Pest, disease and weed management
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Research outcomes: A comprehensive RD&E program that addresses existing and emerging pests, diseases and weeds, allowing sugarcane growers to manage their crops efficiently with minimal environmental impacts. An enhanced industry capacity to deal with incursions of exotic pests, diseases and weeds.
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Item Pachymetra root rot surveys of the Tully district update 2018 : ASSCT peer-reviewed paper(ASSCT, 2019) Shannon, GJ; Magarey, RC; Macgillycuddy, L; Stringer, JK; Lewis, MPachymetra root rot is a soil-borne disease that impacts all sectors of the Australian sugar industry. The disease attacks the root system of sugarcane crops, affecting yields and leading to stool loss and shortened crop cycles, thus impacting the farming, harvesting and milling sectors. Monitoring the disease is, therefore, important so that optimised management practices are adopted, so bringing benefits to the entire value chain. A survey of the Tully district conducted in 2004 showed that pachymetra root rot was widely distributed across the Tully mill area; a second survey undertaken in 2013 sought to determine trends in disease incidence after some significant changes occurred in the cultivar mix. Crop resistance had shifted significantly with a change in cultivar resistance and there was a consequent increase in disease severity. Financial losses from reduced yield were estimated at $5.5 million in 2013; this compares to just under $1.0 million in 2004. This paper reports on a third survey in 2018 that is a five-year update to provide snapshot of the status of this disease in the Tully sugar industry. While the disease is still widespread, its severity has decreased with financial losses estimated to be $3.5 million.Item Effects of pachymetra root rot and nematodes on some elite sugarcane clones in Australia(ASSCT, 2016) Bhuiyan, SA; Croft, BJ; Wong, E; Ogden-Brown, J; Turner, M; Parfitt, R; Magarey, RC; Bull, J; Cox, MCPACHYMETRA ROOT ROT and nematodes are the two most important soil-borne pathogens of sugarcane in Australia. An experiment was established in Yandaran, Queensland in grey forest soil with high Pachymetra spore counts (>100 000 spores/kg). Fifteen elite varieties and one advanced clone, from pachymetra root rot susceptible, intermediate and resistant categories, were planted in the experiment. The experiment was maintained until the second ratoon crop and Pachymetra and nematode populations were assessed in each crop. In addition, the incidence of smut was recorded before harvesting. Cane yield (TCH), commercial cane sugar (CCS) and sugar yield (TSH) were also measured in each crop. Pachymetra spore counts remained significantly lower in resistant varieties compared to susceptible and intermediate varieties until the second ratoon. In intermediate and susceptible varieties Pachymetra spore counts increased substantially, in particular, in second ratoon. In intermediate varieties such as Q232A and Q208A Pachymetra spore counts increased more than three times from plant crop to second ratoon. Numbers of nematodes, in particular root-lesion nematode, more than doubled in the second ratoon crop compared to the plant and first ratoon crops. Only Q248A had significant levels of smut, with 25% and 30% infected plants in the first and second ratoon crops, respectively. Yield reduction was substantial in the second ratoon compared to the plant and first-ratoon crop. Sugar yield decreased by 45% in the second ratoon compared to the first ratoon. Mostly, poor or negative correlations were observed between both Pachymetra spore counts and nematode numbers and yield.Item Does rotating cultivars with intermediate resistance influence pachymetra root rot of sugarcane : ASSCT peer-reviewed paper(ASSCT, 2019) Jensen, AS; Croft, BJ; Parfitt, RC; Brown, PHConcerns have been raised by industry members over lower than expected cane yields associated with high oospore levels in sugarcane cultivars rated to have intermediate resistance to pachymetra root rot. This is a significant issue, as intermediate cultivars represent more than 70% of the sugarcane grown in Australia. It is possible that planting the same intermediate cultivar in successive crop cycles could lead to increased yield losses due to pachymetra root rot. This paper examines the residual soil-borne effect of the current major sugarcane cultivars on the following sugarcane crop in three field trials, located in the Herbert, Central and Southern growing regions. Levels of oospores of Pachymetra chaunorhiza and cane yields were assessed in ratoon crops of replicated cultivar-assessment trials and in subsequent crops of intermediate resistant Q208A (planted on the sites of previous cultivar trials). The relationships between Pachymetra oospore levels and cane yield in Q208A crops and pre-plant oospore levels were examined. High oospore levels occurred in plots planted to some intermediate cultivars, as well as susceptible cultivars. In the following crop of Q208A, which was planted into plots of the previous cultivar trial, Pachymetra oospore levels at harvest were related to oospore levels prior to re-planting at all trial sites. Cane yield (t/ha) of Q208A was significantly related to pre-plant oospore levels at a site near Bundaberg (P=0.0049). Yield losses of 21% were incurred at 120 oospores/g soil in Q208A. Cultivation of Q208A following a crop of Q208A did not result in higher Pachymetra oospore populations or yield losses compared with planting Q208A after other cultivars of similar resistance rating. In the Herbert and Central field trials, Pachymetra oospore levels were lower and there were no significant relationships between oospore levels and yield in Q208A planted at these sites. We demonstrate that significant yield losses in Q208A are associated with high Pachymetra oospore levels that occur under intermediate and susceptible cultivars in the previous crop. There was no evidence to support the hypothesis that repeatedly planting the same intermediate cultivar could lead to host-cultivar-specific virulence in P. chaunorhiza. Greater emphasis should be placed on breeding and selecting highly resistant cultivars that are suited to soil types conducive to PachymetraItem Characterisation and maintenance of the Australian sugarcane mapping populations(BSES, 2003) McIntyre, LThere were two major aims to this project. The first was to identify markers linked to major diseases of sugarcane that were difficult and expensive to select for. The second objective was to determine the cross-transferability of markers by testing the association between markers and traits in other germplasm. Both of these aims have been successfully addressed. Fiji Disease virus (FDV) and Pachymetra are two major diseases of sugarcane. Both require laborious and expensive screening in the field or glasshouse and consequently, only limited numbers of clones can be screened. Thus, both of these traits are candidates for molecular markers. Successful identification of molecular markers associated with these diseases could enable indirect selection for resistance to be undertaken, in the absence of screening, or with reduced screening, for the diseases themselves. Two populations, Q117 x 74C42 and Q96 x Q178, were developed by Dr Nils Berding (BSS038) and each contained more than 200 progeny. Both populations had been previously scored for numerous sugar-related and agronomic traits and marker-trait associations (QTLs) identified for all traits in the Q117 x 74C42 population. One objective in this project was to see if QTLs identified in Q117 x 74C42 would detect the same traits in the Q96 x Q178 population. Unfortunately, in the process of mapping in this second population, it was discovered that the population was a mixture of several very small, different populations. This project objective could not be completed as planned, but was modified, as discussed below. In addition to the approximately 300 markers already scored on the Q117 x 74C42 population (CTA024), a further 1100 amplified fragment length polymorphism markers (AFLPs), simple sequence repeat (SSR) markers and resistance gene analogue (RGAs) were scored. The first two types were used as they are PCR-based, reliable, easy to generate, and the type of markers currently being used in other sugarcane maps. RGAs are potential candidate genes for disease resistance. Unfortunately, during the amalgamation of the marker information, it became apparent that the replanted progeny clones had become “renumbered” in the field. It was thus not possible to combine the two data sets, and consequently, new maps were developed for the Q117 x 74C42 population using just the AFLP, RGA and SSR data. The 1100 markers were used to develop two parental maps. The Q117 map contains 407 markers in 75 linkage groups, while the 74C42 map contains 447 markers in 84 linkage groups.Item Inheritance of resistance to pachymetra root rot : SRDC final report BS27S(BSES, 1994) Croft, BJ; Berding, NGenetical resistance to root pathogens is a sensible strategy for disease control in a perennial crop such as sugarcane. Pachymetra root rot is a serious disease in Queensland and can cause losses of 30-40% in susceptible varieties. An understanding of the mode of inheritance of resistance is important in developing breeding strategies.Item Bioassay for comparing levels of pythium graminicola in soils(BSES, 1987) Croft, BJIn the study of any soil borne pathogen it is essential to have some technique for determining the level of the pathogen in the soil. The levels of Pythium species in soil have been measured by soil dilution plating on selective media (Dick and Ali-Shtayeh 1986. Trans. Br. Mycol. Soc. 86(1):49-62). However species with lobulate sporangia are not frequently isolated on these media and bioassay techniques have been developed for these fungi (Stanghellini and Kronland 1985. Phytopathology 75:1242-1245). In Hawaii, pineapple roots have been used as baits in a bioassay for P. graminicola Subr. (Adair 1972. Hawaii. Plant. Rec. 58:213-240). However, considerable space is required to maintain pineapple plants and they are not always readily available. Poor Root Syndrome (PRS) of sugarcane in Queensland causes serious crop losses (Egan et al. 1984 ASSCT p 1-9). A Pachymetra sp. (formerly referred to as the root rot fungus) which rots the primary roots of the sugarcane plant, and P. graminicola which can restrict fine root development, are two pathogens consistently found in affected soils (Croft and Magarey, 1984 ASSCT Conf. p 55-61). The study of the role of P. graminicola in the sugarcane PRS in Queensland has been hampered by the lack of a means of quantifying the level of this species in soils. This paper outlines the development of a sorghum bioassay (SB) for P. graminicola using sorghum seedling roots.