Final answer:
Sphingomonas is the bacterial genera that produces pigments to protect plant leaves from UV irradiation, as they produce carotenoid pigments with photoprotective and antioxidant properties.
Step-by-step explanation:
The bacterial genera that produces pigments which protect plant leaves from UV irradiation is Sphingomonas. Sphingomonas is known for its ability to produce carotenoid pigments that can shield plants from the harmful effects of UV light.
These pigments function not only as photoprotective agents but they also have antioxidant properties, helping to neutralize reactive oxygen species induced by UV exposure. While other bacterial genera such as Nocardia, Cellulomonas, and Arthrobacter are notable for various characteristics, they are not particularly recognized for UV-protective pigments in plants.