Department of Employment, Economic Development and Innovation Fusarium thapsinum is the dominant species associated with sorghum stalk rot in Queensland and northern New South Wales Lisa Kelly, Malcolm Ryley, Elizabeth Aitken, Yu Pei Tan
Grain sorghum in Australia Grown in Qld and NSW mostly under raingrown conditions 2.7 million tonnes were produced from 767,000 ha in 2008-09 (ABS 2010) Production in Australia is highly variable between seasons largely due to fluctuations in annual rainfall 2
Sorghum lodging Results from interactions of: Climatic stresses (heat, moisture) Anatomical weakness of stalk One or more plant pathogens It causes: Harvesting difficulties Loss of quantity and quality of grain Sam Gall, Pioneer Hi-Bred 2009 Reduced quantity and quality of fodder 3
The role of physiological stress in lodging Various factors can affect assimilate supply, such as water deficit, diseases, insect damage, nutrient imbalance, and light intensity The resulting stress is thought to result in a shortage of available carbohydrate in the stem. Cell death and pith disintegration follows, eventually leading to lodging Sam Gall, Pioneer Hi-Bred 2009 4 Sam Gall, Pioneer Hi-Bred 2009
The role of pathogens in lodging Stalk rotting pathogens are often, but not always, associated with lodging Major stalk rotting pathogens are: Fusarium spp. (fusarium root and stalk rot)* Macrophomina phaseolina (charcoal rot) * Erwinia chrysanthemi (bacterial stalk rot) Colletotrichum graminicola (anthracnose stalk rot) 5
Common stalk rotting pathogens Distinctive symptoms Fusarium pathogens of sorghum have a narrow host range M. phaseolina has a wide host range Fusarium sp. Mixed M. phaseolina 6
Importance of post-anthesis stress not desiccated desiccated Sam Gall, Pioneer Hi-Bred 2009 7
Biology of sorghum stalk rotting Fusarium species Survive between seasons in plant debris and soil, and on seed and alternative hosts Probably infect roots and stems through natural wounds, or injury from insects or machinery and remain latent until stress occurs Can also cause root infection of seedlings and older plants, and head blight 8 Sam Gall, Pioneer Hi-Bred 2009
Fusarium species - previous findings Earlier reports of F. moniliforme sensu lato associated with sorghum most likely refer to F. thapsinum*, F. andiyazi*, F. nygamai, F. proliferatum, and perhaps F. verticillioides Petrovic (2007) found F. thapsinum and F. andiyazi the dominant species associated with sorghum in 2 regions in NSW/sth Qld (14 species in total), with differences in dominance, diversity and composition between regions * Dominant species overseas 9
Fusarium species collections 2008/09, 2009/10 & 2010/11 collections 71 locations; 332 isolates to date Stalks, panicles, seedlings, stubble Central Qld 8 sites, 23 isolates Southern Qld 44 sites, 157 isolates Northern NSW 19 sites, 152 isolates 10
Identification of Fusarium spp. Morphological features Macroconidia & microconidia - morphology, absence/presence, abundance Formation of microconidia: conidiogenous cells, chains or false heads Chlamydospores: absence/presence, formation Secondary characters in vitro Pigmentation Growth rate Molecular techniques Sequencing of the translation elongation factor 1-α gene 11
Abundance of species F. thapsinum F. andiyazi F. semitectum F. chlamydosporum F. proliferatum F. oxysporum F. verticillioides Pathogenic species n = 243 12
Geographic distribution of species 100% 90% % isolates 80% 70% 60% 50% 40% 30% F. verticillioides F. oxysporum F. proliferatum F. chlamydosporum F. semitectum F. andiyazi F. thapsinum 20% 10% Pathogenic species 0% Southern Qld Northern NSW Central Qld (n = 118) (n = 110) (n = 15) 13
Species identified from different sorghum plant parts 100 90 80 70 60 50 40 30 20 10 0 panicles seedlings stubble stalks 14 No. isolates F. thapsinum* F. andiyazi* F. semitectum F. chlamydosporum F. proliferatum* F. oxysporum* F. verticillioides* * pathogenic species
Fusarium head blight 15
Fusarium head blight infection Panicles spray-inoculated with a spore suspension and covered for 48h Only those inoculated at 100% flowering produced symptoms F. thapsinum and F. andiyazi isolated from stalks were pathogenic on panicles and vice versa Lisa Kelly, DEEDI 16
Screening for resistance Seedlings grown in test tubes, inoculated with an agar plug After 10-14 days roots are inspected for discolouration and shoot lengths are measured 17
Screening for resistance Roots of all 3 hybrids had red discolouration, no discolouration in controls Measured shoot length from seed to developing leaflet (1), and shoot length from seed to tip of first leaf (2) 14 % reduction (1) % reduction (2) 12 % reduction in length 10 8 6 4 2 0 Hybrid 1 Hybrid 2 Hybrid 3 18
Summary of findings to date F. thapsinum is the dominant species in all regions, followed by F. andiyazi similar to overseas F. verticillioides is of low frequency, F. nygamai not yet identified Tested isolates of F. thapsinum and F. andiyazi are pathogenic on seedlings, stalks and panicles A seedling test to identify resistant germplasm shows promise 19
Future activities Collect additional isolates from Central Qld* Identify remaining isolates* Develop protocol(s) to rapidly screen germplasm for resistance to the dominant Fusarium species (seedling/stalk/panicle)* Investigate the interactions between the pathogens, stress and staygreen traits Investigate potential IDM strategies for the stalk rot pathogens (eg. tillage practices, rotation, resistance) 20
Acknowledgements Supervisors Mal Ryley, Agri-Science Qld, and Elizabeth Aitken, UQ Yu Pei Tan for assistance with molecular identification Funding from the Grains Research and Development Corporation Northern Grower Alliance for their collaboration Mal Ryley, QPI&F 2009 21