Mycoplasma-like Organisms Associated with Kaincopé and Cape St. Paul Wilt Diseases of Coconut Palms in West Africa

Abstract

Mycoplasma-like organisms were observed in tissue from spear leaf and unopened inflorescences of coconut palms affected with Kaincopé disease in Togo and Cape St. Paul Wilt in Ghana. The findings are discussed in relation to coconut lethal yellowing disease in the Caribbean and Florida.     

Rat Damage to Coconuts in Fiji Part 1 Assessment of Damage

Abstract

The amount of rat damage to immature coconuts was assessed by two methods. The first involved fortnightly recordings of all coconuts produced, including those rat damaged, at representative sites for up to three years. The second method attempted to utilise decay characteristics of rat damaged coconuts as a basis for projecting spot counts of damaged coconuts to long term estimates of damage.

Damage was concentrated on coconuts aged three to six months with most of the damage being inflicted by Rattus rattus. Damage varied considerably from month to month with seasonal trends in damage being apparent at only one site.

Rats clearly favoured particular palms in all plantations, resulting in over 75% of the damage being confined to 30% of the palms. Those selectively attacked were randomly distributed within the survey plots and did not produce significantly fewer harvestable coconuts than those palms seldom attacked.

Tall palms, i.e. over 15 m incurred less damage than those under 10 m.

Decay characteristics of rat damaged coconuts proved to be of limited value as a basis for projecting spot counts to long term losses, but counts of green damaged coconuts accurately reflected the previous 33–35 days damage.

Overall production losses (derived after adjustments for known palm compensation for damage) were relatively low; being 2.7, 2.0 and 1.3 nuts per palm per year during 1970, 1971 and 1972.     

Further studies on root symptoms in coconut palms affected by lethal yellowing disease in Jamaica

Roots were induced by banking moist coir dust around the boles of apparently healthy coconut palms growing in an area where lethal yellowing was spreading rapidly. Samples of roots were removed for inspection at 1–2 wk intervals after the detection of the first symptoms in palms. Frond symptoms were recorded weekly. Comparison of symptoms in roots and fronds of 28 of the 36 palms that developed lethal yellowing confirmed the earlier observations that the roots usually remained symptomless for a variable period of up to 4 months following detection of the first symptoms of the disease. When root symptoms appeared, most of the actively-growing root tips became necrotic within a period of 2–4 wk and the collapse of the root system was closely correlated with the onset of progressive yellowing of fronds.     

Present Status of Field Pests of Sorghum and Millets in India

Abstract

The incidence, economic importance, ecology, biology and control measures are described in brief for common pests of sorghum and millets in India. At present, shoot flies, stem borers, earhead midges, birds and rats are considered major pests. However formerly occasional or minor pests are becoming a menace in some states due to changes in cultural practices. For most of the recently recorded pests, information on factors responsible for their outbreak, bionomics, yield losses etc. is needed before planning the control operations. As an immediate remedy, chemicals have been used extensively, mainly on high yielding varieties and hybrids of sorghums. It is emphasized that studies should be intensified on varietal resistance, mass rearing techniques, predators and parasites and manipulation of population by cultural practices leading to the possibility of using all available methods on an integrated basis for future pest management programmes for sorghum and millets.     

Detection of the mycoplasma-like organism associated with lethal yellowing disease of palms in Florida by polymerase chain reaction

DNA amplification by polymerase chain reaction (PCR) was used specifically to detect the mycoplasma-like organism (MLO) associated with lethal yellowing disease of palms in Florida. For PCR, a pair of oligonucleotide primers was synthesized according to partial sequences of a cloned 1·3 kbp fragment of lethal yellowing MLO-specific genomic DNA isolated from a diseased windmill palm ( Trachycarpus fortunei ). A DNA product of about 1 kbp was specifically amplified by PCR in reaction mixtures containing template DNA derived from either heart, inflorescence or leaf tissues of lethal yellowing-affected palms. PCR performed for 35 cycles with as little as 5 pg of DNA template, in some instances, was sufficient consistently to amplify the same lethal yellowing MLO DNA product from hearts of 11 species comprising 30 symptomatic palms. Similar reliable and reproducible detection of the lethal yellowing MLO in palm inflorescence spikelets was also achieved after 35 cycles of PCR. When template DNA for PCR was derived from tissues of the the most immature emerging leaf, a 40-cycle reaction was sufficient for consistent foliar detection of the pathogen in all coconut palms including palms with earliest visible symptoms of disease.     

Control of Zebra Disease of Agave Hybrids by Breeding for Resistance to Phytophthora spp.

Abstract

A zebra disease resistance factor has been incorporated into the high-yielding Agave hybrid no. 11648 by crossing this hybrid with A. lespinassei. The progeny of three crosses have been screened for resistance to Phytophthora nicotianae, the chief pathogen of zebra disease and results show that 56.7% of the plants have sufficient resistance to be of economic value. The two screening techniques used are described, and the nature of the resistance factor discussed.     

Production of cotton varieties with resistance to Fusarium wilt with special reference to Tanzania

Abstract

Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum (Atk.) Sny. & Hans. is an important disease of cotton in several developing countries where the use of resistant varieties continues to be the most practical method of control. The inheritance of resistance to wilt is complex, involving several major and minor genes. In order to identify resistant genotypes in segregating populations large numbers of plants must be screened using inoculation methods which minimise disease escape. Wilt incidence is increased when plants are attacked by the rootknot nematode (Meloidogyne acrita Chitwood, 1949) Esser et al. 1976. In areas where both organisms occur together, the wilt resistance‐potential of a variety cannot be realised unless it also has resistance to root‐knot. Problems of breeding for wilt resistance are discussed with reference to Tanzania, and methods are described for their application to a wilt‐resistance programme.     

Improving Control of the Vegetable Armyworm

Abstract

Because of recently acquired resistance of armyworm in Cyprus to prophyllactic spraying of methylparathion, a full investigation into the biology of Spodoptera littoralis was launched. It is not yet clear whether immigration to the Island occurs, but some moths can overwinter in “survival pockets” on the South coast. Pheromone traps and sterilisation are suggested as an alternative method of control. A more rational use of pesticides will cause less damage to natural enemies of the pest and reduce further development of resistance.     

Downy Mildew and Ergot of Pearl Millet

Abstract

The average yields of pearl millet in the semi-arid tropics have been stagnating despite the availability of hybrids with high yield potentials. The main reason for this situation is the high degree of susceptibility of hybrids to serious diseases such as downy mildew and ergot. In this paper an attempt has been made to review the present status of knowledge of these diseases and identify the areas of research which need immediate attention. Considerable information is available on the taxonomy and reproduction of the causal fungi but the information on the epidemiology and control is inadequate.     

The floating islands of Rawa Pening

Abstract

The resistance in okra (Abelmoschus esculentus (L) Moench varieties to the leafhopper, Amrasca devastans (Dist.) is governed by nonpreference and antibiosis mechanisms. The variety A.E. 22 was less preferred for oviposition and feeding compared to the susceptible variety Pusa Sawani. The rate of multiplication of the insects on the resistant variety was low compared to the susceptible variety.     

Downy mildew resistance evaluation in 28 grapevine hybrids promising for breeding programs in Trentino region (Italy)

Downy mildew is a major grapevine disease caused by the biotrophic oomycete, Plasmopara viticola. Numerous disease resistance studies of diverse Vitis germplasm have been previously carried out to identify downy mildew resistance sources; however, ratings were mainly reported using leaf disc in vitro testing and foliage field assessment, or upon leaf and cluster field evaluations. In the current study, 28 grapevine hybrid cultivars were screened using leaf disc bioassay, for disease resistance characterization of both existing and wild-collected materials. 16 hybrids were identified as highly resistant or resistant, and will serve as relevant resistance donors in future pre-breeding and breeding programs. All grapevine hybrids were evaluated for foliar and cluster downy mildew resistance in an untreated field trial over three successive years. This study showed that the leaf disc bioassay provided some information on the resistance level of the genotypes under scrutiny, but it was a weak predictor of their resistance level under field conditions on leaves and even more on bunches. These findings are relevant to future applications in both traditional and marker-assisted breeding programs which promote sustainable viticulture.     

Resistance to Root-knot Nematodes (Meloidogyne spp.) in Vegetable Crops

Abstract

The development of root-knot nematode resistant vegetable varieties has provided an alternative control method to chemical and crop rotation. The term resistance is discussed. Work on 18 vegetables is reviewed.

Thirty tomato strains resistant to one or more Meloidogyne sp. are listed, there was a marked absence of reports on varieties resistant to M. hapla. Several workers have observed resistance in some cultivated and wild Solanum spp. The resistance could be increased by further sib and backcrossing experiments. Eggplant varieties tested for resistance to Meloidogyne spp. showed varying degrees of resistance in about 14 varieties. Further backcrossing studies between Solanum melongena and S. sysimbrifolium could provide useful results. Tests on resistance to nematodes in pepper have revealed many resistant varieties. All the pepper varieties tested were susceptible to M. hapla. The nature of resistance in sweet potato has been studied. Some varieties of Cucumis spp. have been found to be resistant to Meloidogyne spp. Since no resistance was found in C. melo, these wild species could be used in the development of a commercial muskmelon variety. Tests with 83 watermelon varieties indicated that all varieties were resistant to M. hapla. It was difficult to find resistance to Meloidogyne spp. in Cucurbita, but tests on wild species have yet to be carried out. Work on lima bean, snap bean, pea, soyabean, cowpea and broadbean has produced a limited number of resistant vegetable varieties, which are described. Since resistance patterns in plants may change under different environmental or biological conditions, it is essential to test varieties under these conditions for a long period before they are released for commercial cultivation. The advantages of using resistant vegetable varieties, as compared with other methods of pest control, are outlined.     

Redesigning sugarcane for resistance to Australian canegrubs: a potential IPM component

Current management options to minimize the impact of canegrubs (larvae of melolonthine scarabs) on Australian sugarcane are heavily dependent on the use of synthetic insecticides. In developing a successful integrated pest management (IPM) programme for canegrubs, control options must be broadened. Plant resistance offers the potential for an easily deliverable and environmentally acceptable management option. Previous anecdotal reports suggest that Australian cultivars vary in their resistance to canegrubs. Many sugarcane clones (Saccharum spp. complex hybrids) have been screened and our studies have shown that there is variability in resistance through the reduction of the amount of tops, roots and stubble and in their effects on canegrub development and survival. Proteinase inhibitors, lectins and avidin have been identified as having activity against Australian canegrubs and are being introduced into the sugarcane genome. Toxins from Bacillus thuringiensis have shown little potential and are not being used further. We present a rationale for using resistant plants as a control option and for the incorporation of plant resistance into the breeding programme. Projected research will screen more sugarcane clones for resistance, study the nature of inheritance, identify chemical mechanisms involved in antibiotic effects, screen further antimetabolites for possible incorporation into the genome, prove the potential resistance of genetically engineered plants and incorporate plant resistance into an IPM programme for canegrubs.     

Diseases of the Oil Palm

Abstract

Thirty two diseases and disorders affecting the oil palm in Africa, Southeast Asia and South America are described with their distribution, economic importance, etiology and control. Of these, nine diseases are considered to be of major economic importance, 19 are of minor importance, and four are due to nutrient deficiencies. The major diseases causing serious economic losses are freckle (Cercospora elaeidis), blast (Pythium splendens and Rhizoctonia lamellifera), vascular wilt (Fusarium oxysporum f. sp. elaeidis). Ganoderma trunk rot (Ganoderma spp.) and Armillaria trunk rot (Armillariella mellea) in Africa; Ganoderma trunk rot, Corticium leaf rot (Corticium solani). Marasmius bunch rot (Marasmius palmivora) in S.E. Asia; sudden wilt and spear rot in S. America. Some of the diseases and disorders of minor economic importance recorded in these areas are anthracnose (Botryodiplodia palmarum, Melanconium sp. and Clomerella cingulata), dry basal rot (Ceratocystis paradoxic), patch yellows (Fusarium oxysporum), crown disease, Cylindrocladium leaf spot (Cylindrocladium macrosporum), algal spot (Cephaleuros virescens), bronze streak, ring spot and little leaf in Africa; Curvularia leaf blight (Curvularia eragrostidis), Leptosphaeria leaf spot (Pestalotiopsis spp.) infectious chlorosis, upper stem rot (Phellinus noxius), stem wet rot, charcoal base rot in S.E. Asia and Leptosphaeria leaf spot and coconut wilt disease in S. America. Little is known, however, about the disease problems in the smaller but rapidly expanding oil palm growing areas of Thailand, Papua New Guinea, India and Sri Lanka. Infectious chlorosis, bronze streak and ring spot have a suspected virus etiology; little leaf, spear rot and stem wet rot are attributed to bacteria and leaf chlorosis, mid-crown yellowing, orange frond and hook leaf to nutrient deficiencies. The etiology of some minor disorders including brown germ, crown disease and several miscellaneous abnormalities is unknown.

Effective control measures, based on the application of various chemicals, have been devised for the leaf diseases but other than precautionary cultural operations, there are no such effective and practical control measures for the root and stem diseases. For this latter group of diseases field transplanting or resistant or tolerant varieties seems to be the best method of control. Seeds selected for tolerance to vascular wilt are being produced on a commercial scale at the Nigerian Institute for Oil Palm Research, Institut de Recherches pour les Huiles et Oleagineux in Ivory Coast and the Unilever Plantations in Cameroun Republic. These efforts need to be supplemented by breeding for resistance to the other major diseases.     

Symptomatological and histopathological observations on oil palms from Brazil and Ecuador affected by fatal yellowing

Fatal yellowing in oil palms from Brazil and Ecuador is characterized by a chlorosis of the young unfolded leaves and a decay of spear leaves. Contrary to healthy-looking palms, diseased palms do not have roots with soft and white tips.In search for a possible causal agent of fatal yellowing, tissues of leaves, the apical region of stems and root tips of healthy-looking and diseased palms were examined by light microscopy. Fungi and bacteria were frequently, but not always found in necrotic lesions in the leaves. These organisms, however, have never been found outside the lesions or in the vascular tissues of affected palms, nor in the tissues of healthy-looking palms. Tyloses frequently occluded the xylem vessels of affected leaves. In a diseased palm from Ecuador hypertrophic cells were found in the epidermal layer of the pinnae of a spear leaf with water-soaked lesions. In the apical region of the stems and roots of diseased palms, only a few meristematic cells could be detected.Samenvatting Speerrot van oliepalmen in Brazilië en Ecuador wordt gekenmerkt door vergeling van de jongere, geheel geopende bladeren en een rot van de speer. In tegenstelling tot palmen zonder ziekteverschijnselen, hebben aangetaste palmen geen wortels met zachte, witte worteltoppen.Weefsel van bladeren, de apex van de stam en toppen van jonge wortels van gezonduitziende en zieke palmen werden m.b.v. de lichtmicroscoop onderzocht op de aanwezigheid van een eventueel pathogeen. Schimmels en bacteriën werden vaak, doch niet altijd, waargenomen in necrotische lesies op de bladeren, maar nooit buiten lesies of in de vaatbundels van zieke palmen en de weefsels van gezond-uitziende palmen. Vaak verstopten thyllen de houtvaten van aangetaste bladeren. In een speerblad van een zieke palm uit Ecuador werden enige gehypertrofieerde cellen waargenomen in de epidermis van pinnae met waterige lesies. In de top van de stammen en wortels werden slechts enkele meristematische cellen waargenomen.     

New South Wales Department of Agriculture,Entomology Branch,Annual Report 1966-7 (extracts)

Abstract

Damage to tea plants due to a root infection was observed on an estate in southern Malawi. Initial symptoms on plants in the infected areas varied from yellowing of leaves on individual branches followed by dieback to a more frequent rapid wilting of the leaves of entire bushes. The bark surface of superficial roots and collar region was covered by a loose mat of coarse fungal mycelium varying from white or cream to pale or bright yellow in colour. Infection was well developed on a large proportion of roots of affected plants before foliage symptoms appeared. The causal agent was identified as Pseudophaeolus baudonii (Pat.) Ryv.; this is the first record of the fungus in Malawi and the first record of its occurrence anywhere on tea. The fungus is widely distributed in Africa on a range of hosts. It is not yet known how the fungus is transmitted and definite control methods cannot be recommended although it is suggested that entire tea crops in diseased areas be removed and the land used for tobacco production. It is unlikely thatP. baudonii will have serious economic effects on tea crops in the area.     

Coffee Berry Disease

Abstract

Coffee Berry disease is caused by a mutant pathogenic strain of Colletotrichum coffeanum Noack which has spread throughout tropical Africa from its point of origin in Kenya. Fruit is attacked in all stages, and total destruction of the crop can be caused. The disease was confined for many years to the higher altitudes, because suitable conditions of temperature and humidity were infrequent in the lower ones. Following the inception of a wetter and cooler climatic phase in E. Africa in 1961, coffee in the lower altitudes is now attacked.

Infection of the fruit is initially by infective conidia produced on the maturing wood of the twigs, where the pathogen “overwinters”. When one crop only is on the tree, this inoculum is more important than that from lesioned fruit; but where a series of over-lapping crops is present, the reverse is the case. In the former situation control can be based on reduction of inoculum from the twigs: in the latter, however, this is ineffective, and control can only be achieved by a series of protective sprays.

Varieties of coffee vary greatly in susceptibility to berry disease. No commercially acceptable variety is, however, completely resistant, although genetic material embodying resistance is available.     

Systemic insecticides for control of Delphacodes kuscheli and the Mal de Río Cuarto virus on maize

Control of the Mal de Río Cuarto virus (MRCV) and its planthopper vector Delphacodes kuscheli was studied on maize hybrids whose seeds had been treated with systemic insecticides. Laboratory tests were performed to determine the effects of seed treatments with insecticides (acephate, carbofuran, imidacloprid) on the survival of the planthopper. Field experiments using four maize hybrids whose seeds had been treated with the insecticides were performed to establish the effect of the latter on MRCV incidence and severity, and on grain yield. MRCV infection was confirmed by DAS-ELISA. Carbofuran was the most effective insecticide in laboratory tests, independently of the hybrid tested, followed by imidacloprid and acephate. MRCV incidences were high in all treatments in the field test under natural planthopper infestations. Disease severity data analysis indicated that the insecticide - hybrid interaction was not significant. Maize hybrid Dekalb 664 and the imidacloprid treatments had the lowest severity means among the four hybrids and three insecticide treatments, respectively. Data for grain yield showed that the insecticide - hybrid interaction was significant and imidacloprid was generally the most effective in the field experiments. A negative correlation was observed between the mean disease severity index and mean grain yield. The results suggest that if an effective systemic insecticide is applied as a seed coating, it may be possible to obtain good control of D. kuscheli, decrease MRCV severity and increase grain yield under field conditions in areas at risk for MRCV.     

A New Approach to Weed Control in Puerto Rican Sugarcane Fields

Abstract

Experiments have been carried out on the south coast of Puerto Rico to determine the susceptibility of Leptochloa filiformis, Echinochloa colonum and Saccharum officinarum-spontaneum-robustum hybrids (sugarcane) to various herbicides applied post-emergence.

Ametryne proved to be the most suitable herbicide for use as a selective post-emergence grass-killer in sugarcane. The crop is resistant to rates of up to 1.6 lb a.i./ac, while very young seedling grasses are highly susceptible to this or lower rates. During tillering, the weed grasses rapidly become resistant and even 3.2 lb a.i./ac (which damages emerged cane) does not kill fully tillered seedlings. The residual pre-emergence effect of ametryne applied over seedling grasses is as pronounced as when this herbicide is applied to clean ground.     

A simple,cheap experimental sprayer

Abstract

The winged bean (Psophocarpus tetragonolobus), a little known tropical legume, is currently attracting international interest as a plant that may have considerable agricultural potential. The plant has, until recently, been considered as a vegetable of minor importance and information on pests and diseases which attack it is scant, fragmented and often unpublished. Current information on false rust, a major disease of the winged bean in Papua New Guinea, is reviewed. The disease is also known to occur in Java, the Philippines and Malaysia. Any of the above ground parts of the winged bean may be attacked, resulting in severe galling and malformation. The causal agent is an obligate fungal parasite Synchytrium psophocarpi. The parasite is simple in structure, consisting of sori, sporangia and zoospores and has a short life cycle. Sporangia are short lived and dispersed mainly by wind. The parasite is thought to be host specific and it is not known whether resting spores exist. Possible methods for field control of the disease have not been tested.