Interaction of geographic isolates of Melampsora medusae and Populus: effect of temperature

Abstract

Twelve isolates of the leaf rust pathogen Melampsora medusae Thüm., collected from six locations across the eastern U.S.A., were tested for their reaction on 18 poplar genotypes at two temperatures of incubation (16 and 26 °C). All isolates were recognized as distinct physiologic races, based on the qualitative and quantitative reaction of the isolates on the cultivars. Temperature was an important factor in determining the level and type of disease expression in most cultivar – isolate combinations. The results support the hypothesis that the physical environment may have an important role in the regulation of this "wild" pathosystem. The high degree of race specificity observed in the Populus genotypes and the polymorphism for virulence in the M. medusae population emphasize the importance of maintaining host diversity to manage this disease.

Variation in leaf phenolics of field‐cultivated willow (Salix myrsinifolia) clones in relation to occurrence of Melampsora rust

“…diseases (DAWSON 1992;HELFER 1992;PEI et al 1993). The occurrence and development of leaf rust is affected by several abiotic factors, such as humidity and temperature (PRAKASH and HEATHER 1986;PRAKASH and THIELGES 1989). Moreover, the phytochemical quality of a host plant can affect the growth and spread of the pathogens.…”

Adaptation of poplar leaf rust to Eastern cottonwood

“…Similar results were reported elsewhere . For example, Prakash & Thielges (1989) found that isolates from northern locations were generally avirulent on clone ST75 (of southern origin) while most isolates of southern origin were virulent on that clone . Also, Shain (1988) reported that 10 clones originating from Stoneville, MS were more susceptible to an isolate of Mmd originating from Kentucky than to an isolate from Michigan .…”

“…Broader adaptation of southern sources of inoculum has been reported before in this system, but never quantified . For example, Prakash & Thielges (1989) and Shain (1988) observed that isolates of northern origin were avirulent on some host genotypes but virulent on others, while isolates of southern origin were virulent on all host genotypes . Jenns & Leonard's (1985) variance ratio was developed to provide an index of durability of resistance and can be loosely interpreted as the ratio of vertical to horizontal resistance .…”

“…Physiologic specialization has been reported for Journal series paper 92-8-81 of the University of Kentucky Agricultural Experiment Station Mmd in North America (Prakash & Thielges, 1987, 1989, for M . larici populina in Australia Chandrashekar & Heather, 1980), and in Europe where a race present in the Netherlands and in Belgium was virulent on four cultivars which were found to be highly resistant to French isolates (Pinon et al ., 1987) .…”

Selection of pathogen agents in weed biological control: critical issues and peculiarities in relation to arthropod agents

“…It is a reasonable strategy to adopt when considering that the majority of pathogens are highly dependent on environmental conditions to cause severe damage on their host. There is evidence that rust fungi, and probably other fungal pathogens as well, can adapt to different climates and consequently generate strains that have slightly different temperature optima to infect their host (Prakash & Heather 1986;Prakash & Thielges 1989). The most damaging pathogens, however, may be difficult to locate in areas where climate is highly conducive to frequent and severe disease epidemics because they may have reduced the distribution and abundance of the host plant to very low levels (Wapshere 1985).…”