Correlation of ethylene synthesis in Citrus fruits and their susceptibility to Alternaria alternata pv. citri

The susceptibility of Fortune (Citrus clementina × Citrus reticulata), Citrus paradisi and Citrus limon fruits to Alternaria alternata pv. citri was investigated using different artificial inoculation methods. The results obtained reveal that the C. paradisi and C. limon fruits are less susceptible to A. alternata pv. citri than Fortune fruits, although all showed symptoms of Alternaria brown spot when the cuticle was broken and the flavedo or flavedo + albedo was removed. Furthermore, it was seen that susceptibility to the fungus decreased as the age of the fruit increased. There was a positive correlation between the susceptibility of the different Citrus fruits to A. alternata pv. citri and their “in vivo” ethylene levels, the most susceptible fruit (Fortune) producing more ethylene during growth than the less susceptible C. limon and C. paradisi. This suggests that ethylene may well be considered as a possible marker of Citrus fruit susceptibility to A. alternata pv. citri. Disease development increased when the Fortune fruits were treated with 1 mM ACC (a precursor of ethylene biosynthesis) or 1 mM Ethephon (an ethylene-releasing compound) prior to inoculation with A. alternata pv. citri. The role of ethylene as a factor involved in disease development is discussed.     

Antifeedant activity of fruit and seed extracts ofMelia azedarach andazadirachta indica on larvae ofSesamia nonagrioides

Methanolic extracts of seeds and fruits of the chinaberry tree,Melia azedarach L. (Meliaceae), showed strong antifeedant activity against 2nd instar larvae ofSesamia nonagrioides Lefèbvre (Lepidoptera: Noctuidae), a very serious pest of maize(Zea mays L.) in Mediterranean countries. Extracts were applied in an artificial diet at concentrations of 1000 and 2000 ppm. The parameters used to evaluate the activity were larval growth rates; quantity of food ingested; phagodepression/phagostimulation index; quantity of frass produced; quantity of material ingested; duration of larval development; and cumulative mortality. Seed extract showed high bioactivity at both doses, while fruit extract proved to be less active, and only at the higher dose used (2000 ppm) did it display a slight antifeedant activity. The activity of theM. azedarach seed extract at the higher dose (2000 ppm) was comparable to that of pure azadirachtin applied at a dose of 1.25 ppm, or to ‘Mubel’, a commercial extract ofAzadirachta indica A. Juss. (Meliaceae), applied at a dose of 75 ppm.     

UV irradiation Alters the Levels of Flavonoids Involved in the Defence Mechanism of Citrus aurantium Fruits against Penicillium digitatum

The effect of UV irradiation on the levels of the flavanone, naringin, and the polymethoxyflavone, tangeretin, in the peel of Citrus aurantium fruits is described, as changes in the synthesis and/or accumulation of these compounds after infection with Penicillium digitatum. The growth of P. digitatum on previously irradiated fruit was reduced by up to 45%. Changes in flavonoid levels were detected, associated with inhibition of fungus growth, the naringin content falling by 69% and tangeretin levels increasing by 70%. The possible participation of naringin and tangeretin in the defence mechanism of this Citrus species is discussed.     

Pathogenicity,colony morphology and diversity of isolates of <Emphasis Type="Italic">Guignardia citricarpa</Emphasis> and <Emphasis Type="Italic">G. mangiferae</Emphasis> isolated from <Emphasis Type="Italic">Citrus</Emphasis> spp.

In the present study, the pathogenicity of 36 isolates of Guignardia species isolated from asymptomatic ‘Tahiti’ acid lime fruit peels and leaves, ‘Pêra-Rio’ sweet orange leaves and fruit peel lesions, and a banana leaf were characterized. For pathogenicity testing, discs of citrus leaves colonized by Phyllosticta citricarpa under controlled laboratory conditions were kept in contact with the peels of fruit that were in susceptible states. In addition, pathogenicity was related to morphological characteristics of colonies on oatmeal (OA) and potato dextrose agar (PDA). This allowed the morphological differentiation between G. citricarpa and G. mangiferae. Polymerase chain reactions (PCRs) were also used to identify non-pathogenic isolates based on primers specific to G. citricarpa. A total of 14 pathogenic isolates were detected during pathogenicity tests. Five of these were obtained from leaf and fruit tissues of the ‘Tahiti’, which until this time had been considered resistant to the pathogen. Given that the G. citricarpa obtained from this host was pathogenic, it would be more appropriate to use the term insensitive rather than resistant to categorize G. citricarpa. A non-pathogenic isolate was obtained from lesions characteristic of citrus black spot (CBS), indicating that isolation of Guignardia spp. under these conditions does not necessarily imply isolation of pathogenic strains. This also applied to Guignardia spp. isolates from asymptomatic citrus tissues. Using fluorescent amplified fragment length polymorphism (fAFLP) markers, typically pathogenic isolates were shown to be more closely related to one another than to the non-pathogenic forms, indicating that the non-pathogenic isolates display higher levels of genetic diversity.     

Susceptibility to imazamox in Italian weedy rice populations and Clearfield® rice varieties

The introduction of imidazolinone‐tolerant rice varieties has made selective Oryza sativa (weedy rice) control possible. We hypothesised that Italian weedy rice populations have variable degrees of susceptibility to imazamox prior to imidazolinone‐tolerant variety introduction. To this end, 149 Italian weedy rice populations collected from fields never before cultivated with imidazolinone‐tolerant varieties were tested in a glasshouse‐based, whole‐plant response screening study. Imazamox was applied to all populations post‐emergence at a rate of 70 g a.i. ha^?1, resulting in 70–90% shoot biomass reduction in the majority of cases. The results prompted a second study of the seedling dose response of four weedy rice populations from the initial study group. Three imidazolinone‐tolerant and one conventional rice variety were also included. The seedling roots were cut six days after germination and exposed to different concentrations of imazamox. The root regrowth associated with each concentration‐exposure was then measured. Imazamox concentrations to inhibit weedy rice root growth by 50% varied by about two orders of magnitude, or between 0.0018 and 0.12 mm . Even with this result, imidazolinone‐tolerant varieties were at least 31.8 times less susceptible than weedy rice populations, suggesting that Italian weedy rice populations were not tolerant to imazamox before introduction of these varieties.     

Antimicrobial activity of essential oils and their components against the three major pathogens of the cultivated button mushroom, Agaricus bisporus

Essential oils of Matricaria chamommilla, Mentha piperita, M. spicata, Lavandula angusti folia, Ocimum basilicum, Thymus vulgaris, Origanum vulgare, Salvia officinalis, Citrus limon and C. aurantium and their components; linalyl acetate, linalool, limonene, α-pinene, β-pinene, 1,8-cineole, camphor, carvacrol, thymol and menthol were assayed for inhibitory activity against the three major pathogens of the button mushroom, Agaricus bisporus, i.e. the fungi Verticillium fungicola and Trichoderma harzianum and the bacterium Pseudomonas tolaasii. The highest and broadest activity was shown by the Origanum vulgare oil. Carvacrol possessed the highest antifungal activity among the components tested.     

First report on Virachola livia Klug. (Lepidoptera: Lycaenidae) and its effects on different pomegranate varieties in Tunisia

Virachola livia Klug 1834 (Lepidoptera: Lycaenidae) was detected for the first time in a cultivated pomegranate orchard in Tunisia in 2006 although it may have been causing damage for several years prior to this. During 2006, 5.2% of the total pomegranate fruit produced in Tunisia was infested by this pest. This invasive species was responsible for 52% of fruit rot at Zerkine locality (Gabès Governorate). Levels of V. livia infection were shown to vary among nine pomegranate varieties; the Klaii, Mezzi and Garoussi varieties were the most susceptible, whereas Gabsi, Jbeli, Andolsi, Tounsi, Zaghweni and Zehri were more tolerant to this lycaenidae. The authors consider that this is due to female preference.     

Citrus black spot intensity and yield losses on sweet orange are affected by Phyllosticta citricarpa inoculum concentration and fruit developmental stage

Citrus black spot (CBS) symptom expression on sweet oranges has been reported to be affected by the fruit developmental stage and inoculum concentration in greenhouse conditions. However, there is little information concerning the period in which the fruit is susceptible in commercial orchards. This study assessed the influence of fruit age and inoculum concentration of Phyllosticta citricarpa on CBS intensity and fruit drop in the field. Two field trials were conducted in commercial ‘Valencia’ orchards in São Paulo state, Brazil. Fruit were inoculated from October (petal fall stage) to July (c.6.5 cm diameter), with 10¹, 10³ and 10⁵ pycnidiospores/ml. CBS symptoms and fruit drop were observed in higher levels for fruit inoculated from October to February than from March to July. In both trials, when fruit were inoculated 10 times from October to July or single-inoculated in November or December, high CBS severities of 11%–22% were observed and the proportion of fruit remaining on the tree was 48%–77%; in contrast, noninoculated fruit had severity below 1.1% and 90% remained on the tree. Inoculations in November or December of green fruit with 1.5–3.0 cm diameter using 10⁵ pycnidiospores/ml were associated with higher CBS intensity and fruit drop and shorter incubation period than inoculations with lower concentrations. This work provides a better understanding of fruit stages and P. citricarpa inoculum concentrations most related to symptom expression and losses under natural conditions and may be helpful for improvement of CBS management in the São Paulo citrus belt.     

Laboratory Evaluation of Citrus Cultivars Susceptibility and Influence of Fruit Size on Fortune Mandarin to Infection by Alternaria alternata pv. citri

Young leaves of 62 citrus cultivars were inoculated with conidia of three Spanish isolates of Alternaria alternata pv. citri, the causal agent of brown spot of citrus. Hybrids with Dancy mandarin, King mandarin or their derivates as a parent, grapefruit cultivars and the mandarin cultivars Guillermina, Emperor, Clemenpons and Esbal were highly susceptible to the pathogen. Satsuma cultivar Clausellina and orange cultivars, with the exception of Sanguinelli, were slightly susceptible. Lemon and lime cultivars were not susceptible, with the exception of Mexican lime (Citrus aurantifolia), which was slightly susceptible. Although this study shows a range of potential hosts for this pathogen, to date the only affected cultivars in Spain are Fortune and Nova mandarins, and Minneola tangelo. The susceptibility of Fortune fruits decreased as diameter increased, being susceptible through the whole season. This was confirmed with field observations in autumn where fruit infections have been detected when the diameter reaches 6–7 cm.     

Inhibitory and stimulatory effects of essential oils and individual monoterpenoids on growth and sporulation of four soil-borne fungal isolates of Aspergillus terreus, Fusarium oxysporum, Penicillium expansum, and Verticillium dahliae

The effect of essential oils and individual monoterpenoids on soil-borne fungi, in pure and mixed cultures, in growth media and in the soil environment, was investigated. Essential oils were extracted from lavender (Lavandula stoechas), oregano (Origanum vulgare subsp. hirtum), sage (Salvia fruticosa) and spearmint (Mentha spicata). The monoterpenoids tested were fenchone, carvacrol, 1,8-cineole, carvone, α-pinene and terpinen-4-ol. Their effect was examined on growth and sporulation of Aspergillus terreus, Fusarium oxysporum, Penicillium expansum and Verticillium dahliae isolated from an organic cultivation of tomato. All tested essential oils and individual monoterpenoids inhibited mycelial growth in all fungi and conidial production in most fungi. The strongest inhibitory activity on mycelial growth was exhibited by oregano and spearmint oils and by carvacrol and carvone, respectively their main constituents. The inhibitory activity was clearly fungistatic in A. terreus and F. oxysporum but fungicidal in V. dahliae. On sporulation, clearly stimulatory effects were observed alongside inhibitory ones. Conidial production was always promoted by α-pinene in P. expansum and by sage oil in F. oxysporum. At certain dosages it was promoted by cineole and carvone in F. oxysporum, and by lavender oil in A. terreus and V. dahliae. Experiments with carvone and carvacrol against mixed fungal cultures in a soil environment showed that V. dahliae was the most sensitive and A. terreus the most tolerant of the four fungi. Our results demonstrate strong but divergent effects and selectivity of action of the lower terpenoids on fungal strains that can become serious pests of tomato. Of special importance is the complete inhibition of growth and conidial production of V. dahliae, a pathogen otherwise very resistant to chemical control.     

Characterization of Citrus tristeza virus isolates in northern Iran

The biological and molecular properties of four Citrus tristeza virus (CTV) isolates isolated from infected Satsuma trees imported from Japan, and growing in citrus groves in northern Iran (Mahdasht orchards, Mazandaran Province), were investigated. CTV-infected samples were collected from sweet orange trees and grafted onto Alemow (Citrus macrophylla Wester) seedlings. On indicator plants, these isolates produced various symptoms including vein clearing and stem pitting on Mexican lime, Alemow, and Citrus hystrix, and yellowing and stunting on sour orange and grapefruit seedlings. Citrus samples were also surveyed for CTV using serological tests. The coat protein (CP) gene of these isolates was amplified using specific primers, yielding an amplicon of 672 bp for all isolates. Sequence analysis showed 98%–99% sequence homology of Iranian isolates with the Californian CTV severe stem-pitting isolate SY568 and 97%–98% homology with the Japanese seedling yellows isolate NUagA. The Iranian isolates were compared by restriction fragment length polymorphism (RFLP) analysis of the CP amplicon for further classification.     

Bacterial fruit blotch of melon: screens for disease tolerance and role of seed transmission in pathogenicity

Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli, is a serious threat to the watermelon and melon industries. To date, there are no commercial cultivars of cucurbit crops resistant to the disease. Here we assessed the level of tolerance to bacterial fruit blotch of various commercial cultivars as well as breeding and wild lines of melon, using seed-transmission assays and seedling-inoculation experiments. Selected cultivars were also tested in a greenhouse experiment with mature plants. All tested cultivars/lines were found to be susceptible to the pathogen, and most of them showed different responses (relative tolerance vs. susceptibility) in the different assays; however, some consistent trends were found: cv. ADIR339 was relatively tolerant in all tested assays, and cv. 6407 and wild lines BLB-B and EAD-B were relatively tolerant in seed-transmission assays. We also provide evidence supporting a strong correlation between the level of susceptibility of a cultivar/line and the ability of the pathogen to adhere to or penetrate the seed. To the best of our knowledge, this is the first attempt to assess melon cultivars/lines for bacterial fruit blotch response.     

Alternaria Brown Spot of Minneola in Greece; Evaluation of Citrus Species Susceptibility

During the last three years, a new disease was observed in northwestern Greece on Minneola trees, hybrid of mandarin and grapefruit. On May small brown necrotic leaf spots surrounded by yellow halo areas of various sizes appeared and covered a major portion of the leaves with extension of necrosis into the veins. On young fruits small, slightly depressed black spots were the first symptoms, which later became 2–7 mm in diameter. Brown spots were observed on the leaves and fruits in several orchards in the same area, causing leaves and fruits to drop. In some orchards over 50% of the fruits were affected. From the fruit and leaf spots the typical small-spore species Alternaria alternata was isolated. Pathogenicity tests were performed by artificially inoculating fruits of Minneola, common mandarin and Clementine. The symptoms of the disease were reproduced only on fruits of Minneola hybrids by the specific strain of the fungus Alternaria alternata pv. citri. Different citrus susceptibility tests indicated that mandarins Minneola, Nova and Page were very susceptible to tested isolates while Clementine SRA and Poros Clementine were not. All lemons and lime Seedless were not susceptible. Grapefruit New Hall was not susceptible, while the Star Ruby was. Orange Lane Late, Navel Late, Oval Poros, Olinda, Navel Athos were not susceptible and only Moro showed reaction being slightly susceptible only to one isolate.     

Effects of defoliation caused by the processionary moth on growth of Crimean pines in western Turkey

An outbreak of the pine processionary moth (PPM), Thaumetopoea wilkinsoni Tams (Lepidoptera: Thaumetopoeidae), began in spring 1998 and lasted 6 years in a Crimean pine (Pinus nigra Arnold) plantation in western Turkey. The effects of PPM on the radial, height and volume growth of Crimean pine trees were investigated by examining the increment losses for three defoliation intensities (groups). PPM activity in Crimean pine stand was assessed through radial increment analysis of cores extracted at breast height. In 2004, increment cores were collected from moderate and high defoliation and low defoliation dominant or co-dominant trees. Based on the sample, annual radial growth indices from 1998 to 2004 were calculated. Growth functions were defined as the cumulative sum of radial, height and volume increment graphically compared between Crimean pine defoliation group sample trees. The sample trees are the same subspecies and varieties. After the defoliations, radial, height and volume growth of low defoliation group trees was found to be significantly greater than that of the other affected groups. During the 1998–2004 period the total radial growth of low, moderately affected and highly affected trees was, respectively, 49, 33 and 31 mm; the total height growth was 3.1, 1.8 and 1.0 m; and the total volume growth was 50, 14 and 10 dm³.     

Scytalidium Wilt of Citrus

In July 1998, a sudden wilt of Star Ruby grapefruit (Citrus paradisi Macf.) occurred in Israel in a region with a warm Mediterranean climate. The wilt of the middle and upper canopy of main limbs was accompanied by gum oozing from the affected branches. The bark of these branches attained a dark colour and the epidermis sloughed off easily revealing a mass of black powder, resulting from copious sporulation of dark conidia. Both the bark and the xylem were intensively colonized with mycelium. The fungus was identified as Scytalidium lignicola Pesante, based on the characteristic mixture of some colourless and dark conidia, produced in branched chains by conversion of the vegetative hyphae. Artificial inoculations induced typical disease symptoms and the fungus was reisolated, thus confirming Koch's postulates. Similar symptoms appeared in Star Ruby interim segments which had been cut and top grafted with various citrus cultivars. This is the first detailed report of pathogenicity of S. lignicola to citrus trees. It is postulated that the disease developed after predisposition of Star Ruby grapefruit trees by comprehensive pruning followed by extremely hot conditions.     

Differential behaviour of sheath blight pathogen Rhizoctonia solani in tolerant and susceptible rice varieties before and during infection

This study characterized the early infection and establishment of the sheath blight pathogen Rhizoctonia solani on a tolerant rice variety, Swarnadhaan (IET 5656), and a susceptible variety, Swarna (MTU 7029). Assays using whole plants showed that disease severity was higher in Swarna than Swarnadhaan. In a detached leaf assay, Swarnadhaan showed a disease index that was 50% less than that with Swarna. Rhizoctonia solani exhibited different growth behaviour in the tolerant and susceptible varieties. The pathogen showed more hyphal growth in the susceptible host than in the tolerant variety. It also showed profuse branching, making intimate contact with the host surface to form more inter‐ and intracellular structures, and greater sclerotial development in the susceptible host compared to the tolerant one. Using light and scanning electron microscopy, it was observed for the first time that the pathogen could intercept host surface structures and use these for anchorage or penetration. Transformed R. solani, expressing green fluorescent protein, was observed using confocal laser scanning microscopy to investigate pathogen behaviour, including the formation of infection cushions and subsequent colonization of the host tissues. This is the first ultrastructural report to characterize the differential behaviour of the sheath blight pathogen in the vicinity and within tolerant and susceptible rice plants.     

植物精油对三种鳞翅目害虫的杀虫活性

测试了27种植物精油对粘虫、棉铃虫和小菜蛾的杀虫活性。结果表明:①用100倍精油丙酮液处理的小麦叶碟饲喂粘虫3龄幼虫48h后,砂地柏果实、玳玳花、甜橙果皮和姜根4种精油对试虫的拒食率均达80％以上;砂地柏果实、玳玳花、甜橙果皮等7种精油对粘虫4龄幼虫历期和蛹重均产生一定的影响,尤以砂地柏果实、玳玳花、甜橙果皮精油致幼虫死亡率最高,砂地柏果实和甜橙果皮精油对蛹重影响最为明显;②以含1％精油的人工饲料饲喂棉铃虫3龄幼虫9天后,山苍子果实、甜橙果皮精油处理组幼虫重量均仅为对照的20％左右,且各精油对幼虫历期、蛹重和化蛹率均有一定的影响;③八角茴香果实精油对小菜蛾的拒食活性达59.1％以上。     

Allelochemical resistance traits of muskmelon (Cucumis melo) against the fruit fly (Bactrocera cucurbitae) in a hot arid region of India

Host plant resistance is an important component for management of the melon fruit fly, Bactrocera cucurbitae (Coquillett), owing to difficulties associated with its chemical and biological control. Various biochemical traits including total sugar, reducing sugar, non-reducing sugar, tannins, phenols, alkaloids, flavinoid and pH contents of fruit were studied on 11varieties/ genotypes of muskmelon, Cucumis melo L., in relation to resistance against B. cucurbitae under field conditions. Significant differences were found in tested varieties/ genotypes for fruit infestation and larval density per fruit. AHMM/BR-1, RM-50 and AHMM/BR-8 were the most resistant; MHY-5, Durgapura Madhu and Pusa Sarabati were moderately resistant; AHMM/BR-13, Pusa Madhuras and Arka Jeet were susceptible; whereas Arka Rajhans and GMM-3 were the highly susceptible varieties/ genotypes to fruit fly in both seasons, 2011 and 2012. The larval density per fruit increased with an increase in percent fruit infestation and there was a significant positive correlation (r = 0.97) between percent fruit infestation and larval density per fruit. Total sugar, reducing sugar, non-reducing sugar and pH were lowest in resistant and highest in susceptible varieties/ genotypes, whereas tannins, phenols, alkaloids and flavinoid contents were highest in resistant and lowest in susceptible varieties/ genotypes. Total alkaloid and pH contents explained 97.96% of the total variation in fruit fly infestation and 92.83% of the total variation in larval density per fruit due to alkaloids and total sugar contents.     

Cultural Characteristics, Pathogenicity and Vegetative Compatibility of Fusarium udum Isolates from Pigeonpea (Cajanus cajan (L.) Millsp.) in Kenya

Seventy-nine single-spore isolates of Fusarium udum, the causal agent of wilt disease of pigeonpea, from Kenya, India and Malawi were characterized according to their cultural characteristics, pathogenicity and vegetative compatibility group (VCG). The isolates exhibited high variation in pathogenicity on a wilt-susceptible pigeonpea variety, and in mycelial growth and sporulation on potato dextrose agar medium. The 79 isolates were categorized into two virulence groups, two groups of radial mycelial growth and four groups of sporulation. Radial mycelial growth showed a moderate negative correlation (r = –0.40; P = 0.01) with sporulation. However, mycelial growth and sporulation had no correlation with virulence. Pairings between complementary nitrate non-utilizing (nit) mutants of F. udum generated on chlorate containing minimal medium revealed that all the isolates belonged to a single VCG (VCG 1) with two subgroups, VCG 1 I and VCG 1 II. Vegetative compatibility was independent of cultural characteristics and pathogenicity. This is the first report of vegetative compatibility in F. udum.