The distribution and spread of citrus canker in Emerald, Australia

Citrus canker is a disease of citrus and closely related species, caused by the bacterium Xanthomonas citri subsp. citri. This disease, previously exotic to Australia, was detected on a single farm [infested premise-1, (IP1). IP is the terminology used in official biosecurity protocols to describe a locality at which an exotic plant pest has been confirmed or is presumed to exist. IP are numbered sequentially as they are detected] in Emerald, Queensland in July 2004. During the following 10 months the disease was subsequently detected on two other farms (IP2 and IP3) within the same area and studies indicated the disease first occurred on IP1 and spread to IP2 and IP3. The oldest, naturally infected plant tissue observed on any of these farms indicated the disease was present on IP1 for several months before detection and established on IP2 and IP3 during the second quarter (i.e. autumn) 2004. Transect studies on some IP1 blocks showed disease incidences ranged between 52 and 100% (trees infected). This contrasted to very low disease incidence, less than 4% of trees within a block, on IP2 and IP3. The mechanisms proposed for disease spread within blocks include weather-assisted dispersal of the bacterium (e.g. wind-driven rain) and movement of contaminated farm equipment, in particular by pivot irrigator towers via mechanical damage in combination with abundant water. Spread between blocks on IP2 was attributed to movement of contaminated farm equipment and/or people. Epidemiology results suggest: (i) successive surveillance rounds increase the likelihood of disease detection; (ii) surveillance sensitivity is affected by tree size; and (iii) individual destruction zones (for the purpose of eradication) could be determined using disease incidence and severity data rather than a predefined set area.

Cynodon dactylon Green Couch Grass, Bermuda Grass 'JT1'

Spontaneous mutation or chance seedling: discovered in the mid-1990s as a superior plant growing in a commercial field of “Common” Cynodon dactylon on Jimboomba Turf Company’s farm at Jimboomba in south-east Queensland. Selection criteria: vigorous lateral spread, high shoot density and turf quality, low inflorescence numbers, and darker green colour. In 1999 after observing the superior turf performance of this mutant plant as a small patch within a much larger paddock of “Common”, vegetative material was taken and propagated in clean ground elsewhere on the farm for multiplication and further trials in a variety of turf situations in south-east Queensland. Propagation: vegetative. Breeder: Lynn Davidson, Jimboomba, QLD. PBR Certificate Number 2640, Application Number 2002/282, granted 24 February 2005.

Cynodon transvaalensis x Cynodon dactylon Hybrid Green Couch Grass, Hybrid Bermuda Grass 'MS-Supreme'

Ploidy: triploid interspecific hybrid (3n = 27 chromosomes). Plant: habit prostrate, creeping, type mat-forming, height very short, longevity perennial, spreading laterally by stolons and rhizomes. Stolon: compound nodes with up to 3 leaves, internode length very short, internode thickness very thin, colour grey-brown (RHS N199A) when exposed to sunlight. Culms: length very short. Leaf blade: shape linear-triangular, length short, width narrow, colour dark green (RHS 137B). Ligule: dense row of short white hairs. Inflorescence: digitate with 3(-4) very short spicate racemes, peduncle very short. (All RHS colour chart numbers refer to 2001 edition.) PBR Certificate Number 2641, Application Number 2002/305, granted 24 February 2005.

Zoysia japonica, Zoysia Grass 'Palisades'

Open-pollination: originated as a chance seedling from Z44 (maternal clonal parent), obtained from Beltsville MD in 1981, with an unknown pollen source from a zoysia grass germplasm field nursery at the Texas Agricultural Experiment Station in Dallas. ‘Palisades’ was selected over the parent Z44 on the basis of its lower tendency to produce thatch, its excellent lateral growth habit and its superior mowing qualities. ‘Palisades’ has been vegetatively propagated, and is uniform in growth expression. No seedling establishment from ‘Palisades’ has been noticed in either greenhouse or field studies. Selection criteria: rapid regrowth and spread by, and/or from, stolons and rhizomes; turf colour and density; tolerance to low mowing; winter hardiness; shade tolerance; low water use requirements. Propagation: vegetative. Breeder: Milton C. Engelke, Dallas, USA. PBR Certificate Number 2594, Application Number 2001/199, granted 26 October 2004.

Cynodon transvaalensis x Cynodon dactylon, Hybrid Green Couch Grass, Hybrid Bermuda Grass 'TL2'

Spontaneous mutation: In 1996, vegetative material (later designated ‘TL2’) taken from a disease resistant mutant plant on the fifteenth green at Novotel Palm Cove resort course near Cairns was included an on-going program of selection and testing of promising ‘Tifgreen’ mutants by Tropical Lawns Pty Ltd. Selection criteria: healthy vigorous growth during the tropical wet season, dense fine-textured appearance under close mowing, and dark green leaves. In subsequent trials, ‘TL2’ was identified as the outstanding plant among selections of mutant ‘Tifgreen’ genotypes from other north Queensland sites in terms of colour, texture and density for greens use. Propagation: vegetative. Breeder: Terry Anderlini, Gordonvale, QLD. PBR Certificate Number 2639, Application Number 2002/268, granted 24 February 2005.

Cynodon dactylon, Green Couch Grass 'TL1'

Chance seedling: observed in about 1989 as a distinctly coarser textured, densely matting, darker green mutant bermuda grass plant growing among the hybrid ‘Tifgreen’ on the eighth green at the Townsville Golf Course. Although ‘TL1’ was selected from a sward of the hybrid Bermuda grass ‘Tifgreen’, its inflorescence structure (4, not 3, racemes per inflorescence), agronomic attributes (e.g. its tolerance to certain herbicides), and its DNA profile are consistent with a chance seedling of Cynodon dactylon rather than a mutant plant of hybrid (C. dactylon x transvaalensis) origin. Selection criteria: exceptionally short stolon internodes resulting in an extremely tight knit stolon mat under close (c. 5-6 mm) but not very close (c. 3-4 mm) mowing; very deep, strong rhizome system; very dark green colour; tolerates shade better than other Australian bermuda grass varieties of common knowledge (except for ‘Plateau’A); and remains low growing under heavy tropical cloud cover even after 6-8 months. Designated ‘TL1’ by Tropical Lawns Pty Ltd and trialed successfully during the late 1990s and early 2000s in high wear situations (e.g. golf tees) in north Queensland. Propagation: vegetative. Breeder: Barry McDonagh, Townsville, QLD. PBR Certificate Number 2638, Application Number 2002/267, granted 24 February 2005.

Cynodon dactylon, Green Couch Grass 'Oz-E-Green'

Spontaneous mutation or chance seedling: discovered in 2001 as a superior plant growing among “Common” green couch on the breeder’s turf farm at Berries Road, Childers. A selected piece of sod was removed and broken into vegetative sprigs to propagate a larger area of this variety elsewhere on the breeder’s property. The original plant has now been multiplied vegetatively three times without showing any discernible off types. Selection criteria: dense prostrate habit and limited inflorescence production (giving a low mowing requirement), high turf quality, dark green colour. Propagation: vegetative. Breeder: Robert William Morrow, Childers, QLD. PBR Certificate Number 2844, Application Number 2004/035, granted 22 August 2005.

Stenotaphrum secundatum, Buffalo Grass 'Sir James'

Spontaneous mutation: discovered in February 2001 as a superior plant growing among “Common” buffalo grass growing on the breeder’s property at Saltash in the Hunter Valley (NSW). The selected material has smaller (finer) leaves and showed better growth and colour than the parent variety with minimal inputs (water, fertiliser) under stressful climatic conditions. Subsequently, it also showed better leaf colour retention than the parent variety during winter. A vegetative plug taken from the original plant has now undergone four subsequent vegetative divisions to expand the original material for performance trials in NSW and Queensland without showing any discernible off types. Main selection criteria: winter colour retention, small leaves, low fertiliser requirement. Propagation: vegetative. Breeder: Brent Redman, Maitland North, NSW. PBR Certificate Number 2715, Application Number 2002/283, granted 18 March 2005.

Cynodon dactylon, Green Couch Grass, Bermuda Grass 'Grand Prix'

‘Grand Prix’ is a selection from a cross between ‘Wintergreen’ and ‘Couch 5’ (also designated C5). ‘Couch 5’ was a selection from an earlier series of crosses by the breeder between ‘Wintergreen’ and a number of Cynodon dactylon accessions, which were collected by the breeder from the Mornington Peninsula area of Victoria between 1986 and 1990. C5 was an experimental breeding line, and was not subsequently reserved as vegetative germplasm. Living material of C5 is no longer in existence. Following the crossing of ‘Couch 5’ and ‘Wintergreen’ in 1998, the resultant seed was germinated on moist blotting paper. Individual seedlings, a total of 150 in number, were planted into 150mm pots and these plants observed during 1998 and 1999. During the summer of 1999-2000, the majority of the seedling plants were culled on the basis of their shoot density, leaf texture, internode length, and colour. In the spring of 2000, the remaining 20 potted seedlings were planted individually into 4m2 plots at the Evergreen Turf farm at Pakenham (Victoria), and allowed to expand fully across these plots. The final selection of Seedling 12 (later designated DN12) in late 2002 was based on shoot density, leaf colour, turf quality, and reduced thatch accumulation as expressed in these plots. Propagation: the original plant has been multiplied through four (4) vegetative expansions prior to PBR application without showing any discernible off types. Breeder: David Nickson, Frankston, VIC. PBR Certificate Number 3133, Application Number 2005/291, granted 12 September 2006.

Cynodon dactylon, Green Couch Grass, Bermuda Grass 'Winter Gem'

‘Winter Gem’ is a selection from a cross between ‘Wintergreen’ and Couch 5 (also designated C5). Couch 5 was a selection from an earlier series of crosses by the breeder between ‘Wintergreen’ and a number of Cynodon dactylon accessions, which were collected by the breeder from the Mornington Peninsula area of Victoria between 1986 and 1990. C5 was an experimental breeding line, and was not subsequently reserved as vegetative germplasm. Living material of C5 is no longer in existence. Following the crossing of Couch 5 and ‘Wintergreen’ in 1998, the resultant seed was germinated on moist blotting paper. Individual seedlings, a total of 150 in number, were planted into 150mm pots and these plants observed during 1998 and 1999. During the summer of 1999-2000, the majority of the seedling plants were culled on the basis of their shoot density, leaf texture, internode length, and colour. In the spring of 2000, the remaining 20 potted seedlings were planted individually into 4m2 plots at the Evergreen Turf farm at Pakenham (Victoria), and allowed to expand fully across these plots. The final selection of Seedling 9 (later designated DN9) in late 2002 was based on shoot density, leaf texture, and retention of winter colour as expressed in these plots. Propagation: The original plant had been multiplied through four (4) vegetative expansions prior to PBR application without showing any discernible off types. Breeder: David Nickson, Frankston, VIC. PBR Certificate Number 3132, Application Number 2005/290, granted 11 September 2006.

Cynodon transvaalensis x Cynodon dactylon, Hybrid Green Couch Grass, Hybrid Bermuda Grass 'P18'

‘P18’ was first produced in 1992 and is a mutant genotype obtained from a hybrid Bermudagrass line believed to be ‘Tifdwarf’, which was grown in a greenhouse owned by H&H Seed Company in Yuma, Arizona. ‘P18’ was selected for its extremely fine leaf texture, its high shoot density under close mowing, its rapid growth rate, and its uniform dark green colour, and was subsequently evaluated for these traits and characteristics. Propagation: vegetative. Breeder: Howard E. Kaewer, Eden Prairie, MN, USA. PBR Application Number 2007/179, Certificate Number 3567, granted 13 August 2007.

Stenotaphrum secundatum, Buffalo Grass 'TF01'

‘TF01’ was selected by the breeder, John Powell, as an isolated and distinctive plant of buffalo grass (Stenotaphrum secundatum) growing among kikuyu grass on the banks of the Bellinger River along its tidal reaches where it was occasionally inundated by brackish water during king tides. It showed shorter internodes than existing buffalo grass varieties of comparable texture within the breeder’s knowledge, and showed good colour retention during periods of drought. Initially designated ‘TF01’, the buffalo grass cultivar was trialled for turf adaptation by Turf Force on their Beaudesert turf farm and characterised in a national buffalo grass project coordinated by the Queensland Department of Primary Industries and Fisheries Turf Research group initiated in 2005. PBR Certificate Number 3624, Application Number 2007/245, granted 25 September 2008.

Cynodon transvaalensis x Cynodon dactylon, Hybrid Green Couch Grass, Hybrid Bermuda Grass 'AGRD'

‘AGRD’ was selected by the breeder, Dr Warren Hunt, from a variant area of winter active turf (probably ‘Tifway’ or ‘Tifgreen’) on a Hong Kong Golf Course in Apr 1996. A selection of this material was imported through vegetative quarantine to New Zealand for evaluation. Following a favourable assessment of its potential as a warm-season turfgrass variety under New Zealand conditions made based on its superior comparative performance relative to other Cynodon accessions in glasshouse and field trials, the New Zealand registered variety ‘Grasslands AgRiDark’ was released in 1999. PBR Certificate Number 3716, Application Number 2004/299, granted 20 January 2009.

Paspalum vaginatum Swartz, Seashore Paspalum 'SDX-1'

‘SDX-1’ originated as an open-pollinated chance seeding in an old green of ‘Adalayd’ seashore paspalum (US Plant Patent 3939) surrounded by an undefined local ecotype of the same species. ‘SDX-1’ was finer textured and had a denser, more prostrate growth habit than its putative parents which are ‘Adalayd’ (maternal) and an undefined parental genotype growing among the surrounding local ecotype. ‘SDX-1’ was compared with other promising seedlings discovered similarly at the same time, and was selected on the basis of its dwarf growth habit, tolerance of low cutting height, turf density, fine-textured growth, and apparent salt tolerance under field conditions. Breeder: Stewart T Bennett, Paul H Tillman, Michael DePew, Enviro Turf LC, Terkonsha, MI, USA. PBR Certificate Number 3660, Application Number 2006/160, granted 16 December 2008.

Chloris gayana, Rhodes Grass 'KP4'

‘KP4’ is based on selected F4 progeny of 8 plants showing a low, creeping, tight-matted, late flowering growth habit. The original parental breeding population was selected from among 1600 diploid Rhodes grass seedlings grown as spaced plants; seven of the selected parental plants were from ‘Katambora’ and the eighth (which did not contribute as a maternal parent beyond the F1 generation) was a seedling from an unreleased accession. Four (4) cycles of mass selection were conducted, in which the selected plants from the previous generation were allowed to inter-cross in isolation in the field, and the resultant progeny later grown as spaced plants in the field for the next cycle of selection. Selection was for the following attributes: prostrate creeping early growth habit with short stolon internodes resulting in a dense stolon mat; leafy appearance; fine leaf and stem; and late flowering (i.e. a long period of vegetative growth before flowering). ‘KP4’ is a synthetic Rhodes grass cultivar multiplied from the selected fourth-generation plants produced by this line of breeding. Breeder: Donald S. Loch, Cleveland, QLD. PBR Certificate Number 3661, Application Number 2006/189, granted 16 December 2008