What is an indicator of manganese (Mn) deficiency in cereals?

The presence of grey speck, which appears as oval spots on new leaves, is a classic indicator of manganese (Mn) deficiency in cereals. Manganese plays a crucial role in various physiological processes, including photosynthesis and the synthesis of chlorophyll. When levels of manganese are insufficient, it disrupts these processes, leading to characteristic leaf symptoms.

In particular, the grey speck symptoms manifest due to the impaired synthesis of chlorophyll, which is essential for the plant's green color. As a result, the leaves may appear pale and develop these distinct oval spots, often indicating that the younger leaves are experiencing the greatest impact from the deficiency. This visual cue helps farmers and agronomists identify and rectify nutrient management issues in crops.

The other choices describe symptoms associated with different nutrient deficiencies or plant stress responses, making them less relevant when specifically identifying manganese deficiency in cereals.