Number Of Diseased Plants Research Articles

Lipopolysaccharides of plant-growth promoting Pseudomonas sp. strain WCS417r induce resistance in carnation to Fusarium wilt

The numbers of diseased plants could significantly be reduced when microconidia of Fusarium oxysporum f.sp. dianthi were inoculated into the stem and viable-, heat-killed cells or purified LPS of the bacterium Pseudomonas sp. strain WCS417r were applied to the roots. Because the competition between F. o. dianthi and the bacterium could be excluded, the disease suppression seems to be due to an induced resistance. Accumulation of phytoalexins was found in the stem segments. No accumulation of these compounds was found when the plants were bacterized but noninfected. It is concluded that cell surface components present in the lipopolysaccharides of the bacterium are the inducing factors. Increased peroxidase activity could be measured in root washes and root extracts after only bacterial preparations were added. No significant differences in peroxidase activity were found in stem extracts. The possible role of increased peroxidase activity in suppression of Fusarium wilt in carnation is discussed.

Induced Resistance and Phytoalexin Accumulation in Biological Control of Fusarium Wilt of Carnation byPseudomonassp. Strain WCS417r

The involvement of mechanisms other than competition for iron in biological control of Fusarium oxysporum f. sp. dianthi of carnation by Pseudomonas sp. strain WCS417r was investigated. Pathogen and antagonist were spatially separated by bacterizing the roots while inoculating the stem with the pathogen. When the roots were bacterized with strain WCS417r 1 wk prior to stem inoculation with F. o. dianthi, the number of diseased plants in all experiments with cultivar Pallas was reduced from about 50 to 20%, and in one experiment with cultivar Lena from 69 to 38% (...)

Potassium, magnesium, and irrigation effects on peanuts grown on two soils

Abstract Research data are limited on K and Wg requirements of peanuts (Arachis hypogaea L.) grown on sandy soils either with or without irrigation. Purposes of this study were (1) to determine Mg, K, and irrigation effects on yield, sound mature kernels (SMK's), and diseases of ‘Florunner’ peanuts grown on two sandy soils and (2) to determine sufficient amounts of Mg and K in peanut leaves and soils. Field experiments were conducted for three years on a Lakeland sand (thermic, coated Typic Quartzipsainments) and a Fuquay loamy sand (siliceous, thermic, Arenic Plinthic Paleudults). Both soils initially tested low in Mehlich 1 extractable K and Mg, but Lakeland was lower than Fuquay in both K and Mg. Factorial treatments were 0, 67, 67 (split into three applications), and 134 kg Mg/ha as MgS04 and 0, 56, 112, and 224 kg K/ha as KC1. Neither irrigation, K, nor Mg treatment affected number of diseased plants. (Sclerotium rolfsii) or pod rot on either soil. Also, yield and % SMK's were not affected by any tre...

Corrigendum - Further studies on epidemiological factors influencing control of banana bunchy top disease and evaluation of control measures by computer simulation

The basic infection rate of bunchy top disease in established bananas averaged 0.0342 new infections per infectious plant per day, but varied seasonally with a maximum in summer. The mean distance of spread for the aphid vector was 15.2 m. The latent period was 59.8 days and correlated with the time required for the growth of 3.7 new banana leaves. A microcomputer program was written to simulate spread of banana bunchy top disease in space and time. In the absence of disease control, disease spread from an initial primary infection in July or January to 124 or 153 infected plants, respectively, in one year. When disease control was maintained by removing diseased plants whenever the number of infected plants exceeded a given threshold, the numbers of diseased plants detected each inspection were positively correlated with the infection threshold, but the numbers of inspections required to maintain control increased markedly as the infection threshold was decreased. A practice of removing apparently healthy plants within 5 m of plants detected with bunchy top disease symptoms in five or more leaves was found to locate about 30% of the remaining undetected infected plants when disease was first detected in a plantation. However, its use as a routine control measure was ineffective in reducing the number of inspections required to maintain control or in reducing the risk of disease spreading to adjoining plantations. Removal of apparently healthy plants within 5 m had some bearing on disease control when applied around plants with disease symptoms in two leaves or less, but also caused a significant loss of healthy plants.

The epidemiology of common root rot in Manitou wheat. II. Effects of treatments, particularly phosphate fertilizer, on incidence and intensity of disease

The effects of various treatments such as herbicide, irrigation, nitrogen, phosphate, and combinations of nitrogen and phosphate on common root rot (Cochliobolus sativus) in naturally infected Triticum aestivum cultivar ‘Manitou’ were studied at Matador, Saskatchewan, by sampling plants at intervals during 1969, 1970, and 1971. The treatments were compared for each of the following variables : number of diseased plants per square metre, percentages of diseased plants, and percentage disease ratings. Usually, disease assessed by each variable was higher in the checks than in the phosphate treatments. The effect of phosphate appeared maximal at midseason (growth stage 9–10.5). The differences between treatments such as herbicide, nitrogen, and irrigation and the checks were insignificant. A comparison with the results of other workers suggests interaction between phosphate and soil type, and between phosphate and cultivar.

The epidemiology of common root rot in Manitou wheat: disease progression during the growing season

Common root rot in Triticum aestivum cultivar Manitou caused primarily by Cochliobolus sativus was followed during plant development in 1969, 1970, and 1971 at Matador, Saskatchewan. Plants were sampled at intervals, and three variables based mainly on the occurrence of lesions on subcrown internodes were studied: number of diseased plants per square meter; percentage of diseased plants; and disease rating which integrated percentage of diseased plants and disease severity on each plant. All variables increased with time, and the progression curves in all 3 years were hyperbolic, indicating that the increases were like those of a simple interest disease as described by Van der Plank. In two of the years, almost 100% of the plants were diseased considerably before the end of the season. The transformation proposed by Van der Plank for simple interest diseases, log10[1/(1 − x)], was applied to the percentages of diseased plants, and regressions were calculated. The slopes of these lines (infection rates) were as follows: 1969, 0.99% plants per day; 1970, 1.32%; and 1971, 1.96%. In 1969 the onset of disease was later than in 1970 and 1971, and there was correspondingly less disease at the end of the growing season.

Epidemiology of blue mould (Peronospora tabacina Adam)

The occurrence of blue mould disease of tobacco in the Ovens Valley district of Victoria was recorded at intervals of 2 weeks in observation rows during six successive seasons. First appearance of the disease was not associated with any particular plant growth stage or time of the year. There was an association with infected transplants and with wet days in the two preceding weeks. Subsequent increase in the number of diseased plants was related to rain on two of three consecutive days. The highest percentages of plants with disease occurred in plots where symptoms appeared before December 24. The percentage of plants with blue mould increased up to the commencement of flowering, usually late in January. There was a time interval of 2–5 weeks from first appearance to maximum percentage of plants diseased, the shorter period occurring when more than 25% of plants were diseased at the first record. The rate of spread of disease between fields was proportional to the number of fields already infected. The disease spread more slowly when the plants were sprayed with fungicides.

The effect of sowing date and spacing on rosette disease of groundnut in Northern Nigeria, with observations on the vector, Aphis craccivora

SUMMARYIn Northern Nigeria, groundnuts planted in June outyielded those planted in July, and, in rows I yard apart, plants spaced at 9 in. gave a heavier total crop than those at 18 in. In two experiments, early sowing reduced the number of rosetted plants per acre; close spacing merely reduced the percentage of plants infected. There was a correlation between the total of aphid‐infested plants during the growing period and the number of diseased plants. Late‐sown crops support more Aphis maccivora, both apterae and alatae. The principal host of the vector during the 6 months dry season is Euphorbia hirta, whereas in East Africa groundnut is the principal host throughout the year. A list of predators is given, with observations on relative numbers of syrphid larvae and aphids.