Severity of phytophthora root rot and pre‐emergence damping‐off in subterranean clover influenced by moisture, temperature, nutrition, soil type, cultivar and their interactions

Abstract

Studies were carried out in controlled environment rooms reflecting field situations. In the presence of the devastating soilborne pathogen Phytophthora clandestina, subterranean clover (Trifolium subterraneum) seedling emergence was significantly affected by moisture, soil type, temperature and cultivar. The level of rotting of tap and lateral roots was significantly affected by nutrition, soil type, temperature and cultivar. There were significant interactions involving temperature, moisture, soil type and cultivar; cultivar resistance, high moisture, high or medium temperature, high nutrition and sand soil all contributed towards less pre‐emergence damping‐off and tap and lateral root disease and to greater clover productivity. Host resistance of subterranean clover cultivars was critical for reducing disease severity and increasing productivity, even when favourable environmental conditions for severe disease occurred. In the presence of P. clandestina, the most resistant cultivar, Seaton Park, performed best under a high temperature, high nutrition and high moisture combination, but showed lower productivity under conditions of low nutrition or lower temperature, even when moisture level was high. In contrast, less resistant cultivars Riverina and Meteora had less disease and greater productivity under low moisture conditions. Findings reflect field observations that pre‐emergence damping‐off and root disease from P. clandestina in subterranean clover is particularly severe under colder conditions and in nutritionally impoverished sandy soils, and demonstrate how variations in soil type, nutrition, moisture, temperature and cultivar have profound effects on the expression and severity of phytophthora pre‐emergence damping‐off and root disease and the productivity of subterranean clover forages.

Critical factors driving aphanomyces damping‐off and root disease in clover revealed and explained using linear and generalized linear models and boosted regression trees

“…() and the current study are widely applicable across soilborne oomycete pathogens of forage legumes. These studies contrast with previous investigations of other pathogens, such as P. clandestina and R. solani , where only analyses of variance were used in an attempt to decipher these complex relationships (You & Barbetti, ,). In the current study, it is noteworthy that there were multiple significant interactions for each dependent variable (emergence, tap and lateral root disease, dry shoot and root weight) and all environmental explanatory variables were significant as part of some interaction or as main effects within these models in relation to dependent variables temperature, soil, moisture, nutrition and variety.…”

“…Experimental design was as described by You & Barbetti (,) as follows: There were four replicate pots for each treatment, with treatments in a full factorial arrangement, and all treatments were kept in their respective temperature‐controlled rooms for the duration of the experiments. All inoculated treatments were repeated using noninoculated soils as control comparisons.…”

“…Experiments were conducted in a similar manner to those of You & Barbetti (,) for other soilborne pathogens of subterranean clover. Briefly, experiments were undertaken in three separate controlled environment rooms with temperatures maintained at 22/17 °C, 18/13 °C or 14/9 °C (day/night) with a 12 h photoperiod and light intensity of 540 μmol m −2 s −1 .…”

“…These temperature ranges also approximate to those used in other studies of soilborne diseases of subterranean clover (e.g. Wong et al ., , ; You & Barbetti, ,).…”

“…The important oomycete soilborne pathogens on subterranean clover include Aphanomyces trifolii , various Pythium species, particularly Pythium irregulare , Phytophthora clandestina and Rhizoctonia solani (Wong et al ., ,; Barbetti et al ., ,, , ; You et al ., , ; Ma et al ., ; O'Rourke et al ., ; Nichols et al ., ; You & Barbetti, ). Recently, Foster et al .…”