Virus-free plants can be produced from virus injected parent plant by:

Question

Accepted Answer

The correct option is 1:

Stem tip culture, more precisely known as **Meristem-tip culture** or **Shoot tip culture**, is the most reliable and widely used technique for the production of virus-free plants from an infected parent. This efficacy is rooted in a fundamental biological principle: in systemically infected plants, the virus typically spreads through the vascular tissues, primarily the phloem. The apical meristem, the dome-shaped region of actively dividing, undifferentiated cells at the very tip of the shoot, generally either lacks a fully developed vascular system or its cells divide at a rate significantly faster than the virus can replicate and move into them. By carefully excising a very small segment of the shoot apex—usually less than 0.5 mm, consisting of the apical dome and a few leaf primordial—and culturing it *in vitro* on a nutrient medium, a new, genetically stable plantlet can be regenerated that is an exact clone of the parent but entirely free of the virus. This process is essential for the commercial propagation of many crops, such as potato, sugarcane, and ornamentals, which are prone to chronic viral infections.

The incorrect option is 2:

**Leaf explant culture** involves taking a piece of differentiated leaf tissue to regenerate a new plant. Unlike the apical meristem, the cells of a mature leaf are fully connected to the plant’s vascular system, meaning that if the parent plant is systemically infected with a virus, the virus particles will have readily invaded the leaf cells. Therefore, culturing a leaf explant is highly unlikely to produce a virus-free plant and often results in the propagation of the viral disease along with the plant tissue. While leaf explants are excellent for general micropropagation and certain organogenesis studies, they cannot be used reliably for the purpose of eliminating viral pathogens.

The incorrect option is 3:

**Ovule culture** is a plant tissue culture technique used to cultivate very young ovules, often utilized in processes like embryo rescue to overcome pre- or post-fertilization barriers in wide crosses or to speed up the breeding cycle. However, the ovule, being a part of the mature floral structure, is not inherently virus-free. Pathogens, including viruses, can be transmitted through the flower and potentially infect the ovule tissue, particularly through the vascular connections of the placenta. Ovule culture’s primary application is reproductive biology and hybrid development, not the specific function of viral elimination, for which it offers no special protective mechanism.

The incorrect option is 4:

**Anther culture** is a technique aimed at producing haploid plants (plants containing half the number of chromosomes, *n*) by culturing the anthers (which contain the male gametes or pollen). The resulting plantlets are genetically different from the parent and are useful for quickly creating homozygous lines in plant breeding programs. The technique does not specifically target or exclude viral particles from the anther tissue or the developing microspores. While some viruses may not readily infect pollen, the method's purpose is genetic manipulation (haploid production), and it is not a primary or standardized method for ensuring a virus-free status in regenerated plants.