Interactions between arbuscular mycorrhizal fungi and Trichoderma harzianum and their effects on Fusarium wilt in melon plants grown in seedling nurseries

BACKGROUND: Biological control through the use of Trichoderma spp. and arbuscular mycorrhizal fungi (AMF) could contribute to a reduction of the inputs of environmentally damaging agrochemical products. The objective of this study was to evaluate the interactions between four AMF (Glomus intraradices, Glomus mosseae, Glomus claroideum and Glomus constrictum) and Trichoderma harzianum for their effects on melon plant growth and biocontrol of Fusarium wilt in seedling nurseries. RESULTS: AMF colonisation decreased fresh plant weight, which was unaffected by the presence of T. harzianum. Dual inoculation resulted in a decrease in fresh weight compared with AMF‐inoculated plants, except for G. intraradices. AMF colonisation level varied with the AM endophyte and was increased by T. harzianum, except in G. mosseae‐inoculated plants. Negative effects of AMF on T. harzianum colony‐forming units were found, except with G. intraradices. AMF alone were less effective than T. harzianum in suppressing disease development. Combined inoculation resulted in a general synergistic effect on disease control. CONCLUSION: Selection of the appropriate AMF species and its combination with T. harzianum were significant both in the formation and effectiveness of AM symbiosis and the reduction of Fusarium wilt incidence in melon plants. The combination of G. intraradices and T. harzianum provided better results than any other tested. Copyright © 2009 Society of Chemical Industry     

Protection of grapevine pruning wounds from infection by Eutypa lata

Background and Aims:  Eutypa dieback is a major threat to the sustainability and productivity of the viticulture industry worldwide. The fungicide benomyl has been the most effective treatment to protect wounds against infection by ascospores of Eutypa lata and to control eutypa dieback. However, because of the withdrawal of benomyl from the market, there is a need to develop alternatives to protect pruning wounds.
Methods and Results:  Twenty-five compounds were evaluated in laboratory experiments and field trials. A selection of the compounds effective at inhibiting germination and/or mycelial growth in the laboratory were further evaluated in the field. Of the 15 fungicides tested, carbendazim was the most effective in reducing colonisation of pruning wounds by E. lata in the field. Other fungicides, including fluazinam, pyrimethanil and pyraclostrobin, reduced colonisation of wounds by E. lata but require further evaluation at higher concentrations. Physical barriers such as acrylic paint (with or without fungicides) and a commercial tree wound paste formulated with fungicides (Garrison) also protected pruning wounds from infection by E. lata .
Conclusions:  Fungicides and physical barriers have been identified for the control of eutypa dieback in grapevines. The registration of Bavistin (carbendazim) and Garrison is being sought for use on pruning wounds on grapevines in Australia.
Significance of the Study:  Protection of pruning wounds is essential for the management of eutypa dieback in grapevines. Identification of alternative methods for disease control will provide significant economic benefits for the grapegrowing industry.     

Diagnosis of grapevine esca disease by immunological detection of Phaeomoniella chlamydospora

Background and Aims: Esca is a devastating disease affecting grapevines all around the world induced by a complex of xylem-inhabiting fungi. Among them, Phaeomoniella chlamydospora has been considered as an early causal agent of the disease facilitating the access of opportunistic saprophytes whose mode of action should be further investigated. P. chlamydospora secreted into its culture medium a variety of polypeptides, the biochemical nature of which permitted us to develop a method of detection based on a serological test. Methods and Results: Polyclonal antibodies raised in rabbit against the polypeptide fraction recognised secreted fungal proteins in low amounts (commonly 1 ng). These antibodies showed a valuable specificity because they cross-reacted with polypeptides excreted by various strains of P. chlamydospora but not with those secreted by many other fungal pathogens commonly found in other grapevine infections. Importantly, as shown by the enzyme-linked immunosorbent assay test and immunolocalisation on ultrathin sections, they did not cross-react with the secreted polypeptides of various fungi intervening in other wood decay diseases, namely Eutypa dieback (Eutypa lata) and Black Dead Arm (Diplodia seriata and Neofusicoccum parvum). Using a serological approach, the presence of P. chlamydospora was detected in canes of selectively infected cuttings. Conclusions: The antibodies raised in rabbit against polypeptides secreted by P. chlamydospora are useful tools to specifically detect the presence of the pathogen. Significance of the Study: These results allow us to propose a reliable dot blot method to detect grapevine infection by P. chlamydospora. This method is non-destructive for grapevines, simple and rapid.     

Fate of Escherichia coli in apple and reduction of its growth using the postharvest biocontrol agent Candida sake CPA‐1

BACKGROUND: Generally, acidic fruits and fruit juices are considered ‘safe’ from a microbiological point of view. However, some outbreaks of foodborne illnesses have been linked to the consumption of unpasteurised cider. The aim of this work was to study the survival of Escherichia coli in apple juice, wounds and flesh and on apple surfaces at different temperatures and to determine the effect of the fungal biocontrol agent Candida sake CPA‐1 against the colonisation of apple by E. coli. RESULTS: Trials were conducted with a mixture of five strains of E. coli isolated from apples. E. coli was unable to grow in apple juice at 5, 15 and 25 °C but survived. At 10 °C and above, E. coli thrived in fresh‐cut apple and wounds. At 5 °C it survived in apple wounds after 27 days of storage and after 21 days in fresh‐cut apples. When E. coli was inoculated in apple wounds together with the yeast antagonist C. sake, its growth was reduced by approximately 1 log cfu wound^?1 at 25 °C. At 5 °C no effect of the biocontrol agent was observed. CONCLUSION: Despite the low pH of apple, a rapid increase in the bacterial population is possible if the temperature is not kept low enough. The biocontrol agent C. sake, developed to prevent fruit decay during storage, could also reduce E. coli growth in wounded apples at abusive temperatures. This would represent an additional benefit of using this biocontrol agent when applied to control postharvest diseases. Copyright © 2009 Society of Chemical Industry     

Improvement of seed quality and field emergence of Fusarium moniliforme infected sorghum seeds using biological agents

Five different cultivars of sorghum seeds infected with a varied degree of Fusarium moniliforme were treated with biocontrol agents. Pure cultures of Pseudomonas fluorescens, Trichoderma harzianum and Chaetomium globosum at the rate of 1×10⁸ cfu g⁻¹ and talcum based formulations of (28×10⁷ cfu g⁻¹), (19×10⁷ cfu g⁻¹) and (4×10⁶ cfu g⁻¹) at the rate of 6 g kg⁻¹ and 10 g kg⁻¹ of seeds were used, respectively. The treated seeds were evaluated for per cent reduction of F moniliforme, seed germination, vigour index and field emergence. It was found that the pure culture of P fluorescens was more effective in reducing the F moniliforme infection followed by T harzianum and C globosum than the Bavistin treated and untreated seeds. Formulations of P fluorescens were effective in reducing the F moniliforme infection and also in increasing the seed germination, vigour index and field emergence, followed by T harzianum and C globosum treatments in comparison with control. © 1999 Society of Chemical Industry     

Increased effectiveness of the Trichoderma harzianum isolate T‐78 against Fusarium wilt on melon plants under nursery conditions

BACKGROUND: The use of isolates of the genus Trichoderma to control Fusarium wilt in melon plants is one of the most recent and effective alternatives to chemical treatments. In this work we have studied the immobilization of the isolate Trichoderma harzianum T‐78 on different carriers as an efficient method to control vascular Fusarium wilt of melon in nurseries. Different formulations were developed: liquids (spore suspension, guar gum and carboxymethylcellulose) and solids (bentonite, vermiculite and wheat bran). RESULTS: The introduction of F. oxysporum resulted in a significant decrease in seedling fresh weight. The treatments which gave a lesser reduction in weight and showing a greater biocontrol effect were the liquid conidial suspension and the solid treatments with bentonite and superficial vermiculite. Microbiological analyses revealed that the conidial suspension and all the solid treatments, except wheat bran, significantly decreased F. oxysporum populations. Of all the treatments assayed, bentonite produced the greatest decline in the F. oxysporum population. CONCLUSIONS: The most effective treatments against Fusarium wilt on melon plants were the solid treatments bentonite and superficial vermiculite. These two treatments gave the greatest plant weight, the lowest percentage of infected plants and the greatest T. harzianum population throughout the assay. Copyright © 2009 Society of Chemical Industry     

Mould infection and aflatoxin contamination of the peanut kernels harvested from spring and fall crops as affected by artificial inoculation of the seeded kernels with Aspergillus flavus and Aspergillus niger

Spring and fall crops of peanut are grown each year in Taiwan. Mould infection and aflatoxin contamination of crops as affected by artificial inoculation of the seeded kernels with conidia of Aspergillus flavus, A niger and a combination of A flavus and A niger (inocula > 10⁵ CFU kernel⁻¹) were determined. Three cultivars, ie Tainan 9, Tainan 11 and Tainan 12, were consecutively grown for fall 1996, spring 1997, fall 1997 and spring 1998 crops with green vegetable pea for rotation. In crops from uninoculated kernels (control), percentages of germination and harvested plants were higher in spring crops than in fall crops. Inoculation with A niger alone or with A flavus resulted in various levels of seed and seedling mortality and lower yields of peanut pods than yields of the other inoculation treatments. When harvested and sized (US No 1), kernels were subjected to examination for mould colonisation and analysis of aflatoxin content. Fairly low percentages were colonised and aflatoxin contents were low or non-detectable. Colonisation and aflatoxin content were independent of artificial inoculation. Average aflatoxin contents in the kernels harvested from all cultivars and crops ranged from 0 to 6.1 µg kg⁻¹. However, the highest levels of aflatoxin content among samples of the four crops were 4.0, 18.2, 9.6 and 36.7 µg kg⁻¹, respectively. © 1999 Society of Chemical Industry     

Colonisation of lettuce by Listeria Monocytogenes

Foodborne illnesses involving ready-to-eat vegetables are increasing. Lettuce is the third most consumed fresh vegetable in the United States with worth approximately $1.9 billion, making it the most valuable leafy crop. Previous reviews have described the survival of pathogenic bacteria such as E. coli O157:H7 and Salmonella on different ready-to-eat vegetables, but the colonisation of lettuce by Listeria has received limited attention. Listeria monocytogenes has high mortality compared to other foodborne pathogens such as Salmonella. This review summarises recent studies on the mechanisms of attachment and colonisation of Listeria on lettuce leaves. We discuss various factors that affect colonisation of lettuce by Listeria in terms of the number of bacteria that can be recovered after inoculation, the effect of washing, different radiation treatments and cultivation systems on the recovery of Listeria. We propose strategies that can be used to minimise the colonisation of lettuce by Listeria to enhance food safety.     

Determination of fiber length and juvenile and mature wood zones from Hevea brasiliensis trees grown in Brazil

The aim of this study was to verify the average fiber length and the juvenile and mature wood zones from Hevea brasiliensis proveniences from a reforestation area in Sao Paulo, Brazil. For this purpose, five Hevea brasiliensis trees were randomly collected from a 50-year-old plantation, located in Balsamo, Sao Paulo, Brazil. The trees were cut and five flat sawn boards were obtained. The juvenile and mature wood zones were determined by fiber length measurement from the pith to the bark. The results showed that: (a) the juvenile wood of this species occurred approx. between 40 and 55 mm, from the pith, and from this point forward, the mature wood zone was found; (b) there was a significant difference between the average fiber length of juvenile wood (1.26?mm) and mature wood (1.51?mm).     

Management practices for Sunmuscat (Vitis vinifera L.): a new drying variety

Sunmuscat grapevines, managed on one of three trellis × two row spacing configurations, and grown on either their own roots or grafted onto Ramsey rootstock, were assessed over nine seasons (1990–1998 inclusive). The three trellis systems comprised (1) a 0.3 m narrow T‐trellis (NT), (2) a 1.2 m wide T‐trellis (WT), both with a 3.3m row spacing and a height of 1.2 m, and (3) a high (1.8 m) hanging cane (HC) system based on bi‐lateral cordons with a 2.2 m row spacing. Vine spacing within rows was 2.4 m irrespective of row width. A trellis drying treatment was compared with hand harvest during 1991–1995. Over the nine seasons, individual WT vines sustained highest yields of fresh grapes (23.7 kg/vine.season) compared to either NT (20.9 kg/vine) or HC vines (20.8 kg/vine) respectively (P < 0.001). However, HC vines expressed a considerable production advantage on a per hectare basis, viz. 41.3 t/ha, due to closer row spacing. Corresponding vineyard productivity for NT and WT vines was 26.4 and 29.9 t/ha respectively. Both WT and HC vines showed significantly higher bunch and shoot numbers than the NT treatment (P < 0.05 and P < 0.001, respectively). Nevertheless, trellis treatment had no effect on fruitfulness, berry weight, bunch weight, total soluble solids or titratable acidity. Taken overall, vines grafted to Ramsey rootstock had higher mean yields than vines on their own roots (i.e. 23.6 and 20.1 kg /vine, respectively P < 0.001) due to more berries per bunch and larger berries, despite having significantly fewer shoots and bunches. There was no long term evidence for incompatibility of Sunmuscat grafted to Ramsey rootstock. Compared to hand harvest of fresh grapes, trellis drying had no effect on yield, shoot and bunch numbers. Development of significantly smaller berries with trellis drying was offset by higher levels of total soluble solids. Sunmuscat is clearly a highly productive variety and is suited to canopy management on tall, cordon‐based hanging cane systems which are also amenable to trellis drying.     

The relationship between longitudinal growth strain and the occurrence of gelatinous fibers in 10 and 11-year-old Eucalyptus globulus Labill.

The potential for using growth strain measured at the stem periphery of standing plantation-grown Eucalyptus globulus Labill. trees as a non-destructive detection method for tension wood was assessed. Two trials were conducted 12 months apart in a 10 to 11 year-old provenance trial of E. globulus located in the Mt. Gambier region of south-eastern Australia. The relationship between the occurrence of gelatinous fibers over varying radial depths of wood tissue and growth strain measured at breast height was investigated. The percentage of gelatinous fibers in wood tissue laid down in approximately the two years prior to taking the growth strain measurement was found to correlate best with growth strain. In an expansion of this work, growth strain was found to be a good indicator of the presence of gelatinous fibers in wood tissue taken from the immediate position where growth strain was measured. Thresholds were found at approximately 800  ue, above which gelatinous fibers were common, and 1,200  ue where gelatinous fibers were always present in each of the three provenances assessed. Tension wood was found to increase in occurrence over the 12 month period in line with a trend of increasing occurrence and severity of tension wood found in earlier work in the plantation.     

Biological control of postharvest green mold decay of oranges by Rhodotorula glutinis

The biocontrol activity of Rhodotorula glutinis on green mold decay of oranges caused by Penicillium digitatum was investigated in vitro and in vivo. Significant control was achieved with a washed cell suspension and an unwashed cell culture mixture of R. glutinis. Treatment of wounds with autoclaved cell cultures or cell-free culture filtrate did not prevent decay. The protection provided by the washed yeast cells was dose-dependent. The higher the concentration of R. glutinis, the better the effect of the biocontrol capacity. At concentrations of yeast of 1×10⁹ colony-forming units per milliliter or higher and pathogen spore suspensions of 5×10⁴ spores per milliliter, green mold was almost inhibited after 4-days incubation at 20 °C. The interval between the pathogen inoculation and the antagonist application significantly influenced the biocontrol ability. The biocontrol efficacy of R. glutinis applied before the pathogen was better than that of applied after the pathogen. Surprisingly, R. glutinis was also effective in controlling green mold at low temperature (4 °C). Rapid colonization of the yeast in wounds was observed during the first 3 days at 20 °C, and remained stable after 5-days incubation. On fruits stored at 4 °C, even after 21 days, the population of R. glutinis in wounded fruits was more than 1,600-fold of what it was just prior to storage. In the test on potato dextrose agar plates, agar disks of R. glutinis nutrient yeast dextrose agar cultures placed on PDA plates seeded with pathogens did not inhibit the growth of P. digitatum. Spore germination of pathogens in potato dextrose broth was greatly controlled in the presence of living cell suspensions.     

Effect of salinity and Ramsey rootstock on ion concentrations and carbon dioxide assimilation in leaves of drip-irrigated, field-grown grapevines (Vitis vinifera L. cv. Sultana)

Salinity treatments of 0.43, 1.7 and 3.4 dS/m were applied through a drip-irrigation system to four-year-old vines of own-rooted Sultana (S_O) and Sultana on Ramsey rootstock (Sr) The vines were planted in spring 1987 and established for two years under irrigation with low salinity (0.43 dS/m) water before commencing the range of salinity treatments in spring 1989. The effects of salinity and rootstock on yield, size and composition of berries, canopy size, lamina CO₂ assimilation, leaf water relations and lamina ion concentrations were studied between veraison and harvest during the second season of salinity treatments. Mature leaves of S_R had higher rates of CO₂ assimilation (leaf area basis) and stomatal conductance than comparable leaves of S_O. The high salinity treatment (3.4 dS/m) reduced CO₂ assimilation rate of S_O but not of S_R. Medium salinity (1.7 dS/m) had no significant effect on CO₂ assimilation rate of either type. Laminae of S_O accumulated significantly higher concentrations of chloride than S_R vines at all salinity levels. There was a significant negative correlation (r²= 0.44) between CO₂ assimilation rate and laminae chloride of S_O. Leaf sodium concentrations increased with increasing salinity, but concentrations in laminae at high salinity were similar in S_O and S_R, with S_R showing no reduction in CO₂ assimilation. Leaf potassium concentrations were higher in S_R, but decreased with increasing salinity, whereas magnesium concentrations were similar in S_O and S_R vines but increased in both at high salinity. Leaf water potential and relative water content were not significantly affected by salinity in either S_O or S_R vines. Both vine types had reduced total leaf area and pruning wood weights as salinity increased, but they were greater in S_R at all salinity levels because of the higher inherent capacity for biomass production in S_R vines. The bigger canopies, lower lamina chloride concentrations and ‘normal’ photosynthesis rates of S_R vines at 3.4 dS/m enabled these vines to mature crops with similar berry weights, sugar contents and fruit yield compared with those of S_O vines at 0.43 dS/m. The research demonstrated the benefit of using Ramsey rootstock for Sultana under saline field conditions and provided a physiological explanation for their higher salt tolerance.     

Pilzhemmende Wirkung von Zedernholzextrakt und Hibaöl auf holzständige Schimmelpilze

Ceratocystis fimbriata , Penicillium glabrum und Trichoderma harzianum in Malzextraktbouillon aufgezeigt. In beiden L?sungen war β-Thujaplicin als bekannte pilzhemmende Substanz nachzuweisen, wobei die Konzentrationen bei 2,5 mM (Zedernholzextrakt) und 165 mM (Hiba?l) lagen. Weitere Ergebnisse in diesem Medium zeigten, da? offensichtlich durch die Eigenschaften des Hiba?ls eine Schw?chung der pilzhemmenden Eigenschaft des β-Thujaplicins erfolgte, wohingegen im Zedernholzextrakt weitere pilzhemmende Substanzen vorzuliegen schienen. Auch konnte die pilzhemmende Aktivit?t von Hiba?l und Zedernholzextrakt gegen die genannten Schimmelpilze auf Kiefernholz best?tigt werden, wobei die Wirkung des Hiba?ls wesentlich ausgepr?gter war.

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Ceratocystis fimbriata , Penicillium glabrum, and Trichoderma harzianum could be demonstrated in malt extract broth. In both solutions, β-thujaplicin as a known antifungal substance could be detected. The concentrations were 2.5 mM (red cedar heartwood extract) and 165 mM (hiba oil). Further results using this growth medium showed that the antifungal activity of β-thujaplicin in hiba oil was obviously decreased due to properties of the oil, whereas other antifungal substances seemed to be present in the cedar extract. Furthermore, the antifungal activity of hiba oil and red cedar heartwood extract could be confirmed on pine wood. In this case, the effect of the hiba oil was much more pronounced.

     

Rootstock effects on salt tolerance of irrigated field-grown grapevines (Vitis vinifera L. cv. Sultana) 2. Ion concentrations in leaves and juice

Field vines of cv. Sultana, grown either on their own roots, or grafted to a range of rootstocks, were drip‐irrigated at three salinity levels (0.40, 1.75 and 3.50 dS/m) over a five‐year period. Rootstocks comprised Ramsey, 1103 Paulsen, J17‐69 and 4 hybrids (designated R1, R2, R3 and R4) derived from parentage involving Vitis champini, V. berlandieri and V. vinifera. Concentrations of Cl^‐, Na+, K+, Ca²⁺ and Mg²⁺ were measured in petioles at flowering, and in laminae and grape juice at harvest, in each year of the trial. Vines on all rootstocks accumulated less chloride in either petioles at flowering or in laminae and juice at harvest compared with vines on own roots at all salinity treatments. By inference, all rootstocks behaved as chloride excluders relative to the roots of own‐rooted vines. 1103 Paulsen was the best chloride excluder based on lowest concentrations of accumulated Cl^‐ in petioles, laminae and grape juice at high salinity. Sultana on R3 rootstock at high salinity accumulated more Na+ in both laminae and grape juice (at harvest) than did Sultana on own roots or on any of the other rootstocks. Laminae K+ at harvest time was reduced at high salinity in Sultana on own roots and on all rootstocks. Concentrations of both Cl^‐ and Na+ in petioles at flowering and in laminae and grape juice at harvest showed no significant correlation with either yield (as kg of fresh grapes per vine) or vigour (as measured by fresh weight of one‐year‐old pruning wood per vine) for any salinity treatment. There was however, a strong positive correlation between yield and the subsequent weight of one‐year‐old pruning wood for all salinity treatments. There was also a negative correlation between Na+ concentrations in petioles at flowering and the subsequent weight of one year‐old‐pruning wood from the 0.40 dS/m treatment. Similar negative correlations were found between Na+ concentration in both laminae and grape juice at harvest time, and the subsequent weight of one‐year‐old pruning wood from the 0.40 dS/m treatment (but not from either the 1.75 or 3.50 dS/m treatments). Based on these findings and those from Walker et al. 2002a we conclude that a high innate vigour of a rootstock combined with moderate to high chloride and sodium exclusion ability represents the best combination for salt tolerance in Sultana grapevines as measured by yield at moderate to high salinity.     

Comparison of the saturated salt and dynamic vapor sorption methods in obtaining the sorption properties of <Emphasis Type="Italic">Pinus pinea</Emphasis> L.

Several methods are available for obtaining the sorption isotherms of wood. Among these, the saturated salt and dynamic vapor sorption methods are the most frequently used ones. For the first time, the hygroscopic response of wood obtained using these two methods is compared. This is done by determining the 35 and 50?°C adsorption isotherms of juvenile and mature wood of Pinus pinea L. The hygroscopic behavior of the two types of wood is different, as the mature wood has a higher moisture content than the juvenile wood in the isotherms studied. Comparison of the static saturated salt method and dynamic vapor sorption shows few significant differences between the equilibrium moisture content obtained by each method during the adsorption process, both in a point by point comparison and in the comparison of quadratic polynomial forms of the Guggenheim Anderson-de Boer model. Moreover, in both methods the point of relative humidity from which multilayer sorption predominates over monolayer sorption is similar.     

HISTOLOGICAL AND BIOCHEMICAL CHANGES IN CORMS OF COLOCASIA ESCULENTA INFECTED BY BOTRYODIPLODIA THEOBROMAE AND SCLEROTIUM ROLFSII

Anatomical studies of the healthy corms of Colocasia esculenta showed an outer corky layer and inner cortex of mainly parenchymatous cells. The ethanol soluble carbohydrates were extracted and identified as maltose, sucrose, glucose and fructose. The two cultivars ‘ikpong’ and ‘cocoindia’ used in these studies also contain appreciable quantities of lipids, proteins and oxalate. The major carbohydrate component of the corm was starch. The two organisms, Botryodiplodia theobromae and Sclerotium rolfsii which were the most important rot pathogens of C. esculenta penetrated and colonised the corm tissue intercellularly and intracellularly. The infected cells were cleared of most of their starch grains and the cells disintegrated within ten days of inoculation. Apart from destroying the histological structure of the corms, the carbohydrate, protein and lipid contents were reduced on infection by both organisms. However, the oxalate content increased after infection by S. rolfsii.     

INTERACTIONS BETWEEN SALMONELLA ENTERICA SUBSPECIES ENTERICA SEROVAR TYPHIMURIUM AND COWPEA (VIGNA UNGUICULATA VARIETY SINENSIS) SEEDS, PLANTS AND PERSISTENCE IN HAY

Dynamics of persistence of Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium), a common food‐ and waterborne zoonotic serovar, on cowpea (Vigna unguiculata variety sinensis), a fodder and green vegetable plant, were studied. The findings revealed that S. Typhimurium not only reduced germination of cowpea seed (P < 0.01), but also caused defects in sprouts (P < 0.02). S. Typhimurium inoculation on seeds before sowing had a more pronounced effect (P < 0.01; i.e., loss in germination and appearance of defective sprouts) than sowing seeds in S. Typhimurium‐inoculated soil. S. Typhimurium persisted in saplings and adult plants up to 45 days of plant age and up to 60 days in hay. The cowpea plants grown in sterile Salmonella‐free soil did not support colonization of S. Typhimurium in different parts. A reduction in the population of Salmonella appeared as early as on the fifth day and decreased with advancing plant age. At 21 days of age, the cowpea plants had no Salmonella in their aerial parts and were free of the pathogen within 3 h of inoculation. Salmonella persisted in stumps of the plants throughout the observation, irrespective of age of the plants at the time of inoculation. The study revealed the persistence and the phytopathogenic potential of Salmonella on cowpea.     

Utilisation of Egyptian rice straw in production of cellulases and microbial protein: Effect of various pretreatments on yields of protein and enzyme activity

Rice straw was chosen as a cheap carbon source for SCP production using a locally isolated fungus identified as Trichoderma harzianum. The chemical constituents of the raw material were cellulose 43%, hemicellulose 26% and relatively low lignin, 16%. The effects of chemical and physical pretreatments on the protein production, cellulase activity and cell mass of T. harzianum have been investigated. Pretreatment of the raw material using a combination of NaOH and high pressure steam treatment increased its microbial digestibility from 24% to 73%. Similar results were obtained by pretreatment with sodium chlorite for holocellulose formation. However, maximum yields of cell mass and protein were obtained by the first method. The organism gave 7.18 g litre^?1 cell mass and 2.50 g litre^?1 mycelial protein. Treatment with sodium chlorite increased cellulase activities but gave a lower fungal yield. When the NaOH was applied with high pressure steam, the organism produced 32.8% crude protein, a yield similar to that given by the same organism cultured on soluble carboxymethylcellulose.     

Systemic damage in leaf metabolism caused by esca infection in grapevines

Background and Aims: Esca is a devastating wood‐decay disease that affects major grape‐producing areas around the world. Xylem pathogenic fungi produce a systemic effect on the development of foliar symptoms and glutathione metabolism in presence of oxidative species. This study focuses on sugar variations in Vitis vinifera leaves, in particular in early events occurring in esca. Methods and Results: Biochemical, cytochemical and molecular methods showed that in esca‐infected grapevines, photosynthetic pigment content did not vary significantly in leaves from apparently healthy canes (AC‐AL), but decreased in leaves without symptoms on symptomatic canes (SC‐AL). Starch grains were more abundant in AC‐AL than in SC‐AL containing wide plastoglobuli and numerous tannins. The starch level increased early, and then decreased with esca development. Fructose increased early by more than threefold, being the predominant soluble sugar in leaves with advanced esca symptoms. Conclusions: In response to damage induced by fungal infection, defence reactions such as fructose increased early and developed in esca leaves to scavenge reactive oxygen species and protect plant tissues. Significance of the Study: Esca infection leads to an early production of fructose involved in defence.