J. D. Atkinson

Cross-protection between strains of apple mosaic virus

Abstract A leaf infection index was used to express in numerical terms the severity of apple mosaic virus (AMV) symptoms. It was demonstrated that mild strains of AMV gave apple trees a high level of protection against infection with severe strains of the same virus. It was also shown that scions carrying a mild strain when worked to trees carrying a severe strain were effectively protected against invasion by the severe strain. Although there was some breakdown in protection in the first and second years after working, in subsequent years protection became more firmly established. The cross-protection reaction provides a useful technique for detecting mild or symptomless strains of AMV. It is suggested that cross-protection could be used to protect orchard trees in areas where field spread of AMV occurs and that it could be used to regenerate apple trees stunted by severe strains of the virus.

Effect of apple mosaic virus on growth and cropping of ‘freyberg’ apple trees

Abstract Over a 12-year period a severe strain of apple mosaic virus (AMV) reduced the growth of ‘Freyberg’ apple trees by 42 percent and, during nine cropping seasons, lowered fruit yield by 26.6 percent. It had no effect on fruit size and no apparent effect on quality.

Occurrence of cherry green ring mottle virus in New Zealand

Abstract A disease of flowering cherry characterised by epinasty of foliagc, stunting of trees, and roughening of bark, and accompanied by excessive graft failures, caused serious losses in two nurseries on Kanzan and three other varieties. The causal agent was diagnosed as cherry grccn ring mottle virus (GRMV). Infection was shown to come from mazzard rootstocks raised from root cuttings taken from sweet cherry nursery trees. Complete control in the nurseries was achieved by the use of mazzard seedling rootstocks. The virus, carried without symptoms, was found to be prevalent in sweet and mazzard cherries and to occur in some peach and nectarine varieties.

Apple rubbery wood virus

Abstract Apple rubbery wood virus (RWV) is widespread in apple and pear varieties in New Zealand, having been found in some trees of all varieties examined. Of 278 apple trees tested, 75 percent were infected; and of 43 pear trees indexed, 70 percent carried the virus. The virus has been found to cause symptoms on two New Zealand produced apple varieties, ‘Gala’ and ‘Splendour’. Symptoms on the former are nearly as severe as those on ‘Lord Lambourne’; on the latter they are less pronounced, being comparable with those on ‘Golden Delicious’. Rubbery wood symptoms have been observed also on ‘Red Delicious’ trees known to be infected with RWV. Apple and pear rootstock and scion varieties free from RWV have been secured from overseas or obtained in New Zealand by the heat treatment/tip culture technique. Most rootstock varieties free from RWV have been secured from overseas, and most scion varieties have been obtained by heat treatment locally. RWV-free material available in New Zealand consists of 19 apple a...

Two diseases of plum causing distortion and internal necrosis of fruits

Summary Plum fruit crinkle, a virus disease of plums, has been found in New Zealand on three trees of the Japanese plum variety Sultan. It causes crinkling and internal necrosis of fruits and transient mottling and faint chlorotic line patterns on leaves. In many respects symptoms resemble those of the serious virus disease known as plum pox in Europe. It is possible that plum pox and plum fruit crinkle are caused by the same disease and that variations in symptoms are the result of host, virus strain, or climatic differences. Plum fruit crinkle has been transmitted experimentally from Sultan to Sultan, George Wilson, and Shiro plum trees. An attempt is being made to eradicate the disease from New Zealand.

Note on a modification in technique for inactivating apple mosaic virus in apple wood by heat treatment

Abstract Since Kunkel (1935) established that exposure of virus-infected trees in pots to temperatures ranging between 34.4° and 36.3°e was effective in treeing peach trees of either peach yellows or peach rosette, heat treatment for the inactivation of different viruses in plants has become established practice.

Field studies with apple mosaic virus

Abstract In a yield trial with the apple cultivar ‘Jonathan’ mild, moderate, and severe strains of apple mosaic virus caused an increasing reduction in yield. Severely infected trees, when in full bearing, produced only one third as much fruit as mosaic-free trees. Moderate and severe strains caused some reduction in the average weight of individual fruit. In another trial, over a 14-year period, no natural spread of infection of apple mosaic was found from a block infected with severe apple mosaic to an adjacent mosaic-free block. Elimination of apple mosaic by heat therapy from budded seedlings was shown to be inconsistent when attempts were made to reduce the heat treatment period to less than 30 days. A number of cultivars bud-inoculated with severe and moderate strains showed varying sensitivity to this virus.

Occurrence of a “Small Fruit” condition of apples in New Zealend

Abstract A “small fruit” condition of apples with symptoms resembling those caused by chat fruit virus has been found on Red Dougherty in Hawkes Bay and on Delicious and Sturmer in Otago. On affected trees the fruit which carry the normal number of seeds are small at harvest time, averaging only 30% to 40% the weight of fruits from healthy trees. On Delicious, affected fruits lack colour, and affected Sturmer trees tend to have an upright habit. In transmission trials with Red Dougherty preliminary results indicate that the condition is transmissible from diseased to healthy trees.

Cherry variegation in New Zealand

Summary Cherry variegation, a non-infectious disease probably arising from bud sports, is widespread in New Zealand. The most characteristic symptom is a white spotting or streaking of leaves sometimes accompanied by distortion or upward rolling of leaf margins. Severely affected trees are stunted and bear small fruits. It has been found on four varieties of sweet cherry and on one Oriental flowering cherry variety. The disease is perpetuated on scions and may appear on the progeny of affected trees. It is considered to be the same as the disease known as variegation, or virus-like variegation, in Europe, and as cherry white crinkle in North America.