Separation of Two Ecotypes of Phytophthora Drechsleri Tucker Occurring in Australian Native Forests

Abstract

A total of 70 isolates of P. drechsleri from Australian native eucalypt forests were separated into two distinct ecotypes. The "northern" ecotype occurred from North Queensland to the south of New South Wales, while the "southern" ecotype occurred in South Australia, Victoria, Tasmania, and New South Wales.The northern ecotype on average grew faster on a variety of media than did the southern one, but ecotypes could not be recognized unequivocally on this basis. The upper temperature limit for growth of the northern ecotype was in the range 36-37' 5°C, while that for the southern was 33-36°C. Ecotypes could be separated on the bases of their growth rates in the presence of 33 .ug/ml Cu2+ ions (23' 54 and 55· 66 % of the growth in the absence of copper by the northern and southern ecotypes respectively), orin the presence of 1 p.p.m. pyronin G (63' 34 and 33· 87 % of the growth in the absence of pyronin G by the northern and southern ecotypes respectively). Both ecotypes showed similar pH optima for growth, similar responses to the effects of exposure at 44°C on subsequent growth at 25°C, and similar degrees of growth inhibition by 0·05 p.p.m. malachite green.It is tentatively suggested that the geographic distribution of the southern ecotype is related to the area enclosed by the 29·4 °C (85°F) isotherm of average daily maximum temperature during the period November to March annually.

Phylogenetic relationship of Phytophthora cryptogea Pethybr. & Laff and P. drechsleri Tucker

“…Moreover, the high-temperature criterion did not always correlate with the other identifying features (Klisiewicz & Beard 1976;Banihashemi & Ghaisi 1993) and as a result, some isolates were described as intermediate between both species (Flowers et al 1973;Shepherd & Pratt 1973;Klisiewicz 1977;Stanghellini & Kronland 1982). This led some investigators to cast doubt upon the validity of temperature response as the main distinguishing feature (Shepherd & Pratt 1973;Klisiewicz 1977), while others simply rejected P. drechsleri as an acceptable species (Bumbieris 1974;Gerrettson-Cornell 1979). Some maintained that P. drechsleri should be kept as an acceptable species until more conclusive data were obtained (Kannaiyan et al 1980;Krö ber 1981).…”

STIMULATION OF SEX ORGAN FORMATION IN PHYTOPHTHORA BY ANTAGONISTIC SPECIES OF TRICHODERMA

“…However, it is apparent that ecological specialization towards response to Trichoderma and other agencies could lead to speciation and other complex phylogenetic relationships in the heterothallic species. Such a phenomenon might account for the occurrence of two ecotypes among isolates of Phytophthora drechsleri from Eucalypt forests in Australia, one A2 and responsive to Trichoderma, the other sterile and nonresponsive (Shepherd and Pratt, 1973). …”

Characterization of an Isolate of Phytophthora Nicotianae Var. Nicotianae From North Queensland

“…The results (Table 3) are similar to those reported by other authors (Tucker 1931;Leonian 1934;Schwinn 1959;Waterhouse 1963) for isolates from other countries. Shepherd and Pratt (1973) have reported that cultures of P. drechsleri Tucker were incapable of growth at 44°C, but when such cultures were returned to 25°C growth would sometimes recommence after a lag period. The tolerance to high temperature of the Queensland isolate of P. nicotianae var.…”

“…Effects of temperature, presence or absence of sterol, and form of nitrogen source on mycelial growth rates were determined according to Shepherd and Pratt (1973). Electronically controlled incubators were used to maintain desired incubation temperatures to ±0'1 DC.…”

“…For comparison of growth on various carbohydrates, the casein hydrolysate basal medium of Shepherd and Pratt (1973) was used with the original carbon source replaced by an 8 mM concentration of the carbohydrate to be studied. Medium pH was adjusted to 6· 5 before autoclaving at 10 Ib/in.…”