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Go to Table of Contents DOES PLANTING DIRTY POTATO SEED REALLY MATTER? R.S.Tegg A and C.R. Wilson A A Tasmanian Institute of Agriculture (TIA), University of Tasmania, 13 St. Johns Ave., New Town, 7008, TAS Email: Robert.Tegg@utas.edu.au ABSTRACT. Certification schemes are in place to protect growers from planting disease containing potato seed; however, the role of seed borne inoculum and its effect on subsequent potato crop production is not fully understood. This study sought to define the role of three key soilborne pathogens, namely Streptomyces scabiei, Spongospora subterranea f.sp.subterranea and Rhizoctonia solani AG3.1 that cause common scab, powdery scab and black scurf of potato, respectively. The aim was to determine the importance of seed borne inoculum (as measured thru tuber peel pathogen DNA levels) of these key pathogens. Cultivars ‘Russet Burbank’ and ‘Innovator’ with varying levels of seed borne inoculum were grown in controlled pot experiments in clean soil. Disease parameters including root galling and necrosis were measured at ~60 days after planting (DAP) with tuber disease scored at plant senescence. The relationship between pathogen DNA levels on the parent tubers and subsequent disease status of the progeny daughter plants and tubers was quantified. For the pathogens S. scabiei and R. solani AG3.1, DNA levels in tuber peel provided a good measure (P
Go to Table of Contents ENHANCED SUBERIN PRODUCTION IN NOVEL POTATO SOMACLONES PROVIDES PROTECTIVE BIO-BARRIER AGAINST TWO KEY SCAB DISEASES T. Thangavel A , R.S. Tegg A and C.R. Wilson A A Tasmanian Institute of Agriculture (TIA), University of Tasmania, 13 St. Johns Ave., New Town, 7008, TAS Email: tamil.thangavel@utas.edu.au ABSTRACT. Enhanced resistance to common scab of potato was obtained by somatic cell selection. An added bonus identified concurrent enhanced resistance to powdery scab, however the mechanism of resistance was not known. This study sought to compare parental cv. Russet Burbank to three disease resistant somaclonal variants. Glasshouse and field experiments tested the performance of these clones in the presence of two soil-borne pathogens, Streptomyces scabiei and Spongospora subterranea f.sp.subterranea. Histological (Fluorescent microscopy) and molecular methods (qRT-PCR) were used to identify the thickness of phellem (periderm) layer, degree of phellem and lenticel suberisation and relative expression of three suberin synthetic genes (CYP833A, StKCS6 and POP_A) from pathogen treated tubers. The variants showed a greater degree of phellem suberisation, and up to 7-fold increased expression of the suberin gene StKCS6 compared to the parent. We hypothesize that this suberisation provides an enhanced physical structure and important barrier for pathogen invasion into tubers and is important for enhanced resistance to common and powdery scab. INTRODUCTION Common and powdery scabs are important soil-borne potato diseases and impose substantial impediments to sustainable and profitable potato production world-wide. Common scab caused by infection of developing tubers with pathogenic Streptomyces spp. has resulted in losses of ~4% to the French fry processing sector, within Australia, through seed and processing tuber rejection and increased processing costs (1). Powdery scab is caused by infection of tubers by the protozoan pathogen S. subterranea. In addition to induction of tuber lesions, it is thought to cause significant yield reduction through root infection (2). There are currently no effective and sustainable management strategies for either disease. Using somaclonal cell selection techniques we obtained variants of the cv. Russet Burbank with extreme resistance to common scab (3). Further screening identified concurrent resistance to powdery scab within the majority of these variants, however the mechanism of resistance was not known. The outer cell wall (periderm or phellem) of potato tubers are the first defence to soil-borne pathogens and their physical and chemical components may determine resistance to pathogen invasion. One important barrier is suberin, a aliphatic and aromatic bio-polyester (1). In glasshouse and field studies we examined the impact of exposure to common and powdery scab pathogens on phellem thickness and suberin synthesis. MATERIALS AND METHODS Disease free mini-tubers were used in all trials. S. scabiei and S. subterranea inoculation methods were adopted from previous studies (1, 2). The specific stage of tuber physiological development was determined by direct examination (1). Tubers of different ages were harvested and stored at either -80°C or in FAA (4°C) for gene expression and histological studies respectively. Histological studies Fluorescent microscopy was used to determine the number of phellem layers. Suberisation in tuber phellem was estimated using the rating scale (0-0% no suberin,1-0-5%, 2-5-15%, 3-15-30%, 4-30-50%, 5-50-75%, 6-75-90%, 7-95% suberin on all cell layers). Gene expression studies RNA extraction and qRT-PCR enabled determination of the relative expression of three genes involved in suberin synthesis in potato tubers (StKCS6, CYP833A & POP_A) between the variants and the parent cultivar following pathogen challenge. Data were normalised to expression of the internal control r18s. RESULTS AND DISCUSSION The Russet Burbank parent had significantly less phellem layers than two of the selected somaclonal variants whilst degree of suberisation in all three variants was significantly higher (Table 1). Table 1. Comparison of the number of phellem cell layers and suberisation between variants and the Russet Burbank parent in glasshouse studies following S. scabiei challenge. Clone No. of phellem layers phellem suberisation R. Burbank (parent) 6.2 0.7 A380 A365 TC10C 8.1 5.5 8.0 1.3 1.5 1.4 LSD (P=0.05) 0.11 0.07 Molecular comparison of elite clone A380 with the parent R. Burbank shows a 7-fold greater expression of the StKCS6 gene in A380 (Fig. 1). This enhanced expression of a suberin expression gene supports the histological results in Table 1. StKCs6 Cyp833A Pop_A Suberin Gene Figure 1. Relative mean fold change in the gene expression of suberin synthetic genes (CYP863A, StKCS6 & POP_A) in tubers harvested from variant line A380 and the Russet Burbank parent. The observed histological and molecular responses were seen at key stages of tuber development, when infection is thought to occur. These results suggest that enhanced suberisation in disease resistant variants may be important in restriction of pathogen infection thorugh the peridermal region and provide resistance to these two tuber diseases. ACKNOWLEDGEMENTS TIA (UTAS) for scholarship support for TT. REFERENCES 1. Khatri, B.B., Tegg, R.S., Brown, P.H. & Wilson, C.R. (2011) Plant Pathology 60: 776-786. 2. Shah, F.A., Falloon, R.E., Butler, R.C. & Lister, R.A. (2012) Australasian Plant Pathology 41: 219-228. 3. Wilson, C.R., Tegg, R.S., Wilson, A.J., Luckman, G.A., Eyles, A., Yuan, Z.Q., Hingston, L.H. & Conner, A. J. (2010) Phytopathology 100: 460-467. 7th Australasian Soilborne Diseases Symposium 40 Relative Gene expression 8 7 6 5 4 3 2 1 0 Russet Burbank (Parent) A380
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 42 and 43: Go to Table of Contents STRATEGIES
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 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
Page 92: Go to Table of Contents Miyan, S. 2

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