Predicting Cereal Root Disease in Western Australia Using Soil DNA and Environmental Parameters

Root diseases have long been prevalent in Australian grain-growing regions, and most management decisions to reduce the risk of yield loss need to be implemented before the crop is sown. The levels of pathogens that cause the major root diseases can be measured using DNA-based services such as PreDicta B. Although these pathogens are often studied individually, in the field they often occur as mixed populations and their combined effect on crop production is likely to vary across diverse cropping environments. A 3-year survey was conducted covering most cropping regions in Western Australia, utilizing PreDicta B to determine soilborne pathogen levels and visual assessments to score root health and incidence of individual crop root diseases caused by the major root pathogens, including Rhizoctonia solani (anastomosis group [AG]-8), Gaeumannomyces graminis var. tritici (take-all), Fusarium pseudograminearum, and Pratylenchus spp. (root-lesion nematodes) on wheat roots for 115, 50, and 94 fields during 2010, 2011, and 2012, respectively. A predictive model was developed for root health utilizing autumn and summer rainfall and soil temperature parameters. The model showed that pathogen DNA explained 16, 5, and 2% of the variation in root health whereas environmental parameters explained 22, 11, and 1% of the variation in 2010, 2011, and 2012, respectively. Results showed that R. solani AG-8 soil pathogen DNA, environmental soil temperature, and rainfall parameters explained most of the variation in the root health. This research shows that interactions between environment and pathogen levels before seeding can be utilized in predictive models to improve assessment of risk from root diseases to assist growers to plan more profitable cropping programs.

First Report of Stem Rot in Canola Caused by Sclerotinia minor in Western Australia

Canola (Brassica napus L.) is a significant oilseed break crop in Western Australia. In late October 2012, canola plants (cv. Jackpot) showing typical symptoms of stem rot with bleached appearance and fluffy white fungal growth on the infected tissues were observed in an experimental plot at Katanning, Western Australia. Severely affected plants were lodged with partially filled pods and shriveled seeds. Small, irregular sclerotia (<2 mm) were found inside the plants and were more concentrated in the root and basal stem than in the upper stem regions. Ten sclerotia from three symptomatic plants were surface sterilized with 1.25% NaOCl for 1 minute, rinsed twice in sterile distilled water and plated on potato dextrose agar (PDA) supplemented with 10 mg liter^-1 Aureomycin. Plates were incubated under a black light at 22 ± 2°C. Sclerotinia minor Jagger was consistently isolated as identified by colony morphology, abundant sclerotia on PDA, and size of sclerotia <2 mm (3). A pathogenicity test was conducted on six 7-week-old canola plants cv. Tawriffic. Mycelial plugs (5 mm diameter) were excised from the margins of actively growing 3-day-old cultures and attached on to the 2nd and the 4th internodes of the main stem with Parafilm. Three plants inoculated with agar plugs without mycelium served as controls. Following inoculation, the plants were kept in a misting chamber for 48 h and then transferred to a growth room at 18 ± 2°C with a 12-h photoperiod. Typical lesions of stem rot similar to those observed in the field were noticed 3 days after inoculation. Within a week, all the inoculated plants were completely girdled by the lesions with stems breaking off and collapsing at the point of inoculation. Small sclerotia formed within lesions on the outside of the diseased stems. S. minor was reisolated from the stems of symptomatic plants, fulfilling Koch's postulates. No symptoms developed on the control plants. S. minor has previously been reported on host plants other than canola in Western Australia (4), canola petals in New South Wales, Australia (2), and also on canola stems in Argentina (1). To our knowledge, this is the first report of occurrence of S. minor on canola in Western Australia. Although S. sclerotiorum is the predominant species causing stem rot in canola in Western Australia, S. minor has the potential to cause significant yield losses under favorable environmental conditions. Correct identification and monitoring a shift in pathogens is essential for implementing effective management strategies and breeding resistant varieties. References: (1) S. A. Gaetán et al. Plant Dis. 92:172, 2008. (2) T. Hind-Lanoiselet et al. Aust Plant Pathol. 30:289, 2001. (3) L. M. Kohn. Phytopathology 69:881, 1979. (4) R. Shivas. J. Royal. Soc. Western Australia 72:1, 1989.

A root disease of Lupinus angustifolius caused by a new species of binucleate Rhizoctonia

A new root disease of narrow-leafed lupins that is common in the northern wheatbelt of Western Australia wa found to be caused by a slow-growing binucleate Rhizoctonia sp. with characteristically narrow hyphae (2–4 µm). The new root disease causes distinct patches of poor growth superficially similar to rhizoctonia bare patch. This root disease of lupins is widespread in the northern lupin-growing areas of Western Australia. The biological nature of the disorder was established by transfer of soil from a patch to a clean area and by treating patches using a soil fumigant (methyl bromide–chloropicrin). The thin binucleate Rhizoctonia sp. (TBR) was isolated directly from soil within, but not outside, patches by using a soil immersion plate technique. Lupins grown in pots inoculated with the TBR developed symptoms consistent with those seen on plants in patches in the field, and the fungus was re-isolated from the diseased roots. Field soil was inoculated with TBR, and in the following year, lupins were sown over the inoculated area and developed patches identical to the stunted patches occurring naturally. The fungus was re-isolated from diseased lupin roots taken from inoculated patches but not from diseased roots from outside patches.

A method for finding stereotaxic coordinates from brain sections

A method for finding the stereotaxic coordinates of brain areas from actual brain sections is presented. It uses a digitizer connected to a computer to gather coordinates from photographs of brain sections. The coordinates are mathematically translated and rotated to yield stereotaxic atlas coordinates of the areas digitized.

Manipulation of ley pastures with herbicides to control take-all

The effect of grass-selective and broad-spectrum herbicides in pasture:wheat rotation experiments were studied from 1981 to 1986 at Esperance, W.A. The quantity of pasture and the proportion of grass present in the pasture phases were determined. Pastures were grazed by sheep. Incidence and severity of take-all and grain yield were measured in the wheat phases. The rotations studied were either a 2 year pasture: 1 year crop or 1 year pasture: 1 year crop. Herbicide treatments greatly decreased the grass content of pastures in the year of application, and this effect carried over to the second year in the 2 year pasture: 1 year crop rotation. Herbicide reduced total pasture yield in the year of application, but not in the year following. Herbicide treatment of pastures decreased the incidence and severity of take-all in the following wheat crop. Crop yields were increased following treated pastures and to a greater extent than could be exdained bv decreased take-all alone. Incidence of take-all depended primarily upon the quantity of grass in the previous pasture (5.4% incidence of take-all per 100 kg ha-1 grass dry matter in the previous pasture). Incidence of take-all was also related to the incidence of take-all in previous wheat crops and the quantity of grass in the pasture in the preceding two years.