摘要:

SUMMARYOutbreaks of the red spider mite (Oligonychus coffeaeNietn.), the purple mite (Calacarus carinatusGreen) and the scarlet mite (Brevipalpus californicusBanks) of tea were closely associated with the monthly rainfall pattern. Peak numbers occurred during the intermonsoonal dry periods. The relationship between mite numbers and the rainfall pattern suggests that control measures should commence at the end of the first month after the dry season begins. More red spider mites, but fewer purple mites, occurred on tea grown under shaded conditions. Observations on the relationship between scarlet mite numbers and shade were inconclusive. It is suggested that, in addition to direct effects of rainfall and shade, mite numbers are determined by certain biochemical processes that take place within the tea leaves.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04682.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYExperimental plots, arranged within commercial strawberry fields, were used to study the effect ofTarsonemus fragariaeinfestations on strawberry yields. Yields and the mean weight of individual fruits were inversely related to mite infestation levels. Yield reductions of over 50% were attributable to this pest.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04683.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYBlack leaf streak of bananas, caused byMycosphaerellasp., prevented fruit of export quality forming and bunches maturing. Some infected leaves lived less than 50 days and were seldom retained until harvest. Maneb or benomyl applied in oil/water emulsions gave good control and benomyl was so effective that plants had ten leaves at harvest and some leaves survived for 245 days. Plants sprayed with maneb or benomyl flowered I month early. No benomyl residues were detected in the fruit exported to New Zealand.The control of black leaf streak by sprays containing oil has caused other leaf diseases to become more prevalent and the ensuing complex disease situation is discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04684.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYNineteen local isolates of the bean anthracnose pathogen have been obtained and tested over the period 1964–70 for pathogenicity on a set of differential cultivars including the sets of four cultivars each used in the alternative systems of Schreiber and Hubberling and of Bannerot and Blondet. The results indicate the existence of a number of races not conforming to those of either system and the ability, when freshly collected, of some isolates with affinities to both α and β races partially to overcome the immunity of the cultivar Cornell 49–242. The implications of the position as now known from these results and a review of the literature for disease‐resistance breeding are discussed. Tests of the Uganda isolates, on a range of other dry bean cultivars, indicate a tendency for α and δ races to be pathogenic on small‐seeded indeterminate viny or indeterminate bush cultivars, whereas β and γ races tend to be pathogenic on larger‐seeded and determ

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04685.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe effects of copper, captafol and Tuzet, applied to coffee in early season (January to April) and in other programmes continuing through the long rains (January to July), on the bark populations ofColletotrichum cofleanumNoack. (the pathogenic CBD strain and the saprophyticccm, ccaandccpstrains),Phomaspp.,Fusarium stilboidesWollenw. and aPhomopsissp. were investigated on branch material from field experiments in Kenya in 1968 and 1969 by a plating technique which estimated sporulating capacity (s.c.)Fungicide application initially caused a non‐specific reduction in s.c., Tuzet being the most effective. With the onset of the long rains this general reduction was not maintained, although during the period between the long and short rains the levels of many fungi in sprayed plots were still below those in the unsprayed control. In contrast, the s.c.of Phomain plots sprayed with copper and ofPhomopsisin those sprayed with Tuzet were higher than on unsprayed plots. The S.C. of the CBD strain was below that in the control only in plots sprayed with captafol.Effects were still evident after the short rains. Some early‐season programmes of all three fungicides increased the s.c. of the CBD strain while continuing programmes of copper and captafol reduced its S.C. relative to that on unsprayed trees. Differences in S.C. at this time were related to infection in the early crop a few weeks later.The initial antisporulent effect of a fungicide appears less important than its persistence and its effect on bark colonization by the different fungi. Early‐season sprays of copper, formerly used to control CBD, may have contributed to an increase in disease hazards by affecting the primary level of the pat

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04686.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYCherry leaf roll, tomato black ring and two previously unrecorded viruses were transmitted toChenopodium quinoafromSambucus canadensisplants imported from the U.S.A. Of the two newly recognized viruses one, code‐named elderberry virus A, has filamentous particles about 650 times 15 nm; the other, named elderberry latent virus (ELV), was transmitted to several herbaceous species but remained symptomless in elder and most other hosts. InC. quinoasap ELV lost infectivity after dilution to 10‐‐5to 10‐‐6, 10 min at 85–90°C, and 7 days at 18°C. Infectivity of nucleic acid extracts was abolished by ribonuclease in 0.2 m sodium chloride. ELV was purified fromC. quinoaleaf extracts that were clarified with chloroform, by precipitation at pH 5 and differential centrifugation. Purified preparations contained numerous isometric particlesc. 30 nm in diameter and a few particlesc. 17 nm in diameter. In 0.06 M phosphate buffer ELV sedimented as a major 112S(calculated for infinite dilution) component and a 48Sminor component. ELV showed no serological relationship to twenty‐seven other isometric plant viruses. Its present cryptogram is R

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04687.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYOrobanche crenataparasitizing beans maintained a slightly higher osmotic pressure than the bean roots, largely because of the higher concentration of sugars in the broomrape tissues. The sugar was withdrawn from the bean mainly as sucrose, which was hydrolysed to glucose and fructose by theOrobanche. These sugars were then rapidly translocated to the developing flower spike. As well as maintaining a high osmotic pressure this hydrolysis ensured a sucrose concentration gradient between host and parasite.In the field, bean plants showed wilt symptoms at about the time that theOrobancheflower spikes emerged. It was found that the higher the level of infection the lower was the water content of the host. This fall in water content was not due to increased water loss by the bean shoots and it seemed unlikely that it was due to water removal by the parasite.It was concluded that the death of the bean was due to desiccation brought about largely by the reduced ability of the carbohydrate‐starved roots to extract water from the soi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04688.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe presence of awns doubled the net photosynthetic rate of wheat ears and also increased the proportion of14CO2assimilated by the ear that moved to the grain. The effect of water supply on photosynthesis and movement of assimilates was greater for leaves than ears, so that drought increased the proportion of assimilate contributed by ear photosynthesis to grain filling from 13% to 24% in the awnless ears, and from 34% to 43% in the awned ears.14C assimilated by the ears was most important to the economy of the upper spikelets and to the distal florets in each spikelet, whereas flag leaf assimilate went mainly to the spikelets in the lower half of the ear, and to the proximal florets.Awns increased grain yield in the dry but not in the irrigated treatment, despite the large contribution of awned ears to grain filling. Either the supply of assimilate did not limit grain yield when water supply was not limiting, or there were compensating disadvantages to awns. However, they did not seem to have any adverse effect on the development of the upper florets, nor did they reduce grain number per ear.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04689.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe effects of topping at different dates, and of different plant populations on dry‐matter production and distribution in Brussels sprouts were studied. Total dry‐matter production per unit area was unaffected by either topping or density. Leaf area was decreased by topping, resulting in a temporary increase in net assimilation rate. Topping resulted in a redistribution of dry matter; that which would have formed new stem and leaf tissue was directed into sprout production.Increasing plant density did not affect the distribution of dry matter but increased the number of smaller sprouts. The apparent optimum plant spacing in this series was 21×21 in (53×53 cm). At maturity assimilation approximately balances respir

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04690.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe effects of completely defoliating sugar beet at different dates from May to October were examined in four years. In each year there were plots given the usual nitrogen fertiliser application to the seedbed, and also in two of the years plots given no nitrogen.At harvest in mid‐November, minimum root weights followed defoliation in July or August, but defoliation in August or later gave minimum sugar contents. When nitrogen was applied to the seedbed sugar yields were smallest after August defoliation; in the absence of nitrogen, July defoliation gave the lowest sugar yields, root yield being smaller but sugar content usually greater than with nitrogen. Up to 40% of the sugar yield was lost by July or August defoliation and late defoliation increased some of the impurities in the root juice. Yields, and recovery from defoliation, were greater with nitrogen than without. Partial defoliation in May had relatively little effect on yield. Defoliation affected the incidence of virus yellows differently in different year

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04691.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY