STUDIES IN RUBUS VIRUS DISEASES I. A LATENT VIRUS OF NORFOLK GIANT RASPBERRY

A selection of Norfolk Giant raspberry is infected with a virus transmissible by Amphorophora rubi Kalt. after short feeding periods on infected plants and persisting for at least 18 1/2 hr. in the aphid. This virus is identified with one which is carried without symptoms by Norfolk Giant and Baumforth's Seedling B, and causes necrosis on Rubus henryi and mosaic symptoms on R. saxatilis , American black raspberry R. occidentalis (var. Cumberland) and the red raspberry varieties Chartham, Mailing Landmark and St Walfried. The virus is present in some commercial stocks of Baumforth's Seedling B, Burnetholm Seedling, and the Mailing varieties Enterprise, Notable and Promise. The name raspberry leaf mottle is proposed.     

STUDIES IN RUBUS VIRUS DISEASES II.

Three diseases characterized by vein chlorosis of varying grades of severity are shown to be graft transmissible to a wide range of raspberry varieties. The diseases are thought to be caused by related strains of a virus transmissible by Doralis (Aphis) idaei V. d. G. and rarely, if at all, by Amphorophora rubi Kalt. It is proposed to refer to the diseases and viruses respectively as mild, moderate and severe vein chlorosis.     

RESOLUTION OF STRAWBERRY VIRUS COMPLEXES IV. THE LATENT PERIOD OF VIRUS 3 IN THE VECTOR

From the time of first feeding on plants infected with strawberry virus 3, 10–19 days elapsed before Capitophorus fragariae became infective, a longer 'latent period' than any previously recorded for an aphid-transmitted virus. The time taken for aphids to develop infectivity after leaving infected plants decreased with increasing duration of the infection feed. Aphids which had fed for 16 days on an infected plant caused infection in the first day of test feeding.     

VIRUS DISEASES OF CACAO IN WEST AFRICA IX. STRAIN VARIATION AND INTERFERENCE IN VIRUS 1A

Cacao virus iA, the most important and prevalent of the viruses that attack cacao in the Gold Coast, occurs in strains that differ widely in their virulence towards cacao. Outbreaks usually contain trees infected with different strains and individual trees are often infected simultaneously with more than one strain; this can be demonstrated by coppicing the trees, and by inoculating sets of test plants with grafts from different parts of one tree. Neither mild nor virulent strains seemed to be consistently dominant in roots or in other parts of cacao trees.
Cacao plants infected with mild strains were nearly always protected against the effects of infection by virulent strains; however, virulent strains entered hosts already infected with mild strains, but usually without causing any symptoms unless the plants were coppiced. The severe symptoms that developed on new growth from such coppiced plants were seldom repeated in later growth. Mealybugs transmitted the virulent strains from leaves with symptoms characteristic of infection by the latter, but not from leaves free from such symptoms. These results suggest that the multiplication of a virulent strain is impeded in plants infected with a mild strain.
In the field, infection with a mild strain protected mature trees against the effects of virulent strains spread by mealybugs. During 3 years in which 273 out of 387 previously uninfected trees became severely diseased, only 35 out of 416 infected with themildstrain developed symptoms of infectionwiththevirulent strain. Five years after infection with the mild strain, trees were yielding I pod per tree more than in the year they were infected, whereas the decrease on trees infected with the virulent strain was 16 pods per tree. Some limitations in the practical application of protection by mild strains, and objections to its use as a control measure, are discussed.     

ANALYTICAL DIFFUSION OF INFLUENZA VIRUS AND MOUSE ENCEPHALOMYELITIS VIRUS

Analytical diffusion has been applied to a study of influenza A virus in mouse lung, influenza A virus in the extra-embryonic fluids of the chick, and mouse encephalomyelitis virus in mouse brain. The results from influenza in mouse lung suggested that about 99 per cent of the infectivity was present in particles 200 mµ in diameter, and 1 per cent in particles 6 mµ in diameter. The results from influenza in extra-embryonic fluids indicated that the preparation was inhomogeneous and that the smallest virus units were about 6 mµ in diameter. The results from mouse encephalomyelitis virus indicated that the preparation was also inhomogeneous, with 10 per cent of the infectivity in particles about 15 mµ in diameter. It has been suggested that in virus preparations normal colloidal particles can act as carriers of much smaller virus units.     

牛病毒性腹泻病毒（BVDV）对牛免疫缺陷病毒（BIV）的激活作用

通过合胞体分析和反转录酶活力测定,首次证明牛病毒性腹泻病毒能激活牛免疫缺陷病毒的复制与表达,并进一步通过转染实验和凝胶电泳漂移分析证明,当ＢＩＶ ＬＴＲ的ＮＦ－ｋ Ｂ区缺失时,ＢＶＤＶ则不能实现其激活作用,ＢＶＤＶ直接或间接诱导牛ＮＦ－ｋＢ因子作用于ＢＩＶ ＬＴＲ的ＮＦ－ｋＢ区实现其激活作用。     

大麦条纹花叶病毒新疆分离物是三组分RNA病毒

大麦条纹花叶病毒新疆分离物(BSMV-XJ)的RNA在乙二醛,二甲亚砜中进行变性电泳,电泳图谱可重复的显示三个组分。将电泳分离的BSMV-RNA各组分在高盐浓度下吸附转移到硝酸纤维素薄膜上,经固定后,与~(32)P标记的病毒总RNA的cDNA行分子杂交。在X光放射自显影图谱上,进一步证实BSMV-XJ为三组分RNA病毒。本文同时就BSMV-RNA不经变性电泳也可以部分吸附转移到硝酸纤维素薄膜上的现象讨论了可能的分子基础。