Resistant annual and herbaceous perennial plant species were identified as key hosts which allow Phytophthora cinnamomi to persist on severely impacted black gravel sites within the Eucalyptus marginata (jarrah) forest of southwest Western Australia. Of the annual and herbaceous perennial plant species present on black gravel sites, 15 out of 19 species were found to be hosts of P. cinnamomi, and 10 of these were symptomless hosts. In particular, the native annual Trachymene pilosa and the two native herbaceous perennials Stylidium diuroides and Chamaescilla corymbosa were commonly found to be hosts of the pathogen. Species from 12 new genera including three from new families (Crassulaceae, Droseraceae and Primulaceae) are reported for the first time to be hosts of P. cinnamomi. The species from which P. cinnamomi was recovered were the native species:

The flower morphology, receptivity and sexual compatibility between genotypes and species were determined in Western Australian sandalwood (Santalum spicatum) and Indian sandalwood (S. album). The results showed that the stigma of both species became receptive at anthesis and reached a peak at 3 or 4 days after anthesis. Pollen tubes took 2 days to grow to the ovary when pollinated at anthesis, and 1 day when pollinated 2 or 3 days after anthesis. The egg apparatus matured at least 2 days after pollination and varied between genotypes. Fertilisation occurred 2 or 3 days following cross pollination. Although 10–40% of ovules were fertilised following intra-specific crosses of both species, the average initial fruit set was much lower: 4% in S. spicatum and 19% in S. album. Most immature fruit (75–80%) abscised following intra-specific pollination. The number of pollen tubes that grew in styles after self-and inter-specific pollination was lower than that for intra-specific pollination. Following self and inter-specific pollination, growth of pollen tubes was arrested in the style, ovary and around the embryo sac; a few penetrated the embryo sac. Initial fruit set was low and developing fruit abscised prematurely. The results indicated that pre- and post-fertilisation mechanisms control self-incompatibility and inter-specific incompatibility between the sandalwood species.

The effect of NaCl on growth was examined for whole plants and callus cultures of a salt-sensitive glycophyte (Phaseolus vulgaris L.), a salt-tolerant glycophyte (Beta vulgaris L.) and two halophytes (Atriplex undulata D. Dietr., which has salt glands, and Suaeda australis (R. Br.) Moq., a succulent). Whole plants were grown in nutrient solution culture at NaCl concentrations of 0.1-250 mM. Callus cultures were initiated from the same seed stock, and similar saline regimes were imposed. Whole plant responses were characteristic for the various types of plants: P. vulgaris showed a decrease in growth with increasing salinity; B. vulgaris showed a slight increase in growth at the intermediate salt level and a decrease at higher levels; A. undulata and S. australis showed well defined growth optima at 62.5 mM and 125 mM NaCl, respectively. Callus cultures of P. vulgaris and the two halophytes grew very poorly when salinity was increased. Callus of B. vulgaris showed the same tolerance to salt as did the whole plants. Thus salt tolerance of the halophytes depends on the anatomical and physiological complexity of the intact plant while callus from B. vulgaris appears to have a mechanism(s) of salt tolerance which operates at the cellular level.

Plants of the eucalypt. Eucalyptus marginata. selected through a glasshouse screening procedure for resistance or susceptibility to Phytophthora cinnamomi, were established in tissue culture and micropropagated. After inoculation with P. cinnamomi, root lesions in clonal lines selected as resistant (RR) to P. cinnamomi were restricted and became contained within four days after inoculation while lesions in roots of those lines susceptible (SS) to P. cinnamomi continued to extend rapidly. Activity of phenylalanine ammonialyase (PAL) was increased above controls in root segments of the RR lines 48 h after inoculation with P. cinnamomi while activity in unselected seedlings and the SS lines was reduced or unchanged. After inoculation, lignin concentration was increased and reached high levels compared with uninoculated control levels in roots of the two RR lines tested. Constitutive levels of phenolics in roots of the RR lines were up to 94% higher than in seedling roots and levels were further increased after inoculation. Levels of phenolics in the other lines and seedlings were unaltered by inoculation. A line derived from resistant seedlings from a susceptible family (RS) had the highest constitutive levels of lignin, which were further increased after inoculation. Resistance to P. cinnamomi in clonally propagated E. marginata seedlings is based on similar mechanisms to those of field resistant species.

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