Determining whether natural spread of apple green crinkle disease occurs, its absence from New Zealand clonal apple rootstocks, and the sensitivity of some new cultivars

Abstract

In an investigative trial to determine if natural spread of apple green crinkle occurs, six trees of Malus domestica Borkh. ‘Granny Smith’ free from this disease and other diseases of a virus or virus‐like nature were planted in 1973 in a rectangular block on a Nelson, New Zealand, research orchard and surrounded by eight trees of the same cultivar infected with moderate green crinkle and six trees with severe green crinkle. Two of the healthy trees had been removed by 1987, but the remaining four were still free from green crinkle after a 20‐year period in 1993, indicating that any insect vectors capable of spreading the disease are unlikely to be present in New Zealand. In another investigation, no infection with green crinkle disease was found in ‘M9’, ‘M26’, ‘Merton 793’, and ‘M106’ clonal apple rootstocks tested from two commercial nurseries engaged in propagating these rootstocks. As a result of inoculation by chip‐budding, two apple cultivars released from the HortResearch apple breeding programme ('Pacific Queen’ and ‘Southern Snap'), and promoted by the New Zealand fruit growing industry, were found to be sensitive to green crinkle disease.

Keywords:

• Malus
• apple cultivars
• apple rootstocks
• green crinkle disease
• natural spread trial