Showing papers on "Leaf spot published in 1981"

The effect of growing beans together with maize on the incidence of bean diseases and pests

Abstract: Compared with mono-cultures, beans grown in association with maize showed generally less incidence of the following diseases and pests: halo blight, bean common mosaic, anthracnose, common blight, scab,Phoma, mildew, bolworm and to a lesser extent angular leaf spot. For white mold and the black beetleSystates the opposite was observed. Rust and aphilds were erratic in this respect.

Components of resistance to Cercospora arachidicola and Cercosporidium personatum in groundnuts

Abstract: SUMMARY The reactions of four groundnut cultivars to inoculation with two leaf spot pathogens (Cercospora arachidicola and Cercospodirium personatum) were investigated Resistant cultivars showed longer latent periods, reduced sporulation and less defoliation; however, none of the cultivars was resistant to both pathogens Numbers of lesions, time to leaflet loss and the percentage of spores which produced lesions were influenced by the concentration of C personatum inoculum applied to the leaves and there were significant cultivar differences in lesion numbers at the lowest inoculum level Only the first two characters were affected by applied spore concentration in the study with C arachidicola Generally it was found that lower inoculum levels gave a better separation of cultivars The level of resistance was similar to that found in the slow resting reaction of cereal crops and should be useful in a groundnut breeding programme

Breeding for resistance to diseases in greengram and blackgram.

Abstract: This review is given on the origin and interrelationship of blackgram and greengram: the symptoms, mode of transmission, and host range of important diseases, namely: mungbean yellow mosaic virus, leaf crinkle virus, leaf curl virus, mosaic mottle virus, Cercospora leaf spot, powdery mildew, root and stem rots, bacterial leaf spot and halo blight. The screening for resistance, sources of resistance, including interspecific hybridization, and induced mutations, as well as the genetics of resistance are treated along with suggestions for future breeding strategies of these crops.

Cotton disease research in Tanzania.

Abstract: Tanzania is one of the largest producers of Upland cotton (Gossypium hirsutum L.) in Africa. The crop is raingrown by smallholders over a large ecologically diverse area with a variety of disease problems. The main diseases are Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum (Atk.) Sny. & Hans.) and bacterial blight (Xanthomonas malvacearum (E. F. Smith) Dowson). Fusarium wilt is established over much of the area close to Lake Victoria where the soils are sandy and acidic. The disease is seed borne but spread is reduced by issuing seed produced in Fusarium free villages. Bacterial blight has become less important due to success in breeding resistant varieties. Verticillium wilt (Verticillium dahliae Kleb.) and root-knot nematode are potentially serious in some areas. Many other diseases occur at the seedling stage or on leaves and bolls but cause crop loss only under unusual environmental conditions or after insect damage. Alternaria macrospora is the most common cause of leaf spot and Colle...

Susceptibility of peanut leaves to 2Cercosporidium personatum.

Abstract: Germination of Cercosporidium personatum conidia did not differ on the leaves of 12 peanut cultivars that were investigated. Although abaxial leaf surfaces retained more conidia and subsequently had more penetration of stomata by germ tubes than did adaxial surfaces, the resulting leaf spot density did not differ. There were indications of a hydrotropic response in stomatal penetration. Variations in stomatal density and stomatal length were not related to resistance to infection. The leaves of peanut plant introductions PI 259747 and PI 341879, both highly resistant to C. personatum, showed a positive regression of leaf spot density on leaf age. A necrotic-type defense reaction appeared to be operative. The leaves of the 10 other cultivars, ranging from highly resistant to highly susceptible to C. personatum, displayed a differential susceptibility to infection related to leaf size; regardless of leaf or plant age, a positive regression of leaf spot density on leaflet area was demonstrated for each of these cultivars. Knowledge of the variation in leaf susceptibility both within and between cultivars enabled standardization in leaf sampling during preliminary screening for resistance to leaf spot caused by C. personatum.

Studies of survival and longevity of the light leaf spot pathogen of brassicas, Pyrenopeziza brassicae

Abstract: Experimental studies showed that conidia of Pyrenopeziza brassicae, cause of light leaf spot of brassicas, can remain infective for at least 10 months, and can germinate at 19 months after storage in a dried state. The pathogen was isolated from viable seed up to 2 months after harvest, but survival for longer periods on seed and natural infection of plants grown from contaminated seed was not demonstrated. Artificial inoculations indicated that susceptibility amongst species closely related to the cultivated brassicas is limited to certain species within the genus Brassica. The significance of these findings to an understanding of the epidemiology of light leaf spot is discussed.

Brown spot disease of citrus caused by Phaeoisariopsis sp.

Abstract: SUMMARY Brown spot disease of Citrus spp. was shown to be caused by Phaeoisariopsis sp. It severely affects all varieties of sweet orange, tangerine, grapefruit, lime and rough lemon, smooth lemon being relatively resistant. Fruits and leaves are much more susceptible than stems on which symptoms are rare. On the young fruit circular, slightly sunken, brown necrotic lesions are often associated with a surrounding ring of raised epicarp, giving the fruit a blistered appearance. Lesions on older fruits are usually flat and brown and surrounded by yellow haloes. Premature abscission, especially of young fruits, is common. Leaf symptoms start as greenish yellow patches and a fully formed leaf spot consists of light brown or greyish centre which is surrounded by a dark brown margin bordered by a yellow halo. Generalised foliar chlorosis, caused by coalescence of several lesions, culminates in premature defoliation. During wet weather, centres of both fruit and foliar lesions sporulate and become black. Stem lesions, dark brown and mostly occurring as extensions of petiole lesions, may coalesce causing stem die-back or resulting in the formation of corky internodal lesions. In artificial culture, the fungus sporulated only on media containing an extract of citrus leaf or fruit peel. The characteristics of the fungus mostly based on examination of structures formed on naturally infected parts of the plant, are described. This is probably the first report of a Phaeoisariopsis sp. on citrus.

Effect of volatile phylloplane fungal metabolites on the growth of a foliar pathogen

Abstract: Volatile fungal metabolites excluded from various leaf-inhabiting microfungi were tested for their mycostatic activity against the growth ofPestalotiopsis funerea Desm., a leaf spot pathogen ofEucalyptus globulus Labill. Findings reveal thatTrichoderma viride andTrichothecium roseum exhibited significant antagonistic action, however,Cladosporium herbarum, Nigrospora sphaerica andPapulaspora sp. showed a stimulating effect. A morphophysiological effect was also observed.

Effect of fungicides on leaf-spot pathogens and the phylloplane mycoflora of groundnut

Abstract: The effects of two fungicides on phylloplane mycoflora and on the Mycosphaerella leaf-spots of groundnut have been investigated. No qualitative differences were found in the phylloplane mycoflora of two cultivars PG1 and M13. The location of leaves on the plants was found to exert significant qualitative and quantitative effects on the phylloplane mycoflora. Benlate sprays greatly increased the phylloplane mycoflora in comparison with control whereas Dithane M45 sprays reduced the mycoflora population. The possibility of resistance induced by the non-pathogenic mycoflora against leaf-spot pathogens is discussed.

Agricultural and horticultural germicide

Abstract: PURPOSE:To titled agent, containing an alpha,omega-polymethylenebisguanidino compound or an acid addition salt thereof as an active constituent, and capable of exhibiting improved germicidal effect particularly on blast and helminthosporium leaf spot of rice plants, blue rot (mold) and green rot (mold) of citrus fruits CONSTITUTION:An agricultural and horticultural germicide containing an alpha,omega- polymethylenebisguanidino compound expressed by the formula (n is 11, 12, 13 or 14) or an acid addition salt thereof, eg 1,12-diguanidinododecane sulfate or 1,11- diguanidinoundecane hydrochloride, as an active constituent The compound expressed by the formula has much greater germicidal activity than the compound expressed by the formula (n is 8, 9 or 10) The germicide is capable of controlling the blast and helminthosporium leaf spot simultaneously and preventing the storage diseases of citrus fruits at a low concentration

Disease incidence in radish and chinese cabbage. I. Major diseases in radish and chinese cabbage grown in alpine areas in Jeonbug Province.

Abstract: Vegetables including Chinese cabbage and radish have been grown in alpine areas such as Muju, Namweon, Jinan and Jangsu during the shortage period of vegetables. The incidence of various diseases, environmental factors such as temperatures and rainfalls, and aphid populations as virus vector were observed at 10-day intervals from July to September in those areas. Disease incidence showed no significant difference among locations. Major diseases in Chin ese cabbage were bacterial soft rot, white spot, downy mildew, mosaic virus, Alternaria leaf spot and Fusarium seedling blight. Major diseases in radish were virus, white rust, black rot, root rot, leaf spot and Fusarium seedling blight. Disease incidence reached peak on Aug. 20 with infection in radish and with infection in Chinese cabbage during the growing season, and declined thereafter. Percentage of infection in each growth stage showed at root thickening stage and at the harvest time in radish; and the head formation stage, at the harvest time. The data indicate that disease incidence in radish increased rapidly at late growing stage and progressively increased in Chinese cabbage Seedling blight caused by Fusarium sp. and root rot caused by Aphanomyces sp. were also observed in those areas. Cool and wet weather appeared to be favorable for disease incidences during the rainy period of growing season although average temperature was about . Populations of aphids were lower in the alpine vegetable growing area than that of flat areas. Aphids as virus vectors from total aphids collected were or 289 virus vectors /993 total aphids in Namweon and or 31 virus vectors/171 total aphids in Muju. The most prerevalent species of aphids was Myzus persicae Sulz.

Studies on Fusicladium Leaf Spot of Pongamia pinnata

Abstract: Fusicladium pongamae Syd. Caused severe foliage blight of Pongamia pinnata Pierre in nurseries. The symptoms, histopathology and pathogenicity of the organism were studied. There was heavy conidiation by the organism which germinated at appropriate humidity and temperature thereby infecting the healthy leaves. Sugars, organic acids and phenolics were observed chromotographically in healthy and the diseased leaves. The increase in the organic acid and phenolics was related with the mechanism of disease resistance during infection processes. Amongst the fungicides tried, bavistin, ziride and benlate were more effective in controlling the infection. Any of these fungicides may be sprayed at 0.2 per cent when the inoculum in the form of spores very less.

Diseases of Ramie (Boehmeria nivea)

Abstract: Ramie, the vegetable fibre, is obtained from the stem of Boehmeria nivea (L.) Gaud, and is used in many textile products. It is grown in tropical, sub-tropical and temperate regions and the main countries where it is grown are China, Brazil and the Philippines. However, it is only a minor crop in terms of world trade. The diseases of ramie are discussed in relation to their occurrence, symptoms and control measures. The major and most widespread diseases are white fungus caused by Rosellinia necatrix, leaf spot caused by Cercosporo spp. and Phyllosticta spp., seedling rot caused by Rhizoctonia solani, cane rot caused by Macrophomina phaseolina and eye rot caused by Myrothecium roridum. A number of diseases of minor importance are also reviewed.

Compatibility of Insecticides and Fungicides for the Control of Chilli White Aphid, Die-Back and Leaf Spot Diseases.

Abstract: The compatibility study conducted for the control of Myzus persicae and leaf spots and die back diseases of chillies showed that combination of insecticides and fungicides like met-hamidophos with maneb/captafol arid FMC 35001 with maneb/captafol had an additive effect in the control of aphids. The systemic inseeticides pirimicarb and methamidophos proved superior in toxicity by giving 89.6 and 85.3 per cent reduction of white aphid population respectively while FMC 35001 gave 77.0 per cent reduction and methyl–pirimiphos 20.44 per cent only. For leaf spot diseases, captafol in combination with insecticides was proved better as against maneb. The die back disease of chillies was checked effectively by most of the insecticidal combinations with maneb and captafol respectively. The different combination of insecticides and fungicides tested was found to be compatible and they were not phytotoxic.

A New Species of Cercoseptoria Causing a Leaf Spot of Ginger

Abstract: (1981). A New Species of Cercoseptoria Causing a Leaf Spot of Ginger. Mycologia: Vol. 73, No. 4, pp. 774-777.