Proper isolation and identification of Phytophthora species is critical due to their broad distribution and huge impact on natural ecosystems throughout the world. In this study, five different sites were sampled and seven methods were compared to determine the Phytophthora community. Three traditional isolation methods were conducted (i) soil baiting, (ii) filtering of the bait water and (iii) isolation from field roots using Granny Smith apples. These were compared to four sources of eDNA used for metabarcoding using Phytophthora-specific primers on (i) sieved field soil, (ii) roots from field, (iii) filtered baiting water and (iv) roots from bait plants grown in the glasshouse in soil collected from these sites. Six Phytophthora species each were recovered by soil baiting using bait leaves and from the filtered bait water. No Phytophthora species were recovered from Granny Smith apples. eDNA extracted from field roots detected the highest number of Phytophthora species (25). These were followed by direct DNA isolation from filters (24), isolation from roots from bait plants grown in the glasshouse (19), and DNA extraction from field soil (13). Therefore, roots were determined to be the best substrate for detecting Phytophthora communities using eDNA.

Phytophthora species isolated from alpine and sub-alpine regions of Australia, including the description of two new species; Phytophthora cacuminis sp. nov and Phytophthora oreophila sp. Nov.

Ascochyta rabiei asexual spores (conidia) were assumed to spread over short distances (~10 m) in a combination of rain and strong wind. The potential distance of conidial spread was investigated in three rainfall and three sprinkler irrigation events. Chickpea trap plants were distributed at the distances of 0, 10, 25, 50 and 75 m from infected chickpea plots before scheduled irrigation and forecast rainfall events. Trap plants were transferred to a controlled temperature room (20 °C) for 48 h (100% humidity) after being exposed in the field for 2-6 days for rainfall events, and for one day for irrigation events. After a 48 h incubation period, trap plants were transferred to a glasshouse (20 °C) to allow lesion development.Lesions on all plant parts were counted after two weeks, which gave an estimate of the number of conidia released and the distance travelled. Trap plants at all distances were infected in all sprinkler irrigation and rainfall events. The highest number of lesions on trap plants were recorded closest to the infected plots -the numbers decreased as the distance from the infected plots increased. There was a positive relationship between the amount of rainfall and the number of lesions recorded. A generalised additive model was developed that efficiently described spatial patterns of conidial spread. With further development, the model can be used to predict the spread of A. rabiei. This is the first systematic study to show that conidia distribute A. rabiei over longer distances than previously reported.

29Ascochyta rabiei asexual spores (conidia) were assumed to spread over short distances 30 (~10 m) in a combination of rain and strong wind. We investigated the potential distance of 31 conidial spread in three rainfall and three sprinkler irrigation events. Chickpea trap plants 32 were distributed at the distances of 0, 10, 25, 50 and 75 m from infected chickpea plots 33 before scheduled irrigation and forecast rainfall events. Trap plants were transferred to a 34 controlled temperature room (20 °C) for 48 h (100% humidity) after being exposed in the field 35 for 2-6 days for rainfall events, and for one day for irrigation events. After a 48 h incubation 36 period, trap plants were transferred to a glasshouse (20 °C) to allow lesion development. 37Lesions on all plant parts were counted after two weeks, which gave an estimate of the 38 number of conidia released and the distance travelled. Trap plants at all distances were 39 infected in all sprinkler irrigation and rainfall events. The highest number of lesions on trap 40 plants were recorded closest to the infected plots -the numbers decreased as the distance 41 from the infected plots increased. There was a positive relationship between the amount of 42 rainfall and the number of lesions recorded. A generalised additive model was developed that 43 efficiently described spatial patterns of conidial spread. With further development, the model 44 can be used to predict the spread of A. rabiei. This is the first systematic study to show that 45 conidia distribute A. rabiei over longer distances than previously reported. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 Keywords: Ascochyta blight, epidemiology, conidial spread, wind-driven rain, chickpea, 62 sprinkler irrigation.63 Introduc)on 64 Chickpea (Cicer arietinum L.) is the second most important legume crop globally and is the 65 most widely grown legume grain crop in Australia with >1,060,000 ha harvested in 2018 66 (FAOSTAT 2020). Ascochyta blight caused by Ascochyta rabiei (syn. Phoma rabiei) is one of 67 the most devastating chickpea diseases worldwide (Pande et al. 2005). With the exception of 68 the Ord region in northern Western Australia, A. rabiei is the major biotic constraint to 69 chickpea production in Australia with almost all chickpea growing areas affected (Bretag et 70 al. 2008). Ascochyta rabiei survives on infected seed, volunteer chickpea plants and infested 71 stubble, forming conidia that initiate primary infection. Infected seed gives rise to infected 72 seedlings through transmission from germinating seeds. Conidia are spread by rain splash or 73 wind driven rain. Pycnidial formation, conidial production, host infection and disease 74 development are favoured by temperatures between 5 and 30 °C (optimum 20 °C), relative 75 humidity > 95 % (Nene 1982), and wetness period of 10 h or more (Khan 1999). A longer 76 wetness period is required for spore germination at sub-optimal temperatures, and infection 77 is rare in hot and dry conditions (Jhorar et al. 1998). Symptoms develop within 5...

Phytophthora cinnamomi has recently been found in highly diverse and fragile alpine and sub-alpine environments previously considered P. cinnamomi and disease free due to low temperatures. In the laboratory, we investigated the ability of P. cinnamomi isolates to adapt to cold and cause disease under conditions comparable to alpine and sub-alpine environments. Initially, the ability of P. cinnamomi isolates to produce sporangia at 10°C (2°C lower than previously reported in the literature) was demonstrated in vitro. The lowest temperature limit for host infection was determined (i.e., 8°C) and the phenotypic plasticity of isolates was then explored in planta in two successive phenotypic plasticity experiments comparing cold 9, 7.5°C, and ambient temperature 25 (±5°C). In the phenotypic plasticity experiment-1, three of the five isolates recovered from plants grown at 9°C produced sporangia and released zoospores (infective propagules) at 7.5°C, even lower than determined initially, i.e., 10°C. No changes were observed in the same set of isolates recovered from plants grown at ambient temperature in the glasshouse as a control, which shows that P. cinnamomi can exhibit phenotypic plasticity and responds rapidly to selection pressure and adapts to new environments. Although P. cinnamomi isolates could produce infective propagules at 7.5°C in vitro, they could not be recovered from inoculated plants grown at 7.5°C after 3 months in phenotypic plasticity experiment-2. More work is, therefore, needed to establish disease development by P. cinnamomi at 7.5°C and below.