Downy mildew of lettuce Effects of nutrients on diseases of lettuce

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1 Downy mildew of lettuce Effects of nutrients on diseases of lettuce Belinda Rawnsley Senior Research Officer South Australian Research and Development Institute (SARDI) Waite Research Precinct Urrbrae, SA Bremia lactucae Obligate pathogen (needs living tissue to survive) Varieties have resistance (Dm) genes to pathotypes of downy mildew Causes leaf lesions and brown brittle leaves

2 Fungi Microdochium panattonianum Survives on debris in soil Causes circular leaf lesions Shot-hole Anthracnose Aim Susceptibility of varieties to disease Anecdotal evidence that high N increases disease Determine if rate and form of nitrogen increases lettuce susceptibility to disease Lettuce Variety Lily NR pills NR pills Boost Pills Roundhouse Boomerang Sure shot Winter Select Nr pills Nr pills Bernadinas Nr pill Cos Quintus Nr pills Red Oak Tekero Green Oak Sansula Green Coral Bellagio Curletta LE 2 Red Coral Bellagio Robinio A Mini Green Cos Tomos LE 291 LE 4 Casino Granadier Ribenas Cartogenus Tested 21 varieties with known and unknown resistance to DM and Anthracnose Inoculated plants in controlled environment growth room (14 C)

3 Tekero Infection of lettuce with spores Downy mildew susceptible varieties Sure shot Winter Select Incidence of plants infected with downy mildew (%) Lily Bernadinas Winter Select Tomos Bellagio Curletta LE 2 LE 4 Bellagio Robinio A LE 291 Sure shot Boomerang Roundhouse Boost Quintus Anthracnose susceptible varieties Effect of Nitrogen on disease 3 forms and 3 rates of Nitrogen N forms Potassium nitrate Calcium nitrate Ammonium nitrate No N in soil mix Plant growth response prior to disease assessment Anthracnose severity

4 Effect of N on plant growth Effect of downy mildew and KNO 3 1 Lily Fresh weight (g) Boomerang Potassium nitr ate (%) high medium low No N Incidence of Downy Mildew (%) low high medium Potassium nitrate KNO3 Effect of downy mildew and Ca(NO 3 ) 2 Effect of downy mildew and (NH 4 ) 2 Incidence of Downy Mildew (%) Incidence of Downy Mildew (%) Calcium nitrate Ca(NO3)2 ammonium nitrate (NH4)2

5 Effect of Anthracnose and KNO 3 Effect of Anthracnose and Ca(NO 3 ) 2 Anthracnose incidence (% plants infected) Anthracnose incidence (% plants infected) Calcium nitrate (%) Potassium nitrate (%) Effect of Anthracnose and (NH 4 ) 2 Conclusion Form of N more important than rate Anthracnose incidence (% plants infected) Results variable Best plant growth = highest disease High KNO 3 increased downy mildew infection High Ca(NO 3 ) 2 reduced anthracnose but also reduced plant growth Variety important Balanced nutrient schedule Ammonium nitrate (%)

6 Future work Trial alternative fungicides in growth room and field conditions (project VG7127) Active ingredient Trade name Copper octanoate (Copper soap) Tricop Potassium bicarbonate Ecocarb Phosphonic acid (Phosphorus Acid) Agri-Fos Hydrogen dioxide Peratec Neem (Azaridachta indica ) oil Trilogy Canola oil Synertrol Horti Oil Tea Tree oil Timorex Gold Acibenzolar-s-methyl Bion WG Chitosan (poly-d-glucosamine) [fish/sea shell protein + trace elements] Aminogro Acknowledgements Funding provided by the Vegetable levy through HAL (project VG) Barbara Hall, Lee Bartlett & Angela Lush (SARDI) Seed companies Growers for providing diseased plants Project team from DPIVic and University of Queensland