Rust of Dry Beans

Rust of Dry Beans


Rust is a common and potentially serious disease of dry as well as snap beans. It is caused by Uromyces appendiculatus (Pers.:Pers.)Unger. The fungus exists in races determined by host reaction to infection. Over 250 such physiological races have been identified. Bean rust development is favored by cool to moderate, wet weather conditions and can occur in either the spring or fall of the growing season. The life cycle of the fungus is divided into five spore stages: spermatia, aeciospores, urediniospores, teliospores, and basidiospores. The fungus overwinters as teliospores in plant debris (bean straw). All five spore stages are found on the bean host. Primary infection begins when basidiospores are produced from teliospores. These spores are windblown to susceptible plants where they germinate and penetrate the upper leaf surface through stoma. A layer of free water is necessary for germination and penetration to occur. A spermagonium (pycnia) containing spermatia forms and spermatia cross-fertilize producing mycelium which grows through the leaf to the lower surface. An aecium, containing aeciospores is produced directly below the spermagonium. Aeciospores reinfect the bean plant producing pustules called uredinia on both leaf surfaces as well as other plant parts. This is the repeating cycle of the fungus. Several generations of urediniospores are produced in a given season and reinfect bean plants. Urediniospores thus serve as inoculum for secondary spread of the disease. In more northern growing bean regions such as western Nebraska and eastern Colorado, these spores also act as primary inoculum when they are wind blown from southern bean growing regions. These spores may also be produced early on volunteer beans and be wind blown to the current season crop. Finally as the plant begins to mature, teliospores are produced in the uredinia, converting it to a telium.

Symptoms


The spermagonium (pycnia) appears as small chlorotic flecks on the upper leaf surface. The aecium, which develops on the lower leaf surface is white in color and also very small (1-2 mm). The uredinia is the most visible symptoms of the disease. Initially they appear as small raised yellow or white spots on upper and lower leaf surfaces. As they the mature, reddish-brown pustules are formed that contain thousands of spores. The epidermis of the leaf is ruptured at this point and spores are easily rubbed off. Uredinia vary in size. Larger pustules may be surrounded by a yellow halo of host tissue which in turn is surrounded by a ring of smaller uredinia (awful close to compendium description but I tried to change it a bit.) As the season progresses, blackish-brown teliospores are produced in the uredinium giving it a darker color and a new name, a telium. When sever infections occur, the leaves curl upward, dry, turn brown, and are shed prematurely. Pod set and fill as well as seed sized are reduced when a severe infection occurs.

Plant Health Management

References

Useful Links

Highlighted Area

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

E-Mail Home Page

Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.