Explanation of each statement:

A) Recombinant inbred lines and double haploid populations have high levels of genetic homozygosity.

• Correct. RILs are produced by many generations of selfing, and doubled haploids are made homozygous in a single step by chromosome doubling of a haploid. Both populations are essentially homozygous at nearly all loci and are often called “immortal” lines in breeding and mapping.

B) Gene pyramiding involves introducing different genes for resistance to a specific pest in different genotypes of a plant species.

• Incorrect. Gene pyramiding means combining or stacking multiple resistance genes (often for the same pest or pathogen) into the same plant genotype so that a single variety carries several R-genes simultaneously. Spreading them across different genotypes is the opposite of pyramiding.

C) Agrobacterium strains with a disarmed Ti plasmid do not require vir genes for transfer of T-DNA.

• Incorrect. “Disarming” removes tumor‑forming genes from the T‑DNA region but keeps the vir (virulence) genes, which are essential for processing and transferring T‑DNA into the plant genome. Without functional vir genes, T‑DNA transfer does not occur.

D) Molecular breeding can be used for crop improvement if the trait of interest is present in naturally occurring populations of the plant.

• Correct. Molecular breeding (e.g., marker‑assisted selection, genomic selection) works by tagging and selecting alleles that already exist in the species’ germplasm. If the trait of interest is present in natural populations, markers can be developed and used to introgress and select that trait efficiently.

Thus, among the four statements, B and C are incorrect, giving answer (4) B and C.