Interactions between the striped stem borer Chilo suppressalis (Walk.) (Lep., Pyralidae) larvae and rice plants in response to nitrogen fertilization

A screenhouse experiment was conducted to examine the damage and compensation in rice plants when injured by the striped stem borer, Chilo suppressalis (Walker), larvae at tillering stage, as well as larval survival and development of the insect at different nitrogen (N) fertilization levels. Potted plants were fertilized at late seedling stage at the rates 0, 200, 400, 600 and 800mgN/pot, respectively. More deadheads were caused as fertilization increased. Plants compensated well for injury at the fertilization concentrations of 200 and 400mgN/pot by producing new tillers, but such compensation did not take place at 600 and 800mgN/pot. Two weeks after infestation, the highest number of remaining healthy tillers was found in plants fertilized at 400mgN/pot. Larval survival varied little among the treatments 200 to 800mgN/pot. Larval weight attainment and/or developmental rate increased with increasing fertilization level from 200 to 600mgN/pot, but both declined rapidly as fertilization reached 800mgN/pot, indicating the great dependence of plant suitability on N fertilization levels. Conclusively, both the compensation response of rice plants and their suitability for C. suppressalis larvae could be significantly affected by N fertilization levels.     

The relative importance of conidia and ascospores as primary inoculum of Venturia inaequalis in a southeast England orchard

Apple scab, caused by Venturia inaequalis, can lead to large losses of marketable fruit if left uncontrolled. The disease appears in orchards during spring as lesions on leaves. These primary lesions are caused by spores released at bud burst from overwintering sources; these spores can be sexually produced ascospores from the leaf litter or asexual conidia from mycelium in wood scab or within buds. The relative importance of conidia and ascospores as primary inoculum were investigated in an orchard in southeast England, UK. Potted trees not previously exposed to apple scab were placed next to (c. 1 m) orchard trees to trap air‐dispersed ascospores. Number and position of scab lesions were assessed on the leaves of shoots from both the potted trees (infection by airborne ascospores) and neighbouring orchard trees (infection by both ascospores and splash‐dispersed, overwintered conidia). The distribution and population similarity of scab lesions were compared in the two tree types by molecular analysis and through modelling of scab incidence and count data. Molecular analysis was inconclusive. Statistical modelling of results suggested that conidia may have contributed approximately 20–50% of the primary inoculum in early spring within this orchard: incidence was estimated to be reduced by 20% on potted trees, and lesion number by 50%. These results indicate that, although conidia are still a minority contributor to primary inoculum, their contribution in this orchard is sufficient to require current management to be reviewed. This might also be true of other orchards with a similar climate.     

Malvastrum leaf curl Guangdong virus is a distinct monopartite begomovirus

Virus isolates GD6, GD7, GD8, GD9 and GD10 were obtained from Malvastrum coromandelianum showing leaf curl symptoms in Guangdong Province of China. A specific 500 bp product was consistently detected in total DNA extracts, amplified with universal primers specific for members of the genus Begomovirus. Analysis of their partial DNA sequences revealed that they are isolates of the same begomovirus species, sharing 92·8%–97·1% nucleotide sequence identity. The complete DNA sequences of both GD6 and GD9 were found to be 2767 nucleotides, with all the characteristic features of begomovirus genome organization. The two isolates have less than 85·2% nucleotide sequence identity with other reported begomoviruses. Consequently, GD6 and GD9 are considered to be isolates of a novel begomovirus species, for which the name Malvastrum leaf curl Guangdong virus (MLCuGdV) is proposed. Sequence analyses suggest that MLCuGdV may have arisen by recombination between viruses related to Papaya leaf curl China virus , Tomato leaf curl Philippines virus and other undiscovered virus ancestors. Neither the DNA-B component nor the DNAβ molecule associated with these begomovirus isolates was found. An infectious clone of GD6 was constructed. GD6 efficiently infected Nicotiana benthamiana , N. glutinosa and Petunia hybrida by agro-inoculation, and Malvastrum coromandelianum by whitefly transmission, inducing leaf curling, vein swelling and stunting symptoms. GD6 was also infectious in N. tabacum , but did not induce observable disease symptoms.     

Effects of Angular Leaf Spot and Rust on Yield Loss of Phaseolus vulgaris

ABSTRACT Three field experiments were conducted in 1997, 1998, and 1999 to investigate the effects of angular leaf spot and rust, separately or combined, on host growth and yield of individual bean plants (Phaseolus vulgaris). In each experiment, three treatments were established by inoculating cv. Carioca with Phaeoisariopsis griseola, Uromyces appendiculatus, or with both pathogens. An additional control treatment was not inoculated, but was sprayed with a fungicide. In the 1997 and 1999 experiments, angular leaf spot reached higher disease levels than rust, whereas in 1998, rust was more severe than angular leaf spot. Host growth, expressed as healthy leaf area duration (HAD), and yield were the highest in 1997 and lowest in 1998. In each experiment, the treatments did not differ significantly to the area under leaf area progress curve, HAD, and healthy leaf area absorption (HAA). All inoculated treatments had significantly more severe disease and less yield than the control treatment. Based on the analysis of 60 plants in each experiment, yield was not related to the areas under disease progress curve for either or both diseases. In 1997 and 1999, yield was related to HAD (R(2) = 0.57 and 0.43) and HAA(R(2) = 0.60 and 0.55). Based on the combined analysis of all 36 plots, angular leaf spot reduced the leaf area because of defoliation, whereas rust did not affect the leaf area. Rust reduced yield more than four times that of angular leaf spot, although the decrease in photosynthesis to angular leaf spot was twice that of rust.     

On estimating non-linear response of fungal development under fluctuating temperatures

Published research concerning disease development often shows that the response of fungal development to temperature is non-linear. Unfortunately, this non-linear response has often been ignored when predicting fungal development under varying temperatures using non-linear models and when deriving fungal development models from data collected under fluctuating temperatures. In this paper, the magnitude of non-linear effects on fungal development is shown to depend on the types of non-linear models and on the extent of temperature fluctuations. A method is described, which has been used in other disciplines to fit non-linear models directly to varying temperatures. Hypothetical data were generated to demonstrate the usefulness of this method. With the underlying rate equation being non-linear, models derived from average temperatures underestimate the rates at intermediate temperatures; the greater the temperature fluctuation, the greater this underestimation.     

Recessive Genes for Resistance to Puccinia striiformis f. sp. hordei in Barley

ABSTRACT Barley genotypes Abyssinian 14, BBA 2890, Grannelose Zweizeilige, PI 548708, PI 548734, PI 548747, and Stauffers Obersulzer are resistant to all races of Puccinia striiformis f. sp. hordei identified thus far in North America. Astrix, BBA 809, Bigo, Cambrinus, Emir, Heils Franken, Hiproly, I5, Mazurka, Trumpf, and Varunda have specific resistance to certain races, whereas Topper and Steptoe are susceptible to all races. Seedlings of parents and F(1), F(2), and F(3) progeny from crosses of resistant genotypes with Topper and Steptoe were tested for resistance to North American P. striiformis f. sp. hordei races PSH-1, PSH-4, PSH-10, PSH-13, and PSH-20. When tested with PSH-1, one recessive gene was detected in BBA 809, BBA 2890, Bigo, Hiproly, and Grannelose Zweizeilige; two recessive genes were detected in Emir, I5, PI 548708, PI 548734, PI 548747, Varunda, and Astrix; and one dominant gene and one recessive gene were detected in Abyssinian 14 and Stauffers Obersulzer. In tests with PSH-4, one recessive gene was detected in BBA 809, two recessive genes were detected in Trumpf, and two partially recessive genes were detected in Astrix. In tests with PSH-13, one recessive gene was detected in BBA 2890, Grannelose Zweizeilige, I5, and PI 548708 and two recessive genes were detected in Abyssinian 14, Hiproly, PI 548734, and PI 548747. In tests with PSH-20, one recessive gene was detected in Bigo and a recessive gene and a dominant gene were detected in Heils Franken. A gene in Cambrinus for resistance to PSH-10 and a gene in Mazurka for resistance to PSH-20 were dominant on the basis of the response of the first seedling leaf but recessive on the basis of the response of the second leaf. Four different types of epistasis were detected. Information on the number of genes, mode of inheritance, and nonallelic gene interactions should be useful in understanding the host-pathogen interaction and in breeding barley for resistance to stripe rust.     

Soybean Brown Stem Rot, Phytophthora sojae, and Heterodera glycines Affected by Soil Texture and Tillage Relations

ABSTRACT Investigations were conducted to determine whether the effects of tillage practices on the prevalence of brown stem rot of soybean (caused by Phialophora gregata), Heterodera glycines, and Phytophthora sojae were confounded by soil texture in samples collected in the fall of 1995 and 1996. Soil and soybean stem samples, along with tillage information, were collected from 1,462 randomly selected fields in Illinois, Iowa, Minnesota, Missouri, and Ohio in collaboration with the National Agricultural Statistics Service. The incidence of brown stem rot was determined from 20 soybean stem pieces collected from each field in a zigzag pattern. The detection frequency of P. sojae (expressed as percent leaf disks colonized) and population densities of H. glycines were determined from soil cores also collected in a zigzag pattern. The soil samples were grouped into various textural classes, and the effect of soil texture and tillage relations on the activities of each pathogen were determined. Both tillage and soil texture affected the incidence of brown stem rot; however, there was no interaction between tillage and soil texture. Conservation tillage had a greater (P < 0.05) incidence of brown stem rot in clay loam and silty clay loam than did conventional tillage. The detection frequency of P. sojae was not affected by tillage, but a tillage x texture interaction (P = 0.013) indicated that the effect of tillage depended on soil texture. There was a greater (P < 0.05) detection frequency of P. sojae in conservation tillage than in conventional tillage in silt loam and loam soils. However, in sandy loam, the detection frequency of P. sojae was greater (P = 0.0099) in conventional tillage than in conservation tillage. Population densities of H. glycines were significantly affected by both tillage and soil texture, but overall, there was no tillage x texture interaction. There was an inverse relationship between population densities of H. glycines and percent clay (r = -0.81, P = 0.01) in no-till fields, but little or no change in nematode densities was observed with increasing clay content in tilled fields. Population densities of H. glycines were less (P < 0.05) in no-till fields than in tilled fields in silty clay loam and clay soils. There was no difference in H. glycines densities between the tillage categories in soils sandier than silty clay loam or clay. The findings emphasize the need for cautious interpretation of the effects of tillage practices on diseases and pathogens in the absence of information on soil texture.     

Use of urea-molasses-multinutrient block and urea-treated rice straw for improving dairy cattle productivity in Vietnam

After conducting a preliminary survey, a feeding trial was carried out to determine the effect of urea-molasses-multinutrient block (UMMB) and urea-treated rice straw (UTRS) as a feed supplement on the productivity of dairy cows. Sixty Holstein-Friesian crossbred cows on 11 smallholder farms were divided equally into control, UMMB and UTRS supplementation groups. Milk yield and feed intake were recorded daily. Milk fat content, body weight and body condition score (BSC) of each cow were determined at two week intervals. Milk samples for progesterone analysis were collected once a week commencing one month after parturition. Data were recorded for date of onset of ovarian activity, estrus, insemination, and conception rate. Milk production increased by 10.3-11.9% and milk fat content increased by 3-5%, therefore, profit for farmers increased by US $0.55-0.73 per cow per day (exchange rate US $1 = VN $11,000). The intervals from calving to onset of ovarian activity (91-94 days), to estrus (110-114 days), to conception (121-122 days) and the calving interval (13.4-13.6 months) in the trial groups were significantly shorter than those in the control group (112, 135, 152 days and 14.4 months, respectively.