Effect of Metschnikowia pulcherrima and methyl jasmonate on apple blue mold disease and the possible mechanisms involved

Phytoparasitica - Metschnikowia pulcherrima alone and in combination with methyl jasmonate [MeJA] was applied for control of blue mold of apple caused by Penicillium expansum. In vitro, MeJA at...     

Chitosan oligomers and copper sulfate induce grapevine defense reactions and resistance to gray mold and downy mildew

ABSTRACT Chitosan (CHN), a deacetylated derivative of chitin, was shown to be efficient in promoting plant defense reactions. CHN oligomers of different molecular weight (MW) and degree of acetylation (DA) triggered an accumulation of phytoalexins, trans- and cis-resveratrol and their derivatives epsilon-viniferin and piceid, in grapevine leaves. Highest phytoalexin production was achieved within 48 h of incubation with CHN at 200 mug/ml with an MW of 1,500 and a DA of 20% (CHN1.5/20), while oligomers with greater MW were less efficient, indicating that a specific MW threshold could be required for phytoalexin response. Treatment of grapevine leaves by highly active CHN1.5/20 also led to marked induction of chitinase and beta-1,3-glucanase activities. CHN1.5/20 applied together with copper sulfate (CuSO(4)) strongly induced phytoalexin accumulation. CuSO(4) alone, especially at low concentrations also elicited a substantial production of phytoalexins in grapevine leaves. Evidence is also provided that CHN1.5/20 significantly reduced the infection of grapevine leaves by Botrytis cinerea and Plasmopara viticola, and in combination with CuSO(4) conferred protection against both pathogens.     

Inhibition on brown rot disease and induction of defence response in harvested peach fruit by nitric oxide solution

Nitric oxide (NO) is an important signal molecule involved in numerous plant responses to biotic and abiotic stresses. The effect of nitric oxide (NO) solution on pathogen infection and defence response of peach (Prunus persica (L.) Batsch) fruit against brown rot disease caused by Monilinia fructicola was investigated. The results showed that 15 μmol l^?1 NO solution did not significantly inhibit spore germination, germ tube length or pathogenicity of M. fructicola, but significantly reduced disease incidence and lesion areas in the fruit. Although 100 μmol l^?1 NO solution effectively inhibited the spore germination, germ tube elongation and pathogenicity of M. fructicola, the high concentration of NO solution caused damage to the fruit. Moreover, 15 μmol l^?1 NO enhanced the activities of chitinase (CHI) and β-1,3-glucanase (GNS) in the fruit. RT-PCR analysis showed that the expression of four genes, CHI, GNS, pathogenesis-related protein 1 and 10 genes (PR-1, PR-10) all increased after NO treatment. Conversely, pretreatment with 100 μmol l^?1 NO scavenger, 2-4-carboxyphenyl-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), rendered the fruit relatively susceptible to pathogen infection and inhibited the defence response of the fruit. These results suggest that NO solution treatment can protect peach fruit from pathogen infection by inducing the activities of the defence enzymes and the expression of PR genes.     

Flavonols of leaves in relation to apple scab resistance

Journal of Plant Diseases and Protection - Phenolic compounds of three scab-resistant apple cultivars ‘Topaz’, ‘Goldstar’ and ‘Gold Rush’ and two susceptible...     

Magnesium oxide nanoparticles induce systemic resistance in tomato against bacterial wilt disease

Bacterial wilt is a serious problem affecting many important food crops. Recent studies have indicated that treatment with biotic or abiotic stress factors may increase the resistance of plants to bacterial infection. This study investigated the effects of magnesium oxide nanoparticles (MgO NP) on disease resistance in tomato plants against Ralstonia solanacearum, as well as its antibacterial activity. The roots of tomato seedlings were inoculated with R. solanacearum and then immediately treated with MgO NP; the treated plants showed very little inhibition of bacterial wilt. In contrast, when roots were drenched with a MgO NP suspension prior to inoculation with the pathogen, the incidence of disease was significantly reduced. Rapid generation of reactive oxygen species such as O₂^?˙ radicals was observed in tomato roots treated with MgO NP. Further O₂^?˙ was rapidly generated when tomato plant extracts or polyphenols were added to the MgO NP suspension, suggesting that the generation of O₂^?˙ in tomato roots might be due to a reaction between MgO NP and polyphenols present in the roots. Salicylic acid‐inducible PR1, jasmonic acid‐inducible LoxA, ethylene‐inducible Osm, and systemic resistance‐related GluA were up‐regulated in both the roots and hypocotyls of tomato plants after treatment of the plant roots with MgO NP. Histochemical analyses showed that β‐1,3‐glucanase and tyloses accumulated in the xylem and apoplast of pith tissues of the hypocotyls after MgO NP treatment. These results indicate that MgO NP induces systemic resistance in tomato plants against R. solanacearum.     

Preventive and curative activity of postharvest potassium silicate treatments to control green and blue molds on orange fruit

Preventive and curative antifungal activities of postharvest treatments with potassium silicate (PSi) against green (GM) and blue (BM) molds were evaluated on oranges (cvs. ‘Valencia’ or ‘Lanelate’) artificially inoculated in rind wounds with Penicillium digitatum and P. italicum, respectively. The most effective PSi concentration, the effect of fungal inoculum concentration, and the influence of temporal and spatial factors on antifungal activity were assessed in in vivo primary screenings. After 6 days of incubation at 20 °C, significant preventive (treatment before fungal inoculation) and curative (treatment after inoculation) activities against GM and BM were observed with PSi at 90 mM (GM and BM incidence reductions of 23 and 52 %, and 23 and 40 %, respectively). In preventive tests, the effectiveness of PSi was influenced by inoculum concentration (10³, 10⁴, 10⁵, or 10⁶ spores ml^-1), but not by the distance between treatment and inoculation sites (10, 20 or 30 mm). PSi applied about 2 h before inoculation showed higher preventive activity than applied before 24, 48 or 96 h. In order to determine the best dip treatment conditions, PSi at 90 mM was tested at 20 or 50 °C for 60 or 150 s in small-scale trials with ‘Lanelate’ oranges artificially inoculated before or after the treatment and incubated for 7 days at 20 °C. Dips at 20 °C for 60 s were selected and subsequently applied on inoculated ‘Valencia’ oranges stored at 5 °C and 90 % RH for up to 6 weeks. Curative postharvest dips effectively reduced the incidence and severity of both GM and BM during cold storage, while preventive dips significantly reduced the severity but not the incidence. Overall, postharvest PSi treatments showed potential as a new tool to be part of non-polluting strategies to control penicillium decay of citrus fruit.     

梨和苹果种质对阿太菌果腐病菌的抗性评价及其防治药剂筛选

为明确不同梨和苹果种质对阿太菌果腐病菌Athelia bombacina的抗性以及筛选防治其有效杀菌剂,采用离体菌丝块有伤接种方法对40份梨种质和154份苹果种质进行病斑直径测定,通过聚类分析法和平均病斑直径法对不同种质进行了抗病性分级,并利用菌丝生长速率法测定了13种常用杀菌剂对阿太菌果腐病菌的毒力。结果表明,根据聚类分析法和平均病斑直径法均可将梨和苹果种质划分为高抗、抗、中抗、感和高感5类。与平均病斑直径法相比,梨和苹果种质分别以欧式距离为14和10作为最佳聚类分割点时进行聚类分析能够更加科学地划分类别,从40份梨种质中筛选出金锤子梨1个高抗种质,仅占总数的2.50%,从154份苹果种质中筛选出垂丝海棠、莫斯科透明、新疆苹果、路边石、伏帅等32个高抗种质,占总数的22.73%。药剂试验结果表明,戊唑醇、腈菌唑、咯菌腈和噻呋酰胺对阿太菌果腐病菌菌丝生长的抑制效果较好,抑制中浓度EC_(50)分别为0.027、0.048、0.054和0.095 mg/L。表明梨和苹果种质均可被阿太菌果腐病菌侵染,但不同种质间抗病性差异明显,戊唑醇是采前防治阿太菌果腐病菌菌丝生长的最佳药剂。     

In vitro screening for resistance to apple proliferation in Malus species

A screening system for apple proliferation resistance was developed, based on in vitro graft‐inoculation with the causal agent ‘Candidatus Phytoplasma mali’. For this, in vitro cultures of the field‐resistant apomictic genotypes Malus sieboldii, H0909, D2212 and the susceptible Malus × domestica genotypes Golden Delicious and rootstock M9 were established, as well as in vitro cultures of Rubinette and Golden Delicious infected with ‘Ca. P. mali’ strains PM4 and PM6, respectively. Healthy in vitro shoots were inoculated by micrografting with infected shoots used as graft tip. After 6 weeks graft contact no significant differences for graft quality were observed between healthy and infected grafts. Mortality of grafts and transmission rates were not significantly different among the different genotypes. The phytoplasma concentration in inoculated shoots was determined at different times post‐inoculation (p.i.) by quantitative real‐time PCR. Infected M. sieboldii and D2212 had lower phytoplasma concentration than the susceptible controls and showed no symptoms. H0909 showed an intermediate behaviour exhibiting lower phytoplasma concentrations with strain PM4 but growth was affected. The dynamics of phytoplasma concentration reached a maximum at 6–8 months p.i. for all genotypes but the values for 3–5 and 10–12 months p.i. were similar. The resistance of M. sieboldii and D2212 was confirmed in vitro. A significant difference in phytoplasma concentration was observed between strains PM4 and PM6.     

Modified plant architecture to enhance crop disease control: genetic control and possible value of upright fruit position in cucumber

Plant architectural features can facilitate disease control by creating unfavourable environments for pathogen growth or limiting pathogen contact with the host. In the case of Phytophthora capsici infection of cucumber (Cucumis sativus), the susceptible fruit typically lie in contact with soil under warm, moist conditions of a full canopy, an ideal location for exposure to inoculum and disease development. We have shown that increased row spacing, trellising and architectural variants that allow for more open canopies, such as shorter vines, reduced branching, or smaller leaves, can modify microclimate as assessed by temperature at the location of developing fruits. However, only trellising reduced infection rates (<3 % infection vs. 22 % for control). A cucumber accession PI308916, with extremely short internodes and resulting upright position of young fruit, also exhibited reduced disease. Fruit of PI308916 were susceptible when inoculated with P. capsici, indicating that reduced infection likely resulted from decreased soil contact. The compact trait is inherited as a single recessive gene, cp. Like many architectural traits, cp may be pleiotropic; PI308916-derived breeding lines were reported to have poor seedling emergence. PI308916 exhibited inconsistent apical hook formation that co-segregated with short internodes in F₂ and backcross generations, and disorganized internodal cortical cell arrangement. The combined phenotypes suggest either pleiotropy or very tight linkage of genes affecting hormone balance or cell division. The narrow chromosome region recently defined by QTL analysis includes candidate gene homologs of meristem related genes modulating cell division or spacing of lateral shoot organs and genes associated with brassinosteroid signaling or cytokinin content.     

Evaluation of screening methods and fruit composition in relation to anthracnose fruit rot resistance in blueberries

Anthracnose fruit rot is an important disease of blueberries, and losses are common in humid growing regions. Most commercial cultivars are susceptible and the disease is usually managed with fungicides. However, a few cultivars are considered resistant. The objectives of this study were to: (i) compare different inoculation techniques for anthracnose fruit rot resistance screening, (ii) screen ripe fruit from a range of blueberry cultivars using selected techniques, and (iii) investigate the role of fruit characteristics in anthracnose fruit rot resistance. The following inoculation methods were evaluated on ripe fruit of a susceptible and resistant cultivar using a conidial suspension: spray, droplet, and injection inoculation of whole fruit; and droplet inoculation of the open surface of cut fruit. All whole‐fruit inoculations yielded similar results. Despite the removal of the epidermis, resistance was also expressed in cut fruit but relatively fewer conidia were produced. The cut‐fruit assay required substantially less time and half the amount of fruit to accomplish than whole‐fruit assays. Detached ripe fruit from 24 cultivars in 2008 and 26 cultivars in 2009 were screened for resistance. Results from the cut‐fruit assay correlated best with published resistance ratings. To determine the possible role of fruit characteristics in resistance, fruit pH, titratable acidity, sugar content and firmness were regressed against various fruit rot resistance measures. Fruit rot resistance was positively correlated with sugar content. On defined media, mycelial growth was restricted as sugar concentration increased and pH decreased, suggesting that fruit composition may play a role in the resistance phenotype.     

Temporal dynamics of brown rot in different apple management systems and importance of dropped fruit for disease development

ABSTRACT Epidemic development of brown rot, caused by Monilinia fructigena, was monitored in integrated and organic apple orchards at two locations in eastern Hungary between 2002 and 2005 on three cultivars with early, midseason, and late ripening periods. Disease incidence and severity measures were affected significantly (P < 0.05) by management system (organic versus integrated) and cultivar, but there was no significant management system-cultivar interaction. Epidemics started 2 to 4 weeks earlier in organic orchards and on the early cv. Prima compared with integrated orchards and the late cv. Mutsu. Disease intensity increased markedly in the final 3 to 5 weeks before harvest and was considerably lower in integrated than in organic orchards. Final brown rot incidence on fruit in the tree was correlated with incidence on dropped fruit on the orchard floor (r > 0.75, P < 0.05), whereby the lag period from the appearance of the first symptomatic fruit on the ground to the occurrence of the first symptomatic fruit in the tree ranged from 2 weeks to 2 months, depending on the cultivar. The inflection point of the disease progress curve was attained first by fruit on the ground, followed successively by fruit in the lower, middle, and upper thirds of the tree canopy. This may indicate that dropped fruit that became infected early provided a source of inoculum for subsequent epidemics by serving as a bridge between sporulation from overwintered fruit mummies in the spring and the first fruit with sporulating lesions in the tree in midsummer. Removal of dropped fruit from the orchard floor resulted in a significantly lower disease incidence on fruit in the tree on all cultivars; thus, drop-removal may be useful as a brown rot management practice in apple orchards.     

SA诱导拟南芥对灰霉病的抗性与木质素含量的关系

对拟南芥植株喷施水杨酸后,接种灰霉病菌(Botrytis cinerea),观察植物对病原物反应的变化。结果表明:喷施水杨酸可以降低拟南芥灰霉病的发生率。在平板培养中,水杨酸对灰霉菌分生孢子的萌发及菌丝的生长均无明显抑制作用,因此认为水杨酸处理后发病率的下降是由于水杨酸处理提高了植物的抗病性,且诱导抗性的持久期在10 d以上。观察中还发现在拟南芥叶片上喷施SA或接种灰霉菌都会使叶片PAL和POD活性上升,进而引起木质素的积累,两者在积累量上和时间程度上具较好的一致性,说明水杨酸诱导拟南芥抗灰霉病的过程中,通过PAL和POD活性的提高进而引起木质素含量的增加,可能是诱导拟南芥产生抗性的机制之一。     

Genetic variability and the inheritance of resistance to cedar-apple rust in apple

Thirteen apple cultivars and selections were evaluated in a greenhouse for their reaction to cedar-apple rust inoculation Five of the cultivars selections developed aecial lesions on their leaves whereas the sixth cultivar Jonathan, showed only pycnial lesions. The responses of the remaining seven resistant cultivars selections ranged from a lack of any visible symptoms to the presence of discrete flecks or continuous chlorotic mottles Quantitative parameters were used for statistical analysis; these included the highest number of pycnial lesions on a leaf/plant ( N ). the largest diameter of pycnial lesions on any leaf/plant (D)), and the calculated infection rating ( IR = ND ). Significant differences were observed among cultivars selections for variables N. D. and IR . Segregation ratios among progenies derived from 16 controlled crosses indicated that resistance to cedar-apple rust was conditioned by two major genes, and both were required in dominant form to confer resistance. However, in three crosses the dual-gene hypothesis was inadequate to explain the reaction of seedlings.     

Pest and disease control with low doses of pesticides in low and ultralow volumes applied to intensive apple trees

In 3 year field experiments on the development of more economical methods for pest and disease control on intensively planted dessert apple trees, low dose applications of one-tenth of the normal quantities of pesticide in one-hundredth, one-tenth and one-fifth of the normal volumes were compared with conventional high volume spraying at 2250 litres/ha. An experimental tractor-mounted mist blower, a motorised knapsack mist blower and a fan-assisted disc sprayer were each used to apply the pesticides in 225, 45 and 22.5 litres of water/ha. Control of the apple-grass aphid, Rhopalosiphum insertum, obtained by low dose spraying of demeton-S-methyl (8 g a.i./ha) combined with azinphos-methyl (37 g a.i./ha) in 225 and 22.5 litres/ha in 1971 and of fenitrothion (70 g a.i./ha) in 225, 45 and 22.5 litres/ha in 1972 and 1973 was almost equal to that obtained by the conventional high volume method. Low dose applications of benomyl fungicide programmes gave poor control of apple scab, Venturia inaequalis in 1971 when the disease incidence on the fruit was very high at 73%, but in 1972 and 1973, when it was moderately high at 42–45%, control was almost equal to that given by the conventional high volume method. Under these conditions all the low dose methods gave better control with benomyl than with dodine/captan programmes.     

Infection of apple fruit by Sphaeropsis pyriputrescens in the orchard in relation to Sphaeropsis rot in storage

Sphaeropsis rot, caused by Sphaeropsis pyriputrescens, is an important postharvest disease of apple in the United States. The objectives of this study were to determine the timing of apple fruit infection in the orchard in relation to development of Sphaeropsis rot in storage and to identify infection courts and mode of penetration by S. pyriputrescens on apple fruit. Fruit of apple cvs Red Delicious, Golden Delicious, and Fuji were inoculated in the orchard from 3 weeks after petal fall to 2 weeks before harvest at 5 to 6-week intervals in three consecutive seasons. All fruit were harvested and stored at 0?ºC to monitor decay development. Light and scanning electron microscopy were used to examine the infection courts and mode of penetration of the fungus on/in the host tissues. At harvest, the fungus was re-isolated from the stem (pedicel), sepal, anther, or filament of the inoculated fruit, but decay did not develop on fruit. Sphaeropsis rot developed on inoculated fruit during cold storage beginning 1–3 months after harvest. Stem-end rot was prevalent on cv. Golden Delicious, whereas calyx-end rot was prevalent on cv. Fuji. Both stem- and calyx-end rots were common on cv. Red Delicious. Infection also occurred at lenticels on fruit skin, particularly on cv. Golden Delicious, but at low incidence. Relationships between the incidence of Sphaeropsis rot in stored apple fruit and the timing of inoculation in the orchard varied with cultivar and year. On cv. Red Delicious apples, the incidence of Sphaeropsis rot generally increased as the timing of infection approached harvest. Histological studies indicated that infection took place through natural openings of plant organs such as stomata on stems and sepals and lenticels on fruit skin. Fungal penetration also was observed at micro-cracks on the stem and sepal and at trichome sockets where mechanical damage occurred in sepals. Direct penetration was observed on the stem and sepal of fruit, but most invasions were restricted between the cuticle and the epidermis. Our results indicate that wounding is not required for infection of apple fruit by S. pyriputrescens, though it may facilitate infections.     

河北省苹果果实黑点病的发病规律及药剂防控研究

近几年,河北省苹果产区苹果果实黑点病大面积发生.该病害在河北省的流行规律以及时空分布尚不清楚,给病害防控带来挑战.2018年对河北省不同市区的4个果园分别进行黑点病调查,并对其在苹果树上的空间分布以及发生时间进行动态监测,开展田间药剂防效试验.结果表明:苹果果实黑点病在7月中下旬开始出现明显症状,果树中层内膛病果率较高...     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.