Mango rootstock, 13-1, is used to combat the problem of:

Correct option is B

The Mango rootstock 13-1 is known for its salt tolerance, making it ideal for cultivation in saline and coastal regions. It helps mango plants grow in soils with high salinity levels, which would otherwise hinder normal root function and plant development. This rootstock is often used in mango breeding programs to improve the adaptability of commercial varieties.