The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, Centre for Horticultural Science, GPO Box 267, Brisbane 4001, Australia.
Department of Plant Sciences, Faculty of Agriculture, Rajarata University of Sri Lanka, Puliyankulama, Anuradhapura, Sri Lanka.
Phytopathology. 2020 Jul;110(7):1294-1304. doi: 10.1094/PHYTO-10-19-0396-R. Epub 2020 May 13.
Australian macadamia production is threatened by a disorder known as abnormal vertical growth (AVG), for which the etiology is unknown. AVG is characterized by vigorous upright growth and reduced lateral branching, flowering, and nut set that results in over 70% yield loss annually. Six commercial macadamia orchards were surveyed in 2012 and again in 2018 to examine spatiotemporal dynamics of the epidemic. Data were subjected to point-pattern and geostatistical analyses. AVG incidence in all orchards showed a better fit to the beta-binomial distribution than the binomial distribution. AVG incidence in the different orchards varied between 5 and 47% in 2012, and 13 and 55% in 2018 and the rate of spread was slow, averaging at about 2% increase in disease incidence per annum. Spatial patterns of AVG were highly aggregated on both survey years and spread was mainly between neighboring trees in a row or trees that were opposite to each other in different rows. Semivariograms showed large range values (approximately 15 to 120), indicating aggregation of AVG-affected trees beyond quadrat levels. Furthermore, clusters of disease were mainly at the edge of the orchard on the first survey date and the disease progressed toward the center of the orchard over time. It is concluded that AVG is caused by an infectious agent, and based on patterns of spread, we hypothesize that spread is facilitated by root grafting or root-to-root contact. Furthermore, a vascular-limited pathogen could be involved that modulates plant hormone production.
澳大利亚澳洲坚果生产受到一种称为异常垂直生长 (AVG) 的疾病的威胁，其病因尚不清楚。AVG 的特征是生长旺盛、直立，侧枝、开花和结实减少，导致每年超过 70%的产量损失。2012 年和 2018 年对六个商业澳洲坚果果园进行了调查，以检查该流行病的时空动态。数据进行了点格局和地统计学分析。所有果园的 AVG 发病率均更符合贝塔二项式分布，而不是二项式分布。2012 年，不同果园的 AVG 发病率在 5%至 47%之间，2018 年在 13%至 55%之间，且传播速度较慢，平均每年发病率增加约 2%。在这两年的调查中，AVG 的空间模式都是高度聚集的，传播主要发生在同一行的相邻树木之间或不同行中相对的树木之间。半方差图显示出较大的范围值（约 15 至 120），表明受 AVG 影响的树木聚集程度超出了方格水平。此外，疾病集群主要出现在第一次调查日期果园的边缘，随着时间的推移，疾病向果园中心发展。结论是 AVG 是由一种传染性病原体引起的，根据传播模式，我们假设传播是由根嫁接或根对根接触促进的。此外，可能涉及一种血管受限的病原体，它可以调节植物激素的产生。
