In addition to being resistant to phylloxera, what else must vine rootstocks be resistant to in sherry country?

Vine rootstocks in sherry country must not only be resistant to phylloxera, but they also need to be suitable for the specific conditions of the region, particularly its unique soil composition. Sherry country, situated in the region of Andalusia, Spain, features a notable amount of limestone in its soil, which influences vine health and grape quality. Rootstocks that are tolerant or resistant to high pH soils and can thrive in limestone-rich environments are necessary for optimal growth and fruit production. This adaptation helps ensure that the vine can effectively absorb nutrients and withstand the challenging climatic conditions of the region.

While other factors such as humidity, high temperatures, and fungal diseases are considerations in viticulture, the specific requirement for limestone resistance is especially crucial for the successful cultivation of vines in the context of sherry production. The characteristics of the soil play a direct role in determining the suitability of rootstocks, making this option the correct answer.