Melon is one of the important cucurbitaceous crops being cultivated widely in India and known for its delicious fruits. Crop is threatened by different biotic stresses including nematodes, fungi and viruses. The use of host resistance is the most economical, eco-compatible and long-lasting strategy to combat plant diseases. Keeping in mind this objective, 64 melon genotypes were screened against the prevalent Meloidogyne incognita, Fusarium oxysporum and tomato leaf curl Palampur virus (ToLCPalV) individually as well as with combined inoculations under artificial conditions. Out of 64 genotypes, three genotypes, MCPS, SM2012-1 and WM11 were found moderately resistant to M. incognita, nine genotypes (MM-KP15103, MM327, MM121103, KP4HM15, MM Sel.-103, SM2013-2, SM2012-1, SM2013-9 and WM11) recorded a resistant reaction against Fusarium wilt while four genotypes, WM11, SM2012-1, SM2013-9 and SM2013-2 exhibited a highly resistant reaction against ToLCPalV. A dendrogram constructed based on the resistance response of all the genotypes divided the genotypes into two groups and all resistant genotypes (MM1804, MM120103, SM2012-1, MM121103, SM2013-2, SM2013-9, WM11 and MM Sel.103) clustered in group II. The resistant genotypes when subjected to simultaneous inoculations of all three pathogens showed an increase in disease severity for each pathogen which negatively altered the resistance response of different genotypes. However, the genotypes SM2012-1, SM2013-9, SM2013-2 and WM-11 showing multiple disease resistance exhibited a good level of resistance even after combined inoculations of three pathogens. This study is the first to our knowledge identifying multiple disease resistance against root-knot nematode, Fusarium wilt and tomato leaf curl Palampur virus in muskmelon.

Leaves of coca are the primary source of cocaine. There is interest in using Fusarium oxysporum as a mycoherbicide in addition to other measures to control coca production, but information on coca physiology, including the stress responses of coca leaves, is limited. Deleafing coca plants stimulates rapid production of new leaves, and young expanding leaves readily abscise if treated with ethylene. Commercial preparations of cell wall degrading enzymes, as well as a 24-kDa elicitor from Fusarium oxysporum, induced significant levels of ethylene production by coca leaves. Ethylene pretreatment of coca leaves enhanced the production of ethylene by coca leaves in response to the cell wall degrading enzyme preparation, Driselase, and the 24-kDa elicitor. However, ethylene pretreatment did not enhance the rate of necrosis induced in response to either Driselase or purified 24-kDa elicitor. Driselase failed to elicit levels of necrosis comparable to the 24-kDa elicitor even at 30-fold higher protein concentrations. The response of coca leaves to the 24-kDa elicitor saturated at 6.7 μg ml−1. Age of coca leaves influenced both the level of resulting necrosis and the amount of ethylene produced in response to protein. Very young leaves produced the highest levels of ethylene and necrosis in response to Driselase and the 24-kDa elicitor. The data suggest that responsiveness of coca leaves to control measures may be synchronized over the first few weeks following defoliation.

Modifications were investigated to improve shelf-life or long-term survival upon storage of an extruded Oryza sativa L. (rice) flour : gluten : clay: oil formulation (C7) of a mycoherbicide, Fusarium oxysporum Schlechtend: Fr. f. sp. erythroxyli strain EN4, that causes vascular wilt in Erythroxylum coca var. coca (coca). Fermentor-produced biomass, which contained abundant desiccation-resistant chlamydospores, was incorporated into various adaptations of C7 and stored at room temperature (22 to 25 C) under moderately high (50 to 60%) and low (0 to 5%) relative humidities (RHs). The effect of RH on shelf-life was not significant up to 4 mo of storage, while the presence of oil, added to improve its extrusion, reduced viability significantly. Addition of Gossypium hirsutum L. (cotton) embryo flour or complete elimination of oil from the formulation improved shelf-life from 3 mo to > 12 mo. Shelf-life was further improved by removing the binding agent gluten in the formulation and replacing it with autoclaved O. sativa flour. Ability of the formulations to produce secondary propagules, tested on 1% water agar, indicated that, while adding oil had no effect, G. hirsutum embryo flour increased desiccation-resistant chlamydospore counts but lowered macroconidial counts. Autoclaved rice flour (MR) significantly improved both macroconidial and microconidial counts without affecting chlamydospore counts. None of the formulations affected the total viable propagule counts. When compared with the original formulation (C7), the modification (MRRP7), with MR, G. hirsutum embryo flour, and without oil, was found to have improved shelf-life at higher temperature and RHs and enhanced potential for secondary chlamydospore formation. These characteristics are important for survival of the formulated F. oxysporum under less expensive storage conditions and, once applied, for survival in the soil.

Biomass abundant in chlamydospores obtained by liquid fermentation of mycoherbicidal strains of Fusarium oxysporum was incorporated into alginate prills with various food substrates and granular formulations such as corn flour : starch, wheat flour : kaolin, rice : wheat flour, and rice : wheat gluten formulations. These fungal strains cause vascular wilts in coca (Erythroxylum coca var. coca) and in poppy (Papavar somniferum). Fungal strain, formulation method, and interaction of these two parameters significantly affected the shelf life of the formulations at room temperature as well as the ability to form secondary propagules on 1% water agar. In bioassays, there were no significant differences among F. oxysporum strain EN4-S formulations in their ability to colonize root tissue or the rhizosphere of E. coca seedlings. The study indicates that most of the formulations meet at least three of the four criteria important for biological control agents to be effective: low losses in viability during the formulation process, satisfactory shelf life at room temperature, abundant secondary chlamydospore formation, and rhizosphere colonization.

The fungal protein Nep1, produced by Fusarium oxysporum f. sp. erythroxyli in liquid culture, caused extensive necrosis to Centaurea maculosa when water solutions of Nep1 (5 µg ml−1) and an organosilicone surfactant (1,1,1,3,5,5,5-heptamethyltrisiloxanyl propyl-methoxy-poly[ethylene oxide]) were applied as foliar sprays. Nep1 did not cause necrosis when applied with a nonionic surfactant or organosilicone surfactant plus unrefined corn oil. Plant age, protein concentration, organosilicone surfactant concentration, and the presence of a dew period influenced the amount of necrosis caused by Nep1. The addition of an 18-h dew period after treatment resulted in an increase of 10% or more in foliar necrosis at the 0.313 and 1.25 µg ml−1 (0.40 and 1.62 g ai ha−1) Nep1 concentrations. Increasing the spray volume from 129 ml m−2 (1,291.3 L ha−1) to 516 ml m−2 (5,165.2 L ha−1) more than doubled the amount of foliar necrosis caused by the 0.313 µg ml−1 (0.40 g ai ha−1 vs. 1.62 g ai ha−1) Nep1 concentration. A maximum necrosis rating of 95% was reached by 1.25 µg ml−1 Nep1 applied at 516 ml m−2 (6.46 g ai ha−1) followed by an 18-h dew period. Nep1 (6.46 g ai ha−1) remained active when coapplied to Centaurea maculosa with the herbicides 2,4-D or glyphosate (0.13 to 2.58 kg ai ha−1), causing foliar necrosis prior to the herbicides killing Centaurea maculosa. An increase in the organosilicone surfactant concentration from 1 to 2 ml ai L−1 was required to achieve levels of Nep1-induced necrosis on Centaurea maculosa acclimated to direct sun comparable to levels achieved on greenhouse-grown plants. Repeated application of Nep1 (6.48 g ai ha−1) 3 wk after an initial treatment (6.48 g ai ha−1) prevented the recovery of acclimated Centaurea maculosa. Greater damage was caused to acclimated Centaurea maculosa when Nep1 was applied near the middle of the day (80% necrosis at 10:00 A.M. and 85% necrosis at 2:00 P.M.) compared to early or late in the day (25% necrosis at 6:00 A.M. and 10% necrosis at 6:00 P.M.).

Greenhouse and laboratory experiments were conducted on common waterhemp and soil collected from 131 soybean fields in Missouri that contained late-season common waterhemp escapes. The objectives of these experiments were to determine the effects of soil sterilization on glyphosate-resistant (GR) and -susceptible (GS) common waterhemp survival, to determine the effects of soil sterilization and glyphosate treatment on infection of GR and GS common waterhemp biotypes by Fusarium spp., and to determine the soil microbial abundance and diversity in soils collected from soybean fields with differences in common waterhemp biotypes and herbicide and crop rotation histories. Common waterhemp biotypes were treated with 1.7 kg glyphosate ae ha−1 or left untreated once plants reached approximately 15 cm in height. Common waterhemp survival was visually assessed at 21 d after glyphosate treatment (21 DAT). To determine Fusarium infection frequency, a single intact common waterhemp root was harvested from each treatment at 0, 3, 7, 14, and 21 DAT and surface sterilized, and 10 to 15–mm common waterhemp root sections were plated on Komada culture medium. After 14 d incubation, fungal colonies were selected from colonized roots and maintained on potato dextrose agar medium amended with antibiotics before identification. Speciation of Fusarium isolates was conducted through microscopic examination of fungal characters and confirmed by sequencing and analysis of ribosomal DNA. Soil samples from 131 different collections were subjected to phospholipid fatty acid (PLFA) analysis and were conducted utilizing gas chromatography to determine the soil microbial community abundance and structure. Common waterhemp plants grown in sterile soils had the highest common waterhemp survival, regardless of biotype. After treatment with glyphosate, survival of GS common waterhemp grown in nonsterile soil was only 29% 21 DAT, whereas survival of GS common waterhemp grown in nonsterile soil was only 10%. Similarly, GR common waterhemp survival was reduced from 83 to 61% following treatment with glyphosate when grown in nonsterile compared to sterile soil. Fusarium spp. were recovered from only 12% of the assayed roots (223 treatments with Fusarium out of a total 1,920 treatments). The greatest occurrence of Fusarium root infection in both GR and GS common waterhemp occurred in nonsterile soils following a glyphosate treatment. Few differences in total PLFA were observed in field soil collected from locations with either GR or GS common waterhemp, and regardless of herbicide or crop history. This research supports previous findings that plant species are more sensitive to glyphosate in nonsterile than sterile soils and indicates glyphosate may predispose plants to soil-borne phytopathogens. This research also suggests that continuous use of glyphosate does not significantly affect soil microbial abundance or diversity.

The soil seed bank is the reserve of viable seeds found in the soil. This reserve contributes to plant population persistence in unpredictable environments; thus, determining its presence is basic to understanding recruitment patterns and population dynamics. Studies of soil seed banks in the Cactaceae are scarce, although these plants are ecologically dominant in American arid and semi-arid environments. Most studies have inferred the presence of seed banks by analysing morphological seed traits or germination of seeds stored in the laboratory for different periods of time. Few studies have determined their presence through evaluation of distribution, density and longevity of seeds in the field. To fill this information gap, we determined the existence of, and studied, the soil seed bank of Stenocereus stellatus, a columnar cactus endemic to central Mexico. This study reports the evaluation of these characteristics in the field and discusses whether this species forms a soil seed bank. We found a higher number of seeds under shrubs than in areas lacking vegetation. Recently dispersed seeds did not germinate because they have primary dormancy. This dormancy was broken after 6 months of burial in the soil. Seeds buried for 10 months entered secondary dormancy and they were not viable at 24 months, probably because of pathogen attack. Considering dormancy and seed longevity, we suggest that S. stellatus has the potential to form a short-term persistent seed bank. However, this should be confirmed by conducting studies on other S. stellatus populations throughout their geographical distribution.

Introduction. Wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is the most important disease of banana worldwide, causing severe yield losses in commercial and local consumption cultivars. Chemical control is currently the most used method to manage the Fusarium wilt of banana, although it is toxic, expensive and dangerous. Therefore, control through genetic improvement is widely encouraged. Hence, breeding was carried out to develop banana hybrids with putative resistance. Materials and methods. Hybridization of identified resistant diploids with commercial triploids and tetraploids was carried out; it resulted in development of 22 hybrids with improved agronomic characters. In a second step, screening of these hybrids for resistance to Foc race 1 was attempted using the double cup method of challenge inoculation with the pathogen in the roots of the hybrids at optimum level. Host responses of the susceptible and resistant hybrids were examined under greenhouse conditions through biochemical and isozyme analysis. Results. Six hybrids among the 22 hybrids with improved agronomic characters were selected based on their yield and they were evaluated for resistance. Three of them were resistant to Foc and the others were susceptible. The resistance mechanism involving the relation of enzymes such as peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine lyase (PAL), and biochemicals such as phenols, proline and lignin showed relatively higher activity in resistant hybrids and parents than susceptible ones. Isozyme analysis of PO and PPO carried out using selected resistant and susceptible hybrids revealed the induction of specific isoforms in the resistant hybrids upon challenge inoculation. Conclusion. Three hybrids were identified as potential hybrids with good yield and resistance to Foc race 1.

Introduction. The causal agent of Panama disease in banana is Fusarium oxysporum f. sp. cubense (FOC). The authors put forward a hypothesis to account for certain disturbances of the natural defence mechanisms of banana plants against Panama disease as a consequence of very low Zn levels which could alter the mechanism of tylose formation. Materials and methods. A long-term experiment was carried out with 2-month-old banana plants in a growth chamber at 23 °C using three different levels of Zn nutrition. The nutrient solutions were inoculated with FOC 1 and FOC 4. Results and discussion. None of the total plants growing in a nutrient solution inoculated with FOC 1 showed infected rhizomes at the end of the experiment, but 75% of the plants growing in pots inoculated with FOC 4 had infected rhizomes. On the other hand, rhizome infection by FOC 4 was influenced by the nutrient solutions. The data showed that the number of plants with damaged rhizomes was significantly higher in the Zn-deficient treatments (100% of plants) than in the normal Zn solution (25% of plants), these internal symptoms being seen to worsen as the presence of Zn decreased in the nutrient solution. Conclusions. The results obtained seem to confirm the role played by Zn nutrition of banana plants in the appearance of Panama disease and are in accordance with our hypothesis concerning the relationships among plant Zn nutrition, plant IAA level, tylose formation and the incidence of the disease. Likewise, under our experimental conditions, race 1 of FOC is confirmed to be non-pathogenic against this banana cultivar, while race 4 is indeed pathogenic.

Soilborne pathogens, especially Fusarium oxysporum, are responsible for damping-off and root necrosis in Eucalyptus nurseries. New technologies are increasingly considering strategies for plant disease control other than chemical fungicides. Among these, natural fungal antagonists, which are colonizers of the root cortex, are potential biocontrol agents. An in vitro system was used: (1) to test the pathogenic effects of F. oxysporum strain Foeu1 which was recovered from a forest nursery soil; (2) to explore the potential of the nonpathogenic F. oxysporum strain Fo47, which is known for its efficiency in biological control, to suppress damping-off of Eucalyptus seedlings; (3) to compare the patterns of root colonization and host response to invasion by the two Fusarium strains inoculated separately in a time-course study. Root inoculation of E. viminalis with F. oxysporum strain Foeu1 caused damping-off in young seedlings in vitro, whilst disease symptoms were not visible in plants inoculated with F. oxysporum strain Fo47 or when both strains (Foeu1 + Fo47) were inoculated simultaneously. Each strain showed similarities in patterns of root tissue colonization, and in the processes of root penetration and initial colonization. Differential effects on root tissue were observed with fungal development within the cortex: ingress of strain Foeu1 was accompanied by severe host-cell alterations whilst no tissue damage occurred with development of strain Fo47.

A pathogenic strain of Fusarium oxysporum f. sp. lycopersici transformed with the glucuronidase (GUS) reporter gene was used to study the colonization process of tomato (Lycopersicon esculentum) roots in hydroponic culture. The plants were treated exactly as those used in a different study with a non-pathogenic strain of F. oxysporum in order to compare the two types of colonization process. The pathogenic strain rapidly colonized the root surface, forming a dense network of hyphae – shown by the GUS staining assay – as early as 48 h after inoculation. The first images of the pathogen penetrating into the epidermis of the root were observed 24 h after inoculation. The plant showed defence reactions mainly in the hypodermis, but also in the cortex. Generally these barriers failed to prevent the centripetal growth of the pathogen towards the stele. The GUS activity moved with the actively growing hyphae into the tissues; the stele appeared intensely stained 7 d after inoculation, whereas by this time the hyphae at the root surface did not show any more staining. The hyphae formed a dense network at the apex of the root, but direct contact between hyphae and living cells was prevented by several layers of sloughed cap cells. Although rarely observed, penetration of the pathogen into the apex was possible and led to a rapid destruction of apical cells. The only differences between this pattern of root colonization and that observed for a non-pathogenic strain of F. oxysporum appear to concern the frequency of dead apices and the intensity of fungal colonization in the cortex. When the pathogen passed around the barrier formed in the hypodermis it always reached the xylem, although this barrier and other defence reactions induced at different levels in the cortex always prevented the non-pathogenic strain from reaching the stele. These observations suggest that the main differences between the two types of interaction – between the plant and either the pathogenic or the non-pathogenic strain – are quantitative rather than qualitative.