STUDIES ON SYSTEMIC FUNGICIDES. I. FUNGICIDAL PROPERTIES OF THE ARYLOXYALKYLCARBOXYLIC ACIDS

A method is described for assessing the systemic activity of compounds in checking the infection of broad bean ( Vicia faba ) by the fungi Botrytis cinerea or B. fabae. Treatment consisted in allowing the roots of young seedlings to stand in a solution containing 10 p.p.m. of the chemical for 2–3 weeks. The plants, together with controls, were then inoculated and when symptoms had had time to develop, the degree of chocolate spot infection was assessed. Several methods of disease assessment were examined and are critically discussed.
Certain phenoxyalkylcarboxylic acids tested by this method consistently gave a reduction in the mean size of fungus lesions on the bean leaves, clearly indicating systemic fungicidal action. The most promising substances were 2:4:6-trichlorophenoxyacetic, pentachlorophenoxyacetic and pentachlorophenoxy iso butyric acids. Further experiments with these compounds involving soil treatment, stem injection and spray application are described, and in most cases systemic fungicidal activity was clearly demonstrated. Certain compounds caused visible damage to the plants or resulted in a reduction in growth.
The results presented indicate that phenoxy acids can be fairly readily translocated in bean plants and that they tend to accumulate in actively growing tissues. It is considered unlikely, however, that they persist for long periods in plant tissue.
In the soil, the compounds appeared to remain effective for a considerable time, particularly the less soluble pentachloro acids, suggesting that soil application might provide a safe and useful method of treatment.     

SYSTEMIC FUNGICIDES INTRODUCTION

The idea of controlling plant diseases by introducing curative chemicals into the plant goes back many years. All the early work, which has been reviewed by Müller (1926), was of an empirical nature and although claims were made from time to time that particular treatments were effective, no clear and reliable method ever became established for controlling a plant disease by internal therapy. Within the last few decades, however, such treatment for certain animal diseases with substances possessing antibacterial properties has given spectacular results. This success in the animal led to a renewed interest in the control of plant diseases by similar means, though it was of course recognized that the animal, with its circulating blood system capable of carrying chemicals rapidly to all tissues, is very different from the plant.     

ANTIBIOTICS AS SYSTEMIC FUNGICIDES AND BACTERICIDES

We have not done a lot, as yet, about systemic fungicides at the Butterwick Research Laboratories, but what we have done has been based on an approach rather different from that of other workers, and may for that reason be of some interest to you.     

TECHNIQUES IN THE BIOASSAY OF SYSTEMIC FUNGICIDES

In the limited time at my disposal, it would be out of the question to attempt an exhaustive survey of the techniques used in testing compounds for the internal treatment of plant diseases, particularly as some of these tests will be considered by the later speakers. This talk will, in fact, be devoted largely to describing the test which we have developed at Long Ashton, and I will try to indicate some of the difficulties which we have encountered. However, before I deal with the particulars, I will try to outline some general principles.     

STUDIES UPON THE COPPER FUNGICIDES

Evidence is presented for the presence, on apple and dwarf bean leaves, of substances which can dissolve copper from dried Bordeaux deposit. The solution of copper is not associated with the bacterial breakdown of these substances. Copper was dissolved by the action of apparently uninjured as well as injured leaves and it is concluded that copper-dissolving substances are liberated from intact leaf surfaces. The capacity of leaves to dissolve copper from dried Bordeaux deposit was not lost by repeated washing of the leaf. This further evidence of the sustained activity of the host plant in bringing copper into solution emphasizes the importance of host action in relation to the fungicidal and phytotoxic action of Bordeaux mixture under field conditions.     

STUDIES UPON THE COPPER FUNGICIDES

A study of the absorption of soluble copper by apple leaves was undertaken with a view to obtaining a better understanding of the mechanism of copper spray damage.
The ability of young apple leaves to absorb copper was found to be relatively high and this may be due to the large number of stomata and hairs present. As the leaves grew more mature this capacity fell, rose again to a maximum in July or August and then fell again as the leaves approached senescence. It is suggested that these changes may be due to seasonal changes in leaf metabolism, which probably affects nutrient absorption by leaves as in roots.
It has been observed in the field that apple leaves are often more susceptible to copper spray damage in the autumn. Since absorption is then at a low level it is concluded that the rate of absorption is not the only factor affecting damage to leaves caused by copper sprays.
The presence of injuries in the leaves has two effects: first, it causes an increased excretion of copper-dissolving substances (Arman & Wain, 1958) and, secondly, it increases the rate at which soluble copper is absorbed. A combination of these two factors may bring about localized spray damage. However, the increase in the absorption of soluble copper caused by the presence of extensive injuries in the leaves was sufficiently small for the conclusion to be drawn that injuries do not normally constitute a major route for the entry of copper into the leaf and it is probable that spray damage can occur in the absence of injuries.     

INVESTIGATIONS ON FUNGICIDES. I. FUNGICIDAL AND SYSTEMIC FUNGICIDAL ACTIVITY IN CERTAIN ARYLOXYALKANECARBOXYLIC ACIDS

Fifty-four aryloxyalkanecarboxylic acids have been examined as systemic fungicides. Of these, four which produced negligible damage in broad-bean seedlings yet conferred systemic fungicidal protection to broad beans against Botrytis fabae and to tomatoes against Alternaria solanixvere studied in detail. The direct fungicidal activity of twenty compounds was assessed against B. fabae and Pythium ultimum. No correlation between fungicidal and systemic fungicidal action toward B. fabae was established. Other possibilities regarding their mode of action as systemic fungicides are discussed. The systemic fungicidal activity of a-phenoxyziobutyric and 2:4:6-trichlorophenoxyacetic acids in beans and of the latter compound in tomato plants was found to depend upon seasonal factors, but for 3-phenoxybutyric and 5-phenoxycaproic acids such variation was not observed. Results obtained in the bean test by two methods of assessment were found to correlate. The potato petiole test (van Raalte) for assessing systemic fungicidal activity was studied and modified. Evidence was obtained that the results might be unreliable owing to toxic effects produced by the compounds on the petiole tissue. Attempts were made to avoid this complication, but when phytotoxicity was eliminated, little fungicidal activity was shown.     

STUDIES ON LYMPHOCYTES

Tritiated thymidine was administered to calves continually for 2 to 8 days via the thymic artery in an attempt to label intensively thymic lymphocytes. Heavily labeled cells which had migrated from the thymus were observed in the spleen, lymph nodes and Peyer's patches. Cell maps were made for the various lymphoid tissues and in all cases the majority of labeled thymic cells were found in the ‘thymus dependent areas’of the spleen and lymph nodes. The number of labeled thymic cells per thousand lymphocytes was highest in the ‘thymus dependent areas’. A few labeled thymic cells were seen in or near the post capillary venules. The labeling pattern in the Peyer's patches was different from that in the spleen and lymph nodes. Labeled thymic cells were not observed in the bone marrow. Heavily labeled cells were not detected in any of the lymphoid tissues of those calves which received continuous intravenous infusion of comparable amounts of tritiated thymidine.     

STUDIES ON LYMPHOCYTES

Some of the time parameters of the cell cycle in bovine thoracic duct lymphocytes have been estimated by analysing labeled mitoses curves, and by double labeling. The two methods gave similar estimates of T_s. Thus, T_s measured directly from labeled mitoses curves varied from 4 to 6 hr, while the estimates from double labeling were 4.8 and 4.5 hr. T _G measured directly from labeled mitoses curves was 5 hr, and estimates of T_G from the values of T_s ranged from 6.3 to 7.7 hr. The present data confirm the short generative cycle of large thoracic duct lymphocytes. Extracorporeal irradiation of the lymph (ECIL) had no detectable effect on the cell cycle or the fractional production rate of the lymphocytes. However, the calculated absolute production was reduced following ECIL, due to a decrease in the absolute number of cells present. The grain count over mitoses after ECIL was approximately one-half that found before ECIL.     

双歧杆菌的辐照育种研究

对生产活菌微生态制剂的双歧杆菌东方101号(df101)菌株进行了60CO辐照育种研究。通过4000～6000rad钴原2次24h循环辐照,选育出df104和df106两个菌株。鉴定结果表明,该两个菌株除在生化反应上略有改变外,其他特性未见任何改变。但选育株在液态培养物中,活存时间与存活率较原株有非常显著的提高。其培养物在室温(20～37℃)保存27个月,df104与df106尚有5.47×10