally in a common garden).

Figure 7

Effect of polyploidy on pathogen resistance. The sign next to the arrow gives the direction of the effect. The sign “+’’ means the higher ploidy level increases the probability of effects, while “−” means the higher ploidy level decreases the probability of effects. Pot represents the combined effect of the polyploidy plant. The gene-for-gene model is the general mechanism of pathogen resistance. In the polyploidy host, high allelic diversity with dominant allele, fixed heterosis, and high expression (desirable) of resistance gene directly influence the pathogen resistance. The validated disease resistance genes and their target pathogens are given as examples [54]. The effects of ploidy-level variation on host adaptability under diverse environmental conditions (biotic and abiotic stress) could indirectly influence parasite resistance.