THE INFLUENCE OF PLANTING DATE AND MANURING ON THE INCIDENCE OF VIRUS DISEASES IN POTATO CROPS

Field experiments with Majestic potatoes were made over six years at Rothamsted to test the effects of varying date of planting and manuring on the yield of tubers and the incidence of the aphid-transmitted leaf roll and Y (rugose mosaic) viruses. Yield was increased by early planting, and by all the manures, especially dung. Early planting also usually increased the incidence of virus disease. Different manures had different effects on disease incidence; the average results from all comparisons showed the largest increase in incidence of both viruses from the use of dung; sulphate of ammonia increased the incidence of leaf roll, and muriate of potash that of rugose mosaic. Counts in two years showed that aphid populations were highest on the earlier planted potatoes, and were increased by dung, sulphate of ammonia and superphosphate, but were reduced by muriate of potash.     

THE EFFECT OF TEMPERATURE ON INFECTION WITH STRAINS OF CUCUMBER MOSAIC VIRUS

Cucumber mosaic virus strains differed in their ability to multiply in plants at 37° C. Some strains multiplied in inoculated leaves and produced systemic symptoms in plants at this temperature; plants systemically infected with one such strain remained infected after prolonged treatment at 37° C. Other strains did not appear to multiply in inoculated leaves at 37° C. and heat treatment was successful in freeing plants from infection with these. Tests with one strain of each type showed both to be rapidly inactivated in expressed sap at 37° C.
Strains of cucumber mosaic virus forming small necrotic local lesions in leaves of french bean var. Canadian Wonder, produced many fewer lesions in plants kept after inoculation at 25° C. for 24 hr. and then at 15° C. than in plants kept continuously at the lower temperature.     

THE EFFECT OF INFECTION WITH TOBACCO ETCH VIRUS ON THE RATES OF RESPIRATION AND PHOTOSYNTHESIS OF TOBACCO LEAVES

Unlike tobacco mosaic virus, which increases the respiration of tobacco leaves within an hour of their being inoculated, a virulent strain of tobacco etch virus did not change respiration rates until leaves showed external symptoms. The respiration rates of inoculated or systemically infected leaves with symptoms rose to 40% above that of healthy leaves, three times the increase produced by tobacco mosaic virus. The increased respiration rate occurred at all times of the year and was maintained through the life of the leaves.
Leaves infected with tobacco etch virus and showing symptoms had a photo-synthetic rate 20% lower than that of healthy leaves.     

降水对玉米产量的影响及边际产量效应分析

在黑龙江省玉米农田生态系统中,降水是限制玉米产量的主要因子,这种限制只能在环境、生产诸因子投入数量一定格局下,才是稳定的,玉米产量随降水量的多少而变化,在降水适量时玉米产量达到最嵩,旱涝均减产,降水的边际产量与各生态因子的关系是：降水边际产量随降水量递增而下降;随积温升高而增加,随土壤有机质含量的提高逐渐下降,对玉米适当增施氮,磷,钾化肥和农肥,玉米的降水边际产量效应均提高,在降水充沛,热量资源丰     

THE EFFECT OF INFECTION WITH TOBACCO MOSAIC VIRUS ON THE RESPIRATION OF TOBACCO LEAVES OF VARYING AGES IN THE PERIOD BETWEEN INOCULATION AND SYSTEMIC INFECTION

Leaves of tobacco plants inoculated with tobacco mosaic virus were divided into three groups: ( a ) inoculated leaves; ( b ) younger non-inoculated leaves present at the time of inoculation; ( c ) leaves formed since inoculation. The respiration rate of each group was compared with that of similar leaves from healthy plants. The respiration rate of inoculated leaves was increased by a constant amount for 3 weeks after inoculation, when it decreased. The respiration rate of group ( b ) leaves was not affected at any time, and that of group ( c ) leaves was decreased by 10% when they showed symptoms. The increased respiration in the inoculated leaves occurred too soon to reflect virus formation, and it is suggested that it reflects an initial change in infected cells preparatory to virus synthesis. The subsequent decrease in respiration may be due to the accumulation of virus which does not contribute to the total leaf respiration.     

香蕉种植密度对蕉园光能利用与产量的影响

本试验研究了福建沿海地区蕉园种植密度与光能利用效率和产量之间的关系。结果表明,适当提高种植密度,可增加香蕉单位空间的光能利用,充分利用地力,改善蕉园生态条件,显著地提高香蕉亩产量。亩植160～180株是沿海地区达到高产稳产的有效措施。     

小鼠生态条件对Friend小鼠白血病病毒感染的影响

本文探讨了Ｆ１小鼠生态条件（鼠龄和免疫状态）对Ｆｒｉｅｎｄ小鼠白血病病毒（Ｆｒ．ＭｕＬＶ）感染的影响。利用对Ｆｒ．ＭｕＬＶ抗性的Ｆｖ４小鼠（含Ｆｖ４抗性基因纯合子的ＢＡＬＢ／Ｃ小鼠）与对Ｆｒ．ＭｕＬＶ敏感的ＢＡＬＢ／Ｃ小鼠交配，获得含Ｆｖ４抗性基因杂合子的Ｆ１小鼠（ＢＡＬＢ／Ｃ×Ｆｖ４）。然后经小鼠腹腔接种Ｆｒ．ＭｕＬＶ病毒液进行攻击，并检查不同鼠龄和免疫状态下的Ｆ１小鼠对Ｆｒ．ＭｕＬＶ的敏感性，以阐明Ｆ１小鼠的鼠龄和免疫状态对Ｆｒ．ＭｕＬＶ感染的影响。结果表明，新生Ｆ１小鼠可发生Ｆｒ．ＭｕＬＶ感染，脾脏中有大量病毒增殖，并引起白血病；免疫抑制剂Ｆｋ５０６投与下的成年Ｆ１小鼠亦可发生Ｆｒ．ＭｕＬＶ的感染，脾脏中有病毒增殖，但不引起白血病；而新生或成年Ｆｖ４小鼠以及成年Ｆ１小鼠可抵抗Ｆｒ．ＭｕＬＶ的感染，脾脏中无病毒增殖，不发病。说明Ｆ１小鼠的鼠龄和免疫状态等生态条件可影响其对Ｆｒ．ＭｕＬＶ感染的敏感性，并且可影响Ｆｖ４基因抗病毒作用。     

EFFECTS OF DARKNESS ON THE CONSTITUTION OF TOBACCO LEAVES AND SUSCEPTIBILITY TO VIRUS INFECTION

An attempt was made to find the causes of increased susceptibility to virus infection when tobacco plants are kept in the dark before inoculation. The changes in certain nitrogen fractions, viz. insoluble-N, amino-N, amide-N, ammonia-N and nitrate-N, and in dry matter and water content were followed in tobacco plants subjected to a period of darkness before inoculation with tobacco aucuba mosaic virus. Only nitrate-N was strongly correlated with the susceptibility to infection, but the evidence suggests that the correlation is indirect and not causal.
Dry matter and water content, determined either as dry matter percentage of fresh weight or measured separately on a leaf-disk basis Ivere found to vary directly with variation in susceptibility.