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1.
Rice blast caused by Magnaporthe oryzae continues to be the most destructive disease of rice worldwide, and is a number one disease of rice in Uganda. We present the footprints of M. oryzae importance, distribution, incidence and severity in the rice growing agro-ecologies of Uganda for 2009/2010, and the potential mitigation measures. Our data show that rice blast affects more than 50% of the cultivated rice area on average, and ranks as the most important disease encountered in the field. Between and within agroecologies, both incidence and severity varied (P < 0.05) reflecting the contribution of different cropping practices on rice blast epiphytotics. The highest blast incidence and severities were recorded in Bugiri, Butaleja, Mbale and Lira farmlands, which are the ancestral rice cultivation areas in Uganda. These areas showed mean yield reductions of >30% relative to other locations, suggesting that rice production history played a significant role in rice blast outbreaks. Broadcasting and drill seeding yielded 42.4% less than transplanted rice. Growing two rice crops per year is one of the methods suggested to increase rice production in Uganda, but there was a higher disease incidence in the late season than in the early season, indicating the need for improved resistant varieties. Four blast resistance genes (Pi9, Piz-t, Pi19 and Piz-5) and the cultivar Tetep had the lowest (≤4) blast severity scores in all the test locations. It could be suggested that these genes are potential resistance sources for developing varieties, which would be more relevant for the double cropping systems.  相似文献   

2.
Rice blast disease is one of the obstacles of rice production not only in Japan but throughout rice producing countries. The effects of fan-forced wind on the incidence of rice blast disease were studied in two successive seasons. Electric fans (5 KW, 110-cm blade diameter) set on the ridge of paddy fields at a height 5 m from the ground level were used to artificially generate wind. In season 1, the fan operated twice daily for 30 min periods at 11:00 pm and 4:00 am from June 15 to September 1. The blocks of the paddy fields were divided into 6 zones according to wind speed and distance from the fan. The wind speed ranged from 2.0 to >7.3 m/s. The incidence of both rice leaf and panicle blast was significantly lower in the zones receiving wind between 2.6 and 7.3 m/s; however, the zone that received a velocity >7.3 m/s was severely affected by leaf and panicle blast. The zone that received the a wind speed of 2.6 m/s or lower exhibited an inefficient reduction of leaf and panicle blast disease, but it was better than in the control fields. In season 2, a wind-forced fan was applied from June 16 to September 9, with the velocity adjusted between ca. 3.0 and 6.0 m/s. The incidence and severity of leaf and panicle blasts (chuff, rachis-branch and neck blast) were efficiently reduced in the wind-treated fields. Fan-forced wind was more effective than the application of conventional chemical fungicides for controlling rice blast disease. These data demonstrate the potential of fan-forced wind for controlling rice blast disease.  相似文献   

3.
The incidence and severity of citrus variegated chlorosis (CVC) caused by Xylella fastidiosa are higher in the northern region of Sao Paulo, Brazil than in the southern region. This phenomenon is partly due to differences in the climate, especially rainfall, as the northern region tends to be drier than the southern region. The progress of CVC under three levels of irrigation was assessed in a grove located in the northern region of Sao Paulo. Trees (10-year-old Natal sweet orange) were arranged in a randomized complete block in a 3 × 2 factorial scheme with three levels of irrigation and two methods of infection with X. fastidiosa. The disease incidence in branches and the number of symptomatic fruits per tree were evaluated for three years. A monomolecular model was used to describe the progress of CVC incidence for all treatments. Irrigation reduced CVC symptoms in trees, especially the number of symptomatic fruits per tree. Based on this significant reduction, citrus irrigation can be used to reduce the main negative effect of CVC: reduced fruit size. Our results also explain the higher incidence of CVC in the northern region of Sao Paulo, where a dry season occurs.  相似文献   

4.
Three demonstration experiments were conducted on commercial greenhouse farms to assess the efficacy of chloropicrin (CP), applied by drip irrigation, in controlling Verticillium wilt and root rot disease complex of bell pepper, in comparison with dazomet at 40 g m−2. Chloropicrin was applied through drip irrigation system at 20, 30 and 40 g m−2 of emulsified commercial formulation. The concentration of CP in water was constant, and the required doses were obtained by delivering different amounts of the irrigation water per area unit (from 12.5 to 33 mm). The highest mean efficacy in reducing the inoculum density of Verticillium dahliae in the soil at all locations was obtained after CP application at 30 and 40 g m−2, about 85 and 86%, respectively. The number of viable microsclerotia recovered from the soil on the day of pepper planting was significantly correlated with the final incidence of Verticillium wilt disease (r = 0.962). The highest mean efficacy in controlling Verticillium wilt of pepper (86.4%) was obtained after soil treatment with CP at 40 g m−2, and ranged from 80.2 to 95.6%. The yield was stronger correlated with root rot severity (r = −0.849**) than with progression of Verticillium wilt, expressed by AUDPC (r = −0.651**). The dominant soil-borne pathogen responsible for pepper root rot was Colletotrichum coccodes. All chemical treatments provided a significant reduction in root rot severity compared to the untreated control. On-thefarm evaluation revealed that soil fumigation with drip-applied chloropicrin presents a feasible option for pepper growers.  相似文献   

5.
The nutritive value of pasture is an important determinant of the performance of grazing livestock. Proximal sensing of in situ pasture is a potential technique for rapid prediction of nutritive value. In this study, multispectral radiometry was used to obtain pasture spectral reflectance during different seasons (autumn, spring and summer) in 2009–2010 from commercial farms throughout New Zealand. The analytical data set (n = 420) was analysed to develop season‐specific and combined models for predicting pasture nutritive‐value parameters. The predicted parameters included crude protein (CP), acid detergent fibre (ADF), neutral detergent fibre (NDF), ash, lignin, lipid, metabolizable energy (ME) and organic matter digestibility (OMD) using a partial least squares regression analysis. The calibration models were tested by internal and external validation. The results suggested that the global models can predict the pasture nutritive value parameters (CP, ADF, NDF, lignin, ME and OMD) with moderate accuracy (0·64 ≤ r2 ≤ 0·70) while ash and lipid are poorly predicted (0·33 ≤ r2 ≤ 0·40). However, the season‐specific models improved the prediction accuracy, in autumn (0·73 ≤ r2 ≤ 0·83) for CP, ADF, NDF and lignin; in spring (0·61 ≤ r2 ≤ 0·78) for CP and ash; in summer (0·77 ≤ r2 ≤ 0·80) for CP and ash, indicating a seasonal impact on spectral response.  相似文献   

6.
Two field surveys were conducted during the 2010 and 2011 cropping seasons to determine the distribution and importance of faba bean root rot, Fusarium solani (Mart) Apple and Sacc. in the northeastern highlands of Ethiopia. The associations of the root rot incidence and severity with independent variables was analyzed using a logistic regression model. The associations of disease incidence and severity with biophysical factors were evaluated. The disease incidence and severity varied among soil types, crop management practices and cropping seasons. Disease incidence and percentage severity index were higher in 2010 (44.6%) than 2011 (44.4%) due to the high rainfall in 2010. Cropping season, soil type, land preparation and weed management practices were significantly associated with faba bean root rot incidence and percentage severity index in a multiple-variable model. A root rot incidence of ≤50% and severity of ≤40% showed high probability of association with season, furrow sowing and weed management practice, whereas vertisols, flat sowing, high soil moisture and high weed density had significant contributions to root rot epidemics. In contrast, elevation, cropping system and crop density were not associated with the root rot incidence and percentage severity index. Our results showed that root rot is a major biotic constraint in the study area and suggested that proper soil drainage and weed management practices could contribute to reduce the impact of the disease until resistant faba bean genotypes are developed and distributed to small-scale faba bean growers in northeastern Ethiopia and other similar areas of the country.  相似文献   

7.
In the Mediterranean farming systems of the Western Australian wheatbelt, crop yields are influenced primarily by the amount and distribution of rainfall and the soil's capacity to hold moisture. The wheatbelt's growing season rainfall varies in the range of 200–400 mm (average) and the plant available water holding capacity (PAWC) of soils is generally in the 40–140 mm range. The grain yield of wheat is sensitive to this combination of small rainfall and small storage capacity.In this study, we explore the relationship between yield and PAWC using a combination of simulation modelling and analysis of field data. Crop yields and soil properties were monitored in detail at 17 locations (PAWCs 43–131 mm) across six seasons (1997–2005). Crop yields were also simulated using the APSIM crop simulator (RMSE = 311 kg/ha) to evaluate the long-term relationship between crop yield and plant available water capacity using 106 years of historical climate data.The relationship between crop yield and PAWC varied with season, and two important factors emerged: (1) for PAWC < 65 mm, there was a linear relationship with crop yields that ranged from 17 kg/ha/mm to 58 kg/ha/mm of PAWC across seasons; (2) for PAWC 65–131 mm the crop yield response to PAWC ranged from 11.5 kg/ha/mm in 45% of seasons to no response.The impact of PAWC on crop yield was reduced in seasons with late rainfall, and magnified in seasons with reduced rainfall late in the growing season. Six distinct season types with different yield–PAWC relationships are identified and season-specific management strategies that exploit within-field variation in PAWC are developed to manage the spatial variation of PAWC in a field.  相似文献   

8.
Cassava (Manihot esculenta Crantz) production is constrained by many factors, including the viral cassava mosaic disease (CMD). This study was conducted to explore the potential of intercropping cassava with legumes to reduce CMD effects on cassava production. Local (Lyongo Kwimba) and improved (Suma) cassava varieties were intercropped with three types of grain legumes (groundnut, Arachis hypogea L. var. Upendo; cowpea, Vigna unguiculata (L.) Walp. var. Vuli; and green gram, Vigna radiata (L.) R. Wilczek var. Imara). Monocrops of cassava with and without NPK fertilizer were included as controls. The experiment was established using a randomized complete block design with four replications in a split-plot arrangement for three seasons. Cassava varieties intercropped with cowpeas, green gram, and groundnuts and cassava monocrops with and without NPK fertilizer constituted the main plot and sub-plots, respectively. Whitefly population counts and CMD severity and incidence were measured at regular intervals. Cropping system had a significant effect (P < 0.05) on whitefly populations and CMD severity. Small whitefly populations (0–7.5 individuals per leaf) and low CMD severity (1–2.4 on a 5-point scale) were recorded in improved and local cassava varieties intercropped with green gram. The local cassava variety intercropped with green gram showed low CMD incidences (0%–40%) in all seasons. Generally, growing cassava with green gram proved effective in reducing whitefly populations and CMD incidence and severity. Intercropping cassava with grain legumes may improve cassava production and food security in CMD-prone areas of the Lake Zone of Tanzania and areas with similar environments.  相似文献   

9.
Yellow mosaic disease (YMD) of black gram is an important production constraint in India. Black gram germplasm, consisting of 344 accessions, originally collected from different geographic regions of India and conserved in National Gene Bank at National Bureau of Plant Genetic Resources, India, were evaluated for their response against YMD. None of the accessions tested was found to be immune, however, considerable variation in disease response was observed among them. Of the 344 accessions, 32 showed resistance in the field during the rainy season (June–September) 2010 as assessed by coefficient of infection (CI) and area under disease progress curve (AUDPC). These accessions were re-evaluated during rainy season (June–September) 2011 and 2012 for their disease resistance along with yield-associated characters. Eight accessions that exhibited consistently highly resistant (HR) or resistant (R) reaction (CI ≤ 9) along with lower AUDPC value (≤650), were further evaluated following inoculation with whiteflies or via agroinoculation. Along with the resistant trait, these eight accessions were also found either similar or even better in their yield potential as compared to check. After artificial inoculation using viruliferous whiteflies under glasshouse, of the eight field-resistant accessions, response of two (IC144901 and IC001572) were categorized as HR as <10% plants exhibited minute yellow specks after 17–22 dpi. Two accessions viz. IC011613 and IC485638 showed <20% incidence with bright yellow specks or spots after 15–20 dpi and were grouped into R category. The resistance of these four accessions was further confirmed through agroinoculation of the infectious cloned viral DNA under controlled conditions. In resistant accessions low accumulation of viral DNA was observed over a period of time. These four accessions could be used in future breeding programmes to develop black gram cultivars resistant to YMD or could be used directly as varieties to manage YMD after adaption to various agro-climatic regions.  相似文献   

10.
Seven-day laboratory bioassays with first-instar Helicoverpa armigera and Helicoverpa punctigera larvae were conducted using leaves from field-grown Bollgard II® cotton during the 2009/10 season and larval mortality and development recorded. Leaves were from three farms in the St George region and two fields on one farm at Emerald in eastern Australia. The Cry1Ac and Cry2Ab content of leaves from the same samples was determined (see Knight et al., 2013) and the relationships between Cry protein content and larval mortality and development were examined. The Cry1Ac protein content was between 3.98 and 12.08 μg/g during the growing season, while Cry2Ab content ranged between 300.6 and 953.3 μg/g. Cry1Ac and Cry2Ab content of leaves were highly correlated (r = 0.8276, P < 0.001). Seven-day mortality of H. punctigera larvae was close to 100% throughout the season. H. armigera mortality was close to 100% early in the season, but fell to ∼65% by mid-to late February in the laboratory bioassays. Fitting three-dimensional non-linear models associating Cry1Ac and Cry2Ab content with H. armigera and H. punctigera mortality elucidated the relative importance of the two proteins in determining larval mortality; for this analysis, data were pooled with data from an isoline study to provide better sampling of the three-dimensional surface being modelled. For both Helicoverpa species, the fitted mortality response to the Cry1Ac protein was close to its maximum at protein concentrations above ∼3 μg/g Cry1Ac. For H. punctigera, response to the Cry2Ab protein was close to maximal once Cry2Ab was greater than ∼200 μg/g. In contrast, the fitted H. armigera mortality response to Cry2Ab increased steadily with concentration up to ∼1200 μg/g Cry2Ab. These responses led to markedly different response surfaces for the two species; H. punctigera mortality was close to 100% at most places on the response surface, while for H. armigera the response surface showed stronger increases in mortality with concentration for Cry2Ab than for Cry1Ac. These results can be interpreted as meaning that at the plant-expressed range of concentrations in Bollgard II cotton the two proteins are approximately equally important for H. punctigera but that changes in Cry2Ab content more strongly influences changes in larval mortality in H. armigera than does Cry1Ac, with Cry1Ac contributing a consistent 40–45% mortality for concentrations above 3 μg/g. For H. armigera, there was no evidence of either synergism or antagonism between Cry1Ac and Cry2Ab proteins (P > 0.05) but this aspect was not testable for H. punctigera because mortality was mostly close to 100%.  相似文献   

11.
In commercial apple orchards in southern Brazil, it is common to avoid hail damage by covering the trees with nets. This study was carried out to assess the effects of both black and white hail netting on the temporal dynamics of Glomerella Leaf Spot disease (GLS) in a commercial ‘Royal Gala’ apple orchard in a high-altitude region of southern Brazil during two growing seasons (2003/2004 and 2004/2005). Apple trees on M9 rootstock, trained to a slender spindle and with a spacing of 5.5 m × 3 m, were left uncovered (control) or covered with black or white hail netting. The incidence and severity of GLS were quantified biweekly from October to February by evaluating 100 leaves distributed randomly on four medium-height branches per plant on each 12 replications per treatment. Disease progress curves were constructed from the data and the epidemics were compared by using four epidemiological measures: the beginning of symptom appearance (BSA), the time to reach the maximum disease intensity (TRMDI), the maximum value of disease severity (Ymax), and the area under the disease progress curve (AUDPC). The highest intensity of GLS was observed in the plants under the black hail netting. Significant reductions in BSA and TRMDI and significant increases in Ymax and AUDPC were found among treatments in both growing seasons. However, no significant differences of GLS were found between the white hail netting and the control in either growing season.  相似文献   

12.
Brown rot, caused by Monilinia fructicola, is the most widespread disease for organic peach production systems in Brazil. The objective of this study was to determine the favorable periods for latent infection by M. fructicola in organic systems. The field experiment was carried out during 2006, 2007 and 2008 using the cultivar Aurora. After thinning fruits were bagged using white paraffin bags, and the treatments were performed by removing the bags and exposing the fruit for four days to the natural infection during each of seven fruit stages from pit hardening to harvest. Throughout the entire growing season, the conidial density and the weather variables were measured and related to the disease incidence using multiple regression analyses. At the fourth day after harvest in each season, the cumulative disease incidence was assessed, and it ranged from 40 to 98%. The incidence of brown rot on fruit that were exposed during the embryo growing stage was lower than that of unbagged fruit throughout the entire season in 2006 and 2008. The relative humidity and the conidia density were significantly correlated to disease incidence. Based on our results, M. fructicola can infect peaches during any stage of fruit development, and control of the disease must be revised to account for organic peach production systems.  相似文献   

13.
The epidemiology of wheat blast, caused by the Triticum pathotype of Pyricularia oryzae, is poorly understood, making it very difficult to manage. We reported on the individual and combined effect of host resistance and fungicide application for managing wheat blast disease on spikes. Two field experiments (Exp. 1 and Exp. 2) were conducted in a region of Brazil where blast is not known to be endemic to evaluate its development as influenced by fungicide and host resistance. Plots of wheat cultivars BR-18 (partially resistant) and Guamirim (susceptible) were either treated with the fungicide epoxiconazole + pyraclostrobin or left non-treated, and then inoculated with a spore suspension of P. oryzae at mid-anthesis. Spike blast incidence and severity, quantified at regular intervals after inoculation, increased over time, and fungicide and cultivar had statistically significant effects (P < 0.005) on both measures of disease and their temporal rates of progress. Relative to Guamirim-non-treated, BR-18-non-treated (resistance alone) led to 44 and 64% control of final incidence and severity, respectively, in Exp. 1, and 3 and 49% control, respectively, in Exp. 2. Guamirim-treated (fungicide alone) led to 65% control of incidence and 77% control of severity in Exp. 1, and 64% control of incidence and 95% control of severity in Exp. 2. For both incidence and severity, fungicide and resistance alone also reduced the temporal rate of progress relative to the susceptible non-treated. However, the greatest overall efficacy was observed when resistance and fungicide were combined, with over 70 and 90% control of final incidence and severity, respectively, and over 75% reduction in the temporal rate of spike blast progress. Based on percent control, the integrated effect of resistance and fungicide was additive for incidence, severity, and their temporal rates of progress, demonstrating the value of combining the two strategies to manage spike blast.  相似文献   

14.
Efficacy of foliar applied fungicides following simulated rainfall for the control of dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) was assessed in a two-year field study on creeping bentgrass (Agrostis stolonifera L.) turf maintained as a golf course fairway. The study was conducted as a randomized complete block design with a factorial arrangement. Fluazinam (0.8 kg a.i. ha−1), chlorothalonil (3.79 kg a.i. ha−1) or iprodione (1.5 kg a.i. ha−1) were applied, then subjected to simulated rainfall (2.54-mm) at intervals of 15-, 30-, 60-min post-application, or no simulated rain. In most cases, simulated rainfall occurring ≤60 min post-application had greater disease than no rain plots; however, few differences occurred among rainfall intervals ≤60 min. Fluazinam provided the greatest dollar spot reduction regardless of simulated rainfall interval throughout the study. Chlorothalonil was most susceptible to losses in efficacy due to simulated rainfall, resulting in the greatest disease incidence of those fungicides evaluated. Iprodione was comparable to chlorothalonil during high disease pressure, although during moderate disease pressure it controlled dollar spot for approximately 7 days before disease increased in plots receiving simulated rain compared to those without simulated rain. These data demonstrate that efficacy of fungicides applied for dollar spot control are affected by rain, and differ in their ability to control disease following post-application rain events. Fluazinam, a recently introduced contact fungicide for use on turfgrass, can provide improved control compared to chlorothalonil or iprodione when rain is eminent.  相似文献   

15.
The expression of foliar and tuber bacterial ring rot (BRR) symptoms in 108 cultivated potato genotypes inoculated withClavibacter michiganensis subsp.sepedonicum was examined in field experiments during 1986 to 1996. Considerable variation in the incidence of foliar BRR symptoms was observed in all plant cultivars, ranging from no detectable symptoms to complete necrosis of the leaves. Similar variability was observed in the incidence of tuber BRR symptoms, and severity of tuber symptoms ranged from no detected symptoms to complete breakdown of the vascular ring that extended throughout the tuber. A decline in the incidence and severity of tuber, but not foliar symptoms, was observed in the later years of the study (P<0.05). Foliar and tuber BRR symptoms generally were positively correlated (P<0.01) prior to 1993 but not in subsequent years (P>0.05) when tuber symptoms declined. Strong correlations were observed between the incidence and severity of foliar BRR symptoms (r=0.41, P<0.01) and between the incidence and severity of tuber BRR symptoms (r=0.96, P<0.001). During the 11 year period, no BRR symptoms were observed in 2,620 uninoculated control plants.  相似文献   

16.
Mango malformation disease (MMD) caused by Fusarium mangiferae severely affects the crop and is widely distributed in almost all mango-growing regions worldwide. Since malformed inflorescences do not bear fruit, MMD is a major constraint to crop production in affected areas. No effective management methods have been reported to date. The airborne nature of dissemination and infection of buds suggest that protection of buds from infection when inoculum prevails may be a plausible method for disease control from season to season. Various fungicides were assessed for their ability to control the pathogen under laboratory, greenhouse and field conditions. Prochloraz was the most effective fungicide in inhibiting F. mangiferae in vitro with a 0.01 μg mL−1 concentration required for 50% fungal growth inhibition. In greenhouse trials, protective and curative activity exceeding 90% was achieved when the fungicide was applied up to 14 days prior or post inoculation. Field experiments conducted over a number of seasons in different regions in Israel indicate that combined sanitation with timely applications of prochloraz resulted in a significant reduction in MMD disease severity and incidence, as well as a significant increase in yield in treated plots. It is assumed that long-term treatment by removal of infected panicles (the main source of inoculum) combined with timely sprays will result in disease reduction annually achieving negligible levels of malformation in treated orchards, in time.  相似文献   

17.
Bulgur is an increasingly popular foodstuff that has existed since antiquity, and one that displays high consumption worldwide. Polishing is a key operation to improve the yellow color of bulgur which, by extension, also improves the competitiveness in business and markets. In this study, the traditional electrical heater-aided mechanical polishing system (EHA-MP) was modified with preheating systems so as to decrease the energy consumption and to improve the bulgur color. Additionally, it was investigated that the effects of the tempering methods (spray and steam) before polishing, the preheating (microwave and infrared, at 40, 60 and 80 °C) by determining changes in the bulgur color (CIE L*, CIE b*, CIE a*, CIE YI), total carotenoid content (TCC), chemical composition (moisture, ash and protein contents, %, d.b.) and the energy consumption of the process. Both tempering methods increased significantly (P ≤ 0.05) the CIE L* and CIE b* values of bulgur. The temperature of polishing increased the TCC of bulgur significantly (P ≤ 0.01). Infrared preheating was the most economical method according to energy consumption. Taken together, these new findings offer new insights and improvements in the bulgur production and its attendant business competitiveness and responds to demands by consumers.  相似文献   

18.
Comparable data are lacking from the range of environments found in sub-Saharan West Africa to draw more general conclusions about the relative merits of locally available rockphosphate (RockP) in alleviating phosphorus (P) constraints to crop growth. To fill this gap, a multi-factorial field experiment was conducted over 4 years at eight locations in Niger, Burkina Faso and Togo. These ranged in annual rainfall from 510 to 1300 mm. Crops grown were pearl millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.) either continuously or in rotation with cowpea (Vigna unguiculata Walp.) and groundnut (Arachis hypogaea L.). Crops were subjected to six P fertiliser treatments comprising RockP and soluble P at different rates and combined with 0 and 60 kg N ha−1. For legumes, time trend analyses showed P-induced total dry matter (TDM) increases between 28 and 72% only with groundnut. Similarly, rotation-induced raises in cereal TDM compared to cereal monoculture were only observed with groundnut. For cereals, at the same rate of application, RockP was comparable to single superphosphate (SSP) only at two millet sites with topsoil pH-KCl<4.2 and annual average rainfall>600 mm. Across the eight sites NPK placement at 0.4 g P per hill raised average cereal yields between 26 and 220%. This was confirmed in 119 on-farm trials revealing P placement as a promising strategy to overcome P deficiency as the regionally most growth limiting nutrient constraint to cereals.  相似文献   

19.
Verticillium wilt is responsible for substantial yield losses in cotton. The use of cultivars with partial resistance to Verticillium wilt is a preferred management strategy. Cotton breeders utilize rating scales based on severity of foliar symptom expression and/or defoliation when making cultivar selections. The objective of this research was to determine the yield relationship with cultivars grouped by both incidence of Verticillium wilt during the boll filling stage, and late season defoliation in fields with a history of Verticillium wilt. Small plot, replicated cultivar trials were conducted over an 11 year period in west Texas. Cultivars were divided into four classes (A–D) based on normalized wilt incidence (NW) and four classes based on normalized defoliation ratings (ND). Classes were determined through a mixed model analysis of cultivars, with T-test comparisons between a partially resistant check (Fibermax 2484B2F) and a susceptible check (Deltapine 0912B2RF). The A and C classes did not differ (P = 0.05) from the partially resistant and susceptible checks, respectively. Classes were used in a mixed model analysis with lint yield. In a model with only NW classes, lint yield decreased significantly as NW increased with least square mean values of 1421, 1385, 1284 and 1204 kg/ha, for classes A, B, C and D, respectively. In a model with both NW and ND classes, the A/A class combination of NW and ND had a significantly (P ≤ 0.05) higher lint yield (1776 kg/ha) than any other combination. NW/ND class combinations of A/B, B/A, B/B, and C/A had intermediate yields, and ND classes of C or D had the lowest yields. Cultivars with both low wilt and defoliation incidences should result in higher yields in fields infested with Verticillium dahliae. Furthermore, these two rating criteria could be used to standardize the process for developing resistant cultivars.  相似文献   

20.
The effects of water stress on Fusarium foot and root rot in durum wheat were investigated in growth chamber, greenhouse and field tests in Tunisia. In the seedling stage, emergence of six durum wheat cultivars in the growth chamber was significantly reduced by inoculation with Fusarium culmorum and water stress (P<0.0001), with more disease under drier conditions. Additionally, the tiller number per mature plant, the 1000 grain weight and disease severity in mature stage were reduced by inoculation in greenhouse studies. In a field test, inoculation with F. culmorum significantly reduced the yield (P<0.001), by more than 17% for Om Rabiaa and 38% for Karim, the two cultivars tested. Yield was also significantly affected by precipitation and irrigation levels. The severity of the disease, estimated by the percentage of white heads, was separately affected by the cultivar (P<0.001) and inoculation (P = 0.0004). Percentage of white heads was 1.5 and 2 × higher in inoculated plants than non-inoculated for Om Rabiaa and Karim cultivars, respectively. Disease severity was highest in treatments with the greatest water stress. This is the first detailed study of water stress and F. culmorum on durum wheat in Tunisia, and indicates that cultivar resistance and irrigation management may be important in the management of Fusarium foot rot.  相似文献   

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