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Go to Table of Contents STRATEGIES FOR MANAGING SCLEROTINIA DROP OF LETTUCE M.E. Matheron and M. Porchas The University of Arizona, Yuma Agricultural Center, Yuma, Arizona 85364 USA. Email: Matheron@cals.arizona.edu ABSTRACT. Sclerotinia drop of lettuce, caused by the fungal pathogens Sclerotinia minor and S. sclerotiorum, can cause significant economic losses. To evaluate different disease management strategies, lettuce was seeded on raised beds in double rows 30 cm apart. After thinning, sclerotia of each pathogen were incorporated into the soil between lettuce rows to a depth of 5 cm. Tested fungicides were applied after thinning or after thinning and 2-weeks later, either as a soil surface spray or soil surface spray followed by cultivation of the treated soil area to a depth of 5 cm. Compared to nontreated plots, the mean disease reduction over four trials was 69, 53, 48, 47, 46, and 30%, respectively, for two soil surface applications of fluazinam, boscalid, iprodione, penthiopyrad, Coniothyrium minitans, and fludioxonil+cyprodanil in plots containing S. minor and 72, 60, 44, 43, 43, and 30%, respectively, for Coniothyrium minitans, fluazinam, iprodione, boscalid, fludioxonil+cyprodanil, and penthiopyrad in plots containing S. sclerotiorum. Two soil surface applications of boscalid and iprodione as well as incorporation of treated surface soil into the bed by cultivation were not consistently better than one application of these products to the bed surface after thinning. No sclerotia germinated in soil flooded for at least 3 weeks at 30 to 33C, indicating this to be the best management tool among those tested for Sclerotinia drop of lettuce. INTRODUCTION Annual lettuce production in the United States currently stands at about 59,000 ha. Of this total, over 24,000 ha are grown and harvested in the autumn and winter months (September through March) in the state of Arizona. Sclerotinia drop of lettuce, caused by the fungal pathogens Sclerotinia minor and S. sclerotiorum, causes significant economic losses in Arizona. An important means of managing this disease is to prevent sclerotia, the survival structures of these pathogens, from germinating and initiating disease in a subsequent crop of lettuce. Chemical, biological, and cultural tools were evaluated for their efficacy in reducing the severity of Sclerotinia drop of lettuce, with the goal of maximizing control of this disease. MATERIALS AND METHODS In these disease control trials, lettuce was seeded on raised beds in double rows 30 cm apart. After thinning, sclerotia of S. minor or S. sclerotiorum were incorporated into the bed between the lettuce rows to a depth of 5 cm. In four field trials, the comparative efficacy of six different products was assessed when applied twice to the bed surface and plants, once after thinning and again about 2 weeks later. In two of these trials, the efficacy of one application of boscalid and iprodione after thinning was compared to the two applications noted above. Also, one or two applications of these fungicides were made as indicated above but was followed by a cultivation to incorporate treated soil into the bed to a depth of 5 cm. Lastly, in three field trials, microplots were established and infested with sclerotia of S. minor or S. sclerotiorum to determine the effect of flooding during the summer for 1 to 4 weeks on their viability. RESULTS Compared to nontreated plots, all six fungicides tested over a 4-year period significantly reduced the severity of lettuce drop caused by S. minor and S. sclerotiorum. Additionally, as shown in Table 1, significant differences in efficacy among some products are evident. In plots infested with S. minor, there was no significant improvement in disease control with two compared to one application of boscalid or iprodione to the soil surface and plants in both trials. Also, incorporation of treated soil into the bed did not significantly enhance disease control compared to soil surface application alone for either fungicide. For plots infested with S. sclerotiorum, significant reduction in disease severity was recorded in one of two trials with two compared to one application of boscalid to the soil surface, but not with iprodione. Also, incorporation of treated soil into the bed by cultivation did not significantly enhance disease control compared to soil surface application for either fungicide in plots infested with S. sclerotiorum. Table 1. Effect of fungicides on the percent reduction of lettuce drop caused by each Sclerotinia species. Treatment S. minor S. sclerotiorum Fluazinam 69 60 Boscalid 53 43 Iprodione 48 44 Penthiopyrad 47 30 Coniothyrium minitans 46 72 Cyprodinil+fludioxonil 30 43 LSD (P=0.05) 21 18 Field microplot studies revealed that a 3- to 4-week flooding of soil containing sclerotia of Sclerotinia minor and S. sclerotiorum in the summer resulted in 100% mortality of these fungal overseasoning structures (Figure 1). The mean soil temperature at a depth of 10 cm, where sclerotia were placed, ranged from 30 to 33C during these trials. % Nonviable sclerotia 100 80 60 40 20 0 1‐week 2‐weeks 3‐weeks 4‐weeks S. minor S. sclerotiorum Figure 1. Effect of soil flooding on viability of sclerotia of Sclerotinia minor and S. sclerotiorum. DISCUSSION Tested conventional and biofungicide products reduced Sclerotinia drop of lettuce up to about 70% of that in nontreated plots. Two soil surface applications of boscalid and iprodione as well as incorporation of treated surface soil into the bed profile was not consistently more effective than one application of products to lettuce bed surface after thinning. Flooding of soil for a minimum of 3 weeks at temperatures from 30 to 33C destroyed the ability of all sclerotia to germinate, indicating that this was the best disease management tool among those tested. 7th Australasian Soilborne Diseases Symposium 29
Go to Table of Contents CEREAL RESISTANCE AND TOLERANCE TO PEST NEMATODES IN THE SOUTHERN REGION R.S. Davey A , B. Gogel C S. Casonato B , G.J. Holloway B and A.C. McKay A A SARDI, Waite, Adelaide. Email: alan.mckay@sa.gov.au B DPI Victoria, Horsham. C The University of Adelaide ABSTRACT Tolerance and resistance classifications for cereal cultivars to economically-important nematodes such as cereal cyst nematode (Heterodera avenae) and root lesion nematodes Pratylenchus thornei and P. neglectus) are important information to grain growers for planning cropping programs to minimise risk of yield loss in current and subsequent season’s crops. In the southern region a new field trial program has been established to assess tolerance using a split plot design in which low and high nematode populations are produced in the preceding season by growing resistant and susceptible hosts; the plots are then over sown in the following season to the test cultivars and tolerance is assessed by comparing yields on the split plots. These trials also provide an opportunity to assess cultivar effects on low and high nematode populations. While analysis of the data is progressing, three broad resistance groups are already apparent. These include cultivars that reduce low and high populations, those that increase low but reduce high populations and those that increase low and maintain/increase high. Intolerant cultivars eg Estoc, were able to support high nematode populations. INTRODUCTION Resistance is usually assessed under controlled conditions using pot assays (1). Such assays do not predict cultivar affects on different nematode densities under field conditions. This paper explores assessing changes in nematode levels in field trials established to assess tolerance, to assess resistance under field conditions to potentially improve information to growers. MATERIALS AND METHODS Tolerance trials for P. thornei were established in 2010 using field pea and narbon beans to create low and high nematode levels in a split plot design. These plots were over sown in 2011 with named cultivars (5 replicates) to assess tolerance to the nematode. The initial and final nematode populations in the low and high split plots were assessed prior to seeding and post harvest respectively using PreDicta B (2). Linear mixed model analyses of the plot yields and final nematode levels were undertaken to assess the tolerance and resistance of each cultivar. and maintained/increased the high; more categories may be evident when analysis of the data is finished. DISCUSSION Assessing changes in nematode levels in field trials established to assess nematode tolerance of new cultivars, has potential to provide grain producers with more information on how to use specific cultivars to manage nematode populations. Replicating these trials across regions and seasons should also provide useful information on variation in nematode multiplication between regions and seasons. Using the tolerance trials to classify nematode resistance of current cultivars also frees capacity of the pot assays to support breeding programs. ACKNOWLEDGEMENTS The southern nematology program is funded by GRDC. Amanda Cook and Wade Sheppard role in managing the field trial and Ian Rileys’ advice and support are gratefully acknowledged. REFERENCES RESULTS 1. Cook, R. and Noel, G.R. (2002). In ‘Plant Resistance to Average initial and final P thornei numbers/g soil for the Parasitic Nematodes’ eds. J.L. Starr, R. Cook and J. Bridge, low and high nematode density plots, sorted by the low final pp71-105. (CAB International) levels are presented in Figure 1. Cultivars vary in the 2. Ophel-Keller, K., McKay, A., Hartley, D., Herdina, and impact they have on the low and high initial nematode Curran, J. (2008). Development of a routine DNA-based densities. The most resistant cultivars reduced both the low testing service for soil-borne diseases in Australia. Aust. Pl. and high nematode populations, others increased the low Path. 37: 243-253. and reduced the high, and the third group increased the low 180 Low initial Low final High inital High final 160 140 120 P. thornei / g soil 100 80 60 40 20 0 Wheat and barley cultivars Figure 2. Average initial and final Pratylenchus thornei/g numbers in the low and high split plots of a field trial established at Minnipa SA 7th Australasian Soilborne Diseases Symposium 30
Page 2 and 3: The following organisations sponsor
Page 4 and 5: Welcome to the Seventh Australasian
Page 6 and 7: 7 th Australasian Soilborne Disease
Page 8 and 9: THURSDAY 20 SEPTEMBER 08:30 Chair -
Page 10 and 11: TABLE OF CONTENTS KEYNOTE SPEAKERS
Page 12 and 13: ANTI-FUNGAL METABOLITES PRODUCED BY
Page 14 and 15: Go to Table of Contents KEYNOTE SPE
Page 16 and 17: Go to Table of Contents BENEFICIAL
Page 18 and 19: Go to Table of Contents PENFLUFEN:
Page 20 and 21: Go to Table of Contents THE ROLE OF
Page 22 and 23: Go to Table of Contents NEMATODE BI
Page 24 and 25: Go to Table of Contents CAN EARTHWO
Page 26 and 27: Go to Table of Contents SUSTAINABLE
Page 28 and 29: Go to Table of Contents EFFECTS OF
Page 30 and 31: Go to Table of Contents DETECTION O
Page 32 and 33: Go to Table of Contents CONTAINMENT
Page 34 and 35: Go to Table of Contents COMPARISON
Page 36 and 37: Go to Table of Contents EFFECT OF S
Page 38 and 39: Go to Table of Contents EFFECT OF T
Page 40 and 41: Go to Table of Contents USING MODEL
Page 44 and 45: Go to Table of Contents STRATEGIES
Page 46 and 47: Go to Table of Contents THE INTERAC
Page 48 and 49: Go to Table of Contents USE OF COVE
Page 50 and 51: Go to Table of Contents EFFECT OF G
Page 52 and 53: Go to Table of Contents DOES PLANTI
Page 54 and 55: Go to Table of Contents ILYONECTRIA
Page 56 and 57: Go to Table of Contents ANTI-FUNGAL
Page 58 and 59: Go to Table of Contents RHIZOCTONIA
Page 60 and 61: Go to Table of Contents THE NEMATOD
Page 62 and 63: Go to Table of Contents SEED POTATO
Page 64 and 65: Go to Table of Contents APPLICATION
Page 66 and 67: Go to Table of Contents EVALUATION
Page 68 and 69: Go to Table of Contents MANAGEMENT
Page 70 and 71: Go to Table of Contents DISTRIBUTIO
Page 72 and 73: Go to Table of Contents FISHING FOR
Page 74 and 75: Go to Table of Contents YIELD RESPO
Page 76 and 77: Go to Table of Contents FREE LIVING
Page 78 and 79: Go to Table of Contents A PITCH FOR
Page 80 and 81: Go to Table of Contents WHAT IS THE
Page 82 and 83: Go to Table of Contents SIMULTANEOU
Page 84 and 85: Go to Table of Contents THE PATHOGE
Page 86 and 87: Go to Table of Contents ASSESSMENT
Page 88 and 89: Go to Table of Contents BREAK CROPS
Page 90 and 91: Go to Table of Contents POPULATION
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Go to Table of Contents Miyan, S. 2
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