Temperature sensitivity of qualitative race‐cultivar interactions in Melampsora medusae Thüm. and Populus species

Abstract

Six mono‐uredospore isolates (races) of Melampsora medusae Thiim. produced qualitatively distinct reactions, in vitro, when incubated at 15 °C on leaf disks of certain cultivars of Populus deltoides Marsh. The infection types in some race‐cultivar combinations were very temperature sensitive with less distinct reactions when incubated at 20 or 25°C. The significance of differential race‐cultivar‐temperature interaction in the epidemiology of M. medusae is discussed.

Effects of pre‐ and post‐inoculation photoperiod on the severity of Melampsora medusae leaf rust of Populus species

“…Leaf discs cut from P. deltoides cv. W79/ 304 and W79/307 raised with a 15 h preinoculation photoperiod gave a mesothetic reaction (infection type 3, Singh & Heather, 1982d) but a highly susceptible reaction (infection type 4) when cut from plants of the same cultivars grown with a 10 h photoperiod. Leaf discs from the P. X euramericana 5^v.…”

“…Urediniospores (mo'no-urediniospore origin) of race 4 of M. medusae were multiplied to obtain at least 20 mg of dried inoculum (Singh & Heather, ]982d). The selection and surface treatment of leaves, the cutting of leaf discs and the inoculation of the latter with 5-mg lots of uredinlcspores in a spore settling tower followed procedures detailed by Singh & Heather (1982d). To obtain sufficient inoculated, replicate discs of all cultivars, raised with the two preinoculation photoperiods, for in.cubation with the two po.st-inociilation photoperiods, it was necessary to repeat the inoculation four times.…”

Pathogenic variation in Melampsora medusae leaf rust of poplars

“…Similar observations have been made in M. medusae and M. larici-populina (KLEB.) in Australia (SINGH & HEATHER, 1982;CHAN-DRASHEKARLZCHEATIGR, 1980). Eight races of M. medusae could be categorized by employing virulence, intermedi- Euphytica36 (1987) ate and avirulence reactions as criteria.…”

“…Both the field spore collections and the mono-uredium derived isolates were cultured on detached leaf segments of cv. I-488, an apparent universal suscept (SINGH & HEATHER, 1982;PRAKASH & HEATHER, 1986a). Dry spores were dusted gently, under aseptic conditions, on surface-treated (0.1% sodium hypochlorite and sterile water series) leaf segments of cv.…”

“…Management of this pathogen in Australia by employing resistant cultivars has been constrained by the existence of several races of M. medusae (SINGH & HEATHER, 1982) and the consequent race-specific resistance of the cultivars. In North America, there is limited evidence of pathogenic variability in M. medusae (SHA~U, 1978).…”