Blight
Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this symptom are called blights. Several notable examples are:
Halo blight
Halo blight of bean is a bacterial disease caused by "Pseudomonas syringae pv. phaseolicola". Halo blight’s pathogen is a gram-negative, aerobic, polar-flagellated and non-spore forming bacteria.This bacterial disease was first discovered in the early 1920s, and rapidly became the major disease of beans throughout the world. The disease favors the places where temperatures are moderate and plentiful inoculum is available.Common beans in moderate temperature regions are victims of halo blights. Main hosts are lima beans, red kidney bean, cranberry yellow eye field beans, snap beans, scarlet runner, kudzu vine and common P.vulgaris. Halo blight is affected by environment factors and enter through plant injuries or natural openings. The development of the Halo blight is highly favored by cool temperature (such as 20–23°C), unlike other common bacterial blights. In warm temperatures (over 24 °C), the production of phaseolotoxin decreases and symptoms become less obvious. Phaseolotoxin is a toxin produced by Halo blight pathogen which causes systemic chlorosis. 
Halo blight causes small water-soaked spots on leaves. These spot progressively turn dark brown and are surrounded by a wide greenish yellow halo. The necrotic spots remain small unlike that of common blight. 
Similar to foliage symptoms, halo blights causes water-soaked spots on vegetative pods. It also causes streaks along pod sutures. If lesions becomes severe on the pods, it may penetrate the pod walls or expand into the pod sutures which causes the seed to be wrinkled and discolored (yellow patches on the seed coat). 
Systemic infections are not common, but occur more favorably in some dry bean varieties. If the disease develops a systemic infection, it will cause curling, yellowing and death of young leaflets.