Virulence and inoculum density‐dependent interactions between clubroot resistant canola (Brassica napus) and Plasmodiophora brassicae

To mitigate the impact and dissemination of clubroot in western Canada, canola (Brassica napus) producers have relied on clubroot resistance traits. However, in 2013 and 2014, new strains of the clubroot pathogen, Plasmodiophora brassicae, emerged that are virulent on most clubroot‐resistant (CR) canola genotypes. Novel strains of the pathogen were inoculated onto two susceptible canola cultivars, one resistant line and six CR cultivars. Although all cultivars/lines showed a susceptible response to inoculation with the new strains of P. brassicae, the severity of disease reaction, root hair infection rates and the amount of P. brassicae DNA present in each canola genotype varied depending on the strain. In addition, the effect of inoculum density on disease severity and gall formation was recorded for one of these new strains on a universally susceptible Chinese cabbage cultivar and one susceptible and 10 resistant canola genotypes. Although root galls were observed at an inoculum density of 10³ spores per mL of soil, clear differentiation of susceptible and resistant reactions among canola cultivars/lines was not observed until the inoculum density reached 10⁵ spores mL^?1. At a spore density of 10⁶ spores mL^?1 and above, all cultivars/lines developed susceptible reactions, although there was some differentiation in the degree of reaction. This study shows the potential to develop a unique disease profile for emergent clubroot pathotypes and shows a useful range of spore densities at which to study new P. brassicae strains.     

Reaction of resistant and susceptible rice genotypes against brown planthopper (<Emphasis Type="Italic">Nilaparvata lugens</Emphasis>)

The study was carried out to assess the reaction of different rice genotypes in response to brown planthopper (BPH)Nilaparvata lugens (Stål.) attack and the possible use of these genotypes in BPH management. The resistant genotypes PTB 33, ADT 45 and ASD 7 and the moderately resistant genotypes CO 43 and KAU 1661 recorded the lowest nymphal preference, fecundity, feeding rate, survival, growth index, population buildup and plant dry weight loss per mg of insect dry weight produced, and more unhatched eggs, longer nymphal development period, days to wilt and higher Functional Plant Loss Index compared with the susceptible genotype TN1. In resistant and moderately resistant genotypes, a greater accumulation of defense enzymes such as peroxidase and polyphenol oxidase in response toN. lugens infestation was recorded one day after infestation, and more pathogenesis-related protein and chitinase activity was noted 3 days after infestation. The activity was sustained for more than a week after infestation compared with the susceptible genotype TN1.     

Examination of resistance to clubroot in accessions of Brassica oleracea using a glasshouse seedling test

A glasshouse test was elaborated for assessing large numbers of seedlings ofBrassica oleracea for resistance to clubroot, a disease caused by the fungusPlasmodiophora brassicae. The method offers good control of inoculum density per plant, and requires 6–7 weeks from sowing. The results from the glasshouse test correlated well with field test results. With this method, 71 accessions ofB. oleracea reported to carry resistance to clubroot, and one susceptible control cultivar were tested with a Dutch clubroot isolate. High levels of resistance were found in several accessions of cabbage, broccoli and curly kale. F₁-populations of resistant cabbage or curly kale × susceptible cabbage were fully susceptible, indicating recessive inheritance of resistance in all cases.     

Metabolic profiles of groundnut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.) genotypes differing in <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> reaction

A total of 60 compounds of known structure, comprising sugars, sugar alcohols, fatty acids, amino acids, organic acids, phenols and sterols were identified in stem extracts of groundnut using GC-MS. Sugars and fatty acids were predominant in stem extracts as compared to other metabolites. Distinguished metabolite patterns were observed in control and 96 h after infection (h.a.i.). Succinic acid, pentitol, scopolin, D-glucose and D-turanose, myo-inositol, fructose and mannitol were observed to be higher in control plants, whereas, D-ribopyranoside, thymol, pentadecanoic acid and octadecanoic acid increased at 24 hai than that of control. Interestingly, phenol related compounds such as phenol, hydroquinone, guaicol-.beta.-d-glucopyranoside, scopolin were also found lower in non-infected stems of TG37A. Moreover, tolerant genotypes (CS 319 and CS 19) had higher content of Thymol-.beta.-d-glucopyranoside, pentitol, D-glucose, D-turanose, scopolin and hydroquinone than that of moderately tolerant and susceptible genotypes. Sugar profiles using Ion chromatography revealed that glucose content decreased in moderately susceptible and susceptible genotype after S. rolfsii infection. Both constitutive and induced levels of cinnamic acid was observed higher in resistant genotypes than that of susceptible ones which was further supported by phenylalanine ammonia lyase activity. Thus, our study demonstrates the biological role of metabolites specifically sugars, phenolics and fatty acids in plant defense responses.     

Effect of susceptible and resistant canola plants on Plasmodiophora brassicae resting spore populations in the soil

Clubroot, caused by Plasmodiophora brassicae, has become a serious threat to canola (Brassica napus) production in western Canada. Experiments were conducted to assess the effect of growing resistant and susceptible canola genotypes on P. brassicae soil resting spore populations under greenhouse, mini‐plot and field conditions. One crop of susceptible canola contributed 1·4 × 10⁸ spores mL^?1 soil in mini‐plot experiments, and 1 × 10¹⁰ spores g^?1 gall under field conditions. Repeated cropping of susceptible canola resulted in greater gall mass compared to resistant canola lines. It also resulted in reduced plant height, increased clubroot severity in susceptible canola, and increased numbers of resting spores in the soil mix.     

Evidence of early defence to Ascochyta lentis within the recently identified Lens orientalis resistance source ILWL180

In plant–pathogen interactions, strong structural and biochemical barriers may induce a cascade of reactions in planta, leading to host resistance. The kinetic speed and amplitudes of these defence mechanisms may discriminate resistance from susceptibility to necrotrophic fungi. The infection processes of two Ascochyta lentis isolates (FT13037 and F13082) on the recently identified ascochyta blight (AB)‐resistant Lens orientalis genotype ILWL180 and two cultivated genotypes, ILL7537 (resistant) and ILL6002 (susceptible), were assessed. Using histopathological methods, significant differences in early behaviour of the isolates and the subsequent differential defence responses of the hosts were revealed. Irrespective of virulence, both isolates had significantly lower germination, shorter germ tubes and delayed appressorium formation on the resistant genotypes (ILWL180 and ILL7537) compared to the susceptible genotype (ILL6002); furthermore, these were more pronounced on genotype ILWL180 than on genotype ILL7537. Subsequently, host perception of pathogen entry led to the faster accumulation and notably higher amounts of reactive oxygen species and phenolic compounds at the penetration sites of the resistance genotypes ILWL180 and ILL7537. In contrast, genotype ILL6002 responded slowly to the A. lentis infection and reaffirmed previous gross disease symptomology reports as highly susceptible. Interestingly, quantification of H₂O₂ was markedly higher in ILWL180 particularly at 12 h post‐inoculation compared to ILL7537, potentially indicative of its superior resistance capability. Faster recognition of A. lentis is likely to be a major contribution to the superior resistance observed in genotype ILWL180 to the highly aggressive isolates of A. lentis assessed.     

Pathogenic and genetic diversity in Plasmodiophora brassicae (clubroot) from Japan

Clubroot disease, caused by Plasmodiophora brassicae Woronin, affects various cruciferous crops. Variations in pathogenicity and virulence are present among field populations of P. brassicae. Many races (pathotypes) have been reported in Japan as well as in other countries using various differential systems. Populations can be classified into four pathotypes using two clubroot-resistant (CR) cultivars of Chinese cabbage as differential hosts in Japan. However, it was recently indicated that each population is often heterogenic and composed of multiple genotypes (races or pathotypes). Breakdown in CR cultivars of Chinese cabbage is a problem in some areas of Japan and may contribute to the selective propagation of minor pathogenic genotypes on the CR cultivars. Clubroot has also been recorded on five species of cruciferous weeds in Japan. In particular, clubroot of Cardamine flexuosa is widely distributed in Japan. Some populations of C. flexuosa are often moderately pathogenic on Chinese cabbage and turnip. Therefore, the epidemiological relationship between clubroot of cruciferous crops and that of the weed has been noted but not thoroughly clarified. The relationship between pathogenic and genetic variations has also been examined among populations from cruciferous crops and weeds in Japan. The result implies an interesting genetic relationship among Williams’ races, among pathotypes determined using CR cultivars of Chinese cabbage and among populations from crops and C. flexuosa. This review includes an introduction of the status of studies on pathogenic and genetic diversity in P. brassicae from Japan.     

Is the parasitization rate of<Emphasis Type="Italic">Diaeretiella rapae</Emphasis> influenced when<Emphasis Type="Italic">Brevicoryne brassicae</Emphasis> feeds on<Emphasis Type="Italic">brassica</Emphasis> plants?

The development time and parasitization rate ofDiaeretiella rapae (M’Intosh) onBrevicoryne brassicae (L.) feeding on differentBrassica cultivars was studied in the laboratory at 20°C. The shortest development time from egg to adult parasitoid was 11.6 days on cabbage cv. ‘Yalova 1’ and the longest was 12.1 days on turnip cv. ‘Antep’ and rapeseed cv. local variety. Females lived significantly longer than males on the host plants used in the study. Females and males had the shortest longevity on rapeseed at 11.1 and 5.1 days, respectively. The highest percent parasitism ofB. brassicae byD. rapae was found on cabbage (40.20%), and the lowest was recorded on turnip (32.64%). Our results demonstrate that parasitism rate could be influenced by the plant quality, probably due to the nutritional status of the aphids or to toxic compounds ingested through the plant. Cabbage, cauliflower and broccoli were found to be suitable plants for the parasitoid, considering the development time of pre-adults, and the parasitization rate ofD. rapae onB. brassicae. http://www.phytoparasitica.org posting Jan. 23, 2007.     

Assessment of the impact of resistant and susceptible canola on Plasmodiophora brassicae inoculum potential

The impact on clubroot severity of growing susceptible canola or mixtures of resistant and susceptible canola genotypes was examined. Bioassays revealed greater clubroot severity and incidence, and reduced plant height, where 100% of a susceptible cultivar had been grown. A higher proportion of susceptible plants within a resistant canola crop increased root hair and secondary infections. Regression analysis of root hair infection and the amount of Plasmodiophora brassicae DNA (as determined by quantitative PCR) revealed strong linear relationships between the two parameters. The linear relationships between root hair infection and P. brassicae DNA were stronger for the resistant cultivar than for the susceptible cultivar when regression analysis was conducted by cultivar over the sampling dates. In conclusion, the cropping of a resistant cultivar reduced clubroot severity, while the presence of susceptible volunteer canola increased inoculum potential. Quantitative PCR was a reliable tool for the quantification of root hair infection.     

Impact of glucosinolate in relation to leafminer,Liriomyza brassicae Riley (Diptera: Agromyzidae) infestation in crucifers

Eight species belonging to the Family Cruciferae were classified to lafminer resistant, tolerant and susceptible on the basis of leafminer infestation. They were analyzed for the glucosinolate content and correlated with leafminer infestation. Total glucosinolate content in general and sinigrin content in particular appeared to have the ability to repel the attack ofLiriomyza brassicae, while gluconapin appeared to attract them. The percentage of infestation, the number of mines and the number of living larvae were estimated for evaluating the glucosinolate efficacy againstL. brassicae on cabbage.     

Impact of glucosinolate in relation to leafminer,Liriomyza brassicae Riley (Diptera: Agromyzidae) infestation in crucifers

Eight species belonging to the Family Cruciferae were classified to lafminer resistant, tolerant and susceptible on the basis of leafminer infestation. They were analyzed for the glucosinolate content and correlated with leafminer infestation. Total glucosinolate content in general and sinigrin content in particular appeared to have the ability to repel the attack ofLiriomyza brassicae, while gluconapin appeared to attract them. The percentage of infestation, the number of mines and the number of living larvae were estimated for evaluating the glucosinolate efficacy againstL. brassicae on cabbage.     

Effect of azadirachtin applied systemically through roots of plants on the mortality,development and fecundity of the cabbage aphid (<Emphasis Type="Italic">Brevicoryne brassicae</Emphasis>)

The effect of low concentrations of azadirachtin applied systemically through root tissues of rape plants (Brassica napus subsp.napus) on the mortality, period of development, longevity and fecundity of the cabbage aphid (Brevicoryne brassicae L.) (Sternorrhyncha: Aphididae) was studied. The concentrations of azadirachtin A tested were: 0.25, 0.05, 0.005, 0.0005 and 0.00005 mg ml⁻¹. The mortality of cabbage aphid nymphs, particularly during the period of ecdysis, increased significantly with increasing concentrations. Azadirachtin had no effect on the length of the development period of the respective immature stages of cabbage aphids. The average longevity of the cabbage aphids decreased with increasing azadirachtin concentration and time spent feeding. The fecundity of aphids decreased after the application of azadirachtin. http://www.phytoparasitica.org posting May 6, 2004.     

Root exudates of potato onion are involved in the suppression of clubroot in a Chinese cabbage-potato onion-Chinese cabbage crop rotation

Clubroot, caused by Plasmodiophora brassicae, has emerged as a serious disease threatening cruciferous crop production throughout the world. Crop rotation with non-host species is commonly practised to avoid clubroot, but it is not known whether rotation crops can control clubroot when the resting spores of P. brassicae remain unaffected. Pot experiments were performed to investigate the response of clubroot in Chinese cabbage to crop rotation with potato onion. The results showed that Chinese cabbage rotated with potato onion exhibited less clubroot disease than Chinese cabbage monoculture. Compared with residues from potato onion, the addition of root exudates from potato onion significantly decreased the disease incidence and index of clubroot (p ≤ 0.05). Potato onion root exudates decreased the number of secondary plasmodia of P. brassicae and the expression of the PRO1 gene of P. brassicae. These results suggest that root exudates from potato onion may play an important role in suppressing clubroot in a Chinese cabbage-potato onion-Chinese cabbage rotation system.     

乌鲁木齐地区甘蓝蚜发生规律初报

甘蓝蚜[Brevicoryne brassicae (Linné)]是烏魯木齐地区十字花科蔬菜上最主要的蚜虫。从9月下旬开始,在晚甘藍、晚苤藍及大白菜等蔬菜靠近地面的根、茎凹陷处,以及叶柄基部和叶片上产卵。蚜卵既可随寄主在菜窖里越冬;也可在菜株残体上露地越冬。露地越冬蚜卵,一般不能成为早春的有效蚜源,因其孵化率极低;孵化出来的少数干母,由于不能及时得到食料或因气候不适合,难以存活。越冬蚜卵于4月下旬孵化,5月中旬末产生有翅蚜,主要先在越冬寄生及冬蘿卜留种株上繁殖;到5月下旬至6月初,才陆續迁飞到春、夏十字花科蔬菜及春油菜上,大量繁殖和为害。7月下旬至8月初,晚甘藍与晚苤藍上的蚜虫便成为大白菜和冬蘿卜苗期的主要蚜源。甘藍蚜在烏魯木齐地区,无論是在菜窖里,或是在露地残株上,均不能以成蚜越冬。     

Dissemination of Plasmodiophora brassicae in livestock manure detected by qPCR

The present study was performed to investigate whether Plasmodiophora brassicae can be disseminated by livestock manure. A quantitative PCR (qPCR) assay was developed and used to detect and quantify P. brassicae in manure samples from naturally and artificially infested chickens and pigs. In naturally infested manure, quantifiable levels of infestation were observed in 7 out of the 28 samples, ranging from 10³ to 10⁷ resting spores per g of manure. The vast majority of the resting spores (76–91%) were viable, as determined by a dual fluorescence viability assay. Clubroot symptoms developed on plants inoculated with P. brassicae resting spores isolated from all seven qPCR‐positive samples. Artificially infested manure samples were produced by feeding chickens and pigs on P. brassicae‐contaminated feed. The levels of infestation were 10³ resting spores per g of manure for both chicken and pig manure sampled 24 and 48 h after feeding, respectively. Spore viability was >80% for both samples, and the disease severity indices were both >40 as indicated by bioassay. This showed that resting spores can survive the digestive tracts of chickens and pigs, and retain strong pathogenicity. The findings indicate that manure dissemination is possible for P. brassicae. Farmers should avoid feeding livestock on P. brassicae‐contaminated feed or applying infested manure as fertilizer on land intended for crucifer crops.     

新疆大白菜病毒病与甘蓝蚜的关系

甘藍蚜、桃蚜和棉蚜的有翅型与无翅型,均能传播大白菜病毒病,其中以甘藍蚜为最主要的传毒介体。一头带毒蚜可使80％的健苗发病;一头无毒蚜經吸毒一分钟的传病率为35％;健苗經一头有毒蚜传毒一分钟,就有10％发病。病毒系非持久性的,蚜虫一次吸毒后的传毒期限为25分钟左右。在烏魯木齐地区,有翅甘藍蚜全年中的迁飞高峯期,都是在7月下旬。証实了这时期与大白菜病毒病的流行,有极密切的关系。当年春、夏季播种的甘蓝和苤藍,尤其是晚甘蓝和晚苤蓝,是大白菜(包括冬蘿卜)苗期的初次毒源和蚜源。初步認为,能感染病毒的几种十字花科及藜科杂草,不是本病病毒和甘藍蚜的重要越夏寄主。     

New chlorinated juvenile hormone analogues and their biological activity

In the search for new juvenile hormone analogues (JHAs), a general approach was chosen based on the substitution of the isoprene unit, that carries the epoxy function in the natural hormone JHIII, by 3,3,3-trichloropropyl, 2,2-dichlorocyclopropyl- methyl, 3,3-dichloroallyl, or 3-chloroprop-2-ynyl groups. Accordingly, several terpenoid aromatic JHAs were prepared with, or without, oxygen atoms in the aliphatic chain. Structure-biological activity relationships of the most active compounds toward the yellow mealworm (Tenebrio molitor) and the large cabbage white butterfly (Pieris brassicae) are given. With a view to preparing synthetically accessible analogues, some alkyl phenyl ethers were also made, which were not branched in the aliphatic chain and were related terminally to the most active compounds. They were only moderately active against insects when tested for morphogenetic activity, but exhibited a good field persistence. The occurrence of a moderate acaricidal activity among these analogues prompted the examination of several 1,4-disubstituted-phenyl derivatives. The ovicidal effectiveness of these products against a susceptible strain of the two-spotted spider mite, Tetranychus urticae, was ten or 100 times higher than that of the well known and highly potent JHAs.     

Infection process of Phoma koolunga on stem and leaf tissue of resistant and susceptible field pea (Pisum sativum)

This study investigates the infection process of Phoma koolunga on field pea (Pisum sativum) stems and leaves using different susceptible and resistant pea genotypes for each tissue, viz. 05P778‐BSR‐701 (resistant) and 06P830‐(F5)‐BSR‐5 (susceptible) for stems and ATC 866 (resistant) and ATC 5347 (susceptible) for leaves. On both resistant and susceptible genotypes, light and scanning electron microscopy showed P. koolunga conidia infect stem and leaf tissues directly via appressoria or stomatal penetration, but with more infections involving formation of appressoria on stems than on leaves. On leaves of the resistant genotype, at 72 h post‐inoculation, P. koolunga penetrated more frequently via stomata (5.2 conidia per 36 893 μm²) than by formation of appressoria (1.8 conidia); yet no such difference was observed on stems of the resistant genotype. In contrast, at the same time point, the number of conidia infecting the susceptible genotype by formation of appressoria on either stems (135 conidia) or leaves (11.3 conidia) was significantly greater than via stomata (8 and 7.3 conidia, stems and leaves, respectively). Mean germ tube length of germinating P. koolunga conidia on both stems (29.8 μm) and leaves (32.9 μm) of the resistant genotype was less than on the susceptible genotype (40.5 and 63.7 μm, stem and leaves, respectively). In addition, there were differences in the number of germ tubes emerging from conidia on resistant and susceptible genotypes. These are the first insights into the nature of leaf and stem resistance mechanisms operating in field pea against P. koolunga.     

Effect of certainBrassica plants on biology of the cabbage aphidBrevicoryne brassicae under laboratory conditions

The development time, mortality, survivorship and reproduction of the cabbage aphidBrevicoryne brassicae (L.) were evaluated on detached leaves of sixBrassica species (cabbage cv. ‘Yalova 1’, cauliflower cv. ‘Early Snowball’, broccoli cv. ‘Marathon’, turnip cv. ‘Antep’, rapeseed cv. local variety, and wild mustard) at a constant temperature of 20°C. Total development time ofB. brassicae was the shortest (8.9 days) on cauliflower and the longest (10.4 days) on cabbage. Mortality of immature stages varied from 16% on cabbage to 88% on turnip. Longevity of the cabbage aphid was the shortest (6.2 days) on mustard, and the longest (21.8 days) on cauliflower. The net reproductive rate was highest (35.98) on cauliflower, and lowest (1.89) on turnip. The intrinsic rate of increase was 0.2345 on cauliflower, followed by 0.2009 on cabbage, 0.1976 on broccoli, 0.1662 on mustard, 0.1357 on rapeseed, and 0.0465 on turnip. Cabbage, cauliflower and broccoli were susceptible host plants for the cabbage aphid. Rapeseed, turnip and mustard showed resistance to the pest.     

Effect of botanical extracts on the biological activity of granulosis virus against <Emphasis Type="Italic">Pieris brassicae</Emphasis>

A granulosis virus strain infecting Pieris brassicae (PbGV) was isolated from the dry temperate region of northwestern Himalayas as a potential microbial agent for its management. The effect of different botanicals (having insecticidal action against P. brassicae) on the bioefficacy of PbGV was evaluated under laboratory conditions using leaf disc bioassays on cabbage for improving the insecticidal performance of the PbGV. The synergistic action of different botanical extracts was evident in terms of reduction in LC₅₀ values against different botanical extracts. Among different extracts, petroleum-ether extract of neem seed kernel (NSK) when combined with PbGV resulted in maximum reduction of LC₅₀ value (4.39 × 10² occlusion bodies [OBs] ml⁻¹) followed by methanolic extract (7.38 × 10² OBs ml⁻¹) and aqueous extract (9.36 × 10³ OBs ml⁻¹) as compared with PbGV alone (1.85 × 10⁴ OBs ml⁻¹) for 2nd instar larvae of the test insect. These trends were found analogous in cases of 3rd and 4th instars of P. brassicae with different solvent extracts of NSK. The other botanicals evaluated, viz., Eupatorium and Artemesia, also resulted in reduction of LC₅₀ values for 2nd, 3rd and 4th instars as compared with PbGV alone when different extracts were combined with virus for bioassays. The studies suggest that the PbGV in combination with botanical pesticides could be more useful as a bio-pesticide against cabbage butterfly (P. brassicae) in IPM programs.