Estimating potato yield responses from chemical control of early blight in Minnesota

The effect of early blight on tuber yield of two potato (Solanum tuberosum L.) cultivars (Russet Burbank and Norland) was evaluated using number and timing of applications of three chemicals to generate different disease epidemics in 1981 and 1982. Under the non-irrigated farming conditions in Minnesota, there were no significant differences among captafol, triphenyltin hydroxide and maneb-Zn in blight control to increase yield. Of the five spray schedules tested, a 7–10 day spray schedule initiated when blight severity exceeded 0.01%, and a 7–10 day schedule initiated when blight was found above the lower third of the plant, generally gave significant, positive yield responses with all three chemicals. At Rosemount in 1982, the greatest yield increases (relative to unsprayed) obtained were 34.9% and 48.6% in total tuber yields for Norland and Russet Burbank, respectively. At Rosemount in 1982, the highest yield increases (relative to unsprayed) obtained were 92.2% and 56.6% in total tuber yields for Norland and Russet Burbank respectively. At Grand Forks in 1981, the highest yield increases were 126.8% and 34.6% in total tuber yields for Norland and Russet Burbank respectively. Across all three experiments, maximum yield losses (percentage of [[yield of ‘healthy’—yield of unsprayed check]/yield of ‘healthy’’]) were 58.4% (US #1 tubers) and 55.9% (total tubers) for cv. Norland and 34.4% (US #1 tubers) and 36.2% (total tubers) for cv. Russet Burbank.     

A method for estimating the loss in tuber yield caused by late blight of potato

A method was developed for estimating tuber yield losses caused by late blight of potato (Phytophthora infestans) (Mont.) de Bary. The method is based on yield and disease data collected for the varieties Green Mountain and Katahdin grown in eastern Canada during the period 1953–1970. The percentage yield loss can be calculated for any disease progress curve. The estimated loss was within 5% of the actual loss in nine cases out of ten.     

Potato yield losses due to early blight in Minnesota fields, 1981 and 1982

In both 1981 and 1982, 51 potato fields were surveyed every 7–10 days for early blight severity and fungicide use. Early blight severity data from each field were used as input to a regression model to estimate yield loss in that field. The model for early maturing potato cultivars was Percent Yield Loss=0.8183+0.6441* (% blight increment between days 56 and 66)+0.6102* (% blight increment between days 66 and 76)+1.3480* (% blight increment between days 76 and 86). The model for late maturing cultivars was Percent Yield Loss=2.1846-4.7734* (% blight on day 56)+0.7440* (% blight on day 76)+ 0.5676* (% blight on day 96). In both 1981 and 1982, early blight was found to be present in all fields of the survey. In 1981, early blight was estimated to have caused mean losses of 6.5% (Red River Valley), 3.7% (Central sands) and 2.3% (Southern muck). In 1982, losses from the same areas were 5.4%, 3.7% and 2.6% respectively. In 1981, individual county losses ranged from 2.3% for Freeborn to 12.9% for Marshall while in 1982 losses were from 2.0% for Freeborn to 6.7% for Clay. Although fungicide use data were incomplete, the county with lowest yield loss had the most fungicide applications.     

Chemical control of potato early blight and its effect on potato yield

Potato early blight infection was reduced significantly by Daconil 2787, Difolatan and Manzate D. Rates of 0.50 1b/A to 1.5 1b/A were effective until inoculum loads increased as the season progressed then the higher rates were significantly more effective than the lower ones. Consistent yield increases in the range of 18 to 39% were demonstrated when early blight was controlled. Statistically significant yield increases were shown in seasons when severe Verticillium wilt or early killing frosts did not shorten the growing season and negate the beneficial effects of early blight control.     

Assessing progenies of potato for resistance to early blight

Summary Progenies from crosses between cultivars varying widely in resistance to early blight (Alternaria solani Sor.), were assessed for resistance as true seedlings in a glasshouse in Scotland. The resistance of a representative sample of surviving genotypes from each progeny was compared with samples of the same progenies not previously exposed to the fungus, both in the glasshouse in Scotland and in the field in Israel. The exposed population was more resistant. Resistance was identified more effectively in adult plants from tubers in the glasshouse than in true seedlings and agreement between glasshouse and field assessment was better when progenies were compared rather than individual genotypes. The mid parent and progeny mean scores of the unexposed population were correlated at both sites, thus confirming that the resistance is heritable. Selecting resistant individuals at the seedling stage is suggested as a useful tool for resistance breeding, having first chosen the best parents for crossing.     

Crop loss prediction tables for potato late blight epidemics

American Journal of Potato Research - The yield loss prediction equation of MacKenzie and Petruzzo was used to determine expected yield losses resulting from over 1000 computer-generated late...     

A method for estimating the decrease in marketable tubers caused by potato late blight

A regression analysis was used to develop a method to estimate the decrease in marketable tubers caused by late blight of potato (Phytophthora infestans), based on estimates of percentage loss in total tuber yield computed from a published method. The economic loss due to late blight in table stocks is the relative percentage marketable yield loss, calculated from the expression: {fx19-01} when total yield losses (in percentage) did not exceed 40%. A graphical method is presented as an alternative. Yield results from seven field experiments conducted in the Maritime Provinces of Canada during the period 1953 to 1971 were used in the study, where marketable tubers were defined as 2 1/4 inch or more in diameter.     

Approaches to control of potato early dying caused byVerticillium dahliae

Potato early dying disease, caused byVerticillium dahliae, may be either suppressed or controlled by a variety of procedures. These methods include the growing of resistant cultivars, attention to cultural management, utilization of pesticides, and solar heating of soils. The greatest successes in control of Verticillium wilt have been achieved with the use of either soil fumigants or clonal resistance, but these approaches have been restricted. Widespread use of fumigants has been limited by cost, and the lack of commercial acceptance has often restricted the utilization of resistant potato cultivars. The Katahdin and Targhee cultivars are currently available with resistance and/or tolerance to this disease. The Russet Burbank potato also possesses a limited degree of resistance to the fungus, and with this resistance, the disease appears to be suppressed by optimal growing conditions. In potato fields that have been cropped for several years, disease suppression in Russet Burbank was found to be related to methods of irrigation and increased nitrogen availability. It is suggested that improved utilization of resistant germplasm and effective use of biological control strategies may ultimately lead to economical control of this disease.     

Integrating a host-resistance factor into the FAST system to forecast early blight of potato

A host resistance factor was integrated into the FAST (Forecaster ofAlternariasolani onTomatoes) system to initiate and to schedule fungicide applications for three levels of potato cultivar susceptibility while maintaining disease control and yield. Four cultivars ranging from susceptible to moderately resistant were each treated with the fungicide chlorothalonil during two field seasons. The five fungicide treatments were a 7-day schedule initiated after 50% flowering; a non-sprayed control; and three FAST application schedules based on combinations of critical levels of cumulative severity (CS, the disease severity values as a function of leaf wetness and temperature) and cumulative rating (CR, the disease rating values as a function of average temperature and hours of relative humidity greater than 90%) values. The FAST system predicted the onset of early blight and subsequent periods conducive for disease development in 1993 and 1994. There were cultivar-by-spray-schedule interactions for both disease severity and yield, suggesting that differences in early blight sus-ceptibility exist between cultivars. Use of the recommended schedules for the cultivar’s targeted level of susceptibility reduced early blight severity and minimized fungicide use while maintaining yield. These results indicate that a host-resistance factor can be incorporated into the FAST system.     

Heterosis and combining ability analysis for resistance to early blight (Alternaria solani) in potato

Summary In an epiphytotic year of early blight, data were recorded on its incidence in 72 progenies (18 females x 4 males) and their parents planted in a randomised complete block design at the Punjab Agricultural University, Ludhiana, India. Combining ability analysis showed that both additive and non-additive gene action were important, with a preponderance of the latter in the inheritance of resistance to early blight. In general, progenies were as good as or better than mid-parent values. Crosses involving both or at least one parent with good general combining ability resulted in heterotic early blight resistant progenies. Promising parents and crosses were identified.     

Breeding for resistance to late blight in the potato

American Journal of Potato Research -     

灰斑病所致大豆品质与产量损失的研究

采用不同病叶、病粒,对大豆灰斑病所致大豆品质和产量的影响进行了研究,结果发现:灰斑病直接影响大豆叶片全N含量及籽粒氨基酸与蛋白质含量.叶片中的全N含量随病情加重而减少,病粒中17种氨基酸总量、蛋白质和脂肪含量与病叶一样也随病情加重而递减.灰斑病引致的大豆产量损失与病粒率和籽粒病指相关密切,与病粒率的相关系数为0.9723,与籽粒病指的相关系数为0.9763.根据相关系数建立两个方程,用(Y)=-0.1890 1.4063X10.7993(X1病粒率)和(Y)=2.6034 1.338X2(X2病指)可预测大豆由灰斑病病粒引致的减产量,用n'=Int[(YBL×100-8)]/(5 1)可预测当年大豆的等级,并以EL=YM×(1-YLL)×PWn'预测经济损失.     

花生品系对白绢病的抗性评价及产量损失研究

选取中国农业科学院油料作物研究所培育的10个花生新品系,通过自然发病和人工接种两种方法进行了白绢病抗性鉴定和产量损失研究。结果表明,在自然发病条件下,10个新品系由白绢病造成的枯萎率为11. 0%~50. 0%,其中7个品系白绢病枯萎率低于30. 0%;白绢病枯萎率与花生荚果产量呈显著负相关(r=-0. 73,P <0. 05)。在田间人工接种条件下,接种2周后,10个品系导致的植株枯萎率为66. 1%~94. 0%,收获前的白绢病枯萎率为66. 1%~97. 4%,均为感病品系;白绢病导致的植株枯萎率与花生荚果产量的相关系数为-0. 85(P <0.05)。产量损失试验表明,在人工接种条件下,所有品系产量损失均超过91. 7%,严重者几乎绝产。综合田间自然发病和人工接种鉴定,获得一份耐病品系16-A13440。     

Evaluation of sprinkler application of fungicides for control of potato early blight in Colorado

Sprinkler application of four fungicides, Du-Ter 47.5% W.P. (0.70 kg/ha), Difolatan 4F (3.51 1/ha), Bravo W-75 (1.68 kg/ha) and Bravo 500 (1.17 1/ha, 1.761/ha and 2.341/ha) were evaluated in Colorado for control of potato early blight caused byAlternaria solani (Ellis & G. Martin) L.R. Jones and Grout and compared to the conventional method of airplane application. Fungicides applied through center pivot irrigation systems generally achieved disease control equal to airplane application. Application of fungicides through both center pivot sprinklers and by airplane effectively reduced early blight infection. Control of early blight by airplane or sprinkler application of fungicides significantly (P = 0.05) increased potato yields in 1978. In other years (1977, 1979 and 1980) fungicide applications which reduced disease severity generally increased tuber yields but the increases were not significant when compared to the control.     

Influence of potato cultivars on the effectiveness of fungicide control of early blight

Three potato cultivars differing in degree of susceptibility to early blight were grown under crop management practices typical for Pennsylvania in 1987 and 1988. There were three experimental treatments: no fungicides, mancozeb with weekly applications initiated at 7 or 8 weeks after planting (early treatment), and weekly applications initiated at first symptoms of disease (late treatment). The no-fungicide control treatment had significantly higher AUDPC values than either treatment with fungicides and the no-fungicide treatment had significantly lower yield in 1987 but not in 1988. Tubers from the no-fungicide control had lower specific gravity. Norchip, the cultivar most susceptible to early blight examined in this study, responded the most in yield increases by the increased fungicide applications.     

The effect of soil pH on yield losses caused by the potato cyst nematodeGlobodera pallida

Summary The effect of soil pH on yield losses due to potato cyst nematodes (Globodera pallida) was investigated in experiments in the field and in a semi-controlled environment. Through annually liming a reclaimed peat soil with about 22% organic matter, plots with pH levels of 4.5, 5.0, 5.5, 6.0 and 6.5 were obtained. In 1990 potato yields in these plots decreased from 45 t/ha at pH 4.5 to 33 t/ha at pH 6.5, whereas the nematode densitites decreased from about 18 to 9 juveniles per g soil. In a container experiment a strong interaction was recorded between soil pH and the presence of nematodes. Tuber yields were about 11% lower at pH 6.5 than at pH 4.5 in the absence of nematodes, but about 44% lower when an initial population of 27 juveniles per g soil was present.