Xylem Occlusions in the Fruit of Cacao (Theobroma cacao) and their Relation to Cherelle Wilt

The anatomy and distribution of the xylem of the fruit of cao(Theobroma cacao) has been investigated by injection and stainingtechniques. The physical symptoms of cherelle wilt (pod wilt), a physiologicalfruitthinning mechanism, have been shown to be caused by occlusionsin the xylem vessels of the fruit-stalk. The initiation of theseocclusions in thought to be associated with the oxidative activityof a cambial or meristermatic band of tissue, which forms newvascular tissue to the pericarp.     

Fusarium Wilt of Bananas in Jamaica: III. Attempted Control

Experiments were set up in an attempt to control wilt in ‘GrosMichel’. Passive measures of eradication and quarantineseldom achieved more than temporary results. Soil disinfectionby fumigants was unpromising. Flood-fallowing, important inCentral America, was not practicable in the West Indies. Applicationto the soil of lime, phosphate, and potash, separately or incombination, had little or no effect on wilt incidence; applicationof nitrogen often resulted in an earlier appearance of wilt.Supplements of various organic materials such as green manures,compost, and bagasse also proved ineffective. Possible reasonsfor these failures are discussed, and various suggestions aremade for the prevention or limitation of wilt in resistant varieties.     

Seasonal Changes in Total Free Sugar Content of Field Cocoa Plants

As part of a study of factors affecting the vegetative and reproductive characteristics of cocoa, Theobroma cacao L., (viz. leaf flushing, flowering, cherelle wilt, pod setting and pod growth), seasonal changes in total free sugar levels of the bark and wood of field cocoa trees growing under medium shade provided by Gliricidia sepium Steud. trees were studied over a period of 13 months. On dry weight basis, sugar content of the bark (13 to 63 mg/g) was higher than that of the wood (9 to 40 mg/g). Free sugar content was significantly correlated with sunshine hours for the whole period, except October-November 1975, and March 1976 when pod load, and flowering and leaf flushing respectively, caused considerable reduction in free sugar levels. The peaks of flowering and flushing coincided with those of sunshine hours and free sugar levels. The results, analysed in terms of the prevailing microclimatic conditions, suggest that light is a limiting factor for photsynthesis of shaded cocoa and that the reported stimulation of flowering and leaf flushing, which accompany shade removal, may be attributed to increased sugar status of the trees due to increased photosynthetic activity.     

Water Stress and Verticillium Wilt Severity on Eggplant (Solanummelongena L.)

Verticillium wilt is one of the most destructive diseases of eggplant (Solanum melongena L.). Some researchers have reported that wilt was encouraged by sufficient soil humidity, while others stated that it was encouraged by drought. This study investigated the water stress effect on the severity of Verticillium wilt on eggplant, as it is reflected on yield, agronomic traits and fruit quality. Thus, eggplant seedlings cv. ‘Tsakoniki’ were transplanted in three rows, each with 20 plants, during the summer of 1995 and 1996 in a plastic greenhouse, at the Agricultural Research Center of Macedonia and Thrace. Ten of the plants in each row were inoculated with the fungus Verticillium dahliae, while the other 10 were used as controls. Rows were irrigated every 2, 4 or 6 days. Soil humidity was calculated before every irrigation in each row. The disease severity was estimated by the disease index (DI) as the combination product of leaf symptom index (LSI) and vascular discoloration index (VDI). In addition, the plant height, early and total commercial yields, fruit numbers of early and total commercial yields, plant weight, the above-ground plant weight, root weight, pH, total soluble solids and fruit brilliance plus colour intensity were measured. The effect of Verticillium wilt on plants irrigated every 2, 4 or 6 days was estimated by the correlation coefficient (r) between LSI and DI and the aforementioned characteristics. Verticillium wilt had a significant but negative effect on all of the measured or calculated characteristics. This effect, however, was independent of the irrigation applied. On average, the early commercial yield was reduced by 40.8% and the final commercial yield by 39.4%. The only quality characteristic that was affected significantly by irrigation was the fruit brilliance and colour intensity (r =?0.640 to ? 0.727, P ≤ 0.01). Finally, the irrigation frequency (every 2, 4 or 6 days) had a significant but negative effect on all of the characteristics measured on the control plants. The only exception was fruit quality. In conclusion, the combined effect of irrigation and Verticillium wilt infection significantly reduced the early and total production of eggplant and spoiled the fruit quality.     

Translocation of phosphorus-32 into wilting and healthy fruits of cacao (Theobroma Cacao)

Summary The uptake of phosphorus into young cacao fruits (cherelles) was studied by applying 1.0 mC of P-32 to tins of soil in which young cacao trees were growing. The radiation from the fruits was measured daily with a shielded end-window G-M tube until the fruit wilted. While the fruit remained healthy accumulation of P-32 was linear and uptake continued for about three days after the fruit stopped growing (the first sign of wilting); uptake of P-32 then ceased. An increase in the count rate as the fruit became flaccid was attributed to reduced self-absorption due to loss of water.The distribution of the radio-active phosphorus in the seeds and pericarp was investigated and comparative analyses of phosphate in wilting and healthy fruits are presented.The results provide additional evidence for the hypothesis that cherelle wilt is analogous to a fruit-thinning mechanism.     

The effect of root-knot nematode on vascular resistance to Fusarium oxysporum f. sp. vasinfectum in the stems of cotton plants

The effect of root-knot nematode (Meloidogyne incognita) on external wilt symptoms and on the cotton plant's vascular response to stem-inoculation with Fusarium oxysporum f. sp. vasinfectum was investigated. Wilt symptoms were more severe in all plants inoculated with both organisms than with the fungus alone but relative wilt resistance of the cultivars was maintained. Greater symptom severity was associated with greater fungal proliferation in the stele and this was related to the ability of the nematode to reduce the efficiency of vascular occlusion. The nematode had no effect on the accumulation of infection-induced terpenoid aldehyde compounds.     

Cherelle Wilt of Cacao: I. POD DEVELOPMENT AND ITS RELATION TO WILT

The growth and development of cacao pods of three differentselections was studied in relation to pod loss through cherellewilt. Pods were observed to be specially liable to wilt at twostages in their development. These periods were called ‘firstwilt’ and ‘second wilt‘ respectively. First wilt reaches its peak at 7 weeks after pollination andis shown to cease as cell walls are laid down in the endosperm.Second wilt reaches its peak at 10 weeks from pollination anddeclines in response to greatly increased pod metabolism. Podswhich wilt during second wilt have larger embryos and smallerpod stalks than comparable healthy pods. It is postulated thatboth types of wilt arise as a result of a lack of hormones producedby the endosperm, causing a decrease in the uptake of waterand food materials and thereby bringing on wilt. This theory is discussed with reference to previous work andto the possible use of growth substances as a control measure.     

Evaluation of the strains of Acinetobacter and Enterobacter as potential biocontrol agents against Ralstonia wilt of tomato

Bacterial wilt (Ralstonia solanacearum) of tomato, Lycopersicon esculentum, causes a considerable amount of damage to tomato in Southern China. Biological control is one of the more promising approaches to reduce the disease incidence and yield losses caused by this disease. Based on antagonistic activity against R. solanacearum and three soil-borne fungal pathogens as well as biocontrol efficacy in the greenhouse, two bacterial strains Xa6 (Acinetobacter sp.) and Xy3 (Enterobacter sp.) were selected out of fourteen candidates as potential biocontrol agents. In order to find a suitable antagonist inoculation method, we compared the methods of root-dipping with soil-drenching in the aspects including rhizocompetence, biocontrol efficacy, and effect of promoting plant growth under greenhouse conditions. The drenching treatment resulted in a higher biocontrol efficacy and plant-yield increase, and this method was also easier to operate in the field on a large scale. Field trials were conducted for further evaluation of these two antagonistic strains. In both greenhouse and field experiments, the strain Xy3 had a better control effect against bacterial wilt than Xa6 did, while Xa6 caused higher biomass or yield increases. As recorded on the 75th day after treatment in two field experiments, biocontrol efficacy of Xy3 was about 65% in both field trials, and the yield increases caused by Xa6 were 32.4 and 40.7%, respectively, in the two trials. This is the first report of an Acinetobacter sp. strain used as a BCA against Ralstonia wilt of tomato.     

Abnormal Stomatal Opening in Coconut Palms Affected with Root (Wilt) Disease

Studies on the stomatal regulation in the root (wilt) affectedcoconut palms (Cocos nucifera L.) revealed that the diseasedpalms had low stomatal resistance compared to the healthy palms,irrespective of their age. The same trend was observed whetherthe determinations were made at different times of the day (6–18h) or under irrigated and unirrigated conditions or in differentseasons (‘dry’ and ‘wet’). Thus, thestomatal regulation was significantly impaired in the diseasedpalms resulting in excessive water loss compared to the healthypalms. Results are discussed with the available literature onother similar disease caused by fungi, bacteria and mycoplasma-likeorganisms in different plants. Key words: Cocos nucifera L., Stomatal resistance, Root (wilt) disease     

Tactics for management of thrips (Thysanoptera: Thripidae) and tomato spotted wilt virus in tomato

Four studies were conducted in Georgia during spring 1999, 2000, 2001, and 2002 to evaluate various management tactics for reducing thrips and thrips-vectored tomato spotted wilt virus (TSWV) in tomato and their interactions relative to fruit yield. Populations of thrips vectors of TSWV, Frankliniella occidentalis (Pergande) and Frankliniella fusca (Hinds), were determined using flower and sticky trap samples. The management practices evaluated were host plant resistance, insecticide treatments, and silver or metallic reflective mulch. Averaged over all tests, the TSWV-resistant tomato 'BHN444' on silver mulch treatment had the largest effect in terms of reducing thrips and spotted wilt and increasing marketable yield. Of the insecticide treatments tested, the imidacloprid soil treatment followed by early applications of a thrips-effective foliar insecticide treatment provided significant increase in yield over other treatments. Tomato yield was negatively correlated with the number of F. fusca and percentage of TSWV incidence. F. occidentalis per blossom was positively correlated with percentage of TSWV incidence, but not with yield. No significant interactions were observed between cultivar reflective mulch main plot treatments and insecticide subplot treatments; thus, treatment seemed to be additive in reducing the economic impact of thrips-vectored TSWV. Control tactics that manage thrips early in the growing season significantly increased tomato yield in years when the incidence of TSWV was high (>17%).     

Integrated management of bacterial wilt (Ralstonia solanacearum) of ginger (Zingiber officinale) in Southwestern Ethiopia

Abstract

Ginger bacterial wilt (GBW) is a destructive disease of ginger in Ethiopia. Field studies were conducted to determine effect of integrated management of GBW, through host resistance and cultural practices, on wilt epidemics at Teppi and Jimma, southwestern Ethiopia in 2017. Treatments were factorial arranged in a randomised complete block design with three replications. Analysis of variance indicated that effect of variety, cultural practices and variety x cultural practice interactions significantly reduced GBW epidemic parameters and enhanced yield at both locations. Boziab recorded lower wilt incidence, area under disease progress curve and wilt progress rates than Local variety. Integration of lemon grass with soil solarisation and fertiliser reduced wilt incidence in Local variety up to 38.3% (Teppi) and 42.05% (Jimma) compared to the control on final wilt assessment date. In Boziab variety, integrated use of lemon grass with soil solarisation and fertiliser reduced wilt incidence up to 42.5% at Teppi and 33.85% at Jimma compared to the control on final date of wilt assessment. The overall results revealed that integrating cultural practices with host resistance are found effective to slow down GBW epidemics and improve ginger productivity; and thus, recommended for the study areas along with other crop management practices.     

Parthenocarpic fruit set in triploid watermelon induced by CPPUand 2,4-D applications

The localized application of the synthetic cytokinin CPPU ((2-chloro-4-pyridyl)-N-phenyl urea) to ovaries at flower opening was as effective as free pollination in setting parthenocarpic fruit in the triploid watermelon cultivar ‘Reina de Corazones’, and increased yield per unit land area by at least 50%, simply due to the lack of requirement for diploid pollen producing plants within the orchard. The application of the synthetic auxin 2,4-D (2,4-dichlorophenoxy acetic acid) as a full coverage spray, was also effective in setting fruit; total yield was however 10% smaller than in the CPPU-treated plots, but the cost of application was much less expensive. These applications had no adverse effect on fruit quality, and their effectiveness in commercial watermelon production was evaluated over 4 years. Localized applications of 2,4-D to ovaries were less effective in setting fruit, and increased hollow fruit.     

Suppression of Fusarium wilt by combining green compost and Trichoderma hamatum

Fusarium wilts, caused by the fungus Fusarium oxysporum, are important diseases of horticultural and agricultural crops and lead to significant yield losses. The pathogen infects the roots and colonizes the vascular tissue, leading to wilting and finally death of the plant. The objective of this study was to investigate the efficacy of amendment of green compost and a Trichoderma hamatum strain against Fusarium wilt of radish. The substrate effects and the effect of a Trichoderma strain were tested in a potting soil bioassay. The tested composts lowered the disease level and had a positive influence on the plant yield (fresh weight and dry weight). Nothwithstanding, only a small dosis effect of the amendment was observed. In the presence of the tested Trichoderma hamatum strain no significant lower disease level was observed. Furthermore, a minor effect on plant yield (fresh weight and dry weight) was observed compared to the amendment with only green compost. Maybe the pathogenic Fusarium oxysporum strain and the Trichoderma strain competed for nutrients, iron could be a limiting factor. One possible approach to improve biological control may be the application of combinations of biocontrol agents.     

The effect of seaweed concentrate on the growth and yield of potassium stressed wheat

The effects of the seaweed concentrate “Kelpak’ on the growth and yield of wheat grown under conditions of varying K supply were investigated. Kelpak had no significant effect on the yield of wheat receiving an adequate K supply, but significantly increased the yield of K stressed plants. The increase in yield was caused by an increase in both grain number and individual grain weight. Although the beneficial effects of seaweed concentrates have often been attributed to their cytokinin content, several lines of evidence suggested that this group of plant growth regulators may not be solely responsible for the observed effects of Kelpak on wheat. Irrespective of the physiological mechanism of action, Kelpak would appear to have considerable potential for increasing yield in K stressed wheat and may therefore reduce the requirement of wheat for K fertilization.     

Biological control of chickpea Fusarium wilt by antagonistic bacteria under greenhouse condition

In this survey, Fusarium oxysporum was isolated from roots infected plants and was shown to be pathogenic. Experiment were carried out with seven antagonistic bacteria. Based on biochemical, Physiological and morphological tests, isolates B-120, B-32, B-28 and B-22 were identified as Bacillus subtilis and isolates Pf-100, Pf-10 and CHAO as Pseudomonas fluorescens. In greenhouse studies, only isolate B-120 (Less than benomyl) reduced Fusarium wilt of chickpea in both seed and soil treatments. The application of antagonistic bacteria had no different effects on plant growth factors. Soil treatment of bacteria had a better effects on plant growth than that of bacterial seed treatment. The use of antagonists (B-120, B-28, B-120 and CHAO) in combination had no significant effect on plant growth factors and reduction wilt disease than that each isolate was applied individually.     

Systemic fungicides in the control of strawberry wilt (Verticillium dahliae)

In a series of experiments between 1970 and 1973 the application of benomyl or thiophanate methyl to field-grown strawberries, planted on Verticillium-mtested land, gave control of wilt for up to 5 months, the duration of control being related to the amount of fungicide applied in the spring. Treatment of inoculated plants grown on in chloropicrin-fumigated soil was effective for at least two seasons. An autumn-planted multi-factorial experiment in heavily-infested soil showed that, to achieve maximum wilt control, it was advantageous to grow cv. Gorella rather than cv. Cambridge Vigour; to drench the runners at planting rather than to dip them in the fungicide suspension; and to use a high concentration (0–075 % a-i-) and large volume (600 ml per plant) for a supplementary treatment in May rather than a lower concentration (0.025 %) ^or smaller volume (400 ml). There were small but significant advantages in applying benomyl rather than thiophanate methyl, and in using 0–2% a.i. suspension at planting rather than 0–05%. No advantage was gained by dividing the spring application into two equal doses applied 2 wk apart. Extrapolation from the logarithmic relation between wilt index and total dose of fungicide applied in the spring suggested that I.I g/plant would have given almost complete control until October; such control had been achieved in an earlier experiment in which 1–2 g/plant was applied. Crop yield in the second year was determined by the treatment applied in the first year, but although these treatments had given significantly better control of wilt in Gorella than in Cambridge Vigour, the greater growth and yield potentials of the latter cultivar had an over-riding effect on crop production; Cambridge Vigour yielded more than Gorella under all chemical treatments, but in the absence of treatment Gorella gave a larger crop than Cambridge Vigour. A proposed regime, entailing spring and autumn applications, is aimed at minimizing the colonization of the plant throughout the year, thus reducing the production of new inoculum and, by limiting the quantity of the pathogen in contact with the systemic chemicals, minimizing the probability of selecting fungicide-resistant variants of V. dahliae.     

The relationship between pathogenic fungal metabolities (fusaric and picolinic acid), endogenous ethylene evolution and the development of ethylene-like symptoms

Summary The effects of fusaric acid (5-n-butylpicolinic acid), picolinic acid (2-pyridine carboxylic acid), and picloram (4-amino-3, 5, 6-trichloropicolinic acid) on endogenous ethylene production by tomato cuttings and elongation growth of oat coleoptile sections were measured. Ethylene production by tomato cuttings was substantially stimulated by treatment with 1×10⁻³ and 1×10⁻⁵ M picoloram and to a lesser extent by 1×10⁻³ M fusaric acid; picolinic acid had little effect. The ethylene levels produced in response to fusaric acid are not high enough to account for the ethylene injury observed in Fusarium wilt. Fusaric acid inhibited oat coleoptile extension, picolinic acid had little effect, and picloram promoted growth.     

Land use intensification affects soil microbial populations, functional diversity and related suppressiveness of cucumber Fusarium wilt in China’s Yangtze River Delta

The extent of soil microbial diversity in agricultural soils is critical to the maintenance of soil health and quality. The aim of this study was to investigate the influence of land use intensification on soil microbial diversity and thus the level of soil suppressiveness of cucumber Fusarium wilt. We examined three typical microbial populations, Bacillus spp., Pseudomonas spp. and Fuasarium oxysporum, and bacterial functional diversity in soils from three different land use types in China’s Yangtze River Delta, and related those to suppressiveness of cucumber Fusarium wilt. The land use types were a traditional rice wheat (or rape) rotation land, an open field vegetable land, and a polytunnel greenhouse vegetable land that had been transformed from the above two land use types since 1995. Results generated from the field soils showed similar counts for Bacillus spp. (log 5.87–6.01 CFU g⁻¹ dw soil) among the three soils of different land use types, significantly lower counts for Pseudomonas spp. (log 5.44 CFU g⁻¹ dw soil) in the polytunnel greenhouse vegetable land whilst significantly lower counts for Fusarium oxysporum (log 3.21 CFU g⁻¹ dw soil) in the traditional rice wheat (or rape) rotation land. A significant lower dehydrogenase activity (33.56 mg TPF kg⁻¹ dw day⁻¹) was observed in the polytunnel greenhouse vegetable land. Community level physiological profiles (CLPP) of the bacterial communities in soils showed that the average well color development (AWCD) and three functional diversity indices of Shannon index (H′), Simpson index (D) and McIntosh index (U) at 96 h incubation in BIOLOG Eco Micro plates were significantly lower in the polytunnel greenhouse vegetable land than in both the traditional rice wheat (or rape) rotation land and the open field vegetable land. A further greenhouse experiment with the air-dried and sieved soils displayed significantly lower plant growth parameters of 10-old cucumber seedlings as well as significantly lower biomass and total fresh fruit yield at the end of harvesting at day 70 in the polytunnel greenhouse vegetable soil sources. The percentages of Fusarium wilt plant death were greatly increased in the polytunnel greenhouse vegetable plants, irrespective of being inoculated with or without Fusarium oxysporum f. sp. cucumerinum. Our results could provide a better understanding of the effects of land use intensification on soil microbial population and functional diversity as well as the level of soil suppressiveness of cucumber Fusarium wilt.     

The Effect of Applications of a Synthetic Cytokinin on Shoot Dominance and Grain Yield in Spring Barley

Spring barley cv Ark Royal was grown in pots in the open, andsoil drenches containing 6-benzyl-aminopurine were repeatedlyapplied during the pre-heading phase starting either ‘early’when the main shoot apex had reached the glume primordium stage,during tillering, or ‘later’ at the anther primordiumstage, at the start of stem elongation Although grain yield was unaffected by the ‘late’cytokinin treatments, it was increased by up to 57 per centby the ‘early’ treatments. The increase was dueto greater grain yields of the smaller shoots of each plantthere was no effect on the yields of the two largest shootsor on the total number of fertile shoots The increased grain yield of these smaller shoots was attributableto increased weights of their individual kernels, especiallyin the basal and distal parts of the ears such that a greateruniformity of kernel size within the ear was achieved Thus the cytokinin treatment increased uniformity both betweenshoots and between spikelets within the ears Hordeum vulgare L, spring barley, cytokinin, 6-benzylaminopunne, shoot dominance, harvest index, grain yield     

SOME SOIL FACTORS AFFECTING VERTICILLIUM WILT OF ANTIRRHINUM

Variations in the application rates of chalk and superphosphate and the omission of all the fertilisers had no visible effect on the incidence of wilt caused by any of the five Verticillium species.
he literature dealing with the influence of soil conditions upon the Verticillium wilt of a wide range of host plants is reviewed. It is shown that the species V. alboatrum, V. dahliae, V. nigrescens, V. nubilum and V. tricorpus vary inter se in their pathogenicity to Antirrhinum majus, and that their infectivity may be influenced by soil treatments. Thus, in pot cultures, the incidence of antirrhinum wilt induced by Verticillium dahliae and V. nigrescens was reduced by increasing sulphate of potash or ammonium sulphate; or by decreasing soil moisture. Very wet soil and heavy dressings of hoof-and-horn were the only conditions under which V. nubilunt and V. tricorpus induced wilt symptoms. Z7. albo-atrunt was the most virulent species tested; none of the soil treatments decreased its pathogenicity.