Effect of harvest seasons on the incidence of seed-borne mycoflora of three Amaranthus cultivars

Fifteen fungal species were found to be associated with seeds of three cultivars ofAmaranthus cruentus L. There was a seasonal variability in the frequency of isolation, distribution and quantity of these seed-borne fungi among cultivars. The wetness, high temperature and air humidity that accompanied harvests of the first and second seasons greatly increased the number and amount of seed-borne fungi. Least number and mean percentage seed infection were recorded for NHAc₁₀₀ while NHAc₃₀ and NHAc₃₃ carried highest percentage inoculum of these pathogens. The seed testa of all cultivars was found to harbour the highest number and amount of some of these pathogens also in the second season. These seed-borne fungi,Choanephora cucurbitarum, Rhizoctonia solani andPythium aphanidermatum were highly pathogenic on seedlings of NHAc₃₃ and NHAc₃₀. Five of these seed-borne mycoflora have not been recorded onAmaranthus in Nigeria.     

Prevalence and control of wheat (Triticum aestivum L.) seed borne fungi in farmer-saved seeds

High incidence of diseases associated with the use of seeds saved from previous harvests as desire of maintaining local varieties with special attributes is of increased concern in wheat industry worldwide. Prevalent of seed-borne fungi in farmer-saved seeds and seed dressing fungicides to prevent infection from seeds to seedlings was studied in Northern Tanzania. One hundred and thirty five untreated farmer-saved seed lots were collected randomly from farmers. Alternaria alternata, Bipolaris sorokiniana, Drechslera tritici, Fusarium graminearum, Fusarium moniliforme, Aspergillus flavus, Cladosporium sphaerospermum, Epicoccum purpurascens, Pyricularia oryzae and Penicillium corylophilum were fungi isolated in farmer-saved seeds. Mean seed infection was 29% causing average grain yield loss of 1.2 mt/ha^?1. Seed dressing with Metalaxy plus (Methyl carboxaitide), Mancozeb (Manganase-zinc salt) and Baytan (Chlorophenoxy ethanol) increased seed germination by 14, 13 and 17%, respectively, and grain yield by 28, 20 and 18%, respectively. Farmer-saved seeds were heavily infected by fungi with low grain yield performance.     

Incidence of seed-borne fungi and aflatoxins in Sudanese lentil seeds

Thirteen seed samples of lentil (Lens esculenta) were incubated on agar plate and moist filter papers (Moist Chambers) at 28 ± 2 °C for determination of the incidence of seed-borne fungi. Aflatoxins content of the seeds was measured using the bright greenish-yellow fluorescence test (BGYF) and thin-layer chromatography (TLC). Sixty-nine species and seven varieties, which belong to 24 genera of fungi, were isolated from this crop. Of these fungi, 51 species and two varieties are considered new for this crop, whereas seven genera and 13 species are new to the mycoflora of the Sudan. The genus Aspergillus (13 species and 6 varieties) which comprising 44% of the total colony count was the most prevalent genus followed by Rhizopus (2 species, 19%), Penicillium (6 species) and Fusarium (8 species) (12%), Chaetomium (3 species) and Cladosporium (5 species) (6%), where the 18 genera (1–4 species) showed very low level of incidence (19%). Of the possible pathogens of lentil plants, F. oxysporum the main cause of vascular wilt was recovered from seeds of this crop. Thin layer chromatographic analysis of chloroform extracts of 13 seed samples showed that only one samples was naturally contaminated with aflatoxins B₁, B₂, G₁ and G₂ (14.3 μg/kg). This revised version was published online in June 2006 with corrections to the Cover Date.     

Occurrence and distribution of tomato seed-borne mycoflora in Saudi Arabia and its correlation with the climatic variables

One hundred samples of tomato seeds were collected in 2011 and 2012 from tomato-cultivated fields in Saudi Arabia and screened for their seed-borne mycoflora. A total of 30 genera and 57 species of fungi were recovered from the collected seed samples using agar plate and deep-freezing blotter methods. The two methods differed as regards the frequency of recovered seed-borne fungi. Seven fungi among those recovered from tomato seeds, which are known as plant pathogens, were tested for their pathogenicity and transmission on tomato seedlings. The recovery rate of these pathogens gradually decreased from root up to the upper stem, and did not reach to the stem apex. The distribution of tomato seed-borne fungi was also investigated throughout Saudi Arabia. In this concern, Al-Madena governorate recorded the highest incidence of fungal flora associated with tomato seeds. The impact of meteorological variables on the distribution of tomato seed-borne mycoflora was explored using the ordination technique (canonical correspondence analysis). Among all climatic factors, relative humidity was the most influential variable in this regard. Our findings may provide a valuable contribution to our understanding of future global disease change and may be used also to predict disease occurrence and fungal transfer to new uninfected areas.     

Herbal remedies for the management of seed-borne fungal pathogens by an edible plant Decalepis hamiltonii (Wight & Arn)

Abstract

Antifungal activity-guided assay of solvent extracts of Decalepis hamiltonii (Wight & Arn) (Asclepiadaceae) against important phytopathogenic fungi, known to cause diseases in sorghum, maize and paddy proved to be highly significant. Among the five solvent extracts tested, Petroleum ether extract showed highly significant antifungal activity. Phytochemical analysis revealed that the antifungal active principle is a phenolic compound. TLC separation of the phenolic fraction using chloroform as an eluting solvent revealed the presence of seven bands but the antifungal activity was observed only in band five with R_f value 0.77. The antifungal active compound is identified as 2-hydroxy-4-methoxybenzaldehyde based on Nuclear Magnetic Resonance (NMR) and mass spectral analysis. The Minimal inhibitory concentration (MIC) varied between 200 μg ml^?1 and 700 μg ml^?1 depending on the fungal species. Seed treatment of the active principle significantly increased seed germination and seed vigour with a corresponding decrease in seed mycoflora. The antifungal active compound was effective against all the 24 fungal species tested suggesting broad-spectrum antifungal activity. Comparative evaluation of the active principle with the synthetic fungicides revealed that the antifungal activity of the active principle obtained from the plant is better than that of synthetic fungicide. This plant being an edible one can be exploited in the management of seed-borne pathogenic fungi and the prevention of biodeterioration of grains and mycotoxin elaboration during storage.     

Studies on seed-borne fungi of wheat in seed health testing programme

Seed mycoflora associated with wheat was studied on different media with a particular reference to Blotter and potato dextrose agar (PDA) procedures of ISTA. Seed-borne fungi, viz. Fusarium moniliforme, Rhizopus spp., Mucor spp., Alternaria alternata, Aspergillus niger, Aspergillus flavus, Curvularia lunata, Drechslera spp, Alternaria spp. and Penicillium spp., were isolated from the variety HD264. Blotter method was found to be the best media for the isolation of mycoflora whether borne externally or internally. Total number and frequency of occurrence of fungi were recorded. The effect of seed treatment with different chemicals and eco-friendly botanicals was analysed on germination, and growth, better percentage of seed germination and reduction in fungal pathogen were due to biochemical seed treatment.     

Quick and accurate detection of Sclerotinia sclerotiorum and Phomopsis spp. in soybean seeds using qPCR and seed‐soaking method

Seed‐borne pathogenic fungi can cause serious damage to soybean crops by reducing the germination, vigour and emergence of the seeds. Special attention should be paid to pathogen detection in seeds to prevent its introduction in disease‐free areas. Considering the importance of rapid and successful diagnosis of seed‐borne pathogenic fungi in soybeans, this study evaluated a method to detect Sclerotinia sclerotiorum and Phomopsis spp. in seeds using quantitative polymerase chain reaction (qPCR). Naturally infested samples were subjected to detection using qPCR and blotter test, and the findings were compared. Using soybean seeds soaked in water, both pathogens were detected at an infestation level up a 0.0625% (one infected seed out of 1,599 healthy seeds) by qPCR. This technique allowed the detection of 300 fg of S. sclerotiorum and 30 fg of Phomopsis spp. DNA in the seed samples. Phomopsis spp. was detected in 40.7% of the evaluated seed batches (81 batches) and S. sclerotiorum was detected in 32.1% of the evaluated batches, although most of the seeds had low infestation levels. It was up to 28.5 times more efficient to use qPCR rather than blotter test to detect pathogens with a low incidence of occurrence in soybean seeds. If routinely used to test healthy seeds, qPCR would contribute to reducing soybean losses due to diseases as well as decreasing the costs required to control those diseases.     

Deteriorative changes of maize,groundnut and soybean seeds by fungi in storage

This paper deals with investigations on fungal infection, moisture content, germinability and deterioration of three seeds, viz., maize (starchy), groundnut (oily) and soybean (proteinaceous) in storage at the locality of Santiniketan, West Bengal, India, under natural condition for 1 year. The airspora of storage environment was trapped using culture plate method. Different species of Aspergillus (A. candidus, A. flavus, A. niger, A. terreus, and A. ruber) were dominant followed by Rhizopus, Penicillium, Curvularia, Fusarium, Alternaria, etc. Seed moisture was maximum in the rainy season followed by a gradual decrease during longer storage. A gradual decrease in field fungi with simultaneous increase in storage fungi accompanied by a reduction in germinability occurred in all seeds as storage proceeded. A gradual loss of carbohydrate (both soluble and insoluble) content in all the seeds were recorded. A loss of protein content was recorded followed by a small increase. Oil content decreased in prolonged storage with simultaneous increase in fatty acid. This revised version was published online in June 2006 with corrections to the Cover Date.     

Factors affecting the control of seed-borne Septoria nodorum by laboratory application of phenyl mercuric acetate to wheat seed

The effects of distribution of fungicide between seeds and of post-treatment storage on control of seed-borne Septoria nodorum by phenyl mercuric acetate (PMA) were investigated. Uneven distributions of fungicide were obtained by mixing treated with untreated seed. Redistribution of PMA occurred during initial mixing of the seed and during storage; this increased the effectiveness of fungicide in the mixed seed batch when the application rate was moderately high (0–5 jug Hg/seed). Redistribution apparently occurred over the seed surfaces and from seed to seed rather than by penetration into the seeds. Penetration into the seed by PMA was relatively unimportant in controlling S. nodorum.     

Assessment of mycoflora and infestation of insects,vector of <Emphasis Type="Italic">Aspergillus</Emphasis> section <Emphasis Type="Italic">Flavi</Emphasis>, in stored peanut from Argentina

The occurrence of spoilage fungi and Aspergillus section Flavi populations, the aflatoxins incidence, the role of insects as vectors of mycotoxin-producing fungi and the AFs-producing ability of the isolated species throughout the peanut (Arachis hypogaea L.) storage period were evaluated. Analyses of fungal populations from 95 peanut seed samples did not demonstrate significant differences between the incidences in each sampling period. Aspergillus section Flavi were isolated during all incubation periods. Cryptolestes spp. (Coleoptera: Cucujidae) were collected in August, September and October with 18, 16 and 28% of peanut samples contaminated, respectively. Insects isolated during August showed 69% of Aspergillus section Flavi contamination. A. flavus was the most frequently isolated (79%) from peanut seeds and from insect (59%). The greater levels of AFB₁ were detected in September and October with a mean of 68.86 μg/kg and 69.12 μg/kg respectively. The highest proportion of A. flavus toxigenic strains (87.5%) was obtained in June. The presence of Aspergillus section Flavi and insect vectors of aflatoxigenic fungi presented a potential risk for aflatoxin production during the peanut storage period. Integrated management of fungi and insect vectors is in progress.     

Mycoflora and aflatoxin production in pigeon pea stored in jute sacks and iron bins

The mycoflora, moisture content and aflatoxin contamination of pigeon pea (Cajanus cajan (L.) Millisp) stored in jute sacks and iron bins were determined at monthly intervals for a year. The predominant fungi on freshly harvested seeds wereAlternaria spp.,Botryodiplodia theobromae, Fusarium spp. andPhoma spp. These fungi gradually disappeared from stored seeds with time and by 5–6 months, most were not isolated. The fungi that succeeded the initially dominant ones were mainly members of the generaAspergillus, Penicillium andRhizopus. Population of these fungi increased up to the end of one year storage. Higher incidence of mycoflora andAspergillus flavus were recorded in jute-sack samples throughout the storage period. The moisture content of stored seeds was found to fluctuate with the prevailing weather condition, being low during the dry season and slightly high during the wet season. The stored seeds were free of aflatoxins for 3 and 5 months in jute sacks and iron bins respectively. The level of aflatoxins detected in jute-sack storage system was considerably higher than that occurring in the iron bin system. Of 196 isolates ofA. flavus screened, 48% were toxigenic in liquid culture (54% from jute sacks and 41% from iron bins).     

Seed germination in a tomato male-sterile mutant is resistant to osmotic, salt and low-temperature stresses

Seed germination in a male-sterile 7B-1 mutant in tomato is reletively more resistant to the inhibitory effects of a high osmoticum induced by mannitol and polyethylene glycol, to various salts, including NaCl, Na₂SO₄, KCl and K₂SO₄, and to low-temperature stress, compared to the wild-type (WT) seeds. The inhibitory effects of various stresses could be partly or completely overcome by fluridone (FLU), an inhibitor of abscisic acid (ABA) biosynthesis. However, lower concentration of fluridone was required for the 7B-1 mutant than for WT seeds, and the mutant seeds were more sensitive to the inhibitory effects of exogenous ABA. The data suggest that 7B-1 seed has a pre-existing level of elevated ABA which imparts resistance to the various stresses. The ability to regulate male sterility in the 7B-1 mutant by photoperiod, as previously reported by Sawhney (1997), and its resistance to abiotic stresses, as reported here, makes this a useful system for tomato breeding and in hybrid programs. Received: 11 May 2000 / Accepted: 4 June 2000     

Impact of Apion ulicis Forster on Ulex europaeus L. Seed Dispersal

The impact of the weevil Apion ulicis on the dispersal and quality of gorse (Ulex europaeus) seeds was examined in southern Chile in 1991 and 1992. Seed dispersal was assessed by counting the number of seeds captured by rows of seed traps placed at 0.7, 1.4, and 2.8 m from 12 weevil-infested and 12 weevil-free gorse plants arranged in a split-plot randomized complete block design. Seed weight and germinability were also measured. The influence of gorse pod location on host utilization by the weevil and the hypothetical subsequent change on seed dispersal were also studied. Gorse seed production and dispersal were significantly (P ≤ 0.001) decreased by A. ulicis in 1991 but not in 1992. Individual seed weight and germinability were not adversely affected by weevil infestation. Pod location did not affect host utilization by the insect, nor did it influence seed dispersal or quality.     

Effect of temperature and moisture content on Egyptian peanut seed-borne fungi

In peanut seeds adjusted to various levels of moisture content (8.5 %, 13,5 %, 17.5 % and 21 % on a dry-weight basis) and stored for six months at 5°, 15°, 28° and 45 °C, seed-borne fungi were monthly identified and counted using the dilution plate method, and the germinability of seeds was tested. The total count of seed-borne fungi (recovered at 28 °C) increased regularly and the germinability declined with the rise moisture content and with the lengthening of the storage period. At 5°, 15° and 28 °C,A. fumigatus was almost the most dominant fungal species followed by several fungi such asAspergillus flavus, A. niger, A. terreus, Penicillium funiculosum, P. notatum, Pyrenochaeta decipians andScopulariopsis brevicaulis. The degree of dominance of each fungal species depended upon the conditions of storage and the length of storage period.A. flavus gained its highest count in seeds adjusted to 13.5 % stored at 15 °C for 1 month.Penicillium predominated at 17.5 % and 21 %, and at 13.5 % and 17.5 % when the seeds were stored for long periods at 5° and 15 °C respectively.The total count of thermophilic fungi (recovered at 45 °C) significantly increased with the rise of moisture content and with the lengthening of the storage period between 1 and 2 months and regularly declined after 4 months.A. fumigatus was so extremely dominant that it was the main component of the total fungal flora. Several fungi truly thermophilic were isolated also. They were,Mucor pusillus, Humicola grisea var.thermoidae, H. insolens, H. lanuginosa (Thermomyces lanuginosus) andSporotrichum thermophile.     

Effects of storage,mucilage presence,photoperiod, thermoperiod and salinity on germination of Farsetia aegyptia Turra (Brassicaceae) seeds: implications for restoration and seed banks in Arabian Desert

Seed viability and germination are key factors in the success of restoration efforts, especially when stored seeds are used. However, the effect of seed storage on germination of most of the native Arabian species is not well documented. We investigated the effect of storage time and role of the seed mucilage in regulating germination, dormancy, salinity tolerance and consequential survival strategy of F. aegyptia in an unpredictable arid desert setting. Effect of light and temperature during germination was studied under two photoperiods and two thermoperiods using intact and de-mucilaged seeds. Presence of mucilage and thermoperiod did not affect the germination. However, seed collection year and photoperiod had a highly significant effect on the germination. Increasing salinity levels decreased the germination of F. aegyptia but ungerminated seeds were able to germinate when salinity stress was alleviated. Seed storage at room temperature enhances the germination percentage, indicating that F. aegyptia seeds have physiological dormancy and it can be alleviated by after-ripening at dry storage. In addition, F. aegyptia seeds show ability to germinate at lower salinity concentration and remain viable even at higher saline conditions, indicating their adaptability to cope with such harsh environmental conditions.     

紫花苜蓿种子对逆境贮藏条件的反应

以陇东紫花苜蓿 (MedicagosativaL .cv .“Longdong”)种子为材料 ,在室温、35℃和 35℃ +10 %的种子含水量 (SMC) 3种贮藏、接种或不接种燕麦镰刀菌 (Fusariumavenaceum (Fr.)Sacc .)的条件下 ,1年贮藏期内对各逆境处理的种子每隔 6 0d进行 1次标准发芽试验 ,2 0℃恒温、第 10d统计种子的发芽率和死亡率 ,试验结束时计测种子幼苗的长度和感病率 ;在大田条件下观测各处理种子的出苗率 ,确定催腐 (CD)与各种贮藏条件下的苜蓿种带真菌种类和检出率 .结果表明 ,随着贮藏温度和种子含水量等逆境贮藏条件胁迫的加剧 ,苜蓿种带真菌检出率逐渐增高 ,从室温、35℃条件下的 10 %上升到CD +35℃ +10 %SMC条件下的 2 9% ;抗病性逐渐减弱 ,35℃ +10 %SMC条件下幼苗的感病率和种子死亡率显著 (P <0 .0 5 )高于室温和 35℃下的感病率和种子死亡率 ;室内种子发芽率和田间出苗率逐渐下降 ,35℃ +10 %SMC条件下的种子的发芽率和田间出苗率显著 (P <0 .0 5 )低于在室温和 35℃下的发芽率和田间出苗率 ;幼苗生长受到抑制 ,35℃ +10 %SMC条件下的苗长和根长显著 (P <0 .0 5 )低于在室温和 35℃下的幼苗长度 .随着贮藏时间的延长 ,种子真菌检出率和田间出苗率下降 ,幼苗感病率增加 .与未接种的对照相比 ,接种燕麦镰刀菌的种子     

Grass seed infection following inundation with Pyrenophora semeniperda

Seed infection by the seed-borne pathogen Pyrenophora semeniperda was demonstrated following inundative applications of the fungus to several annual grass weeds and wheat. The optimum time for applying inoculum was found to be around mid-anthesis in wheat. Applications of inoculum during and after anthesis in field experiments resulted in seed infection that manifested as stromatal development which affected germination or reduced seedling vigour. In an initial field experiment, >70% of Bromus diandrus seeds exhibited stromata of P. semeniperda. In a field comparison of inoculum types, conidial suspensions resulted in the greatest level of seed infection of B. diandrus compared with several types of inoculum containing mycelium fragments. Inundation of Avena fatua, Lolium rigidum, Hordeum leporinum, Vulpia bromoides and B. diandrus under field conditions with conidia of P. semeniperda also resulted in either the failure of infected seeds to germinate or a reduction of seedling vigour. It is concluded that the use of P. semeniperda as a seed-borne bioherbicide may be a biologically reasonable tactic, and the many logistical and technological constraints impeding its development are discussed.     

The Effect of Glumes on Fungal Infection of Germinating Seed of Spelt (Triticum spelta L.) in Comparison to Wheat (Triticum aestivum L.)

The influence of fungi on seedling emergence of naked and hulled spelt (Triticum spelta L.) and winter wheat (Triticum aestivum L.) was investigated. Seeds were sown in flat trays and placed in a growth chamber under stress conditions (low temperature and water logging) for four weeks, followed by favourable growth conditions. At weekly intervals, 150 seeds were removed, surface sterilized, and investigated for fungi. Pythium aristosporum Vanterpool, a causal agent of damping-off, was found to be best adapted to the unfavourable conditions and to be a major cause of pre-emergence damping-off. The frequency of seed-borne fungi decreased during the stress period, whereas soil-borne fungi survived and could be isolated from seeds and glumes in the following period with more favourable growth conditions. Seedlings from hulled seeds of spelt emerged more frequently than from naked kernels of spelt and both emerged at a higher rate than from seeds of winter wheat. This is good evidence that glumes protect seeds against fungal colonization and therefore increase the fitness of spelt under unfavourable germinating conditions.     

The impact of different seed priming agents and priming durations on stand establishment and biochemical attributes of Stevia rebaudiana Bertoni

Stevia (Stevia rebaudiana Bertoni) is an alternative sugar crop currently gaining importance in several geographic regions of the world. Generally, crop is propagated by seeds; however, low seed germination hinders the adaptability of the crop in different cropping systems. Seed priming with different compounds improves germination of several arable crops under stressful and benign environmental conditions. This study evaluated the role of different seed priming agents and priming durations on stand establishment, allometric and yield-related traits, and steviol glycosides contents of Stevia in two different experiments. The first experiment consisted of five different seed priming agents (i.e., hydropriming with distilled water, ascorbic acid, potassium chloride, benzyl amine purine and unprimed seeds) and five priming durations (0, 8, 16, 24 and 32 h). Seed priming with potassium chloride (KCl) and benzyl amine purine (BAP) for 32 h improved stand establishment and biochemical attributes of Stevia seeds. Therefore, these two seed priming agents along with unprimed seeds were included in the second experiment to quantify their impact on allometric and yield-related traits and steviol glycosides contents. Seed priming with both KCl and BAP resulted in better allometric traits (plant height, number of leaves per plant, leaf area and chlorophyll index) compared with unprimed seeds. Similarly, seed priming with KCl resulted in higher fresh and dry biomass production of stem and leaves. Nonetheless, higher stevioside and rebaudioside A contents were recorded for the seeds primed with KCl, whereas unprimed seeds resulted in the lowest values. It is concluded that Stevia seeds must be primed with KCl for 32 h before sowing to get higher seed germination, leaf yield and steviol glycosides contents. Nonetheless, the role of KCl priming in improving abiotic stress tolerance of Stevia must be explored in the future studies.     

Diversity of plant oil seed-associated fungi isolated from seven oil-bearing seeds and their potential for the production of lipolytic enzymes

Commercial oil-yielding seeds (castor, coconut, neem, peanut, pongamia, rubber and sesame) were collected from different places in the state of Tamil Nadu (India) from which 1279 endophytic fungi were isolated. The oil-bearing seeds exhibited rich fungal diversity. High Shannon-Index H′ was observed with pongamia seeds (2.847) while a low Index occurred for coconut kernel-associated mycoflora (1.018). Maximum Colonization Frequency (%) was observed for Lasiodiplodia theobromae (176). Dominance Index (expressed in terms of the Simpson’s Index D) was high (0.581) for coconut kernel-associated fungi, and low for pongamia seed-borne fungi. Species Richness (Chao) of the fungal isolates was high (47.09) in the case of neem seeds, and low (16.6) for peanut seeds. All 1279 fungal isolates were screened for lipolytic activity employing a zymogram method using Tween-20 in agar. Forty isolates showed strong lipolytic activity, and were morphologically identified as belonging to 19 taxa (Alternaria, Aspergillus, Chalaropsis, Cladosporium, Colletotrichum, Curvularia, Drechslera, Fusarium, Lasiodiplodia, Mucor, Penicillium, Pestalotiopsis, Phoma, Phomopsis, Phyllosticta, Rhizopus, Sclerotinia, Stachybotrys and Trichoderma). These isolates also exhibited amylolytic, proteolytic and cellulolytic activities. Five fungal isolates (Aspergillus niger, Chalaropsis thielavioides, Colletotrichum gloeosporioides, Lasiodiplodia theobromae and Phoma glomerata) exhibited highest lipase activities, and the best producer was Lasiodiplodia theobromae (108 U/mL), which was characterized by genomic sequence analysis of the ITS region of 18S rDNA.