Ground Cover Supplement : GC Supplement - Root and crown diseases 2014
11 Crown rot CULTIVATION CAN EXACERBATE CROWN ROT stubble management practices such as cultivation can lead to increased infection and expression of crown rot By dr steven simpfendorfer WHILE PATHOGEN LOAD is important in crown rot expression, soil moisture level and temperature during grain-fill are the driving forces behind the extent of yield loss caused by the disease. Northern region research shows even a low starting inoculum level can cause up to 25 per cent yield loss if the crop becomes severely stressed during grain- fill (Figure 1A). In years of high crown rot load, the seasonal finish plays the major role in crown rot expression: a soft finish (no moisture stress) resulting in very little disease damage while a hot dry finish can halve crop yields (Figure 1B). CULTIVATION While cultivation can reduce inoculum loads by speeding up stubble decomposition, in years of low rainfall (and reduced stubble degradation) cultivation can increase the crown rot infection rate of subsequent winter cereals. Cultivation (even shallow) distributes infected residue more evenly across paddocks and into the below-ground infection zones for crown rot. Crown rot infection occurs when physical contact is made between infected residue and the underground 'crown' of cereal plants. Cultivating crown-rot-infected cereal stubble effectively breaks the inoculum into smaller pieces and spreads it more evenly through the paddock -- increasing the chance of it coming into contact with emerging cereal plants. Cultivation also results in a loss of soil moisture, which may also increase the expression of crown rot in a dry year. Stubble burning does not remove inoculum from below ground and, depending on the timing of the burn, significant levels of soil moisture storage can be lost through the lack of stubble cover during the fallow period. This can have a significant effect on the expression of crown rot later in the season. PHOTO: QUEENSLAND DAFF crown rot Crown rot has three distinct and separate phases: survival, infection and expression. SURVIVAL The crown rot fungus survives as a cottony growth (called mycelium) inside winter cereal stubble and grass weed residues, which have been infected in previous seasons. The crown rot fungus can survive inside plant residues for as long as the residues remain intact – sometimes for years if soil and weather conditions slow its decomposition. INFECTION Soil moisture stimulates the growth of mycelium from infected stubble and weed residues to infect newly emerged winter cereals either via underground plant parts such as the coleoptile, sub-crown internode or crown tissue, or above-ground leaf sheathes at the soil surface. Direct contact between infected stubble and crop plants is required for infection. Wet seasons coupled with high stubble inoculum loads can lead to significant build-up of paddock inoculum levels. EXPRESSION Moisture and temperature stress throughout flowering and grain-fill trigger the crown rot fungus to proliferate in the base of infected tillers, restricting water movement from the roots through the stems and producing characteristic whiteheads that contain either no grain or lightweight, shrivelled grain. SOURCE: NSW DPI FIGURE 1 Impact of crown rot inoculum load (A) and moisture stress during grain-fill (B) on yield loss to crown rot in 2007. a) % yield loss with addition of crown rot 0 --10 --20 --30 --40 --50 --60 0.5 g/m 1 g/m Crown rot inoculum load 2 g/m --25% --14% --9% b) % yield loss to crown rot Increasing moisture/heat stress during grain-fill in 2007 Breeza (irrigated) Goondiwindi Tamworth Mallawa Rowena North Star Collarenebri Weemelah Croppa Creek Millie Cryon A B 0 --10 --20 --30 --40 --50 --60 INTER-ROW SOWING In a no-till system, the crown rot fungus becomes confined to the previous cereal rows and is more reliant on infection through the outer leaf sheathes at the soil surface. This is why inter-row sowing (using GPS guidance) in no-till systems has been shown to halve the number of plants infected with crown rot, resulting in a five to 10 per cent yield increase. Cultivation or harrowing negates the benefits of inter-row sowing as a crown rot management strategy. □ grdc research code dAn00175 more information: Dr Steven Simpfendorfer, NSW DPI, 02 6763 1261, steven. email@example.com Typical crown rot symptoms in wheat showing honey-brown discoloration on the lower leaf sheaths and internodes of bread wheat tillers at flowering. Pictured are glasshouse-grown wheat plants inoculated with the fungus at the seedling stage as part of crown rot research being carried out by the Queensland Department of Agriculture, Forestry and Fisheries.
GC Supplement - Cereal foliar fungal diseases
GC Supplement - Managed environment facilities