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1.
This paper deals with a study on the effects of mixtures of partially resistant cultivars in focus forming plant diseases. The focus expansion velocity in a mixture of two partially resistant cultivars depends on four parameters, the focus expansion velocity in a crop of cultivar 1 only and in a crop of cultivar 2 only, the net-reproduction in a crop of cultivar 1 and of cultivar 2, respectively.An explicit equation is developed for the damage of a cultivar mixture where the crop is infected by two physiological races of the pathogen. It is shown that cultivar mixtures exist where damage is smaller than in crops of either of the two cultivars only. A simple explicit formula is given on the basis of which it can be decided whether an optimal mixture exists for a given pathosystem.  相似文献   

2.
This study follows on from a previous study showing that binary mixtures of wheat cultivars affect the evolution of Zymoseptoria tritici populations within a field epidemic from the beginning (t1) to the end (t2) of a growing season. Here, we focused on the impact of interseason sexual reproduction on this evolution. We studied mixtures of susceptible and resistant cultivars (carrying Stb16q, a recently broken-down resistance gene) in proportions of 0.25, 0.5 and 0.75, and their pure stands. We determined the virulence status of 1440 ascospore-derived strains collected from each cultivar residue by phenotyping on seedlings. Virulence frequencies in the ascospore-derived population were lower in mixtures than in pure stands of the resistant cultivar, especially in the susceptible cultivar residues, as at t2, revealing that the impact of mixtures persisted until the next epidemic season (t3). Surprisingly, after sexual reproduction the avirulence frequencies on the resistant cultivar residues increased in mixtures where the proportion of the susceptible cultivar was higher. Our findings highlight two epidemiological processes: selection within the pathogen population between t1 and t2 driven by asexual cross-contamination between cultivars (previous study) and sexual crosses between avirulent and virulent strains between t2 and t3 driven by changes in the probabilities of physical encounters (this study). Mixtures therefore appear to be a promising strategy for the deployment of qualitative resistances, not only to limit the intensity of Septoria tritici blotch epidemics, but also to reduce the erosion of resistances by managing evolution of the pathogen population at a pluriannual scale.  相似文献   

3.
Mixtures of cultivars with contrasting levels of resistance can suppress infectious diseases in wheat, as demonstrated in numerous field experiments. Most studies focus on airborne pathogens in bread wheat, while splash-dispersed pathogens have received less attention, and no studies have been conducted in durum wheat. We conducted a 2-year field experiment in Tunisia to evaluate the performance of cultivar mixtures with varying proportions of resistance (0%–100%) in controlling the polycyclic, splash-dispersed disease septoria tritici blotch (STB) in durum wheat. To measure STB severity, we used a high-throughput method based on digital image analysis of 3,074 infected leaves collected from 42 and 40 experimental plots during the first and second years, respectively. This allowed us to quantify pathogen reproduction on wheat leaves and to acquire a large data set that exceeds previous studies with respect to accuracy and precision. Our analyses show that introducing only 25% of a disease-resistant cultivar into a pure stand of a susceptible cultivar provides a substantial reduction of almost 50% in disease severity compared to the susceptible pure stand. However, incorporating two resistant cultivars instead of one did not further improve disease control, contrary to predictions of epidemiological theory. Susceptible cultivars can be agronomically superior to resistant cultivars or be better accepted by growers for other reasons. Hence, if mixtures with only a moderate proportion of the resistant cultivar provide a similar degree of disease control as resistant pure stands, as our analysis indicates, such mixtures are more likely to be accepted by growers.  相似文献   

4.
Focus expansion of bean rust in cultivar mixtures   总被引：1，自引：0，他引：1  
Radial expansion of foci in mixtures of susceptible and resistant bean cultivars was studied at two sites in Ethiopia. The foci expanded in a wave-like fashion. At Ambo (1990), radial expansion velocity ranged from 6 cm per day in mixtures with 20% susceptible plants to 15 cm per day in plots with the susceptible plants only. At Debre Zeit, the velocity ranged from 3 cm per day in a mixture with 20% susceptible plants to 16 cm per day in plots with 100% susceptible plants. At both sites the radial expansion velocity of foci correlated linearly with the logarithm of the fraction of susceptible plants in the mixture. Velocities of focus expansion at Ambo and Debre Zeit were approximately equal in plots consisting of susceptible plants only. At lower proportions of susceptible plants the velocities at Debre Zeit were lower than at Ambo. Indications were given as to the environmental factors responsible for the observed difference between sites. At each site, the variation between plots showed a clear spatial pattern, probably due to environmental factors.  相似文献   

5.
The effect of two‐component rice cultivar mixtures on the control of rice blast disease was studied in three different experiments under rainfed upland conditions in the Madagascar Highlands. The mixtures involved a susceptible cultivar (either susceptible or very susceptible) and a resistant cultivar in different mixture arrangements (random or row mixtures) and with different proportions of the susceptible cultivar (50, 20 and 16·7%), which were compared to the susceptible cultivar grown in a pure stand. The effect of these mixtures on the incidence and severity of leaf and panicle blast was measured weekly, and on yield and yield components at harvest time. The mixture effect was more efficient in reducing disease with a proportion of 16·7% susceptible component than with a proportion of 50%. Blast epidemic was significantly reduced in all three experiments. However, under high blast pressure, there was no reduction in the disease by the end of the epidemic and yields of the susceptible cultivar were almost zero whatever the mixture. In two other experiments performed under lower blast pressure, disease incidence and severity were significantly lower in mixtures, and yields of the susceptible cultivars grown in mixtures were higher than those of their respective pure stands. Cultivar mixtures are a promising strategy that could contribute to a more sustainable cultivation of rice under upland conditions in the context of subsistence agriculture in Madagascar, where all cropping operations are manual.  相似文献   

6.
The use of cultivar mixtures is increasingly practical in wheat stripe rust management. Field experiments with wheat cultivar mixtures were conducted to determine their effects on temporal and spatial patterns of stripe rust epidemics in three regions. In the Beijing and Gangu fields, where the epidemics were caused by artificial inoculation, disease incidence and the area under the disease progress curve (AUDPC) of the cultivar mixtures were significantly lower (P < 0.05) than those of the susceptible pure stands. We defined the relative effectiveness of cultivar mixture on disease development related to that in pure stands (REM). The results demonstrated that in many treatments of mixtures of susceptible cultivar with resistant cultivars at various ratios in different locations, their effects on disease reduction were positive (REM < 1). The reduction of epidemic rate in cultivar mixtures expressed in either early season or late season depended on the initial pattern of disease and cultivar mixture treatments. Semivariograms were used to determine the spatiotemporal patterns of disease in the Gangu field. The spatial analysis showed clear spatial patterns of the disease in all four directions of the fields on susceptible pure stands but not on cultivar mixtures. The results implied that the mechanisms of cultivar mixture on disease management might include the interruption of disease spatial expansion and a physical barrier to pathogen inoculum by resistant cultivars.  相似文献   

7.
The effects of two mixtures of resistant and susceptible apple cultivars on the development of scab caused by Venturia inequalis were observed in an experimental orchard over four years, initially for two years without fungicides against scab, and subsequently for two years with a moderate fungicide schedule. The row-by-row and within-row mixtures included a susceptible cultivar and a resistant cultivar in equal proportions. Without fungicides, the results showed a significant reduction of disease incidence over both years (7·3 to 21·3%), and severity in the second year (35·4%) in the within-row mixtures, compared to the monoculture of the susceptible cultivar. The best results were obtained when the within-row mixture was associated with moderate fungicide treatments; in this case the reduction in disease incidence reached 75·1% on leaves and 69·7% on fruits during the growth phase. The characteristics of the Venturia inaequalis / Malus  ×  domestica pathosystem and the results obtained in this experiment suggest a moderate but not negligible ability of cultivar mixtures for reducing epidemics of the disease.  相似文献   

8.
The multiplication of Soil-borne wheat mosaic virus (SBWMV) was studied in mixtures of two winter wheat (Triticum aestivum) cultivars, one susceptible (Soissons) and the other resistant (Trémie). Two seed mixtures of susceptible and resistant varieties in ratios of 1 : 1 and 1 : 3 and their component pure stands, i.e. each variety grown separately, were grown in a field infected with SBWMV. The presence of the virus was detected using DAS-ELISA from January to May. The resistant cultivar Trémie showed no foliar symptoms nor could the virus be detected in the leaves or roots. In May, about 88% of plants of susceptible cultivar Soissons grown in pure stands were infected. At this time, the disease reduction relative to pure stands was 32.2% in the 1 : 1 mixture and 39.8% in the 1 : 3 mixture. Optical density (OD) values from ELISA of the infected plants in the two mixtures were consistently lower than that of the infected plants in cultivar Soissons in pure stands. The ELISA index (EI) calculated using three scales of OD values was 65.5% in the susceptible cultivar in pure stands. The value for this index was 19.1% in the 1 : 1 mixture and 7.9% in the 1 : 3 mixture. The plants of the resistant cultivar Trémie infected in the same field and transferred in January to a growth cabinet at 15 °C multiplied the virus and produced viruliferous zoospores. These results show that the resistant cultivar Trémie plays a role in disease reduction in the cultivar mixtures in field conditions. Possible reasons for this are discussed.  相似文献   

9.
Disease seventy and crop yield were compared in monocultures and mixtures of two wheat cultivars. one susceptible and one resistant to Puccinia graminis f. sp. tritici. Part of each plot was inoculated and part treated with fungicide. Rust seventy was inversely related to the proportion of resistant plants present. Weight of grain in 100 heads of the susceptible cultivar increased as the amount of rust decreased. The susceptible cultivar yielded less than the resistant cultivar in monoculture, but was a stronger competitor in mixtures. Competitive abilities of the cultivars were independent of severity of rust in the mixtures studied.  相似文献   

10.
Pure stands of a yellow rust-susceptible wheat cultivar, pure stands of a resistant cultivar, and a 1 : 1 random mixture of resistant and susceptible cultivars were compared to populations in which strips or hills of the cultivars were alternated to attain genotype units (units of the same host genotype) that were larger in area than that of a single wheat plant. These four host populations were grown in plots of different sizes in order also to alter the number of units per host population. The goal was to determine if increasing the number of genotype units in mixed populations of large genotype units improved disease control relative to pure-line populations by increasing the amount of inoculum exchange among genotype units. Random mixtures of the two cultivars always provided better disease control than did alternating strips or hills. Evidence for an effect of genotype unit number on the efficacy of mixtures for rust control was found in only one of three experiments. Random mixtures of the two cultivars increased grain yield relative to the pure stand mean, but alternating strips did not.  相似文献   

11.
Late blight, caused by Phytophthora infestans , is the most severe disease of potato worldwide. Controlling late blight epidemics is difficult, and resistance of host cultivars is either not effective enough, or too easily overcome by the pathogen to be used alone. In field trials conducted for 3 years under natural epidemics, late blight severity was significantly lower in a susceptible cultivar growing in rows alternating with partially resistant cultivars (mixtures) than in unmixed plots of the susceptible cultivar alone. Partially resistant cultivars behaved similarly in unmixed and mixed plots. Mixtures of cultivars reduced disease progress rates and sometimes delayed disease onset over unmixed plots, but did so significantly only for the slowest epidemic. This suggests that reduction of area under the disease progress curve (AUDPC) in mixtures resulted from the cumulative action of minor effects. Disease distribution was focal in all plots at all dates, as shown by Morisita's index values significantly exceeding 1. Significant yield increases for the susceptible cultivar, and occasionally for the partially resistant ones, were observed in mixed-cultivar plots compared with single-cultivar plots. These results show that cultivar mixtures can significantly reduce natural, polycyclic epidemics in broadleaved plants attacked by pathogens causing rapidly expanding lesions.  相似文献   

12.
The use of cultivar mixtures to control foliar fungal diseases is well documented for windborne diseases, but remains controversial for splash‐dispersed diseases. To try to improve this strategy, a cultivar mixture was designed consisting of two wheat cultivars with contrasted resistance to Mycosphaerella graminicola , responsible for the rainborne disease septoria tritici blotch (STB), in a 1:3 susceptible:resistant ratio rather than the 1:1 ratio commonly used in previous studies. The impact of natural STB epidemics in this cultivar mixture was studied in field experiments over 4 years. Weekly assessments of the number of sporulating lesions, pycnidial leaf area and green leaf area were carried out on the susceptible cultivar. In years with sufficient STB pressure, disease impacts on the susceptible cultivar in the mixture were always significantly lower than in the pure stand (e.g. 42% reduction of pycnidial leaf area for the three upper leaves in 2008 and 41% in 2009). In years with low STB pressure (2010 and 2011), a reduction of disease impacts was also shown but was not always significant. After major rainfall events, the number of sporulating lesions observed on the susceptible cultivar after one latent period was reduced on average by 45% in the mixture compared to the pure stand. All the measurements showed that a susceptible cultivar was consistently protected, at least moderately, in a mixture under low to moderate STB pressure. Therefore, the results prove that the design of an efficient cultivar mixture can include the control of STB, among other foliar diseases.  相似文献   

13.
Five winter wheat cultivars, six two-component cultivar mixtures, and one four-way mixture were grown in the presence of yellow rust, eyespot, both diseases, and neither disease for three seasons. On average, mixtures reduced the severity of yellow rust relative to their component pure stands by 53%. The four-component mixture provided better yellow rust control than did the two-way mixtures. Eyespot severity was reduced through mixing only in the absence of yellow rust and by only three of the seven mixtures (mean reduction = 13%). Yellow rust was 13% less severe in the presence of eyespot, and eyespot was 10% more severe in the presence of yellow rust. Averaged over all years, the mixtures increased yield relative to the pure stands by 6·2, 1·7, 7·1, and 1·3% in the presence of yellow rust, eyespot, both diseases, and neither disease, respectively. Two mixtures provided significant yield increases over the means of their component pure stands (7% and 9%) in the presence of eyespot even though one of them did not significantly reduce eyespot severity. Accounting for all disease treatments and years, four mixtures provided distinctly higher yield increases than the other three. In mixtures containing a resistant cultivar and a cultivar susceptible to eyespot, yield loss by the susceptible cultivar was not compensated for by increased yield of the resistant cultivar. The mixtures showed improved yield stability relative to the pure stands, with the four-component mixture being particularly stable.  相似文献   

14.
ABSTRACT Cultivar mixtures can reduce potato late blight severity on susceptible cultivars. While alternating rows of susceptible and resistant cultivars would be more acceptable than random mixtures for commercial use, they increase the genotype unit area, which is an unfavorable factor for mixture efficiency, and have been minimally efficient when disease pressure is high. The effects of disease pressure on the performance of alternating rows of cultivars possessing various types and levels of resistance were investigated in 2000 and 2001 near Quito, Ecuador, where natural pressure of late blight is high. The experiments included the highly susceptible cvs. Cecilia in 2000 and LBr37 in 2001, as well as C114 (moderately resistant) and PAN (highly resistant), planted as pure stands and as the three possible two-way combinations. Different disease pressures were obtained with three spraying schedules of a contact fungicide: nontreated, one spray every second week, and one spray weekly. The area under the disease progress curve (AUDPC) on the susceptible cultivar was 0 to 20% less in mixed than in pure plots when no fungicide was applied, 13 to 26% less with a biweekly application of fungicide, and 32 to 53% less with a weekly application. These values are comparable to those obtained in previous experiments in smaller plots with designs maximizing the distance between susceptible plants. No significant differences in mixture performance were observed according to the resistant cultivar included. Effects on yield were minimal, because of the impact of factors other than late blight. Disease pressure therefore appears as a major factor conditioning the efficiency of potato cultivar mixtures against late blight.  相似文献   

15.
许韬  徐志  徐媛  段霞瑜 《植物保护》2014,40(3):87-93
对品种混合种植控制小麦白粉病的效果以及对小麦穗重、千粒重、蛋白质等指标的影响进行了研究,为混合种植控制白粉病提供理论依据和品种组合。在对37个小麦品种进行SSR多样性分析的基础上,选用8个生产品种（后备品种）,按品种数3、4、5、6、8进行组合,在田间以随机区组设计种植混播组合和单播小区,人工接种白粉菌,比较各小区中小麦白粉病的AUDPC值、穗重、千粒重和粗蛋白差异。结果表明,8个品种亲缘关系较远;4品种混种时AUDPC最小,穗重最重。26个品种混种组合中有防治效果的组合占到73.08%,相对防效为1.23%~56.65%;混种未对穗重和粗蛋白含量造成负面影响。品种多样性种植可以用做调控小麦白粉病的一项措施。  相似文献   

16.
Seven 5—month-old sugarcane cultivars difTering in resistance to leaf scald disease were inoculated by the decapitation technique with Xanthomonas albilineans. The effects of disease progress and incidence on yields were studied for the plant (first harvest) and two ratoon crops (second and third harvest). The percentage of diseased stalks and disease severity at first harvest 5 months after inoculation were 0·7 and 0·4, respectively, for the most resistant cultivar and 71·0% and 63·3, respectively, for the most susceptible cultivar. They decreased in all cultivars in both ratoon crops, but were still important in one cultivar (B69379). Significant ( P = 0·05) yield reductions of 12% and 21% occurred in two of the seven cultivars (B69566 and B69379, respectively). The number of symptomatic sugarcane stalks in the first ratoon crop (second harvest) was lower than the number of stalks colonized by the pathogen. Symptoms and yield losses of cultivars R570 and B69566 varied with the crop. Yield losses occurred in cultivar R570 only in the plant crop when this cultivar displayed numerous symptoms. Cultivar B69566 appeared to recover from the disease to a certain extent from the plant to the second ratoon crop (third harvest), as did the resistant cultivars in the first ratoon crop. In contrast, severe leaf scald symptoms were observed in the case of cultivar B69379 regardless of the crop, and significant yield losses occurred in the two ratoon crops. These results support the recommendation that cultivar B69379 should not be replanted in Guadeloupe.  相似文献   

17.
X.‐M. Xu 《Plant pathology》2011,60(5):857-865
A simulation study was conducted to investigate epidemic development of a race‐specific pathogen in cultivar mixtures over six consecutive seasons where the spatial position of each mixture component was systematically altered between seasons. Results showed that, even for a relative large genotype unit area in a mixture, altering cultivar positions between seasons could, on average, increase disease suppression by a third over the corresponding mixture without position changes between seasons. Overall, the disease suppression achieved by mixtures with position change between seasons was close to that achieved by random mixtures. Greater redistribution distance of overwintered inoculum reduced the disease control efficacy achieved by change in the position of individual mixture components between seasons. It is therefore concluded that using mixtures with a relatively large genotype unit area together with systematic changes in the spatial positions of individual mixture components between seasons is a feasible option for integrated disease management.  相似文献   

18.
Four winter wheat ( Triticum aestivum ) cultivars and three two-component cultivar mixtures were planted in a replacement series both inoculated with or protected from yellow rust ( Puccinia striiformis ) in three environments. Each cultivar was susceptible to one or two of the rust races used. Mixtures yielded, on average, 7 and 4% more than their component pure stand means under inoculated and rust-free conditions, respectively. Though all yield components were affected by yellow rust, seed weight was the component that was most consistently influenced. The component genotypes within mixtures varied considerably with respect to yield, and the yield of the same component cultivar included in different mixtures sometimes differed significantly. The correlation between yellow rust severity/tiller and grain yield/tiller in mixture differed among cultivars and depended on their companion cultivar. Variance component analysis indicated that yellow rust was the most important experimental variable influencing grain yield. There was no relationship between yield of the cultivars in pure stands and their yields or competitive abilities in mixture. Disease did not change the competitive ranking of cultivars in mixture. Mixtures with complementary, negative, and overcompensatory interactions were identified. On average, mixtures showed no greater yield stability than did pure stands.  相似文献   

19.
Joint action of fungicides in Mixtures: Theory and practice   总被引：1，自引：0，他引：1  
Y. Cohen  Y. Levy 《Phytoparasitica》1990,18(2):159-169
Fungicide mixtures aimed at the control of multiple target organisms have been used since the middle of this century. In the 1970s synergistic mixtures of site-specific (high resistance-risk) fungicides with multi-site (low resistance-risk) fungicides became available with the aim to provide adequate disease control while maximizing evolutionary problems for the pathogen. In the 1980s there were introduced mixtures of negatively correlated fungicides, in which each ingredient is capable of controlling pathogen genotypes resistant to the other ingredient. Such fungicides are currently deployed in the form of homogeneous mixtures (tank mixes, prepacked mixtures). A new strategy is under development in which different fungicides are applied to different adjacent plants. Diversification of cultivars and fungicides in a crop may minimize the buildup of resistance and maximize disease control.  相似文献   

20.
Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria  相似文献   

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