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'Abnormal vertical growth' : A disorder threatening the viability of the Australian macadamia industry

O'Farrell, P. and Le Lagadec, D. and Searle, C. (2016) 'Abnormal vertical growth' : A disorder threatening the viability of the Australian macadamia industry. Acta Horticulturae, 1109 . pp. 143-150. ISSN 05677572 (ISSN); 9789462611030 (ISBN)

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Article Link(s): http://dx.doi.org/10.17660/ActaHortic.2016.1109.23

Abstract

'Abnormal vertical growth' (AVG) was recognised in Australia as a dysfunction of macadamia (Macadamia spp.) in the mid-1990s. Affected trees displayed unusually erect branching, and poor flowering and yield. Since 2002, the commercial significance of AVG, its cause, and strategies to alleviate its affects, has been studied. The cause is still unknown, and AVG remains a serious threat to orchard viability. AVG affects both commercial and urban macadamia. It occurs predominantly in the warmer-drier production regions of Queensland and New South Wales. An estimated 100,000 orchard trees are affected, equating to an annual loss of $ 10.5 M. In orchards, AVG occurs as aggregations of affected trees, affected tree number can increase by 4.5% per year, and yield reduction can exceed 30%. The more upright cultivars 'HAES 344' and '741' are highly susceptible, while the more spreading cultivars 'A4', 'A16' and 'A268' show tolerance. Incidence is higher (p<0.05) in soils of high permeability and good drainage. No soil chemical anomaly has been found. Fine root dry weight of AVG trees (0-15 cm depth) was found lower (p<0.05) than non-AVG. Next generation sequencing has led to the discovery of a new Bacillus sp. and a bipartite Geminivirus, which may have a role in the disease. Trunk cinctures will increase (p<0.05) yield of moderately affected trees. Further research is needed to clarify whether a pathogen is the cause, the role of soil moisture in AVG, and develop a varietal solution.

Item Type:Article
Business groups:Horticulture and Forestry Science
Keywords:AVG M. integrifolia M. tetraphylla Upright branching Yield decline
Subjects:Plant culture > Economic botany
Plant culture > Fruit and fruit culture > Nuts
Deposited On:12 Aug 2016 02:16
Last Modified:15 Aug 2016 06:19

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