Assessment of partial resistance to powdery mildew in Chinese wheat varieties

Field trials in two cropping seasons and two locations in central China were conducted on 60 Chinese autumn‐sown wheat varieties to assess their partial resistance to powdery mildew. Mean levels of disease severity ranged from close to 0 to more than 90%. The method of inoculation and the location in which trials were conducted affected the relative performance of the varieties, but these effects were much smaller than the main effect of variety. The area under the disease progress curve was highly correlated with final disease severity, but both were poorly correlated with apparent infection rate. Disease severity was regressed against frequencies of virulence in the Blumeria graminis (syn. Erysiphe graminis) f sp. tritici populations in the trial plots. A vertical distance (D) from the mean mildew severity to the fitted line was calculated for each variety and was used to quantify partial resistance. Five of the 60 varieties, ‘Hx8541’, ‘E28547’, ‘Chuan1066’, ‘Zhe88pin6’ and ‘Lin5064’, consistently expressed relatively low levels of disease despite high frequencies of virulence in the pathogen and had consistently high D‐values. They may therefore have good levels of partial resistance.     

Resistance to early blight of tomato with respect to various parameters of disease epidemics

Resistance to early blight in the tomato was assessed by examining various parameters of the progress of the disease. Artificial inoculation and the scoring technique were standardized. Test plants were inoculated with 125cfu/ml of a 12-day-old culture of a pathogenic isolate of Alternaria solani. Screening under artificial conditions was more informative than that under natural epidemic conditions. Tomato cultivars CLN-2071-C, CLN-2070-A, BSS-174, and DTH-7 with resistance expressed as slow blighting against four pathogenic isolates of A. solani, were selected for cultivation in disease-prone areas. Disease intensity increased with the age of plants under the same inoculum load. The area under the disease progress curve (AUDPC) was positively correlated with the percentage disease index and negatively with resistance. Calculation of the apparent infection rate (r) was more informative for natural epidemics than for artificial conditions. The sequential apparent infection rate between observation periods was better correlated with disease progress than was the total apparent infection rate between the first and last observations. A double sigmoidal disease progress curve during the same cropping season was characteristic of some varieties when fungal infection took place during the vegetative phase of crop growth.     

Combining superior agronomic performance and terminal heat tolerance with resistance to spot blotch (Bipolaris sorokiniana) of wheat in the warm humid Gangetic Plains of South Asia

Seven hundred twenty-nine lines of diverse wheat germplasm lines were evaluated in eight locations of three countries (India, Nepal and Bangladesh) of South Asia for 5 years (1999–2000 to 2003–2004) through Eastern Gangetic Plains Screening Nursery (EGPSN) organized by CIMMYT South Asia, Nepal, for agronomic performance and tolerance to spot blotch of wheat. Each year, the number of lines represented a new set of 150 lines that included six common checks and a different local check at each of the eight locations. One hundred and five lines, 21 in each year, advanced from EGPSN were also tested for 5 years (2000–2001 to 2004–2005) in five locations of South Asia through Eastern Gangetic Plains Yield Trials (EGPYT) to verify spot blotch tolerance and superior yield performance of the selected germplasm. Many lines yielded significantly more than the best check and possessed high levels of spot blotch resistance under warm humid environments of South Asia. The most promising 25 lines have been listed as sources of strong resistance, with 9 lines better yielding than the best resistant check PBW 343 in fewer days to maturity. Most of these superior lines represented elite CIMMYT germplasm and around half were derived from Kauz and Veery. The line EGPYT 67, Kauz//Kauz/Star/3/Prinia/4/Milan/Kauz, was the best for spot blotch resistance, yield, days to maturity, and 1000 grain weight (TKW). The next two lines in the order of merit were EGPYT 84 (Mrng/Buc//Blo/Pvn/3/Pjb 81) and EGPYT 69 (Chirya3/Pastor). The results demonstrate that additional spot blotch resistant wheat genotypes with high grain yield and TKW, and early maturity, have become available as a result of the regional and international collaboration in South Asia.     

Fungicide efficacy of dry bean white mold [Sclerotinia sclerotiorum (Lib.) de Bary,causal organism] and economic analysis at moderate to high disease pressure

White mold [Sclerotinia sclerotiorum (Lib.) de Bary, causal organism] is an economically damaging disease of dry bean (Phaseolus vulgaris L.). Producers often require fungicides to control moderate to high disease levels. Evaluation of fungicide efficacy and cost is critical to make cognisant management decisions. Four field studies were conducted at the Huron Research Station, near Exeter, Ontario in 2012 and 2013. Commercially available synthetic fungicides and a biofungicide seed treatment were evaluated for efficacy in suppressing white mold of dry bean and a subsequent economic analysis was conducted. Area under the disease progress curve (AUDPC) was calculated using disease intensity (incidence × severity) ratings. The untreated control and biofungicide seed treatment had the highest AUDPC values, and in addition to the two applications of the low rate of fluxapyroxad + pyraclostrobin and two applications of penthiopyrad, had the lowest yields. The most efficacious products with regard to disease suppression and yield response were two applications of boscalid, all rates of fluazinam and thiophanate-methyl, and two applications of the high rate of fluopyram + prothioconazole. Two applications of the high rate of fluazinam had the lowest AUDPC, which was nearly 60% lower than the untreated control. Two applications of the high rate of thiophanate-methyl was the highest yielding treatment, recovering 70% of yield lost from untreated plots. Economic impacts varied with planting dates. For the first planting, profit margins for all fungicide treatments, with the exception of two applications of penthiopyrad, two applications of the low rate of fluxapyroxad + pyraclostrobin, and the biofungicide seed treatment, were significantly greater than the untreated control. For the second planting, only profit margins for all fluazinam treatments were significantly greater than the untreated control. This study identifies new economically viable fungicide options for dry bean producers to control white mold.     

Effect of microwave radiation on dry bean seed infected with Xanthomonas axonopodis pv. phaseoli with and without the use of chemical seed treatment

Common bacterial blight (Xanthomonas axonopodis pv. phaseoli) is a seed-borne disease that is difficult to control in dry bean (Phaseolus vulgaris L.). Laboratory and field studies were conducted over a two-year period to determine the effect of microwave radiation on navy (cv. Navigator and Envoy) and pinto (cv. AC Ole) bean. Laboratory tests resulted in a 12 to 25% decrease in germination following 50–60 s of radiation, while less than a 10% loss was observed between 0 and 40 s. Pathogen viability was also tested, however the incidence of pathogen infection was low and no correlation was observed between exposure time and the incidence of colonization. In field studies conducted at Morden, MB (2012) and Ridgetown and Exeter, ON (2012–2013) microwave radiation and two chemical seed treatments (copper hydroxide 53.8% and pyraclostrobin + fluxapyroxad + metalaxyl) were evaluated for their effect on emergence, disease infection, seed pick, yield and return on investment. The application of microwave treatment decreased emergence by up to 7%, but did not impact the other parameters measured. Chemical treatment alone or in combination with microwave treatment also did not affect emergence, disease incidence, yield, seed pick, or return on investment.     

Identification and Characterization of Slow Rusting Components in Pea (Pisum sativum L.)

Three hundred and forty five accessions of pea of diverse origin, height, leaf types and disease reaction were screened for rust disease severity and area under disease progress curve (AUDPC). The frequency of slow rusting types in the tall, dwarf, early and late groups appeared comparable. Of the 345 accessions, forty-four genotypes were evaluated for disease intensity, which was converted into AUDPC, number of pustules/leaf and pustule size. Wide range of variation was found for these traits. The slow rusting attribute of 16 genotypes was further confirmed by testing these under unprotected (inoculated) and protected (fungicidal spray) conditions for two successive years for disease intensity by assessing the AUDPC, seed yield/plot, and 100-seed weight. The fast rusting genotypes exhibited lower AUDPC, accompanied with increased seed yield and seed weight when grown under the protected condition, as compared to those raised under the unprotected condition. The genotypes Pant P 11, FC 1, HUDP 16, JPBB 3 and HUP 14 appeared as slow rusting genotypes.     

DNA methylation changes in fusarium wilt resistant and sensitive chickpea genotypes (Cicer arietinum L.)

DNA methylation plays an important role in the regulation of gene expression in biotic and abiotic stresses. In the present study, a methylation-sensitive amplified polymorphism (MSAP) analysis was performed to profile DNA methylation changes in seven resistant and sensitive chickpea genotypes following inoculation with Fusarium oxysporum f. sp. ciceris. In all, 27468 DNA fragments, each representing a recognition site cleaved by either or both of two isoschizomers, were amplified using nine selective primer pairs. DNA methylation was evaluated in leaves, stems and roots in control and inoculated plants. Extensive cytosine methylation alterations were found in the pathogen-treated genotypes compared with the corresponding control, including hypermethylation and demethylation as well as the potential conversion of methylation types. For all genotypes, the percentage of demethylated sites were more than methylated sites in infected plants compared with the corresponding control. No significant differences were observed for banding patterns in infected and control leaf tissues, while the differences between percentage of unchanged, methylated and demethylated sites were significant in stem and root tissues. The total numbers of methylated polymorphic bands ranged from 137 to 154 bands in Sel95th1716 and Arman, accounting for 36.81%–44.64% of all bands, respectively. Ten fragments that were differentially amplified between infected and control plants were isolated and sequenced in three tissues separately. Most of sequenced fragments showed homology with disease related genes in GenBank. The results suggest that significant differences in cytosine methylation exist between resistant and sensitive chickpea genotypes, and that hypermethylation or hypomethylation of specific genes may be involved in the chickpea resistance to Fusarium wilt.     

小麦品种多样性对白粉病及产量和蛋白质的影响

 对品种多样性控制小麦白粉病的效果以及对产量和蛋白质的影响进行了研究,为利用品种多样性控制白粉病提供理论依据和技术支持。采用SSR技术分析5个小麦品种的亲缘关系;2008年和2009年按组合所含品种数为2、3、4和5个进行组合,在田间种植混种组合和单播小区,人工接种白粉菌,比较各小区中小麦白粉病的AUDPC值、产量和蛋白质变化。结果表明,5个品种亲缘关系相对较近;2个品种混合时以抗感搭配较好,随着抗病品种比例增加控病效果增强;2008年混合种植中有防治效果的组合占54.55%,相对防效为10.02%~47.58%,2009年有防治效果的组合占23.08%,相对防效在1.85% 到18.96 % 之间;在适当的组合中,如京冬8号/轮选987、京双16/京411/京冬8号对小麦白粉病有控制效果,混种不会影响产量和蛋白质含量;当有大量能克服本地品种抗性的外来菌源时混合种植的控病效果降低。品种多样性可以用做防治小麦白粉病的一项措施。     

Development of an assessment key and techniques for field screening of tea (Camellia sinensis L.) cultivars for resistance to blister blight

Blister blight caused by the biotrophic fungus, Exobasidium vexans Massee, is the most problematic foliar disease of tea in Sri Lanka. A reliable and accurate method is needed for field assessment of severity of the disease for epidemiological studies, formulating disease control strategies and crop improvement programmes. A field assessment key with 0–6 scores was developed for blister blight, considering the lowest (0) and highest (>30%) limits of disease severity observed in the field and different stages of symptom development. The key was validated by six raters, 3 experienced and 3 inexperienced. The field assessment trials made using the key were accurate and precise (R² > 0.80). The area under the disease progress curve (AUDPC), calculated using the disease severity levels obtained using the assessment key, was used to combine multiple observations of disease progress into a 0–9 susceptible scale. Ascending numbers in the scale represent increasing susceptibility. The new scale was proposed to discriminate blister blight resistance in tea accessions/cultivars in field screening. Screening trials for validation of the susceptible scale, conducted using tea cultivars of known resistance or susceptibility levels and newly developed accessions of tea, at three locations, revealed that the 0–9 scale is simple to apply, offers a fine discrimination of blister blight resistance levels, and allows objective evaluation.