VIRUS DISEASES OF CACAO IN WEST AFRICA

Increasing the number of Pseudococcus njalensis per test plant increased the infection rate with cacao virus 1A and 1M to 95 % with twenty-five insects. Young leaves with the red vein-banding symptoms were better sources of virus than mature leaves, and there was evidence of virus localization in the plant. It was estimated that Ps. njalensis nymphs took about 16 min. to penetrate plant tissues with their stylets.
Infection rates increased with time of test feeding up to 50 min. The virus was non-persistent in the feeding insect, but persisted up to 36 hr. in insects starved after the infection feed. Starvation before the infection feed increased the infection rate with infection feeds up to 10 hrs., after which the infection rate with pre-starved insects declined to the level attained by unstarved insects.     

VIRUS DISEASES OF CACAO IN WEST AFRICA

Of the tested plants which are indigenous to West Africa, three species in the Bombacaceae and four in the Steruliaceae are susceptible to one or more of four viruses from cacao, three occurring in the Gold Coast and one in Nigeria. These species are less affected than cacao by the viruses; some show transient leaf symptoms and others are symptomless carriers. The development of spines on the stems of Ceiba pentandra seedlings is suppressed by infection with virus 1 A.
In general, the indigenous species are more difficult to infect than cacao, and mealybugs do not become infective as readily when feeding on them as when feeding on infected cacao. The availability of the viruses to vectors seems to be correlated with severity of symptoms, and transmission from infected plants to cacao becomes less frequent with increasing duration of infection.
Ceiba pentandra trees were found naturally infected in the Gold Coast and Nigeria. In the Western Province of the Gold Coast, Cola chlamydantha trees in cacao farms and forests were naturally infected with viruses apparently identical with those causing swollen shoot of cacao there.
There is little doubt that C. chlamydantha trees are an important source of virus for cacao trees. Whenever possible these and other alternative hosts growing near to cacao should be destroyed.     

一种新病毒——兔出血症病毒的鉴定初报

从我国新发生的一种家兔急性败血性传染病死兔内脏抽提物中,观察到典型的病毒粒子,回归兔可引起典型发病,再从病死兔内脏回收到同样病毒,证明该病系病毒性传染病,暂定名为“兔病毒性出血症”,病原暂定为“兔出血症病毒”。经初步鉴定,认为本病毒可能是一种首次发现的新病毒,属双股RNA病毒。但从病毒大小和核酸节段看,又不同于呼肠病毒科。最终归属正在进一步研究。     

VIRUS DISEASES OF CACAO IN WEST AFRICA VIII. THE SEARCH FOR VIRUS-RESISTANT CACAO

The methods used and the results of 10 years' search for cacao resistant to swollen-shoot disease are described. Selection among the trees surviving in farms devastated by this virus disease led to the discovery of mild virus strains which can protect trees against virulent strains.
When tested by graft inoculation with virulent virus, none of the selections showed any immunity or resistance save that conferred by previous mild-strain infection. A low degree of tolerance was found in some selections.
Local selections and a range of new introductions were tested by mealybug infection, and only types from the Upper Amazon region of Ecuador were consistently resistant to infection. This genetical resistance seems to be strongest in cacao from the Nanay peninsula, near Iquitos.     

COPPICING EXPERIMENTS ON THE SPREAD AND CONTROL OF CACAO SWOLLEN-SHOOT DISEASE IN NIGERIA

A coppicing technique was used to determine the incidence and distribution of latent and unrecognized infection around naturally occurring outbreaks of cacao swollen-shoot virus disease in Western Nigeria. All the apparently healthy trees within 30 yards of eighty outbreaks of various sizes were coppiced and most of the infected stumps which regenerated showed symptoms within a year.
The distribution of the infected stumps around thirty-five outbreaks studied in detail is expressed by the equation log₁₀ I = a + bx. I is the estimated intensity of infection in the coppiced stumps at distance x from the nearest infected tree removed at the time of coppicing. The constant a determines the height of the peak of the infection gradient and increases with outbreak size, whereas the slope of the gradient, determined by the negative constant b , is similar around all outbreaks.
The results are consistent with information on the movement of the mealybugs and spread of cacao swollen-shoot virus in outbreaks. Moreover, they indicate that outbreaks are controlled most economically by removing all obviously infected trees and adjacent apparently healthy ones. Control does not require the destruction of all the trees around outbreaks up to a distance of 30 yards as done previously, but can be achieved by felling fewer trees, the actual number depending on the size of the outbreak.     

新城病毒浓缩法的初步报告

近年来国内农业科举研究机关进行新城病疫苗的制造,一般制造的疫苗为鸡胚富尔马林疫苗或鸡胚化毒力减弱病毒疫苗(粟寿初与马闻天,1950;李善达,1951;杜念兴,1954)。作者在过去报告中(高尚荫,1952)曾指出在其它条件固定的情况下,有机     

STREAK—A VIRUS DISEASE OF TOMATOES

A comparison of streak disease of tomatoes, derived from commercial glasshouses, and experimental streak produced by combined inoculation of the viruses of potato mosaic and tobacco mosaic, is given in detail.
The characters employed in comparison are the host range of each virus and its resistance to various temperatures, to different concentrations of alcohol, and to ageing in vitro .
Glasshouse streak and tobacco mosaic show an equal resistance to alcohol, heat and ageing in vitro , and have, in addition, an identical host range. Treatment for 1 hour with 90 per cent, alcohol and for 10 minutes at 85⁰ C. did not destroy the infectivity of either of these viruses.
Glasshouse streak is shown not to contain the virus of potato mosaic, but is of itself able to produce necrosis in tomatoes without the participation of potato mosaic. The factors underlying this have not been determined.
It is concluded that tobacco mosaic and the mosaic of glasshouse streak are probably identical, and that much of the streak occurring in glasshouses is due to a single virus, and not a mixed infection of this with potato mosaic.     

BARK-SPLIT–A VIRUS DISEASE OF PLUMS

The bark-split disease of plums commences with necrotic lesions in the outer bark, causing depressions on the surface; these lesions extend in area and depth, resulting in split and roughened bark, and crippling or killing trees of sensitive varieties like Cambridge Gage.
The causal virus was transmitted by grafting in the dormant season, but, probably because it is localized in older tissues, it was rarely transmitted or scion-perpetuated by summer budding.
About 90% of Common Plum clonal rootstocks from East Malling Research Station's layer-beds were found to be infected. Apparently virus-free Common Plum was propagated by cuttings from the roots of Common Plum under normal Cambridge Gage trees.
A different type of bark-split disease developed on Shiro Plum inoculated with virus from a tree of Quetsche Précoce de Zimmer. Leaf symptoms accompanying infection with this and with the virus from Common Plum were similar.
Bark-split disease is compared and contrasted with diamond canker of French Prune in California, and features that distinguish bark-split from bacterial canker are described.     

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.     

我国新城疫病毒分离株生物学特性的研究

本文系统地比较了我国不同地区分离的、有地区代表性的11株新城疫病毒分离物和北京株(国内攻毒株)的毒力范围,某些生物学特性,抗原性关系及对鸡的致病特征,结果所试验的分离株均属速发性嗜内脏型毒株。各株血凝素的热稳定性、凝集解脱速度、凝集哺乳动物红细胞的能力及对福尔马林的敏感性,均有明显差异。试验还表明,北京株和中监所分离株等对不同年龄鸡的致病表现也不同。 交叉血凝抑制试验和交叉鸡胚中和试验表明:各新城疫病毒株相互间的抗原性有较小程度的差异(r值0.66～1.11);其免疫原性也强弱不同,尤其是新疆株和内蒙株,其血清的血凝抑制抗体效价高于其它毒株,与部分毒株的差异极为显著(P<0.01),可能是制造新城疫灭能苗的优良毒株。