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University of Southern Queensland New Midge Resistance for Australian Grain Sorghum A Dissertation Submitted by Adam Hardy Bachelor of Applied Science For the Award of Doctor of Philosophy 2007 i Abstract The development and commercial release of midge resistant grain sorghum hybrids in Australia has been one of the real success stories of the sorghum industry. Almost all the current commercial sorghum hybrids grown contain a significant baseline of midge resistance that has greatly reduced that pest status of this insect. However while breeding efforts have been successful, it seems only one mechanism of resistance remains present in commercial hybrids. This mechanism of resistance known as ‘ovipositional-antixenosis’ is polygenic in nature and has contributed to the gradual reduction in the genetic base of commercial sorghum hybrids, potentially limiting the advancement of other agronomic traits. In order to expand both the level of resistance and the genetic diversity within Australian commercial sorghum hybrids, research was undertaken to capture new sources of midge resistance. Initially the goal of this work was to isolate and characterise the most promising new antibiosis sources of midge resistance previously documented within international breeding lines. However as the work progressed the discovery of a previously undescribed tolerance source of midge resistance led to more detailed studies of midge larval biology within a narrow range of sorghum germplasm lines to better characterise the resistance mechanism. To complete this work a new water-injection technique was developed to allow more precise studies of midge larval biology where previous traditional screening methods were deemed inadequate. Using this method several antibiotic lines were shown to contain diverse modes of action, while the tolerance mechanism of resistance was confirmed and more accurately characterised. In all cases plant characters within the developing spikelet were associated with each resistance mechanism. Overall, one source of resistance, found in lines derived from the Indian land race line DJ6514, was identified as superior to the others tested. Germplasm derived from this source was found to confer inter-related antibiosis and tolerance mechanisms. Both mechanisms were indirectly shown to be caused by the unique ii antibiotic properties of the developing caryopsis. Larval mortality (antibiosis) increased in this line, in line with increased feeding against the developing caryopsis. A second tolerance mode of action was also linked to anti-feeding properties of the developing caryopsis. Larvae were recorded at higher than normal rates feeding away from the caryopsis resulting in the survival of both larvae and grain in a significant proportion of spikelets. This escape ‘tolerance’ mechanism of resistance was confirmed indirectly in several studies and could be artificially induced in other genotypes when larval feeding against the caryopsis was delayed. As such the resistance is better described as antixenosis to caryopsis feeding. When both resistance mechanisms are present, the resistance isolated from DJ6514 was found to cause a three to four fold increase in seed set in resistant lines. This source of resistance has been directly selected for incorporation into the Australian breeding program and has been shown to be inherited simply as a single gene that needs to be deployed on both sides of the breeding program to ensure stable expression. When breeding efforts are complete a new suite of highly resistant and genetically diverse midge resistant sorghum hybrids will emerge into the marketplace. iii Declaration I certify that the ideas, experimental work, results, analyses, software and conclusions reported in this dissertation are entirely my own effort, except where otherwise acknowledged. I also certify that the work is original and has not been previously submitted for any other award, except where otherwise acknowledged. ……………… Date: iv Previously Published Material Some parts of this work have been previously published and presented at several scientific conferences. All the work in Chapter 5 was published in: Hardy, A.T., Franzmann, B.A. & Sutherland, M. W. (2001) ‘Artificial infestation of sorghum spikelets with eggs of Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) by water injection’, Australian Journal of Entomology, Vol. 40, pp. 380-385. Some of the screening results in Chapter 7 were used in: Hardy, A., Tao, Y. & Franzmann, B. 2001, ‘New Host-Plant Resistance to the Sorghum Midge and the Use of Molecular Marker Mediated Selection’, Proceedings of the Fourth Australian Sorghum Conference, Kooralbyn – Gold Coast Hinterland, CD Rom. Various parts of this research have also been presented in various forms at the following conferences: 2000 31st Annual Scientific Conference of the Australian Entomological Society 2001 Fourth Australian Sorghum Conference 2006 Fifth Australian Sorghum Conference v Acknowlegements Many have contributed to the work in this thesis over nearly a decade. Thanks to you all. Casual staff on university breaks have spent countless hours in the field and lab during summer. Lawrie Smith, Ken Duzza, Andrea Gerard, Petro Ioannis, Ashley Moore, Tammy Bull and James Mclean. QDPI&F biometricians Dave Butler, Kerry Bell and Alison Kelly gave me invaluable advice and assistance with statistical analyses. Nat Parker and Chris Freebairn took some of the great midge photos in this thesis. Thanks also to the sorghum breeding team at Hermitage for all their help in developing material for testing and for advice and assistance in the finer points of plant breeding. To my supervisors Dr Mark Sutherland, Dr Dave Jordan and Dr Bernie Franzmann, and my friends Cam and Heather Fletcher, I am deeply grateful for the long hours spent reviewing manuscripts and discussing the best way to write this thing. In particular I would like to thank Bernie for the many years of support and gentle guidance. Bernie you have always treated me more like a son than a student. This research was funded by GRDC and QDPI&F. To my beautiful wife Rosita, who kept me going to get this thing finished. You are also a great editor and a most cherished love of my life, thank you my darling. Finally I would like to dedicate this thesis to my parents, who over many years have sacrificed much for their kids. Even though you are highly unlikely to ever fully read this thing, mum and dad, this one’s for you! vi Table of Contents CHAPTER 1 Review of Literature........................................................ 1 Introduction............................................................................................................ 1 Sorghum Midge Biology ........................................................................................ 2 Grain Sorghum Biology......................................................................................... 7 Integrated Pest Management ................................................................................ 8 IPM of sorghum midge......................................................................................... 8 The contribution of midge resistant sorghum to IPM.......................................... 9 A rating scheme for midge resistant hybrids in Australia ................................. 10 Economic Impact on Industry ............................................................................ 11 Benefits of resistant hybrids to farmers ............................................................. 13 The emerging success of IPM in Australian grain sorghum.............................. 15 Host Plant Resistance Theory ............................................................................. 17 Durability of resistance...................................................................................... 17 Resistance mechanisms and components........................................................... 18 Ovipositional antixenosis................................................................................... 20 Antibiosis............................................................................................................ 21 Tolerance ........................................................................................................... 22 Midge Resistant Germplasm............................................................................... 23 Rationale and Structure ...................................................................................... 24 Chapter 2 – A search for new sources of midge resistance ........................... 24 Chapter 3 – A closer examination of larval antibiosis................................... 25 Chapter 4 – The water injection technique .................................................... 25 Chapter 5 – Using the water injection method to study larval antibiosis ...... 25 Chapter 6 – Is there a link between antibiosis and tolerance? ....................... 26 Chapter 7 – The inheritance of antibiosis ...................................................... 26 Chapter 8 – General discussion and future developments ............................. 26 CHAPTER 2 A Search for New Sources of Midge Resistance ......... 27 Introduction.......................................................................................................... 27 Materials and Methods........................................................................................ 28 Stage 1 – Screening for antibiosis.....................................................................

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