It is hard to predict how changes in the climate and the atmosphere’s chemistry will affect the prevalence and virulence of agricultural diseases. But there is a risk that such changes will make some plant infections more common in all climatic zones, perhaps catastrophically so. Part of the problem is that centuries of selective breeding have refined the genomes of most high-value crops. They are spectacular at growing in today’s conditions but genetic variations that are not immediately useful to them have been bred out. This is good for yields but bad for coping with changes. A minor disease or even an unknown one could suddenly rampage through a genetically honed crop.

With reference to the above passage, the following assumptions have been made:
I. Global climate change can result in the migration of several plant diseases to new areas.
II. Scientific understanding of the wild relatives of our present crops would enable us to strengthen food security.
Which of the above assumptions is/are valid?

The correct option is Both I and II.

Let us analyze the given assumptions based on the passage:

Analysis of Assumption I:
The passage mentions that "changes in the climate and the atmosphere’s chemistry" may "make some plant infections more common in all climatic zones". If infections become common across all climatic zones due to climate change, it logically implies that these plant diseases can migrate or spread to new geographic areas/climatic zones where they might not have been prevalent previously. Therefore, Assumption I is valid.

Analysis of Assumption II:
The passage highlights that "centuries of selective breeding have refined the genomes of most high-value crops" and "genetic variations that are not immediately useful to them have been bred out," making them vulnerable to changing conditions and diseases. To overcome this lack of genetic variation and strengthen crop resilience (and thus food security), relying on scientific understanding of the wild relatives (which retain genetic diversity) is a valid implicit assumption for addressing the core issue discussed. Therefore, Assumption II is valid.

Thus, both assumptions I and II are valid inferences/assumptions grounded in the context of the passage.